El Niño-Southern Oscillation - Observations and Modeling

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www.pages-igbp.org ne w s in Tridacna spp . region. The presence ofsymbiontsprovides themultitudeofcolors commonly observed giant, long-lived bivalves are reef dwelling organisms characteristic of the Indo-Pacific Beyond justbeautiful-Tridacna Vol 21 Kiefer Harrison, Lucien von Gunten and Thorsten Pascale Braconnot, Chris Brierley, P. Sandy Editors: Oscillation Niño-Southern El Mini section on data assimilationMini section p. 72-79 • No2 spp. are faithfully recording paleoENSOvariability. These • August 2013 Inside PAGES

Celebrating 20 years Committee and an Interim Secretariat Guest scientists In this issue we celebrate 20 years of PAGES with an Interim Director. You can check the We are pleased to welcome two guest news. You can read our paleobibliographic names of the personnel on the Future Earth scientists to the PAGES office this sum- analysis on the next page, and take a trip website (www.icsu.org/future-earth) and mer: Gisela Winckler from the Lamont- back in time and enjoy the first ever copy of keep informed via their media, including Doherty Earth Observatory, US and Bernd Announcements PAGES news from 1993. A reprint is includ- a newsletter and a blog. Our current um- Zolitschka from the University of Bremen, ed in this issue as an insert (it was much brella program IGBP has decided to sunset Germany. Among other things, they are smaller then). by the end of 2015. The PAGES SSC has de- working alongside PAGES staff to edit up- cided that over the next two years PAGES coming editions of PAGES news. You can Communications update should join the Future Earth network, while learn more about our Guest Scientists and PAGES has now joined the Twitter-sphere. at the same time continuing to collaborate the work they are doing on the PAGES web- Follow us to get all the latest news: with other organizations. site > People > Guest Scientists. @PAGES_IPO. You can also subscribe to our new YouTube channel: Past Global IGBP Scientific Committee in Bern Introducing the new mini section Changes, and of course, we’ve still got the In April, PAGES, together with ProClim We hope you enjoy our first Science Facebook fan page: PAGES Past Global and the Oeschger Centre, hosted the IGBP Highlights mini section; in this issue it fo- Changes. Scientific Committee Meeting in Bern. IGBP cuses on Data Assimilation. The new mini SC members came together from around section format will feature 4-5 articles Staff update the globe to discuss potential synthesis focusing on a specific topic, and might Welcome to our two new staff mem- projects, IGBP’s legacy and how best to appear more regularly in future issues de- bers: Nicole Wegmüller (Finance and transition into the new integrated Future pending on demand. Office Manager) and Leonie Goodwin Earth super-program in the coming years. (Communications and Project Officer). Upcoming newsletters Support for meetings The next two issues of PAGES news will fo- PAGES OSM and YSM During its meeting in June, the PAGES SSC cus on dust and on annual recorders of the The Open Science and Young Scientists granted support for a total of ten scientific past. While the dust issue is already closed, Meetings continue to resonate. We re- and educational meetings. The next dead- suitable articles for the annual record- cently uploaded videos of seven plenary line for applying for PAGES meeting sup- ers issue are still welcome. Contributions talks with the accompanying PowerPoint port is 20 September 2013. Support can should explore the question of how natu- slides and some short video montages to be sought for workshop-style meetings ral archives with annual resolution are ap- our YouTube channel: Past Global Changes. relevant to PAGES Foci and Cross-Cutting proaching the temporal resolution of in- You can also read reports on the YSM activi- Themes. The three eligible categories are strumental records. Submissions should be ties written by the participants, starting on PAGES Working Group meetings, work- discussed with Bernd Zolitschka (zoli@uni- page 89. shops with a training or education focus, bremen.de) and be submitted before the and an open call for other workshops that 15th of September. As always, you are invit- PAGES umbrella programs are relevant to PAGES science. Application ed to submit Science Highlights, Program The transformation of the landscape of guidelines and forms can be found on the News, and Workshop Reports for the Open Global Environmental Change programs PAGES website > My PAGES > Meeting Section of PAGES news. Author guidelines is taking shape. The new Future Earth Support. can be found on the PAGES website > My program has now established a Scientific PAGES > Newsletter.

New on the PAGES Bookshelf Tracking Environmental Change Using Lake Sediments, Volume 5 Data Handling and Numerical Techniques Editors: H. John B. Birks, André F. Lotter, Steve Juggins, John P. Smol Springer, 2012

Another volume in the “Development in Paleoenvironmental Research Series”, this book is the first of its type to cover the full range of modern data-analytical and statistical techniques used in paleolimnology and paleoecology. It features numerical and statistical techniques, such as exploratory data analysis, error estimation, clustering, ordination and modern statistical learning techniques. It also includes case studies on human impact, lake development and climate change.

PAGES news • Vol 21 • No 2 • August 2013 20 years of PAGES news Annoucements Annoucements

Figure 1: Paleobibliographic analysis of PAGES news.

he four-page insert included in this between the number of pages and the conditions and for creating predictive cli- Tissue is a copy of the first ever PAGES number of science highlights articles (r2= matic models. Paleoclimatic and paleoen- news created 20 years ago in Spring 1993. 0.92; P<0.01), with early issues usually con- vironmental data have the unique ability We thought this milestone provided an taining one article and more recent issues to provide detailed insights into ecosys- opportunity to reflect on how far PAGES 15±2. If this trend continues over the next tem responses to climate change at differ- news has come in that time, but also how 20 years, PAGES news will be a daunting ent time scales, which can inform future many of the issues discussed in our first 100 pages thick and feature 35 articles by policymaking. newsletter still remain pertinent today. the year 2033! We hope you enjoy a little trip back A quantitative paleobibliographic Hans Oeschger, the first chair of in time via our first issue. And for anyone analysis reveals the steady growth of PAGES, observed in his introduction to the thinking about replying to the Call for Title PAGES news in the last 20 years. We found first issue that global change research is Suggestions advertisement on the last evidence of five distinct stylistic eras and advancing at a remarkable pace, and many page: Although we have happily stuck to observed that the number of pages in of the issues he highlighted back in 1993 the “unimaginative title” PAGES news for each issue has increased 12-fold from four are still relevant today. An improved un- 20 years, we are, of course, still open to in 1993 to around 50 in current issues (Fig. derstanding of past global change is cru- your suggestions for improvement. 1). Likewise there is a strong correlation cial for evaluating present environmental

PAGES Calendar

Paleofire data synthesis using R Ramsar Wetlands: Ecological Character 02 - 06 Oct 2013 - Besançon, France 06 - 08 Nov 2013 - Queenscliff, Australia

Holocene Circum-Arctic Peatland Carbon Dynamics PMIP Ocean Workshop 2013 12 - 16 Oct 2013 - Bethlehem, USA 04 - 06 Dec 2013 - Corvallis, USA

PALSEA 2013 Workshop Age Models, Chronologies, and Databases 21 - 24 Oct 2013 - Rome, Italy 13 - 16 Jan 2014 - Belfast, Northern Ireland

Joint PAGES 2k & PAST2k-PMIP Workshop PAGES Focus 4 workshop 04 - 06 Nov 2013 - Madrid, Spain 03 - 07 Feb 2014 - Leuven, Belgium

www.pages-igbp.org/calendar/upcoming 47

PAGES news • Vol 21 • No 2 • August 2013 Editorial: El Niño-Southern Oscillation - observations and modeling

Pascale Braconnot1, C. Brierley2 and S.P. Harrison3,4 1Laboratoire des Sciences du Climat et de l’Environnement, unité mixte CEA-CNRS-UVSQ, Saclay, France; [email protected] 2Department of Geography, University College London, UK; 3Department of Biological Sciences, Macquarie University, North Ryde, Australia; 4Centre for Past Climate Change and School of Archaeology, Geography and Environmental Sciences, University of Reading, UK

he El Niño-Southern Oscillation same climate models used for future be regarded as a basis for future ENSO T(ENSO) is one of the major climate climate projections offer new opportu- research. Individual contributions

Science Highlights: Editorial Highlights: Editorial Science phenomena affecting our global en- nities for improving our understanding address how one can extract ENSO- vironment (Figs. 1 and 2), but current of ENSO. One of the foci of the work- relevant climate information from tree understanding of ENSO is limited. ing group on climate variability in the rings, corals, giant bivalves, or shells, Instrumental records are too short to 3rd phase of the Paleoclimate Modeling and how modeling can be used to test allow us to document its spectrum of Intercomparison Project (PMIP3; explicit hypotheses to improve the in- variability and there is little knowledge Braconnot et al. 2012a) is to foster the terpretation of paleoclimate records of how variability alters with changes synthesis of high-resolution data and as well as to infer the mechanisms of in the climate mean state, for example the development of new data-model climate change. The articles also il- with anticipated global warming. comparison methodologies to exam- lustrate some fundamental questions In the PAGES news issue “Paired ine changes in ENSO. that need to be addressed in preparing perspectives on global climate change” multi-proxy reconstructions of past (2012), Amy Clement highlighted some The future of ENSO research ENSO behavior and in analyzing paleo- important issues about the decadal The suite of papers presented in this climate modeling results. We consider variability, predictability and modeling newsletter is one outcome of the these studies to be the first step to- of ENSO with global warming. As point- PMIP workshop on “Tropical climate wards a comprehensive evaluation of ed out by Julien Emile-Geay in the same variability with a focus on last mil- whether climate models incorporate issue, paleoclimate data are a valuable lennium, mid-Holocene and Last the right physics and feedbacks to re- resource to improve our understand- Glacial Maximum” which took place produce the diversity of ENSO events. ing of these issues, even though the in the south of France in September past does not provide direct analogs 2011 and was co-sponsored by PAGES Pulling the pieces together for the future. Analyses of high-reso- (Braconnot et al. 2012b). The articles An exciting development, showcased lution paleoclimate indicators and the provide an overview of high-resolution in this special issue, is that many dif- possibility of long simulations with the records and modeling studies that can ferent types of records exist that

Figure 1: La Niña event of 1999. Left: Positive (purple) and negative (blue) sea surface temperature anomalies. Right: Positive (blue) and negative (brown) rainfall anomalies (mm). The four El Niño regions referred to in the following articles are depicted in the right panel. Images from NASA. 48

PAGES news • Vol 21 • No 2 • August 2013 Science Highlights: Editorial Highlights: Editorial Science

Figure 2: El Niño event of 1997. Left: sea surface temperature anomalies. Blue: negative, purple: positive. Right: Rainfall anomalies (mm). Brown: negative, blue: positive. Images from NASA. document short term climate variabil- atmosphere (see Capotondi et al. p. 58 hypothesis testing. To facilitate this, ity (see Elliot et al. p. 54 and Carré et or Lazareth et al. p. 66). Nevertheless, the community needs to synthesize al. p. 56) and that pooling information with improved model physics, in- more primary data across regions and from multiple types of records pro- creased spatial resolution, more rou- realms. This will allow us to capitalize vides a pan-tropical picture of ENSO. tine incorporation of tracers (e.g. on the improvements in process un- The contributions here and in other isotopes) and biogeochemistry, and derstanding that are emerging from recent papers (e.g. Cobb et al. 2013), the ability to run much longer simula- both data analyses and modeling ex- demonstrate that the process-level un- tions, state-of-the-art models are in- periments. The other requirement is derstanding of individual records has creasingly yielding important insights developing statistical and analytical improved over recent years (see Elliot into ENSO. Model simulations show tools that combine the two sources et al. p. 54 or McGregor et al. p. 52). that ENSO displays non-stationary of information (data and model out- This includes the recognition that it is behavior in space and time, includ- puts) to disentangle the evolution of rare for paleoclimate records to reflect ing the strength of ENSO teleconnec- mean state, seasonality, and interan- a single climate variable (e.g. temper- tions (Capotondi et al. p. 58, Merkel et nual to decadal variability. To develop ature or salinity) or aspect of climate al. p. 68). The simulations imply that these approaches and tools, we see a variability (e.g. seasonal phasing or the ENSO phenomenon has to be de- need for a dedicated activity within magnitude changes in mean frequency coupled into different components, the PAGES and PMIP communities that or in extremes). The challenge now is such as mean state, hydrology and brings together the full range of ex- to find ways to synthesize the dispa- teleconnections that change indepen- pertise. This is the only way to answer rate aspects of the records and to take dently depending on the forcing (see the fundamental questions about the advantage of the wider range of infor- Braconnot et al. p. 64). The lessons relationships between the background mation available to provide an over- learned from models and their integra- climate state, the seasonal cycle and view of ENSO variability (see Russon et tion with observations pose ambitious ENSO variability. al. p. 62 or Thompson et al. p. 60). challenges to the interpretation of the ENSO-relevant signal in paleoclimate Selected references Modeling improvements records (Russon et al p. 62, Brierley p. Full reference list online under: A second important development is 70, Lazareth et al. p. 66). http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf the improvement in modeling capacity Braconnot P et al. (2012a) Nature Climate Change 2: 417-424 and analytical approaches. Coupling Towards data and model Braconnot P, Harrison SP, Tudhope S, Michaut C (2012b) PAGES news between different components of the integration 20(1): 51-52 climate system is notoriously difficult It is a pivotal time for the ENSO com- Cobb KM et al. (2013) Science 339: 67-70 and this poses problems for simulat- munity. We see a real need for new ac- ing aspects of the climate system, such tivities. First and foremost, there needs as ENSO, that are primarily driven by to be a more integrated approach the coupling between the ocean and to combining data and modeling for 49

PAGES news • Vol 21 • No 2 • August 2013 Myanmar monsoon drought variability inferred by tree rings over the past 300 years: linkages to ENSO

Rosanne D’Arrigo1, J. Palmer2, C. Ummenhofer3, N.N. Kyaw4 and P. Krusic5 1Lamont-Doherty Earth Observatory (LDEO), Palisades, USA; [email protected] 2Gondwana Tree-Ring Laboratory, Canterbury, New Zealand; 3Woods Hole Oceanographic Institution, Woods Hole, USA; 4Forest Department, Naypyidaw, Myanmar; 5Bert Bolin Centre for Climate Research, Sweden University, Stockholm, Sweden A new tree-ring record of teak from Myanmar yields information about past tropical monsoon rainfall variability, including sustained drought conditions, and climatic effects of the El Niño-Southern Oscillation (ENSO), dating back nearly four centuries. Science Highlights: ENSO Science

xtreme climatic conditions linked to the and seasonally variable and not very well progress in chronology development has EAsian monsoon and modulated by the understood. Myanmar’s location in the been made in recent years that now al- ENSO system, such as droughts and floods, transition zone between the South Asian lows us to reconstruct past climate in severely impact human populations. In and East Asian monsoon systems results tropical Asia from tree rings (e.g. Cook et al. 2008, Cyclone Nargis caused >138,000 fa- in a particularly complex spatial pattern of 2010, Monsoon Asia Drought Atlas MADA; talities and more than an estimated 10 bil- precipitation variability. Buckley et al. 2007, 2010; Ummenhofer et lion US$ in economic damage. However, al. 2013). our knowledge of monsoon climate and Asian Monsoon The MADA tree-ring dataset was ENSO-related impacts remains limited, dendroclimatology analyzed for past changes in the Palmer not the least due to sparse paleoclimatic Gleaning additional information on the Drought Severity Index (PDSI) and thus pro- information. Such information is especially long-term climate variability of Myanmar vided evidence for major droughts and wet scarce for Myanmar, which is directly im- and greater monsoon Asia relies on records events in Southeast Asia (e.g. Indonesia, pacted by the effects of the monsoon but from natural or historical paleoclimatic ar- Thailand, and Vietnam). However, in the where even instrumental climate records chives. Tree rings are often ideal as they can case of Myanmar, tree-ring data coverage and related studies of monsoon climate yield precisely dated, annual time series, is still exceedingly sparse and represents a dynamics are rare. Much of the country also referred to as “chronologies”, dating sizeable gap in paleoclimate information of experiences pronounced wet and dry back centuries to millennia. Studying tropi- monsoon Asia. Here we present a new re- seasons linked to the seasonality of the cal tree rings poses considerable difficulties cord for Myanmar that can be incorporated monsoon. Myanmar rainfall correlates sig- because of the lack of pronounced seasons into the MADA network. nificantly with indices of ENSO and Indian at low latitudes where monsoonal rainfall monsoon rainfall (e.g. All India Summer occurs, and the associated obstacles in Myanmar teak Monsoon Rainfall and Core Indian Rainfall), identifying tree species that can be dated Teak (Tectona grandis) is one of the tree spe- although these relationships are spatially for dendrochronology. Nevertheless, much cies that has been used most successfully

Figure 1: Map of Myanmar and adjacent southern monsoon Asia. Pink dot is Maingtha Forest Reserve (MFR) teak tree-ring site north of Mandalay. Background shows monthly Global Precipitation Climatology Centre rainfall data for the period 1951-2007, averaged for May–October when the majority of Myanmar annual rainfall occurs. The figure shows the lower mean rainfall in central Myanmar (modified from D’Arrigo et al. 2011). 50

PAGES news • Vol 21 • No 2 • August 2013 Science Highlights: ENSO Science

Figure 2: Tree-ring width chronology of teak (in dimensionless indices or values) for central Myanmar, spanning 1613-2009 AD, with sample depth (number of individual tree samples). Sample depth is near its peak over much of the chronology, gradually declining prior to the middle 1700s. Plot labels time of Strange Parallels (SP) drought in the 1700s (Buckley et al. 2007, 2010), the late Victorian Great Drought (VGD), and narrow ring at time of 1997-98 “El Niño of the Century” (modified from D’Arrigo et al. 2011). for tropical dendroclimatology. It is endem- ENSO. With the IITM All-India monsoon rain- paleoclimate records published for this ic to Myanmar, but due to its great com- fall index, correlation for May-Jun is r = 0.36 country, is significantly and positively cor- mercial value it is now rapidly disappear- (p < 0.01, n = 57). Correlations are stronger related with local and regional precipita- ing across the country. Our new ring width using the core northeast Indian monsoon tion as well as with larger scale indices of chronology of teak for the Maingtha Forest rainfall index, which represents the region Indian monsoon core rainfall, particularly Reserve is one of the first high-resolution of India opposite the Bay of Bengal from over northeastern India. The Myanmar proxy records that were developed for Myanmar (23°N, 76°E). Averaged over Jan- teak records also correlate negatively with Myanmar (Figs. 1 and 2; D’Arrigo et al. 2012). Jun (1950-2006), the correlation is r = 0.46 Niño-3 SST, consistent with the tenden- It is based on 38 individual series from 20 (p < 0.001). For East Uttar Pradesh, a subdi- cy for El Niño warm events to be linked living trees and spans the years 1613-2009 vision of this core region, the correlation is to drought over Southeast Asia, as they AD. Teak growth at the site is positively 0.47 since 1950 (Jan-Jul, p < 0.001, n = 57); were following the pronounced 1997- correlated with rainfall and PDSI variabil- and r = 0.29 over the maximum common 1998 warm event. Thus, this teak record ity over Myanmar, during and prior to the period (p < 0.001, n = 136; 26°N, 82°E). reflects not only local conditions, but also May-September wet monsoon season. The Myanmar teak chronology corre- the large-scale strength of the circulation Accordingly, the Maingtha Forest Reserve lates negatively with Niño-3 SST (Jul-Aug, of the Asian monsoon-ENSO system. The record reveals past variability of Myanmar r = -0.27, p < 0.05, n = 60). This is consistent timing of the inferred drought conditions hydroclimate. with the tendency for positive Niño-3 SSTs, coincides with megadroughts identified Monthly correlations between the as during El Niño warm events, to be linked elsewhere in southeastern Asia, including Myanmar teak ring-width chronology (Fig. to drought conditions and decreased teak Thailand and Vietnam (Buckley et al. 2007, 2) and instrumental PDSI (1950-2003 AD) growth over southeast Asia, due to the 2010), and which are attributed to vari- were computed for the region overlap- eastward migration of the Walker circula- ability in the tropical Indo-Pacific climate ping our teak site (15-25°N, 95-105°E), for tion. Notably, Myanmar teak growth in the system and the Intertropical Convergence the period, from the year prior to the cur- year 1999, following the so-called “El Niño Zone. Overall, our results indicate much rent year of radial growth to the current of the Century” of 1997-1998, is the low- potential for generating reconstructions of year. Statistically significant (95% level), est of any year on record (Fig. 2). The year monsoon climate dynamics for Myanmar positive correlations were found for the 1998 also shows the lowest annual rainfall and the wider region from tree-ring data. months concurrent and just prior to the value for central Myanmar. Myanmar teak wet monsoon season, from around April growth is also below average during the Note to August. Correlations with PDSI are stron- Strange Parallels drought (Fig. 2) found MADA dataset available online at the NOAA gest when averaged over May and June across southeast Asia in the 1700s. The late Paleoclimatology website, International Tree- Ring Databank (ITRDB). (r = 0.32, n = 54), reflecting the importance Victorian Great Drought was associated of moisture availability for teak growth in with a major ENSO warm episode (1876 References central Myanmar around the time of mon- to 1878) and is perhaps the most spatially Buckley B et al. (2010) PNAS 107: 6748-6752 soon onset. Comparison with local monthly pervasive and severe drought in the MADA Buckley B et al. (2007) Climate Dynamics 29: 63-71 station rainfall records (e.g. for Mandalay tree-ring data set for monsoon Asia (Cook Cook E et al. (2010) Science 328: 486-489 D’Arrigo R et al. (2011) Geophysical Research Letters 38, and Yangon) further confirms that teak et al. 2012; Buckley et al. 2007, 2010). doi:10.1029/2011GL049927 growth in central Myanmar is controlled by Ummenhofer C et al. (2013) Climate Dynamics 40: 1319-1334 moisture availability. The potential of the new Myanmar This teak record also correlates sig- record nificantly with larger-scale climate indices, Our new teak tree-ring width chronol- including those for core Indian rainfall and ogy from central Myanmar, one of the first 51

PAGES news • Vol 21 • No 2 • August 2013 Coral microatoll reconstructions of El Niño-Southern Oscillation: New windows on seasonal and interannual processes

Helen V. McGregor1, C.D. Woodroffe1, M. Fischer2, M.K. Gagan3 and D. Fink2 1School of Earth and Environmental Sciences, University of Wollongong, Australia; [email protected] 2Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Lucas Heights, Australia; 3Research School of Earth Sciences, The Australian National University, Canberra, Australia Porites coral microatolls show δ18O signal reproducibility and fidelity comparable to more conventional coral Science Highlights: ENSO Science growth forms. Longer-lived and fossil microatolls, which grow in suitably flushed environments, contain δ18O signals that can significantly extend instrumental records of the El Niño-Southern Oscillation.

orites corals are the most commonly Microatolls provide information about 1998b; Nurhati et al. 2009) also show simi- Pused genus for reconstructing El Niño- past water levels, from which sea level, lar patterns and magnitude of variability. Southern Oscillation (ENSO). This herma- climatic, or tectonic histories have been Together, the results show that Porites mi- typic coral is found in all tropical reef en- derived (Natawidjaja et al. 2004; Sieh et al. croatolls can be used interchangeably vironments (Veron 2000) with a variety of 2008; Smithers and Woodroffe 2001; Taylor with dome-shaped corals to reconstruct growth forms. Climate reconstructions of a et al. 2008, 1987; Woodroffe and McLean tropical climate variability. century or more have been obtained from 1990; Woodroffe et al. 2012; Zachariasen 18 the most common, dome-shaped Porites et al. 1999). Microatolls also have the ENSO and δ O in modern growth form, whereby the colonies, be- advantage of sampling a narrow depth microatolls at Kiritimati Island ginning from the substrate, grow outward range over long periods of time, which is Kiritimati Island is optimally located and upward towards the ocean surface desirable when reconstructing depth-de- (Evans et al. 1998a) for reconstructions (Knutson et al. 1972). Domed structures, pendent, ENSO-related variables, such as of ENSO. The island lies within the dry however, are not the only Porites growth sea surface temperature (SST) and sea sur- equatorial zone of the central Pacific, and form. face salinity (SSS), together with changes in the NINO3.4 index region where SST in ocean dynamic height, in the tropical variations define ENSO events (Bjerknes Coral microatolls Pacific. 1969; Ropelewski and Halpert 1987). In Porites coral microatolls are found on Studies of domed Porites show that this region El Niño events result in marked shallow reefs where reef topography en- there can be significant differences in positive SST anomalies of up to 3°C in the ables individual colonies to grow up to skeletal δ18O on the sides and tops of the boreal winter, whereas La Niña events the average spring low tide level. Further corals and this is equally a concern for produce negative SST anomalies of 1-2°C upward growth is limited due to expo- laterally-growing microatolls (e.g. Cohen (Wyrtki 1975; Fig. 2a). Rainfall also shows a sure of the upper coral surface at low tide and Hart 1997; McConnaughey 1989). dominant ENSO signal with higher annual (Stoddart and Scoffin 1979). At this point, However, testing of δ18O variability within precipitation during El Niño years. the coral then grows laterally, resulting in and between Porites sp. microatolls living Porites microatolls from Kiritimati reg- a flat-topped discoid growth morphology on reef flats around Kiritimati (Christmas) ister these climatic variations. Variations in termed “microatoll” (Fig. 1). Island in the central Pacific ocean, demon- a composite (stacked) monthly microat- Coral microatolls can live for decades strates no significant differences between oll δ18O record spanning the years 1978- to many centuries (McGregor et al. 2011a), δ18O records from different growth orien- 2007 show a strong inverse correlation are distributed broadly across the Indo- tations within a single microatoll, or be- of r = -0.71 with SST and records major El Pacific region (Scoffin and Stoddart 1978), tween records from microatolls in differ- Niño events (McGregor et al. 2011b; Fig. and their preservation potential is particu- ent reef settings (McGregor et al. 2011b). 2a). This is similar to findings for domed- larly high due to the possibility for rapid Moreover, δ18O records from microatolls Porites from Kiritimati where 70% of the burial beneath sand and coral rubble and from conventional domed Porites variance is shared with SST (Evans et al. through storm ridge or beach deposition. from elsewhere on the atoll (Evans et al. 1999). The stacked microatoll δ18O record

Figure 1: Porites coral microatoll image and X-radiograph. A) Porites coral microatolls on a reef flat at low tide. B) Positive X-radiograph cross- section through a Porites microatoll. Dark and light bands are the high and low-density bands, respectively, that form as the coral grows. Starting from the center, the coral grows upwards until further upward growth is constrained by exposure during the minimum low water level (in this case, 1997/1998). Lateral growth then ensues resulting in a discoid microatoll structure. The location of the living surface in 2007 when the coral was collected is indicated. Dashed lines indicate the outline of coral pieces not X-rayed. 52

PAGES news • Vol 21 • No 2 • August 2013 annual scale, the microatoll δ18O, which peaks in July-August, varies predominantly in-phase with SST, rather than with rainfall. The annual maximum in Kiritimati rainfall occurs in March-April, due to the position of the Intertropical Convergence Zone (ITCZ) (An and Choi 2010; Horel 1982; Mechoso et al. 1995; Waliser and Gautier 1993). That the microatoll δ18O tracks SST at the annual and interannual scale is important; SST variations in the

NINO3.4 Index region are used to define Highlights: ENSO Science ENSO variations. Accordingly, microatoll δ18O from the NINO3.4 region, such as Kiritimati Island, can be used to reconstruct past ENSO variations at multiple timescales.

