During an almost three months long expedition in the Arctic Ocean, the Beringia 2005, dissolved gaseous mercury (DGM) was measured continuously in the surface water. The DGM concentration was measured using an equilibrium system, i.e. the DGM in the water phase equilibrated with a stream of gas and the gas was thereafter analysed with respect to its mercury content. The DGM concentrations were calculated using the following equation, DGM = Hg-eq / k(H’) where Hg-eq is the equilibrated concentration of elemental mercury in the gas phase and k(H’) is the dimensionless Henry’s law constant at desired temperature and salinity. During the expedition several features were observed. For example, enhanced DGM concentration was measured underneath the ice which may indicate that the sea ice acted as a barrier for evasion of mercury from the Arctic Ocean to the atmosphere. Furthermore, elevated DGM concentrations were observed in water that might have originated from river discharge. The gas-exchange of mercury between the ocean and the atmosphere was calculated in the open water and both deposition and evasion were observed. The measurements showed significantly enhanced DGM concentrations, compared to more southern latitudes. (C) 2008 Elsevier B.V. All rights reserved.

Part of the Beringia 2005 expedition covered the North Atlantic Ocean. During this passage, dissolved gaseous mercury (DGHg) in seawater and atmospheric concentrations of total gaseous mercury (TGHg), carbon monoxide (CO), and ozone (O-3) were measured continuously at high resolution. In addition, meteorological parameters such as wind speed and water temperature were measured continuously by the ship’s meteorological instrumentation. The DGHg concentration was measured using a continuous equilibrium system where the elemental mercury in the sea water was equilibrated with a stream of gas. The DGHg concentration was calculated using DGHg=Hg-eq/k(H), where Hg-eq is the concentration of elemental mercury in the equilibrated air and k(H), is the dimensionless Henry’s law constant. The degree of saturation was determined directly from the measurements S = Hg-eq/TGHg. The water sampled had an average DGHg concentration of 58 +/- 10 fM and the average TGHg concentration was determined to 1.7 +/- 0.1 ng m(-3). The water sampled was under- and super-saturated with respect to elemental mercury covering a large range of saturation of 70 to 230% resulting in an average degree of saturation of 150 +/- 30%. Therefore, both evasion and deposition of elemental mercury were observed in the sampled water. In the light of the average flux, 2.1 +/- 1.8 pmol m(-2) h(-1), it is concluded that mostly evasion occured during the sampling period. (C) 2011 Elsevier B.V. All rights reserved.

The particulate content of samples of the surface microlayer water collected from the open water between ice floes at latitudes 88degrees to 89degreesN in August 2001 was examined by transmission electron microscopy. Concentrations varied from 2 x 10(7) ml(-1) to more than 10(14) ml(-1) although bacterial counts made in the same samples varied by only about 50%. Size distributions of the particles were also very variable with modal diameter sizes of 10 nm in some samples and 50 nm in others, the 50-nm particles appearing to be clusters of the 10 nm ones. A mucus-like material held the particles together in rafts, strings or in balls. The largest particles were compact electron-opaque aggregates of smaller particles. The particles appeared to have very similar characteristics to the "microcolloids" observed in bulk seawater in lower latitude oceans. X-ray analyses of the elements with atomic numbers >16 showed all signals to be weak, suggesting a mainly organic composition. The elements that were most commonly greater than background levels were all those associated with marine biological activity. Rapid aggregation of polymers to form colloids has been noted and is likely to be an important cause of the observed variability of particulate concentrations in the surface microlayer. The possibility of an equally rapid dispersal under the influence of ultraviolet light is raised. (C) 2004 Elsevier B.V. All rights reserved.

