Regional-scale phytoplankton dynamics and their association with glacier meltwater runoff in Svalbard

[摘要] Arctic amplification of global warming has accelerated mass loss of Arcticland ice over the past decades and led to increased freshwater discharge intoglacier fjords and adjacent seas. Glacier freshwater discharge is typicallyassociated with high sediment load which limits the euphotic depth but mayalso aid to provide surface waters with essential nutrients, thus havingcounteracting effects on marine productivity. In situ observations from a fewmeasured fjords across the Arctic indicate that glacier fjords dominated bymarine-terminating glaciers are typically more productive than those with onlyland-terminating glaciers. Here we combine chlorophyll  a fromsatellite ocean color, an indicator of phytoplankton biomass, with glaciermeltwater runoff from climatic mass-balance modeling to establish astatistical model of summertime phytoplankton dynamics in Svalbard (mid-Juneto September). Statistical analysis reveals significant and positivespatiotemporal associations of chlorophyll  a with glacier runoff for7 out of 14 primary hydrological regions but only within 10  km distance from the shore. These seven regions consist predominantly of themajor fjord systems of Svalbard. The adjacent land areas are characterized bya wide range of total glacier coverage (35.5  %  to 81.2  % )and fraction of marine-terminating glacier area(40.2  %  to 87.4  % ). We find that an increase in specificglacier-runoff rate of 10  mm  water equivalent per 8  d periodraises summertime chlorophyll  a concentrations by5.2  %  to 20.0  % , depending on the region. During the annual peak discharge we estimate that glacier runoff increases chlorophyll  a by 13.1  % to 50.2  % compared to situations with no runoff. This suggests that glacier runoff is animportant factor sustaining summertime phytoplankton production in Svalbardfjords, in line with findings from several fjords in Greenland. In contrast,for regions bordering open coasts, and beyond 10  km distance from theshore, we do not find significant associations of chlorophyll  a withrunoff. In these regions, physical ocean and sea-ice variables controlchlorophyll  a , pointing at the importance of a late sea-ice breakupin northern Svalbard, as well as the advection of Atlantic water masses alongthe West Spitsbergen Current for summertime phytoplankton dynamics. Our methodallows for the investigation and monitoring of glacier-runoff effects on primaryproduction throughout the summer season and is applicable on a pan-Arcticscale, thus complementing valuable but scarce in situ measurements in bothspace and time.

[学科分类] 大气科学