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Abstract: During the R/V Xuelong Arctic cruise in summer 2008, we investigated bacterioplankton and picophytoplankton abundance, biomass, spatial distribution, and these variables'' relationship with environmental variables in the Western Canada Basin. The bacterioplankton and picophytoplankton abundances in the upper 200m of the water column were 0.17–8.38×105 cellsml−1 and 0.01–17.71×106 cellsL−1, respectively. The average integrated bacterioplankton and picophytoplankton biomasses in the upper 100m of the water column were 413.3 and 118.8mgCm−2, respectively. Microbial biomass was comparable with previous reports and distributed mainly in the upper 50m of the water column. The bacterioplankton and picophytoplankton biomasses decreased with increasing latitude. Compared with eastern transects, which were strongly influenced by an influx of Pacific water, the western transects had relatively low temperature, high salinity, high nutrients, and high biomass. No significant relationships were detected between assemblages and water temperature or salinity, expect for one between bacterioplankton and salinity in the latitudinal transects. However, a significant negative correlation between picophytoplankton and nutrients and a significant positive correlation between bacterioplankton and picophytoplankton were observed. We suggest that this was mainly caused by the relatively low picophytoplankton biomass, occurrence of heavy stratification (nutricline), and the subsurface chlorophyll maxima (SCM) in study area. Heavy melting of sea ice in summer increases the stratification, which obstructs nutrient supplementation from deep waters, and this might increase the role of microbial assemblages in the upper water column in the Arctic basin area. [Copyright &y& Elsevier]

Geochemical observations of continental outcrops and marine sediments provide insights into the nature of bedrock and erosion in Antarctica. The accelerated melt of ice shelves has increased the flux of terrigenous materials to the marginal seas and has changed the sedimentological environment. We characterized the provenance of the surficial fine-grained detrital sediments in the front ends of major ice shelves in the Amundsen Sea, Ross Sea, and Prydz Bay sections through comparisons to proximal rocks using the elemental compositions, as well as the Sr and Nd isotopic compositions, of the clay-size (<2 μm) fraction, rock samples, and bulk sediments and some residual fractions. The results show that the 87Sr/86Sr ratios of clay-size sediments range from 0.70962 to 0.71662, 0.70936 to 0.71960, and 0.72569 to 0.73492, and that the εNd values range from −2.1 to +0.8, −10.9 to −1.43, and −22.3 to −17. 3 in the Amundsen Sea, Ross Sea, and Prydz Bay, respectively, while those of rocks range from 0.70350 to 0.77080 and from 5.1 to −22.4 in all three areas. Elemental compositions of both bulk sediments and the clay-size fraction in the Western Ross Sea have similar patterns to those in Prydz Bay, showing that most major elements (e.g., Mg, Ca, and Fe) are lower than in the upper continental crust (UCC). Chondrite-normalized rare earth elements (REEs) are highest in the bulk sediments of the Amundsen Sea and lowest in the clay-size fraction of all three sections. We concluded that clay-size sediments in the Western Amundsen Sea shelf are largely from the Eastern Amundsen Sea coastal area, while some sediments reflect contributions from the Hobbs Coast due to gravitational currents. The Western Ross Sea can receive sediments from both East Antarctica and West Antarctica, while the clay-size fractions of western sites in Transect R (a latitudinal transect near Inexpressible Island, East Antarctica) in this study are mainly from southeastern Victoria Land, transported northward by bottom currents. The contribution from coarse ice-rafted debris (IRD) is minor, possibly because of blocking by the Drygalski Ice Tongue. The clay-size sediments of Eastern Prydz Bay are largely contributed by Princess Elisabeth Land and western Wilhelm II Land, while those in Western Prydz Bay are possibly derived from the Lambert-Amery Ice Shelf system and the western coast. These very fine-grained sediments are generally affected by oceanic currents (e.g., Antarctic Coastal Currents and Antarctic Bottom Currents). Most residual fraction show very similar εNd values to the bulk of clay-size sediments. It indicates that authigenic phases are generally sourced from similar regions to the silicate component of clay-size sediments. [ABSTRACT FROM AUTHOR]

