Physical and ecological processes at a moving ice edge in the Fram Strait as observed with an AUV

Small-scale investigations of physical and biogeochemical parameters have been carried out with an autonomous underwater vehicle (AUV) at a moving ice edge in the Fram Strait. The AUV was equipped with various sensors to study the complex interactions between physical and ecological processes along the ice edge and the associated meltwater front. The AUV covered two cross-front sections of 9 km and recorded high resolution vertical profiles of the physical and biogeochemical properties between 0 and 50 m water depth at a horizontal station spacing of 800–1000 m. In both physical and biogeochemical terms, the measurements revealed a complex structure of the water column. The distribution of phytoplankton biomass (chlorophyll a) and nutrients was highly in- homogeneous. Chlorophyll a concentrations of 5 micro g/l were detected at the frontal interface in a small corridor just 2–4 km wide and only 5 m deep. Nutrients at the surface were depleted, yet, compared to previous studies of this region, were still present in the euphotic zone. Below the euphotic zone, nitrate concentrations of 8 micro mol/l and oxygen saturation values of 100% resulted in a “dome-like” pattern – suggestive of vertical transport processes. Based on these measurements, three different zones featuring individual biogeochemical characteristics were identified in the cross-front sections. Atmospheric forcing and the presence of the melt water front are assumed to be mainly responsible for the complexity of the water column. Localized vertical transport events seem to have occurred before our investigations. Furthermore, wind driven frontogenesis likely contributed to vertical water movements. All processes had an effect on the biological processes along the observed meltwater front

Dissolved Organophosphate Esters and Polybrominated Diphenyl Ethers in Remote Marine Environments: Arctic Surface Water Distributions and Net Transport Through Fram Strait

Organophosphate esters (OPEs) have been found in remote environments at unexpectedly high concentrations, but very few measurements of OPE concentrations in seawater are available, and none are available in subsurface seawater. In this study, passive polyethylene samplers (PEs) deployed on deep-water moorings in the Fram Strait and in surface waters of Canadian Arctic lakes and coastal sites were analyzed for a suite of common OPEs. Total OPEs ( ∑11OPE) at deep-water sites were dominated by chlorinated OPEs, and ranged from 6.3 to 440 pg/L. Concentrations were similar in eastern and western Fram Strait. Chlorinated OPEs were also dominant in Canadian Arctic surface waters (mean concentration ranged from \u3c DL to 4400 pg/L), while nonhalogenated alkyl/aryl-substituted OPEs remained low (1.3–55 pg/L), possibly due to the greater long-range transport potential of chlorinated OPEs. Polybrominated diphenyl ethers (PBDEs) were found at much lower concentrations than OPEs

Exchange of warming deepwaters across Fram Strait

Current meters measured temperature and velocity on 11 moorings from 1997 to 2014 in 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 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 mesoscale flows with periods of approximately 1–2 weeks advect the water masses across Fram Strait. These flows are 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 early 1990s, it does not reflect the properties of Norwegian Sea Deep Water. We propose that it currently mostly fills the deep Greenland Sea.Versión del editor2,421

Summertime plankton ecology in Fram Strait - a compilation of long- and short-term observations

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