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The Medieval Climate Anomaly in Antarctica Palaeogeography, Palaeoclimatology, Palaeoecology 532 (2019) 109251 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo Review article The Medieval Climate Anomaly in Antarctica T ⁎ Sebastian Lüninga, , Mariusz Gałkab, Fritz Vahrenholtc a Institute for Hydrography, Geoecology and Climate Sciences, Hauptstraße 47, 6315 Ägeri, Switzerland b Department of Geobotany and Plant Ecology, Faculty of Biology and Environmental Protection, University of Lodz, 12/16 Banacha Str., Lodz, Poland c Department of Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany ABSTRACT The Medieval Climate Anomaly (MCA) is a well-recognized climate perturbation in many parts of the world, with a core period of 1000–1200 CE. Here we are mapping the MCA across the Antarctic region based on the analysis of published palaeotemperature proxy data from 60 sites. In addition to the conventionally used ice core data, we are integrating temperature proxy records from marine and terrestrial sediment cores as well as radiocarbon ages of glacier moraines and elephant seal colonies. A generally warm MCA compared to the subsequent Little Ice Age (LIA) was found for the Subantarctic Islands south of the Antarctic Convergence, the Antarctic Peninsula, Victoria Land and central West Antarctica. A somewhat less clear MCA warm signal was detected for the majority of East Antarctica. MCA cooling occurred in the Ross Ice Shelf region, and probably in the Weddell Sea and on Filchner-Ronne Ice Shelf. Spatial distribution of MCA cooling and warming follows modern dipole patterns, as reflected by areas of opposing temperature trends. Main drivers of the multi-centennial scale climate variability appear to be the Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO) which are linked to solar activity changes by nonlinear dynamics. 1. Introduction 2014; O'Donnell et al., 2011; Ramesh and Soni, 2018). Cooling and an increase in snowfall in East Antarctica seems to have led to a gain in ice Until recently, the Antarctic Peninsula and West Antarctica were sheet mass and thickening of ice rises over the past 15 years (Goel et al., among the most rapidly warming regions on Earth. Between the 1950s 2017; Martin-Español et al., 2017; Philippe et al., 2016; Zwally et al., and 1990s temperatures on the Antarctic Peninsula increased by more 2015). East Antarctic marine-terminating glaciers show no systematic than 0.3 °C/decade (Stenni et al., 2017; Turner et al., 2016; Vaughan change over the past 50 years (Lovell et al., 2017). Lastly, also the et al., 2003), with even higher warming rates reported for Byrd Station surface layers of the Southern Ocean south of 45°S has predominantly in West Antarctica (Bromwich et al., 2013; Bunde et al., 2014; Nicolas cooled over that past three decades (Armour et al., 2016; Fan et al., and Bromwich, 2014). Since the late 1990s, however, this warming has 2014; Kusahara et al., 2017; Latif et al., 2017), whilst the subpolar essentially stalled. Rapid cooling of nearly 0.5 °C per decade occurred abyssal waters are warming (Sallée, 2018). on the Antarctic Peninsula (Favier et al., 2017; Fernandoy et al., 2018; On a century scale, no significant statistical warming trend can be Turner et al., 2016). This already impacted the cryosphere in parts of found for most Antarctic stations (Ludescher et al., 2016). Antarctic the Antarctic Peninsula, including slow-down of glacier recession, temperatures appear to be still well within the range of natural varia- surface mass gains of the peripheral glaciers and a thinning of the active bility. Natural climate factors such as multidecadal ocean cycles still layer of permafrost in the northern Antarctic Peninsula islands (Engel dominate over anthropogenic climate drivers, such as CO2 (Chylek et al., 2018; Oliva et al., 2017; Seehaus et al., 2018). At the same time, et al., 2010; Favier et al., 2017; Jones et al., 2016; Ludescher et al., temperatures in West Antarctica over the past two decades appear to 2016; Smith and Polvani, 2017; Steig et al., 2013; Turner et al., 2016). have plateaued or slightly cooled (Bromwich et al., 2013; Jones et al., On interannual to decadal scale, a general anti-phase has been ob- 2016; Steig et al., 2009). However, temperature records in West Ant- served between the temperatures of East Antarctica and Antarctic arctica are few, often discontinuous and show opposing trends from Peninsula/West Antarctica (Schneider et al., 2006). The Transantarctic location to location (Shuman and Stearns, 2001) which complicates Mountains act as a dividing line for the temperature trends of the two modern trend analysis in this part of Antarctica. In contrast, East Ant- regions, reflecting the topographic constraint on warm air advection arctica has not experienced any significant temperature change since from the Amundsen Sea basin (Nicolas and Bromwich, 2014). Un- the 1950s (e.g. Yang et al., 2018) and some areas appear to have even fortunately, climate models still fail to reproduce