The Amundsen Sea Polynya International Research Expedition (ASPIRE)

In search of an explanation for some of the greenest waters ever seen in coastal Antarctica and their possible link to some of the fastest melting glaciers and declining summer sea ice, the Amundsen Sea Polynya International Research Expedition (ASPIRE) challenged the capabilities of the US Antarctic Program and RVIB Nathaniel B. Palmer during Austral summer 2010–2011. We were well rewarded by both an extraordinary research platform and a truly remarkable oceanic setting. Here we provide further insights into the key questions that motivated our sampling approach during ASPIRE and present some preliminary findings, while highlighting the value of the Palmer for accomplishing complex, multifaceted oceanographic research in such a challenging environment

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

Dynamics of dissolved iron and other bioactive trace metals (Mn, Ni, Cu, Zn) in the Amundsen Sea Polynya, Antarctica

Abstract The Amundsen Sea Polynya is experiencing large increases in glacial meltwater input and hosts an extremely productive and long-lasting summer phytoplankton bloom, suggesting a crucial role for natural Fe fertilization. Early summer distributions and dynamics of the dissolved bioactive metals Fe, Mn, Zn, Cu and Ni were investigated during a three week period in 2010–2011, using GEOTRACES-compliant methods. Dissolved Fe was very low (0.06–0.12 nmol kg−1) in the upper 20 m of the central polynya, suggesting that the sub-maximal rates of in situ primary productivity reported previously for this growth phase of the bloom are attributable to insufficient Fe availability. Weeks after the sampling period, phytoplankton biomass accumulated to peak bloom conditions, implying a continuous supply of bioavailable Fe to the euphotic zone. The dominant biologically-relevant Fe source was meltwater-enriched seawater flowing from the Dotson Ice Shelf cavity and delivering Fe at 0.7 nmol kg−1 to the broader polynya. The modest Fe content of Circumpolar Deep Water (CDW; 0.3 nmol kg−1), invading through cross-shelf troughs, was strongly augmented by benthic Fe inputs, which may combine with glacial meltwater dFe in the Dotson outflow. Sea ice melting provided a modest local Fe flux, insufficient to drive large annual blooms. Dissolved Mn was strongly reduced in surface waters, but displayed a subsurface maximum likely advected through the region from shallow coastal sediments. Nutrient-type elements Zn, Cu and Ni had large to small dynamic ranges, respectively, and increasing concentrations with depth, indicating uptake and remineralization within the polynya system. Surface water drawdown ratios of metals and nutrients provided novel estimates of metal quotas (metal/P) for the dominant bloom phytoplankton, Phaeocystis antarctica. At one unique mature bloom station, Zn and Cu were scavenged to low concentrations throughout the 350 m water column, a possible result of intense removal onto sinking Phaeocystis biodetritus. The Amundsen Sea appears to be a model region for studying the biogeochemical consequences of increased glacial meltwater inputs

Sources and fluxes of dissolved iron in the Bellingshausen Sea (West Antarctica): The importance of sea ice, icebergs and the continental margin