The fate of halocarbons, naturally produced volatile halogenated organic compounds, in young Arctic sea ice was studied to better understand the role of sea ice in halocarbon cycling. In early spring, halocarbons were measured in sea ice frozen in core holes, during 12 days of formation and freezing. In order to understand which factors govern halocarbon concentration and distribution, salinity, temperature and biological parameters were monitored in the growing sea ice. It was found that sea ice participates in the cycling of halocarbons between sea and air. Sea ice concentrations and distributions of these compounds were influenced by production in the ice, where ice-inhabiting microorganisms caused local increases in halocarbon concentrations. Moreover, the halocarbon ice concentration decrease/change with time did not follow ice salinity, suggesting that additional removal processes caused sea ice to be a source of halogens to overlying air. The net production rate of bromoform in the surface of newly frozen ice was estimated to 14 pmol L-1 d(-1) and the maximum removal rate was 18 pmol L-1 d(-1). In addition frost flowers on newly formed sea ice were identified as contributors of halocarbons to the atmosphere with halocarbon concentrations in the same order of magnitude as in sea ice brine. (C) 2013 Elsevier B.V. All rights reserved.

The common assumption that the ratio between particulate organic carbon (POC) and particulate Th-234 obtained from shallow sediment traps and filterable particles are representative of the ratio in the total particle settling flux should be treated with caution in view of well-known biases associated with tethered shallow sediment traps and the decoupling between size and settling velocity of many natural particle regimes. To make progress toward reliably constraining the POC/Th-234 ratio on truly settling particles, we have tested here a settling collection technique designed to remove any hydrodynamic bias; split flow-thin cell fractionation (SPLITT). These first results from a North Sea fjord and an open Baltic Sea time-series station indicates that the POC/Th-234 ratio on the more complete particle-settling spectrum, isolated with SPLITT, was higher than the POC/Th-234 ratio obtained simultaneously from tethered shallow sediment traps in seven out of seven parallel deployments with an average factor of 210%. The POC/Th-234 ratio from the SPLITT was either in the same range or higher than that obtained on filtered “bull’ particles. To explain this novel data we hypothesize that the slowest settling fraction is organic-matter rich and does not strongly complex Th-234 (i.e., high POC/Th-234). We suggest that this ultra-slow sinking fraction is better collected by SPLITT than with tethered sediment traps because of minimized hydrodynamic bias. This was tested using the ratio of POC/Al as a tracer of detrital mineral-ballast influenced settling velocity. The higher POC/Al ratios in SPLITT samples relative to in traps is consistent with the hypothesis that SPLITT is better suited for collecting also the slow-settling component of sinking particles. This important slow-settling component appears to here consist primarily of non-APS/TEP components of plankton exudates or other less-strongly Th-234-complexing organic matter. Further applications of the SPLITT technique are likely to return increasingly new insights on the composition (including “truly settling” POC/Th-234) of the total spectrum of particles settling out of the upper ocean. (c) 2005 Elsevier B.V. All rights reserved.

The central Arctic Ocean remains largely unexplored when it comes to the presence and cycling of mercury and its methylated forms including mono- and dimethylmercury (MMeHg and DMeHg, respectively). In this study, we quantified total Hg (Hg_T) and methylated Hg species in seawater, ice cores, snow, brine, and water from melt ponds collected during the SWEDARCTIC 2016 expedition to the Amerasian and Eurasian side of the Lomonosov Ridge. In the water column, concentrations of Hg_T, MMeHg and DMeHg ranged from 0.089 to 1.5 pM, <25 to 520 fM and from <1.6 to 160 fM, respectively. Hg_T was enriched in surface waters while MMeHg and DMeHg were low at the surface (i.e. in the polar mixed layer) and enriched at a water depth of around 200–400 m. A 1:2 ratio of DMeHg to MMeHg was observed in the water column suggesting a lower ratio in the central parts of the Arctic Ocean than what has previously been reported from other parts of the Arctic Ocean. At the ice stations, average HgT ranged from 0.97 ± 1.2 pM in the ice cores to 27 ± 17 pM in melt pond waters and average MeHg_T (total MeHg) from 28 ± 15 fM in brine to 130 ± 18 fM in melt pond water. The Hg_T observed in melt ponds and brine was an order of magnitude greater than HgT observed in surface waters and Hg_T in the upper part of the ice-cores was ~4–8 times higher HgT in comparison to lower layers. Our study suggests that ice may act as a source of Hg_T to surface waters but not to be a likely source of the methylated Hg forms. Unlike elemental Hg, DMeHg did not enrich in surface waters covered by ice. Concentrations of DMeHg observed in the ice cores and other samples collected from the ice stations were low, suggesting ice to not act as a source of DMeHg to the atmosphere nor to surface waters.

