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We develop an optical classification of marine particle assemblages from an extensive dataset of particle optical properties collected in the Chukchi and Beaufort Seas. Hierarchical cluster analysis of the spectral particulate backscattering-to-absorption ratio partitioned the dataset into seven optically-distinct clusters of particle assemblages, each associated with different characteristics of particle concentration, composition, and phytoplankton taxonomic composition and size. Three phytoplankton-dominated clusters were identified. One was characterized by small-sized phytoplankton that are typically associated with regenerated production, and comprised samples from the subsurface chlorophyll- a maximum in oligotrophic waters of the Beaufort Sea. The other two clusters represented diatom-dominated particle assemblages in turbid shelf waters with differing contributions of photoprotective pigments. Such situations are generally associated with significant new production. Two clusters were dominated by organic nonalgal material, one representing clear waters off the shelf, the other representative of post-diatom bloom conditions in the Chukchi Sea. Another distinct cluster represented mineral-dominated particle assemblages that were observed in the Colville and Mackenzie River plumes and near the seafloor. Finally, samples in a cluster of mixed particle composition were scattered throughout all locations. Optical classification improved performance of predictive bio-optical relationships. These results demonstrate a capability to discriminate distinct assemblages of suspended particles associated with specific ecological conditions from hyperspectral measurements of optical properties, and the potential for identification of ecological provinces at synoptic time and space scales from optical sensors. Analogous analysis of multispectral optical data strongly reduced this capability. [ABSTRACT FROM AUTHOR]

Seawater chromium (Cr) isotope and concentration data are presented from multiple sites in the Arctic Ocean, and three locations in the Atlantic and Pacific Oceans. A 2400-m profile illustrates the heterogeneity of δ 53 Cr in the Arctic Ocean with depth and water-mass source (Pacific vs. Atlantic). The highest δ 53 Cr values occur in Pacific-sourced waters, which also have the lowest Cr concentration. Chromium concentration and δ 53 Cr data from these locations, in conjunction with published data for the South Atlantic Ocean, yield a simple logarithmic function, as predicted by Rayleigh fractionation in a closed system. The observed Cr isotope signature is hypothesized to arise from fractionation during the reduction of Cr(VI) in surface waters and oxygen minimum zones, scavenging of isotopically light Cr(III) to deeper water and sediment, and subsequent release of this seawater-derived Cr(III) back into seawater, either as organic complexes with Cr(III) or after oxidation to Cr(VI). The isotopic fractionation factor ( ε ) associated with Cr cycling in seawater is estimated to be − 0.80 ± 0.03 ‰ ( 2 σ ) . Samples from the sea-ice affected Surface Mixed Layer of the Arctic Ocean (∼10 m depth) deviate from the general trend, and samples proximal to rivers illustrate geographic variation in δ 53 Cr values for continental runoff, but prompt loss of this signature away from the source. [ABSTRACT FROM AUTHOR]

Isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGTs) and grain size distribution were investigated in surface sediments from the western Arctic Ocean including the Chukchi Sea and the adjacent northern Bering Sea to understand their source and transportation in the Arctic region and test environmental proxies derived from the GDGT composition. Coarse sediments such as sand and silty sand are distributed in the Yukon and Mackenzie River estuaries, the northern Bering Sea near Bering Strait, and some areas of the outer shelf of the Bering Sea. In the Chukchi Sea, silt, grading from sandy to clayey silt, predominates and becomes finer northward towards the deep Arctic Ocean Isoprenoid GDGTs are abundant on the outer shelf and slope of the Chukchi Sea and the upper slope of the Bering Sea. The higher abundances are attributed to a combination of higher production of marine Archaea (Thaumarchaeota) at the shelf edge, redeposition of GDGT-carrying fine particles, and better preservation of GDGTs at sites with higher sedimentation rates. The TEX 86 - and TEX 86 L -derived temperatures are not consistent with sea surface temperatures in the study area, with unrealistically high TEX 86 - and TEX 86 L -derived temperatures in samples north of 73 °N probably biased by factors other than temperature. Branched GDGTs are abundant on the Chukchi shelf and in the Yukon and Mackenzie River estuaries. At the shelf edge of the Chukchi Sea, both branched and isoprenoid GDGTs are abundant, indicating common concentration processes such as sediment redeposition and efficient preservation at sites with high sedimentation rates. Sediments from the western Arctic Ocean north of 75 °N, the Yukon and Mackenzie River estuaries, and the Yukon River have higher cyclization ratio of branched tetraethers (CBT) than sediments from the Chukchi and Bering Seas, suggesting two different sources of branched GDGTs inferred as soil and marine bacteria. [ABSTRACT FROM AUTHOR]