ENSO signal in fossil microatoll δ18O Fossil Porites microatolls, which were growing in well-flushed environments, offer opportunities to reconstruct tropical SST and ENSO variability beyond the limits of the instrumental record. Initial studies confirm reduced ENSO variability during the middle Holocene (Woodroffe et al. 2003). Individual ENSO events in the late Holocene (Fig. 2e) however, appear at least as intense as those experienced in the past two decades (Woodroffe et al. 2003). One particular El Niño event from 1740 yr BP (Fig. 2e) shows a negative δ18O excursion to ~5.6‰, which suggests substantial ad- Figure 2: Variability of Kiritimati Island records. A) Comparison of the stacked microatoll δ18O record (red line) dition of 18O-depleted rainfall (Woodroffe 18 with Kiritimati SST (blue line) and monthly rainfall (green line). The stacked δ O is a composite of three microatoll and Gagan 2000). The stronger ENSO in records from Kiritimati. The microatoll δ18O record is strongly anti-correlated with Kiritimati SSTs (r = -0.71) and is sensitive to El Niño events (yellow bars). B) Annual-scale and (C) interannual-scale wavelets for the stacked the late Holocene may represent tighter microatoll δ18O (red, y-axis inverted), SST (blue), rainfall (green). D) The circular phase plots show the calendar coupling in the Pacific between the more month (and 95% confidence intervals) when, on average, the wavelets in B) and C) reach their maximum value. southerly ITCZ, the east Pacific cold tongue In general the microatoll δ18O record tracks SST variations. The rainfall is in phase with the SST and coral δ18O data at the interannual scale, but is out of phase at the annual scale. E) Profile of a 18δ O microatoll from Kiritimati dated and the Southern Oscillation, which could at ~1740 yr BP, placed on a new floating age scale (unpublished data) that shows El Niño events (yellow bars) amplify ENSO precipitation variability and 18 similar to those of the past few decades. Black horizontal line is the mean δ O. Figure modified after McGregor et associated teleconnections. Such a sce- al. (2011b), and Woodroffe and Gagan (2000). SST and rainfall data from ERSSTv3b (Smith et al. 2008) and GPCPv2 (Adler et al. 2003), respectively. nario is consistent with terrestrial paleoclimate records indicating a marked increase also corresponds with anomalously high variance is recorded in the stacked mi- in El Niño activity from ~3000 yr BP. We are rainfall years (Fig. 2a); annual mean coral croatoll δ18O record. The record (Fig. 2b,c) undertaking further analysis of fossil coral δ18O values of less than -5.3‰ are found tracks SST variability at interannual (ENSO; microatolls and their annual and interan- only in years when total annual rainfall is 53% of the δ18O variance) and annual nual variability to test this scenario. above 1800 mm. In addition to local SST timescale (14%), consistent with existing and rainfall, the microatoll δ18O signal is analyses of instrumental tropical Pacific Note also negatively correlated with both SST SSTs (Chiu and Newell 1983). Changes at Data are archived at WDC-paleoclimatology and precipitation amount over a broad annual and interannual scales at Kiritimati http://hurricane.ncdc.noaa.gov/pls/paleox/f? p=519:1:4336223539645946::::P1_STUDY_ area of the equatorial Pacific (McGregor are reminiscent of the climate signal of ID:12278 et al. 2011b). Since most of the covariance the eastern equatorial Pacific (Chen et al. between δ18O, SST and precipitation is due 1994; Mitchell and Wallace 1992). Selected references to ENSO, the spatial correlations reflect the ENSO events occur irregularly every Full reference list online under: characteristic ENSO pattern. 2-8 years, yet individual events show a http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf distinctive SST pattern tied (or “phase- Evans MN, Kaplan A, Cane MA (1998a) Paleoceanography 13: 502-516 ENSO and seasonal cycle variance locked”) to the seasonal cycle, such that patterns Mitchell TP, Wallace JM (1992) Journal of Climate 5: 1140-1156 El Niño SST anomalies peak during the McGregor HV et al. (2011b) Geochimica et Cosmochimica Acta 75: Understanding ENSO annual and interan- boreal winter (DJF). The interannual com- 3930-3944 nual cycle variance and interactions can ponent of SST and rainfall records for Woodroffe CD, Gagan MK (2000) Geophysical Research Letters 27(10): 1511-1514 provide important information on ENSO Kiritimati Island show maxima in February, Woodroffe CD, Beech MR, Gagan MK (2003) Geophysical Research Letters processes (Guilyardi et al. 2009). ENSO as does microatoll δ18O (Fig. 2d). At the 30, doi: 10.1029/2002GL015868 53

PAGES news • Vol 21 • No 2 • August 2013 Giant clam recorders of ENSO variability

Mary Elliot1, K. Welsh2 and R. Driscoll3 1Laboratoire de Planetologie et Geodynamique, Université de Nantes, France; [email protected] 2School of Earth Science, University of Queensland, St. Lucia, Australia; 3School of GeoSciences, University of Edinburgh, UK

Giant clam stable isotope profiles from Papua New Guinea faithfully record all the major El Niño events between 1986 and 2003, thus illustrating the usefulness of this archive to reconstruct past ENSO variability.

onsiderable uncertainty remains Here we specifically illustrate the use- ENSO variability for short windows of about the response of the El Niño- fulness of one bivalve species, Tridacna time over the past 130 ka (Tudhope et Science Highlights: ENSO Science C Southern Oscillation (ENSO) to future gigas (Fig. 1) as a natural archive for al. 2001). These records are however climate scenarios (Merryfield 2006). paleo-ENSO. Massive Porites spp. cor- extremely rare because of the ten- Reconstructions of past changes in als and Tridacna spp. clams are both dency for the porous Porites skeleton seasonality and ENSO from natural ar- reef-dwelling, aragonite secreting or- to undergo diagenetic alteration dur- chives have a key role in providing in- ganisms. Their annual bands can be ing periods of subaerial exposure. An formation for understanding both the subsampled and analyzed to derive advantage of T. gigas is that they have full range of variability and the sensi- profiles of oxygen isotope ratios (δ18O) relatively impervious and finely layered tivity of ENSO to changes in climate which have been shown to reflect the shells that inhibit infiltration of ground boundary conditions. Geochemical combined effects of regional sea sur- waters that would lead to the diagenet- time series extracted from skeletons of face temperature (SST) and sea water ic processes of dissolution, recrystal- annually banded reef-building corals δ18O from which they precipitate their lization and precipitation of secondary and mollusks constitute powerful re- aragonite structures (Tudhope et al. calcite. Finally, while coral δ18O show an cords in this regard. A number of excit- 1995; Welsh et al. 2011). Time series of isotopic disequilibrium, Tridacna spp. ing recent studies have illustrated how δ18O in modern and fossil corals col- precipitate their shells in isotopic equi- clams (i.e. bivalves) can be used in pa- lected in northern Papua New Guinea in librium. This provides the possibility to leoenvironmental studies (e.g. Sano et the heart of the Western Pacific Warm more accurately quantify past changes al. 2012; Wanamaker et al. 2012). Pool have been used to reconstruct in absolute SST and see water δ18O.

Figure 1: Photo of a live Tridacna gigas from Heron Island. T. gigas are reef dwelling mollusks which have symbiotic algae living within their mantle. Valves are 50 cm from end to end. Photo K. Welsh. 54

PAGES news • Vol 21 • No 2 • August 2013 different biological controls on carbonate formation and different growth rates.

Giant Clams as recorders of ENSO events In northern Papua New Guinea precipitation and temperatures are coupled on seasonal and interannual timescales. El Niño periods are associated with lower than average SST and drier conditions,

whereas La Niña periods are associated Highlights: ENSO Science with higher than average SST and wet- ter conditions. The associated changes in see water δ18O and SST will thus have cumulative effects on shell δ18O, which will become more positive during El Niño and more negative during La Niña phases. The comparison of the ENSO index with the T. gigas and Porites δ18O records shows that each El Niño event is recorded in the shell and coral profile by isotopic shifts of around 1.0 to 1.2‰ toward more positive values (Fig. 2) reflecting the combined influence of lower temperatures and decreased rainfall. During the El Niño phase of the Southern Oscillation, the region experiences relative drought and slightly reduced SSTs (~-0.2 to -0.5°C anomaly, see Fig. 2). These factors combine to 18 Figure 2: Comparison of T. gigas δ18O profile with ENSO index, local temperature and rainfall data. A) NINO3.4 drive skeletal δ O to heavy values, with index, (B) 3pt smoothed monthly rainfall anomaly (mm day-1, NASA/GPCPV2) for 146.25°E, 6.25°S, (C) T. gigas SST explaining about 30-50% of the δ18O record, (D) Porites δ18O profiles and (E) 3pt smoothed monthly SST anomaly (from IGOSS) for the same grid skeletal δ18O range. box as the rainfall data. Y-axes of the δ18O are inverted. The shaded bands indicate El Niño events. Take away message Calibration shell close to isotopic equilibrium as We show that shells of T. gigas can be To illustrate the potential of T. gigas has been shown previously (e.g. Aharon used to produce multi-decadal climatic as paleo-ENSO recorders, we obtained et al. 1991). records, hence providing a valuable re- a high-resolution δ18O profile from a source for investigating changes to the modern specimen that we compared Comparison of bivalve and frequency and strength of ENSO events to modern Porites coral δ18O profiles coral profiles in the past. The excellent reproduc- and an ENSO index. Samples were col- A striking feature is the high degree of ibility of clam and coral δ18O profiles lected from three localities along the resemblance between the coral and bi- illustrates the strength of using these Huon Peninsula in northern Papua New valve records despite their geographic archives to reconstruct large-scale hy- Guinea. Profiles of δ18O were obtained separation of approximately 30 km and drographic changes. by subsampling the annual growth their average δ18O offset of ~4‰ (Fig. bands using high precision microdrill- 2). Profiles correlate in detail on the References ing devices. The age of the coral and seasonal and on the interannual levels. Elliot M et al. (2009) Palaeogeography, Palaeoclimatology, Palaeoecology 280: 132-142 bivalve δ18O profiles were obtained in- This correlation is particularly interest- Sano Y et al. (2012) Nature Communications 3: 761, doi:10.1038/ncom- dependently (i.e. they were not tuned ing given that paleoclimate archives ob- ms1763 to one another) by counting the annual tained from coastal areas characterized Tudhope AW et al. (2001) Science 291: 1511-1517 growth bands when visible and using by strong SST and salinity gradients can Welsh K et al. (2011) Earth and Planetary Science Letters 307: 266-270 the δ18O maxima and minima to posi- potentially be significantly influenced tion the warmest and coolest months. by the local micro-environmental hy- The T. gigas δ18O profile covers the pe- drography. Our results clearly show riod 1986-2002 and the Porites δ18O re- that corals and clams record large-scale cords cover the period 1987-2001 (Fig. regional patterns. Furthermore, the 2). Average SSTs at the Huon Peninsula good correlation between δ18O coral are around 29°C with an annual range and bivalve profiles remains constant of 0.5-1.5°C in monthly means. The pre- although measurements have been dicted equilibrium skeletal annual aver- obtained from different carbonate se- age δ18O is -1.6‰. Therefore, our results creting organisms with fundamentally confirm that T. gigas precipitate their 55

PAGES news • Vol 21 • No 2 • August 2013 Reconstructing ENSO in the Eastern Tropical Pacific from short-lived marine mollusks

Matthieu Carré1, S. Purca2 and J.P. Sachs3 1UM2-CNRS-IRD, Institut des Sciences de l'Evolution de Montpellier, France; [email protected] 2Instituto del Mar del Peru, Callao, Peru; 3School of Oceanography, University of Washington, Seattle, USA Shells of mollusks from offshore Peru were analyzed to reconstruct variability of the seasonal cycle and ENSO. The data provide insights into past changes in ENSO-related interannual variability in the Eastern Tropical Pacific and in the spatial structure of ENSO. Science Highlights: ENSO Science he focus of much paleoclimate work similarities with the approach of coral interannual variability. The amplitude Ton ENSO has been on records span- studies in that it produces floating win- of the annual cycle (ΔT) on the coast is ning multiple decades, such as those de- dows of climate record at a very high, also clearly related to the Niño1+2 index, rived from corals. Such long records are, often monthly, resolution. It also shares with larger amplitudes during El Niño however, relatively rare, especially in the similarities with the approach of analyz- and smaller ones during La Niña. As a Eastern Tropical Pacific. This important ing many foraminifera shells individually result, the variance of the annual cycle limitation for studying past changes in from the same sediment layer (Koutavas amplitude, Var(ΔT), on the Peruvian coast the spatial pattern of ENSO activity can et al. 2006; Leduc et al. 2009) in that pa- over any period of time is an indicator of be compensated for by obtaining re- leoclimate statistics are estimated from a ENSO variance generally in the Niño1+2 cords from a larger number of shorter- random sample. Isotopic records in mol- region (Fig. 1a). lived organisms. In this case, information lusks enable independent reconstruc- Oxygen stable isotopes (δ18O) in about past climate is not available as a tions of the seasonal cycle. This approach marine shells from central and southern continuous record, but is compiled to ex- is valid for any coastal mollusk species Peru primarily reflect SST variability since tract climate statistics. that faithfully records at least one annual seawater δ18O is not significantly affect- Carré et al. (2013) recently presented SST cycle, and therefore opens up new ed by freshwater input and evaporation a technique that responds to the critical opportunities for direct, quantitative pa- (Carré et al. 2013). Mesodesma donacium need for quantitative estimates of tropi- leo-ENSO reconstructions in the Eastern shells grow continuously throughout the cal marine interannual variability. This Tropical Pacific, using either archeologi- year and record the full annual cycle of technique uses the shells of marine mol- cal shell middens or uplifted fossil shell coastal SST in Peru over a window of 1 to lusks that live for 1-4 years, and thus al- banks from Peru. 4 years at a monthly resolution (Fig. 1b). low us to reconstruct the seasonal range Modern shells (n=13) collected during of sea surface temperature (SST). These ENSO characterization in the the late 20th century provide a random data can then be compared to coral re- Niño1+2 region sample cumulatively providing about 25 cords and GCM outputs. The technique SST variability on the Peruvian coast years of statistics that faithfully repro- of using marine mollusk shells shares is largely dominated by ENSO-related duces the skewed distribution of ENSO

Figure 1: A) Annual mean SST and precipitation for the 1950-2010 period. Location of the Niño1+2 region in the Eastern Tropical Pacific and the Peruvian localities mentioned. B) Polished section of a M. donacium shell, and the associated δ18O plotted on a time scale. The shell was continuously sampled so that every data point integrates about one month. The chronology was determined using shell growth lines. Triangles indicate seasonal extrema used for the calculation of seasonal amplitudes ΔT. 56

PAGES news • Vol 21 • No 2 • August 2013 Science Highlights: ENSO Science

Figure 2: A) Distributions of annual Niño1+2 index from 1950 to 2002, seasonal ΔT values in Callao, Peru from 1950 to 2002 excluding extreme El Niño events in 1982-83 and 1997-98, and ΔT values calculated from a modern sample of M. donacium shells from Ica, Peru. B) Results of Monte Carlo simulations undertaken to estimate the uncertainties of mollusk-derived paleoclimate reconstructions. Plots show the true value (green), the ensemble average value (black line), and the standard error (blue area) vs. the sample size, for the reconstruction of the mean and variance of ΔT. anomalies of this period in Callao, Peru biases (the mean value of the error pop- the shape of their SST distributions. The and in the Niño1+2 region (Fig. 2a). It ulation) and of the standard error (the Eastern Pacific mode is characterized by should be noted that the extreme warm standard deviation of the error popula- positively skewed SST distributions while events of 1982-83 and 1997-98 are not tion) (Fig. 2b). This shell sample yields the Central Pacific mode produces a sym- recorded in the data as the exceptionally thus an estimate of mean annual tem- metric distribution. warm conditions induced mass mortality perature with a precision of ±0.4°C, of Such a change in ENSO asymmetry in the mollusks. However, such events are ENSO variance with a precision of ±30%, has been noted since the 1990s (Yeh et so extraordinary even at the millennial and of ENSO skewness with a precision al. 2009; Boucharel et al. 2011; Dewitte scale (Rein 2007) that they are arguably of ±0.3. This procedure can also be used et al. 2012). La Niña cold events generate not representative of ENSO (Takahashi et to evaluate the relative contributions of negatively skewed SSTs in the Niño1+2 al. 2011). The mollusk shells are comple- error sources, and improve our under- region. The ENSO anomaly distribution mentary to rainfall-related archives as standing of the proxy (Carré et al. 2012). obtained from the modern Peruvian they are sensitive to variability in the ma- This sample will be used as a modern shell sample faithfully reproduces the rine manifestation of ENSO while rainfall- reference to normalize past reconstruc- positive skewness of the late 20th cen- related archives are more sensitive to oc- tions, minimize systematic biases due to tury ENSO, even without recording the casional catastrophic events induced by the archive or to local effects, and allow most extreme ENSO events (Fig. 2a). the atmospheric anomalies of extreme meaningful comparisons with coral re- Fossil mollusk shell samples from Peru ENSO events (Rein 2007). cords and climate simulations. could therefore potentially be used to track past changes in the frequency of Estimating the reconstruction Discriminating Central from Eastern Pacific and Central Pacific events, uncertainties Eastern Pacific modes in the past and provide novel insights into the rela- Estimating reconstruction uncertain- Capotondi et al. (2013, this issue) present tionships between ENSO modes and the ties is a necessary challenge in paleocli- some recent developments in our under- mean climate. mate studies if meaningful comparisons standing of ENSO diversity. Two types with GCM simulations are to be made. of El Niño events, Central Pacific events Selected references To estimate the reconstruction error, we and Eastern Pacific events, have been Full reference list online under: used an in situ instrumental time series defined by the location of the maximum http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf and simulated the reconstruction pro- SST anomaly (Ashok et al. 2007). Because Carré M et al. (2013) Palaeogeography, Palaeoclimatology, Palaeoecology cess (forward proxy model). This was of their significantly different impacts, 371: 45-53 done by randomly extracting short time the question of the evolution of ENSO Carré M, Sachs JP, Wallace JM, Favier C (2012) Climate of the Past 8: samples and adding different types of in both the past and future, should now 433-450 noise to them representing uncertainty also address the variable contribution of Rein B (2007) Quaternary International 161: 56-66 Takahashi K, Montecinos A, Goubanova K, Dewitte B (2011) Geophysical sources (such as analytical error, random Central Pacific and Eastern Pacific ENSO Research Letters 38, doi:10.1029/2011GL047364 growth breaks, or temperature toler- events. In the Niño1+2 region, in the far Yeh S-W et al. (2009) Nature 461: 511-514 ance). Iterating this process thousands of Eastern Pacific, Eastern Pacific and Central times provides an estimate of systematic Pacific modes can be distinguished by 57

PAGES news • Vol 21 • No 2 • August 2013 Challenges in understanding and modeling ENSO

Antonietta Capotondi1, E. Guilyardi2 and B. Kirtman3 1CIRES, University of Colorado, Boulder, USA; [email protected] 2LOCEAN, Institut Pierre Simon Laplace, Paris, France; 3RSMAS/MPO, University of Miami, USA

Some new exciting directions in ENSO research explore inter-event differences in spatial patterns, teleconnections and impacts, asymmetries between warm and cold phases, and the role of extra-tropical regions in triggering ENSO events. However, large uncertainties remain regarding ENSO projections.

he El Niño–Southern Oscillation Science Highlights: ENSO Science T(ENSO) is a naturally occurring fluc- tuation that originates in the tropical Pacific region and affects ecosystems, agriculture, freshwater supplies, hurri- canes and other severe weather events worldwide. Over the last thirty years significant progress has been made in improving our understanding of the dynamic processes underlying ENSO, including the ocean-atmosphere feedbacks that are essential to this coupled phenomenon. The oscillatory nature of ENSO, al- ternating between El Niño and La Niña events, can be described in terms of the recharge and discharge of warm water to and from the equatorial thermocline (“recharge oscillator”; Jin 1997) or in terms of thermocline depth changes associated with wave propagation (“de- layed oscillator”, e.g. Suarez and Schopf 1988). These simple paradigms of ENSO as a linear oscillator capture basic dynamical processes; however, they fail to explain differences among events and asymmetries between warm and cold Figure 1: Composite spatial pattern of SST anomalies for the “canonical” (top) and “Central Pacific”(bottom) El Niño types (SODA 2.0.2/3) from 1958 to 2007 computed with the approach of Kug et al. (2009). Canonical El Niños episodes. Moreover, they ignore the im- are characterized by a boreal winter (DJF) Niño3 index larger than 0.5°C and larger than the Niño4 index (red and portant role of stochastic atmospheric blue dashed boxes, respectively), and vice versa for the Central Pacific El Niño (from Capotondi, in press). Observed phenomena (e.g. westerly wind bursts) El Niño events can be described as blends of these two end-member types. and other non-linear effects. Understanding and predicting the various authors). They argued that this Choi et al. 2011; McPhaden et al. 2011). diverse characteristics of El Niño and La type of El Niño is not the same as the “ca- A number of other studies dispute the Niña events is important since their re- nonical” El Niño because its center of ac- statistical significance of the distinc- gional climatic impact can vary heavily tion is in the central Pacific instead of the tion between the two El Niño types or depending on the longitudinal location eastern Pacific, as illustrated in Figure 1. at least of the increasing occurrence of of the SST anomalies. Also, understand- It was also suggested that Central Pacific the Central Pacific variety. They argue ing how teleconnections vary depend- El Niños have become more frequent either that the reliable observational ing on the event type is crucial when in recent decades, and their frequency record is too short to detect such a dis- proxy records are used to reconstruct may increase further with global warm- tinction (Nicholls 2008; McPhaden et past ENSO. Hence, exciting new research ing (Yeh et al. 2009). Subsequent ob- al. 2011), or that they have found no developments have emerged to address servational and modeling studies have trend using other approaches (Giese this observed ENSO diversity. tried to define the Central Pacific El Niño and Ray 2011; Newman et al. 2011; Yeh more precisely or differently (Kug et al. et al. 2011). Other authors alternatively Understanding ENSO dynamics 2009; Kao and Yu 2009). However, as yet suggest to distinguish between other The first development is a renewed inno agreement has been reached on the types of El Niño, such as standard and terest in inter-event differences and the best way to characterize the new Central extreme El Niños (Lengaigne and Vecchi related “El Niño Modoki” debate. Based Pacific-type of El Niño. Some studies 2010; Takahashi et al. 2011). Due to the on a statistical analysis of SST in the have tried to distinguish the central asymmetric nature of the warm and cold tropical Pacific, Ashok et al. (2007) sug- Pacific and eastern Pacific (canonical) phases of ENSO, Kug and Ham (2011) gested the existence of another type of warm events based on their underlying could not identify analogous distinc- El Niño, called Central Pacific El Niño (or dynamical processes, and their relation- tions for La Niña, neither in observations Date Line El Niño or El Niño Modoki by ship with the oceanic mean state (e.g. nor in the simulations of the Climate 58

PAGES news • Vol 21 • No 2 • August 2013 example by bridging ENSO theoretical frameworks and climate modeling. Resulting innovations include the development of indices that can be used to assess the stability of ENSO in Coupled General Circulation Models (CGCMs), and intermediate models that can be used to predict ENSO characteristics from aspects of the mean state. By focusing on the key processes affecting ENSO dynamics (e.g. the thermocline feed-

backs or the wind stress response to SST Highlights: ENSO Science anomalies), these new approaches have much potential to accelerate progress and improve the representation of ENSO in complex climate models. Not only can these new methods help address the question of whether the characteristics of ENSO are changing in a changing climate, but potentially they can also improve the reliability of centennial-scale climate projections and predictions on seasonal time scales.

