Foehn winds link climate-driven warming to ice shelf evolution in Antarctica

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Atmospheres 120 (2015): 11,037–11,057, doi:10.1002/2015JD023465.Rapid warming of the Antarctic Peninsula over the past several decades has led to extensive surface melting on its eastern side, and the disintegration of the Prince Gustav, Larsen A, and Larsen B ice shelves. The warming trend has been attributed to strengthening of circumpolar westerlies resulting from a positive trend in the Southern Annular Mode (SAM), which is thought to promote more frequent warm, dry, downsloping foehn winds along the lee, or eastern side, of the peninsula. We examined variability in foehn frequency and its relationship to temperature and patterns of synoptic-scale circulation using a multidecadal meteorological record from the Argentine station Matienzo, located between the Larsen A and B embayments. This record was further augmented with a network of six weather stations installed under the U.S. NSF LARsen Ice Shelf System, Antarctica, project. Significant warming was observed in all seasons at Matienzo, with the largest seasonal increase occurring in austral winter (+3.71°C between 1962–1972 and 1999–2010). Frequency and duration of foehn events were found to strongly influence regional temperature variability over hourly to seasonal time scales. Surface temperature and foehn winds were also sensitive to climate variability, with both variables exhibiting strong, positive correlations with the SAM index. Concomitant positive trends in foehn frequency, temperature, and SAM are present during austral summer, with sustained foehn events consistently associated with surface melting across the ice sheet and ice shelves. These observations support the notion that increased foehn frequency played a critical role in precipitating the collapse of the Larsen B ice shelf.National Science Foundation Office of Polar Programs Grant Numbers: ANT-0732983, ANT-0732467, ANT-0732921; NSF Graduate Research Fellowship Grant Number: DGE-1144086; NASA Earth and Space Science Fellowship Program Grant Number: NNX12AN48H2016-05-0

Circumpolar Deep Water Impacts Glacial Meltwater Export and Coastal Biogeochemical Cycling Along the West Antarctic Peninsula

Warming along the Antarctic Peninsula has led to an increase in the export of glacial meltwater to the coastal ocean. While observations to date suggest that this freshwater export acts as an important forcing on the marine ecosystem, the processes linking ice–ocean interactions to lower trophic-level growth, particularly in coastal bays and fjords, are poorly understood. Here, we identify salient hydrographic features in Barilari Bay, a west Antarctic Peninsula fjord influenced by warm modified Upper Circumpolar Deep Water. In this fjord, interactions between the glaciers and ocean act as a control on coastal circulation, contributing to the redistribution of water masses in an upwelling plume and a vertical flux of nutrients toward the euphotic zone. This nutrient-rich plume, containing glacial meltwater but primarily composed of ambient ocean waters including modified Upper Circumpolar Deep Water, spreads through the fjord as a 150-m thick layer in the upper water column. The combination of meltwater-driven stratification, long residence time of the surface plume owing to weak circulation, and nutrient enrichment promotes phytoplankton growth within the fjord, as evidenced by shallow phytoplankton blooms and concomitant nutrient drawdown at the fjord mouth in late February. Gradients in meltwater distributions are further paralleled by gradients in phytoplankton and benthic community composition. While glacial meltwater export and upwelling of ambient waters in this way contribute to elevated primary and secondary productivity, subsurface nutrient enhancement of glacially modified ocean waters suggests that a portion of these macronutrients, as well any iron upwelled or input in meltwater, are exported to the continental shelf. Sustained atmospheric warming in the coming decades, contributing to greater runoff, would invigorate the marine circulation with consequences for glacier dynamics and biogeochemical cycling within the fjord. We conclude that ice–ocean interactions along the Antarctic Peninsula margins act as an important control on coastal marine ecosystems, with repercussions for carbon cycling along the west Antarctic Peninsula shelf as a whole

The Case for a Sustained Greenland Ice Sheet-Ocean Observing System (GrIOOS)