Despite the important roles of shallow-water sediments in global biogeochemical cycling, the effects of ocean acidification on sedimentary processes have received relatively little attention. As high-latitude cold waters can absorb more CO2 and usually have a lower buffering capacity than warmer waters, acidification rates in these areas are faster than those in sub-tropical regions. The present study investigates the effects of ocean acidification on sediment composition, processes and sediment-water fluxes in an Arctic coastal system. Undisturbed sediment cores, exempt of large dwelling organisms, were collected, incubated for a period of 14 days, and subject to a gradient of pCO2 covering the range of values projected for the end of the century. On five occasions during the experimental period, the sediment cores were isolated for flux measurements (oxygen, alkalinity, dissolved inorganic carbon, ammonium, nitrate, nitrite, phosphate and silicate). At the end of the experimental period, denitrification rates were measured and sediment samples were taken at several depth intervals for solid-phase analyses. Most of the parameters and processes (i.e. mineralization, denitrification) investigated showed no relationship with the overlying seawater pH, suggesting that ocean acidification will have limited impacts on the microbial activity and associated sediment-water fluxes on Arctic shelves, in the absence of active bio-irrigating organisms. Only following a pH decrease of 1 pH unit, not foreseen in the coming 300 years, significant enhancements of calcium carbonate dissolution and anammox rates were observed. Longer-term experiments on different sediment types are still required to confirm the limited impact of ocean acidification on shallow Arctic sediment processes as observed in this study. [ABSTRACT FROM AUTHOR]

Abstract: In addition to ocean acidification due to a gradual anthropogenic CO2 uptake, strong seasonal variations in the carbonate system occur in the Arctic Ocean as a result of physical and biological processes. Understanding this seasonal variability is critical for predicting the onset of calcium carbonate mineral (Ω) undersaturation with increasing atmospheric CO2 concentrations. However, these variations are currently poorly understood because of a lack of winter data due to the challenging field conditions in this season. Here we report observations over an annual cycle of the carbonate system of surface waters in the Atlantic gateway to the Arctic Ocean, covering the region between Svalbard and mainland Norway. Dissolved inorganic carbon (DIC) concentrations ranged from 2137–2148μmolkg−1 in winter to 1986–2094μmolkg−1 in summer, and total alkalinity (TA) concentrations between 2312–2341μmolkg−1 in winter and 2199–2317μmolkg−1 in summer. This resulted in an increase in TA:DIC ratios from 1.077–1.090 in winter to 1.106–1.112 in summer, mainly due to the biological uptake of CO2 during spring and summer. Similarly, a significant seasonal variability was observed in Ω (0.4–0.9), with lowest saturation states in winter (Ωaragonite ~1.8–2.1) and highest in spring and summer (Ωaragonite ≈2.4). Analysis of the biogeochemical and physical processes that impact aragonite saturation states (Ωar) showed biological production to be the most important factor driving seasonal variability in Ωar in this area, accounting for 45–70% of the difference between winter and summer values. Future changes in these processes may alter the seasonal cycle of the carbonate system in both amplitude and timing, and further observations are required to determine the progress of ocean acidification in the Atlantic waters entering the Arctic Ocean. [Copyright &y& Elsevier]

The climatically-important compound dimethylsulfide (DMS) has been reported to be abundant in the Arctic, particularly in the marginal sea ice zone. Due to these high concentrations, it may play an important role in climate control. A DMS monthly climatology for July through October was created employing various ocean characteristics and spatial modeling techniques commonly used for describing species distributions in ecology. Comparisons between observed and predicted values of surface seawater DMS concentrations led to r values of 0.61, 0.87, 0.66, and 0.37 for July, August, September, and October, respectively. Measurement data used for model development for July through October were variably distributed spatially. For October only, data were sparse and clustered, resulting in the poor results obtained for this month. Mean sea ice concentration and surface nitrate concentrations were found to be important predictors of surface seawater DMS concentrations. A negative relationship between sea ice concentration and DMS, and a two-phase relationship between nitrate and DMS were found. The two-phase relationship may be indicative of how DMS concentrations are affected when nitrate is the limiting nutrient. From July to September, predicted DMS concentrations were generally lowest under the sea ice. High monthly DMS concentrations (up to 10.7 nM) were predicted in the seasonal ice zone. The highest DMS concentrations in September (~2.6 nM) were predicted along the ice edge. In order to create more accurate climatologies and to increase our understanding of sulfur cycling in the Arctic, a higher spatial and temporal distribution of DMS measurements is required. [ABSTRACT FROM AUTHOR]