We report on the chemical saturation of CaCO(3) in the waters of the Arctic Ocean calculated from total alkalinity (AT) and total dissolved inorganic carbon (C(T)) Data based on four different expeditions are presented: International Arctic Ocean Expedition (IAOE-91), Arctic Ocean Section 94 (AOS94), Polarstern Arctic ‘96 expedition (ACSYS 96), and Joint Ocean Ice Study 97 (JOIS 97). The results show a lysocline at around 3500 in for aragonite and that most of the Arctic Ocean sea floor lies above the lysocline for calcite. The only anomaly is the low degree of saturation at the shelf break depth in the Canadian Basin seen in the sections of the AOS94 and JOIS 97 cruises, correlated with nutrient maxima and very low 0, concentration, suggesting decomposition of organic matter. The insignificant variability in degree of saturation between the deep waters of the different basins in the Arctic Ocean indicates a very low sedimentation/remineralisation of organic soft matter. (c) 2004 Elsevier B.V. All rights reserved.

Carbon system data from five expeditions over the time period of 1991 to 2005 in the central Arctic Ocean are evaluated with respect to the partial pressure of carbon dioxide in the surface waters. Nearly all waters were undersaturated with values typically below 300 mu atm. In the areas occupied during several expeditions the variability is substantial, making it unrealistic to produce a coherent pCO(2) map. The potential oceanic uptake of CO2 in the Arctic Ocean is evaluated as the difference in calculated total dissolved inorganic carbon at equilibrium with the atmosphere and that measured. The uptake capacity as computed from the undersaturation of the surface waters, although not homogenous across the separate basins, is on average 13 +/- 3 g C m(-2) within the surface mixed layer of the central Arctic Ocean. The uptake capacity is dependent on several variables and processes, many likely to change as the Arctic environment responds to different climate forcings. For instance, the projected decrease in summer sea ice cover allows for air sea equilibrium resulting in an estimated potential increase in CO2 uptake of 1.3 +/- 0.3 Tg C year(-1). Other factors influencing the uptake capacity of the surface mixed layer that are discussed in this contribution are changes in the depth of the surface mixed layer, temperature and primary production, all impacting the partial pressure of CO2. (C) 2010 Elsevier B.V. All rights reserved.

The uptake of atmospheric carbon dioxide in the water transported over the Bering-Chukchi shelves has been assessed from the change in carbon-related chemical constituents. The calculated uptake of atmospheric CO2 from the time that the water enters the Bering Sea shelf until it reaches the northern Chukchi Sea shelf slope (similar to 1 year) was estimated to be 86 +/- 22 g C m(-2) in the upper 100 m. Combining the average uptake per m(3) with a volume flow of 0.83 x 10(6) m(3) s(-1) through the Bering Strait yields a flux of 22x10(12) g C year(-1). We have also estimated the relative contribution from cooling, biology, freshening, CaCO3 dissolution, and denitrification for the modification of the seawater PCO2 over the shelf The latter three had negligible impact on PCO2 compared to biology and cooling. Biology was found to be almost twice as important as cooling for lowering the pCO(2) in the water on the Bering-Chukchi shelves. Those results were compared with earlier surveys made in the Barents Sea, where the uptake of atmospheric CO2 was about half that estimated in the Bering-Chukchi Seas. Cooling and biology were of nearly equal significance in the Barents Sea in driving the flux Of CO2 into the ocean. The differences between the two regions are discussed. The loss of inorganic carbon due to primary production was estimated from the change in phosphate concentration in the water column. A larger loss of nitrate relative to phosphate compared to the classical Delta N/Delta P ratio of 16 was found. This excess loss was about 30% of the initial nitrate concentration and could possibly be explained by denitrification in the sediment of the Bering and Chukchi Seas. (c) 2004 Elsevier B.V. All rights reserved.

