Large organic matter pools accumulate in Arctic sea ice due to the activity of algae and other microorganisms that live within the ice. In seasonal (first-year) sea ice, the build up of organic matter coincides with a spring bloom of ice algae, which are responsible for a significant fraction of total annual marine primary production in the Arctic. Loss of organic matter from seasonal ice in the Arctic is thought to be minor until late spring, when material begins to be exported from the ice into the water column. The algae themselves are mostly exported from the ice within the initial flux period. However, large organic pools that remain in the ice after the loss of algae will also eventually be exported as the ice melts. The ecological and biogeochemical connections between the organic material in sea ice and other components of the Arctic marine system, therefore, depend on the fate of the exported material, i.e., whether it is retained and consumed in the water column, consumed by the benthos, or sequestered in the sediments. This in turn, depends largely on the sinking rate and nutritional quality of particles released from the ice. Available data on the sinking rates of ice algae are highly divergent, while the characteristics of particles formed from other large organic pools in sea ice have received little study. The role in particle formation of exopolymeric substances (EPS) produced by ice algae is key to this proposal. The importance of EPS to particle coagulation and sinking rate is well established for temperate water columns. In sea ice, EPS comprise 20-70% of total particulate organic carbon, but their role in the sinking rate and composition of particles exported from sea ice is poorly understood. Based on previous studies, we predict both positive and negative effects of EPS on particle sinking rate depending on EPS quantity. EPS will also increase the ratio of carbon to nitrogen (C:N) in the organic matter, which serves as a nutritional indicator. Thus, the relative amount of EPS available during particle formation is likely critical. Based on documented trends in the EPS content of first-year Arctic sea ice, we specifically predict slower sinking rates and higher C:N in particles produced after the export of ice algae, and from the upper levels of the ice column. We also predict slower sinking rates and higher C:N where snow cover is thicker. Using well-established techniques, we will measure the sinking rates of particles released from melted sea-ice cores and test our hypotheses by relating the observed sinking rates to variables such as EPS concentration in the ice. Changes in the contribution of the sea-ice community to different flux periods will be investigated using microscopy and DNA-based molecular techniques. Finally, to help explain the spatial variability in the EPS content of sea ice, we will quantify EPS production rates of cultured ice algae as a function of light level.
|Effective start/end date||1/1/11 → 12/31/14|
- NSF-GEO-PLR: Office of Polar Programs (OPP): $308,804.00
particulate organic carbon