Abstract: As part of the ARK-XXII/2 Polarstern expedition in summer 2007, dissolved Ba was analyzed in the Eurasian Basins and the Makarov Basin including the Alpha and Mendeleyev Ridges as well as on the adjacent shelves. The data was compared with data of dissolved Al and Si from the same cruise. Superimposed on the gradual increase of concentration with depth by dissolution of the particle rain, we observe different flow patterns in intermediate waters along the track. In the Atlantic and Intermediate Depth Water (AIDW) in the Amundsen Basin the influence from Eurasian shelf water can be seen in slightly enhanced concentrations of dissolved Ba compared with Al and Si. At the same time Al concentrations decrease with distance from the Eurasian shelves. Source waters to the Atlantic Layer Water (ALW) in the Makarov Basin have the same background Ba concentrations as the Nansen AIDW. We describe the distributions of the elements in the Deep Eurasian and Bottom Water (DEBW) by deep shelf convection as well as diffusion from sediments controlling concentrations in the Nansen DEBW while in the Amundsen DEBW diffusion from sediments appears to be more important. In the Makarov Basin inflow from the Canadian Basin and overflow from the Amundsen Basin at 2000m depth at the Lomonosov Ridge are required to explain the composition of bottom waters. [Copyright &y& Elsevier]

Abstract: Dissolved barium has been shown to have the potential to distinguish Eurasian from North American (NA) river runoff. As part of the ARK-XXII/2 Polarstern expedition in summer 2007, Ba was analyzed in the Barents, Kara, Laptev seas, and the Eurasian Basins as well as the Makarov Basin up to the Alpha and Mendeleyev Ridges. By combining salinity, δ18O and initial phosphate corrected for mineralization with oxygen (PO4*) or N/P ratios we identified the water mass fractions of meteoric water, sea ice meltwater, and marine waters of Atlantic as well as Pacific origin in the upper water column. In all basins inside the lower halocline layer and the Arctic intermediate waters we find Ba concentrations close to those of the Fram Strait branch of the lower halocline (41–45nM), reflecting the composition of the incoming Atlantic water. A layer of upper halocline water (UHW) with higher Ba concentrations (45–55nM) is identified in the Makarov Basin. Atop of the UHW, the Surface Mixed Layer (SML), including the summer and winter mixed layers, has high concentrations of Ba (58–67nM). In the SML of the investigated area of the central Arctic the meteoric fraction can be identified by assuming a conservative behavior of Ba to be primarily of Eurasian river origin. However, in productive coastal regions biological removal compromises the use of Ba to distinguish between Eurasian and NA rivers. As a consequence, the NA river water fraction is underestimated in productive surface waters or waters that have passed a productive region, whereas this fraction is overestimated in subsurface waters containing remineralised Ba, particularly when these waters have passed productive shelf regions. Especially in the Laptev Sea and small regions in the Barents Sea, Ba concentrations are low in surface waters. In the Laptev Sea exceptionally high Ba concentrations in shelf bottom waters indicate that Ba is removed from surface waters to deep waters by biological activity enhanced by increasing ice-free conditions as well as by scavenging by organic matter of terrestrial origin. We interpret high Ba concentrations in the UHW of the Makarov Basin to result from enrichment by remineralisation in bottom waters on the shelf of the Chukchi Sea and therefore the calculated NA runoff is an artefact. We conclude that no NA runoff can be demonstrated unequivocally anywhere during our expedition with the set of tracers considered here. Small contributions of NA runoff may have been masked by Ba depletion and could only be resolved by supportive tracers on the uptake history. We thus suggest that Ba has to be used with care as it can put limits but not yield quantitative water mass distributions. Only if the extra Ba inputs exceed the cumulative biological uptake the signal can be unequivocally attributed to NA runoff. [Copyright &y& Elsevier]

