Description: During the 4th International Polar Year 2007–2009 (IPY), it has become increasingly obvious that we need to prepare for a new era in the Arctic. IPY occurred during the time of the largest retreat of Arctic sea ice since satellite observations started in 1979. This minimum in September sea ice coverage was accompanied by other signs of a changing Arctic, including the unexpectedly rapid transpolar drift of the Tara schooner, a general thinning of Arctic sea ice and a double-dip minimum of the Arctic Oscillation at the end of 2009. Thanks to the lucky timing of the IPY, those recent phenomena are well documented as they have been scrutinized by the international research community, taking advantage of the dedicated observing systems that were deployed during IPY. However, understanding changes in the Arctic System likely requires monitoring over decades, not years. Many IPY projects have contributed to the pilot phase of a future, sustained, observing system for the Arctic. We now know that many of the technical challenges can be overcome. The Norwegian projects iAOOS-Norway, POLEWARD and MEOP were significant ocean monitoring/research contributions during the IPY. A large variety of techniques were used in these programs, ranging from oceanographic cruises to animal-borne platforms, autonomous gliders, helicopter surveys, surface drifters and current meter arrays. Our research approach was interdisciplinary from the outset, merging ocean dynamics, hydrography, biology, sea ice studies, as well as forecasting. The datasets are tremendously rich, and they will surely yield numerous findings in the years to come. Here, we present a status report at the end of the official period for IPY. Highlights of the research include: a quantification of the Meridional Overturning Circulation in the Nordic Seas (“the loop”) in thermal space, based on a set of up to 15-year-long series of current measurements; a detailed map of the surface circulation as well as characterization of eddy dispersion based on drifter data; transport monitoring of Atlantic Water using gliders; a view of the water mass exchanges in the Norwegian Atlantic Current from both Eulerian and Lagrangian data; an integrated physical–biological view of the ice-influenced ecosystem in the East Greenland Current, showing for instance nutrient-limited primary production as a consequence of decreasing ice cover for larger regions of the Arctic Ocean. Our sea ice studies show that the albedo of snow on ice is lower when snow cover is thinner and suggest that reductions in sea ice thickness, without changes in sea ice extent, will have a significant impact on the arctic atmosphere. We present up-to-date freshwater transport numbers for the East Greenland Current in the Fram Strait, as well as the first map of the annual cycle of freshwater layer thickness in the East Greenland Current along the east coast of Greenland, from data obtained by CTDs mounted on seals that traveled back and forth across the Nordic Seas. We have taken advantage of the real-time transmission of some of these platforms and demonstrate the use of ice-tethered profilers in validating satellite products of sea ice motion, as well as the use of Seagliders in validating ocean forecasts, and we present a sea ice drift product – significantly improved both in space and time – for use in operational ice-forecasting applications. We consider real-time acquisition of data from the ocean interior to be a vital component of a sustained Arctic Ocean Observing System, and we conclude by presenting an outline for an observing system for the European sector of the Arctic Ocean.

Description: The development and decline of a phytoplankton spring bloom dominated by the prymnesiophyte Phaeocystis pouchetii were studied in Balsfjord, northern Norway between 30 March and 27 May 1992. At a fixed station, the concentration and composition of suspended particulate matter was monitored and compared to the particulate matter collected in sediment traps at six different depths. Direct sedimentation of phytoplankton contributed a minor fraction to particle flux and was confined to a few diatom genera. No evidence was found for pronounced aggregation of Phaeocystis colonies during bloom decline or direct sedimentation of either Phaeocystis colonies or single cells, Particle flux was dominated by faecal-pellet sedimentation during most of the study period, suggesting zooplankton grazing to be a main loss factor. Despite an abrupt decrease in faecal-pellet sedimentation after the decline of the bloom, particulate-carbon sedimentation rates remained high. High post-bloom sedimentation rates were characterized by elevated C/N and C/Chl a ratios of largely amorphous sedimented material. Post-bloom sedimentation coincided with a decrease in transparent exopolymeric particles (TEP) in the surface layer, suggesting that this change resulted from aggregation and sedimentation of carbon-rich exopolymeric material accumulated in the surface layer in the course of the bloom. While organic-carbon accumulation indicates the significance of disintegration of Phaeocystis colonies, post-bloom mucilage sedimentation could be a secondary pathway for the vertical flux of Phaeocystis-derived organic matter.

