FluxLetter

The Newsletter of FLUXNET Vol. 2 No. 2, June, 2009

Highlighting Sites in Northern Alaska & North East Highlight FLUXNET sites Russia The Arctic Observatory Network by Eugénie S. Euskirchen and M. Syndonia Bret-Harte

Flux stations were recently Arctic Observatory Network models. In This Issue: established in two locations in (AON) program. The other flux In northern Alaska during the the Arctic during the Interna- stations that participate in this summer of 2007, we established tional Polar Year (2007 -2009). network are located near two flux stations on either side These flux stations are located in Abisko, Sweden and Zackenberg, of a flux station that had been FLUXNET site: Greenland, as well as a series of previously established in 2005. northern Alaska, near the Toolik “The Arctic Observatory Field Station, which is owned sites across Arctic Canada. The This forms a transect of three Network” and operated by the Institute of goal of making flux measure- stations in three representative Eugénie S. Euskirchen and M. Syndo- ments made at these sites is to: undisturbed types of Arctic , University of nia Bret-Harte …….. .….Pages 1-3 Alaska, Fairbanks, and which is 1) quantify and understand the the arctic foothills of the Brooks the site of the Arctic Long-Term controls of carbon, water, and Range: heath tundra, tussock Editorial: Ecological Research (LTER) pro- energy exchange at each site, 2) tundra, and wet sedge tundra Conservation of Surface Fluxes in a gram, and at the North East permit cross-site synthesis of the (fen). Furthermore, the largest- Numerical Model Science Station near Cherskii, carbon, water, and energy fluxes ever tundra fire in northern Jinkyu Hong……….…...... Pages 4-5 Russia. These two observatories across the representative terres- Alaska occurred ~39 km north- help to establish a network of trial in the Arctic, west of our sites in the summer observatories across the Arctic, and 3) parameterize and validate of 2007, burning ~90,000 ha. which is funded through the NSF ecosystem and land-surface This provided the opportunity to FLUXNET graduate student : establish three more flux sta- Donatella Zona ...... Pages 6-7 tions during the summer of 2008

in tussock tundra ecosystems of varying burn severity: severely FLUXNET young scientist: burned, moderately burned, and Adrian V. Rocha……...... Page 8 an unburned control site. The objective of establishing sites in these disturbed ecosystems is to Research: obtain information about the Measuring air-ice CO2 fluxes in integrated impacts of tundra fires the Arctic on terrestrial ecosystems in the Heinesch B, Yernaux M, Aubinet M, tundra foothills, and to begin Geilfus N-X, Papakyriakou T, Carnat documenting the recovery proc- G, Eicken H, Tison J-L, B.Delille ...... Pages 9-10 ess. In addition to measuring the carbon, water, and energy fluxes at these sites, a full suite of me- Presence and absence of permafrost teorological data is also col- Torben R. Christensen, Mikhail lected. We also use chambers Mastepanov and Margareta Johans- to measure NEE during summer son…………………….Pages 11-13 field campaigns.

Figure 1: Map of sites in the Arctic Observatory Network FLUXNET SITE cont. on page 2 Page 2

Sites in Northern Alaska & North East Russia FLUXNET SITE cont. from page 1

At the end of August, 2008, a A micrometeorological station was installed on a tall tower (40 m) near the North East Science Station. The greater height of this tower is necessary to ac- count for the heterogeneity of the landscape and vegetation. The ecosystems of the North East Science Station are repre- sentative of the coastal plain of Northeast Siberia, a one million km2 area of carbon-rich loess that accumulated carbon during the Pleistocene and have been gradually been releasing this carbon to the and ocean through thawing of previously frozen soils during the Holocene. The carbon content of these soils is much greater than that of the perma- frost soils in North America. This system at the North East B Science Station includes: 1) an covariance system to measure the fluxes of water, carbon, and energy, 2) A meth- ane analyzer to measure the concentration of at a height of 30m which will subse- quently be used by NOAA in

Figure 2: Coarse root CO2 efflux measurement at the Kissoko site the development of a regional methane flux model, 3) a closed -path eddy-covariance system to be used in conjunction with the methane analyzer to meas- ure a local methane flux, and 4) a full suite of meteorological data. Three existing 10 m tall towers are also located near this tower, and have been collecting data for 8 years. Maintaining flux stations over a full annual cycle in the Arctic is Figure 2: In (a), maintaining the eddy covariance equipment in northern Alaska is a challenge in winter. In (b), the tundra fire in northern Alaska burned for approximately 3 months, and was the largest tundra fire ever recorded in Alaska. Three flux towers have subsequently a challenge due to the long, been located within the burned area. Photo Credits: Roy Stehle (a); Bureau of Land Management Fire Service (b); FLUXNET SITE cont. on page 3 Page 3

