Ice characteristics, and mercury content of ice, air and underlying seawater in the eastern Beaufort Sea

The Arctic sea-ice environment has been undergoing dramatic changes in the past decades; to which extent this will affect the deposition, fate, and effects of chemical contaminants remains virtually unknown. Here, we report the first study on the distribution and transport of mercury (Hg) across the ocean-sea-ice-atmosphere interface in the Southern Beaufort Sea of the Arctic Ocean. Despite being sampled at different sites under various atmospheric and snow cover conditions, Hg concentrations in first-year ice cores were generally low and varied within a remarkably narrow range (0.5-4 ng/L), with the highest concentration always in the surface granular ice layer which is characterized by enriched particle and brine pocket concentration. Atmospheric Hg depletion events appeared not to be an important factor in determining Hg concentrations in sea ice except for frost flowers and in the melt season when snowpack Hg leaches into the sea ice. The multiyear ice core showed a unique cyclic feature in the Hg profile with multiple peaks potentially corresponding to each ice growing/melting season. The highest Hg concentrations (up to 70 ng/L) were found in sea-ice brine and decrease as the melt season progresses. As brine is the primary habitat for microbial communities responsible for sustaining the food web in the Arctic Ocean, the high and seasonally changing Hg concentrations in brine and its potential transformation may have a major impact on Hg uptake in Arctic marine ecosystems under a changing climate.

Absorption characteristics, major elements and chl a content of samples from Pond 19 at Zackenberg, NE Greenland

1. Shallow arctic lakes and ponds have simple and short food webs, but large uncertainties remain about benthic-pelagic links in these systems. We tested whether organic matter of benthic origin supports zooplankton biomass in a pond in NE Greenland, using stable isotope analysis of carbon and nitrogen in the pond itself and in a 13C-enrichment enclosure experiment. In the latter, we manipulated the carbon isotope signature of benthic algae to enhance its isotopic discrimination from other potential food sources for zooplankton. 2. The cladoceran Daphnia middendorffiana responded to the 13C-enrichment of benthic mats with progressively increasing d13C values, suggesting benthic feeding. Stable isotope analysis also pointed towards a negligible contribution of terrestrial carbon to the diet of D. middendorffiana. This agreed with the apparent dominance of autochthonous dissolved organic matter in the pond revealed by analysis of coloured dissolved organic matter. 3. Daily net production by phytoplankton in the pond (18 mg C/m**2/day) could satisfy only up to half of the calculated minimum energy requirements of D. middendorffiana (35 mg C/m**2/day), whereas benthic primary production alone (145 mg C/m**2/day) was more than sufficient. 4. Our findings highlight benthic primary production as a major dietary source for D. middendorffiana in this system and suggest that benthic organic matter may play a key role in sustaining pelagic secondary production in such nutrient-limited high arctic ponds.

Sampling data, experimental data and fecal pellet characteristics of water pump samples in the strait of Øresund between Denmark and Sweden during 2004/2005

Copepod fecal pellets are often degraded at high rates within the upper part of the water column. However, the identity of the degraders and the processes governing the degradation remain unresolved. To identify the pellet degraders we collected water from Øresund (Denmark) approximately every second month from July 2004 to July 2005. These water samples were divided into 5 fractions (<0.2, <2, <20, <100, <200 µm) and total (unfractionated). We determined fecal pellet degradation rate and species composition of the plankton from triplicate incubations of each fraction and a known, added amount of fecal pellets. The total degradation rate of pellets by the natural plankton community of Øresund followed the phytoplankton biomass, with maximum degradation rate during the spring bloom (2.5 ± 0.49 d**-1) and minimum (0.52 ± 0.14 d**-1) during late winter. Total pellet removal rate ranged from 22% d**-1 (July 2005) to 87% d**-1 (May). Protozooplankton (dinoflagellates and ciliates) in the size range of 20 to 100 µm were the key degraders of the fecal pellets, contributing from 15 to 53% of the total degradation rate. Free-living in situ bacteria did not affect pellet degradation rate significantly; however, culture-originating bacteria introduced in association with the pellets contributed up to 59% of the total degradation rate. An effect of late-stage copepod nauplii (>200 µm) was indicated, but this was not a dominating degradation process. Mesozooplankton did not contribute significantly to the degradation. However, grazing of mesozooplankton on the pellet degraders impacts pellet degradation rate indirectly. In conclusion, protozooplankton seems to include the key organisms for the recycling of copepod fecal pellets in the water column, both through the microbial loop and, especially, by functioning as an effective 'protozoan filter' for fecal pellets.