Compositional studies of organic matter on the East Siberian Arctic Shelf (ESAS) suggest that different terrestrial carbon pools have different propensities for transport and/or degradation. The current study combined laboratory-based microbial degradation experiments with earlier published degradation-diagnostic composition of several classes of terrestrial biomarkers on the same sediments to investigate differences and driving forces of terrestrial organic matter (TerrOM) degradation in two biogeochemically-contrasting regimes of the ESAS. The incubation-based anaerobic degradation rates were consistently higher (by average factor of 6) in the East Siberian Sea Kolyma Paleoriver Channel (ESS-KPC) (15 mu mol CO2 g OC-1 day(-1)) compared to the Laptev Sea Buor-Khaya Bay (LS-BKB) (2.4 mu mol CO2 g OC-1 day(-1)). The reported molecular markers show similarities between the terrestrial carbon pools in the two systems, but impose contrasting degradation regimes in combination with the incubation results. For the LS-BKB, there was a strong relationship between the degradation rates and the three lignin phenol-based degradation proxies (r(2) = 0.93-0.96, p < 0.01, linear regression) and two wax lipid-based degradation proxies (r(2) = 0.71 and 0.66, p < 0.05, linear regression). In contrast, for the ESS-KPC system, there was no relationship between incubation-based degradation rates and molecular marker-based degradation status of TerrOM. A principal component analysis indicated that short-chain fatty acids and dicarboxylic acids from CuO oxidation are mainly of terrestrial origin in the LS-BKB, but mainly of marine origin in the ESS-KPC. Hence, the microbial degradation in the western (LS-BKB) system appears to be fueled by TerrOM whereas the eastern (ESS-KPC) system degradation appears to be driven by MarOM. By combining molecular fingerprinting of TerrOM degradation state with laboratory-based degradation studies on the same ESAS sediments, a picture evolves of two distinctly different modes of TerrOM degradation in different parts of the ESAS system. (C) 2014 Elsevier B.V. All rights reserved.

Dissolved methane and nitrous oxide in seawater were measured along a 6700 km transect of the North-West Passage between the North Atlantic Ocean and Beaufort Sea in the Arctic Ocean. Over- and under-saturation with respect to atmospheric equilibrium were observed for both gases. Methane and nitrous oxide were in the range of 58-528% and 82-181% saturation, respectively. Under-saturation was attributed to melt-water with low methane and nitrous oxide, while over-saturation was found under multi-year sea-ice. Elevated methane was also found in the vicinity of the marginal ice zones and the Mackenzie River plume. Our data support both water column and sedimentary sources of methane and nitrous oxide. We found first-order methane oxidation in surface seawater with a rate constant of 3.8 x 10(-3) h(-1). Based on these results and a conceptual model, we suggest that future sea-ice retreat may decrease the residence times of methane and nitrous oxide in the surface Arctic Ocean and thus enhance the sea-air flux of these climatically active gases. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.

Despite the distance from large anthropogenic emission sources, toxic mercury is transported via the atmosphere and oceans to the Southern Ocean. Seawater samples were collected at selected stations and were analysed for total mercury (HgT) (8 stations), dissolved gaseous mercury (DGM) (62 stations) and methylmercury (12 stations) during winter (Weddell Sea), spring (Weddell Sea) and summer (Amundsen and Ross Seas) in the Southern Ocean. The HgT distribution in water columns was found to not vary significantly with depth. In the Weddell Sea the average column concentration was higher in spring (2.6 +/- 1.3 pM, 2 stations) than in winter (2.0 +/- 1.0 pM, 6 stations). We hypothesize that the seasonal HgT increase is due to atmospheric deposition of particulate Hg(II) formed during atmospheric mercury depletion events (AMDEs), as well as the addition of inorganic mercury species from melting sea ice and snow. Furthermore, HgT concentrations found in this study were significantly higher than previously measured in the Southern Ocean (Cossa et al., 2011), which was hypothesized to be due to seasonal variations in atmospheric deposition. The average water column DGM concentration in the Weddell Sea was 454 +/- 254 fM in winter and 384 +/- 239 fM in spring. The lowest average DGM concentration was found in summer in the Amundsen and Ross Seas (299 +/- 137 fM). The highest observed concentration in winter was hypothesized to be caused by the larger sea ice coverage, which is known to reduce the evasion of Hg(0) from the sea surface. The average monomethylmercury (MMHg) concentration in the Weddell Sea was 60 +/- 30 fM in winter (6 stations) and 95 +/- 85 fM in spring (2 stations), showing no significant seasonal difference. In the Amundsen and Ross Seas the summer average concentration of MeHg (MMHg and dimethylmercury; DMHg) was 135 +/- 189 fM (4 stations). The highest MeHg concentration was found in modified circumpolar deep water, which is known to have high primary production. 2017 Elsevier B.V. All rights reserved.

