Virginie Galindo

Biological and physical processes influencing sea ice, under‐ice algae, and dimethylsulfoniopropionate during spring in the Canadian Arctic Archipelago

This study presents temporal variations in concentrations of chlorophyll a (Chl a), particulate and dissolved dimethylsulfoniopropionate (DMSPp and DMSPd) in the sea ice and underlying water column in the Canadian Arctic Archipelago during the spring of 2010 and 2011. During both years, bottom ice Chl a, DMSPp and DMSPd concentrations were high (up to 1328 µg L−1, 15,082 nmol L−1, and 6110 nmol L−1, respectively) in May and decreased thereafter. The release of bottom ice algae and DMSPp in the water column was gradual in 2010 and rapid (8 days) in 2011. Bottom brine drainage during the presnowmelt period in 2010 and a rapid loss of the snow cover in 2011 coinciding with rain events explain most of the difference between the 2 years. During both years, less than 13% of the DMSPd lost from the ice was detected in the water column, suggesting a rapid microbial consumption. An under-ice diatom bloom developed in both years. In 2010, the bloom was dominated by centric diatoms while in 2011 pennates dominated, likely reflecting seeding by ice algae following the faster snowmelt progression induced by rainfall events in 2011. Both under-ice blooms were associated with high DMSPp concentrations (up to 185 nmol L−1), but pennate diatoms showed DMSPp/Chl a ratios twice higher than centrics. These results highlight the key role of snowmelt and precipitation on the temporal pattern of ice-DMSP release to the water column and on the timing, taxonomic composition, and DMSP content of phytoplankton under-ice blooms in the Arctic.

Sea ice breakup and marine melt of a retreating tidewater outlet glacier in northeast Greenland (81°N)

Rising temperatures in the Arctic cause accelerated mass loss from the Greenland Ice Sheet and reduced sea ice cover. Tidewater outlet glaciers represent direct connections between glaciers and the ocean where melt rates at the ice-ocean interface are influenced by ocean temperature and circulation. However, few measurements exist near outlet glaciers from the northern coast towards the Arctic Ocean that has remained nearly permanently ice covered. Here we present hydrographic measurements along the terminus of a major retreating tidewater outlet glacier from Flade Isblink Ice Cap. We show that the region is characterized by a relatively large change of the seasonal freshwater content, corresponding to ~2 m of freshwater, and that solar heating during the short open water period results in surface layer temperatures above 1 °C. Observations of temperature and salinity supported that the outlet glacier is a floating ice shelf with near-glacial subsurface temperatures at the freezing point. Melting from the surface layer significantly influenced the ice foot morphology of the glacier terminus. Hence, melting of the tidewater outlet glacier was found to be critically dependent on the retreat of sea ice adjacent to the terminus and the duration of open water.