the regional Antarctic cooled during the most recent decades (Clem et al., 2018; Favier et al., temperature and snowfall development and generally overestimate the 2017; Jones et al., 2016; Marshall et al., 2014; Nicolas and Bromwich, magnitude of the forced response (Favier et al., 2017; Jones et al., 2016; ⁎ Corresponding author. E-mail addresses: [email protected] (S. Lüning), [email protected] (M. Gałka), [email protected] (F. Vahrenholt). https://doi.org/10.1016/j.palaeo.2019.109251 Received 2 April 2019; Received in revised form 24 June 2019; Accepted 25 June 2019 Available online 29 June 2019 0031-0182/ © 2019 Elsevier B.V. All rights reserved. S. Lüning, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 532 (2019) 109251 Tang et al., 2018). A better understanding of natural variability on (IOD) and the Atlantic Multidecadal Oscillation (AMO) (e.g. Li et al., multi-decadal, centennial and millennial-scales will help to further re- 2014; Zhang et al., 2015). The various ocean cycles are partly inter- fine these models and calibrate them with the pre-industrial climate linked (Wyatt and Curry, 2014). Other factors that may have affected development by way of hindcasts (Fogt et al., 2017; Goosse, 2017; pre-industrial climate change are solar activity changes (e.g. Barbara Mayewski et al., 2017). et al., 2016; Bentley et al., 2009; Christ et al., 2015; Costa et al., 2007) This paper focuses on the Medieval Climate Anomaly (MCA), a and volcanic eruptions (e.g. Yang and Xiao, 2018). A detailed overview distinctive rapid climate fluctuation that has been documented from of important potential drivers of natural climate variability in Antarc- many parts of the world. The best-studied region is the mid and high tica can be found in Supplement Texts 1a–h. latitude North Atlantic realm where numerous studies documented a pronounced warm phase during the MCA. This historically led to the 4. Material and methods introduction of the term ‘Early Medieval Warm Epoch’ (Lamb, 1965), which subsequently changed in the literature to ‘Medieval Warm 4.1. Literature review Period’ (MWP), and finally to ‘Medieval Climate Anomaly’ (MCA) (e.g. Grove and Switsur, 1994). It is generally agreed today that the core The mapping project is based on a comprehensive literature period of the MCA comprises ca. 1000–1200 CE. Nevertheless, different screening process during which all available published Antarctic pa- time schemes and durations have historically been used in the litera- laeotemperature case studies were evaluated towards their temporal ture, with the widest scheme comprising 800–1300 CE (e.g. Crowley coverage, types of climate information and data resolution. Suitable and Lowery, 2000; Esper and Frank, 2009; Mann et al., 2009). papers including the MCA core period 1000–1200 CE were earmarked Here we concentrate on the MCA core period 1000–1200 CE and for a thorough analysis. Generally, studies should contain at least one attempt to map temperature patterns across the Antarctic region based palaeotemperature data point within the MCA period, either quantita- on proxy data from 60 published sites (Fig. 1). We investigate which tive or just qualitative. A total of 60 Antarctic localities with one or parts of Antarctica experienced warming during the MCA and which more MCA palaeotemperature proxy curves were identified (Figs. 1–3; areas cooled. Likely drivers of the observed pre-industrial south polar Tables 1 and S1). This Antarctic review forms part of an attempt to climate change of the past 1500 years are discussed. A recent Antarctic palaeoclimatically map the MCA on a global scale (Lüning et al., 2019a; temperature reconstruction by Stenni et al. (2017) based solely on ice Lüning et al., 2018; Lüning et al., 2019b; Lüning et al., 2017). cores suggests a warm MCA that is followed by significant cooling of the Little Ice Age (LIA) after 1250 CE that lasts until 1950 CE. Overall, the 4.2. Palaeoclimate archives and data types authors note a long-term cooling trend for the last 2000 years. We are complementing the ice core data with other palaeotemperature proxies MCA climate reconstructions of the publications high-graded by the from marine and terrestrial sediment cores as well as radiocarbon ages screening process comprised of several natural archives, namely (1) of glacier moraines, elephant seal colonies and penguin rookeries. sediment cores from marine, lakes, peatlands, (2) ice cores from the Whilst this approach adds more data points, it also diversifies the Antarctic Ice Sheet and smaller peripheral ice caps, (3) dating of glacier source of palaeoclimatic information. A better understanding of the pre- moraines and elephant seal colonies. Data types include (a) pa- industrial Antarctic climate history, and in particular of natural warm laeontology (diatoms, palynology), (b) inorganic geochemistry (δ18O, phases, provides crucial input for climate model calibration and re- δ2H, deuterium excess in ice cores; δ18O in foraminifera and lake car- finement.
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