For the first time elemental mercury in air and surface seawater was measured continuously in the remote seas of western Antarctica. A major contributor to atmospheric emissions of the toxic and globally dispersed pollutant mercury is the re-evasion from water surfaces, due to a supersaturation of dissolved gaseous mercury (DGM) in surface water. In this study the degree of saturation and mercury flux at the air-sea surface interface have been estimated from continuous measurements of gaseous elemental mercury (GEM) or total gaseous mercury (TGM) in air, DGM in surface water and meteorological parameters. The measurements were performed during winter and spring (2013) in the Weddell Sea and during summer (2010/2011) in the Bellingshausen, Amundsen and Ross Seas, and show spatial and seasonal variations. The average DGM concentration in surface water in open sea was highest during spring (12 +/- 7pg L-1) and lowest during summer (7 +/- 6.8 pg L-1), resulting in a net evasion of mercury during spring (1.1 +/- 1.6 ng m(-2)h(-1)) and a net deposition during summer (-0.2 +/- 1.3 ng m(-2)h(-1)). In open sea, higher average concentrations of GEM (or TGM) and DGM were found close to the Drake Passage compared to in the Bellingshausen and Weddell Seas. Emission sources from the South American continent, identified with back trajectories, were suggested to explain the observed variations. The yearly mercury evasion from open sea surfaces in the Southern Ocean was estimated to 30 ( -450-1700) tons, using the average (and min and max) flux rates obtained in this study. Higher DGM was measured under sea ice (19-62 pg L-1 compared to in open sea due to a capsuling effect, resulting in a theoretical prevented evasion of 520 (0-3400) tons per year. Diminishing sea ice and higher water temperatures in polar regions could result in increased mercury evasion to the atmosphere. However, the contribution of the Southern Ocean to the global modeled annual emissions of mercury from sea surfaces would probably only be a few percent. (C) 2016 Elsevier B.V. All rights reserved.

Particulate organic matter, including microorganisms, small water-insoluble particles and microaggregates, can form a substantial part of the summer aerosol over the open leads of the central Arctic Ocean. The increased presence of leads during the summer melt increases the biological activity of the region possibly resulting in accumulation of organic material, especially in the surface microlayer. Preferential microlayer enrichment of particulate and dissolved organic matter and gases might be reflected in derived aerosols. The subsurface seawater and microlayer concentrations were determined for dimethyl sulfide (DMS) and its biogenic precursor dimethylsulfoniopropionate (DMSP), dissolved combined amino acids (DCAA) and individual aminoacids, proteins, chlorophyll a (chl a) and bacterial cells as well as bacterial production. Enrichment factors and surface excess concentrations in the surface microlayer were calculated. Concentrations of particulate and dissolved DMSP, chl a-containing material, and bacterial cells were consistently enriched in arctic lead microlayers at 89 degrees N in August 2001. DMS, protein and DCAA concentrations, however, were not in excess in surface microlayers, although proteins were occasionally enriched. The average mole % DCAA composition was similar in subsurface and microlayer water. Enrichment spikes and excess concentrations followed freezing events and did not co-occur with enhanced bacterial production. (C) 2007 Elsevier B.V. All rights reserved.

