Description: The export and composition of particles has been measured by means of annually moored sediment traps at the AWI long-term observatory HAUSGARTEN in Fram Strait (79°/4°E) in 200-300m depth since the year 2000. The area of investigation west of Spitsbergen at a water depth of 2500m is temporally covered by sea ice during the course of the year. It is further influenced by the inflow of warm Atlantic waters at the surface as well as recirculating of the warm waters modified by out-flowing cold arctic waters. With our study we aim at tracing effects of environmental changes in pelagic system structure and impacts on the fate of organic matter produced in the upper water column in a region that is anticipated to react very sensible to climate change. We present data on the export of total particulate matter (TPM), particulate organic carbon and nitrogen (POC/PON), biogenic particulate silica (bPSi), carbonate (CaCO3) and protist composition achieved during the period 2000 - 2009. We observed a bimodal seasonal sedimentation pattern for almost all flux components. Annual fluxes showed greatest variation for TPM and CaCO3 (3-5 fold), and a drastic decrease in bPSi, a proxy for diatoms. The export of organic carbon and total biogenic matter on the other hand hardly showed any variation (1-2 fold) since the begin of the measurements in the year 2000. The results obtained during the 9 year period of the study are compared to the findings of sediment trap studies conducted in the Fram Strait during the end of the eighties and we will discuss our findings in regard to the changing environmental conditions in the area.

Description: In 2009 scientists at the Alfred Wegener Institute (AWI) Helmholtz Centre of Polar and Marine Research in Bremerhaven established the PEBCAO-group. Since then the group is investigating the “Plankton Ecology and Biogeochemistry in the Changing Arctic Ocean” in a uniquely synchronized approach. This involves the integration of molecular genetic investigations with traditional plankton investigations, optical parameters, microbiology, work on key species (e.g. Phaeocystis sp. or Calanus sp.), and finally the composition of organic matter. The work is carried out in the Central Arctic Ocean and the Fram Strait, where it is complementing a monitoring program on phytoplankton and vertical particle flux that has been carried out along ~79°N and in the AWI HAUSGARTEN for more than ten years. This is done in cooperation with oceanographers and deep-sea biologists. Combining the long-term data (1998-2012) with the integrative approach of PEBCAO we revealed a trend towards slightly higher chlorophyll a in the WSC during summer that is accompanied by a shift from diatoms to Phaeocystis sp. and other small pico- and nanoplankton. Furthermore, a clear zonation in the waters of the East Greenland Current (EGC), the West Spitsbergen Current (WSC) as well as for the mixing zone of both (MW) was identified in all parameters. The PEBCAO approach is an example for a successful and synergistic integration of molecular biodiversity studies with classical approaches of biological oceanography.

Description: In the Arctic, under-ice primary production is limited to summer months and is not only restricted by ice thickness and snow cover but also by the stratification of the water column, which constrains nutrient supply for algal growth. RV Polarstern visited the ice-covered Eastern Central basins between 82 to 89°N and 30 to 130°E in summer 2012 when Arctic sea ice declined to a record minimum. During this cruise, we observed a widespread deposition of ice algal biomass of on average 9 g C per m2 to the deep-sea floor of the Central Arctic basins. Data from this cruise will contribute to assessing the impact of current climate change on Arctic productivity, biodiversity, and ecological function.

Description: The unique long-term record assessed at the HAUSGARTEN deep-sea observatory is one of the best data sets available to study Arctic marine ecosystem dynamics. The observatory is located in the eastern Fram Strait representing one of the most sensitive areas with regard to Climate Change in the North. One of the key elements of our work at HAUSGARTEN is our multidisciplinary approach. Year-round measurements and annual sampling campaigns comprise the water column, the benthic boundary layer, and the deep-sea benthos. Our studies since 1999 show remarkable changes in marine key variables. Decreases of sea-ice extent and sea-ice thickness as well as strong fluctuations in the inflow of North-Atlantic water masses in the past decade are accompanied by changes in zooplankton, as indicated by a shift in composition of swimmers in sediment traps, which subsequently might also have influenced the food availability to the deep-sea benthos. Whether driven by Climate Change or by natural variations, these observations allow conclusions for a strong coupling between particle flux, distribution and the deep benthic ecosystem.