Figure 2: Standard deviation of Niño3 SST anomalies for thirteen CMIP5 model experiments. Blue bars, pre-industrial Looking forward control experiments; orange bars, years 90-140 from the 1% year-1 CO increase experiments; red bars, years 50-150 2 At present, we don’t know enough about after an abrupt four-fold CO2 increase. Model names are given on the x-axis. Error bars indicate the standard deviations over 50-year windows of Niño3 anomalies in the multi-century control experiments. Thus, when the how ENSO has changed in the past (the Niño3 standard deviation in one of the CO2 runs falls outside the error bar, the changes are deemed significant (modified from Guilyardi et al. 2012b). As in CMIP3, this new set of model simulations does not provide a clear detection problem) and what caused trend for ENSO strength in a warming climate. the changes i.e. the contribution from external forcing vs. that due to internal Model Intercomparison Project version sources and mechanisms proposed may variability (the attribution problem). 3 (CMIP3). Due to the large societal rel- explain the diversity of El Niño events, Given the much too short reliable obser- evance of the impacts of ENSO, it is im- both in observations and in models. vational record (both for ENSO and for portant to predict not only whether an the external forcing fields, Wittenberg El Niño (or La Niña) event is expected, ENSO in climate models and 2009), the complexity and diversity of but if possible which expression the future projections the paradigms and processes involved, anomaly will take. Fueled by these early Most of our understanding of the rep- and the shortcomings of current state- studies, new questions are now emerg- resentation of ENSO in climate models of-the-art models, understanding the ing asking, for instance, if discrete has been derived from the analysis of causes of ENSO property changes, both classes of ENSO events emerge from the model simulations of the Climate in the past and in the future, remains a observations, paleoclimate records and Model Intercomparison Project versions considerable challenge. For instance model simulations, or if ENSO diversity is 3 (CMIP3) and 5 (CMIP5). While the mod- Collins et al. (2010) concluded that it is better described as a continuum with a els appear to reproduce some of the ba- not yet possible to say whether ENSO few characteristic extremes (e.g. Wu and sic processes and feedbacks associated activity will be enhanced or damped in Kirtman 2005). with ENSO, the details of the SST anom- future climate scenarios, or if the fre- Other new lines of research in ENSO aly patterns as well as the temporal evo- quency of events will change (Fig. 2). diversity include revisiting the relative lution of the anomalies often differ from Paleoclimatic and paleoceanographic roles of the ocean and the atmosphere the observed, and reflect model biases reconstructions have the potential to in shaping ENSO (Kitoh et al. 1999; or erroneous atmosphere-ocean inter- initiate the next quantum leap. Guilyardi et al. 2004; Dommenget 2010; actions (Capotondi et al. 2006, Guilyardi Clement et al 2011; Lloyd et al. 2011) and et al. 2009; Guilyardi et al. 2012a). For Selected references exploring the role of regions outside the example, in most of the CMIP3 mod- Full reference list online under: tropical Pacific in triggering ENSO events els, the largest anomalies are located http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf (Vimont et al. 2003; Izumo et al. 2010; further west along the equator than Ashok K et al. (2007) Journal of Geophysical Research 112, Terray 2011; Wang et al. 2011). An exam- in observations. Furthermore, in many doi:10.1029/2006JC003798 ple of remote influence is the seasonal models ENSO events tend to occur more Capotondi A., Wittenberg A, Masina S (2006) Ocean Modeling 15: footprinting mechanism (Vimont et al. frequently and regularly than in the real 274-298. 2003): Atmospheric variability originat- world. While the models keep improving Collins M et al. (2010) Nature Geoscience 3 (6): 391-397 Guilyardi E et al. (2009) Bulletin of the American Meteorological Society ing in the North Pacific can impact the in their simulation of ENSO, no quan- 90: 325-340 subtropical ocean during winter, and the tum leap was seen in CMIP5 compared Guilyardi E et al. (2012a) Bulletin of the American Meteorological Society resulting springtime SST anomalies alter against CMIP3 (Guilyardi et al. 2012b). 93: 235-238 the atmosphere-ocean system in the Over the past few years, new prom- tropics during the following summer, fall ising methods have emerged, which and winter. The diversity of geographical could improve ENSO simulations, for 59

PAGES news • Vol 21 • No 2 • August 2013 Coral-model comparison highlighting the role of salinity in long-term trends

Diane M. Thompson1, T.R. Ault1, M.N. Evans2,1, J.E. Cole1,3, J. Emile-Geay4, A.N. LeGrande5 1Department of Geosciences, University of Arizona, Tucson, USA; [email protected] 2Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, USA; 3Department of Atmo- spheric Sciences, University of Arizona, Tucson; USA; 4Department of Earth Sciences, University of Southern California, Los Angeles, USA; 5NASA Goddard Institute for Space Studies and Center for Climate Systems Research, Columbia University, New York, USA We use a simple proxy model to compare climate model simulations and coral records over the 20th century. While models and observations agree that the tropical oceans have warmed, they disagree on the extent and

Science Highlights: ENSO Science origin of freshening.

he response of the tropical Pacific Ocean and the oxygen isotopic ratio of seawater found that this simple model was able to to anthropogenic climate change re- (δ18O ) at the time of growth; the latter is in capture the spatial and temporal pattern of T sw mains uncertain, in part because we do turn strongly related to sea-surface salinity ENSO and the linear trend observed in corals 18 not fully understand how the region has re- (SSS). As direct measurements of δ Osw are from 1958 to 1990. Modeling pseudocorals sponded to anthropogenic change over the scarce, we model the expected δ18O anoma- with temperature and salinity individually th th 18 20 century. Analysis of 20 century temper- lies of corals (δ Opseudocoral) as a function of also demonstrated that although warming ature and salinity trends is hindered by lim- sea-surface temperature (SST) and salinity accounts for the majority of the observed 18 ited historical data, lack of long-term in situ anomalies: δ Ocoral trend (60% of trend variance), salin- measurements, and disagreement among ity also plays an important role (40% of trend ∆δ18O = a ∆SST + a ∆SSS coupled general circulation model (CGCM) pseudocoral 1 2 variance). The addition of the SSS term im- -1 hindcasts. High-resolution paleoclimate We define coefficient a1 as -0.22 ‰ ºC proved agreement between modeled pseu- records, particularly the large network of based on the relationship between tem- docoral and observed coral δ18O trends over tropical Pacific coral oxygen isotope records, perature and the isotopic composition of pseudocoral trends modeled from SST only are an alternate means of assessing tropi- the skeleton in well-studied coral genera (Thompson et al. 2011). cal climate trends. However, these natural (e.g. Evans et al. 2000). Coefficient a is esti- 2 th archives of past climate are biased by their mated from basin-scale regression analysis 20 century trends 18 th limited spatial and temporal distribution of available observations of δ Osw on SSS When driven with the output from 20 and their biologically mediated response to (LeGrande and Schmidt 2006; LeGrande century simulations of a subset of CGCMs climate. By converting native climate vari- and Schmidt 2011). Uncertainty in the ap- from the third phase of the Coupled Model ables (e.g. temperature and net freshwater plication of the resulting bivariate model Intercomparison Project (CMIP3) sampled flux) into synthetic (“pseudo”) proxy records arises from the assumed independence and at the coral locations, none of the pseudo-

via an explicit proxy system model (“forward linearization of a1 and a2 and substitution of coral networks reproduced the magnitude model”), we can directly compare historical the second term for a direct dependence on of the secular trend, the change in mean 18 climate data and climate model simulations δ Osw. state, or the change in ENSO-related vari- with coral records, and assess biases and un- We apply this simple forward model ance observed in the actual coral network 18 certainties associated with each. of δ Opseudocoral to generate synthetic coral from 1890 to 1990 (Thompson et al. 2011). (pseudocoral) records from historical ob- Applying this same approach to the newer Pseudocoral modeling servations and CGCM simulations of tem- (CMIP5) suite of historical climate simula- The stable oxygen isotope ratio (δ18O) of cor- perature and salinity (Thompson et al. 2011). tions, we find that large discrepancies still al aragonite is a function of the temperature When driven with historical climate data, we remain in the magnitude (Fig. 1), spatial pattern and ENSO-related variance of the simulated and observed trends. Differences 18 between observed and simulated δ Ocoral trends may stem from the simplicity of our 18 forward model of δ Ocoral, biological bias in the coral records, or model-inherent bias in the CGCM SST and SSS fields. Although we cannot yet completely rule out a non-climatic origin for the ampli- 18 tude of the observed δ Ocoral trend, previous work highlights biases in simulated salinity fields as a potential source of the observed- simulated trend discrepancy (Thompson et al. 2011). We found that the suite of CMIP3 and CMIP5 CGCMs simulate weak and heterogeneous salinity trends that are Figure 1: Magnitude of the trend slope (‰ per decade), computed by linear regression through the trend principal indistinguishable in magnitude from that th component (PC) in corals (far left) and pseudocorals modeled from Simple Ocean Data Assimilation (SODA) 20 of unforced control runs (Fig. 1). Further, century reanalysis (Carton and Giese 2008; Compo et al. 2011), a 500-year control run from the CGCM version CM2.1 of the Geophysical Fluid Dynamics Laboratory (GFDL cm2.1) (Wittenberg et al. 2009), and all CMIP-3 and CMIP-5 the pseudocoral simulations (Fig. 1) illus- 18 model ensembles (average of all models from each modeling group). In each case, δ Ocoral was modeled from trate that the magnitude of the simulated SST and SSS (1), SST only (2), and SSS only (3). Error bars depict ± 1 standard deviation of the regression estimate. 18 δ Ocoral trend can be less than the sum of 60

PAGES news • Vol 21 • No 2 • August 2013 Region Observed slope Monthly ModelE2 Annual ModelE2 Decadal ModelE2 ModelE2 at observations

Tropical Pacific 0.27 0.35 0.35 0.36 0.32 South Pacific 0.45 0.33 0.33 0.37 0.30 Indian Ocean 0.16 0.33 0.35 0.35 0.27

Table 1: Slope of the regional δ18Osw-SSS relationship calculated from observations (LeGrande and Schmidt 2006) and the GISS ModelE2 control simulation. Annual and decadal series were calculated by averaging the monthly data at yearly and 10-year intervals.

18 18 the individual trends arising from tempera- valid approximation for δ Osw, but also that of the δ Osw-SSS relationship simulated for ture and salinity when the temperature and this relationship does not vary significantly the tropical regions in the GISS model were salinity trends are confounding at the coral through time or within regions. Although generally higher and more spatially consis- sites (as observed for SODA modeled pseu- this assumption does not likely hold at the tent than those calculated from the limited Highlights: ENSO Science docorals). However, given the limited num- millennial timescale (e.g. LeGrande and observations (LeGrande and Schmidt 2006; ber of historical SSS observations, much Schmidt 2011), it may be appropriate for Table 1). If we analyze only model output uncertainty remains in the sign and magni- simulating tropical variability during the corresponding to the location and time of tude of the 20th century salinity trend. When past century. Here we assess the stability of observations, the data-model discrepancy is 18 forward-modeling pseudocorals with data the δ Osw-SSS relationship through space reduced but not eliminated (Table 1). These from two recent versions of an extended and time on monthly to decadal timescales discrepancies likely arise from the scarcity of 18 reanalysis (SODA v2.2.4 and v2.2.6; Ray and using a control simulation of an isotope- paired δ Osw and SSS observations as well as Giese 2012), we found that even the rela- enabled version of the Goddard Institute for from the modeling of precipitation process- tive contribution of temperature and salinity Space Studies model (GISS ModelE2, pro- es, and will be reduced by a combination of to the observed pseudocoral trend differs vided by A. LeGrande). In these simulations, continued seawater sampling and model 18 (Fig.1); this discrepancy likely arises from the the relationship between δ Osw and SSS was development. choice of wind field used in the reanalyses generally regionally consistent over month- If the current observational dataset (G. Compo, personal communication). These ly to decadal timescales (Table 1), suggest- underestimates the true magnitude of the 18 18 results suggest a need for improved simula- ing that the substitution of SSS for δ Osw is δ Osw-SSS slope, our simple forward model tion of moisture transport and additional unlikely to impose low-frequency variability will underestimate the magnitude of the 18 18 proxy reconstructions of salinity and δ Osw on the modeled pseudocorals. However, we true δ Ocoral trend when a significant fresh- 18 to better understand their relationship and find that the slope of the δ Osw-SSS relation- ening is observed. Estimates of uncertainty 18 the sign and magnitude of their change. ship and its sensitivity to timescale varies in the δ Osw-SSS slope should be incorpo- within the broad regions of Table 1, par- rated in future work simulating pseudo- 18 δ Osw vs SSS: insights from isotope ticularly between the eastern and western coral trends. Nonetheless, the salinity trend enabled simulations Pacific (Fig. 2). Similar regional variability in CMIP3 and CMIP5 models is weak, and 18 18 In substituting the δ Osw-SSS relationship in the slope of the δ Osw-SSS relationship near zero, suggesting that the uncertainty 18 calculated from the limited observational was observed in an isotope enabled ver- in the δ Osw-SSS relationship is not likely 18 dataset for δ Osw, our simple forward model sion of the UK Met Office model (HadCM3; the source of the difference in the coral and assumes that this relationship is not only a Russon et al. 2013). Additionally, the slopes pseudocoral trend magnitude. The presence of a significant freshening in historical observations suggests that this discrepancy is more likely due to an underestimation of the 20th century freshening in the CGCMs.

Acknowledgements We thank A. Wittenberg, B. Giese and G. Compo for contributing data and analysis products, and all those responsible for the PMIP3/CMIP5 simulation archives. Supported by NOAA’s Climate Change Data and Detection Program (NA10OAR4310115 to JEG, MNE, DMT; NA08OAR4310682 to JEC) and P.E.O International.

Selected references Full reference list online under: http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf

Evans MN, Kaplan A, Cane MA (2000) Paleoceanography 15(5): 551-563 LeGrande A, Schmidt G (2011), Paleoceanography 26, doi:10.1029/2010PA002043 LeGrande AN, Schmidt GA (2006) Geophysical Research Letters 33, doi:10.1029/2006GL026011 Russon, T, Tudhope AW, Hegerl GC, Collins M, and Tindall J (2013) Climate of the Past Discussions, 9, 741-773 Thompson DM et al. (2011) Geophysical Research Letters, doi:10.1029/2011GL048224

18 Figure 2: Slope of the GISS ModelE2 simulated δ Osw vs. salinity relationship at each gridbox on monthly (top) and decadal (bottom) timescales. Decadal series were calculated by averaging the monthly data at 10-year intervals. 61

PAGES news • Vol 21 • No 2 • August 2013 The response of pseudo-corals to ENSO in an isotope- enabled climate model

Tom Russon1, A.W. Tudhope1, G.C. Hegerl1, M. Collins2 and J. Tindall3 1School of GeoSciences, University of Edinburgh, UK; [email protected] 2College of Engineering, Mathematics and Physical Sciences, University of Exeter, UK; 3School of Earth and Environment, University of Leeds, UK

Coral stable isotope records provide information on past ENSO variability. However, separating the contributions from variability in ocean temperature and the hydrological cycle to such records remains challenging. Model simulations using water isotope-enabled climate models provide powerful tools to explore this. Science Highlights: ENSO Science he stable oxygen isotopic composi- ENSO, such as the local precipitation- relationship remains stationary through- Ttion of the aragonite of reef-dwelling evaporation balance, but others relate in- out the period of interest. An example 18 corals (δ Ocoral) relates to both the tem- stead to the integrated hydrological his- of a case in which the first assumption perature, taken here as being the sea sur- tory of the precipitation. In regions with a may be compromised is if the source re- face temperature (SST), and the isotopic very active hydrological cycle, where the gion for precipitation changes with the 18 18 composition of the seawater (δ Osw) in δ Osw contribution is thought to domi- magnitude of ENSO events. The second 18 which calcification occurred. The relation- nate the overall δ Ocoral signal, records assumption may be compromised if the 18 ship between δ Ocoral and SST, derived have been used to infer past changes in dominant spatial “modes” of ENSO vari- from modern calibrations, generally has precipitation, rather than SST (Cole and ability change through time (Yeh et al. a slope that is close to the value of -0.2‰ Fairbanks 1990). Fully quantifying the 2009; Capotondi et al., this issue). Climate K-1 found for inorganically precipitated spatial pattern of relative contributions model realizations of the response of 18 18 18 carbonates (e.g. Gagan et al. 2000; Zhou from SST and δ Osw to δ Ocoral remains a δ Osw to ENSO fluctuations have the po- and Zheng 2003). Some long-lived corals challenge for interpreting these records. tential to better constrain the validity of generate sufficiently high growth rates as such assumptions. 18 Limitations of the instrumental to allow measurement of δ Ocoral at sub- annual resolution over multiple decades record Representing pseudo-corals 18 in an isotope-enabled climate (e.g. Carré et al., this issue). These proper- Instrumental records of δ Osw are not ties provide a strong basis for using fossil available for most coral bearing loca- model 18 corals δ Ocoral to reconstruct SST variabil- tions and those that do exist are typi- Only a few coupled Ocean/Atmosphere ity associated with the El-Niño Southern cally too short to allow robust quantifi- General Circulation Models (GCMs) in- 18 Oscillation (ENSO) over the Holocene and cation of inter-annual changes in δ Osw clude the additional hydrological cycle LGM (e.g. Tudhope et al. 2001; Cobb et al. (Schmidt 1999; LeGrande and Schmidt processes required to directly simulate 18 18 2003). 2006). However, the δ Osw contribution water isotope variables such as δ Osw. 18 However, δ Ocoral also depends di- can be estimated empirically from an Modeling pseudo-coral records based on 18 18 rectly on δ Osw, which is in turn influ- instrumental SST record, provided that the use of δ Osw proxy variables such as 18 enced by a range of factors. Some of (1) the ENSO-related δ Osw fluctuations salinity, provide a strategy to avoid this these factors may be closely coupled to relate linearly to those in SST and (2) this limitation (Thompson et al. 2011, this

18 18 18 -1 Figure 1: The percentage of modeled interannual δ Ocoral variance accounted for by δ Osw, assuming a SST - δ Ocoral slope of -0.2‰ K . The 10% and 50% levels are contoured in red and green respectively and the location of the NINO4 region is highlighted in gray. 62

PAGES news • Vol 21 • No 2 • August 2013 Science Highlights: ENSO Science

18 18 Figure 2: Scatter plots of modeled monthly inter-annual anomaly data within the NINO4 box. A) δ Osw plotted against SST. B) δ Ocoral plotted against SST, with the assumed -1 18 slope of -0.2‰ K used to calculate δ Ocoral shown as a dashed line. Points are color coded according to their SST anomaly values, such that those lying in the upper and lower standard deviations of the SST data are highlighted red and blue, and are associated with El-Niño and La-Niña events respectively. issue). However, work with the isotope- accounted for by the inter-annual vari- effectively adds (a relatively small degree 18 18 enabled Goddard Institute for Space ance of modeled δ Osw is less than 10% of) noise to the δ Ocoral record. However, Studies ModelE-R shows that the slopes (red contour in Fig. 1) across much of the during larger El-Niño events a weak an- 18 18 of the δ Osw-salinity relationships may subtropical eastern and equatorial Pacific, ti-correlation between SST and δ Osw differ when calculated over temporal and but higher in the Warm Pool, South becomes evident (lower right quadrant spatial patterns of variability (LeGrande Pacific Convergence Zone, and central of Fig. 2a), such that for SST anomalies and Schmidt 2009). The results presented American coastal regions. This affirms exceeding ~1.5K, a deviation from the 18 18 here are based on a 750-year long pre- that the δ Osw contribution is indeed im- imposed slope of the δ Ocoral -SST rela- industrial control simulation of another portant in regions of high precipitation tionship becomes noticeable (lower right isotope-enabled coupled GCM, the UK variability (Tudhope et al. 2001; Cole and quadrant of Fig. 2b). For large El-Niño Met Office’s HadCM3 (Russon et al. 2013; Fairbanks 1990). Consequently, whilst events, estimating NINO4 SST directly 18 18 Tindall et al. 2009). The inter-annual vari- eastern Pacific pseudo-coral δ Ocoral from δ Ocoral would result in a relative ability of the tropical climate in HadCM3 could be reasonably used as a proxy of overestimation of the true SST anomaly is known to be dominated by processes SST fluctuations, this is not the case for all by over 20%. This effect would compli- exhibiting spatial and temporal patterns locations. However, only in very limited cate attempts to accurately infer the 18 resembling, albeit with significant biases, regions does the δ Osw contribution ex- relative magnitudes of the SST anomalies those of the observed ENSO phenom- ceed 50% (green contour in Fig. 1). Even during El-Niño events of different magni- 18 enon (Collins et al. 2001; Guilyardi et al. within the high precipitation regions, tude from proxy records of δ Ocoral alone. 2006). For this study, the water isotope there are no locations where one would regimes were brought to equilibrium by expect the SST contribution to be neg- Acknowledgements first running the model for an additional ligible. Therefore, interpreting western This work was funded by NERC grant NE/ 300 years from an assumed initialization Pacific corals as solely (or even predomi- H009957/1 18 state. The pseudo-coral δ Ocoral field is nantly) dependent on either temperature then calculated directly by inputting the or precipitation appears misguided for Note 18 The model data presented here are available monthly-mean SST and δ Osw data for many locations in the model. the ocean grid resolution of 1.25º by 1.25º upon request from the corresponding author. over the tropical Pacific (30ºS-30ºN and Non-linearity between SST and 18 120ºE-80ºW) into a linear formulation of δ Osw Selected references the standard isotope paleo-temperature The regional relationships between mod- Full reference list online under: 18 18 http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf equation, with an assumed δ Ocoral to SST eled SST and δ Osw are not always simple. slope of -0.2‰ K-1. For example, in the western equatorial LeGrande AN, Schmidt GA (2006) Geophysical Research Letters 33, Pacific NINO4 region (grey rectangle in doi:10.1029/2006GL026011 18 Quantifying the δ Osw Fig. 1), little relationship is seen between LeGrande AN, Schmidt GA (2009) Climate of the Past 5(3): 441-455 contribution 18 Russon T et al. (2013) Climate of the Past 9: 1543-1557 modeled SST and δ Osw during La-Niña Modeled inter-annual fluctuations in (blue crosses), neutral (grey crosses) and Thompson DM et al. (2011) Geophysical Research Letters 38, doi: 10.1029/2011GL048224 δ18O vary inversely with those in SST even moderate El-Niño (red crosses) re- sw Tindall JC, Valdes PJ and Sime LC (2009) Journal of Geophysical Research across almost the entire tropical Pacific gimes (Fig. 2a). This results in pseudo- 114, doi:10.1029/2008JD010825 18 region such that they combine positively. coral δ Ocoral values that lie close to the 18 The fraction of the inter-annual variance imposed δ Ocoral -SST slope (Fig. 2b). 18 18 of pseudo-coral δ Ocoral that could be In such situations, the δ Osw variability 63

PAGES news • Vol 21 • No 2 • August 2013 ENSO and changes in the mean state in Holocene simulations

P. Braconnot1 and Y. Luan1,2 1Laboratoire des Sciences du Climat et de l’Environnement, Gif-sur-Yvette, France; [email protected] 2State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Beijing, China

Simulations suggest that Pacific interannual changes in sea surface temperature (SST) are smaller than SST seasonality, whereas the opposite is modeled for precipitation. Nonstationarity in ENSO patterns may affect the interpretation of past variability changes from climate records. Science Highlights: ENSO Science

igh-resolution paleoclimate indica- presence of melting remnant ice sheets in example, the cold tongue (i.e. the equa- Htors provide a unique opportunity the northern hemisphere during the Early torial region in the Pacific with cold SSTs) to reconstruct and understand how sea- Holocene, may have partially offset the of normal years penetrates too far west sonal climate variability and the El Niño- impact of the insolation forcing. In this along the equator (not shown), as does Southern Oscillation (ENSO) have evolved study, simulations of the Early Holocene the equatorial warming associated with in the past. However, most climate inter- and the Mid-Holocene are used to infer El Niño events (Fig. 1a,c). As a result the pretations of paleorecords assume sta- how the slow variation of the Earth’s or- horseshoe structure of El Niño’s SST and tionarity, i.e. that the modern relationship bital parameters affected ENSO variability precipitation patterns seen today in the between a given climate sensor and ENSO (Luan et al. 2012). We also conducted a western Pacific is not well pronounced. was the same in the past, which might not set of sensitivity experiments to exam- This discrepancy can lead to misinterpre- be true. Therefore, one of the difficulties ine how meltwater release and the pres- tation when comparing simulated chang- is to infer how changes in mean state ence of remnant northern hemisphere ice es with high-resolution coral records and variability have shaped the evolu- sheets may have impacted ENSO charac- from the central equatorial Pacific region tion of SST and other environmental teristics (Braconnot et al. 2012; Marzin et (Brown et al. 2008). In addition, simula- factors, such as precipitation and wind, al. in press). The different model years in tions of ENSO variability are also damped in the past. Using a suite of simulations the simulations were classified either as in the eastern Pacific when compared performed with the climate model of the El Niño, La Niña, or normal years based with modern observations. Institut Pierre Simon LaPlace (IPSL-CM4; on the December-January-February Marti et al. 2010), we discuss the relative SST anomalies in the Niño3 region Spatial variability of ENSO effects of different Holocene forcings on (150°W-90°W, 5°S-5°N). Anomalies were patterns seasonality and interannual variability only classified as El Niño or La Niña events Our simulations indicate that over time between the early Holocene and the pre- when they crossed a SST threshold of changes in forcing influence the loca- industrial period. 1.2 times the standard deviation derived tion and intensity of the maximum SST from the pre-industrial SST time series. and precipitation anomalies. In the Early Sensitivity experiments ENSO is the dominant mode of SST Holocene for example, insolation forcing Previous simulations and model data and precipitation variability in all of the slightly damps the strength of the peak comparison have established that long- simulations. However, both the pre-indus- of the event (Fig. 1) compared with pre- term changes in insolation affected ENSO trial and past El Niño event simulations industrial control simulations. In these variability in the Holocene (Clement et are affected by biases common to most Early Holocene examples a major reduc- al. 2000; Moy et al. 2002). However, the climate models (Zheng et al. 2008). For tion is simulated west of the maximum

Figure 1: Composite sea surface temperature (SST) anomaly and precipitation anomaly maps during El Niño events as simulated by the IPSL-CM4 climate model for pre- industrial and Early Holocene (9.5 ka BP) climates. The anomalies describe the departures from normal years in each simulation at the peak of the event in December-January. Isolines are plotted every 0.5°C for SST with a refinement of 0.25°C around the 0 line, and every 1 mm -1d for precipitation with a refinement of 0.5 mm -1d around the 0 line. The red and blue dashed boxes in the lower left panel show the Niño3 and Niño4 regions, respectively. 64

