Influence of the physical environment on polar phytoplankton blooms: A case study in the Fram Strait

Abstract

The Fram Strait is the main gateway for water, heat and sea-ice exchanges between the Arctic Oce the North Atlantic. The complex physical environment results in a highly variable primary production in and time. Previous regional studies have defined key bottom-up (ice cover and stratification from melt controlling the light availability, and wind mixing and water transport affecting the supply of nutrients top-down processes (heterotrophic grazing). In this study, in situ field data, remote sensing and moc techniques were combined to investigate in detail the influence of melting sea-ice and ocean properties development of phytoplankton blooms in the Fram Strait region for the years 1998-2009. Satellite-retri chlorophyll-a concentrations from temporarily ice-free zones were validated with contextual field data. were then integrated per month on a grid size of 20 x 20 km, resulting in 10 grids/fields. Factors teste their influence on spatial and temporal variation of chlorophyll-a were: sea-ice concentration from sz and sea-ice thickness, ocean stratification, water temperature and salinity time-series simulated b ice-ocean model NAOSIM. The time series analysis for those ten ice-free fields showed a regional separ according to different physical processes affecting phytoplankton distribution. At the marginal ice zon melting sea-ice was promoting phytoplankton growth by stratifying the water column and poten seeding phytoplankton communities. In this zone, the highest mean chlorophyll concentration ave for the productive season (April-August) of 0.8 mgC/m3 was observed. In the open ocean the phytoplz variability was correlated highest to stratification formed by solar heating of the upper ocean layers. C zone around Svalbard showed processes associated with the presence of coastal ice were rather suppre than promoting the phytoplanlcton growth. During the twelve years of observations, chlorophyll concentrz significantly increased in the southern part of the Fram Strait, associated with an increase in sea s temperature and a decrease in Svalbard coastal ice.