Sites in Northern Alaska & North East Russia FLUXNET SITE cont. from page 2

cold, dark winters that make the sites less accessible and cause ice to form on the sensitive equip- A ment. Snow is on the ground for most of the year, with the snow season starting at the be- ginning of September and ending by the first week of June. Fur- thermore, line power is not available, and power outages are a problem. Routine site visits are essential during the snow season, and are often extended in order to diagnose and fix any problems. We have held two workshops in 2008 for the AON participants in which we identified topics of synthesis based on data collected at the sites across network. We will hold another workshop in 2010. We have also estab- lished an AON website: http:// aon.iab.uaf.edu/index.html where more information about the project and data are available. B

Research team: University of Alaska Fairbanks: Brian M. Barnes, M. Syndonia Bret-Harte, Eugénie S. Euskirchen, Anja N. Kade, Glenn J. Scott, Katey M. Walter Ecosystems Center, Marine Biological Laboratory: John E. Hobbie, Bonnie L. Kwiatkowski, Edward B. Rastetter, Adrian V. Rocha, Gaius Shaver, Gabrielle Tomalsky-Holmes, North East Science Station: Sergei Zimov, Nikita Zimov

Contact information: Eugénie Euskirchen [email protected]

Figure 3: In (a), the tall (40 m) tower in Northeast Russia, and in (b) a smaller tower located within the footprint of the tall tower. Photo Credit: Sergei Zimov Page 4

Opinion Contribution: Conservation of Surface Fluxes in a Numerical Model by Jinkyu Hong

The Atmospheric numerical increasing grid resolution in a However, due to nonlinear re- are fed into a fine grid simulation models solve the differential model due to nonlin- sponses of surface fluxes to for initial and boundary condi- equations of conservation of ear responses of surface fluxes environmental conditions, sur- tions. Accordingly, it is inevitable momentum, mass and thermody- to spatial variations in surface face fluxes are not conserved in to have some bias in surface namic energy. As a result, the properties, and a concept of different grid resolutions (i.e., fluxes simulated from a coarse conservation of momentum, scale-invariance of surface fluxes F ≠ F grid size due to Jensen’s inequal- M mass and thermodynamic energy was proposed so that a bio- ity. is a strong constraint and thus sphere model made consistent Numerical models from LES It was concluded that the nonlin- has been carefully checked in estimates of surface fluxes as (Large-eddy simulation) to ear effects were negligible and modeling atmospheric flows. grid resolution changed (Fig. 1). mesoscale, regional climate and thus the scale-invariance of sur- However, the concept of surface Ideally, the scale-invariance of earth system models apply nest- face fluxes was satisfied (Sellers flux conservation with different surface fluxes produces similar ing procedure to examine the et al., 1992, 1995, 1997). How- grid sizes had not been clearly surface fluxes in spite of different detail structures of small domain. ever, we should note that there addressed before Sellers et al. grid sizes following Jensen’s ine- In this nesting procedure, atmos- was no interaction between (1992, 1995, 1997). These pio- quality (e.g., pheric and surface conditions surface fluxes and atmospheric neering studies focused on artifi- FF= conditions due to an off-line M from a mother domain (i.e. a cial loss/gain of surface fluxes as domain having coarse grid size) simulation in their studies. That is, it was assumed that atmos- pheric conditions such as down- ward radiation, , tempera- ture and were homoge- neous in a whole domain. In- deed, the test of this scaling issue in fully coupled models (e.g., LES, mesoscale model or earth system model) has re- mained unresolved so far. We recently checked the conserva- tion of surface fluxes in an at- mospheric mesoscale model and found that surface fluxes were not conserved as grid size in the model increased (Hong and Kim, 2008) (Fig. 2). In the early stage of numerical integration, radia- tive forcing and surface condi- tions are considerably homoge- neous because relatively homo- geneous fields were fed from a Figure 1. The concept of (dis)aggregation and scale-invariance of surface fluxes in the model adapted from Sellers et al. (1992). F is surface mother domain to a domain of

Ffxxx= (123 , , ,...) flux as a function of xi (e.g. topography, surface conductance, moisture) and we can write . Thus, complete finer grid size for boundary con- 1 F ≡ fxda() ditions. Therefore, the nonlinear A ∫∫ i values of F over an entire domain are calculated from A where A is the area of domain and the brackets denote area effects are trivial in such homo-

F ≡ fx( i ) F average over A. However, because of practical reason, F over an entire domain is calculated: M where M is an estimate geneous conditions and thus the F of . cont. on page 5 Page 5