PAGES news • Vol 21 • No 2 • August 2013 SST anomaly found in the pre-industrial control simulation, and another important reduction occurs on the South- American coast. Figure 1 therefore illustrates that the teleconnections between the different parts of the Pacific basin, as well as between the Pacific and the Indian Ocean, vary depending on the mean climate state. This further suggests that the climatic relationships between regions today are not stationary in time. Science Highlights: ENSO Science Changing seasonality and interannual variability accross time Figure 2: Sensitivity experiments: Diagrams of precipitation (mm d-1) averaged over the Niño3 and Niño4 regions in Insolation forcing also affects the season- the Pacific Ocean. Groups of columns show the magnitude of the seasonal cycle and the peak (December) magnitude of El Niño and La Niña events for each of the simulations discussed in the text: pre-industrial (CTRL), Early ality of SST and precipitation. Changes in Holocene (9.5 ka BP, EHnF), Early Holocene with a fresh water flux mimicking ice sheet melting in the North Atlantic the magnitude of the seasonal cycle of (EHwF) and Early Holocene with the presence of remnant Laurentide and Fennoscandian ice sheets (EHIS). See precipitation mirror the changes in the Braconnot et al. (2012) for details on the methodology and statistical significance. The magnitude of the seasonal cycle is computed as the difference between maximum and minimum monthly values at the annual time scale. seasonal cycle of SSTs. El Niño and La Niña anomalies correspond to the value at the peak of the event in December. Figure 2 shows the Early Holocene insolation only simulations (EHnF), and reconstructions, which are primarily de- west Pacific is affected differently by forc- pre-industrial control runs (CTRL) for termined by the relative sensitivity of ings, but that SST variations during the two regions; the West (Niño4 region; climate sensors to seasonality and inter- Holocene were predominantly influenced 160°E-150°W, 5°S-5°N), and East (Niño3 annual variability, must take this into ac- by changes in seasonality driven by the region; 150°W-90°W, 5°S-5°N). Compared count in their calibrations in order to de- Earth’s orbital parameters such as insola- with the pre-industrial control run, the rive robust reconstructions. tion. seasonal cycle of precipitation (“seas” in In the central to western part of the Linking the development of an El Fig. 2) was increased in the West (Niño4 basin, changes in seasonality and interan- Niño event with changes in the seasonal region) and decreased in the East (Niño3 nual variability act in opposite directions, evolution of the thermocline depth is a region) in the Early Holocene. These pre- and our results suggest that only the nat- key factor explaining the damping of the cipitation changes follow SST changes ural archives that are sensitive to precipi- simulated ENSO in the IPSL models (Luan (not shown). It indicates that the seasonal tation would register large ENSO changes et al. 2012). Our sensitivity experiments variability in insolation was in phase with in the Early Holocene. show that fresh water fluxes partially the SST seasonal cycle in the West and counteract the insolation-driven season- out of phase, in the East. The SST seasonal Role of additional forcings al phasing and the melting remnant ice cycle is further amplified by the east-west The addition of a fresh water flux in the sheets strongly affect the mean thermo- asymmetry of cloud feedback and the North Atlantic in the Early Holocene cline depth and east-west gradient in SSTs dynamic response of SST to anomalous simulations leads to increased interan- (Luan et al. submitted). However, it seems westerly winds in the eastern equato- nual variability and a slight increase in that precipitation and SSTs do not neces- rial Pacific (Luan et al. 2012). As a conse- seasonality (Fig. 2; EHwF) compared with sarily vary with the same relative strength quence, seasonality had a larger effect the simulation in which only insolation on seasonal and interannual timescales on SSTs than do changes in interannual is changed (Fig. 2; EHnF). This suggests when subject to the same sensitivity ex- ENSO variability, even in the east Pacific the fresh water flux partially offsets the periments. These findings suggest that a (Braconnot et al. 2012). changes due to insolation compared better understanding of the controls and With regards to precipitation, we with the pre-industrial simulation (Fig. timescales of variability is necessary to note a reduction of larger absolute mag- 2). This result is similar to the results of interpret paleo-records of past ENSO vari- nitude associated with El Niño and La fresh water flux experiments under mod- ability correctly, and that paleo-records Niña events in both the Niño3 and Niño4 ern (Timmermann et al. 2007) or glacial should be used with caution to test how regions when compared with the pre- (Merkel et al. 2010; see also Merkel et al., well models reproduce changes in ENSO industrial control runs (Fig. 2). Thus, both this issue) conditions. The presence of ice variability. seasonality and interannual variability sheets (Fig. 2; EHIS) in the simulations, damp the SST and precipitation variations leads to a strong reduction in seasonality Selected references in the eastern Pacific, whereas seasonality and a further damping of interannual pre- Full reference list online under: enhance and variability damp precipita- cipitation variability compared with the http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf tion in the central Pacific. insolation-only simulation. Particularly in Braconnot P, Luan Y, Brewer S, Zheng W (2012) Climate Dynamics 38: Our analyses have implications the western Pacific, the results suggest 1081-1092 when interpreting records of past ENSO that the remnant ice-sheets in the Early Clement AC, Seager R, Cane MA (2000) Paleoceanography 15(6): 731-737 variability across different regions. In the Holocene may have offset the amplifica- Merkel U, Prange M, Schulz M (2010) Quaternary Science Reviews eastern Pacific, Early Holocene seasonal- tion of precipitation seasonality. 29(1-2): 86-100 Luan Y et al. (2012) Climate of the Past 8: 1093-1108 ity and interannual SST and precipita- Zheng W et al. (2008) Climate Dynamics 30: 745-762 tion variability are reduced compared Towards a better understanding with SST and precipitation variability in Our results show that the pattern of the pre-industrial run. Therefore climate ENSO anomalies between the east and 65

PAGES news • Vol 21 • No 2 • August 2013 A controversial insight into Southwest Pacific mid- Holocene seasonality: from corals to models

Claire E. Lazareth1, M.G. Bustamante Rosell1, N. Duprey1, N. Pujol2, G. Cabioch1,§, S. Caquineau1, T. Corrège2, F. Le Cornec1, C. Maes3, M. Mandeng-Yogo1 and B. Turcq1 1IPSL/LOCEAN, UPMC/CNRS/IRD/MNHN, Institut de recherche pour le développement France Nord, Bondy, France; [email protected] 2University of Bordeaux, Environnements et Paléoenvironnements Océaniques et Continentaux, Talence, France; 3Laboratoire d’Etudes en Géo- physique et Océanographie Spatiales, Institut de Recherche pour le Développement, Toulouse, France; §To Guy, in memoriam

Science Highlights: ENSO Science “Seasonal amplitude was higher in the Southwest Pacific during the mid-Holocene,” say the corals. “It was not,” reply the models. “More work is needed,” agree the researchers…

n the Southwest (SW) Pacific, the sea- Isonal changes in seawater surface characteristics, such as temperature (SST) and salinity (SSS), are governed mainly by the position and intensity of the South Pacific Convergence Zone (SPCZ) and by the occurrences of El Niño and La Niña events. The SPCZ is a southeast narrow cloudy belt that influences the wind and rain conditions from Papua New Guinea to French Polynesia (Trenberth 1976). During the austral summer, the SPCZ moves southwest whereas during the austral winter it moves north. Consequently, waters in the SW Pacific are generally warmer and less saline during the austral summer, and colder and saltier in winter. At the interannual time scale, the main changes in SST and SSS in the SW Pacific relate to El Niño-Southern Oscillation (ENSO) dynamics, with a periodicity of ca. 2-7 years (Trenberth 1976). During an El Niño event, warm waters of the equatorial West Pacific (the Warm Pool) and connected precipitation mi- Figure 1: Comparison between coral (blue) and model run (orange) results in terms of sea surface temperature (SST; °C) characteristics in the New Caledonia region for the present (light colors) and the mid-Holocene (dark colors) grate toward the central and eastern situations. A) Monthly coral time series from New Caledonia, at present (light blue, Stephans et al. 2004; Stephans Pacific. Consequently, the SW Pacific SST et al. 2005) and from a coral fossil from the mid-Holocene (5.5 ka BP, dark blue; Lazareth et al. 2013). B) Monthly decreases slightly while precipitation de- time series from the CCSM PMIP2-models for the New Caledonia region (160-164°E 20-24°S), at present (light orange) and at the mid-Holocene (6 ka BP; dark orange; Otto-Bliesner et al. 2006). C, D) Monthly SST histograms creases strongly, leading to higher SSS and calculated seasonal amplitude. (e.g. Delcroix 1998). The opposite occurs during La Niña events. Therefore, knowl- 1 cm year-1 for massive forms. The chemi- (e.g. different orbital forcings, ice sheets, edge of past water characteristics at a cal composition of skeletal aragonite re- greenhouse gas concentrations) can be seasonal resolution has the potential to flects the properties of the water in which used to simulate past climatic changes. provide information on the position and the coral has lived. In tropical areas, stud- Many model simulations exist for the intensity of the SPCZ as well as on the oc- ies focus on the massive Porites sp. cor- mid-Holocene (e.g. 19 in the Paleoclimate currence of ENSO events. Mid-Holocene als. The Strontium/Calcium (Sr/Ca) ratio Modelling Intercomparison Project (6 ka BP) hydrographic proxy data from (Corrège 2006) is a robust proxy for SST in [PMIP2] database; http://pmip2.lsce.ipsl. the SW Pacific are rare. However, this is a these corals. The stable oxygen isotopic fr/; Braconnot et al. 2007). Their main key period, characterized by a change in ratio (δ18O) is used, combined with Sr/Ca, forcing is a millennial-scale change in ENSO amplitude that is unfortunately not to reconstruct the isotopic composition the seasonality of insolation. For the SW 18 yet entirely understood. of surface seawater (δ Osw), which is in Pacific region, the insolation for January turn closely related to SSS (via the evapo- to March was lower than at present while Corals and numerical models: ration vs. precipitation budget). it was higher for August to October. tools to look back in time Climate models, based on current To gain an insight into SW Pacific Past seasonal data on SST and SSS can be knowledge of the various compartments mid-Holocene mean climate at sea- obtained from archives such as massive of the Earth system, help understand sonal resolution and hence into ENSO coral skeletons. The aragonitic skeleton modern climate variability and predict characteristics, we studied corals from of coral is secreted by polyps over several future changes. Climate models with ex- New Caledonia and Vanuatu which have decades or centuries, at a rate of around ternal forcings different to current ones been dated to 5.5 ka BP and 6.7-6.5 ka 66

PAGES news • Vol 21 • No 2 • August 2013 brought by the southward displacement of the SPCZ. The reconstructed high mid-Holocene SSS suggests that in the SW Pacific at 6.7-6.5 ka BP the SPCZ was located further north than nowadays (Duprey et al. 2012). At that time, ENSO variability was reduced by 20-30% compared to the modern ENSO. It remains uncertain, however, whether the reduced ENSO variability reflects a real trend in ENSO dynamics or if it resulted from a

weaker coupling between the precipita- Highlights: ENSO Science tion regime and the SPCZ.

Are proxy data and models compatible for 6 ka BP? While coral records suggest a reduced SPCZ influence in the SW Pacific, possibly from 6.7-6.5 to 5.5 ka BP, the PMIP2 model maps of precipitation reveal only a small shift of the SPCZ towards the northeast and a decrease in associated precipita- Figure 2: Multi-model mean maps for the winter season (July-August-September, JAS). Six PMIP2 simulations tion during the winter months (Fig. 2b). having similar resolution and reproducing correctly the mean seasonal cycle in the New Caledonia region have been used. The arrow points to New Caledonia. A) SST multi-model maps at 0 ka (left) and difference (6 ka – 0 ka; These small changes, although in the right). B) Multi-model mean precipitation field at 0 ka (left) and 6 ka (right). Modified from Lazareth et al. (2013). right direction, are, however, not sufficient to simulate an increase in the SST BP respectively. A ~1 cm-thick slab, cut by the corals was higher than nowadays seasonality in the SW Pacific region at 6 along the axis of maximum growth of (Fig. 1a). This difference is mainly due ka BP. the coral colonies, was X-rayed to reveal to colder mid-Holocene winters. In the The modeled insolation-driven the annual growth bands. To ensure the New Caledonia region, the histogram hemispheric change in seasonality is not skeleton was well preserved, pieces were of both the modern and mid-Holocene reflected in the SW Pacific proxy data. collected and analyzed for their mineral- coral-reconstructed SST monthly values This suggests the models have difficulty ogy using X-ray diffraction, and for their (Fig. 1c), and the 0 ka BP model outputs in reproducing mid-Holocene changes in microstructure using scanning electronic (Fig. 1d) show two modes, correspond- coupled ocean-atmosphere circulation in microscopy. If the skeleton preserva- ing to the positions of the SPCZ in win- this region. This could be due to known tion was found to be satisfactory, the ter (July-August-September, JAS) and in model biases in representing the current, slab was continuously sampled at 1-mm summer (December-January-February, and thus also the 6 ka BP, SPCZ, and to steps, providing on average one sample DJF). In the 6 ka BP coral results however, the models’ large grid size to which the per month of coral growth. The samples colder temperatures prevail in the winter SPCZ seasonal displacement is sensitive. were then dissolved and analyzed to de- mode, with a wider distribution. We in- On the other hand, corals are shallow wa- termine their chemical composition. The terpret this as reflecting a more variable ter organisms and the SST and SSS they New Caledonia coral was too short (~20 position and/or a weakening of the SPCZ record may not be valid for open oceans. years) to investigate ENSO dynamics and during mid-Holocene winters. None of Clearly, more data and new model runs as the δ18O proved to be partly altered, the PMIP2 models for the New Caledonia are needed to understand the amplitude only the SST reconstructed with Sr/Ca will region reproduce an increase in seasonal and geographical pattern of western be discussed here. SST amplitude in the mid-Holocene and Pacific mid-Holocene changes. The 6 ka BP PMIP2 model simulations the bi-modality is maintained (Fig. 1d). show a cooling of the tropical Pacific SST The models generally follow the insola- Selected references (Zheng et al. 2008) and a decrease in sea- tion change: a warmer winter and a cold- Full reference list online under: sonal SST amplitude (south of 10°S and er summer, leading to reduced seasonal- http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf between 160-260°E for the South Pacific) ity (Fig. 1b). Braconnot P et al. (2007) Climate of the Past 3: 261-277 related to the insolation change. The re- For the Vanuatu corals, Sr/Ca and Corrège T (2006) Palaeogeography Palaeoclimatology Palaeoecology 232: sults obtained on the New Caledonia δ18O were measured as proxies for SST 408-428 coral were compared with the six simula- and SSS, respectively, and data from the Delcroix T (1998) Bulletin de l'Institut Français d'Etudes Andines 27: tions for which monthly data were avail- longest colony were used to highlight 475-483 Duprey N et al. (2012) Paleoceanography 27, doi:10.1029/2012PA002350 able and which correctly reproduced the ENSO characteristics during the early Trenberth KE (1976) Quarterly Journal of the Royal Meteorological Society current SST cycle in the New Caledonia mid-Holocene. The precipitation regime 102: 639-653 region on four 2° by 2° grid points (164- in Vanuatu at 6.7-6.5 ka BP was differ- 168°E, 20-24°S). ent from the current one. Fossil corals indicate peaking SSS in summer (DJF) The SPCZ at 6 ka BP: Where was whereas low SSS would have been ex- it located? pected from the reduced summer insola- In the New Caledonia lagoon, the mid- tion at that time. Indeed, summer today Holocene SST seasonal amplitude as seen is accompanied by strong precipitation 67

PAGES news • Vol 21 • No 2 • August 2013 Interannual variability in the tropical Pacific and associated atmospheric teleconnections during the last glacial period

Ute Merkel, M. Prange and M. Schulz MARUM - Center for Marine Environmental Sciences, University of Bremen, Germany; [email protected] Simulations of the climate of Marine Isotope Stages 2 and 3 suggest pronounced ENSO variability during the Heinrich Stadial 1 period when the Atlantic overturning circulation was weaker. Our model results also highlight

Science Highlights: ENSO Science the nonstationarity of ENSO teleconnections through time.

well-known example of coupled approach with a focus on a period of events by hosing freshwater into the A ocean-atmosphere interaction on relatively regular Dansgaard-Oeschger modern ocean and thereby demonstrate interannual timescales is the El Niño- variability around 35 ka BP. When 35 ka that a slowdown of the AMOC may have Southern Oscillation (ENSO) phenom- BP boundary conditions (greenhouse a pronounced impact on the tropical enon in the tropical Pacific. Consensus is gas concentrations, orbital parameters, Pacific (e.g. Timmermann et al. 2007). still lacking about how ENSO will behave continental ice sheet distributions) are One of our major findings was that under future climate conditions, even in prescribed, the model simulates a very interannual (about 1.5-8 years) variabil- the latest generation of comprehensive weak Atlantic meridional overturning ity in sea surface temperatures (SST) of climate models (Guilyardi et al. 2012). circulation (AMOC) of about 7 Sv, which the eastern tropical Pacific was distinctly Major goals of paleoclimatic re- is much weaker than the preindustrial increased in our Heinrich Stadial 1 simu- search are to provide constraints on the value of 12 Sv, but also weaker than the lation compared to pre-industrial times, possible range of changes in response ~10 Sv simulated for the LGM. Therefore, whereas variability in our LGM and MIS3 to modified boundary conditions and we consider the simulated 35 ka BP cli- simulations was systematically reduced, to identify possible feedback and ampli- mate as a stadial climate state. The coun- albeit only weakly (Fig. 1). Modern ENSO fication mechanisms in the climate sys- terpart of an interstadial climate state is dynamics studies show that stronger tem. In this context, climate models are induced in the model by a 0.1 Sv fresh- ENSO variability is dynamically linked valuable tools for investigating different water extraction from the North Atlantic to a weaker annual cycle of SST and to climate scenarios that have occurred in over ~300 model years, thereby forcing a a weaker meridional asymmetry of SST the past. Most ENSO studies, however, resumption of the AMOC to ~14 Sv. across the equator in the eastern tropi- are limited to the two priority periods Our set of experiments also includes cal Pacific (Guilyardi 2006; Xie 1994). Our specified by the Paleoclimate Modeling a simulation of a Heinrich Stadial 1 sce- model results show that these relation- Intercomparison Project (PMIP): the Mid- nario. This is set up by imposing a fresh- ships also hold for the different simu- Holocene, and the Last Glacial Maximum water perturbation of about 0.2 Sv to lated glacial climate states. In particular, (LGM; e.g. Zheng et al. 2008). However, a simulated LGM ocean state over 360 our Heinrich Stadial 1 simulation exhib- proxy data from the tropical Pacific model years. This is motivated by ear- its a much weaker north-south contrast (e.g. Stott et al. 2002; Leduc et al. 2009; lier studies which mimic past Heinrich in eastern tropical Pacific SST than under Dubois et al. 2011) suggest that ENSO also changed on millennial timescales, e.g. in association with pronounced abrupt climate changes related to the Dansgaard-Oeschger stadials and inter- stadials during Marine Isotope Stage 3 (MIS3, 59-29 ka BP).

Modeling ENSO for different glacial climate states The first modeling studies that addressed MIS3 were limited to intermediate complexity models (e.g. Ganopolski and Rahmstorf 2001; van Meerbeeck et al. 2009; Ganopolski et al. 2010), a regional model approach (e.g. Barron and Pollard 2002), or an atmosphere-only setup (Sima et al. 2009), unsuitable to capture the complexity of ENSO dynamics. Recently, the first simulations of MIS3 climate in a comprehensive coupled climate model were accomplished with the US National Center of Atmospheric Research's CCSM3 model (Merkel et Figure 1: ENSO variability of sea surface temperature in the eastern tropical Pacific (Niño3 region: 150°W-90°W, al. 2010). The study used a timeslice 5°S-5°N) for different simulated climatic states. 68

PAGES news • Vol 21 • No 2 • August 2013 deviations from the modern spatial distribution of anomalies (Fig. 2). In particular, the teleconnections to the North American continent and the North Atlantic region seem to be strongly altered in terms of amplitude and spatial structure in the LGM and MIS3 simulations. This difference is probably caused by the presence of the glacial continental ice sheets and the glacial cooling of the North Atlantic, which both affect

the position of the upper-tropospheric Highlights: ENSO Science jetstream and atmospheric storm tracks, and thus the tropical-extratropical signal propagation. The typical intensifi- cation of the Aleutian low forced by El Niño (Fig. 2a) seems to be present during the LGM but is less pronounced, and the atmospheric bridge to the North Atlantic region seems to be interrupted, as no clear large-scale pattern is simulated there (Fig. 2b). The MIS3 stadial conditions (Fig. 2c) bear more resemblance to the control simulation over the North Pacific, whereas over the North Atlantic, the ENSO influence is clearly reduced, similar to the LGM situation. This points to a complex interplay of atmospheric dynamics with the various forcings in the different climatic states.

The need to learn more about glacial climatic states In summary, our modeling study confirms that ENSO variability responds to various glacial climatic states. However, ENSO variability does not appear to be linearly linked to the strength of Figure 2: ENSO teleconnections during boreal winter (Dec.-Feb.): El Niño minus La Niña composites of sea level the AMOC. This calls for more detailed pressure [hPa] for (A) pre-industrial control climate, (B) Last Glacial Maximum (LGM), and (C) Marine Isotope Stage analyses, for instance in the form of 3 (MIS3) stadial climate. Figure modified from Merkel et al. 2010. glacial hosing studies in a multi-model modern conditions. This is attributed to At the Tahiti location, the coral and the approach (Kageyama et al. 2013). The an atmospheric signal communication model are also quantitatively consis- different roles of the AMOC and the vari- from the strongly cooled North Atlantic tent, as both suggest a strengthening ous glacial boundary conditions with into the tropical Pacific. of interannual SST variability by 20-30% respect to their impact on ENSO need compared to modern conditions. to be further disentangled. Likewise, we Model-data comparison emphasize that the concept of station- Further insights into tropical Pacific vari- Modern and past ENSO ary teleconnections should only be ap- ability can be achieved through model- teleconnections plied to past climatic states with caution data intercomparison. Felis et al. (2012) Modern ENSO is well known for its atmo- as they may be altered by different past present findings from a fossil coral re- spheric teleconnections of near-global boundary conditions and forcings inter- trieved during IODP Expedition 310 extent. Understanding how teleconnec- nal and external to the climate system. near Tahiti. The coral has been dated to tions operate, both in the atmosphere Heinrich Stadial 1. Its fast growth rate and the ocean, is particularly relevant for Selected references allows sampling at monthly resolution the validity of paleoclimatic reconstruc- Full reference list online under: and provides a unique opportunity to tions, as they generally assume that at- http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf investigate interannual SST variability mospheric teleconnection patterns are Felis T et al. (2012) Nature Communications 3, doi:10.1038/ncomms1973 in the southwestern tropical Pacific dur- stable. This may be particularly critical in Guilyardi E et al. (2012) CLIVAR Exchanges 58(17): 29-32 ing that period. The coral record exhib- the interpretation of proxy records not Kageyama M et al. (2013) Climate of the Past 9: 935-953 its pronounced variability at interan- stemming from the core ENSO region. Merkel U, Prange M, Schulz M (2010) Quaternary Science Reviews 29: nual ENSO frequencies during Heinrich A composite analysis of atmospheric 86-100 Stadial 1, consistent with the basin- patterns (e.g. of sea level pressure) dur- Zheng W et al. (2008) Climate Dynamics 30: 745-762 wide increase in ENSO variability in our ing all El Niño and La Niña events in the Heinrich Stadial 1-analogue simulation. different simulations revealed obvious 69

PAGES news • Vol 21 • No 2 • August 2013 ENSO behavior before the Pleistocene

Chris Brierley Department of Geography, University College London, UK; [email protected]

The Pliocene was characterized by a weak equatorial sea surface temperature gradient in the Pacific, confusingly reminiscent of that seen fleetingly during an El Niño. Data also show interannual variability in the Pliocene, raising questions about ENSO’s dependence on the mean climate state.

he behavior of the El Niño–Southern during the warm intervals of the Miocene Oxygen isotope records from fossil cor- Oscillation (ENSO) in pre-Pleistocene (5.96-5.32 Ma; Galeotti et al. 2010), Eocene als (MacGregor et al., this issue) from the Science Highlights: ENSO Science T climates is highly uncertain. This uncer- (45-48 Ma; Huber and Caballero 2003; Lenz Philippines show power spectra similar tainty is rooted in a fundamental lack of et al. 2010) and Cretaceous (70 Ma; Davies to recent corals, hence likely representing evidence. However, several, recent studies et al. 2011, 2012) from layered deposits or ENSO variability (Watanabe et al. 2011). focusing on past warm climates are begin- varved sediments showing a strong peak in Analyses of individual foraminifera from ning to address this issue. These studies the 3-5 years range. It has also been seen in the Eastern Equatorial Pacific (Scroxton et were motivated by suggestions that the the Eocene (50 Ma; Ivany et al. 2011) from al. 2011) find several instances of isotopic climate of the early Pliocene was a “per- analysis of power spectra of carbon iso- compositions outside the range predicted manent El Niño” – a term that has led to topes in fossil driftwood and bivalves. All for the present-day seasonal cycle. This much confusion. After looking at the new of these analyses have used records gath- has been interpreted as showing an active evidence for ENSO, I will discuss the histo- ered in locations far away from the tropical ENSO cycle. Unfortunately, a foraminifer ry of the term “permanent El Niño”, before Pacific, such as Antarctica. However, ENSO does not live through an annual cycle (un- suggesting that it should be consigned to teleconnections depend on the mean cli- like mollusks; e.g. Carré et al., this issue), so history as well. mate state (Merkel et al., this issue) and changes in the seasonal cycle (Braconnot may therefore have been different in these and Luan, this issue) are a potential source Pre-Pliocene ENSO early warm periods. The plausibility of as- of uncertainty. Detection of interannual variability re- sumed teleconnections of that time can be Despite the complications associ- quires paleoclimate indicators that moni- confirmed with climate model simulations ated with each individual study, a picture tor changes over short timescales such of the period (Galeotti et al. 2010; Huber & is emerging in which ENSO is a pervasive as the thickness of varved sediments and Caballero 2003; Ivany et al. 2011). feature of past climate. However, a sys- isotope ratios in long-lived fossil mollusks tematic effort will be needed to provide or corals. Once a record spanning sufficient Pliocene ENSO quantitative information from these pre- years has been recovered, its power spectra Two studies have found evidence of ENSO- Pliostocene intervals that could qualify for can be analyzed for frequencies represen- style periodicity during the Pliocene (Fig. data-model comparisons. tative of ENSO. ENSO has been detected 1) from locations in the Tropical Pacific.

Figure 1: Variation in the Sea Surface Temperature in the Equatorial Pacific over the past five million years. The estimates come from two ocean cores in the West (ODP 806 at 150°E) and the East (ODP 847 at 95°W). Two different types of record are used to reconstruct the temperatures: Mg/Ca (Wara et al. 2005) and alkenones (Dekens et al. 2007; Pagani et al. 2010). The period described as lacking ENSO variability (i.e. the period of the “permanent El Niño”) from a mistaken interpretation of Fedorov et al. (2006) is shown in orange. Times with observed ENSO variability, as found by Scroxton et al. (2011) and Watanabe et al. (2011), are marked in green. The time-slab used by PlioMIP and its precursors is marked as “mPWP”. Figure modified after Fedorov et al. (2013). 70

PAGES news • Vol 21 • No 2 • August 2013 Science Highlights: ENSO Science

Figure 2: Niño 3.4 SST anomalies in two model simulations; a control (green) and one with an equatorial SST gradient that is approximately halved (red). The shaded area represents four standard deviations from a 30-year running window (Fedorov et al. 2010).