Abstract: Here we report the first optical, sensor-based profiles of nitrate from the central Makarov and Amundsen and southern Canada Basins of the Arctic Ocean. These profiles were obtained as part of the International Polar Year program during spring 2007 and 2008 field seasons of the North Pole Environmental Observatory (NPEO) and Beaufort Gyre Exploration Program (BGEP). These nitrate data were combined with in-situ, sensor-based profiles of dissolved oxygen to derive the first high-resolution vertical NO profiles to be reported for the Arctic Ocean. The focus of this paper is on the halocline layer that insulates sea ice from Atlantic water heat and is an important source of nutrients for marine ecosystems within and downstream of the Arctic. Previous reports based on bottle data have identified a distinct lower halocline layer associated with an NO minimum at about S=34.2 that was proposed to be formed initially in the Nansen Basin and then advected downstream. Greater resolution afforded by our data reveal an even more pronounced NO minimum within the upper, cold halocline of the Makarov Basin. Thus a distinct lower salinity source ventilated the Makarov and not the Amundsen Basin. In addition, a larger Eurasian River water influence overlies this halocline source in the Makarov. Observations in the southern Canada Basin corroborate previous studies confirming multiple lower halocline influences including diapycnal mixing between Pacific winter waters and Atlantic-derived lower halocline waters, ventilation via brine formation induced in persistent openings in the ice, and cold, O2-rich lower halocline waters originating in the Eurasian Basin. These findings demonstrate that continuous sensing of chemical properties promises to significantly advance understanding of the maintenance and circulation of the halocline. [ABSTRACT FROM AUTHOR]

The article offers information on the Arctic Ocean data in the CARbon IN the Atlantic (CARINA). It offers guidelines for quality controlling chosen parameters within the Arctic Ocean data included in the CARINA data set and checking for offsets between the individual cruises. It reports the main method in determining offsets between cruises includes regional multi-linear regression, after a first rough basin-wide deep-water estimate of each parameter.

The article offers information on the Nordic Seas and Arctic Ocean chlorofluorocarbon (CFC) data in CARbon IN the Atlantic (CARINA). It presents an overview of the quality control of the CFC data for the Arctic Mediterranean Seas region. It highlights the combination of tools for the secondary quality control of the CFCs including the evaluation of depth profiles and CFC ratios, surface saturations, and crossover analysis.

The article discusses the quality control (QC) procedures and methods of the CARbon IN the Atlantic (CARINA) database used to investigage the carbon relevant hydrographic and hydrochemical parameters in the Artic, Atlantic and Southern Ocean. Technical details of the QC and tools which have been developed and used in the project are given, including procedures for crossover analysis and least square models. It provides an overview of the methods and techniques used for the QC of the database.

Abstract: Molecular organic biomarkers together with trace element composition were investigated in sediments east of Barrow Canyon in the western Arctic Ocean to determine sources and recycling of organic carbon in a continuum from the shelf to the basin. Algal biomarkers (polyunsaturated and short-chain saturated fatty acids, 24-methylcholesta-5,24(28)-dien-3β-ol, dinosterol) highlight the substantial contribution of organic matter from water column and sea-ice primary productivity in shelf environments, while redox markers such as acid volatile sulfide (AVS), Mn, and Re indicate intense metabolism of this material leading to sediment anoxia. Shelf sediments also receive considerable inputs from terrestrial organic carbon, with biomarker composition suggesting the presence of multiple pools of terrestrial organic matter segregated by age/lability or hydrodynamic sorting. Sedimentary metabolism was not as intense in slope sediments as on the shelf; however, sufficient labile organic matter is present to create suboxic and anoxic conditions, at least intermittently, as organic matter is focused towards the slope. Basin sediments also showed evidence for episodic delivery of labile organic carbon inputs despite the strong physical controls of water depth and sea-ice cover. Principal components analysis of the lipid biomarker data was used to estimate fractions of preserved recalcitrant (of terrestrial origin) and labile (of marine origin) organic matter in the sediments, with ranges of 12–79%, 14–45%, and 37–66% found for the shelf, slope, and basin cores, respectively. On average, the relative preserved terrestrial organic matter in basin sediments was 56%, suggesting exchange of organic carbon between nearshore and basin environments in the western Arctic. [Copyright &y& Elsevier]