Conservation of Surface Fluxes in a Numerical Model cont. from page 4

scale-invariance of surface fluxes is satisfied. As numerical integra- tion progresses, spatial hetero- geneities are, however, gener- References ated in the model, which pro- Hong, J., Kim, J. 2008. Scale-dependency duces the substantial nonlinear- of surface fluxes in an atmospheric mesoscale model: effect of spatial het- ity. erogeneity in atmospheric conditions. Scientific implications are: 1) Nonlin. Processes in Geophys. 15, 965- One should carefully apply the 975. nesting procedures because the Sellers, P.J, Heiser, M.D., Hall, F.G. modeled surface fluxes can have 1992. Relationships between surface artificial gain/loss due to the conductance and spectral vegetation 2 failure of the scale-invariance as indices at intermediate (100 m – 15 2 the spatial heterogeneity grows km ) length scales. J. Geophys. Resear. up in the model; and 2) model 97, 19033-19060. bias will not necessarily result Sellers, P.J., Heiser, M.D., Hall, F.G., from intrinsic model inaccuracy Goetz, S.J., Strebel, D.E., Verma, S.B., when spatial variability in atmos- Desjardins, R.L., Schuepp, P.M, pheric conditions prevails. One MacPherson, J.I. 1995. Effects of spatial possible remedy for scale- variability in topography, vegetation dependency of surface fluxes in a cover and soil moisture on area- model will be to rectify surface averaged surface fluxes: A case study fluxes and corresponding scalar using the FIFE 1989 data. J. Geophys. concentration and wind in a Resear. 100, 25607-25629. coarse grid domain by assimilat- Sellers, P.J., Heiser, M.D., Hall, F.G., ing surface fluxes aggregated in a Verma, S.B., Desjardins, R.L., Schuepp, P.M., MacPherson, J.I. 1997. The impact fine grid domain into a mother of using area-averaged land surface domain. properties - Topography, vegetation

condition, soil wetness - In calculations Figure 2. Comparison of sensible (H) and latent heat fluxes (LE) in domain 2 (D2: 20 km contact: of intermediate scale (approximately 10 grid size) and domain 1 (D3: 1 km grid size) after aggregating to 20 km spatial scale Jinkyu Hong around a flux tower at 05:00 UTC on August 26 and 30 respectively. km2) surface-atmosphere heat and Global Environment Lab/Dept. moisture fluxes. J. Hydrol. 190, 269-301. of Atmospheric Sciences, Yonsei University, Korea [email protected] Page 6

Highlight Graduate Student Donatella Zona

My name is Donatella Zona, I Arctic at the Barrow Environ- were established that slowed or north site having a water table am a Ph.D student at the Univer- mental Observatory (BEO) in prevented the water from mov- above the surface for the entire sity of California Davis. I will 2005 as part of the NSF Biocom- ing from the north site to the summer (Fig. 2), on average +6 graduate in 2 weeks, and I am plexity in the Environment- Cou- south towards the natural outlet cm, while the central and south currently dealing with formatting pled Biogeochemical Cycles. I of the basin and the associated sites had an average water table and printing of my dissertation… was lucky to be involved in this drainage channel. This resulted of -3 and -2 cm, respectively. My Ph.D research is in Barrow, project for my Ph.D research. in a difference in water table Results from the initial year of Alaska, under the direction of The target of this manipulation heights between the three treat- the manipulation show a signifi- Prof. Walter Oechel and Prof. experiment includes increasing ment areas, with the north and cant impact of the observed Susan Ustin. The focus of my and decreasing the water table the central sites having the high- variation and progression in

over large areas of tundra and est water table (respectively on water table on CO2 and CH4 research is the study of CO2 and observing the effects over the average over the entire season fluxes. Contrary to common CH4 fluxes from the arctic tun- dra. Tundra soils accumulation of diverse microtopography of the of -5 cm and -4 cm) and the expectation, we showed that the large amounts of organic materi- region. The experiment was south the lowest (on average -10 effect of a decrease in water als due to their generally cold designed to investigate the link cm). In summer 2008, water was table is not necessarily a de- and anaerobic soil conditions. between CH4 and CO2 fluxes pumped from the central area crease in CH4 release. An in- The large amount of carbon (measured with eddy covariance and a nearby lake to the north crease in water table above the stored in the Arctic tundra soil towers, see Fig. 2) as affected by section (from the beginning of surface could increase the diffu- could be significant current and changes in soil water, over com- June to the end of August), while sive resistance to CH4 release. plex terrain. During the first year the south area was kept as con- Additionally, a drop in water future global sources of CH4 and of the manipulation (2007) dikes trol (Fig. 2). This resulted in the table below the surface may not CO2 release. Soil drying in areas of continuous permafrost has been reported and appears to be due to an increasing gap be- tween potential summer evapo- transpiration and summer pre- cipitation (Oechel et al., 1993; Oechel et al., 2000). On the other hand, some Arctic areas on continuous permafrost are showing increased lake numbers and/or extent (Smith et al., 2005). This could result in ex- tensive new areas of anaerobic soils. Therefore, even under scenarios of warming and drying of the Arctic, many regions un- derlain by continuous permafrost are likely to show increased water availability and anoxic condition in the soil in coming decades. Because trace gas fluxes are so tightly linked to soil mois- ture and water table in the Arc- tic, my professor (Walter Oechel) initiated a large-scale manipulation in the Alaskan Figure 1 - Donatella Zona at one of the three CO2 and CH4 eddy covariance towers in the NSF Biocomplexity experiment, in Barrow, Alaska, in the beginning of summer 2008. cont. on page 7 Page 7