Total organic carbon content, methane isotopic composition and hydrocarbon characteristics of ODP Leg 180 sites

The organic geochemistry of Sites 1108 and 1109 of the Woodlark Basin, offshore Papua New Guinea, was studied to determine whether thermally mature hydrocarbons were present in the penetrated section and, if present, whether they are genetically related to the penetrated "coaly" interval. Both the organic carbon and pyrolysis data indicate that there is no significant hydrocarbon source-rock potential at Site 1108. The hydrocarbons encountered during drilling appear to be indigenous and not migrated products or contaminants. In contrast, the coaly interval at Site 1109 contains zones with significant hydrocarbon-generation potential. Several independent lines of evidence indicate that the coaly sequence encountered at Site 1109 is thermally immature. The Site 1108 methane stable-carbon isotope composition does not display a clear trend with depth as would be expected if it was solely reflecting a maturation profile. The measured isotopic composition of methane has most probably been altered by fractionation during sample handling and storage. This fractionation would result in isotopically heavier values than would be obtained on free gas. The organic geochemical data gathered indicate that Site 1108 can be safely revisited and that the organic-rich sediments encountered at Site 1109 were not the source of the gas encountered at Site 1108.

Ice and chlorophyll a concentration and mesozooplankton characteristics during two 'On Thin Ice' cruises, northern Svalbard waters

The spatial variation in mesozooplankton biomass, abundance and species composition in relation to oceanography was studied in different climatic regimes (warm Atlantic vs. cold Arctic) in northern Svalbard waters. Relationships between the zooplankton community and various environmental factors (salinity, temperature, sampling depth, bottom depth, sea-ice concentrations, algal biomass and bloom stage) were established using multivariate statistics. Our study demonstrated that variability in the physical environment around Svalbard had measurable effect on the pelagic ecosystem. Differences in bottom depth and temperature-salinity best explained more than 40% of the horizontal variability in mesozooplankton biomass (DM/m**2) after adjusting for seasonal variability. Salinity and temperature also explained much (21% and 15%, respectively) of the variability in mesozooplankton vertical distribution (ind./m**3) in August. Algal bloom stage, chlorophyll-a biomass, and depth stratum accounted for additional 17% of the overall variability structuring vertical zooplankton distribution. Three main zooplankton communities were identified, including Atlantic species Fritillaria borealis, Oithona atlantica, Calanus finmarchicus, Themisto abyssorum and Aglantha digitale; Arctic species Calanus glacialis, Gammarus wilkitzkii, Mertensia ovum and Sagitta elegans; and deeper-water inhabitants Paraeuchaeta spp., Spinocalanus spp., Aetideopsis minor, Mormonilla minor, Scolecithricella minor, Gaetanus (Gaidius) tenuispinus, Ostracoda, Scaphocalanus brevicornis and Triconia borealis. Zooplankton biomasses in Atlantic- and Arctic-dominated water masses were similar, but biological ''hot-spots'' were associated with Arctic communities.

(Table 2) Production characteristics of phytoplankton and selected related factors at bottle sampling stations in the subtropical and tropical Atlantic Ocean

