Marine ecosystem changes linked to climate and terrestrial freshwater inputs in a Northeast Greenland fjord over the Holocene

Decreasing sea-ice extent and retreating and thinning of Greenland’s glaciers are rapidly changing Arctic coastal environments by warming and freshening the sea surface and impacting light availability. In Arctic fjords, productivity is significantly influenced by the position of glacier termini, and the present retreat of the Greenland Ice Sheet will increase the number of fjords surrounded only by land-terminating glaciers in the future. This will most likely affect the productivity and ecosystem structure of coastal marine areas. To predict future cryosphere change and its impacts, it is essential to understand climate and ecosystem variability beyond the instrumental era.  

Here we present a high-resolution reconstruction of coastal marine ecosystem change and its linkages to terrestrial freshwater and organic matter inputs in Young Sound fjord, Northeast Greenland, over the Holocene. The reconstructions are based on marine sediment-core proxies: organic-walled palynomorphs (including e.g. dinoflagellate cysts and pollen), sympagic and pelagic biomarkers (highly branched isoprenoids and sterols) and a set of geochemical indicators (sediment organic carbon, nitrogen, their stable isotopes, and biogenic silica). The results suggest a relatively cold early Holocene with extensive sea-ice cover and low productivity. Warmer and more variable conditions take hold after approximately 9 kyr with increasing productivity, species richness and terrestrial freshwater inputs, with colder conditions seen after approximately 3.5 kyr with high productivity coupled with higher ice-algae contribution. The results also indicate that this near-shore marine ecosystem is clearly influenced by local forcings, such as terrestrial freshwater and organic matter inputs, suggesting that the continuous melting of the Greenland Ice Sheet will affect marine productivity and ecosystem structure in Greenland’s fjord systems, with potential impacts on biodiversity and sustainability of fisheries.