Arctic seawater concentrations of two currently used pesticides, endosulfan and γ-HCH, were collated from a variety of cruises undertaken throughout the 1990s up to 2000 for different regions of the Arctic Ocean. Surface seawater concentrations for α- and β-endosulfan ranged from <0.1– 8.8 (mean 2.3) pg/L and 0.1–7.8 (mean 1.5) pg/L, while γ-HCH concentrations were ∼100 fold higher than α-endosulfan, ranging between <0.70 and 894 (mean 250) pg/L. Geographical distributions for α-endosulfan revealed the highest concentrations in the western Arctic, specifically in the Bering and Chukchi Seas with lowest levels toward the central Arctic Ocean. In contrast, γ-HCH revealed higher concentrations toward the central Arctic Ocean, with additional high concentrations in the coastal regions near Barrow, Alaska and the White Sea in northwest Russia, respectively. A fugacity approach was employed to assess the net direction of air-water transfer of these two pesticides, using coupled seawater and air concentrations. For a-endosulfan, water-air fugacity ratios (FR) were all <1 indicating netdepositionto all regions of the Arctic Ocean, with the lowest values (0.1–0.2) evident in the Canadian Archipelago. Given the uncertainty in the temperature- adjusted Henry's Law constant (factor ∼10), it is plausible that equilibrium may have been reached for this compound in the western fringes of the Arctic Ocean where the highest water concentrations were observed. Similarly, FR values for γ-HCH were generally <1 and in agreement with other separate studies, although, like α-endosulfan, net deposition predominated over the Canadian Archipelago. In the central and eastern regions of the Arctic Ocean, as well as in the two coastal areas of this study, the fugacity ratios for γ-HCH where -∼1 indicating conditions approaching equilibrium. The elevated water concentrations and higher FRs in these coastal areas support the assessment that riverine/coastal sources are important for this chemical, but less so for α-endosulfan for which air to water transfer during the ice-free summer months is likely to be the major contemporary source to the Arctic. It is recommended that archived extracts of river water be reanalyzed for α-endosulfan to confirm this. [ABSTRACT FROM AUTHOR]

Abstract: A physical–chemical–biological model of the Barents Sea is used to simulate the necessary conditions for primary production. The model is validated to in situ current measurements and temperature fields, and is compared with physical and chemical data from a section across the central part of the basin. The results show that the section is placed in a region with mesoscale variability and significant horizontal gradients. The results are therefore sensitive not only to forcing conditions, but to the growth of instabilities. Alternatives for interpreting the field data are suggested. An example of a “hidden” feature only a few grid points away suggests that a different approach combining the spatial and temporal variabilities may allow for a better validation. [Copyright &y& Elsevier]

Abstract: We report on the chemical saturation of CaCO3 in the waters of the Arctic Ocean calculated from total alkalinity (A T) and total dissolved inorganic carbon (CT). 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 m 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 O2 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. [Copyright &y& Elsevier]

We report concentrations of 231Pa, 230Th, and 232Th measured in unfiltered seawater samples from three stations occupied during the 1994 Arctic Ocean Section; at the western edge of the Canada Basin, in the Makarov Basin, and in the Amundsen Basin at the North Pole. The North Pole data agree well with previously published profiles from the Amundsen Basin. 230Th and 231Pa concentrations in the Canada and Makarov Basins are intermediate between those reported previously for the Beaufort Sea and the Alpha Ridge, reinforcing the observation that scavenging rates are variable in the western and central Arctic and can be as rapid as in the Eurasian Basin and other oceans. Thorium-232 data indicate that relatively high rates of scavenging under the permanent ice cover are driven at least in part by offshore transport of detrital particulate material. A comparison of water column 230Th 231Pa ratios throughout the Arctic suggests that there may be little basin-scale fractionation of these two isotopes in this ocean, contrary to expectations based on the relatively large area of the continental shelves and their contrasts with the deep basins. Models of shelf–basin exchange and 230Th/231Pa scavenging, incorporating available constraints, support this suggestion and point to the need for more data from the Arctic shelves, where the imprint of Th/Pa fractionation, if any, is expected be most pronounced. [Copyright &y& Elsevier]

The article discusses the prospective effect of global warming on phytoplankton in ocean water affected by sea ice meltwater and river runoff. The authors predict that the smallest phytoplankton cells in the Arctic Ocean will thrive while larger ones will not. It notes ocean stratification conditions and chemistry that will change with global warming. The authors compare and contrast upper-ocean bacterio-plankton, picophytoplankton, and larger nanoplankton and their responses to ocean temperature changes. Biomass in the forms of chlorophyll and fucoxanthin is discussed.