Abstract

The melting of sea ice, increased terrestrial runoff and meltwater from the Greenland Ice Sheet contribute to increased freshening and stratification of Arctic seas. However, the impacts on ecosystem structure and carbon cycling are still poorly quantified. We studied copepod abundance, grazing, and carbon turnover in Young Sound, Northeast Greenland, during the ice-free period from mid-July to early October 2014 at four stations along the freshwater gradient from the inner fjord to the Greenland Sea. Freshwater enters the fjord as surface runoff from land-terminating glaciers and forms a surface layer of high turbidity and low salinity limiting light availability and nutrient replenishment. This resulted in the inner station consistently having lower biomass of chlorophyll a, (average 21 mg m−2) compared to the outer station (47 mg m−2) and phytoplankton cells smaller than 10 μm constituted 89% at the inner station compared to 59% at the outer station. Copepod grazing rates were low on these small cells, which resulted in low copepods community grazing at the freshwater impacted site in the inner fjord. Daily grazing impact by copepods was about half of the daily primary production during July and August in the outer region of the fjord, but grazing impact was always less than 10% of the daily primary production in the inner fjord and in the late part of the open water season at all stations. Our study shows that meltwater driven stratification results in dominance of small phytoplankton cells, which directly impacts secondary producers and reduces transfer to higher trophic levels.

DOI: 10.1002/lno.10633