The “permanent El Niño” of the was no ENSO variability before 3 Ma, al- distribution (Fedorov et al. 2010). These Early Pliocene though this is not what the authors intend- simulations (Fig. 2) appear to show a rela- One of the factors fuelling the hunt for ed (Alexey Fedorov, personal communica- tionship between equatorial SST gradient ENSO in pre-Pleistocene warm climates tion) and is certainly not what is shown by and the amplitude of ENSO, but not its pe- was the idea that the early Pliocene was the more recent studies described above. riod (Fedorov et al. 2010). This result could in state of “permanent El Niño”. Mg/Ca easily be model dependent, but offers a records (a proxy for sea-surface tempera- Equatorial SST gradient and ENSO scenario for a weak ENSO around 4.2 Ma, tures, SST) from the Western and Eastern in models the time for which proxy data suggest that Equatorial Pacific (Wara et al. 2005) sug- The mid-Pliocene warm period (3.3-3.0 the SST gradient was very small (open or- gest that no temperature gradient existed Ma; marked “mPWP” in Fig. 1) has been ange box in Fig. 1). along the equatorial Pacific around four the focus of sustained effort by the data million years ago (4 Ma; Fig. 1). Subsequent and modeling communities, most re- Conclusion work shows similar results for the equa- cently under the auspices of the Pliocene The introduction of the term “permanent torial SST gradient in the early Pliocene. Model Intercomparison Project (PlioMIP; El-Niño” in the literature has caused confu- Reconstructions of the SST gradient during Dolan et al. 2012). This period is one mil- sion, but it has also motivated paleoclima- older periods need further work, but pre- lion years later than the minimal SST gradi- tologists to look for (and find) evidence of liminary data suggest that a reduced SST ent identified by Wara et al. (2005), but is interannual ENSO variability in deep time. gradient is not solely a feature of the early thought to share similar climate forcings The assertion that there was no ENSO vari- Pliocene (LaRiviere et al. 2012) although (Fig. 1). Haywood et al. (2007) found ENSO ability before 3 Ma, wrongly attributed to it may not be a ubiquitous feature of all variability in both mid-Pliocene and mod- Fedorov et al. (2006), is not true. However, warm climates (Nathan and Leckie 2009). ern simulations. However, the equatorial the relationship between a Pacific mean An El Niño event (the warm phase of temperature gradient of the mid-Pliocene state with a minimal equatorial SST gradi- the ENSO oscillation) is characterized by a simulation was hardly smaller than in the ent and related ENSO properties merits lack of SST gradient along the equatorial modern simulation. Subsequent simula- further investigation. We have made prog- Pacific. Although Wara et al. (2005) empha- tions performed with updated boundary ress towards uncovering ENSO behavior sized that their Mg/Ca records reflected conditions (Dowsett et al. 2010), similarly on geologic timescales, but there is still a the mean climatic state, i.e. a change in the show a lack of strong reductions in the long way to go. long-term average climate rather than a equatorial temperature gradient between change in interannual variability, they de- the mPWP and the modern day (Haywood Selected references scribed their observation using the short- et al. 2013) – in comparison with the halv- Full reference list online under: hand of “a permanent El Niño”. The term ing seen in the paleo-observations (Fig. 1). http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf was propagated by Fedorov et al. (2006), Attempts have been made to force Fedorov A, Brierley C, Emanuel K (2010) Nature 463: 1066-1070 who used model simulations to examine coupled models to replicate a mean state Fedorov A et al. (2006) Science 312: 1485-1489 how such a state could be maintained. with a weak SST gradient in the equato- Scroxton N et al. (2011) Paleoceanography 26(2), doi: They emphasized the similarity between rial Pacific. One approach has been to in- 10.1029/2010PA002097 the long-term average state and the condi- crease the background ocean vertical dif- Wara MW, Ravelo AC, Delaney ML (2005) Science 309: 758-761 tions seen during recent El Niños. This sim- fusivity (Brierley et al. 2009), potentially Watanabe T et al. (2011) Nature 471: 209-211 ile has been read as an assertion that there to represent a changed tropical cyclone 71

PAGES news • Vol 21 • No 2 • August 2013 Editors: H. Goosse and A. Paul

Overview of data assimilation methods

Gregory J. Hakim1, J. Annan2, S. Brönnimann3, M. Crucifix4, T. Edwards5, H. Goosse4, A. Paul6, G. van der Schrier7and M. Widmann8 1Department of Atmospheric Sciences, University of Washington, Seattle, USA; [email protected] 2Research Institute for Global Change, JAMSTEC, Yokohama Institute for Earth Sciences, Japan; 3Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Switzerland; 4Earth and Life Institute and Georges Lemaître Centre for Earth and Climate Research, Université catholique de Louvain, Belgium; 5Department of Geographical Sciences, University of Bristol, UK; 6MARUM and Department of Geosci- 7 8

Science Highlights: Data assimilation Highlights: Data Science ences, University of Bremen, Germany; KNMI, De Bilt, The Netherlands; School of Geography, Earth and Environmental Sciences, University of Birmingham, UK We present the data assimilation approach, which provides a framework for combining observations and model simulations of the climate system, and has led to a new field of applications for paleoclimatology. The three subsequent articles explore specific applications in more detail.

ata assimilation involves the combi- data and numerical models, and studies In weather prediction, data assimilation Dnation of information from observa- using these resources are typically per- uses observations to initialize a forecast tions and numerical models. It has played formed independently. Data assimilation (Lorenc 1986; Kalnay 2003; Wunsch 2006; a central role in the improvement of provides a mathematical framework that Wikle and Berliner 2007). Since the short- weather forecasts and, through reanalysis, combines these resources to improve the term forecast typically starts from an accu- provides gridded datasets for use in cli- insight derivable from either resource in- rate analysis at an earlier time, called the mate research. There is growing interest in dependently. The three articles that fol- prior estimate, the model provides rela- applying data assimilation to problems in low describe the current activity in this tively accurate estimates of the weather paleoclimate research. Our goal here is to emerging field of study: transient state observations. Data assimilation involves provide an overview of the methods and estimation (Brönnimann et al., this issue), optimizing the use of these independent the potential implications of their applica- equilibrium state estimation (Edwards et estimates to arrive at an analysis (i.e. esti- tion. al., this issue), and paleo data assimilation mate of the weather or climate state) with Understanding of past climate vari- for parameter estimation (Annan et al., a smaller error than the model short-time ability provides a crucial benchmark ref- this issue). Here we provide an overview forecast or the observations. erence for current and predicted climate of these methods and how they relate For Gaussian distributed errors, the change. Primary resources for deriving to existing practices in the paleoclimate result for a single scalar variable (singly- past understanding include paleo-proxy community. dimensioned variable of one size), x, given

prior estimate of the analysis value, xp, and observation y is (1)

where xa is the analysis value. The innovation, xxxxxxxxx, represents the information from the observation that differs from the prior estimate. This comparison requires a “conversion” of the prior to the observation, which is accomplished by xx. For example, in a paleoclimate application, xxxxx may estimate tree-ring width derived temperature data from a climate model (Fig. 1). The weight applied to the innovation is determined by the Kalman gain, K, (2)

where cov represents a covariance. The error variances associated with the observation and the prior estimate of the Figure 1: Schematic illustration of how the innovation is determined in data assimilation for a tree-ring example. observation are given by and , re- Proxy measurements are illustrated on the left, and model estimates of the proxy on the right. The observation σp σy operator provides the map from gridded model data, such as temperature, to tree-ring width, which is used to spectively. Equation (1) represents a linear compute the innovation. Images credit: Wikipedia. regression of the prior on the innovation 72

PAGES news • Vol 21 • No 2 • August 2013 of xx, and therefore subject to similar uncertainty.

Current and future directions Research on paleoclimate data assimilation is rapidly developing in many areas. For climate state estimates, a wide range of methods are currently under exploration (see Brönnimann et al., this issue), including nudging climate models to large- scale patterns derived from proxy data (Widmann et al. 2010), and variational (Gebhardt et al. 2008) and ensemble approaches (Bhend et al. 2012). Ensemble approaches involve many realizations of climate model simulations, each of which

is weighted according to their match to assimilation Highlights: Data Science the proxy data, either in the selection of members (Goosse et al. 2006) or through a linear combination. Among the important obstacles to Figure 2: Data assimilation for scalar variable x assuming Gaussian error statistics. Prior estimate, given by the progress in paleoclimate data assimila- dashed blue line, has mean -0.25 and variance 0.5. Observation y, given by the dashed green line, has mean 1.0 tion, some challenges are generic, such and variance 0.25. The analysis, given by the thick red line, has mean 0.58 and variance 0.17. The parabolic gray as improving the chronological dating curve denotes a cost function, J, which measures the misfit to both the observation and prior; it takes a minimum at the mean value of x . From Holton and Hakim 2012. quality of proxy records and reducing the a uncertainties of the paleoclimate data. (the denominator of K is the innovation state estimation in paleoclimatology in- Other problems are more specific to data variance). Equivalently, the Kalman gain volves proxy data having timescales of assimilation, such as the development of weights the innovation against the prior, years to centuries or longer, which gener- proxy forward models. Moreover, proxy resulting in an analysis probability density ally exceeds the predictability of climate data typically represent a time average, in function with less variance, and higher models, which are on the order of a de- contrast to instantaneous weather obser- density, than either the observation or the cade. Consequently, relative errors in the vations, although solutions that involve prior (Fig. 2, red solid line, dashed green model estimate of the proxy are usually assimilating time averages have been pro- line and dashed blue line respectively). much larger in paleoclimate applications. posed to tackle this problem (Dirren and Generalizing (1) and (2) to more than one Hoever, data assimilation reconstruction Hakim 2005; Huntley and Hakim 2010). variable is straightforward, with scalars may still be performed, at great cost sav- Model bias is also problematic for paleo- becoming vectors and variances becom- ings, since the model no longer requires climate data assimilation, especially for ing covariance matrices (for details see integration and each assimilation time regions with spatially sparse proxy data. Brönnimann et al., this issue). These cova- may be considered independently (Bhend While the field of paleoclimate data riance matrices provide the information et al. 2012). assimilation is still in its infancy, these that spreads the innovation in space and Paleoclimate data assimilation at- challenges are all under active research. to all variables through a Kalman gain ma- tempts to improve upon climate field Merging climate models and proxy data trix. reconstructions that use purely statisti- has a bright future in paleoclimate re- Application of data assimilation to cal methods. One well-known statistical search (e.g. the P2C2 program of the U.S. the paleoclimate reconstruction problem approach for climate field reconstruction National Science Foundation), and it is involves determining the state of the cli- (Mann et al. 1998; Mann et al. 2008) in- likely that paleoclimate data assimilation mate system on the basis of sparse and volves limiting field variability to a small will play a central role in this endeavor. noisy proxy data, and a prior estimate set of spatial patterns that are related to from a numerical model (Widmann et al. proxy data during a calibration period. Selected references 2010). These data are weighted according Data assimilation, on the other hand, Full reference list online under: to their error statistics and may also be retains the spatial correlations for loca- http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf used to calibrate parameters in a climate tions near proxies, which may be lost in Annan J, Hargreaves J, Edwards N, Marsh R (2005) Ocean Modelling 8(1): model (Annan et al. 2005). a small set of spatial patterns, and also 135-154 spreads information from observations in Bhend J et al. (2012) Climate of the Past 8: 963-976 Relationship to established time through the dynamics of the climate Goosse H et al. (2006) Climate Dynamics 27: 165-184 methods model. Another distinction between data Widmann M et al. (2010) Climate of the Past 6: 627-644 While there are similarities between assimilation and field reconstruction ap- Wikle CK, Berliner ML (2007) Physica-D 230: 1-16 the application of data assimilation to proaches concerns the observation op- weather and paleoclimate, there are also erator, xx, which often involves biological important differences. In weather predic- quantities of proxy data that have uncer- tion, observations are assimilated every 6 tain relationships to climate. Statistical re- hours, which is a short time period com- constructions directly relate proxy data to pared to the roughly 10-day predictabil- the set of spatial patterns, which is essen- ity limit of the model. However, transient tially an empirical estimate of the inverse 73

PAGES news • Vol 21 • No 2 • August 2013 Transient state estimation in paleoclimatology using data assimilation

Stefan Brönnimann1, J. Franke1, P. Breitenmoser1, G. Hakim2, H. Goosse3, M. Widmann4, M. Crucifix3, G. Gebbie5, J. Annans and G. van der Schrier7 1Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Switzerland; [email protected] 2Department of Atmospheric Sciences, University of Washington, Seattle, USA; 3Earth and Life Institute and Georges Lemaître Centre for Earth and Climate Research, Université catholique de Louvain, Belgium; 4School of Geography, Earth and Environmental Sciences, University of Birmingham, UK; 5Department of Physical Oceanography, Woods Hole Oceanographic Institution, USA; 6Research Institute for Global Change, JAMSTEC, Yokohama Institute for Earth Sciences, Japan; 7KNMI, De Bilt, The Netherlands Data assimilation methods used for transient atmospheric state estimations in paleoclimatology such as covariance-based approaches, analogue techniques and nudging are briefly introduced. With applications differing widely, a plurality of approaches appears to be the logical way forward.

eliable estimations of past climate states Rare the foundations of paleoclimatology.

Science Highlights: Data assimilation Highlights: Data Science Traditionally, statistical reconstruction techniques have been used, but recent developments bring data assimilation techniques to the doorstep of paleoclimatology. Here we give a short overview of transient atmospheric state estimation in paleoclimatology using data assimilation. An introduction to data assimilation as well as applications for equilibrium state estimation and parameter estimation are given in the companion papers to this special section (see also Wunsch and Heimbach 2013). Data assimilation combines information from observations with numerical models to obtain a physically consistent estimate (termed “analysis”) of the climate state. It has been hugely successful in generating three-dimensional atmospheric data sets of the past few decades. The “Twentieth Century Reanalysis Project” (Compo et al. 2011) extended the approach as far back as 1871, but there is a limit to further extension, because conventional data assimilation relies on the availability of state observations. Paleoclimate proxies do not capture atmospheric states, but time-integrated functions of states, such as averages, in the simplest case. Therefore, for assimilating proxies, other Figure 1: Schematic overview of assimilation approaches. Arrows denote steps in the procedure.

methods are required than those applied in where x is the analysis, xb is a model forecast, Focusing on the seasonal scale, Bhend et al. atmospheric sciences. We briefly present be- y are the observations (or proxies), H is the (2012) use the EnKF without updating the low, three groups of assimilation methods observation operator that mimics the obser- initial conditions (termed EKF here), which for transient atmospheric state estimation vation (or proxy) in the model space, B is the are no longer important on this scale (rather, in paleoclimatology: “Classical” covariance- background error covariance matrix and R is predictability comes from the boundary based approaches such as the Kalman Filter the observation error covariance matrix (of- conditions, including sea-surface tempera- or variational techniques; approaches based ten assumed to be diagonal). The solution to tures). This conveniently allows one to use on analogues such as Particle Filters; and (1) in the classical Kalman form is: pre-computed simulations. Because x does nudging techniques. A schematic view of not serve as new initial condition, it can be x = x + BHT(R+HBHT)-1 (y-Hx ) (2) these methods is given in Figure 1. Note that b b small and can be a vector of averaged model other methods may be used for the ocean where H is the Jacobian of H. Variational ap- states (e.g. all monthly averages of a season (see Gebbie 2012). proaches can be used to approximate the so- for three variables). H can be a simple proxy lution. In the Ensemble Kalman Filter (EnKF), forward model, i.e. a time-integrated function Covariance-based approaches B can be estimated from the ensemble, of elements of x. The assimilation problem can be formulated and each member is updated individually. Covariance-based approaches are pow- as a cost function J, assuming Gaussian prob- Normally x is a state vector. However, Dirren erful but computationally intensive and can ability distributions: and Hakim (2005) have successfully extended be sensitive to assumptions (e.g. of Gaussian the concept to time averages. distributions), to the treatment of covariance J(x) = (x-x )T B-1 (x-x ) + (y-H[x])T R-1 (y-H[x]) (1) b b Data assimilation entails that x serves as matrices, or to the behavior of the observa- an initial condition for the next forecast step. tion operator. 74

PAGES news • Vol 21 • No 2 • August 2013 30 simulations performed with ECHAM5.4 at a resolution of T63/L31 (ca. 2° x 2°), with sea- surface temperatures and external forcings as boundary conditions. The unconstrained ensemble mean (Fig. 2 top) shows the effect of boundary conditions, here resulting in cooler than average summer temperatures following the large, but not yet localized volcanic eruption in 1809. Anomalies are small and smooth which is typical for an ensemble mean. The EKF analysis was constrained by historical instrumental observations using Eq. (2). The EKF ensemble mean suggests a more pronounced cooling over northern Europe, but over most regions (due to lack of observations)

it is close to the unconstrained ensemble assimilation Highlights: Data Science mean. BEM was constrained with tree rings from 35 locations. The VS-lite tree growth model (Tolwinski-Ward et al. 2011) was used as H and Eq. (3) was minimized. BEM identifies member 01 as the best fitting one. This member exhibits large anomalies in Alaska and Eurasia, but due to the small ensemble size little regional skill is expected (Annan and Hargreaves 2012). For instance, it does not fit well with instrumental observations over Europe. The same member in the EKF analy- Figure 2: Northern hemisphere temperature anomalies for April to September 1810 (relative to 1801-1830) from the unconstrained ensemble mean, the EKF ensemble mean, BEM (member 01), and the EKF analysis for the BEM sis (Fig. 2, bottom) shows a better correspon- member. Circles indicate locations and anomalies of the assimilated instrumental measurements; red squares dence, but we loose the advantage of having the locations of tree-ring proxies. the full 6-hourly model output available. approaches require a huge pool of possible Analogue approaches analogues (Annan and Hargreaves 2012). Limitations and future directions Reverting to cost function (1), we can also Paleoclimatological applications are much look for an existing x, e.g. by choosing among Nudging approaches more disparate than atmospheric sciences in different ensemble members. The cost func- Nudging approaches (Widmann et al. 2010) terms of time, time scales, systems analyzed, tion (1) reduces to: do not explicitly minimize a cost function. The and proxies used. Therefore, a plurality of distance between model state and observa- data assimilation approaches is a logical way J(x) = (y-H[x])T R-1 (y-H[x]) (3) for x ϵ {x , x ,...,x } tions is reduced by adding tendencies to (a forward. However, all approaches still suffer 1 2 n subspace of) the model state at each time from problems and uncertainties. Ensemble New ensemble members are then generated step, similar to an additional source term in approaches (PF, EnKF, EKF) provide some for the next time step by adding small pertur- the tendency equations. Following our nota- information on the methodological spread, bations to x and the final analysis is a continu- tion: which however represents only one (difficult ous simulation. The Particle Filter (PF, Goosse to characterize) part of the whole uncertainty. x = x + G (F[y] - x) (4) et al. 2010) approach uses a distribution of x b Further uncertainties are related to model to calculate a weighted sum of cost function where F[y] represents the target field (derived biases, limited ensemble size, errors in the contributions to (3). using up-scaling method F from observations forcings and proxy data. Validation of the ap- In the Proxy Surrogate Reconstruction or proxies y) in the dimension of the model proaches using pseudo proxies in toy models approach (PSR, Franke et al. 2011) and the (sub-)space. G is a relaxation parameter. and climate models and validation of the re- Best Ensemble Member approach (BEM, The Forcing Singular Vectors method sults using independent proxies is therefore Breitenmoser et al., in preparation) pre-com- (van der Schrier and Barkmeijer 2005) ma- particularly important. Any approach, how- puted simulations are used with {x1,x2,...,xn} nipulates the tendency equations as well, ever, fundamentally relies on a good under- denoting different slices of a long simulation but adds a perturbation, which modifies the standing of the proxies. for PSR or in the case of BEM, the same slice model atmosphere in the direction of the tar- in an ensemble of simulations. The “analysis” get pattern only. Selected references in both cases is a sequence of short, discon- Full reference list online under: tinuous simulations. In contrast to EnKF, H Examples http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf may be non-differentiable (e.g. H can be a Figure 2 shows April-to-September averages Bhend J et al. (2012) Climate of the Past 8: 963-976 complex forward model driven by the full of surface air temperature obtained from Dirren S, Hakim GJ (2005) Geophysical Research Letters 32, simulation output). R may be non-diagonal, two assimilations approaches (EKF and BEM) doi:10.1029/2004GL021444 and x may be very large (e.g. six-hourly model for the year 1810 relative to the 1801-1830 Goosse H (2010) Journal of Geophysical Research 115, output over a 6 month period). However, to mean. Both approaches are based on the doi:10.1029/2009JD012737 van der Schrier G, Barkmeijer J (2005) Climate Dynymics 24: 355-371 reconstruct the state of systems including a same ensemble of simulations described in Widmann M et al. (2010) Climate of the Past 6: 627-644 large number of degrees of freedom, these Bhend et al. (2012). The ensemble consists of 75

PAGES news • Vol 21 • No 2 • August 2013 Best-of-both-worlds estimates for time slices in the past

Tamsin L. Edwards1, J. Annan2, M. Crucifix3, G. Gebbie4 and A. Paul5 1Department of Geographical Sciences, University of Bristol, UK; [email protected] 2Research Institute for Global Change, JAMSTEC, Yokohama Institute for Earth Sciences, Japan; 3Earth and Life Institute and Georges Lemaître Centre for Earth and Climate Research, Université catholique de Louvain, Belgium; 4Department of Physical Oceanography, Woods Hole Oceano- graphic Institution, USA; 5MARUM - Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Germany

We introduce data assimilation methods for estimating past equilibrium states of the climate and environment. The approach combines paleodata with physically-based models to exploit their strengths, giving physically consistent reconstructions with robust, and in many cases, reduced uncertainty estimates.

hose seeking to understand the complete exploration of model uncer- sum of squared differences weighted TEarth’s past usually take one of two tainties in parameters, structure, and by the uncertainties, though some use approaches: reconstructing paleocli- inputs. Another advantage of a focus on ad-hoc or fuzzy metrics (e.g. Guiot et

Science Highlights: Data assimilation Highlights: Data Science mate and paleo-environmental states time slices is that for eras studied by the al. 2000; Wu et al. 2007; Gregoire et al. from proxy data derived from natural Paleoclimate Model Intercomparison 2010). For non-continuous variables, archives such as ice cores and trees; Project (PMIP) relatively large quantities for example with a threshold, variables or simulating them with earth system of paleodata and simulations are avail- must be transformed or a non-Gauss- models that contain theoretical knowl- able. Most data assimilation estimates ian metric chosen (e.g. Stone et al. edge of physical processes. of equilibrium paleo-states are there- 2013). Proxy-based reconstructions are fore of the Last Glacial Maximum (LGM: Optimisation methods search for based on observations of the real world, 21 ka cal BP), the most recent era for the simulation with the minimum dis- but most consider data points indepen- which annual mean climate is substan- tance from paleodata. One approach dently rather than accounting for cor- tially different to the present that also uses numerical differentiation of the relations in space, time and between has a long history of study by PMIP. model with respect to the parameters, climate variables. Therefore they risk We use model simulations in pa- essentially least-squares fitting of a line being physically inconsistent. Models leo-state estimation because models or curve to one-dimensional data (e.g. incorporate aspects of physical consis- provide links across different locations, LeGrand and Wunsch 1995; Gebbie and tency, but are imperfect and are tested times (relevant to transient or multi- Huybers 2006; Marchal and Curry 2008; during development only with present state estimation) and state variables. Burke et al. 2011; Huybers et al. 2007; day observations. This has two advantages: it helps ensure Paul and Losch 2012). Another approach Data assimilation produces “best- the resulting state is physically consis- generates an ensemble of simulations of-both-worlds” estimates that combine tent, and it also means we are not limit- using many different parameter values observational and theoretical informa- ed to assimilating the same variables we and then selects the members with the tion while not ignoring their limita- wish to estimate. We could assimilate smallest model-data distance (“per- tions. We discuss data assimilation for data in one place to estimate another, or turbed parameter ensemble” methods; estimating past equilibrium states of assimilate temperature data to estimate e.g. Gregoire et al. 2010). the earth system such as climate and precipitation, or assimilate variables Updating methods combine model vegetation. We use the term “paleodata” corresponding to the outputs of a mod- and paleodata estimates. Typically the for measurement-based data: either the el to estimate variables corresponding model estimates are generated with a observations of proxies or the statistical to the inputs. The last are termed “in- perturbed parameter ensemble, which reconstructions derived from them. version” methods, such as estimating permits well-defined sampling of pa- atmospheric variables or terrestrial car- rameter uncertainties; the model esti- Aims and methods bon from paleo-vegetation records (e.g. mates are reweighted with the model- Equilibrium state, or “time slice”, data Guiot et al. 2000; Wu et al. 2007; Wu et data distance using Bayesian updating assimilation is estimation of a snapshot al. 2009; Pound et al. 2011) or estimat- (e.g. Guiot et al. 2000; Wu et al. 2007; in time during which it is assumed the ing oceanic variables from paleo-tracer Wu et al. 2009; Holden et al. 2009; state variables are not changing. The records (e.g. LeGrand and Wunsch 1995; Schmittner et al. 2011). state estimates may be the primary sci- Roche et al. 2004). entific aim or simply a “bonus” of cali- Data assimilation requires the fol- Interpretation brating model parameters (Annan et al., lowing ingredients: paleodata with un- Figure 1 illustrates some strengths of this issue). certainty estimates, simulations with data assimilation. The model propa- Time slice estimation is a natural uncertainty estimates, and a metric to gates information from LGM surface starting point in data assimilation be- quantify the dissimilarity, or “distance”, air temperature (SAT) reconstructions cause it is more straightforward than es- between the two. Climate state esti- over land to other regions, and to sea timating a transient state (Brönnimann mates are obtained by searching for the surface temperatures (SST). In this ex- et al., this issue) and is particularly ap- simulation(s) closest to the paleodata ample assimilating SAT reconstructions propriate if spatial patterns are more (“optimization”) or calculating a weight- produces an SST estimate with a warm- important than temporal changes or if ed combination of the two (“updating”). ing at the LGM in the northern North the model is computationally expen- Distance is usually measured with Atlantic, which is consistent with the sive. For a given computational resource the standard metric for normally dis- SST reconstructions. Uncertainties are time slice estimation permits more tributed model-data differences, i.e. the reduced relative to the model estimate 76