This study was conducted to estimate the potential for natural iron fertilization in the Bellingshausen Sea, a remote region in the Pacific sector of the Southern Ocean. Seawater samples were collected during early austral spring 2007 near the continental margin, in the wake of an iceberg and near Peter I Island in order to identify and quantify Fe sources to the upper ocean. We concomitantly collected sea ice cores for Fe analysis during a time series sampling program on an ice floe. Looking at the upper 200m, our seawater data together with other published data suggest a large-scale exponential meridional decrease of DFe concentrations with increasing distance from the coastline noticeable up to 1400km to the north into the ACC. From this DFe gradient we estimated DFe fluxes into the upper mixed layer of the Bellingshausen Sea using a simple one-dimensional horizontal and vertical diffusion/advection model. We also estimated the melting input from sea ice and icebergs. DFe fluxes were compared for three biogeochemical provinces: ice covered continental shelf, marginal ice zone near the continental margin, and the open ocean. Fe in sea ice decreased with time enabling us to estimate a melt flux of 0.3μmol/m2/d DFe. We found that going from the continental shelf to the open ocean the dominant Fe fluxes gradually change from horizontal advection on the continental shelf (54% of a total DFe flux of 7.6±5.0μmol/m2/d) via sea ice melt in the pack ice near the continental margin (56% of a total DFe flux of 0.55±0.18μmol/m2/d) to vertical advection (58% of a total DFe flux of 0.038±0.027μmol/m2/d) in the ice free open ocean. A significant DFe flux of 0.6μmol/m2/d was estimated for iceberg melting, but this flux took place below the upper mixed layer and was not taken into further account. Fueling the high horizontal flux on the continental shelf is likely benthic diffusion and sediment resuspension. This is indicated by enhanced total dissolvable Fe (TD-Fe) and dissolved Fe (DFe) in the upper 200m close to Peter I Island, and near the seafloor at the other stations. Also mid-depth TD-Fe increases near the continental margin were observed.Comparison of estimates of biogenic Fe fixation (based on estimates for Southern Ocean carbon fixation) with the fluxes computed here, indicates an excess of new DFe input on the continental shelf and increasing Fe limitation going from the continental margin towards the open ocean.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

The role of polynyas on the atmospheric budget of methane

info:eu-repo/semantics/inPres

An exceptional winter sea-ice retreat/advance in the Bellingshausen Sea, Antarctica

The exceptional sea-ice retreat and advance that occurred in the Bellingshausen Sea, Antarctica during August 1993 was the largest such winter event in this sector of the Antarctic during the satellite era. The reasons for this fluctuation of ice are investigated using passive microwave satellite imagery, ice motion vectors derived from the satellite data, in-situ meteorological reports and near-surface winds and temperatures from the European Centre for Medium-range Weather Forecasts (ECMWF) numerical weather prediction model. The ice edge retreat of more than 400 km took place near 80degreesW from approximately 1-15 August, although the southward migration of the ice edge was not continuous and short periods of advance were also recorded. Between 16 August and 2 September there was almost continuous sea-ice recovery. The rate of change of the ice edge location during both the retreat and advance phases significantly exceeded the southward and northward velocity components of ice within the pack, pointing to the importance of ice production and melting during this event. During the month, markedly different air masses affected the area, resulting in temperature changes from +2degreesC to -21degreesC at the nearby Rothera station. 'Bulk' movement of the pack, and compaction and divergence of the sea ice, made a secondary, but still significant, contribution to the observed advance and retreat. The ice extent fluctuations were so extreme because strong meridional atmospheric flow was experienced in a sector of the Southern Ocean where relatively low ice concentrations were occurring. The very rapid ice retreat/advance was associated with pronounced low-high surface pressure anomaly couplets on either side of the Antarctic Peninsula

Local controls on sediment accumulation and distribution in a fjord in the West Antarctic Peninsula: implications for palaeoenvironmental interpretations

We analyse surface sediment and its distribution in Flandres Bay, West Antarctic Peninsula, in order to understand modern day sediment dispersal patterns in a fjord with retreating, tidewater glaciers. The surface sediment descriptions of 41 cores are included in this study. The sediment facies described include muddy diatomaceous ooze, diatomaceous mud, pebbly mud, sandy mud and mud, with scattered pebbles present in most samples. In contrast to a traditional conceptual model of glacial sediment distribution in fjords, grain size in Flandres Bay generally coarsens from the inner to outer bay. The smallest grain size sediments were found in the bay head and are interpreted as fine-grained deposits resulting from meltwater plumes and sediment gravity flows occurring close to the glacier front. The middle of the bay is characterized by a high silt percentage, which correlates to diatom-rich sediments. Sediments in the outer bay have a high component of coarse material, which is interpreted as being the result of winnowing from currents moving from the Bellingshausen Sea into the Gerlache Strait. Palaeoenvironmental reconstructions of glacial environments often use grain size as an indicator of proximity to the ice margin. After a detailed analysis of a large number of cores collected in the study area, our findings highlight the variability in sedimentation patterns within a fjord and provide a valuable evidence of the complexity that may occur in the sedimentary record