Rapid mass loss from the Greenland Ice Sheet (GrIS) is affecting sea level and, through increased freshwater and sediment discharge, ocean circulation, sea-ice, biogeochemistry, and marine ecosystems around Greenland. Key to interpreting ongoing and projecting future ice loss, and its impact on the ocean, is understanding exchanges of heat, freshwater, and nutrients that occur at the GrIS marine margins. Processes governing these exchanges are not well understood because of limited observations from the regions where glaciers terminate into the ocean and the challenge of modeling the spatial and temporal scales involved. Thus, notwithstanding their importance, ice sheet/ocean exchanges are poorly represented or not accounted for in models used for projection studies. Widespread community consensus maintains that concurrent and long-term records of glaciological, oceanic, and atmospheric parameters at the ice sheet/ocean margins are key to addressing this knowledge gap by informing understanding, and constraining and validating models. Through a series of workshops and documents endorsed by the community-at-large, a framework for an international, collaborative, Greenland Ice sheet-Ocean Observing System (GrIOOS), that addresses the needs of society in relation to a changing GrIS, has been proposed. This system would consist of a set of ocean, glacier, and atmosphere essential variables to be collected at a number of diverse sites around Greenland for a minimum of two decades. Internationally agreed upon data protocols and data sharing policies would guarantee uniformity and availability of the information for the broader community. Its development, maintenance, and funding will require close international collaboration. Engagement of end-users, local people, and groups already active in these areas, as well as synergy with ongoing, related, or complementary networks will be key to its success and effectiveness

Ecosistemas marinos antárticos después del rompimiento de barreras de hielo

Widespread thinning and retreat of ice shelves along the margins of Antarctica provide a unique opportunity to understand the evolution of Antarctic coastal ecosystems and the consequences of abrupt global change in high latitudes. As dark environments isolated from the atmosphere, the under-ice-shelf ecosystems remain mostly unknown. After ice shelf breakup there is an opportunity to study the evolution of the coastal ecosystem exposed to the atmosphere after millennia. One of the more active regions is the Larsen Ice Shelf, on the NW of the Weddell Sea. After the ice shelf breakup, phytoplankton grow in the presence of light; primary production rates observed are amongst the highest in Antarctica. Zooplanktonic and benthic communities in the marine food web can feed on this newly synthesized carbon. In this way, regions previously unproductive are now able to absorb carbon dioxide and contribute to its absorption by the ocean.Los desprendimientos en las barreras de hielo antárticas proveen una oportunidad única para entender la evolución de ecosistemas costeros y las consecuencias de cambio global abrupto en altas latitudes. Los ecosistemas desarrollados debajo de las barreras de hielo han estado aislados de la atmósfera por miles de años y permanecen en gran medida desconocidos hasta el presente. Una de las regiones más activas al respecto es el este de la Península Antárctica donde varias barreras de hielo han ido desapareciendo en los últimos 100 años, en un gradiente de norte a sur. El evento más reciente fue el desprendimiento de un témpano gigantesco de 5.800 Km2 de la barrera Larsen C, denominado A68, el 12 de julio de 2017. Una vez que la barrera de hielo desaparece, las aguas subyacentes se encuentran expuestas a la atmósfera en condiciones para sostener crecimiento del fitoplancton. El carbono orgánico producido puede a su vez alimentar zooplancton y bentos y mantener una trama trófica marina. De esta manera, áreas previamente no productivas pueden ahora absorber dióxido de carbono y contribuir a la absorción del mismo por aguas oceánicas

Surface total dissolvable iron data collected during an August 2015 cruise to Sermilik Fjord, East Greenland

This dataset contains discrete total dissolvable iron (TdFe) data collected from the surface of Sermilik Fjord in SE Greenland in August 2015 aboard the RV Adolf Jensen. Surface samples were collected using a trace metal clean sampler fixed to a plastic pole. Samples were taken while the ship was steaming at approximately 1 knot in order to minimize contamination from the ship. All bottles and plasticware were cleaned using trace metal clean procedures outlined in the U.S. GEOTRACES protocols. Unfiltered samples were placed in separate trace metal clean 250 mL low-density polyethylene bottles and immediately acidified to pH 1.8 with 4 mL Optima HCl (Fisher Scientific) and stored until analysis using standard addition methods and cathodic stripping voltammetry 4 months later in the lab at the Woods Hole Oceanographic Institution

Hydrographic sensor and bottle data collected during an August 2015 cruise to Sermilik Fjord, East Greenland

