Arctic sea ice can incorporate sediment and associated chemical species during its formation in shallow shelf environments and can also intercept atmospherically transported material during transit. Release of this material in ice ablation areas (e.g. the Fram Strait) enhances fluxes of both sediments and associated species in such areas. We have used a suite of natural (7Be, 210Pb) and anthropogenic (137Cs, 239Pu, 240Pu) radionuclides in sea ice, sea-ice sediments (SIS), sediment trap material and bottom sediments from the Fram Strait to estimate transit times of sea ice from source to ablation areas, calculate radionuclide fluxes to the Fram Strait and investigate the role of sea-ice entrained sediments in sedimentation processes. Sea ice intercepts and transports the atmospherically supplied radionuclides 7Be and 210Pb, which are carried in the ice and are scavenged by any entrained SIS. All of the 7Be and most of the excess 210Pb measured in SIS collected in the Fram Strait are added to the ice during transit through the Arctic Ocean, and we use these radionuclides as chronometers to calculate ice transit times for individual ice floes. Transit times estimated from the 210Pb inventories in two ice cores are 1–3 years. Values estimated from the 7Be/210Pbexcess activity ratio of SIS are about 3–5 years. Finally, equilibrium values of the activity ratio of 210Pb to its granddaughter 210Po in the ice cores indicate transit times of at least 2 years. These transit times are consistent with back-trajectory analyses of the ice floes. The latter, as well as the clay-mineral assemblage of the SIS (low smectite and high illite content), suggest that the sampled sea-ice floes originated from the eastern Siberian Arctic shelf seas such as the eastern Laptev Sea and the East Siberian Sea. This result is in agreement with the relatively low activities of 239,240Pu and 137Cs and the 240Pu/239Pu atom ratios (∼0.18, equivalent to that in global fallout) in SIS, indicating that prior global atmospheric fallout, rather than nuclear fuel reprocessing facilities, forms the main source of these anthropogenic radionuclides reaching the western Fram Strait at the time of sampling (1999). Transport of radionuclides by sea ice through the Arctic Ocean, either associated with entrained SIS or dissolved in the ice, accounts for a significant flux in ablation areas such as the Fram Strait, up to several times larger than the current atmospheric flux in the area. Calculated fluxes derived from sea-ice melting compare well to fluxes obtained from sediment traps deployed in the Fram Strait and are consistent with inventories in bottom sediments. 240Pu/239Pu atomic ratios lower than 0.18 in bottom sediments from the Fram Strait provide evidence that plutonium from a source other than atmospheric fallout has reached the area. Most likely sources of this Pu include tropospheric fallout from atomic weapons testing of the former Soviet Union prior to 1963 and Pu released from nuclear reprocessing facilities, intercepted and transported by sea ice to the ablation areas. Future work is envisaged to more thoroughly understand the actual mechanisms by which radionuclides are incorporated in sea ice, focusing on the quantification of the efficiency of scavenging by SIS and the effect of melting and refreezing processes over the course of several years during transit.

Atom ratios of 240Pu to 239Pu in bottom sediments from the Fram Strait are used to provide evidence for the long distance dispersion of Pu in the Arctic Ocean. In particular, low (<0.18) 240Pu/239Pu ratios indicate that plutonium from sources in the Kara Sea and Novaya Zemlya is transported across the basin toward the North Atlantic. The results have implications for the ability of sea ice to incorporate, intercept, and transport contaminants in the Arctic Ocean. They demonstrate that the fates of sea ice and associated contaminants in the Arctic Ocean are closely coupled, with the release of the particulate load and associated chemical species occurring in principal sea ice ablation areas such as the Fram Strait.