Highlight Graduate Student cont. from page 6

Figure 2: Agnes de Grandcourt harvesting aboveground biomass. The living and dead biomass is separated by species and organs.

Figure 2 Site of the manipulation during June 2008. Blue arrows indicate the locations of the three eddy towers, while yellow arrows indicate the location of the dikes.

decrease CH4 emissions, when contact: Donatella Zona there is a concurrent increase in [email protected] Further Reading thaw depth, and therefore soil Oechel, W. C., G. L.Vourlitis, , S. J. volume available for methano- website Hastings, R.C. Zulueta, L. Hinzman, and D. Kane (2000), Acclimation of ecosys- genesis (see Zona et al., 2009). http://gcrg.sdsu.edu tem CO2 exchange in the Alaskan The comprehensive results that Arctic in response to decadal climate describe the effect on CO2 Note: Donatella finished her warming, Nature 406, 978-981. fluxes are in preparation. PhD on June 11th, 2009 under Oechel, W. C., S. J. Hastings, G. L. the direction of Prof. Walter Vourlitis, M. Jenkins, G. Riechers, and N. Grulke (1993), Recent Change of Oechel and Prof. Susan Ustin. Arctic tundra ecosystems from a net sink to a source, Na- ture, 361, 520-523. Smith L. C., Y. Sheng, G. M. MacDonald, L. D. Hinzman (2005), Disappearing Arctic Lakes, Science, 308, 1429. Zona, D., W. C. Oechel, J. Kochendor- fer, K. T. Paw U, A. N. Salyuk, P. C. Olivas, S.F. Oberbauer, and D. A. Lipson (2009) Methane fluxes during the initiation of a large-scale water table manipulation experiment in the Alaskan Arctic tundra, Global Biogeocheical. Cycles, 23, GB2013, doi:10.1029/2009GB003487 Zona D., W. C. Oechel, K. M. Peterson, R. J. Clements, K. T. Paw U, and S. L. Ustin, Characterization of carbon fluxes of a drained lake basin chronosequence on the Alaskan Arctic Coastal Plain, submitted to Global Change Biology Figure 3 Donatella Zona at one of the three CO2 and CH4 eddy covariance towers Page 8

