Description: Time series length-frequency data are presented for Themisto amphipods collected as swimmers by moored sediment traps since 2000 at the AWI deep-sea observatory HAUSGARTEN (79°N/4°E) in the eastern Fram Strait. Amphipod occurrences increased significantly from 2000 to 2009 at 200-300 m depth, and the North Atlantic species Themisto compressa was continuously present in the samples starting in 2004. We present year-round records of large adult Themisto amphipods, including the appearance of T. libellula with a total body length of up to 56.7 mm and juveniles starting from 4.0 mm. The length of T. abyssorum ranged from 4.2-25.6 mm, whereas it varied for T. compressa from 8.8-24.4 mm. Length-frequency analysis indicated a life span of 2 years for T. abyssorum and at least 3 years for T. libellula. The absence of juveniles for T. compressa suggested its reproduction in southern subarctic areas and its occasional northward migration with warmer Atlantic water into the eastern Fram Strait. The seasonal and long-term size structure of the three pelagic species was consistent over the course of the study, indicating no changes occurred in cohort development due to increasing abundances or warming water temperatures.

Description: The Arctic Ocean is changing severely since one decade. Extremely low ice coverage in late summer has been recorded since 2007 with a new minimum in 2011. The zone of the receding ice edge is known for its high primary productivity in polar waters, but depending on light and nutrient availability productivity in the ice can also be high. We don’t know yet what the influence of less ice will be for the future Arctic Ocean ecosystem. Several scenarios are under discussion. Chlorophyll a is a measure of biomass standing stock of phytoplankton and can give information on surface as well as depth distribution of autotrophic biomass in the ocean. Chlorophyll a measurements also serve as ground truth data used to validate productivity estimates by remote sensing from space. Here we present a data set obtained since 1991 during several cruises carried out on RVs Polarstern, Lance & Maria S Merian to the Fram Strait, Greenland Sea and to the central Arctic Ocean including Laptev and Kara Seas. Almost every year samples have been taken from at least six different depth horizons within the upper 100 meters of the water column in the Fram Strait and Greenland Sea. During five expeditions sampling has been carried out to the central Arctic Ocean between the years 1993 and 2011. The plankton of distinct depth samples has been filtered onto glass-fibre filters and chlorophyll a concentrations were analyzed with a fluorometer and/or a photometer as a measure of phytoplankton standing stock. Here we will focus on the seasonality and interannual variability in the chlorophyll a distribution. A comparison of spring, summer and fall in-situ data show highest values in April and May decreasing towards summer. In fall, only a small fraction of the chlorophyll a concentrations measured reach values above 1 µg L-1, most concentrations were below 0,1 µg L-1 in Greenland Sea and Fram Strait. Whereas highest values above 10 µg L-1 have been recorded in the Kara Sea in the vicinity of Ob and Yenisei, lowest chlorophyll a concentrations were found in the ice-covered Arctic Ocean (〈 0,5 µg L-1). In the future, data obtained in-situ will be compared with data retrieved by satellites to gain a broader view of the biomass distribution of phytoplankton in the entire Arctic Ocean. Some first examples will be shown. Shifts in chlorophyll a concentration patterns can partly be attributed to variations in sea-ice distribution and eventually to climate changes. Long-term trends in chlorophyll concentration patterns reveal slight alterations in biomass in the investigated regions of the Arctic Ocean. This can be the result of differences in productivity possibly leading to changes in trophic interactions, and in sequestration efficiency of CO2 in the ocean.

Description: Current estimates of global marine primary production range over a factor of two. At high latitudes, the uncertainty is even larger than globally because here in-situ data and ocean color observations are scarce, and the phytoplankton absorption shows specific characteristics due to the low-light adaptation. The improvement of the primary production estimates requires an accurate knowledge on the chlorophyll vertical profile, which is the basis for most primary production models. To date, studies describing the typical chlorophyll profile based on the chlorophyll in the surface layer did not include the Arctic region or, if it was included, the dependence of the profile shape on surface concentration was neglected. The goal of our study was to derive and describe the typical Greenland Sea chlorophyll profiles, categorized according to the chlorophyll concentration in the surface layer and further monthly resolved. The Greenland Sea was chosen because it is known to be one of the most productive regions of the Arctic and is among the Arctic regions where most chlorophyll field data are available. Our database contained 1199 chlorophyll profiles from R/Vs Polarstern and Maria S Merian cruises combined with data of the ARCSS-PP database (Arctic primary production in-situ database) for the years 1957–2010. The profiles were categorized according to their mean concentration in the surface layer and then monthly median profiles within each category were calculated. The category with the surface layer chlorophyll exceeding 0.7 mg C m−3 showed a clear seasonal cycle with values gradually decreasing from April to August. Chlorophyll profiles maxima moved from lower depths in spring towards the surface in late summer. Profiles with smallest surface values always showed a subsurface chlorophyll maximum with its median magnitude reaching up to three times the surface concentration. While the variability in April, May and June of the Greenland Sea season is following the global non-monthly resolved relationship of the chlorophyll profile to surface chlorophyll concentrations described by the model of Morel and Berthon (1989), it deviates significantly from that in other months (July–September) where the maxima of the chlorophyll are at quite different depths. The Greenland Sea dimensionless monthly median profiles intersect roughly at one common depth within each category. Finally, by applying a Gaussian fitting with 0.1 mg C m−3 surface chlorophyll steps to the median monthly resolved chlorophyll profiles of the defined categories, mathematical approximations have been determined. These will be used as the input to the satellite-based primary production models estimating primary production in Arctic regions.