Description: The Long-Term Ecological Research (LTER) site HAUSGARTEN is located in Fram Strait, representing one of the most sensitive regions with regard to Climate Change in the North. The unique long-term record assessed at the observatory is one of the best data sets available to study Arctic marine ecosystem dynamics. HAUSGARTEN represents a network of 20 sampling sites arranged along a bathymetric transect (1000-5500 m) and along a latitudinal transect following the 2500 m isobath. Annual water and sediment sampling as well as the year-round deployment of moorings and free-falling systems, which act as local observation platforms, has taken place since 1999. Multidisciplinary research activities at HAUSGARTEN cover almost all compartments of the marine ecosystem from the pelagic zone to the benthic realm. Time-series studies at HAUSGARTEN already exhibited trends from which, at the moment, we do not know whether these already indicate Climate Change induced lasting alterations of the system or simply reflect natural variability on multi-year time scales, e.g. in relation to variations in the Arctic Oscillation. Water temperatures in the Fram Strait generally increased over the last years. For the period 1997-2012, there was a positive linear trend in Atlantic Water mean temperature of 0.1°C per year. A massive temperature increase was observed within the upper 500-1000 m of the water column between the summers of 2005 and 2008. Records from moored instruments at the central HAUSGARTEN site (2500 m) between 1999 and 2013 showed a similar overall increase in water temperature at 2 m above the seafloor. Water temperature as well as sea ice transport and melting showed to be the main factors influencing the amount and occurrence of the phytoplankton in Fram Strait. During the last decade, chlorophyll a biomass has slightly increased in the eastern part of the passage, whereas it was relatively constant in the colder western parts. Microscopic and molecular studies revealed a shift in micro- and nanoplankon populations from diatoms to Phaeocystis pouchetii and smaller flagellates. For the zooplankton, we observed a decrease in polar species and an increase in boreal species. Alterations in planktonic assemblages affect the flux of organic matter (food/energy) to the seafloor. Analyses of various biogenic sediment compounds between 2000 and 2005 revealed a generally decreasing transfer of detritus to the seafloor and subsequently decreasing microbial biomass and bacterial richness in the sediments. A comparison of footage between 2002 and 2007 demonstrated a parallel decrease in megafaunal densities at 2500 m water depth. Since then, we observed a reverse trend with increasing food availability at the seafloor and again increasing microbial biomass in the sediments. First results from photo/video surveys in 2011 showed again rising megafauna densities, probably reflecting a direct effect of (again) enhanced organic matter availability for the benthos. The remarkably rapid response of the benthic community to variations in food/energy supply is in contrast to earlier assumptions on the sensitivity of deep-sea ecosystems and obviously involves shifts in the species composition, thereby affecting benthic biodiversity as well as the functional diversity at the deep seafloor.

Description: As our current knowledge of biological and biogeochemical processes in the Arctic Ocean is mostly based on snapshots measurements obtained during summer and mostly limited to shelf regions, baseline information is missing to assess the impact of climate change on the biological carbon pump, particularly in the Central Arctic Ocean. Measurements on larger spatial and temporal scales are therefore urgently needed to monitor the response of the carbon cycle to warmer conditions in the Arctic Ocean. In this context, a call to maintain, develop and coordinate observing activities relying on bio-mooring arrays and long-term sequential sediment traps, key tools to detect change in the biogeochemical and ecological functioning of Arctic marine ecosystems, was made in a community white paper presented at the Arctic Observing Summit in 2013 (Forest et al., 2013). To answer this call, international cooperation for the development of an Arctic biogeochemical observatory network is needed. The development of such an international observatory network may be implemented through joint projects among existing programs and expanded to joint deployments of multidisciplinary moorings to fill geographical gaps, combine efforts and expertise, and share instruments and costs. To highlight the relevance of international collaboration, results from an ongoing joint project comparing export fluxes obtained in the Siberian Arctic Ocean by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research in Germany and ArcticNet, a Network of Centre of Excellence in Canada are presented. The combination of export flux measurements obtained at different periods and locations help to accurately assess the impact of reduced ice cover on primary productivity and carbon export in the Siberian Arctic Ocean. The Arctic Observing Summit 2014 represents a good opportunity to identify additional potential partners and discuss future collaborative projects.

Description: A critical question regarding the organic carbon cycle in the Arctic Ocean is whether the decline in ice extent and thickness and the associated increase in solar irradiance in the upper ocean will result in increased primary production and particulate organic carbon (POC) export. To assess spatial and temporal variability in POC export, under-ice export fluxes were measured with short-term sediment traps in the northern Laptev Sea in July-August-September 1995, north of the Fram Strait in July 1997, and in the Central Arctic in August–September 2012. Sediment traps were deployed at 2–5 m and 20–25 m under ice for periods ranging from 8.5 to 71 h. In addition to POC fluxes, total particulate matter, chlorophyll a, biogenic particulate silica, phytoplankton, and zooplankton fecal pellet fluxes were measured to evaluate the amount and composition of the material exported in the upper Arctic Ocean. Whereas elevated export fluxes observed on and near the Laptev Sea shelf were likely the combined result of high primary production, resuspension, and release of particulate matter from melting ice, low export fluxes above the central basins despite increased light availability during the record minimum ice extent of 2012 suggest that POC export was limited by nutrient supply during summer. These results suggest that the ongoing decline in ice cover affects export fluxes differently on Arctic shelves and over the deep Arctic Ocean and that POC export is likely to remain low above the central basins unless additional nutrients are supplied to surface waters.