Highlight Young Scientist Adrian V. Rocha

I’ve always enjoyed the out- seen before. I found it exciting growth from environmental Woods Hole, MA to determine doors, but never thought that I that these instruments were variations and decouple photo- how burn severity influences would get to work in such beau- monitoring the “breathing” of synthesis from plant growth. It post-fire energy and mass ex- tiful places as the Northern the , and decided to use was during this project that I changes in arctic tundra. Fires Hardwood of Michigan, these data to understand how gained an appreciation for the often create a mosaic of patches the boreal forests of Manitoba, clouds and aerosols influenced biology and internal dynamics of that differ in burn severity, and Canada, the freshwater wetlands canopy photosynthesis and wa- the vegetation, and decided to we took advantage of one of the of California, and the Arctic ter use efficiency for my thesis focus on these processes for my largest fires to occur on the tundra of Alaska’s North Slope. (Rocha et al. 2004). dissertation. I found similar North Slope (the Anaktuvuk I feel extremely privileged to After completing my thesis, I relationships between plant River Fire) to determine how have such a fulfilling career, these patches influence and am indebted to those that vegetation recovery and have fostered my scientific post fire surface exchanges interests. of mass and energy. We are My scientific interests began running three eddy covari- to take shape working as a ance towers along a burn research assistant for Lars severity gradient and com- Pierce and Fred Watson at bining these data with satel- the California State University lite information to deter- of Monterey Bay (CSUMB). mine the importance of fire My job was to run around the induced landscape heteroge- bush in the early hours of the neity in scaling up the flux morning to measure the pre- measurements to the region. dawn water potential in chap- We are very excited about arral plants. The data that I this project, and encourage collected would eventually be future collaboration with used to parameterize an eco- members of the Fluxnet system model, but I was more community. interested in the excitement of being in the bush while Figure 1: Adrian at an eddy covariance tower in Alaska everyone else was asleep. I returned to California to pursue growth and photosynthesis in a contact: Adrian Rocha actually couldn’t believe that I a Ph.D. with Mike Goulden at Southern Californian freshwater [email protected] was getting paid for having so the University of California, marsh (Rocha and Goulden much fun, and after a field season Irvine. During the second year 2009), and determined that of collecting data I decided to of my dissertation several lab within plant carbon storage and Further Reading members and I traveled to allocation was important for Rocha, A.V. and M.L. Goulden (2009) pursue a career in . Why is marsh productivity so high? I pursued a Masters degree with Thompson, Manitoba, Canada to linking the annual “breathing” of New Insights from Eddy Covariance and core hundreds of trees in order the forest to plant growth. Biomass Measurements in a Typha Peter Curtis at the Ohio State Marsh. Agricultural and Forest Meteor- University after graduating from to understand the relationship ology. 149, 159-168. CSUMB. My first field season between tree growth and forest I am two weeks away from re- Rocha, A.V., M.L. Goulden, A.L. Dunn, physiology. We were surprised turning to the North Slope of and S.C. Wofsy. (2006) On linking was at the University of Michigan interannual ring width variability with Biological Station (UMBS), where to find a poor relationship be- Alaska for my second summer observations of whole-forest CO2 flux. Global Change Biology. 12:1378-1389 Peter managed an eddy covari- tween canopy photosynthesis field season. I am working with and ring width and attributed my postdoctoral advisor’s Gauis Rocha, A.V., H.B. Su, C. Vogel, H.P. ance tower in a Northern Hard- Schmid, and P.S. Curtis (2004) Photo- wood Forest. The instrumenta- this unusual pattern to carbohy- Shaver and Ed Rastetter from synthetic and water use efficiency drate reserves (Rocha et al. the Marine Biological Labora- responses to diffuse radiation by an tion on the tower was impres- aspen-dominated northern hardwood sive and unlike anything I had 2006), which can buffer plant tory’s Ecosystems Center in forest. Forest Science. 50:793-801 Page 9

Measuring air-ice CO2 fluxes in the Arctic Heinesch B, Yernaux M, Aubinet M, Geilfus N-X, Papakyriakou T, Carnat G, Eicken H, Tison J-L, B.Delille

Sea ice covers about 7% of this assumption is not supported gate pCO2 dynamics in the sea- they would dissolve within the Earth’s surface at its maximum by studies of the permeability of ice realm and related CO2 fluxes. sea ice or in the underlying wa- seasonal extent, representing ice to gases and liquids, which The processes by which the ter. Such dissolution consumes one of the largest biomes on the show that sea ice is permeable at CO2 exchange between the CO2 and therefore acts as a sink planet. For decades, sea ice has temperatures above -10°C. Re- ocean and the atmosphere can for atmospheric CO2. Other been considered by the scientific cently, uptake of atmospheric take place are the following. processes can potentially act as community and biogeochemical CO2 over sea-ice cover has While CO2-enriched brines are sinks of CO2. First, sea ice hosts modellers involved in assessing been reported (Delille et al., expelled from the ice, carbonate algae communities, which imply 2007; Semiletov et al., 2004; minerals could remain trapped in primary production. Second, oceanic CO2 uptake as an inert and impermeable barrier to air- Zemmelink et al., 2006) support- the brine tubes and channels during sea-ice growth, most of sea exchange of gases. However, ing the need to further investi- until spring and summer, when the impurities (solutes, gases,

Figure 1: Set up of the mast with sonic , air intake of the CO2 analyser and radiometer over sea ice near Barrow (Alaska) in January 2009. The temperature was -35°C. cont. on page 10 Page 10

cont. from page 9 Measuring air-ice CO2 fluxes in the Arctic

the magnitude of fluxes. The system deployed in Barrow 2 ]

-1 should allow us to follow these s

-2 processes and to budget the net

1 20 CO2 transfer from the atmos-

mol m phere to the ice over winter and μ

spring. 0 28 March 2009 12 April 2009 27 April 2009 15 This project is supported by the CO2 fluxCO2 [ -1 Fonds de la Recherche Scienti- fique, the National Science Foun- 10 ]

-1 dation and the University of -2 Alaska Fairbanks. We are in- debted to the Barrow Arctic 5 Science Consortium and the -3 North Slope Borough for their logistical support. Wind speed [m s speed Wind -4 0