Description: o detect and track the impact of large-scale environmental changes in a transition zone between the northern North Atlantic and the central Arctic Ocean, and to determine experimentally the factors controlling deep-sea biodiversity, the Alfred Wegener Institute for Polar and Marine Research (AWI) established the deep-sea long-term observatory HAUSGARTEN in 1999, which constitutes the first, and until now only open-ocean observatory in a polar region. HAUSGARTEN observatory in the eastern Fram Strait includes 17 permanent sampling sites along a depth transect (1000 - 5500 m water depth) and along a latitudinal transect following the 2500 m isobath crossing the central HAUSGARTEN station. Multidisciplinary research activities at HAUSGARTEN cover almost all compartments of the marine ecosystem from the pelagic zone to the benthic realm. Regular sampling as well as the deployment of moorings and different free-falling systems (bottom-lander) which act as local observation platforms, have taken place since the observatory was established in summer 1999. Frequent visual observations with towed photo/video systems allow assessing large-scale distribution patterns of mega/epifaunal organisms as well as their temporal development. To determine the factors controlling deep-sea biodiversity, various biological short- and long-term experiments are carried out at the deep seafloor using Remotely Operated Vehicles (ROV) at regular intervals over the past 12 years. Since the beginning of our investigations which includes the IPY period from 2007-2009 we monitored an abyssal warming, significant alterations in the species composition in the pelagic realm, a decrease in the quality of organic matter supply to the deep sea as well as considerable shifts in both, microbial and megafauna community composition at great water depths.

Description: The Arctic Ocean is quite vulnerable and sensitive to climatic changes and has received increasing attention in recent years because of the drastic decrease of sea ice cover and extent. These environmental changes are expected to have severe consequences for the structure of the pelagic system and trophic interactions, and thus for cycling of organic matter and carbon sequestering. The composition of particulate organic matter is measured at the so-called ‘HAUSGARTEN’ – a deep-sea long-term observatory of the AWI, in order to track respective shifts. The observatory is situated in the eastern Fram Strait at ~ 79°N and 4°E. Since 1998, yearly sampling has been carried out in the water column during cruises in summer, and sedimenting particles are collected by year-round moored sediment traps. Here we present results obtained from water samples collected near the central station at the HAUSGARTEN during expeditions with RV Polarstern in 1998, 2003, 2004, 2006, 2007, 2009 and 2010. The composition of the dominant groups of phytoplankton and protozooplankton in the upper 100m was investigated qualitatively as well as quantitatively by light microscopy. This time-series enables us to trace possible changes in relation to environmental factors such as temperature, salinity and sea ice cover. Diatoms dominated the phytoplankton in the years 1998 and 2003. These years were characterized by longer periods of sea ice cover and relatively cold water temperatures. Coccolithophorids, mainly composed of Emiliania huxleyi, prevailed in the samples from 2004. During the following years until 2010, which had a low presence or complete absence of sea ice, phytoplankton was dominated by the prymnesiophyte Phaeocystis pouchetii. Concomitant to the shift in phytoplankton composition, we also noted an increase in protozooplankton abundance (ciliates and tintinnids) in the samples. The observed changes in the species composition of unicellular protistian plankton is also partly reflected in the composition of sedimenting matter at the central HAUSGARTEN mooring, indicating just as well modifications in element cycling in the changing Arctic Ocean.

Description: As part of the HAUSGARTEN long-term observatory, sediment trap deployments were carried out before, during, and after the anomalously warm Atlantic Water inflow observed from 2005 to 2007 in the eastern Fram Strait. Downward export of particulate organic carbon (POC), zooplankton fecal pellet carbon (FPC), and biogenic particulate silica (bPSi) were measured from August 2002 to June 2003 and from July 2004 to July 2008 to indirectly assess the impact of the warm anomaly on phytoplankton and zooplankton production in the region. Lower and less frequent bPSi and FPC fluxes were observed during most of the warm anomaly period, indicating a decrease in the production of diatoms and fecal pellets under warmer conditions. The simultaneous increases and decreases in bPSi and FPC export suggest that zooplankton production was indirectly affected by an increase of water temperature through a change in diatom production. Biogenic silica and fecal pellet export always increased in the presence of ice cover in the sediment trap area, even during the warm anomaly period, suggesting that sea ice is a key factor influencing the frequency of export events in the eastern Fram Strait. Very low ice concentrations in 2005 and 2006 may partly be due to the warm anomaly, although solar radiation and ice drift due to wind stress also govern ice cover extent in the region. Nevertheless, the long-term measurements of export fluxes in the eastern Fram Strait showed that warmer conditions resulted in an intensified retention of bPSi and fecal pellets in the upper water column when associated with a reduction in ice cover.