This model study investigates the role of Siberian river runoff for the transport of possible river contaminants in the Arctic Ocean. Three-dimensional coupled ice-ocean-models of different horizontal resolution are applied to simulate the dispersion of river water from Ob, Yenisei and Lena. These Siberian rivers are supposed to be important sources for various contaminants. The relevant processes which are considered in this study include the dispersion of dissolved or suspended contaminants in the water column and the transport of contaminated particles, incorporated into drifting sea ice.Circulation model results from both spatial scales explain the main pathways and transit limes of Siberian river water in the Arctic Ocean. Kara Sea river water clearly dominates in the Siberian branch of the Transpolar Drift, while the Lena water dominates in the Canadian branch. River water concentrations in Nares Strait, Canadian Archipelago, are similar to those in the northern Fram Strait. Special emphasis is given to the seasonal variability of the river plume in the Kara Sea. Particle tracking simulations on the regional scale illustrate that Ob and Yenisei tracers behave differently. Yenisei tracers leave the Kara Sea quite fast towards the Arctic Ocean or the Laptev Sea, but Ob tracers spread also in the southern Kara Sea, in particular at lower levels.A comparison of simulated freezing rates and particle concentrations in Siberian coastal waters suggests that during autumn, the incorporation of particles into freezing sea ice near the estuaries of Ob and Yenisei is very likely. Simulated ice trajectories, started close to the Lena river delta easily reach the multi-year Transpolar Drift within one winter. Ice trajectories from Ob and Yenisei estuaries, however, mostly drift towards the Parents Sea where the ice melts close to Svalbard. The model study confirms that contaminant transport through sediment-laden sea ice offers a short and effective pathway for pollutant transport from Siberian rivers to the Barents and Nordic Seas. (C) 2000 Elsevier Science B.V. All rights reserved.

A transport assessment of particle-bound and dissolved artificial radionuclides (137Cs and 239,240Pu) by sea-ice and dense-water formed in western Kara Sea flaw leads close to the Novaya Zemlya dumping sites is presented in this study. We both performed a “best estimate” based on available data, and a “maximum assessment” relying on simulated constant releases of 1 TBq 137Cs and 239,240Pu from individual dumping bays. The estimates are based on a combination of (i) the content of particulate matter in sea-ice; (ii) analytical data and numerical simulations of radionuclide concentrations in shelf surface deposits, suspended particulate matter (SPM), and the dissolved phase; and (iii) estimates of lead-ice and dense-water formation rates as well as modeling results of local ice drift pathways. In the “best estimate” case, 2.90 GBq 137Cs and 0.51 GBq 239,240Pu attached to sea-ice sediments can be exported from the lead areas toward the central Arctic basin. The radionuclide burden of the annually formed dense lead water in the “best estimate” amounts to 4.68 TBq 137Cs and 0.014 TBq 239,240Pu. In the “maximum assessment”, potential export-rates of ice-particle bound 137Cs and 239,240Pu toward the central Arctic would amount to 0.64 and 0.16 TBq, respectively. As much as ≈900 TBq 137Cs and ≈6.75 TBq 239,240Pu could be annually taken up by 34.75 dense-water rejected in the lead area. Assuming the (unlikely) instantaneous release of the total 137Cs and 239,240Pu inventories (≈1 PBq and 10 TBq, respectively) from the Novaya Zemlya dumping sites into the dissolved phase, the dense lead water locally formed during one winter season could take up ≈90% of the Cs and ≈68% of the Pu released.

The paper presents the results of the joint project carried out in Germany in order to assess the consequences in the marine environment from the dumping of nuclear wastes in the Kara and Barents Seas. The project consisted of experimental work on measurements of radionuclides in samples from the Arctic marine environment and numerical modelling of the potential pathways and dispersion of contaminants in the Arctic Ocean. Water and sediment samples were collected for determination of radionuclide such as 137Cs, 90Sr, 239 + 240Pu, 238Pu, and 241Am and various organic micropollutants. In addition, a few water and numerous surface sediment samples collected in the Kara Sea and from the Kola peninsula were taken by Russian colleagues and analysed for artificial radionuclide by the BSH laboratory. The role of transport by sea ice from the Kara Sea into the Arctic Ocean was assessed by a small subgroup at GEOMAR. This transport process might be considered as a rapid contribution due to entrainment of contaminated sediments into sea ice, following export from the Kara Sea into the transpolar ice drift and subsequent release in the Atlantic Ocean in the area of the East Greenland Current. Numerical modelling of dispersion of pollutants from the Kara and Barents Seas was carried out both on a local scale for the Barents and Kara Seas and for long range dispersion into the Arctic and Atlantic Oceans. Three-dimensional baroclinic circulation models were applied to trace the transport of pollutants. Experimental results were used to validate the model results such as the discharges from the nuclear reprocessing plant at Sellafield and subsequent contamination of the North Sea up the Arctic Seas.