Time (AlasKa Standard Time) contact: Figure 2 : CO flux and wind speed in April 2009 over sea-ice in Barrow (Alaska). 2 Bernard Heinesch particulate matter) are expelled a meteorological mast equipped high enough to measure CO2 [email protected] from the pure ice crystals at the for eddy-covariance measure- fluxes that are typically below 1 -2 -1 ice-water interface. The CO2 ments was installed on landfast mmol m s . Despite low tem- rejected into the boundary layer sea-ice near Barrow (Alaska), 1 perature at the ice-snow inter- will either diffuse or be convec- km off the coast, from end of face (-14°C), we observe in April References tively driven downward into the January 2009 to beginning of some effluxes from the ice to Burba, G.G., McDermitt, D.K., Grelle, A., Anderson, D.J. and Xu, L.K., 2008. underlying water, removing CO2 June 2009, before ice break-up. the atmosphere (see figure 2). Addressing the influence of instrument from the surface water. During There is some concerns about This is consistent with the CO 2 surface heat exchange on the measure- spring, melting of CO2-depleted using open-path analyzer in cold oversaturation of sea-ice brines ments of CO2 flux from open-path gas sea ice would decrease pCO2 of environment (Burba et al., 2008) observed at the site. The fluxes analyzers. Global Change Biology, 14(8): surface waters. Such a mecha- so the mast was equipped with a are triggered by wind speed over 1854-1876. Delille, B., Jourdain, B., Borges, A.V., nism would act as a sink for CO closed-path analyser to- 7 m s-1 suggesting that wind 2 Tison, J.L. and Delille, D., 2007. Biogas atmospheric CO2. On the whole, gether with a C-SAT 3D sonic pumping trough the snow (snow (CO2, O-2, dimethylsulfide) dynamics in spring sea ice appears to act as a anemometer. These data were thickness was about 20 cm) is spring Antarctic fast ice. and CO2 sink that may be significant supported by continuous meas- one of the main process control- , 52(4): 1367-1379. Semiletov, I., Makshtas, A., Akasofu, S.I. in the budget of CO2 fluxes in ure of solar radiation, snow ling the air-ice fluxes at that and Andreas, E.L., 2004. Atmospheric the Polar Oceans (Delille et al., depth, ice thickness and tem- time. CO2 balance: The role of Arctic sea ice 2007; Zemmelink et al., 2006). perature profile in the ice. Bio- As the sea ice is warming up, the - art. no. L05121. Geophysical Research However, previous studies are geochemical data necessary for partial pressure of sea ice brines Letters, 31(5): 5121-5121. sparse, and limited in term of the understanding of the CO is expected to decrease signifi- Zemmelink, H.J. et al., 2006. CO2 2 deposition over the multi-year ice of spatial and temporal coverage. dynamics in sea-ice were ob- cantly and to pass the threshold the western Weddell Sea - art. no. In January 2009, we started a tained through regular ice cor- of saturation. Sea ice would then L13606. Geophysical Research Letters, 33(13): 13606-13606. study that aims to robustly fol- ing. shift from a source to a sink for low up CO2 exchange between First results coming from this atmospheric CO2. In addition, land fast sea-ice and the atmos- campaign show that the resolu- increase of temperature will phere during the winter and tion of the eddy-covariance increase the permeability of sea spring season. To this aim, technique in these conditions is ice, promoting the increase of Page 11

Presence and absence of permafrost

– implications for atmospheric exchanges of CO2 and CH4 Torben R. Christensen, Mikhail Mastepanov and Margareta Johansson

Permafrost, soil that stays fro- such as towns in northern Sibe- terms of atmospheric exchange pirically based understanding of zen for two or more years in a ria or oil and gas pipelines of C, in the form of CO2 and what permafrost does to the row, is a hot topic that has at- through areas underlain by per- CH4, the potential for additional dynamics and interannual vari- tracted a lot of attention in both mafrost, the thawing represents releases are, hence, probably ability in atmospheric (and dis- the scientific and popular litera- a serious and extremely expen- greater from these areas than solved run-off) fluxes of organic ture in recent years. Permafrost sive issue to deal with. Thawing anywhere else in the . carbon is therefore still very underlies 25% of the land areas permafrost may however even While the potential release from poor. in the northern hemisphere. be an issue with global implica- the huge stocks of carbon is Basic features of how these With a warming climate that is tions through changes in natural significant, the actual data and ecosystems are functioning with particularly pronounced at high ecosystem greenhouse gas emis- year-round monitoring of atmos- and without permafrost have northern latitudes, where most sions. pheric exchanges are still rare recently been discovered. Schuur permafrost is present, many Permafrost areas in the circum- and continuous flux measure- et al. (2009) showed from a questions have been raised re- polar North is estimated to hold ments of CO2 are limited to a central Alaskan site how old garding what may happen to more than 1600 Gt of organic C handful of sites. Continuous organic previously frozen carbon ecosystems and their functioning including almost 300 Gt in the monitoring of CH4 fluxes is even gets respired as the permafrost in the areas when permafrost form of peat (McGuire et al. in rarer; the number of operational thaws and in Siberian thaw lakes thaw. In areas with infrastructure press; Tarnocai et al. in press). In sites is less than five. Our em- methane was shown formed on recently thawed old organic deposits (Walter et al., 2007). The interannual and across-site

