Description: The natural cosmogenic radionuclide 7Be (T1/2 = 53.4 d) is supplied to the surface ocean from the atmosphere and, in the Arctic Ocean, can be used as a tracer of the efficiency with which sea ice intercepts the atmospheric fluxes of chemical species and of the importance of ice as a transport mechanism for particulate matter and chemical species. Analyses of 7Be in samples of surface water, surface sea ice, water beneath the ice, sea ice sediments, and precipitation from the Eurasian Basin of the Arctic Ocean show that the fraction of sea ice coverage determines the amount of 7Be in the surface water. When sea ice coverage is 〈40%, the 7Be inventory in the upper ocean (130 ± 19 Bq m−2) is in good agreement with that expected from the inventory from 7Be atmospheric flux (128 ± 21 Bq m−2). In contrast, when ice coverage is 〉80%, the water column inventory drops to 58 ± 20 Bq m−2. The 7Be inventory in sea ice is 39 ± 23 Bq m−2, and mass balance calculations show that sea ice can intercept 30 ± 18% of the atmospheric flux of 7Be during the studied period. We suggest that other atmospherically transported contaminants should be similarly intercepted. 7Be in the ice also can be used to estimate that the annual transport and release of sediment to the ablation area of the Fram Strait is ∼500 g m−2, a value comparable to previously measured fluxes in sediment traps deployed in the area.

Description: The Arctic Ocean is characterized by being covered by sea ice with a large degree of seasonal variability between summer and winter. Along the whole life cycle of sea ice, diverse physical and chemical processes determine the concentration of the sea-ice sediments (SIS) and the chemical species entrapped in it and their final fate. Initially, sea ice incorporates particles (SIS) and associated chemical species (metals, nutrients, contaminants, etc.) during its formation mainly in the continental shelves, while dissolved solutes are excluded. As sea ice drifts offshore to the central Arctic Basin, it intercepts chemical species from the atmosphere and, the sediments in the ice may also incorporate some chemical solute compounds from the surface waters by scavenging (although this is likely small). Eventually, transported components, chemical species and SIS, are released to the underlying water column during melting. Thus, sea ice becomes an important transpo rt and distribution agent. However, the efficiency of interception of atmospheric fluxes by sea ice, the origin of the entrapped SIS and transit times of sea ice in the Arctic, as well as the importance of the transport of chemical species and particulate matter (SIS) and its release in the ablation area are all poorly understood. In an attempt to address these questions, a suite of natural (7Be and 210Po-210Pb) and artificial (137Cs, 239,240Pu) radionuclides were analysed in samples from precipitation, sea ice, surface water, water beneath ice and sea-ice sediments collected during the ARK XXII/2 expedition in 2007. The distributions of 7Be and 210Pb showed enrichment in sea ice (129 ± 90 and 5.1 ± 2.9 Bq·m-3, respectively) with respect to surface water (7.1 ± 1.3 and 1.1 ± 0.36 Bq·m-3, respectively). Given that only 4% of the total amount of 210Pb in sea ice comes from seawater and that any 7Be (T1/2 = 53 days) trapped in sea ice during its formation has decayed during drift, the direct atmospheric flux appears as the most important source of both radionuclides in sea ice. From mass balance calculations we estimate that sea ice intercepts about 30% of the 7Be atmospheric flux. This figure may be extrapolated to other chemical species with atmospheric sources, such as metals, nutrients, and contaminants. Given that 7Be and 210Pb are intercepted and accumulated during sea ice transit and also scavenged by SIS, we can use both radionuclides to assess sea ice transit time. Using the 210Pb inventory in ice floes respect to the 210Pb atmospheric flux intercepted by sea ice and the 7Be/210Pbex activity ratio in SIS, we estimated transit times from less than 0.5 to 3 years along the Eurasian Basin. Results are consistent with information reported by satellite maps and back-trajectories analysis of the sampled sea ice floes. Indeed, the SIS presence indicates that the ice floes come from continental shelves, and their origin can be constrained using artificial radionuclides (137Cs and the 239,240Pu) in SIS. Data shows that most of the SIS in the Eurasian Basin originated from the Siberian shelves, in agreement with back-trajectory analyses and main drift patterns. The relevance of sea ice as a significant transport and source of radionuclides in melting areas, such as the Fram Strait, is reflected in the annual fluxes of dissolved 7Be and 210Pb carried by sea ice (67 ± 55 and 13 ± 7 Bq·m-2·y-1, respectively), which are comparable to atmospheric inputs in this region (113-131 and 10-18.3 Bq·m-2·y-1, for 7Be and 210Pb). In addition, the annual mass flux of SIS to the Fram Strait, assessed using a 7Be mass balance and the mean annual ice area efflux through the Fram Strait, is on average 240 (4.5 - 1700) ·106 tons. As a reference, the discharge of sediment load from Arctic rivers is of about 115·106 tons per year.

