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

• AUV-based high resolution observations of frontogenesis at a meltwater front.
• First direct observations of front related vertical transports at a meltwater front.
• High resolution biogeochemical cross sections through ice associated euphotic zone.
• Rapid ecological response on front and ice related processes.

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 inhomogeneous. Chlorophyll a 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, were still present in the euphotic zone. Below the euphotic zone, nitrate concentrations of 8 µmol l−1 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.