variability of CO2 exchange in continuous permafrost ecosys- tems are driven primarily by growing-season dynamics and moisture conditions. Growing-

season rates of CO2 uptake by these ecosystems have been shown in several studies to be closely related to the timing of snow melt, with earlier snow- melt resulting in greater uptake

of atmospheric CO2 (Aurela et al., 2004; Groendahl et al., 2006). The annual C budget is not only controlled by growing-season exchange, but to a large extent by the losses during the shoulder (snow melt/soil thaw and senes- cence/soil freeze) and winter seasons (Johansson et al., 2006). These more complex impacts on the annual budgets become Figure 1. The Zackenberg valley in NE Greenland, an area underlain by continuous permafrost. The automatic chambers were used for the studies of methane emission dynamics during freeze in (Mastepanov et al., 2008). Local inhabitants, the muskoxen, are present in the more important when moving background. Photo credit: Charlotte Sigsgaard. cont. on page 12 Page 12

Presence and absence of permafrost cont. from page 11 out of permafrost regions and (Figure 2), a distinct feature not percentage of methane in this northern Sweden, the Abisko into climatically milder off season previously observed and not gas can be more than 50% area, where permafrost has been conditions. seen in the subarctic studies (Tokida et al., 2005). When the monitored for decades. The In northern Sweden we have most likely since no earlier flux soil is starting to freeze from the surface active layer that thaws documented changes in perma- studies in continuous permafrost surface down, a gas-proof layer every summer has become frost dynamics and effects on regions have extended into the is forming and it propagates thicker during the last three ecosystems and their feedbacks frozen season. After further downwards. The permafrost decades. In nine mires along a on climate in terms of methane investigation together with at- works as a gas-proof bottom 100 km long transect the trend emissions (Christensen et al., mospheric scientists we have preventing the gas to migrate has been similar and in some 2004; Johansson et al., 2006) and preliminary concluded that it deeper down. As the ice has mires the permafrost has even in relation to catchment scale could well be a likely general lower density than water, the disappeared completely greenhouse gas exchanges feature of permafrost areas and freezing process is causing in- (Åkerman & Johansson, 2008). (Christensen et al., 2007). Here in fact it helps to explain the crease of the volume of the This trend is reflected also in the thawing permafrost generally observed seasonal dynamics in freezing zone, raising the pres- larger scale modeling of the leads to wetter hydrological atmospheric methane concentra- sure in the unfrozen layer. This whole of permafrost (palsa) conditions and subsequently tions during the autumn process preconditions the mires in northern Scandinavia greater emissions at the land- (Mastepanov et al., 2008). squeezing of the gas with high (Fronzek et al., 2006) and from scape scale. The seasonal and The mechanism behind the methane content to the atmos- observations in North America interannual pattern is at the freeze-in emissions in continuous phere. An additional hypothe- (Vallee & Payette, 2007; Turet- subarctic site rather predictable permafrost areas is hypothesized sized necessary condition for the sky et al., 2007). On the whole and the emissions rather stable as a release of methane from the late-season methane burst to this uniform trend towards from year to year (Jackowicz- subsurface pool accumulated occur is the presence of some transformation of permafrost Korczyński et al., submitted). In over the growing season (Figure channels for the pressurized gas landscapes calls for an under- contrast we observed some 3). The methane is present to get out to the atmosphere. standing of ecosystem fluxes surprising and interesting autumn mainly in gaseous form in en- We suggest it may be residuals both where the permafrost is emission dynamics at our high trapped gas bubbles below the of vascular plant tissues, or some still present and where it has arctic measurement site in NE water table level. The volume of cracks in the frozen upper soil disappeared. From the few data Greenland (Figure 1). These the gas phase in the peat beneath layer. we have our understanding is as findings (Mastepanov et al., 2008) the water table can be significant Back in the geographical margins shown above that these ecosys- show a second seasonal peak of (from 0 to 19% - Tokida et al., of the permafrost zone is the tems with and without perma- emissions during the freeze-in 2005), while the volumetric intensively studied region of frost differ significantly in their

Figure 2. Schematic illustration of the seasonal dynamics of emissions as observed in Zackenberg (light blue) and subarctic Sweden (green) respectively. These very different seasonal patterns reflects differences depending on both the length of the growing season and the special emission patterns with the freeze-in burst observed in a continuous permafrost environment (based on

cont. on page 13 Page 13

Presence and absence of permafrost cont. from page 12

FluxLetter The Newsletter of FLUXNET

Vol.2 No.2 June, 2009

FluxLetter is produced quarterly at the FLUXNET Figure 3. A hypothesis illustrated for how the freeze-in burst of methane emission in continuous permafrost environments emerges. As the Office with support from the ground freezes primarily from the surface down the pressure builds up in the unfrozen zone and the accumulated gas in the soil gets pressed out through physical cracks and pores remaining in place from senesced vascular plants. National Science Foundation.