PAGES news • Vol 21 • No 2 • August 2013 allow greater freedom in specifying the behavior of climate-proxy relationships (such as nonlinearity and multi-modal uncertainties) and enables uncertainties to cascade through the causal chain to allow full probabilistic quantification of the unknown state. Using physically -based forward models for reconstruction, i.e. data assimilation, incorporates information about the relationships between locations, times and variables and therefore minimizes the risk of physical implausibility. The long-term goal may be forward physical modeling of the whole causal chain from radiative forcings to proxy archives (e.g. Roche et

al. 2004; Stone et al. 2013). assimilation Highlights: Data Science For paleo-simulations, we do not need models to be complex or state- of-the-art, but we do need to estimate their uncertainties. If they are complex it is difficult to generate their deriva- tives with respect to the parameters. If they are expensive it is difficult to sample, and therefore to assess, their uncertainties. Thoughtful experimental design with statisticians, and perhaps also statistical modeling of the physical model (known as “emulation”; e.g. Schmittner et al. 2011), can help in this regard. A research priority is to estimate the discrepancy between a model and Figure 1: LGM annual mean temperature anomalies from: A) surface air temperature (SAT) reconstructions based on pollen and plant macrofossils (Bartlein et al. 2010); B) sea surface temperature (SST) reconstructions based on reality at its best parameter values, and multiple ocean proxies (MARGO et al. 2009); C, D) simulations from the HadCM3 general circulation model (mean how this varies across different eras. of 17 member perturbed parameter ensemble; Edwards, unpublished data). Data assimilation estimates generated New updating methods are emerging by updating with SAT reconstructions (E, F), and both SAT and SST reconstructions (G, H). Gray areas indicate regions with low signal-to-noise: magnitude of temperature anomaly is less than 3σ of uncertainty estimates. that use the PMIP multi-model ensemble to explore structural uncertainties. in most locations (grayed out areas are corresponding to a particular distribu- For example, Annan and Hargreaves reduced). tion of model-data differences (“likeli- (2013) use the linear combination of en- How should we interpret assimi- hood function” in Bayesian terms). This semble members that best matches the lated paleo-states? Optimization meth- might preclude the use of non-standard paleodata. ods select a single best simulation so variables such as biomes. These challenges are worth tackling the state estimate is physically self- Data assimilation is a statistical for the substantial benefits. Information consistent according to the model. But modeling technique and should be from paleodata can be extrapolated to the state estimate from updating meth- evaluated. Testing the method with other locations, times and state vari- ods is a combination of multiple model pseudo-paleodata can help avoid the ables, and uncertainties are smaller (or simulations and paleodata, therefore (literal) pitfalls of finding local rather at worst, the same) than those of the interpretation requires more care. An than global minima in high-dimension- individual model or proxy-based esti- ensemble mean anomaly of zero might al spaces. mates. correspond to a wide spread of positive and negative results; this would Future directions Selected references be reflected in large model uncertain- Data assimilation is a formal method Full reference list online under: ties. A spatially coherent signal with that not only highlights model-data http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf small uncertainty might emerge from discrepancies but also corrects them. It Bartlein P et al. (2010) Climate Dynamics 37(3-4): 775-802 an ensemble after assimilating a single can be challenging, because it requires Guiot J et al. (2000) Ecological Modelling 127(2-3): 119-140 “pinning point” from paleodata; this sig- a process-based model and reliable esti- Schmittner A et al. (2011) Science 334: 1385-1388 nal should be physically consistent be- mation of uncertainties for both paleo- MARGO et al. (2009) Nature Geoscience 2: 127-132 cause it arises from the model physics. data and simulations. Stone EJ, Lunt DJ, Annan JD, Hargreaves JC (2013) Climate of the Past 9: Such considerations are common to all For paleodata, difficulties may arise 621-639 multi-model ensemble summaries and from dating and time averaging. But im- reanalyses. provements in estimating reconstruc- For statistically meaningful results tion uncertainties can be made by us- it is essential to use a distance met- ing forward modeling approaches (e.g. ric grounded in probability theory, i.e. Tingley et al. 2012). These approaches 77

PAGES news • Vol 21 • No 2 • August 2013 Parameter estimation using paleodata assimilation

James D. Annan1, M. Crucifix2, T.L. Edwards3 and A. Paul4 1RIGC/JAMSTEC, Yokohama, Japan; [email protected] 2Georges Lemaitre Centre for Earth and Climate Science, Université Catholique de Louvain, Belgium; 3School of Geographical Sciences, Bristol University, UK; 4MARUM, University of Bremen, Germany

In addition to improving the simulations of climate states, data assimilation concepts can also be used to estimate the internal parameters of climate models. Here we introduce some of the ideas behind this approach, and discuss some applications in the paleoclimate domain.

stimation of model parameter values state vector), and propagates this vector powerful methods such as Markov Chain Eis of particular interest in paleoclimate through the augmented set of equations Monte Carlo (Hargreaves and Annan 2002) and climate change research, since it is the and Particle Filtering (Crucifix and Rougier x = f (x) (2) formulation of model parameterizations, θ 2009). Figure 1 presents the results of θ = 0 (3)

Science Highlights: Data assimilation Highlights: Data Science rather than the initial conditions, which is ˙ one parameter estimation experiment by the main source of uncertainty regarding Thus,˙ the existing methods and technol- Hargreaves and Annan (2002). the climate’s long-term response to natu- ogy for estimating the state x can, in prin- In the case of more complex and ral and anthropogenic forcings. ciple, be directly applied to the estimation higher resolution models, the problems We should recognize at the outset of (x, θ), or in other words, the joint estima- of identifiability and computational cost that the question of a “correct” param- tion of state and parameters. are most commonly addressed by the eter value might in many cases be quite While this approach is conceptually use of equilibrium states. Here, the full contentious and disputable. There is, for straightforward, there are many practi- initial condition of the model is irrelevant, example, no single value to describe the cal difficulties in its application. The most at least within reasonable bounds, and speed at which ice crystals fall through widespread methods for data assimila- the dimension of the problem collapses the atmosphere, or the background rate tion, including both Kalman filtering down to the number of free parameters; of mixing in the ocean, to mention two and 4D-VAR, rely on (quasi-)linear and typically ten at most, assuming many parameters which are commonly varied Gaussian approaches. However, the aug- boundary conditions are not also to be es- in General Circulation Models (GCMs). mented model g is likely to be substan- timated. With this approach, much of the Generally the best we can hope for is to tially more nonlinear in its inputs than the detailed methodology of data assimilation find a set of parameter values, which per- underlying model f , due to the presence as developed and practiced in numerical

form well in a range of circumstances, and of product terms such as θi xj (Evensen et weather prediction, where the huge state to make allowances for the model’s inad- al. 1998). dimension is a dominant factor, ceases to equacies, i.e. structural errors due to inad- Further challenges exist in applying be so relevant. equate equations and parameterizations. this approach due to the wide disparity in While some attempts at using stan- However, inadequacies will always be relevant time scales. Often the initial state dard data assimilation methods have been present no matter how carefully param- has a rapid effect on the model trajectory performed (e.g. Annan et al. 2005), a much eter values are chosen: this should serve within the predictability time scale of the broader range of estimation methods as a caution against over-tuning. model, which is typically days to weeks for can also be used. With reasonably cheap It may not be immediately clear how atmospheric GCMs. On the other hand, the models and a sufficiently small set of pa- one can use proxy-derived observational full effect of the parameters only becomes rameters, direct sampling of the param- estimates of climatic state variables such apparent on the climatological time scale, eter space with a large ensemble may be as temperature or precipitation to es- which may be decades or centuries. feasible. A statistical emulator, which pro- timate the values of a model’s internal vides a very fast approximation to running parameters. However, from a sufficiently Applications the full model, may help in more compu- abstract perspective, the problem of pa- Methods for joint parameter and state es- tationally demanding cases (e.g. Holden et rameter estimation can be considered as timation in the full spatiotemporal domain al. 2010). equivalent to state estimation, via a stan- continue to be investigated for numerical One major target of parameter esti- dard approach in which the state space of weather prediction, where data are rela- mation in this field has been the estima- a dynamical model is augmented by the tively plentiful. But identifiability, that is tion of the equilibrium climate sensitivity. inclusion of model parameters (Jazwinski the ability to uniquely determine the state This may either be an explicitly tunable 1970; Evensen et al. 1998). To see how this and parameters given the observations, is model parameter in the case of simpler works, consider a system described by a much larger problem for modeling past models, or else an emergent property of a dynamical model f, which uses a set of climates, where proxy data are relatively the underlying physical processes, which internal parameters θ and propagates a sparse in both space and time. are parameterized in a more complex state vector x through time through a set Therefore, data assimilation in paleo- global climate model. The Last Glacial of differential equations: climate research generally finds a way to Maximum is a particularly popular inter- reduce the dimension of the problem. One val for study, due to its combination of a x = f (x) (1) ˙ θ such approach is to reduce the spatial di- large signal to noise ratio and good data We can create an equivalent model g(x, mension, even to the limit of a global av- coverage over a quasi-equilibrium in- θ) which takes as its state vector (x, θ) (in erage. For example, a three-variable glob- terval (Annan et al. 2005; Schneider von which the parameter values have simply ally averaged conceptual model for glacial Deimling et al. 2006; Holden et al. 2010; been concatenated onto the end of the cycles has been tuned using flexible and Schmittner et al. 2011; Paul and Losch 78

PAGES news • Vol 21 • No 2 • August 2013 Science Highlights: Data assimilation Highlights: Data Science

Figure 1: Experiment with 350 ka of data assimilated. The red line at the top is the normalized summer solar insolation forcing at 65° N. The black dot-dashed lines are normalized proxy data from Vostok (ice volume and atmospheric CO2 concentration) and SPECMAP (deep ocean temperature) cores. Data to the left of the vertical magenta line were used to tune parameters, with the right hand side used as validation of the model forecast, which (over a range of experiments) shows substantial skill for a duration of around 50-100 ka. The dark blue lines show the mean of the ensemble and the light blue lines show one standard deviation of the ensemble. Modified from Hargreaves and Annan (2002).

2012). The methods used for studying the variability while still retaining a transient spectrum of methods to be applied on a LGM in order to estimate the equilibrium and time-varying forced response may case-specific basis. climate sensitivity have covered a wide make use of temporal data such as tree range of techniques including direct sam- rings over the last few centuries (Hegerl et Selected references pling of parameter spaces (with and with- al. 2006). In that case, the spatial dimen- Full reference list online under: out the use of an emulator), Markov Chain sion can still be reduced, e.g. by averaging http://www.pages-igbp.org/products/newsletters/ref2013_2.pdf Monte Carlo methods, the variational ap- to a hemispheric mean. A similar approach Annan JD et al. (2005) SOLA 1: 181-184 proach using an adjoint model, and the was used by Frank et al. (2010) to estimate Crucifix M, Rougier J (2009) The European Physical Journal-Special Topics Ensemble Kalman Filter. In general, more the carbon cycle feedback. 174(1): 11-31 costly models require stronger assump- Paleoclimate simulations provide the Hargreaves JC, Annan JD (2002) Climate Dynamics 19: 371-381 tions and approximations due to compu- only opportunity to test and critically eval- Holden PB et al. (2010) Climate Dynamics 35: 785-806 tational limitations. uate climate models under a wide range Paul A, Losch M (2012) Perspectives of parameter and state estimation in paleoclimatology: In, Berger A et al. (Eds) Climate Change: Approaches which aim at averaging of boundary conditions. This suggests that Inferences from Paleoclimate and Regional Aspects, Springer, out the highest frequencies of internal we need to continue to develop a broad 93-105 79

PAGES news • Vol 21 • No 2 • August 2013 Impact of climate and sea level change on coastal evolution Accra, Ghana, 8-12 October 2012

Kwasi Appeaning-Addo, S.W. Laryea, B.A. Foli and C.L. Allotey Department of Marine and Fisheries Sciences, University of Ghana; [email protected] Workshop Reports Workshop

he third West African Quaternary covering sea level rise, coastal erosion and The meeting participants then went on a TResearch Association (WAQUA) work- climate change issues. In particular, the guided tour of coastal communities along shop, hosted by the Department of Marine presentations addressed the impact of sea- the eastern coast of Ghana. One of them and Fisheries Sciences, University of level changes on coastal tourism develop- was Keta, a coastal town in the Volta Region Ghana, was held at the Institute for Local ment; the linkages between sea-level rise that was partly destroyed by sea erosion at Government Studies in Accra. The objec- and ground water quality, hydrodynam- the end of the 20th century. Keta is situated tive of the workshop was to identify how ics, upwelling and biogeochemistry in the on a sandspit separating the Gulf of Guinea humans adapted to past climatic and sea Gulf of Guinea; paleoclimatic evidences from the Keta Lagoon. Due to this double level changes, and to discuss future adapta- from the quaternary coastal deposits from waterfront, the city area is particularly vul- tion strategies through a multidisciplinary Nigeria; dynamics of ocean surges and their nerable to erosion. It is flooded from the approach. impacts on the Nigerian coastline; and the ocean front during high tides and from the Twenty-seven scientists from five effect of climatic extreme events on res- lagoon front during heavy runoff, especial- countries attended the workshop. The in- ervoir water storage in the Volta Basin in ly in the rainy seasons. During devastating augural lecture was given by Dr. Thomas Ghana. erosion events between 1960 and 1980, Kwasi Adu of the Geological Survey The workshop provided a platform for more than half of the town area has been Department of Ghana. He spoke about the scientists to share knowledge and informa- washed away. The photo (Fig. 1) shows Keta causes of sea-level rise and coastal change, tion on their respective areas of research. in 1985. Since 1999 more than 80 million and their implications for coastal regions. At the end of the presentation sessions, the US$ have been invested to protect, restore His lecture stressed the fact that important plenum agreed that research on sea-level and stabilize the coast of Keta. planning decisions for sea-level rise should rise should be particularly encouraged and The next WAQUA workshop will be be based on the best available scientific that further activities to bring together held in Senegal in 2014. knowledge and careful consideration of scientists working in this area should be long-term benefits for a sustainable future. organized. To stimulate interest and ex- Acknowledgements He recommended that decisions on adap- pose students to new methods, regular in- We express our sincere gratitude to INQUA, PAGES, tation or mitigation measures should also ternational workshops or summer schools PAST and the University of Ghana for sponsoring this workshop. We are also grateful to the local take into consideration economic, social, will be held to bring together students and hosts, the Department of Marine and Fisheries and environmental costs. experts from within and outside the sub- Sciences, University of Ghana and the Ghanaian Sixteen scientific papers were pre- region. Institute of Local Government Studies. sented and discussed on various topics

Figure 1: This photo from 1985 shows a section of the Keta town destroyed by sea erosion. Photo by Beth Knittle. 80

PAGES news • Vol 21 • No 2 • August 2013 Holocene land-cover change in Eastern Asia for climate modeling Shijazhuang, China, 9-11 October 2012

Marie-José Gaillard1 and Qinghai Xu2 1Department of Biology and Environmental Science, Linnaeus University, Kalmar, Sweden; [email protected] 2

Key Laboratory of Environmental Change and Ecological Construction, Hebei Normal University, Shijiazhuang, China Reports Workshop

his workshop was held at Hebei of the workshop are (i) the building of the lectures, results were presented for TNormal University in China, and a large network of experts from Eastern historical, paleoecological and pollen- contributed to the PAGES Focus 4 Asia, Europe and USA now working to- based reconstructions; pollen-vegeta- theme Land Use and Cover (LUC). A ma- gether to understand past changes in tion relationships; past human-impact jor goal of LUC is to achieve Holocene land use and land cover in Eastern Asia, studies; and model scenarios of anthro- land-cover reconstructions that can be (ii) that all existing East Asian pollen pogenic land-cover changes in the past. used for climate modeling and test- databases will be integrated into the Some of the conference was also dedi- ing hypotheses on past and future ef- NEOTOMA Paleoecology Database by cated to reviewing the state of existing fects of anthropogenic land cover on 2014 (coordinated by Eric Grimm, Illinois pollen databases and more generally, climate. Collaborations initiated be- State University, USA), and (iii) that a re- database building. tween Linnaeus University (Sweden; view paper will be prepared with the Plenary and group break-out dis- M.-J Gaillard), University of Hull working title “Past land-use and anthro- cussions focused on more technical (Britain, Jane Bunting), Hebei Normal pogenic land-cover change in Eastern aspects such as improving pollen da- University (China; Q. Xu and Y. Li), the Asia - evaluation of current achieve- tabases, especially for the East Asian French Institute (Pondicherry, India; A ments, potentials and limitations, and region; planning the review paper; Krishnamurthy) and Lucknow University future avenues”. It is planned to submit and scientific topics such as the use of (India; P. Singh Ranhotra) are in line with this article this fall. It will include 1) a re- pollen-based and historical land-cover the goals of Focus 4-LUC and follow the view of Holocene human-induced veg- reconstructions for the evaluation of strategy of the European LUC-relevant etation and land-use changes in Eastern model scenarios of past anthropogenic LANDCLIM project (Gaillard et al. 2010). Asia based on results presented at the land-cover change (Fig. 1), and the inte- The aim of these collaborations is to workshop; 2) a discussion of the exist- gration of model scenarios with paleo- develop quantitative reconstructions ing anthropogenic land-cover change ecological or historical reconstructions. of past vegetation cover in India and scenarios (HYDE, Klein Goldewijk et China using pollen-vegetation model- al. 2010; KK 10, Kaplan et al. 2009) in References ing and archaeological/historical data the light of the reviewed proxy-based Gaillard MJ et al. (2010) Climate of the Past 6: 483-678 together with other land-cover model- knowledge; and 3) a discussion on the Kaplan J, Krumhardt K, Zimmermann N (2009) Quaternary Science Reviews 28: 3016-3034 ling approaches. implications of these results for future Klein Goldewijk K, Beusen A, Janssen P (2010) The Holocene 20: 565-573 The objective of this workshop in climate modeling and the study of past Olofsson J, Hickler T (2008) Vegetation History and Archaeobotany 17: China was to initiate the necessary col- land cover-climate interactions. 605-615 laborations and activities to make past These significant outcomes are the land-cover reconstructions possible in result of three intense days of presen- Eastern Asia. The three major outcomes tations and discussion sessions. During

Figure 1: Anthropogenic deforestation in Eastern Asia at AD 1 simulated by three different approaches: A) Olofsson and Hickler (2008); (B) HYDE (History Database of the Global Environment) version 3.1 (Klein Goldewijk et al. 2010); and (C) Kaplan et al. (2009). Note the large differences in land-cover between the different models used.

PAGES news • Vol 21 • No 2 • August 2013 Palaeo50: The priority research questions in paleoecology

Oxford, UK, 13-14 December 2012

Anson W. Mackay1, A.W.R. Seddon2,3 and A.G. Baker2 1Environmental Change Research Centre, University College London, UK; [email protected] 2 3

Workshop Reports Workshop Oxford Long-Term Ecology Laboratory, University of Oxford, UK; Department of Biology, University of Bergen, Norway

aleoecological studies provide in- of Maryland, USA); Biodiversity, conser- plenary. The eight reserve questions that Psights into ecological and evolu- vation and novel ecosystems (Lindsey obtained the most votes were selected tionary processes, and help to improve Gillson, University of Capetown, South to complete the list of 50 priority ques- our understanding of past ecosystems Africa), Biodiversity over long time scales tions. and human interactions with the envi- (Kathy Willis, University of Oxford, UK), Working group discussions were of- ronment. But paleoecologists are often Ecosystems and biogeochemical cy- ten heated and passionate. Compromises challenged when it comes to processing, cles (Ed Johnson, University of Calgary, won by the chairs and co-chairs were dif- presenting and applying their data to im- Canada), Quantitative and Qualitative ficult but necessary. It is important that prove ecological understanding and in- reconstructions (Stephen Juggins, the final 50 priority questions are not form management decisions (e.g. Froyd University of Newcastle, UK), and seen as a definitive list, but as a starting and Willis 2008) in a broader context. Approaches to paleoecology (John Birks, point for future dialogue and research Participatory exercises in, for example, University of Bergen, Norway). ideas. conservation, plant science, ecology, and Each working group also had a co- The final list of 50 priority questions marine policy, have developed as an ef- chair, responsible for recording votes and full details of the methodology is fective and inclusive way to identify key and editing questions on a spreadsheet, currently under review, and the publi- questions and emerging issues in sci- and a scribe. Workshop participants were cation will be announced through the ence and policy (Sutherland et al. 2011). allocated into one of six parallel working PAGES network. With this in mind, we organized the first groups tasked with reducing the number priority questions exercise in paleoecol- of questions from 180 to 30 by the end Acknowledgements ogy with the goal of identifying 50 priori- of day one. This was an intensive process We thank PAGES for generously providing sup- ty questions to guide the future research involving considerable debate and edit- port. We also acknowledge sponsorship from the British Ecological Society, the Quaternary agenda of the paleoecology community. ing. During day two, these 30 questions Research Association and the Biodiversity The workshop was held at the were winnowed down further with each Institute, University of Oxford. Biodiversity Institute of the University group arriving at seven priority ques- of Oxford. Participants included invited tions. The seven questions from each experts and selected applicants from group were then combined to obtain 42 References an open call. Key funding bodies and priority questions. Each working group Froyd CA, Willis KJ (2008) Quaternary Science Reviews 27: 1723-1732 stakeholders were also represented at had a further five reserve questions, Sutherland WJ et al. (2011) Methods in Ecology and Evolution 2: 238-247 the workshop, including the US NSF, which everyone voted on in the final IGBP PAGES, UK NERC, and UK Natural England. Several months prior to the workshop, suggestions for priority questions had been invited from the wider community via list-servers, mailing lists, society newsletters, and social media, particularly Twitter (@Palaeo50). By the end of October 2012, over 900 questions had been submitted from almost 130 individuals and research groups. Questions were then coded and checked for duplication and meaning, and similar questions were merged. The remaining 800 questions were re-distributed to those who had initially engaged in the process. Participants were asked to vote on their top 50 priority questions. At the end of November the questions were grouped into 50+ categories, which in turn were allocated to one of six workshop themes to be chaired by an ex- pert: Human-environment interactions in the Anthropocene (Erle Ellis, University Figure 1: Flowchart of the selection process for the 50 priority research questions. 82

PAGES news • Vol 21 • No 2 • August 2013 The Agulhas System and its role in changing ocean circulation, climate, and marine ecosystems

Stellenbosch, Republic of South Africa, 8-12 October 2012

Rainer Zahn1, W.P.M. de Ruijter2, L. Beal3, A. Biastoch4 and SCOR/WCRP/IAPSO Working Group 1365 1Institut de Ciència i Tecnologia Ambientals, Universitat Autònoma de Barcelona, Bellaterra, Spain; [email protected] 2 3

Institute for Marine and Atmospheric Research, Utrecht University, The Netherlands; Rosenstiel School of Marine and Atmospheric Science, Reports Workshop University of Miami, USA; 4GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany; 5www.scor-int.org/Working_Groups/wg136.htm

his conference was held in recogni- global warming when freshwater pertur- the Current affect plankton communities, Ttion of the significance of the Agulhas bation in the North might weaken it. But large predators, pelagic fish stocks, and Current to ocean physical circulation, these feedbacks are not easy to trace, and possibly even facilitate the northward sar- marine biology and ecology, and climate direct observations and climate models dine runs swimming against the vigorous at the regional to global scale. The con- have been the only way to indicate the southward flow of the Agulhas Current. ference centered on the dynamics of the possible existence of such far-field tele- The meteorological relevance of the Agulhas Current in the present and the connections to date. This is where marine Agulhas Current was also demonstrated, geological past; the influence of the cur- paleo-proxy profiles prove helpful. They for example its role as a prominent source rent on weather, ecosystems, and fisher- reveal the functioning of the Agulhas of atmospheric heat and its significance ies; and the impact of the Agulhas Current Current under a far larger array of climatic in maintaining and anchoring storm on ocean circulation and climate with a boundary conditions than those present tracks. Among other things, these affect notable focus on the Atlantic Meridional during the short period of instrumental the atmospheric westerly Polar Front Jet Overturning Circulation (AMOC). 108 observations. For instance altered condi- and Mascarene High, with onward conse- participants from 20 countries, includ- tions in the past with shifted ocean circu- quences for regional weather patterns, in- ing seven African countries, attended lation and wind fields stimulated Agulhas cluding extreme rainfall events over South the conference, of which a quarter were water transports from the Indian Ocean to Africa. young researchers at the PhD student the Atlantic, the so-called Agulhas leak- The conference developed a number level. Participants came from the areas of age, at very different rates from today’s. of recommendations; two key ones being ocean and climate modeling, physical and A number of the paleo-records that were that efforts should be made to trace the biological oceanography, marine ecology, shown at the meeting demonstrated a link impacts of the Agulhas leakage on the paleoceanography, meteorology, and ma- between Agulhas leakage and Dansgaard/ changing global climate system at a range rine and terrestrial paleoclimatology. The Oeschger-type abrupt climate changes in of timescales, and that sustained obser- Agulhas Current attracts interest from the North Atlantic region, suggesting that vations of the Agulhas system should be these communities because of its signifi- salt-water leakage may have played a role developed. Implementing these recom- cance to a wide range of climatic, biologi- in strengthening the AMOC and sudden mendations would constitute a major chal- cal and societal issues. climate warming in the North. lenge logistically and the Western Indian The current sends waters from the Marine ecosystems were also shown Ocean Sustainable Ecosystem Alliance Indian Ocean to the South Atlantic. This to be measurably impacted by the (WIOSEA) was identified as a possible inte- is thought to modulate convective activ- Agulhas system. Notably, the high vari- grating platform for the cooperation of in- ity in the North Atlantic. It is possible that ability associated with the prominence ternational and regional scientists toward it even stabilizes the AMOC at times of of mesoscale eddies and dipoles along these goals. This would involve capacity building and training regional technicians and scientists, which could be coordinated through partnerships with the National Research Foundation in South Africa. The conference was held under the auspices of the American Geophysical Union Chapman Conference series and organized by the Scientific Committee on Oceanic Research (SCOR)/ World Climate Research Program (WCRP)/ International Association for the Physical Sciences of the Oceans (IAPSO) Working Group 136. Additional sponsorship came from the International Union of Geodesy and Geophysics; US NSF; NOAA; PAGES; Institute of Research for Development (IRD) France; and the Royal Netherlands Institute for Sea Research.

References Figure 1: A model perspective of Agulhas leakage and the interbasin water transports between the Indian Ocean and Atlantic. A high-resolution Agulhas model (1/10°, gray box), is nested in a (1/2°) global ocean/sea ice model Biastoch A, Böning CW, Schwarzkopf FU, Lutjeharms JRE (2009) Nature 462: 495-499 to simulate temperature and magnitude of currents (see Biastoch et al. 2009). 83

PAGES news • Vol 21 • No 2 • August 2013 IPICS First Open Science conference

Presqu’île de Giens, France, 1-5 October 2012

Jérôme Chappellaz1, Eric Wolff2 and Ed Brook3 1Laboratoire de Glaciologie et Géophysique de l’Environnement, Université Joseph Fourier Grenoble, St Martin d’Hères, France; [email protected] 2British Antarctic Survey, Cambridge, UK; 3College of Earth, Ocean, and Atmospheric Sciences, Oregon State Workshop Reports Workshop University, Corvallis, USA

Figure 1: Inside the drilling trench at NEEM, Greenland. The North Greenland Eemian (NEEM) ice drilling is an international project managed by the Centre for Ice and Climate, Denmark, involving 14 nations. In Summer 2010, it recovered ice from the Eemian dating back from 130 ka BP, helping to describe the warming and ice sheet shrinking at a time of unusually high Arctic summer insolation (NEEM community members 2013). Photo: Jérôme Chappellaz.

