Description: Between Greenland and Spitsbergen, Fram Strait is a region where cold ice-covered Polar Water exits the Arctic Ocean with the East Greenland Current (EGC) and warm Atlantic Water enters the Arctic Ocean with the West Spitsbergen Current (WSC). In this compilation, we present two different data sets from plankton ecological observations in Fram Strait: (1) long-term measurements of satellite-derived (1998-2012) and in situ chlorophyll a (chl a) measurements (mainly summer cruises, 1991-2012) plus protist compositions (a station in WSC, eight summer cruises, 1998-2011); and (2) short-term measurements of a multidisciplinary approach that includes traditional plankton investigations, remote sensing, zooplankton, microbiological and molecular studies, and biogeochemical analyses carried out during two expeditions in June/July in the years 2010 and 2011. Both summer satellite-derived and in situ chl a concentrations showed slight trends towards higher values in the WSC since 1998 and 1991, respectively. In contrast, no trends were visible in the EGC. The protist composition in the WSC showed differences for the summer months: a dominance of diatoms was replaced by a dominance of Phaeocystis pouchetii and other small pico- and nanoplankton species. The observed differences in eastern Fram Strait were partially due to a warm anomaly in the WSC. Although changes associated with warmer water temperatures were observed, further long-term investigations are needed to distinguish between natural variability and climate change in Fram Strait. Results of two summer studies in 2010 and 2011 revealed the variability in plankton ecology in Fram Strait.

Description: The copepod Temora longicornis depends on constant prey availability. Given that climate change may induce food regime shifts, our research goal was to understand copepod energy allocation in relation to diet quality. The working hypothesis was that Temora performs better on the diet whose elemental ratio is closest to its own. Diatoms (Diat) and dinoflagellates (Dino) cultured in nutrient-replete (+) and nitrogen-depleted (-) conditions were fed to the copepods. Ingestion, respiration, excretion, and egg and faecal pellet production rates were measured. Carbon (C) and nitrogen (N) budgets were built to investigate differences in dietary C and N partitioning. Copepods fed with nitrogen-depleted diatoms (Diat-), which had the most different C:N ratio to that of T. longicornis, had high metabolic losses and low growth. In contrast, copepods fed with nitrogen-rich dinoflagellates (Dino+) of closer C:N ratio had high metabolic losses, but the highest investment into somatic and reproductive tissue. The results indicate that, under the current climate scenario and nutrient-replete conditions, dinoflagellates are a better food source for T. longicornis. Furthermore, ingestion, respiration, and faecal pellet integrity are adversely affected by low quality food; and egestion is a main pathway in copepods for eliminating excess carbon.