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Estimation of the transport of sea-ice sediment load and atmospheric accumulation in sea ice using 210Pb and 7Be

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Camara-Mor, P. , Masque, P. , Garcia-Orellana, J. , Cochran, J. K. , Stimac, I. and Hanfland, C. (2010): Estimation of the transport of sea-ice sediment load and atmospheric accumulation in sea ice using 210Pb and 7Be , Int. Symposium on sea ice in the physical and biogeochemical system, Tromsoe, Norway. May 31 - June 6 .
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From its formation until melting, sea ice is subject to diverse chemical, physical and structural processes that affect its properties and the role that it plays in the Arctic Ocean. During sea ice formation, it incorporates particles and their associated chemical species (metals, nutrients, contaminants, etc.) but excludes chemical dissolved solutes. In the open Arctic Ocean, sea ice intercepts chemical species from the atmosphere and, presumably in a minor proportion, may also incorporate some chemical solute compounds from the surface waters that can be scavenged by sea-ice sediments. Thus, sea ice drift becomes an important and relatively rapid agent for the transport and distribution of particulate matter and chemical compounds in the Arctic Ocean. Eventually, these materials are released into the underlying water column during melting. This discharge occurs on a relatively short timescale, enhancing sedimentation rates and biological productivity in ice ablation areas. Pb-210 and Be-7 are natural particle-reactive radionuclides with half-lives of 22.3 y and 54 d, respectively, and can be used as tracers of sea-ice processes. A first aim of this work is to estimate the sediment load of sea ice and the associated sediment flux to the water column in the Fram Strait by melting. Through mass balance of the distribution of both Pb-210 and Be-7, considering their atmospheric inputs, interception of sea-ice and inventories in the ocean and ice, the load of sea-ice sediments would range from 5 to 100 g/m2. This would lead to an annual release of sediments in the Fram Strait of 10 to 240 g/m2·y. These estimates are consistent with sediment fluxes estimated by using sediments trap deployed in the area, as well as with direct observations of presence of sediments in sea ice. A second result derived from the study of the distribution of Be-7 in the Arctic Ocean is the efficiency of sea ice in intercepting and accumulating the atmospheric inputs of chemical species such as metals, nutrients or organic contaminants, which can be of up to 44%. The redistribution of this load and the eventual release in ablation areas such as the Fram Strait during melting periods of relatively short duration points to the relevance of sea ice as a transport agent of atmospherically deposited load, that should receive further attention in terms of its impact in biogeochemical cycles in the area..

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