In October and November 2002, high and relatively high values of chlorophyll a concentration at the sea surface (Cchl) were observed in the English Channel (0.47 mg/m**3), in waters of the North Atlantic Current (0.25 mg/m**3 ), in the tropical and subtropical anticyclonic gyres (0.07-0.42 mg/m**3), and also in the southwestern region of the southern subtropical anticyclonic gyre (usually 0.11-0.23 mg/m**3). The central regions of the southern subtropical anticyclonic gyre (SATG) and the North Atlantic tropical gyre (NATR) were characterized by lower values of Cchl (0.02-0.08 mg/m**3 for the SATG and 0.07-0.14 mg/m**3 for the NATR). At most of the SATG stations, values of surface primary production (Cphs) varied from 2.5 to 5.5 mg C/m**3 per day and were mainly defined by fluctuations of Cchl (r = +0.78) rather than by those of the assimilation number (r = +0.54). Low assimilation activity of phytoplankton in these waters (1.3-4.6 mg chl a per hour) pointed to a lack of nutrients. Analysis of variability of their concentration and composition of photosynthetic pigments showed that, in waters north of 30°N, the growth of phytoplankton was mostly restricted by deficiency of nitrogen, while, in more southern areas, at the majority of stations (about 60%), phosphorus concentrations were minimal. At low concentrations of nitrates and nitrites, ammonium represented itself as a buffer that prevented planktonic algae from extreme degrees of nitric starvation. In tropical waters and in waters of the SATG, primary production throughout the water column varied from 240 to 380 mg C/m**2 30° per day. This level of productivity at stations with low values of C chl (<0.08 mg/m**3) was provided by a well-developed deep chlorophyll maximum and high transparency of water. Light curves of photosynthesis based on in situ measurements point to high efficiency of utilizing penetrating solar radiation by phytoplankton on cloudy days.

(Table 3) Air temperatures, and snow and ice characteristics of fresh and brackish water lakes in the Northwest Territories, Canada

The algorithms designed to estimate snow water equivalent (SWE) using passive microwave measurements falter in lake-rich high-latitude environments due to the emission properties of ice covered lakes on low frequency measurements. Microwave emission models have been used to simulate brightness temperatures (Tbs) for snowpack characteristics in terrestrial environments but cannot be applied to snow on lakes because of the differing subsurface emissivities and scattering matrices present in ice. This paper examines the performance of a modified version of the Helsinki University of Technology (HUT) snow emission model that incorporates microwave emission from lake ice and sub-ice water. Inputs to the HUT model include measurements collected over brackish and freshwater lakes north of Inuvik, Northwest Territories, Canada in April 2008, consisting of snowpack (depth, density, and snow water equivalent) and lake ice (thickness and ice type). Coincident airborne radiometer measurements at a resolution of 80x100 m were used as ground-truth to evaluate the simulations. The results indicate that subsurface media are simulated best when utilizing a modeled effective grain size and a 1 mm RMS surface roughness at the ice/water interface compared to using measured grain size and a flat Fresnel reflective surface as input. Simulations at 37 GHz (vertical polarization) produce the best results compared to airborne Tbs, with a Root Mean Square Error (RMSE) of 6.2 K and 7.9 K, as well as Mean Bias Errors (MBEs) of -8.4 K and -8.8 K for brackish and freshwater sites respectively. Freshwater simulations at 6.9 and 19 GHz H exhibited low RMSE (10.53 and 6.15 K respectively) and MBE (-5.37 and 8.36 K respectively) but did not accurately simulate Tb variability (R= -0.15 and 0.01 respectively). Over brackish water, 6.9 GHz simulations had poor agreement with airborne Tbs, while 19 GHz V exhibited a low RMSE (6.15 K), MBE (-4.52 K) and improved relative agreement to airborne measurements (R = 0.47). Salinity considerations reduced 6.9 GHz errors substantially, with a drop in RMSE from 51.48 K and 57.18 K for H and V polarizations respectively, to 26.2 K and 31.6 K, although Tb variability was not well simulated. With best results at 37 GHz, HUT simulations exhibit the potential to track Tb evolution, and therefore SWE through the winter season.