Description: Meroplankton is often neglected in Arctic zooplankton studies, so our knowledge about their seasonal dynamics is limited. To investigate the highly dynamic nature of meroplankton, we sampled the zooplankton community in a high-Arctic fjord in West-Spitsbergen bi-weekly from December 2011 to December 2012. Five significantly different seasonal meroplankton assemblages were identified, representing winter, early spring, spring, summer and autumn. Meroplankton persistently dominated the zooplankton community during the productive seasons in both abundance (41–91%) and biomass (54–98%). Cirripedia and Bivalvia larvae occurred in particularly high numbers and dominated during spring and summer respectively. In the remaining seasons, the meroplankton diversity and abundance were comparatively poor, but interestingly Bryozoa larvae were present mainly during winter. Chlorophyll a and day length were identified as the main environmental variables structuring the meroplankton assemblage, followed by hydrography. Timing of the spring bloom determined the onset of the "meroplankton-boost" and from the observed hydrography, local rather than advective processes shaped the meroplankton community. Our investigation suggests that benthic invertebrate larvae play a significant role in the pelagic ecosystems in Arctic coastal regions, tightly linking the pelagic and benthic realms, thus deserving more attention in future studies.

Description: The Adventfjorden time series station (IsA) in Isfjorden, West Spitsbergen, Norway, was sampled frequently from December 2011 to December 2012. The community composition of microbial eukaryotes (size, 0.45 to 10 μm) from a depth of 25 m was determined using 454 sequencing of the 18S V4 region amplified from both DNA and RNA. The compositional changes throughout the year were assessed in relation to in situ fjord environmental conditions. Size fractionation analyses of chlorophyll a showed that the photosynthetic biomass was dominated by small cells (〈10 μm) most of the year but that larger cells dominated during the spring and summer. The winter and early-spring communities were more diverse than the spring and summer/autumn communities. Dinophyceae were predominant throughout the year. The Arctic Micromonas ecotype was abundant mostly in the early-bloom and fall periods, whereas heterotrophs, such as marine stramenopiles (MASTs), Picozoa, and the parasitoid marine alveolates (MALVs), displayed higher relative abundance in the winter than in other seasons. Our results emphasize the extreme seasonality of Arctic microbial eukaryotic communities driven by the light regime and nutrient availability but point to the necessity of a thorough knowledge of hydrography for full understanding of their succession and variability.

Description: Photophysiological and biochemical characteristics were investigated in natural communities of Arctic sea ice algae and phytoplankton to understand their respective responses towards variable irradiance and nutrient regimes. This study revealed large differences in photosynthetic efficiency and capacity between the 2 types of algal assemblages. Sea ice algal assemblages clearly displayed increased photoprotective energy dissipation under the highest daily average irradiance levels (〉8 µmol photons m-2 s-1). In contrast, phytoplankton assemblages were generally light-limited within the same irradiance ranges. Furthermore, phytoplankton assemblages exhibited more efficient carbon assimilation rates in the low irradiance range compared to sea ice algae, possibly explaining the ability of phytoplankton to generate substantial under-ice blooms. They were also able to readily adjust and increase their carbon production to higher irradiances. The Arctic is warming more rapidly than any other oceanic region on the planet, and as a consequence, irradiance levels experienced by microalgae are expected to increase due to declining ice thickness and snow cover, as well as enhanced stratification. The results of this study suggest that sea ice algae may have less capacity to adapt to the expected environmental changes compared to phytoplankton. We therefore anticipate a change in sea ice-based vs. pelagic primary production with respect to timing and quantity in a future Arctic. The clearly distinct responses of sea ice algae vs. phytoplankton need to be incorporated into model scenarios of current and future Arctic algal blooms and considered when predicting implications for the entire ecosystem and associated biogeochemical fluxes.

Description: As part of a joint project on the fate of phytoplankton in Balsfjorden in Northern Norway, we investigated the trophic fate and sedimentation potential of Phaeocystis pouchetii by tracing the transition of biomarker patterns from a phytoplankton bloom to sediment traps and during a gut passage experiment. The phytoplankton biomass during the spring bloom 1996 was dominated by colonial P. pouchetii (ca. 85 %) and four members of the diatom family Thalassiosiraceae (ca. 10%). Particulate organic carbon in sediment traps largely consisted of fecal material from the Arctic krill Thysanoessa sp.. Sterol and fatty acid biomarker patterns in the phytoplankton bloom could be reproduced by combining the individual biomarker patterns of the isolated phytoplankters P. pouchetii and Thalassiosira decipiens in a ratio of ca. 75:25. In a laboratory experiment, Arctic krill (Thysanoessa raschii) fed with similar efficiency on Phaeocystis colonies and the Thalassiosiraceae. During gut passage, the abundance of Thalassiosiraceae biomarkers in fecal strings increased relative to Phaeocystis biomarkers, while biomarkers from krill became dominant. This transition of biomarker patterns due to gut passage in T. raschii closely resembled the biomarker transition from the surface bloom to material in sediment traps at 40-170 m depth, which was mainly composed of krill fecal strings. We conclude that krill grazed efficiently on Phaeocystis colonies in Balsfjorden, and caused sedimentation of Phaeocystis-derived organic matter below the euphotic zone via fecal strings. Hence, both transfer to higher trophic levels and sedimentation of Phaeocystis-derived organic matter can be more effective than commonly believed.