The paper presents the results of a joint project combining numerical model studies and field work in order to investigate the dispersion of anthropogenic radioactivity in the Arctic Ocean. The results obtained underline the essential difference between the dispersion of dissolved contaminants in water and the transport of particulate material in sea ice. Coupled ice-ocean models on different spatial scales are applied to study the transit times and major pathways for radioactive contaminant transport in the water column. One of the main sources for radioactive pollution in the Arctic, the discharge of the Sellafield reprocessing plant, was simulated from 1965 until now. The results are compared with measurements and hypothetical release scenarios computed for the the dump sites of radioactive waste in the Kara Sea. Our comparison reveals that the Sellafield signal is by one or two orders of magnitude higher than any potential contamination from Kara Sea dump sites, even if a ’worst case’ scenario is assumed. In order to assess the role of sea ice in contaminant transport, sedimentological data from the Kara Sea and the Arctic Ocean were analysed. The results show that fine-grained Kara Sea sediments from dump site areas are predestined for entrainment into newly forming ice. Observed buoy drifts and simulated trajectories confirm that the Arctic Transpolar Ice Drift is a rather short pathway for pollutant dispersion from the Arctic Ocean to the adjacent Nordic Seas. However, compared to the large volume and contaminant flux in the ocean, the contaminant dispersion by sea ice plays a minor role.

The main objective of this research paper is to estimate the new-ice production in the Laptev Sea flaw lead during the 1991/1992 winter season. A one-dimensional energy balance model was applied to calculate ocean-to-atmosphere heat flux and the resulting new-ice formation over open water. For a detailed estimate of regional ice production, the flaw lead was divided into 14 sections based on the analysis of NOAA-satellite images and Russian ice charts. Opening and maintenance of the lead sections are controlled by offshore winds, whereas closing of open water is caused by onshore winds. Since the orientation of the lead varies from section to section, the same regional wind forcing can cause different local lead behavior. Model results reveal that the seasonally accumulated thickness of new ice formed in the different lead sections—under the assumption of instantaneous lateral new-ice removal from the water surface—varies from 1.3 m to 13 m over temporarily open water and may reach 20 m over permanently open water. The corresponding ice volume produced in the sections varies between 3.4 km3 and 59 km3 and amounts to 258 km3 for the entire lead. The significant regional variations in new-ice production are due to differences in (i) the number of days that a lead section is open (open-lead days), (ii) the oceanic heat loss during open-lead days, and (iii) the areal extent of the lead sections. As compared to other studies,—at least during 1991/1992 winter season—the Laptev Sea flaw lead produced between 28 and 617% more initial sea ice than the Kara, Barents, East Siberian and Chukchi leads. Despite its limited areal extent of roughly 36,000 km2, which represents only 8% of the entire Laptev Sea, the flaw lead produces about 32% of the annual shelf ice. The ice production in the flaw lead is 5.3 times higher than the remainder of the shelf (7.4 m vs. 1.4 m). Furthermore, the Laptev Sea flaw lead produces 2.6% of the ice annually formed the entire Arctic Mediterranean Sea and contributes about 9% to the volume of the Siberian branch of the Transpolar Drift Ice System. This makes the Laptev Sea flaw lead a significant producer of Arctic sea ice on local and regional scales, whereas the contribution of lead ice to the entire volume of annually formed pack in high northern latitudes amounts only to roughly 1.3%.