Little is known regarding the distribution of volatile halogenated organic compounds (halocarbons) in Antarctic waters and their relation to biophysical variables. During the austral summer (December to January) in 2007-08 halocarbon and pigment concentrations were measured in the Amundsen (100-130 degrees W) and Ross Sea (158 degrees W-160 degrees E). In addition, halocarbons were determined in air, snow and sea ice. The distribution of halocarbons was influenced to a large extent by sea ice, and to a much lesser extent by pelagic biota. Concentrations of naturally produced halocarbons were elevated in the surface mixed layer in ice covered areas compared to open waters in polynyas and in the bottom waters of the Ross Sea. Higher concentrations of halocarbons were also found in sea ice brine compared to the surface waters. Incubations of snow revealed an additional source of halocarbons. The distribution of halocarbons also varied considerably between the Amundsen and Ross Seas, mainly due to the different oceanographic settings. For iodinated compounds, weak correlations were found with the presence of pigments indicative of Phaeocystis, mainly in the Ross Sea. Surface waters of the Amundsen and Ross Seas are a sink for bromoform (saturation anomalies, SA, -83 to 11%), whereas sea ice was found to be both a source and sink (SA -61-97%). In contrast, both surface waters and sea ice were found to be a source of chloroiodomethane (SA -6-1 200% and 91-22 000 resp.). Consequently, polar waters can have a substantial impact on global halocarbon budgets and need to be included in large-scale assessments. (C) 2012 Elsevier B.V. All rights reserved.

The Amundsen Sea, West Antarctica, is home to the most productive polynyas of the Southern Ocean, where summer primary production can reach 3 g C m(-2) d(-1). The remoteness of this region has meant that systematic studies of biogeochemistry in the Amundsen Sea polynyas have been limited, despite their importance to overall Antarctic shelf productivity and proximity to the fastest thinning glaciers on the continent. Particulate iron inputs to the productive shelf waters of the Amundsen Sea may be important to the overall bioavailability of Fe in this region of natural Fe fertilization. Here we discuss findings from the US-Swedish 2007-08 expedition aboard the I/B Oden, during which 12 stations were sampled for particulate trace metal analyses at depths of 8-800 m in the eastern and central polynyas as well as in sea ice covered waters, both on the Amundsen continental shelf and in deep waters north of the shelf break. Suspended particulate samples were collected in two size fractions, 0.45-5 mu m and >5 mu m. Particulate Fe concentrations ranged from as low as 10 pmol L-1 in open Antarctic Circumpolar Current (ACC) waters off the continental shelf to >100,000 pmol L-1 near the Crosson Ice Shelf, and were dominated by particles > 5 mu m at all stations. The relative concentrations of total particulate Fe, Al, Mn and P show the near-ubiquitous influence of crustal particles in the water column at stations on the Amundsen continental shelf. However, many samples had Fe/Al and Mn/Al ratios substantially in excess of mean crustal ratios, especially in the small size fraction (0.45-5 mu m), suggesting that more labile Fe oxyhydroxides and authigenic MnO2 phases, resulting from sediment resuspension, are also present at relatively high concentrations. In contrast, Fe/P ratios indicate that Fe associated with biogenic particles rarely accounts for more than 20% of total particulate Fe, even in offshore stations. A detailed examination of particulate elemental composition and spatial distribution in the context of water mass temperature and salinity gradients suggests that particle delivery processes associated with melting ice shelves and sediment resuspension dominate the particulate Fe sources to the Amundsen Sea water column. (C) 2013 Elsevier B.V. All rights reserved.

The short-lived thorium isotope Th-234 (half-life 24.1 days) has been used as a tracer for a variety of transport processes in aquatic systems. Its use as a tracer of oceanic export via sinking particles has stimulated a rapidly increasing number of studies that require analyses of Th-234 in both marine and freshwater systems. The original Th-234 method is labor intensive. Thus, there has been a quest for simpler techniques that require smaller sample volumes. Here, we review current methodologies in the collection and analysis of Th-234 from the water column, discuss their individual strengths and weaknesses, and provide an outlook on possible further improvements and future challenges. Also included in this review are recommendations on calibration procedures and the production of standard reference materials as well as a flow chart designed to help researchers find the most appropriate Th-234 analytical technique for a specific aquatic regime and known sampling constraints. (c) 2005 Elsevier B.V. All rights reserved.