PICS (International Partnerships in white papers (www.pages-igbp.org/ipics). future we will see that many new ice core IIce Core Sciences) is the key planning Notably, it covered questions of climate drilling projects had their roots at IPICS’ 1st group for international ice core scientists. variability at different time scales (from OSC. Proving that ice core scientific out- Established in 2005, it now includes sci- the last 2000 to 1 M years), biogeochemi- puts remain of prime importance to high- entists from 22 nations and aims at defin- cal cycles, dating, and ice dynamics. New impact journals, the Chief Editor of Nature ing the scientific priorities of the ice core challenges, such as studying the bacterial as well as an editor of Nature Geoscience community for the coming decade. IPICS content of ice cores, and new methodolo- attended the full five days of the event. lies under the common umbrella of IGBP/ gies were also the focal point of specific IPICS’ next OSC will take place in 2016. PAGES, SCAR (Scientific Committee on sessions. Over the five days of the confer- An open call for bids to organize it will be Antarctic Research) and IACS (International ence, all attendees gathered for the ple- launched in 2013. Association of Cryospheric Sciences). nary sessions combined with long poster IPIC’s First Open Science conference, sessions. These sessions offered valuable Acknowledgements organized by the European branch of and efficient networking opportunities. The organizers thank the generous financial sup- IPICS (EuroPICS), took place in a beauti- The full program can be found at: www. port of many sponsors: European Descartes Prize of the EPICA project, ERC project ICE&LASERS ful setting on the French Côte d’Azur. 230 ipics2012.org (Grant # 291062), LabEX OSUG@2020 project scientists gathered from 23 nations, with Among the various results presented of the Grenoble Observatory for Earth Sciences a good mix of both junior and senior sci- at this occasion, significant information and Astronomy, European Polar Board, SCAR, entists present. While most of the partici- was provided on two big recent proj- PAGES, IACS, Aix-Marseille University, Versailles – pants work on ice cores, a significant num- ects of the ice core community: the WAIS St Quentin University, Fédération de Recherche ber were scientists working on marine and Divide deep drilling in West Antarctica, ECCOREV, IRD, LGGE, LSCE, Picarro, LabEX project L-IPSL, Collège de France and IPEV. Efficient continental records as well as on climate and the NEEM deep drilling in North-West administrative and financial handling of the modeling. The sponsorship received from Greenland. Ice core projects from outside conference was provided by the Floralis com- several institutions, agencies and projects, polar regions were also well represented, pany. Special thanks to Stéphanie Lamarque enabled us to invite ten keynote speak- with results obtained from the Andes, the and Audrey Maljean from Floralis for their help ers as well as six scientists from emerging Alps and the Himalayas. over the two years of conference preparation. countries. The beautiful and peaceful setting The program followed IPIC’s main of the conference center enabled strong References scientific objectives as outlined in four and efficient networking; no doubt, in the NEEM community members (2013) Nature 493: 489-494 84

PAGES news • Vol 21 • No 2 • August 2013 Analyzing paleolimnological data with R

Isle of Cumbrae, Scotland, 16-20 August 2012

Diego Navarro1 and Steve Juggins2 1Instituto de Investigaciones Marinas y Costeras, CONICET, Universidad Nacional de Mar del Plata, Argentina; [email protected] 2School of Geography, Politics and Sociology, Newcastle University, Newcastle upon Tyne, UK Workshop Reports Workshop

aleolimnology has grown rapidly over This recent workshop, held in the com- and calculation of rates of change. The fi- Pthe last two or three decades in terms fortable facilities of the Millport Marine nal lectures dealt with the application of of the number of physical, chemical, and Biological Station, trained researchers on techniques for quantitative environmental biological indicators analyzed and the the theory and practice of analyzing pa- reconstructions. The theory and assump- quantity, diversity and quality of data gen- leolimnological data using R. The course tions underpinning each method were erated. Such growth has presented paleo- was led by Steve Juggins (Newcastle introduced in short lectures, after which limnologists with the challenge of dealing University) and Gavin Simpson (University the students had the opportunity to ap- with highly quantitative, complex, and College London, recently moved to the ply what they had learned, to data sets multivariate data to document the timing University of Regina), two of the research- and real environmental questions, during and magnitude of past changes in aquatic ers that have contributed in the develop- practical sessions. There was also time in systems, and to understand the internal ment and application of different statisti- the evenings for sessions on important R and external forcing of these changes. To cal tools and packages for paleoecology tips, advanced R graphics, special topics cope with such tasks paleolimnologists within the R community. proposed by the assistants, and for the continuously add new and more sophis- A total of 31 participants from a range students to work on their own data. ticated numerical and statistical methods of continents (North and South America, The course was conveniently orga- to help in the collection, assessment, sum- Europe, Asia, and Africa), career stages nized just prior to the 12th International mary, analysis, interpretation, and com- (PhD students to faculty) and scientific Paleolimnology Symposium (Glasgow, munication of data. Birks et al. (2012) sum- backgrounds (paleolimnology, palynolo- 20-24 August 2012), which enabled all marize the history of the development of gy, diatoms, chironomids, sedimentology) of the workshop participants to attend quantitative paleolimnology and provide enjoyed four long days of training in statis- the symposium and encouraged further an update to analytical and statistical tical tools and working on their own data. discussions throughout the following techniques currently used in paleolimnol- Initially, participants were introduced to R week. PAGES covered travel and course ogy and paleoecology. software and language, tools for summa- costs for five young researchers from de- R is both a programming language rizing data, exploratory data analysis and veloping countries (Turkey, South Africa, and a complete statistical and graphi- graphics. The following lectures and prac- Macedonia, and Argentina) all of who cal programming environment. Its use tical sessions focused on simple, multiple were very grateful for the opportunity to has become popular because it is a free and modern regression methods; cluster attend. and open-source application, but above analysis and ordination techniques used all because its capability is continuously to summarize patterns in stratigraphic References enhanced by new and diverse packages data; hypothesis testing using permuta- Birks HJB, Lotter AF, Juggins S, Smol JP (2012) Tracking Environmental Change Using Lake Sediments: Data Handling and Numerical developed and generously provided by a tions for temporal data, age-depth mod- Technique, Developments in Paleoenvironmental Research 5. large community of scientists. eling, chronological clustering, smoothing Springer, 745 pp and interpolation of stratigraphic data;

Figure 1: Participants during the R workshop. Photo by S. Juggins. 85

PAGES news • Vol 21 • No 2 • August 2013 The Sun and its role in climate change Workshop of the PAGES Solar Working Group – Davos, Switzerland, 5-7 September 2012

Juerg Beer Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf, Switzerland; [email protected]

Workshop Reports Workshop etter understanding the Sun and its Brole in climate change is an important but difficult goal. It is important because to properly assess the anthropogenic effect on climate change an accurate quantification of the natural forcing factors is required. But it is difficult because: (1) natural forcing records are generally not well quantified; (2) the response of the climate system to forcings is non-linear due to various feedback mechanisms and can only be estimated using complex climate models; (3) in spite of their complexity models may not comprise all relevant processes and have to be validated, but the instrumental records of climate forcing and climate response are generally too short for this pur- pose and the data set needs to be comple- mented by proxy data; (4) proxy data are derived from natural archives and are only indirectly related to the physical parameters of interest, and their calibration is based on assumptions that may not be fully valid on longer time scales; (5) instrumental and proxy data reflect the combined response to all forcings, and not only the influence of the Sun. Furthermore, the climate system shows internal unforced variability. All this makes Figure 1: Image of a solar magnetic filament burst. Image by NASA. separation and quantification of the individual forcings very difficult. addressed in more detail in subsequent • UV forcing and possibly also precipitat- The main aim of the first workshop of meetings: ing particles have significant impacts on the solar forcing working group was to as- • Physical solar models are not yet capable atmospheric chemistry and dynamics and sess the present state of the art and iden- of explaining many observed features need to be included in models. tify knowledge gaps by bringing together such as solar cycles and changes in total • Detection and attribution of solar forc- experts from the solar, the observational solar irradiance (TSI) and solar spectral ir- ing is often hampered by volcanic erup- and paleo-data, and modeling communi- radiance (SSI). tions occurring simultaneously. Strategies ties. • There are still unresolved discrepancies to separate solar and volcanic forcings The workshop was organized jointly between different composites of TSI based could be to select periods of low volcanic with FUPSOL (Future and past solar influ- on the same satellite data. activity (e.g. roman period), to consider ence on the terrestrial climate), a multi- • Semi-empirical models are relatively suc- regional effects that differ for different disciplinary project of the Swiss National cessful in explaining short-term changes forcings, and to look for multi-decadal to Science Foundations that addresses how in TSI and SSI on time scales of days to centennial solar cycles with well-defined past solar variations have affected climate, years. However, on multi-decadal time periodicities. and how this information can be used to scales input data and instrumental TSI and constrain solar-climate modeling. FUPSOL SSI data for comparison are missing. As an opening spectacle to the workshop, also aims to address the key question of • TSI and SSI reconstructions based on a medium-sized flare initiated a long, mag- how a decrease in solar forcing in the next proxies suffer from large uncertainties in netic filament burst out from the Sun (Fig. decades could affect climate at global and their amplitudes. 1). Viewed in the extreme ultraviolet light, regional scales. • The most recent minimum, between so- the filament strand stretched outwards Here are some examples of open lar cycle 23 and 24, and probably also the until it finally broke and headed off to the questions and problems that were upcoming minimum provide a glance of left. Some of the particles from this erup- identified in this workshop, and will be the Sun at its lowest activity level ever ob- tion hit Earth in September 2012, generat- served during the satellite era. ing a beautiful aurora. 86

PAGES news • Vol 21 • No 2 • August 2013 The backbone of PAGES 2k: data management and archiving

Lucien von Gunten, D.M. Anderson2, B. Chase1, M. Curran1, J. Gergis1, E.P. Gille2, W. Gross2, S. Hanhijärvi1, D.S. Ka ufman, T. Kiefer, N.P. McKay1, I. Mundo1, R. Neukom1, M. Sano1, A. Shah2, J. Tyler1, A. Viau1, S. Wagner1, E.R. Wahl2 and D. Willard 1PAGES 2k data managers

2NOAA Paleoclimatology branch members News Program Full affiliations listed here: www.pages-igbp.org/products/newsletters/ref2013_2.pdf The PAGES 2k Network and NOAA collaborate closely to optimize data compilations, and to build structures to facilitate ongoing supply and dynamic use of data. It is thus an successful example for a large trans-disciplinary effort leading to added value for the scientific community.

he PAGES 2k Network has formed to study central place to continuously compile datas- The new data submission template is also op- Tclimate change over the last two millennia ets considered relevant to their studies. timized for taking advantage of NOAA’s archi- at a regional scale, based on the most com- val structure, which follows international con- prehensive dataset of paleoclimate proxy-re- Populating the database ventions for data description and archiving, cords possible. In 2011, at its second network A two-step approach was applied for entering and the Open Archive Initiative Protocol for meeting in Bern, Switzerland (von Gunten et the 2k data into the database in order to serve Metadata Harvesting. This allows PAGES 2k al. 2012) the network formally acknowledged demands for both speediness and thorough- data to be visible beyond the NOAA web site. that the envisioned data-intensive multi- ness. A new feature of the NOAA-Paleo archive proxy and multi-region study must be built First, all records used for the first syn- is the search capabilities that allow for project- on the foundations of efficient and coordinat- thesis article on regional temperature recon- specific searches by a logical operator (e.g. ed data management. In addition, the group structions (PAGES 2k Consortium 2013) were “PAGES 2K AND Monsoon”). Additional func- committed to PAGES general objective to pro- made available on a “data synthesis products” tionalities are planned that will, for example, mote open access to scientific data and called page dedicated to the paper (hurricane.ncdc. allow the user to select a subset of proxy data for all records used for, or emerging from the noaa.gov/pls/paleox/f?p=519:1:::::P1_STUDY_ for a region, and generate a single download- 2k project to be publicly archived upon publi- ID:14188). This ensured that the records were able file of the requested data in NetCDF, cation of the related 2k studies. made publicly available exactly at the time of ASCII, or ExcelTM formats. publication and in a format that will remain Architects of the home for 2k data identical with the data files supplementing 2k data management - next steps The National Climatic Data Center at the article. In a second step, all these records In the next phase of the project starting now, the National Oceanic and Atmospheric are currently being (re)submitted to NOAA the 2k network will work on completing the Administration (NOAA) offered to host the with more detailed metadata information database of paleoclimate records of the last primary 2k data archive. They set up a dedi- than before using a new submission protocol. 2000 years to eventually produce new synop- cated NOAA task force to tailor the 2k data Additionally, many new and already stored tic climate reconstructions. The proxy records archive to the specific needs of the 2k project records that were not used for the PAGES 2k will be collected according to the new NOAA and to coordinate archiving with NOAA's data temperature synthesis are (re)formatted to data submission protocol. The prior use of this architecture and search capabilities. The 2k the new submission protocol. This will allow template during the collection and analysis groups nominated regional data managers to improved search and export capabilities for phases of the project has the following advan- provide input from the users’ end. a wealth of records that can currently only be tages: 1) all records are collected in the same, Over the last two years, the regional 2k accessed individually. uniform format allowing for the inclusion of data managers have worked closely with all relevant information, 2) the files are easily NOAA to tailor the database infrastructure Improved data submission protocol computer readable for data analyses, and 3) and prepare the upload of the 2k data. In addi- The data submission process is a crucial step no additional formatting is required for the tion, they provided expertise to help promote for the long-term success of a database. On subsequent submission to the NOAA-Paleo improvements in NOAA’s archival of paleosci- the one hand, it should contain as much archive. entific data in general. Since the data manag- relevant information as possible in order to For large, data-intensive studies a good ers of the regional 2k groups are spread across maximize the value of the data. On the other data management strategy is crucial. The ex- the globe, the collaboration was organized hand, it should remain simple enough to keep perience from the PAGES 2k project suggests around bi-monthly teleconference meetings the threshold for data providers as low as pos- that setting up a data manager team and in- under the lead of NOAA. In spite of the occa- sible. The NOAA task force and 2k data man- volving archivist partners such as NOAA at an sional unearthly meeting hours for some, the agers therefore created a substantially revised early stage of the project is key to handling interaction between the 2k data and NOAA submission template file. This new protocol data efficiently. database groups has worked fruitfully, as the allows including more comprehensive in- This new collaborative data storing ef- following achievements show. formation relating to the proxy records, and, fort is only possible thanks to the members crucially, is organized in a structured format of the regional 2k groups who provide their The 2k database that allows machine reading and automated data and metadata inventories with the aim The paleoclimatology program at NOAA has searching for defined metadata information. to make the global network of paleoclimate set up a dedicated 2k project site with sub- This is critical in order to maximize the useful- datasets publicly available. pages for all regional groups (www.ncdc. ness of the data to other scientists, as it addi- noaa.gov/paleo/pages2k/pages-2k-network. tionally allows them to reprocess underlying References html). This page was created early in the features of the records such as the chronology PAGES 2k Consortium (2013) Nature Geoscience 6: 339-346 project to provide the regional groups with a or proxy calibrations. von Gunten L, Wanner H, Kiefer T (2012) PAGES news 20(1): 46 87

PAGES news • Vol 21 • No 2 • August 2013 Updated Latin American Pollen Database: Version 2013 in preparation for NEOTOMA

Suzette G.A. Flantua1,2, H. Hooghiemstra1, E. Grimm3 and V. Markgraf4 1Institute of Biodiversity Ecosystem Dynamics, University of Amsterdam, Netherlands; [email protected] 2Palinología y Paleoecología, Universidad Los Andes, Bogotá, Colombia; 3Illinois State Museum, Springfield, USA;4 Institute of Arctic and Alpine Program News Program Research, University of Colorado, Boulder, USA

he Latin American Pollen Data Base, better countries represented has increased from 15 database to make a significant contribution Tknown as the LAPD, is an extensive data- to 29. to LAPD and thus stimulate global collabora- base of pollen from peat and lake cores and In the meantime, the “NEOTOMA” data- tion, and data input and use by other research surface samples. It covers the areas of Central base (www.NEOTOMAdb.org) was developed groups. The data of the newest pollen sites will America, the Caribbean, and South America. through an international collaborative effort be kept on “standby” in an offline database The database was launched in 1994 by a re- of individuals from 23 institutions. This cyber and made publicly available once the related search group headed by Vera Markgraf at the infrastructure was designed to manage large research papers are accepted for publication. University of Colorado, USA, and its manage- multiproxy datasets, which makes it easy to We would like to make researchers aware ment moved to the University of Amsterdam explore, visualize, and compare a wide vari- of the much richer palynological information in 1998, where it was hosted by Robert ety of paleoenvironmental data. This is why it now available for Latin America and we hope Marchant at the Institute of Biodiversity was chosen as the primary archive site for the the pollen community will recognize LAPD- Ecosystem Dynamics (IBED). Global Pollen Database. The LAPD data in the NEOTOMA as an important archive, where the The LAPD started as a website where 1997-list is now available through NEOTOMA original authors are cited and acknowledged palynologists were encouraged to share their (Fig. 1), and the complete 2013 LAPD inven- to have contributed to the database. We em- data. Unfortunately, after the project ended tory with metadata will soon be available phasize the great opportunity to promote in 2003 no further updates were made to the through NEOTOMA Explorer (http://ceiwin5. multidisciplinary research on a continental website and the related database, and the cei.psu.edu/Neotoma/Explorer/). scale and international scientific cooperation. list of pollen data of Latin America quickly Although all LAPD data will be incorpo- We invite anyone with questions, doubts, became outdated. Recognizing the urgency rated in NEOTOMA, the LAPD database will or relevant information to contact us through for an updated LAPD, the group at IBED de- still exist as an independent entity. There will Suzette Flantua and to support this global cided to revive it. Supported by three grants be a LAPD page within the existing NEOTOMA palynological initiative for an improved inte- from the Amsterdam-based Hugo-de-Vries- website which can be used to obtain informa- gration of knowledge and efforts. Foundation (Van Boxel and Flantua 2009; tion on updated pollen sites, the pollen data, Flantua and Van Boxel 2011), Suzette Flantua and events related to LAPD. It was also pro- References initiated a search for studies published after posed to form a Latin American NEOTOMA Flantua SGA, Van Boxel JH (2011) Reviving the Latin American Pollen Database (LAPD). IBED, University of Amsterdam; dare.uva.nl/ 2003. While the exploration for pollen records group of paleoecological researchers to man- document/447756 continues, this new “LAPD 2013” inventory age the database, and upload and control the Grimm EC et al. (2013) Pollen Methods and Studies. Databases and their contains 1478 pollen sites throughout Latin quality of the data. application. In: Elias SA Mock CJ (Eds) Encyclopedia of Quaternary Science 2, Elsevier, 831-838 America, multiplying by a factor of three As almost no new data has been contrib- Van Boxel JH, Flantua SGA (2009) Pilot study of the geographical distri- the number of sites compared with the last uted to LAPD since 2003, IBED is in the pro- bution of plant functional types in the Amazonian lowlands. IBED, update in 1997 (463 sites). The number of cess of digitalizing and uploading their pollen University of Amsterdam; dare.uva.nl/document/447756

Figure 1: NEOTOMA and LAPD pollen sites. Red dots: existing NEOTOMA database; blue dots: African Pollen Database; yellow dots: inventoried sites for inclusion from Latin America and Japan. (Figure from Grimm et al. 2013). 88

PAGES news • Vol 21 • No 2 • August 2013 A brief report on the 2nd PAGES Young Scientists Meeting in Goa, India

1 2 Rajeev Saraswat and Britta Jensen Scientists Meeting 2013 Young 1Micropaleontology Laboratory, National Institute of Oceanography, Goa, India; [email protected] 2School of Geography, Archaeology, Palaeoecology, Queen’s University, Belfast ack in 2009, PAGES experimented with a In the keynote talk Alan Mix of Oregon State addressing various topics such as signing re- Bdifferent type of meeting for the first time University reflected back upon his career as a views vs. double-blind reviews and what edi- – the inaugural Young Scientists Meeting climate scientist, which began during a time tors expect in a good review. It became clear (YSM) in Corvallis, USA. Recently several 1st of discovery defined by a paucity of data - a during this session that many YSM partici- YSM alumni worked together with PAGES to stark contrast to the present, with its wealth pants did not feel their training had prepared build on the success of that inaugural meet- of data and the commensurate need for new them adequately for the peer-review process. ing with another YSM. The 2nd YSM took approaches to interpreting it. He emphasized During breakout sessions, participants place from the 11-12 February 2013 at the the need for more interaction among paleo- divided into groups and deliberated on four International Centre Goa in India. It brought scientists and the increased need for more challenges facing young paleoscientists. together graduate students, post-doctoral fel- quantitative climate data, which can be better More detailed summaries of the breakout lows and early career scientists from around utilized by the modeling community. and “The Art of” sessions are reported else- the globe to share their research, network, The three “The Art of” sessions were a where in this issue of PAGES news. A key present and attend workshops and panel newly framed item in the YSM program and theme emerged across all groups: Many of discussions designed to address the specific aimed to provide young scientists with practi- the big important issues and problems fac- challenges and opportunities facing early ca- cal information about data sharing, reviewing ing early-career paleoscientists are similar the reer paleoscientists. A total of 79 participants and communicating science (see the follow- world over and may be dealt with through in- from over 27 countries attended the meeting. ing articles). ternational efforts. However, just as many are Participants were welcomed by S. Rajan, In “The Art of Sharing Data”, David specifically local, and therefore will require lo- Director of the National Center for Antarctic Anderson from the Institute of Arctic and cal solutions. and Ocean Research, the Goan host insti- Alpine Research, and National Climatic Data There was, of course, plenty of opportu- tution. Thorsten Kiefer, PAGES Executive Center, highlighted the importance of sharing nity for social interaction with one another, Director, then outlined the rationale behind data, and in particular, making data publicly as well as with the organizers and guests. the meeting and expressed the hope that the available through archiving. He discussed the Communal meals, the icebreaker, and a din- YSM would foster multi-disciplinary, interna- data-rich world we live in where the sharing ner on one of the famous Goan casino boats tional interaction and collaboration amongst and archiving of data can increase the visibil- featuring a Bollywood show, gave partici- the next generation of paleoscientists. ity of an individual’s research tremendously, pants an opportunity to bond with each oth- The meeting was structured around sev- and how easy accessibility to datasets will en- er while enjoying Indian culture and food. en themes: Climate Forcings; Regional Climate courage the community to develop new and To conclude, participants thanked PAGES Dynamics; Global Earth-System Dynamics; novel quantitative approaches to interpreting for taking the initiative to hold the YSM, and Human-Climate-Ecosystem Interactions; them. requested such meetings be convened more Chronology; Proxy Development, Calibration In “The Art of Communicating Science” often. We would also like to gratefully thank and Validation; and Modeling. Gavin Schmidt from the NASA Goddard the generous sponsors, listed below, whose Twenty participants gave oral presen- Institute for Space Studies suggested ways contributions directly assisted many young tations and many others presented post- to convey science to different audiences and scientists travel to and attend the meeting. ers around each of these themes. A written how to tackle controversies and criticism. He peer-feedback activity provided presenters recommended the use of simple language Sponsors included: The Ministry of Earth Sciences, with valuable feedback on their presentation with common examples and as many pic- Government of India; National Centre for Antarctic and Ocean Research, India; US National Science and ways to improve. The best presentations tures and graphs as possible, instead of tables Foundation; and the Swiss National Science received an award, including one year of free and technical jargon. Foundation; Asia-Pacific Network for Global Change online access to the Nature Geoscience jour- “The Art of Reviewing” panel included Research; System for Analysis, Research and Training; nal: Ilham Bouimetarhan (Bremen, Germany) Alicia Newton, Editor of Nature Geoscience; IGBP, Brazil Regional Office; National Oceanic and and Vladimir Matskovsky (Moscow, Russia) Denis-Didier Rousseau, Co-Editor-in-Chief of Atmosphere Administration, USA; National Institute received prizes for the best oral presentations, Climate of the Past; Chris Turney, Asian and of Ocean Technology, India; Indian National Centre for Ocean Information Services, India; Indian and Jesper Björklund (Göteberg, Sweden), Australasian Regional Editor for the Journal Institute of Tropical Meteorology, India; Oeschger Gayatri Kathayat (Xi’an, China), and Timothée of Quaternary Science; and moderator Alberto Centre for Climate Change Research, University of Ourbak (Niamey, Niger), for the best poster Reyes, of Queen’s University, Ireland. They Bern, Switzerland; and the International Association presentations. fielded many questions from the audience, of Sedimentologists. 89

PAGES news • Vol 21 • No 2 • August 2013 The Art of Communicating Science: traps, tips and tasks for the modern-day scientist

Heidi Roop1, G. Martínez-Méndez2 and K. Mills3 1Antarctic Research Centre, Victoria University of Wellington, New Zealand; [email protected] 2MARUM Center for Marine Environmental Sciences, University of Bremen, Germany; 3Department of Geography, Loughborough University, UK

n a true test of modern-day communi- public is not insurmountable but requires Ication, the participants at the 2nd PAGES an understanding of what works and what Young Scientists Meeting travelled virtually does not work. Falling into typical science from the 26°C heat of a Goan afternoon to communication traps can quickly turn an a brisk -2°C morning in New York City to join interview, article or outreach event into a Gavin Schmidt (NASA, USA) for a lesson in counterproductive debate or an unintend- Young Scientists Meeting 2013 Young the art of science communication. During ed source of misleading information. Here this session, Gavin then delved into the nuts are some common traps and points on what and bolts of why scientists are ethically obli- does not work: gated to publicly communicate their science • Avoid talking too much about technical de- and how communicating it well is an increas- tails and avoid technical debates ingly challenging but important aspect of • Avoid using jargon that you don’t take time our profession. This article highlights Gavin’s to explain tips for effective public communication, • Avoid scientific stereotypes, e.g. arrogance some common traps scientists fall into, and or elitism tasks or next steps our community needs to • Avoid triggering issues of free speech, data take to improve the public’s access to accu- access, and secrecy rate, high-quality scientific information. • Do not respond poorly to criticism by get- Despite the general public's interest in ting angry or taking it personally science, it is often hard to know where to go • Always distinguish between personal opin- for accurate (and understandable) scientific ion and scientific consensus information. In a world of rapid and wide • Try to understand the context in which dissemination of knowledge and opinions, your statements will be heard or read it is increasingly important to communicate • Try to defuse pseudo-debates but do not outside the scientific community. Not only ignore them do we have an obligation to communicate • Avoid sensationalism and over-extrapolat- broadly, due to the typically high proportion ed conclusions of science funding coming from the tax- payer, but broad communication is essential In order to get your audience to engage with to avoid misuse or misinterpretations of our your science, you have to engage with your Figure 1: The use of imagery is an effective way to work and to slow the propagation of scien- audience. Several easy tips that can improve convey messages to the general public. Which illus- tific misconceptions. the strength and resonance of your message tration would you choose for a public lecture? Image sources: US National Snow and Ice Data Center. Crucially, many of the important scien- include: tific concepts that need to be conveyed are • Listen to what your audience is interested Our collective task is to ensure access to simply not “news”. For example, the physics in or concerned about appropriate and understandable scientific of greenhouses gases will undoubtedly nev- • Use imagery and animations. These can of- information. The key to success relies on a er make the headlines yet it is a fundamental ten create a deeper connection for the audi- collaborative approach in which we all rally building block to being literate in the issue ence (e.g. see Fig. 1) together and begin to communicate the of climate change. Communicating these • Make it personal: use personal, relatable importance of science and the scientific pro- types of facts requires scientists to step be- stories that remind people that we are “nor- cess. En masse we can begin to change the yond traditional avenues of communication. mal”. Personal anecdotes often generate ex- public perception of science, and can con- Gavin emphasizes that we, as a community, citement and engagement tribute to developing a more scientifically need to engage with social media and web- • Always remember the big picture and the literate society. Making use of the above tips, based communications, in addition to tradi- reasons why you are a scientist learned from the frontlines of public science tional means of communication (e.g. press • Be a credible and trustworthy guide and communication, can help to initiate this pro- releases, interviews and essays). People in- take advantage of the generally held feeling cess and move our community in the right creasingly rely on the internet as a primary of public admiration towards scientists direction. Now it is time to get blogging, source of information, which means there is • Promote the investigative nature of science writing, and tweeting! a need to provide more accurate and appro- • Provide accessible context outside of the priate information online through scientists’ technical literature For further reading, see Gavin’s recommen- blogs, videos, and social media platforms. • Always underscore what can and cannot dation: www.skepticalscience.com/docs/ We need to use this diverse set of tools to be concluded from your work Debunking_Handbook.pdf not only convey our expertise but impor- tantly, to engage with different audiences. As mentioned above, we live in an increas- The challenge of clearly communicat- ingly connected world with growing ac- ing the intended scientific message to the cess to information (and misinformation). 90

