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: Current meters measured temperature and velocity on 12 moorings from 1997 to 2014 in the deep Fram Strait between Svalbard and Greenland at the only deep passage from the Nordic Seas to the Arctic Ocean. The sill depth in Fram Strait is 2545 m. The observed temperatures vary between the colder Greenland Sea Deep Water and the warmer Eurasian Basin Deep Water. Both end members show a linear warming trend of 0.11±0.02°C/decade (GSDW) and 0.05±0.01°C/decade (EBDW) in agreement with the deep water warming observed in the basins to the north and south. At the current warming rates, GSDW and EBDW will reach the same temperature of -0.71°C in 2020. The deep water on the approximately 40 km wide plateau near the sill in Fram Strait is a mixture of the two end members with both contributing similar amounts. This water mass is continuously formed by mixing in Fram Strait and subsequently exported out of Fram Strait. Individual measurements are approximately normally distributed around the average of the two end members. Meridionally, the mixing is confined to the plateau region. Measurements less than 20 km to the north and south have properties much closer to the properties in the respective basins (Eurasian Basin and Greenland Sea) than to the mixed water on the plateau. The temperature distribution around Fram Strait indicates that the mean flow cannot be responsible for the deep water exchange across the sill. Rather, a coherence analysis shows that energetic mesoscale flows with periods of approximately 1-2 weeks advect the deep water masses across Fram Strait. These flows appear to be barotropically forced by upper ocean mesoscale variability. We conclude that these mesoscale flows make Fram Strait a hot spot of deep water mixing in the Arctic Mediterranean. The fate of the mixed water is not clear, but after the 1990s, it does not reflect the properties of Norwegian Sea Deep Water. We propose that it currently mostly fills the deep Greenland Sea.

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 communities in the region. Lower and less frequent bPSi fluxes were observed during most of the warm anomaly period, reflecting a shift in phytoplankton community composition towards dominance of small-sized phytoplankton under warmer conditions. Lower FPC fluxes observed concurrently with the lower bPSi fluxes may indicate a decrease in fecal pellet production due to changing feeding conditions. In addition, the export of smaller fecal pellets in fall 2005 and spring 2006 suggests a dominance of smaller zooplankton during the warm anomaly. Nonetheless, bPSi and FPC export always increased in the presence of ice cover in the area above the sediment trap, 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. The scarcity of ice over the sampling area 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. Overall, the warm anomaly resulted in a shift in the composition of the export fluxes when associated with an absence of ice cover in the eastern Fram Strait.