functioning and this calls for budget of a subarctic landscape. Philoso- Arctic to . Ecological more continuous measurements phical Transactions of the Royal Society A: Monographs, in press. Mathematical, Physical and Engineering Schuur, E.A.G., J.G. Vogel, K.G. Crum- both to document ongoing Sciences, 365, 1643-1656. mer, H. Lee, J.O. Sickman & T.E. Oster- changes and to gain a process Fronzek, S., Luoto, M. & Carter, T.R., kamp (2009) The effect of permafrost understanding for the purpose of 2006. Potential effect of climate change thaw on old carbon release and net modeling large scale transitions on the distribution of palsa mires in carbon exchange from tundra. Nature, in permafrost affected ecosys- subarctic Fennoscandia. Climate Research 459, 556-559. 32 (1): 1-12. Tarnocai, C., Canadell, J.G., Schuur, tems and their interactions with Groendahl, L., T. Friborg & H. Soegaard E.A.G., Kuhry, P., Mazhitova, G. & climate. (2006) Temperature and snow-melt Zimov, S. In press. Soil organic carbon controls on interannual variability in pools in the northern circumpolar contact: carbon exchange in the high Arctic. permafrost region. Global Biogeochemical Theoretical and Applied Climatology, 88, Cycles. Torben R. Christensen 111-125. Tokida, T., T. Miyazaki, M. Mizoguchi & GeoBiosphere Science Centre, Lund Jackowicz-Korczyński, M., T.R. Chris- K. Seki (2005) In situ accumulation of University, Sweden tensen, K. Bäckstrand, P.M. Crill, T. methane bubbles in a natural wetland [email protected] Friborg, M. Mastepanov, & L. Ström soil. European Journal of , 56, (submitted revised version) Annual 389-396. cycles of methane emission from a Turetsky MR, Wieder RK, Vitt DH, et

subarctic peatland. J. Geophys. Res. al., 2007. The disappearance of relict References Johansson, T., N. Malmer, P.M. Crill, T. permafrost in boreal north America: Aurela, M., T. Laurila & J.P. Tuovinen Friborg, J.H. Akerman, M. Mastepanov & Effects on peatland carbon storage and (2004) The timing of snow melt con- T.R. Christensen (2006) Decadal vege- fluxes. Global Change Biology 13, 1922- This issue of FluxLetter was trols the annual CO2 balance in a tation changes in a northern peatland, 1934. edited, designed and produced by: subarctic fen. Geophysical Research greenhouse gas fluxes and net radiative Vallee S & Payette S., 2007. Collapse of Letters, 31, 4. forcing. Global Change Biology, 12, 2352- permafrost mounds along a subarctic Christensen, T.R., T. Johansson, H.J. Rodrigo Vargas 2369. river over the last 100 years (northern Dennis Baldocchi Akerman, M. Mastepanov, N. Malmer, Mastepanov, M., C. Sigsgaard, E.J. Quebec). Geomorphology 90, 162-170. T. Friborg, P. Crill & B.H. Svensson Dlugokencky, S. Houweling, L. Strom, Walter, K.M., M.E. Edwards, G. Grosse, FLUXNET Office, 137 Mulford (2004) Thawing sub-arctic permafrost: M.P. Tamstorf, & T.R. Christensen S.A. Zimov & F.S. Chapin (2007) Ther- Hall, University of California, Effects on vegetation and methane (2008) Large tundra methane burst mokarst lakes as a source of atmos- Berkeley, CA 94720 emissions. Geophysical Research Letters, during onset of freezing. Nature, 456, pheric CH4 during the last deglaciation. ph: 1-(510)-642-2421 31, L04501. 628-U58. Science, 318, 633-636. Fax: 1-(510)-643-5098 Christensen, T.R., T. Johansson, M. McGuire, A.D., Anderson, L.G., Chris- Åkerman, H.J. & M. Johansson (2008) Olsrud, L. Ström, A. Lindroth, M. tensen, T.R., Dallimore, S.,Guo, L., Thawing permafrost and thicker active We plan to make the FLUXNET Mastepanov, N. Malmer, T. Friborg, P. Hayes, D.J., Heimann, M., Lorenson, layers in sub-arctic Sweden. Permafrost newsletter a powerful information, Crill & T.V. Callaghan (2007) A catch- T.D. , Macdonald, R.W., and Roulet, N. and Periglacial Processes, 19, 279-292. networking, and communication ment-scale carbon and greenhouse gas Sensitivity of the carbon cycle in the resource for the community. If you want to contribute to any section or propose a new one please contact the FLUXNET Office. THANKS!!