Description: 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..

Description: Summary Meteor Cruise M81/1 was dedicated to the investigation of the distribution of dissolved and particulate trace metals and their isotopic compositions (TEIs) in the full water column of the tropical Atlantic Ocean and their driving factors including main external inputs and internal cycling and ocean circulation. The research program is embedded in the international GEOTRACES program (e.g. Henderson et al., 2007), which this cruise was an official part of and thus corresponds to GEOTRACES cruise GA11. This cruise was completely dedicated to the trace metal clean and contamination-free sampling of waters and particulates for subsequent analyses of the TEIs in the home laboratories of the national and international participants. Besides a standard rosette for the less contaminant prone metals, trace metal clean sampling was realized by using a dedicated and coated trace metal clean rosette equipped with Teflon-coated GO-FLO bottles operated via a polyester coated cable from a mobile winch that was thankfully made available by the U.S. partners of the GEOTRACES program for this cruise. The particulate samples were also collected under trace metal clean conditions using established in-situ pump systems. The cruise track led the cruise southward from the Canary Islands to 11°S and then continued northwestward along the northern margin of South America until it reached Port of Spain, Trinidad & Tobago. The track crossed areas of major external inputs including exchange with the volcanic Canary Islands, the Saharan dust plume, as well as the plume of the Amazon outflow. In terms of internal cycling the equatorial high biological productivity band, as well as increased productivity associated with the Amazon Plume were covered. All major water masses contributing the Atlantic Meridional Overturning Circulation, as well as the distinct narrow equatorial surface and subsurface east-west current bands were sampled. A total of 17 deep stations were sampled for the different dissolved TEIs, which were in most cases accompanied by particulate sampling. In addition, surface waters were continuously sampled under trace metal clean conditions using a towed fish.

Description: Abstract ID: 11526 PosterID: A0020 We are focused on determining the total concentrations of the anthropogenic radionuclides 239Pu, 240Pu, 237Np, and 137Cs in depth profiles from 2010 Atlantic GEOTRACES sections. Data from the equatorial region (A11) compared to GEOSECS data indicate water column inventories of 137Cs have increased over the last 40 years, while those of Pu are variable. By comparison, Pu and 237Np water column inventories are similar to regional soil core inventories, whereas 137Cs inventories are significantly higher, further suggesting continued supply of 137Cs to the open ocean. Water column 240Pu/239Pu inventory ratios are indicative of global fallout (~0.18). Deviations of the water column 237Np/239Pu inventory ratio from the average global fallout value (~0.48) can be used to estimate Pu-particulate fluxes, which are comparable to sediment trap data and may be used to assess scavenging at different locations along the cruise track. Data from mid and high latitude regions (A02) will be compare them to GEOSECS data; inventories and ratios will be used to identify additional contaminant sources, as water mass tracers, and to elucidate important processes such as scavenging and remineralization.

Description: The natural cosmogenic radionuclide 7Be (T1/2 = 53.4 d) is supplied to the surface ocean from the atmosphere and, in the Arctic Ocean, can be used as a tracer of the efficiency with which sea ice intercepts the atmospheric fluxes of chemical species and of the importance of ice as a transport mechanism for particulate matter and chemical species. Analyses of 7Be in samples of surface water, surface sea ice, water beneath the ice, sea ice sediments, and precipitation from the Eurasian Basin of the Arctic Ocean show that the fraction of sea ice coverage determines the amount of 7Be in the surface water. When sea ice coverage is 80%, the water column inventory drops to 58 ± 20 Bq m−2. The 7Be inventory in sea ice is 39 ± 23 Bq m−2, and mass balance calculations show that sea ice can intercept 30 ± 18% of the atmospheric flux of 7Be during the studied period. We suggest that other atmospherically transported contaminants should be similarly intercepted. 7Be in the ice also can be used to estimate that the annual transport and release of sediment to the ablation area of the Fram Strait is ∼500 g m−2, a value comparable to previously measured fluxes in sediment traps deployed in the area.