Habitat characteristics and energy budget of the ocean quahog (Arctica islandica)

We compared lifetime and population energy budgets of the extraordinary long-lived ocean quahog Arctica islandica from 6 different sites - the Norwegian coast, Kattegat, Kiel Bay, White Sea, German Bight, and off northeast Iceland - covering a temperature and salinity gradient of 4-10°C (annual mean) and 25-34, respectively. Based on von Bertalanffy growth models and size-mass relationships, we computed organic matter production of body (PSB) and of shell (PSS), whereas gonad production (PG) was estimated from the seasonal cycle in mass. Respiration (R) was computed by a model driven by body mass, temperature, and site. A. islandica populations differed distinctly in maximum life span (40 y in Kiel Bay to 197 y in Iceland), but less in growth performance (phi' ranged from 2.41 in the White Sea to 2.65 in Kattegat). Individual lifetime energy throughput, as approximated by assimilation, was highest in Iceland (43,730 kJ) and lowest in the White Sea (313 kJ). Net growth efficiency ranged between 0.251 and 0.348, whereas lifetime energy investment distinctly shifted from somatic to gonad production with increasing life span; PS/PG decreased from 0.362 (Kiel Bay, 40 y) to 0.031 (Iceland, 197 y). Population annual energy budgets were derived from individual budgets and estimates of population mortality rate (0.035/y in Iceland to 0.173/y in Kiel Bay). Relationships between budget ratios were similar on the population level, albeit with more emphasis on somatic production; PS/ PG ranged from 0.196 (Iceland) to 2.728 (White Sea), and P/B ranged from 0.203-0.285/y. Life span is the principal determinant of the relationship between budget parameters, whereas temperature affects net growth efficiency only. In the White Sea population, both growth performance and net growth efficiency of A. islandica were lowest. We presume that low temperature combined with low salinity represent a particularly stressful environment for this species.

Environmental characteristics, and growth traits and leaf chemistry of tundra plants in a warming experiment at Alexandra Fiord

Understanding plant trait responses to elevated temperatures in the Arctic is critical in light of recent and continuing climate change, especially because these traits act as key mechanisms in climate-vegetation feedbacks. Since 1992, we have artificially warmed three plant communities at Alexandra Fiord, Nunavut, Canada (79°N). In each of the communities, we used open-top chambers (OTCs) to passively warm vegetation by 1-2 °C. In the summer of 2008, we investigated the intraspecific trait responses of five key species to 16 years of continuous warming. We examined eight traits that quantify different aspects of plant performance: leaf size, specific leaf area (SLA), leaf dry matter content (LDMC), plant height, leaf carbon concentration, leaf nitrogen concentration, leaf carbon isotope discrimination (LCID), and leaf d15N. Long-term artificial warming affected five traits, including at least one trait in every species studied. The evergreen shrub Cassiope tetragona responded most frequently (increased leaf size and plant height/decreased SLA, leaf carbon concentration, and LCID), followed by the deciduous shrub Salix arctica (increased leaf size and plant height/decreased SLA) and the evergreen shrub Dryas integrifolia (increased leaf size and plant height/decreased LCID), the forb Oxyria digyna (increased leaf size and plant height), and the sedge Eriophorum angustifolium spp. triste (decreased leaf carbon concentration). Warming did not affect d15N, leaf nitrogen concentration, or LDMC. Overall, growth traits were more sensitive to warming than leaf chemistry traits. Notably, we found that responses to warming were sustained, even after many years of treatment. Our work suggests that tundra plants in the High Arctic will show a multifaceted response to warming, often including taller shoots with larger leaves.

(Table 1) Results of measurements of productive characteristics of phytoplankton and environmental parameters in the Barents Sea in September-October 1997

The described studies were carried out in the eastern part of the sea during the end of the summer seasonal succession from September 1 to October 12, 1997. Concentration of chlorophyll a in the surface layer varied from 0.09 to 1.24 mg/m**3; it tended to increase in the southern regions (<74°N). Primary production in the water column (P_p) varied from 24 to 214 mg C/m**2/day and was on average 91 mg C/m**2/day. The low level of P_p seems to result from combination of physical and chemical environmental factors unfavorable for photosynthesis (e.g. deficiency of nutrients and low values of insolation and temperature) and intensive grazing of phytoplankton by zooplankton. The lower boundary of the photosynthetic layer in open waters was located at depth 60-75 m; irradiance there was 0.1-0.5% of incident irradiance. In deep-water regions (>200 m) the subsurface maximum of chlorophyll occurred in the layer at 20-40 m; usually this maximum resulted in formation of additional maxima of primary production.