Twenty-four repeat hydrographic transects occupied across Barrow Canyon from 2010 to 2013 are used to study the seasonal evolution of water masses in the canyon from July–October as well as the occurrence of upwelling. The mean sections revealed that the Alaskan coastal water is mainly confined to the eastern flank of the canyon, corresponding to a region of sloped isopycnals indicative of the surface-intensified Alaskan Coastal Current which advects the water. The Pacific-origin winter water is found at depth, banked against the western flank of the canyon. Its isopycnal structure is consistent with a bottom-intensified flow of this dense water mass out of the canyon. For the months that were sampled, the Alaskan coastal water is most prevalent in August and September, while the coldest winter water is observed in the month of August. It is argued that this newly ventilated winter water is delivered to the canyon via pathways on the central Chukchi Shelf, as opposed to the coastal pathway. Roughly a third of the hydrographic sections were preceded by significant up-canyon winds and hence were deemed to be under the influence of upwelling. During these periods, anomalously salty water is found throughout the eastern flank of the canyon, and, on occasion, Atlantic water fills the deepest part of the section. Using atmospheric reanalysis data, it is shown that upwelling occurs when the Beaufort High is strengthened and the Aleutian Low is deepened. Two modes of storm tracks were identified: northward progressing storms (mode 1) and eastward progressing storms (mode 2), both of which can drive upwelling. Mode 1 is prevalent in July–August, while mode 2 is more common in September–October. These seasonal patterns appear to be dictated by regional variations in blocking highs. [ABSTRACT FROM AUTHOR]

Ice melting in the Antarctic summer and upwelling of the Circumpolar Deep Water (CDW) near the Antarctic continent have been suggested to regulate the distributions of microbial communities. However, an understanding of these relationships in the Indian Ocean sector of East Antarctica is lacking. We report on the distribution and relationships of virio- and picoplankton at 77 stations (including 29 stations throughout the entire water column and 48 stations from the epipelagic zone) from 35° to 78°E and 62° to 70°S, covering the Cosmonaut Sea, Cooperation Sea and Prydz Bay. The epipelagic stations were grouped into four clusters based on the virio- and picoplankton composition and abundance. Clusters three and four, which corresponded with areas of upwelling and ice retreat, had high abundances of autotrophic picoeukaryotes; this resulted in subsequent high abundances of heterotrophic prokaryotes and virioplankton. Cluster one and two stations correspond with a high nutrient, low chlorophyll (HNLC) area, where the abundances of autotrophic and heterotrophic picoplankton are low. Viruses were significantly correlated with heterotrophic prokaryotes in the ice-covered areas but more strongly correlated with autotrophic picoeukaryotes in areas associated with ice-edge blooms. Throughout the water column in the Cooperation Sea, nutrient supply from the upwelling of the CDW induced an increased abundance of heterotrophic prokaryotes, particularly in the meso- and bathypelagic zones of stations in the northern part of the area. High viral abundances were detected in the meso- and bathypelagic zones of stations with high abundances of virio- and picoplankton in the epipelagic zone. This study shows that the summer distribution of virio- and picoplankton in the Indian Ocean sector of East Antarctica was mainly controlled by ice-melting and upwelling of the CDW. [ABSTRACT FROM AUTHOR]

Abstract: Phytoplankton carbon and nitrogen production in newly opened waters of the Western Arctic Ocean were measured using a 13C–15N dual isotope tracer technique in summer 2008, when Arctic sea ice was at its second lowest extent since 1979. Daily integrated carbon-uptake rates were highest (675.8±931.3mgCm–2 d–1) in ice-free shelf regions of the Chukchi Sea. In deeper regions, the daily integrated carbon-uptake rates (73.5±45.0mgCm–2 d–1) in newly opened deep waters with adjacent sea ice cover (10–90%) were significantly higher than those (32.0±22.8mgCm–2 d–1) in ice-free deep waters. The average contributions of small cell-size phytoplankton (0.7–5μm) to total carbon-uptake rates were 19.8%, 62.8%, and 55.5% in shelf regions, ice-free deep waters, and newly opened waters, respectively, although the average biomass contributions of the small phytoplankton was 54.9–96.5% of total algal biomass in the three study areas. Daily total nitrogen-uptake rates were similar between newly opened deep waters and ice-free deep waters, although nitrate assimilation rates were higher in newly opened waters compared to ammonium uptake rates in ice-free waters. Lower carbon- and nitrate-assimilation rates in ice-free waters were due to strong stratification in the euphotic layer caused by melted sea ice, which limited nutrient availability to phytoplankton, although phytoplankton had greater light availability in ice-free waters than in newly opened waters. [Copyright &y& Elsevier]