C040-03
Greenland Icebergs as a source of sediment and micronutrients to the ocean domain

Friday, 11 December 2020: 10:38
Virtual
Irina Overeem, University of Colorado at Boulder, CSDMS/INSTAAR, Boulder, CO, United States, Ethan Pierce, Institute for Arctic and Alpine Research, Boulder, United States, Bent Hasholt, University of Copenhagen, Department of Geosciences and Natural Resource Management, Copenhagen, Denmark, Thomas M Marchitto Jr, Univ Colorado, Boulder, CO, United States, Jasmine S S Hansen, University of Colorado Boulder, Geological Sciences, Boulder, CO, United States, Asa K Rennermalm, Rutgers University, New Brunswick, NJ, United States and Sasha Z Leidman, University of California Davis, Davis, CA, United States
Recorded Presentation
Abstract:
The Greenland Ice Sheet is a critically important and rapidly changing component of the Arctic climate and North Atlantic Ocean system. Estimates from satellite observations and modeling combined find that the Greenland Ice Sheet loses 260-380 Gt of ice per year. The current mass imbalance of the ice sheet provides a significant freshwater and sediment flux to the global oceans. Yet, sediment flux originating from calving glaciers, so-called ice-rafted debris, is a much less known component of the Greenland Ice Sheet's decay. Satellite data now constrains the flux of icebergs themselves, sparse sediment data suggests as much as ~2.8 Gt of sediment rafts with them each year.

Lacking a better quantification is prohibiting our understanding of the controls of the biological carbon pump in the North Atlantic. Its ecosystem is known to be nutrient limited, and we speculate that enhanced fluxes of micronutrients promote vigorous phytoplankton blooms. Once plankton dies off, it sinks into deep water and sequesters carbon. Thus, icebergs may be fertilizing the ocean and dampen global warming. Until we better quantify sediment rafting with icebergs, and its geochemical composition, we will not be able to quantify this mechanism.

Over two exploratory field campaigns in 2018 and 2019, we have collected triplicate samples of iceberg sediment concentration from 24 bergy bits and icebergs in Scoresby Sund, East Greenland, and 25 icebergs in Gothab Fjord, West Greenland. Samples are analyzed for volume and weight sediment concentration and analyzed with inductively coupled plasma mass spectrometry for iron content. Preliminary results demonstrate very large variations in sediment concentration, both within single icebergs and between icebergs. To further develop a database of iceberg sediment concentrations, we developed detailed sampling protocols to be shared amongst glaciologists to further expand the data with samples of opportunity from differn caving fronts and possibly different lithologies of bedrock parent material.

Here we will discuss sampling startegies, and highlight some of new sediment flux reconstructions that allow us better to quantify accuracy of the determination of sediment transport by calving. Ultimately, the data will be used to develop a coupled model of glacier dynamics and sediment entrainment.

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