PAGES news • Vol 21 • No 2 • August 2013 The Art of Reviewing: Holding up quality in the scientific quality control system

Rajani Panchang1, A. Govin2 and C. Omuombo3 1Geology & Palaeontology Group, Agharkar Research Institute, Pune, India; [email protected] 2MARUM Center for Marine Environmental Sciences, University of Bremen, Germany; 3Department of Geology, University of Nairobi, Kenya

ver since the publication of the EPhilosophical Transactions of the Royal Society by Henry Oldenburg (1665, Fig. 1), scientists have acknowledged the importance of relaying research findings to a wider scientific community. Currently, publishing scientific findings in peer- Scientists Meeting 2013 Young reviewed journals, brands the research work as “credible”. These peer-reviewed scholarly articles improve the quality of science and are used as a metric for scientific performance, which is essential for career advancement. The Program Committee of the 2nd PAGES YSM recognized the need to contribute to building capacity in the art of reviewing among young paleo-scientists. To this end, editors from prominent paleoscience journals, namely Nature Geoscience (Alicia Newton), Journal of Quaternary Science (Chris Turney) and Climate of the Past (Denis-Didier Rousseau) were invited to be part of a panel discussion highlighting the aims and process of peer-reviewing. The discussion commenced with the importance of peer reviewing in science and the responsibility journal editors have to maintain the integrity and quality of science. Accordingly, the nominated reviewers bear the responsibility of scrutinizing the quality and clarity of the scientific content in the manuscript and providing constructive criticism to help authors improve it. From the editor’s perspective, feedback on a manuscript should indicate if the Figure 1: Introduction by Henry Oldenburg to the first issue of the Philosophical Transactions of the Royal Society (Oldenburg 1665). conclusions are new, if the study builds upon the existing literature, and above all A major issue for editors is finding suitable sink in for a few days, before writing the assess if the evidence presented supports reviewers, as often the best-known ex- review. This process helps sharpen one’s the conclusions. perts in the field lack time. Nevertheless, ideas and thinking on the issues covered On the question of “How to differ- it is fine ot politely turn down the oppor- in the manuscript. entiate a poor review from a good one?”, tunity of reviewing a paper if you lack the While it remains important that the the panelists’ collective reply was: A good time or the expertise the paper demands, authors cite the most recent papers rele- review demands useful and constructive or in the event of conflicting research in- vant to the study, it is equally important to criticism that identifies the strengths and terests. On the other hand, if you agree to check if the authors cite the original pio- weaknesses of a manuscript and gives rec- do a review, you should keep your word neer works. In case you do not have access ommendations with supporting justifica- and not decline the responsibility after to the references the authors cite, you can tions. As a reviewer, never go by dogmas and several months of doing nothing with the ask for the papers from the editors rather don’t reject new ideas, if they are supported manuscript. than provide a poorly informed review. with data and systematic methodology. If The experienced referees on the panel Therefore, working on the review of a the work is promising, but has not attained reminded young scientists to be aware of manuscript ahead of the deadline allows its best form, insist that authors take on the the time pressures involved in reviewing. time to build initial impressions, verify cit- burden of more work to justify their novel A thorough review of a paper takes a mini- ed references and reserve sufficient time ideas and research. Always be polite, objec- mum of two to three days depending on for constructive feedback, steps that en- tive and respectful to the author(s), regard- one’s efficiency and ability. Anticipating sure a thorough review. Finally, submitting less of whether you recommend the editor this pressure allows one to set aside ample the report on time also ensures a smooth accepts or rejects the manuscript. time to read the paper and let the ideas and efficient evaluation, and makes the 91

PAGES news • Vol 21 • No 2 • August 2013 new results swiftly available, to the benefit if possible. However, the main task of a re- To conclude, the guiding line for a scien- of science overall. viewer is to evaluate the science of a study tist should be “publish or perish”! But at the Ethics are a critical aspect in the art and not necessarily correct the language end of this session, we found a new one: of reviewing, and an area in which young of the manuscript. Instead of spending “Peer review: love it or hate it, it’s an integral reviewers may need to develop. As a re- time correcting spelling mistakes at the part of every scientist’s life.” (Welsh 2010). viewer, one has the moral responsibility to expense of evaluating the scientific con- So do not panic if an editor picks you to be put aside one’s own research and publica- tent, the reviewer can mention the need the chosen one! tion interests, be honest and fair with the for copy-editing to the editor. authors and consider the interests of the Although demanding and time-con- Additional information on the art of reviewing is available in published articles, e.g. Smith respective journal. The same is true for an suming, reviewing manuscripts provides a 1990; Provenzale and Stanley 2006; Rosenfeld editor or reviewer while dealing with con- unique opportunity to improve one’s criti- 2010, and on these dedicated websites: users. flicting reviews or accepting risky ideas. cal thinking and writing skills, stay updat- ecs.soton.ac.uk/hcd/reviewing.html; A test of one’s integrity as a reviewer is ed on cutting-edge research techniques bcl.hamilton.ie/~barak/how-to-review.html; whether or not you are able to put your and ensure the quality and integrity of elsevier.com/reviewers/home; Young Scientists Meeting 2013 Young name to the review, i.e. disclose your iden- published science. This interactive session councilscienceeditors.org/i4a/pages/index. cfm?pageid=3331 tity. on “The Art of Reviewing” brought to light To ensure the editor can build an that about half of the ~80 early-career References adequate assessment of the reviews, it participants had reviewed papers either Oldenburg H (1665) Philosophical Transactions 1: 1-22 is crucial that the reviewer clearly states on behalf of their supervisors or directly Provenzale JM, Stanley RJ (2006) Journal of Nuclear Medicine Technology 34: 92-99 which topics are outside his or her area of for journals; however, most of them had Rosenfeld RM (2010) Otolaryngology - Head and Neck Surgery 142: 472- expertise. This allows the editor to identify never received formal training in review- 486 additional experts, if needed. One should ing. Consequently, the young scientists Smith AJ (1990) Computer 23: 65-71 not shy away from providing detailed re- unanimously expressed the wish for for- Welsh J (2013) Discoblog: Year's Best Peer Review Comments: Papers That "Suck the Will to Live", blogs.discovermagazine.com/dis- views, so that a paper can be improved to mal training in reviewing as part of their coblog/2010/12/15/years-best-peer-review-comments-papers- near perfection. This can include provid- doctoral education. that-suck-the-will-to-live/ ing grammar and language amendments

The Art of Data Sharing: key in future climate science

Aurora Elmore1, F. Lehner2 and J. Franke2 1Department of Geography, Durham University, UK; [email protected] 2Oeschger Centre for Climate Change Research, University of Bern, Switzerland

t the PAGES Young Scientists AMeeting, 11-12 February 2013, in Goa, India, 79 young researchers Box 1: Examples of databases, software, and sample repositories. from around the world gathered to The number of databases, open-source software and repositories is growing, providing extensive resources for scientists to engage in data-intensive research. discuss research, to network, and to exchange ideas for the future of cli- Databases mate research. Initiated by a talk on Pangaea, Data publisher for Earth & Environmental sciences, www.pangaea.de “The Art of Data Sharing” given by World Data Center for Paleoclimatology, www.ncdc.noaa.gov/paleo David Anderson, head of the World Neotoma, A paleoecology database and community, www.neotomadb.org Data Center for Paleoclimatology at JANUS, Data from the Integrated Ocean Drilling Program, www-odp.tamu.edu/database the National Oceanic and Atmospheric Core Curator’s Database, the Index to Marine and Lacustrine Samples, www.ngdc.noaa. Administration (NOAA), a lively discus- gov/mgg/curator sion arose on the benefits and potential PAGES list of databases, www.pages-igbp.org/my-pages/data of data sharing for future research. Fortunately, many researchers al- Software Calib, the radiocarbon calibration program, http://calib.qub.ac.uk/calib ready upload their data and computer Analogue, Analogue and weighted-averaging methods for paleoecology, code to an Internet database to be http://analogue.r-forge.r-project.org available for future projects. Therefore, Singular Spectrum Analysis, A toolkit for spectral analysis, www.atmos.ucla.edu/tcd/ssa a wealth of databases and software Ocean Data View, a software package for the exploration and analysis of oceanographic exist that are open and easily acces- and other data, http://odv.awi.de sible (see Box 1). These include data KNMI Climate Explorer, an online tool to visualize and analyze climate data with a large from classical proxy archives such as ready-to-use database, climexp.knmi.nl tree rings, ice cores, lake and marine sediments, as well as model output, reanalysis, observations and a multitude

PAGES news • Vol 21 • No 2 • August 2013 Young Scientists Meeting 2013 Young

Figure 1: Sharing and combining data and model simulations allows for a better understanding of past climate variability. Temperature anomalies relative to 1961-1990 in a reconstruction (Mann et al. 2009) and a Last Millennium simulation with a comprehensive coupled model (Community Earth System Model). White areas indicate no reconstruction data; the same areas have been masked in the model output for comparability. of free algorithms, scripts and software researchers who are working towards in the form of a “data citation index”. packages. establishing their careers and thus can- Usually, data compilation studies do Not only can researchers use these not afford to not be credited for their not cite every individual data paper archives to compare with their own new work. But in reality, such cases occur that went into the compilation - mainly data, but also groundbreaking studies rarely and the vast majority of scientists to prevent the bibliography from ex- seeing the large-scale picture can result sharing their data experience only ben- ploding. A “data citation index”, follow- from compiling or reanalyzing existing efits from it, including more citations ing the example of the classical citation data sets (e.g. Lisiecki and Raymo 2005; and often even additional co-author- index for papers, could provide an ef- Mann et al. 2008; Andrews et al. 2012). ships. ficient way of crediting the papers un- These kinds of data compilation proj- Another barrier to uploading re- derlying data compilation studies with- ects are time-intensive. However, when search data seems to be the author's out generating lengthy bibliographies. fed back to the database, the resulting worry about data being misused or With limitless potential for compi- data can be highly beneficial for the misrepresented. Providing detailed me- lation studies to generate truly inno- paleoscience community as it avoids ta-information about the data and cor- vative science and the relative ease of duplication of effort. Data compilation responding error bars greatly reduces uploading data, we hope many readers efforts can also be funding-efficient, as the risk of inappropriate use of data. consider using these great resources some funding agencies have already However, the largest hindrance seems and, of course, helping them to grow. requested proposals specifically based to result from confusion about which on that approach. Some general ideas data repository to use and how to for- References for future compilation-style research mat the data. To this end, many data Andrews T et al. (2012) Geophysical Research Letters 39, doi: 10.1029/2012GL051607 include time-slice reconstructions and repositories have helpful “read-me” files Lisiecki LE, ME Raymo (2005) Paleoceanography 20: 1-17 comparison between transient model and staff support to help with the up- Mann ME et al. (2008) PNAS 205: 13252-13257 simulations and sensitivity experiments loading, so that the researcher hardly Mann ME et al. (2009) Science 326: 1256-1260 conducted by different institutes. has to spend much additional effort. Some journals and funding agen- So, why do not all researchers cies are now mandating that authors share their data? archive data that appear in publications The idea of being “scooped” seems to and discussants at the YSM were united be one of the most important fears in their hope that this trend towards preventing researchers from upload- open access continues. ing their published data; this seems One way to encourage and credit to be particularly important for young data sharing in the future could be 93

PAGES news • Vol 21 • No 2 • August 2013 Breakout Group A: What should the research questions and priorities in paleoscience be for the next 10 years?

Sylvia Dee1 and Francesco Muschitiello2 1Department of Geological Sciences, University of Southern California, Los Angeles, USA; [email protected] 2Department of Geological Sciences, Stockholm University, Sweden

ow can we improve model-based of high-resolution proxy reconstructions: used to establish regional calibrations and Hestimates and predictions? How can We need more high-quality data from transfer functions to allow proxy-based we improve the production of paleo data? under-represented regions. We also need reconstructions to capture not only high- How can we better constrain past rates of new proxies for several climate variables. frequency climate variability, but also a change in the Earth system? These ques- Also high on our wish list are solid con- quantifiable climatic parameter such as tions, among others, were identified as straints upon previously unresolved cli- temperature or precipitation. Young Scientists Meeting 2013 Young key priorities for future paleoscience dur- mate system components such as clouds Finally, we need to compile datasets ing our breakout sessions at the YSM. and aerosols. We require better solar and and make them available in a quality-con- We identified that model-based cli- volcanic forcing reconstructions, and we trolled, well-documented and easy-to-use mate sensitivity estimates and the abil- should strive to understand the underly- form. Strict formats for “big data” should ity to correctly capture climate feedbacks, ing causes of discrepancies between the be employed in a globally acknowledged abrupt transitions, and threshold behavior different forcing reconstructions available. framework. The field could vastly benefit in models are key to predicting climate To improve the quality of our proxy from larger collaboration with computer and associated changes. Integrated earth- networks we need to employ replication, software engineers and informatics sci- system modeling with improved feed- high-resolution dating, statistical analysis ence to improve efficiency and manage- back interactions will be required to study and multi-proxy approaches in our re- ability of earth science datasets. whole-earth system dynamics. search. Data uncertainty estimates should Furthermore, assessing climate mod- always be clearly stated. Process stud- el performance requires better datasets ies and controlled experiments must be

Breakout Group B: Advocating the relevance of paleo- research to a funding agency or policy maker

Ilham Bouimetarhan1 and Hans Christian Steen-Larsen2 1MARUM-Center for Marine Environmental Sciences, University of Bremen, Germany; [email protected] 2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, USA

ear policy makers and funders of sci- are likely to bring greater environmental future projections and predictions of po- Dence, risks as the environment is already subject tential impacts likely to affect people in We understand your need to base to substantial stress. Furthermore, due to the short-term and in coming decades. your decisions and investments on stron- the increased complexity of modern soci- While paleoscientific research is able ger arguments of the important role that eties extreme events are likely to become to highlight some of the environmen- paleo-research plays in international ef- more costly, as recently illustrated by tal risks threatening our planet, much forts to understand and emphasize the Hurricane Sandy’s effect on New York City. remains to be learned, and this kind of social, economic, and geopolitical implica- Paleoscientists are undertaking enor- research will still need more financial in- tions of Earth’s changing climate. We are mous efforts to assess the high complexity vestment in order to thoroughly examine also acutely aware of many unanswered of Earth’s climate system and gain a better other scientific questions. While it might questions and substantial uncertainties understanding of the general forces con- not provide direct applications, or solu- that currently exist, and always will exist, trolling global climate change. Integrating tions for engineering a better future, pa- in paleo-research, as in any other field of local and regional climate information leoscientific research makes a substantial science. However, it is now evident that from marine and terrestrial environ- contribution to constraining the possible better projections of future climate and ments all over the world has allowed, for scenarios of future environmental and cli- environmental change, which form the example, the identification of important matic changes. We encourage you there- basis of decisions on national and interna- feedbacks in the climate system; this is fore to let paleoscience evidence guide tional greenhouse gas emission policies, crucial if we are to avoid being surprised you towards wise decisions on policy and require consultation with information by abrupt climatic events. The results of science funding in the context of the high from Earth’s past. this research have helped us to better un- priority challenges facing humanity. Repeatedly during its history, Earth’s derstand the role human activities play climate has changed abruptly within just a in causing a large part of the changes in Yours sincerely, few decades. Climatic variability including the Earth’s climate system, namely the sig- Ilham Bouimetarhan and Hans Christian changes in the magnitude and frequency nificant increase in global temperatures. Steen-Larsen of extreme events such as droughts and Moreover, many paleoclimate results are On behalf of the PAGES Young Scientists floods has often had a devastating impact now being effectively assimilated with 2013 on local societies, and events in the future climate models in order to provide better 94

PAGES news • Vol 21 • No 2 • August 2013 Breakout Group C: Challenges and solutions for enhanced paleoscience communication

Heidi Roop1 and Elisabeth Dietze2 1Antarctic Research Centre, Victoria University of Wellington, New Zealand; [email protected] 2Climate Dynamics and Landscape Evolution, German Research Centre for Geosciences, Germany

t the 2nd YSM there was consensus among internet platforms, classrooms, media outlets a major obstacle preventing the effective com- Athe young international paleoscientists and other informal science education venues munication of our research. Coursework and that there is a great need to better develop can be highly productive and rewarding, but other training opportunities, beyond short skills for communicating with different types also difficult and time consuming to develop. workshops, are needed to instruct researchers of non-academic audiences. Clear and effec- To address this problem and to facilitate pa- how to effectively and concisely communicate tive communication to the public is becoming leoscience communication, we propose to link the significance of their research to any audi- increasingly important as current and future with the PAGES scientist database and outline ence. In a highly inter-connected world, it is Scientists Meeting 2013 Young climatic and environmental changes are fre- researchers availability for specific outreach critical that scientists develop an appropriate quently a major focus in the media and poli- activities (e.g. classroom visits, blog articles, level of fluency and understanding of how to tics. However, for the paleoscience community Skype calls, laboratory tours, radio interviews). use communication tools ranging from social there remains the challenge of properly con- This type of additional database should be media to informal writing. veying the concept of past change on longer communicated through educational networks Ultimately, communicating our scientific timescales. Facilitating better public under- such as Polar Education International (PEI). The results should become a regular and profes- standing of the scientific process is required ultimate hope is that this freely accessible da- sionally recognized part of the scientific pro- to break down barriers and have objective tabase can begin building lasting relationships cess. Developing the skills to effectively share discussions, especially regarding the issue of between the public and local researchers by our science will undoubtedly increase our future climate change. making it easy for the public to find local sci- broader impacts, and PAGES is in a unique A productive discussion at the YSM about entists. An encouraging example is the Social position to facilitate this development in the how to address the challenges we face in com- Media Knowledge Exchange (www.smke.org), paleoscience community. Already the YSM has municating paleoscience resulted in two po- which provides a platform for early career sci- stimulated discussion, and we hope that this tential solutions: entists in history and archeology to share their dialogue can continue in the broader PAGES First, as scientists, we need to be proac- research with non-academic audiences. network to strengthen and broaden our sci- tive in making our research available in our Second, the current lack of formal train- ence communication skills into the future. local communities. Creating connections with ing opportunities in science communication is

Breakout Group D: Key educational ingredients to ensure the success of future paleoscientists

Rajani Panchang1 and Julie Richey2 1Agharkar Research Institute, Pune, India; [email protected] 2U.S. Geological Survey, St. Petersburg, USA

he breakout sessions at the 2nd YSM proved understand the value and limitations of proxy language borders, and thus its knowledge Tto be an extremely useful exercise that re- records. Conversely, those generating proxy facilitates the effective communication of sci- sulted in concrete suggestions for future direc- records need to be capable of understanding ence. Accordingly, some participants from tions for PAGES and the broader scientific com- and using model results to make proxy-model countries in which English is not the first lan- munity. The topic of our group was discussed comparisons. guage did express the need for formal train- in two subgroups by a total of 21 participants Students should be encouraged to coming in reading and writing English. They also from 12 countries. plete a small research project before opting wished that some of their science education One of the key recommendations was for a doctoral program so that they can as- had been in English. that future paleoscience students need bet- sess their interest as well as aptitude for re- Earth science is currently not part of the ter computational skills. In the early days of search. This could be offered as a Bachelor’s required curriculum in many countries, and paleoclimate research, students could turn 50 or Master’s dissertation, as is already common the need and importance for elevating earth analyses into a dissertation, but with modern practice in some countries, e.g. the USA. This science education at the primary and second- methodological advances, students can now also led to the idea of offering supervisors ary school level was expressed. Regarding the produce hundreds or thousands of geochemi- more incentives (e.g. research assistance or much more advanced career stage paleocli- cal measurements. In addition to expertise teaching time exemption) for investing time matologists, participants expressed the con- in micropaleontology, palynology, organic and energy in short-term (i.e. masters-level) re- cern that “paleoclimate” is not as lucrative as geochemistry, etc., students need to have the search students. Inspired by the panel discus- mining and petroleum! Although not related quantitative skills to statistically analyze that sion on peer reviewing, it was also suggested to education, the breakout group argued that data, and effectively put it in the context of a that reviewing should be made a formal part better incentives and job opportunities will wealth of other paleoclimate archives. of graduate education. be key conditions to ensure the success of the Paleoclimate modelers should have more Over time English has become the sin- next generation of paleoscientists. training in geosciences so that they can better gle global language bridging international 95

PAGES news • Vol 21 • No 2 • August 2013 Announcements Impressum

- Inside PAGES 46 - 20 years of PAGES news 47 PAGES International Project Office - PAGES calendar 47 Zähringerstrasse 25 Contents 3012 Bern - Switzerland Special Section: El Niño-Southern Oscillation Tel.: +41 31 631 56 11 Fax: +41 31 631 56 06 Editorial: [email protected] - El Niño-Southern Oscillation - observation and modeling 48 www.pages-igbp.org Science Highlights: - Myanmar monsoon drought variability over the past 300 years: linkages to ENSO 50 R. D’Arrigo, J. Palmer, C. Ummenhofer, N.N. Kyaw and P. Krusic Editors: - Coral microatoll reconstructions of El Niño-Southern Oscillation 52 Series Editors: H.V. McGregor, C.D. Woodroffe, M. Fischer, M.K. Gagan and D. Fink Lucien von Gunten and Thorsten Kiefer - Giant clam recorders of ENSO variability 54 M. Elliot, K. Welsh and R. Driscoll Guest Editors: - Reconstructing ENSO in the Eastern Tropical Pacific from short-lived marine mollusks 56 Pascale Braconnot, Chris Brierley, Sandy M. Carré, S. Purca and J.P. Sachs P. Harrison - Challenges in understanding and modeling ENSO 58 A. Capotondi, E. Guilyardi and B. Kirtman Text Editing: Leonie Goodwin - Coral-model comparison highlighting the role of salinity in long-term trends 60 Layout: Lucien von Gunten D.M. Thompson, T.R. Ault, M.N. Evans, J.E. Cole, J. Emile-Geay, A.N. LeGrande - The response of pseudo-corals to ENSO in an isotope enabled climate model 62 Cover image: T. Russon, A.W. Tudhope, G.C. Hegerl, M. Collins and J. Tindall Photo of a Tridacna spp. giant bivalve - ENSO and changes in the mean state in Holocene simulations 64 by Kevin Welsh. P. Braconnot and Y. Luan - A controversial insight into Southwest Pacific mid-Holocene seasonality 66 C.E. Lazareth, M.G. Bustamante Rosell, N. Duprey, N. Pujol, G. Cabioch, et al. Hardcopy circulation: 2550 - Interannual variability in the Tropical Pacific during the last glacial period 68 U. Merkel, M. Prange and M. Schulz - ENSO behavior before the Pleistocene 70 ISSN 1811-1602 C. Brierley Printed on recycled paper by Mini Section: Data assimilation methods Läderach AG - Bern, Switzerland - Overview of data assimilation methods 72 G.J. Hakim, J. Annan, S. Brönnimann, M. Crucifix, T. Edwards, H. Goosse, et al. - Transient state estimation in paleoclimatology using data assimilation 74 S. Brönnimann, J. Franke, P. Breitenmoser, G. Hakim, H. Goosse, et al. - Best-of-both-worlds estimates for timeslices in the past 76 T.L. Edwards, J. Annan, M. Crucifix, G. Gebbie and A. Paul - Parameter estimation using paleo-data assimilation 78 J.D. Annan, M. Crucifix, T.L. Edwards and A. Paul

Workshop Reports: - Impact of climate and sea level change on coastal evolution 80 - Holocene land-cover change in Eastern Asia for climate modeling 81 - Palaeo50: The priority research questions in paleoecology 82 - The Agulhas System: its role in ocean circulation, climate, and marine ecosystems 83 - IPICS First Open Science conference 84 - Analyzing paleolimnological data with R 85 - The Sun and its role in climate change 86

Program News: - The backbone of PAGES 2k: data management and archiving 87 - Updated Latin American Pollen Database 88

Young Scientists Meeting 2013 - A brief report on the 2nd PAGES Young Scientists Meeting 89 R. Saraswat and B. Jensen - The Art of Communicating Science 90 H. Roop, G. Martínez-Méndez and K. Mills - The Art of Reviewing 91 The PAGES International Project Office R. Panchang, A. Govin and C. Omuombo and its publications are supported - The Art of Data Sharing 92 by the Swiss and US National Science Aurora Elmore, F. Lehner and J. Franke Foundations and NOAA. - Reports from the YSM breakout groups 94 S. Dee, F. Muschitiello | I. Bouimetarhan, H-C. Steen-Larsen | H.Roop, E. Dietze | © 2013 96 R. Panchang, J. Richey

PAGES news • Vol 21 • No 2 • August 2013