Focus 2: How does loss of sea ice and freshening affect biogeochemical cycling in Arctic coastal areas?
Focus 2 will assess the effects of freshening caused by sea ice melt, both locally and advected in from the East Greenland current system, on coastal waters.
Theme 2.1 - Estimate freshwater exchange between fjord and shelf.
The coast of East Greenland receives ice melt from both the ice sheet and local sea ice melt. Up to 90% of coastal freshwater comes from advected sources. Fjord-shelf exchange in Greenland is pivotal for regional marine biological production and global biogeochemical and physical processes. In surface waters, fjord-shelf exchange is chiefly governed by freshwater export. Freshwater from the ice sheet is deposited in the fjord systems and then exported onto the Greenland shelf. As water leaves the fjord, even more water is pulled in to replace it. Input and export of freshwaters affect water column mixing, supplies nutrients into fjords or out to the shelf seas and can stimulate primary productivity after post-spring bloom nutrient depletion has occurred. Greenland's fjords and shelves are highly susceptible to changes in this exchange due to the export of freshwater from the ice sheet. Surface freshwater export intensifies stratification hindering the vertical supply of nutrients. This has cascading effects on phytoplankton blooms, secondary biological production, fisheries, and the overall ecosystem function. Despite its significance, understanding of the trajectory of change and the mechanisms behind it remains precursory.
Theme 2.2 – Understand hydrographic restructuring after ice loss and freshening and its effects on biogeochemical cycling.
The impact of sea ice and freshwater influx on the water column's physical structure and biogeochemistry is unclear. Freshwater influx upon melt creates strong stratification, hindering mixing and causing inorganic carbon and nutrient gradients. Freshwater also directly dilutes inorganic carbon and alters alkalinity, while freshwater run-off from land carries carbon, nutrients, and alkalinity. Conversely, winter sea ice formation and associated brine release aid in re-mixing and re-distributing nutrients and inorganic carbon in the winter. With reduced sea ice cover, this freeze-melt cycle will change affect the distribution of inorganic carbon and nutrients available to primary producers. This will affect biological communities and CO2 uptake. We expect while the water column may freshen over the long term, brine release during winter ice formation may counteract summer stratification, but as ice forms from fresher and fresher water, this mechanism may be lost, ultimately impeding nutrient renewal to surface waters during winter.