Soil characteristics of cryosols from two sites on King George Island, maritime Antarctica

This study presents soil temperature and moisture regimes from March 2008 to January 2009 for two active layer monitoring (CALM-S) sites at King George Island, Maritime Antarctica. The monitoring sites were installed during the summer of 2008 and consist of thermistors (accuracy of ±0.2 °C), arranged vertically with probes at different depths and one soil moisture probe placed at the bottommost layer at each site (accuracy of ± 2.5%), recording data at hourly intervals in a high capacity datalogger. The active layer thermal regime in the studied period for both soils was typical of periglacial environments, with extreme variation in surface temperature during summer resulting in frequent freeze and thaw cycles. The great majority of the soil temperature readings during the eleven month period was close to 0 °C, resulting in low values of freezing and thawing degree days. Both soils have poor thermal apparent diffusivity but values were higher for the soil from Fildes Peninsula. The different moisture regimes for the studied soils were attributed to soil texture, with the coarser soil presenting much lower water content during all seasons. Differences in water and ice contents may explain the contrasting patterns of freezing of the studied soils, being two-sided for the coarser soil and one-sided for the loamy soil. The temperature profile of the studied soils during the eleven month period indicates that the active layer reached a maximum depth of approximately 92 cm at Potter and 89 cm at Fildes. Longer data sets are needed for more conclusive analysis on active layer behaviour in this part of Antarctica.

Characteristics and changes of thermokarst lakes in Canada, Russia and Sweden

Peat plateaus are widespread at high northern latitudes and are important soil organic carbon reservoirs. A warming climate can cause either increased ground subsidence (thermokarst) resulting in lake formation or increased drainage as the permafrost thaws. A better understanding of spatiotemporal variations in these landforms in relation to climate change is important for predicting the future thawing permafrost carbon feedback. In this study, dynamics in thermokarst lake extent during the last 35-50 years has been quantified through time series analysis of aerial photographs and high-resolution satellite images (IKONOS/QuickBird) in three peat plateau complexes, spread out across the northern circumpolar region along a climatic and permafrost gradient. From the mid-1970s until the mid-2000s there has been an increase in mean annual air temperature, winter precipitation, and ground temperature in all three study areas. The two peat plateaus located in the continuous and discontinuous permafrost zones, respectively, where mean annual air temperatures are below -5°C and ground temperatures are -2°C or colder, have experienced small changes in thermokarst lake extent. In the peat plateau located in the sporadic permafrost zone where the mean annual air temperature is around -3°C, and the ground temperature is close to 0°C, lake drainage and infilling with fen vegetation has been extensive and many new thermokarst lakes have formed. In a future progressively warmer and wetter climate permafrost degradation can cause significant impacts on landscape composition and greenhouse gas exchange also in areas with extensive peat plateaus, which presently still experience stable permafrost conditions.

Age determination and sea surface temperature reconstruction from marine and lake records, Iberian Peninsula

Selected multi-proxy and accurately dated marine and terrestrial records covering the past 2000 years in the Iberian Peninsula (IP) facilitated a comprehensive regional paleoclimate reconstruction for the Medieval Climate Anomaly (MCA: 900-1300 AD). The sequences enabled an integrated approach to land-sea comparisons and, despite local differences and some minor chronological inconsistencies, presented clear evidence that the MCA was a dry period in the Mediterranean IP. It was a period characterized by decreased lake levels, more xerophytic and heliophytic vegetation, a low frequency of floods, major Saharan eolian fluxes, and less fluvial input to marine basins. In contrast, reconstruction based on sequences from the Atlantic Ocean side of the peninsula indicated increased humidity. The data highlight the unique characteristics of the MCA relative to earlier (the Dark Ages, DA: ca. 500-900 years AD) and subsequent (the Little Ice Age, LIA: 1300-1850 years AD) colder periods. The reconstruction supports the hypothesis of Trouet et al. (2009, doi:10.1126/science.1166349), that a persistent positive mode of the North Atlantic Oscillation (NAO) dominated the MCA.