This dataset contains hydrographic observations from Sermilik Fjord in SE Greenland, collected in August 2015 aboard the RV Adolf Jensen, including discrete data derived from water sample analyses and corresponding CTD sensor data. CTD data were collected using a Seabird 25Plus Sealogger equipped with a SBE 43 dissolved oxygen sensor, a Satlantic PAR LOG sensor, and a Wetlabs / Seabird ECO Triplet (chlorophyll-a and CDOM fluorescence, as well as backscattering at 700 nm). Discrete samples for nitrate, phosphate, silicate, and ammonium, were filtered through a sterile 0.22 µM Sterivex filter using standard protocols and kept frozen at -20 °C for later analysis at the Woods Hole Oceanographic Institution Nutrient Analytical Facility. Dissolved nutrient concentrations were quantified using a SEAL AA3 four-channel segmented flow analyzer

Surface total dissolvable iron and hydrographic data collected during an August 2015 cruise to Sermilik Fjord, East Greenland

This dataset contains hydrographic observations from Sermilik Fjord in SE Greenland, collected in August 2015 aboard the RV Adolf Jensen

Influence of Phytoplankton Advection on the Productivity Along the Atlantic Water Inflow to the Arctic Ocean

Northwards flowing Atlantic waters transport heat, nutrients, and organic carbon in the form of zooplankton into the eastern Greenland Sea and Fram Strait. Less is known of the contribution of phytoplankton advection in this current, the Atlantic Water Inflow (AWI) spanning from the North Atlantic to the Arctic Ocean. The in situ and advected primary production was estimated using the physical-biological coupled SINMOD model over a region bounded by northern Norway coast (along the Norwegian Atlantic Current, NAC), the West Spitsbergen Current (WSC) and the entrance to the Arctic Ocean in northern Fram Strait. The simulation results show that changes in phytoplankton biomass at any one location along the AWI are supported primarily by advection. This advection is 5–50 times higher than the biomass photosynthesized in situ, seasonally variable, with minimum contribution in June, at the time of maximum in situ primary production. Advection in the NAC transports phytoplankton biomass from areas of higher production in the south, contributing to the maintenance of phytoplankton productivity further north. In situ productivity further decreases north of Svalbard Archipelago, at the entrance to the Arctic Ocean. Excess in situ annual production in northern WSC is exported to the Arctic Ocean during the growth season (April to September). The balance between in situ and advected primary production defines three main regions along the AWI, presumably modulated by the spatial and temporal variability of copepod grazing. As the sea ice reduces its annual extent and warmer waters enter the Arctic Ocean, ecological characteristics of the ice-free WSC with its AWI signature could extend north and east of Svalbard and into the central Arctic. Advection thus constitutes an important link connecting marine ecosystems of the Arctic and Atlantic Ocean, mainly at the gateways

Asynchronous Accumulation of Organic Carbon and Nitrogen in the Atlantic Gateway to the Arctic Ocean

Nitrogen (N) is the main limiting nutrient for biological production in the Arctic Ocean. While dissolved inorganic N (DIN) is well studied, the substantial pool of N bound in organic matter (OM) and its bioavailability in the system is rarely considered. Covering a full annual cycle, we here follow N and carbon (C) content in particulate (P) and dissolved (D) OM within the Atlantic water inflow to the Arctic Ocean. While particulate organic carbon (POC), particulate organic nitrogen (PON), and dissolved organic carbon (DOC) accumulated in the surface waters from January to May, the dissolved organic nitrogen (DON)-pool decreased substantially (Δ – 50 μg N L-1). The DON reduction was greater than the simultaneous reduction in DIN (Δ – 30 μg N L-1), demonstrating that DON is a valuable N-source supporting the growing biomass. While the accumulating POM had a C/N ratio close to Redfield, the asynchronous accumulation of C and N in the dissolved pool resulted in a drastic increase in the C/N ratio of dissolved organic molecules (DOM) during the spring bloom. This is likely due to a combination of the reduction in DON, and a high release of carbon-rich sugars from phytoplankton, as 32% of the spring primary production (PP) was dissolved. Our findings thus caution calculations of particulate PP from DIN drawdown. During post-bloom the DON pool increased threefold due to an enhanced microbial processing of OM and reduced phytoplankton production. The light absorption spectra of DOM revealed high absorption within the UV range during spring bloom indicating DOM with low molecular weight in this period. The absorption of DOM was generally lower in the winter months than in spring and summer. Our results demonstrate that the change in ecosystem function (i.e., phytoplankton species and activity, bacterial activity and grazing) in different seasons is associated with strong changes in the C/N ratios and optical character of DOM and underpin the essential role of DON for the production cycle in the Arctic