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

The marginal ice zone (MIZ) and the meltwater front of a moving ice tongue in the Fram Strait were investigated using the autonomous underwater vehicle (AUV) “PAUL” of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research in Bremerhaven, Germany. PAUL was equipped with physical and biogeochemical sensors to study the complex interaction between physical processes and ecological responses along an ice edge. PAUL covered two cross-front sections of 9 km length each and recorded high resolution vertical profiles of the physical and biogeochemical properties. In both physical and biogeochemical terms, the measurements revealed a complex structure of the water column. The distribution of phytoplankton and nutrients was highly inhomogeneous. Phytoplankton concentrations of 5 µg·l^-1 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, elevated levels were still present in the euphotic zone. Below the euphotic zone, nitrate concentrations and oxygen saturation values resulted in a “dome-like” pattern – suggestive of vertical transport processes. Based on these measurements, four different zones featuring individual biogeochemical characteristics could be identified in the cross-front sections. The atmospheric forcing and the evolution of the ice cover contributed to the complexity of the MIZ. Large scale upwelling as well as more localized upwelling and downwelling events seem to have occurred. Furthermore, submesoscale frontogenesis could have taken place at the melt water front. All of the processes had an effect on the ecological conditions along the observed ice tongue.