The ocean moderates the world’s climate through absorption of heat and carbon, but how much carbon the ocean will continue to absorb remains unknown. The North Atlantic Ocean west (Baffin Bay/Labrador Sea) and east (Fram Strait/Greenland Sea) of Greenland features the most intense absorption of anthropogenic carbon globally; the biological carbon pump (BCP) contributes substantially. As Arctic sea-ice melts, the BCP changes, impacting global climate and other critical ocean attributes (e.g. biodiversity). Full understanding requires year-round observations across a range of ice conditions. Here we present such observations: autonomously collected Eulerian continuous 24-month time-series in Fram Strait. We show that, compared to ice-unaffected conditions, sea-ice derived meltwater stratification slows the BCP by 4 months, a shift from an export to a retention system, with measurable impacts on benthic communities. This has implications for ecosystem dynamics in the future warmer Arctic where the seasonal ice zone is expected to expand.

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Gröhsler, T., Oeberst, R., Schaber, M., Larson, N., and Kornilovs, G. 2013. Discrimination of western Baltic spring-spawning and central Baltic herring (Clupea harengus L.) based on growth vs. natural tag information. – ICES Journal of Marine Science, 70: 1108–1117. In the Baltic Sea, several stocks of herring (Clupea harengus L.) are surveyed and managed separately. For assessment purposes, a spatial stock separation based on ICES subdivisions is implemented. However, especially in the western Baltic, the distribution areas of two stocks, the western Baltic spring-spawning herring and the central Baltic herring, overlap. Results of regularly conducted surveys for assessment purposes indicated variable degrees of mixing of both stocks in the survey area, based on conspicuous differences in weights/lengths within certain age groups, especially in an area known for overlapping distribution of both stocks. At present, varying fractions of the central Baltic herring stock have not been taken into account during regular surveys conducted in the western Baltic, leading to possible undetected biases in assessment indices derived from these surveys. Additionally, methods otherwise applied for stock separation of Baltic herring so far are based on parameters that cannot readily be derived during regular surveys. In this paper, we present a simple and quick method to reliably allocate herring to either stock based on a separation function derived from survey-based length-at-age data, thus facilitating a more precise estimate of biomass and abundance indices from regular surveys and commercial fisheries.

The European eel Anguilla anguilla has shown decreased recruitment in recent decades. Despite increasing efforts to establish species recovery measures, it is unclear if the decline was caused by reduced numbers of reproductive-stage silver eels reaching the spawning area, low early larval survival, or increased larval mortality during migration to recruitment areas. To determine if larval abundances in the spawning area significantly changed over the past three decades, a plankton trawl sampling survey for anguillid leptocephali was conducted in March and April 2011 in the spawning area of the European eel that was designed to directly compare to collections made in the same way in 1983 and 1985. The catch rates of most anguilliform leptocephali were lower in 2011, possibly because of the slightly smaller plankton trawl used, but the relative abundances of European eel and American eel, Anguilla rostrata, leptocephali were much lower in 2011 than in 1983 and 1985 when compared to catches of other common leptocephali. The leptocephali assemblage was the same in 2011 as in previous years, but small larvae of mesopelagic snipe eels, Nemichthys scolopaceus, which spawn sympatrically with anguillid eels, were less abundant. Temperature fronts in the spawning area were also poorly defined compared to previous years. Although the causes for low anguillid larval abundances in 2011 are unclear, the fact that there are presently fewer European and American eel larvae in the spawning area than during previous time periods indicates that decreased larval abundance and lower eventual recruitment begin within the spawning area.