Search

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 ( 7 Be, 210 Pb) and anthropogenic ( 137 Cs, 239 Pu, 240 Pu) 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 7 Be and 210 Pb, which are carried in the ice and are scavenged by any entrained SIS. All of the 7 Be and most of the excess 210 Pb 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 210 Pb inventories in two ice cores are 1–3 years. Values estimated from the 7 Be/ 210 Pb excess activity ratio of SIS are about 3–5 years. Finally, equilibrium values of the activity ratio of 210 Pb to its granddaughter 210 Po 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 239,240 Pu and 137 Cs and the 240 Pu/ 239 Pu 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. 240 Pu/ 239 Pu 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.

For at least a decade, U.S. funding agencies and university campuses have promoted the expansion of interdisciplinary research. At the same time, federal and local programs have sought to increase the participation of women and minorities in science, mathematics, and engineering. Research has focused on each of these trends independently, but very few studies have considered their interaction by asking how intellectual preferences for and professional consequences of interdisciplinary science might be influenced by gender, race, and/or ethnicity. Focused specifically on gender, this paper considers the expectation that women will be more drawn to interdisciplinary research, and explores the learning styles, work preferences, and career behaviors that might anticipate and/or explicate gender differences in interdisciplinary science. Principal mechanisms by which researchers engage in interdisciplinarity – cross-fertilization, team-collaboration, field-creation, and problem-orientation – are tested for evidence of gendering using preliminary empirical data from three studies. The results of this exploratory analysis offer clues about possible tendencies and raise questions about the potential costs and benefits for those who adopt them.

Earth Science instruction is challenged today by rapid information growth and a need to integrate information from a number of disciplines. Fortunately, most of this information is in digital form, so the computer's capacity to integrate, process and display data can help students learn from data. The Lamont Data Viewer, originally developed for research, has been modified to help students with this task. With it, students can view large data sets as maps, cross-sections or x–y plots of subdata sets or make calculations on the data set and view the resulting data as similar displays. All calculations and data transformations are made on a large Lamont server with the resulting figure or table being transmitted to the user via the Internet. Consequently, students can easily and rapidly access and process large data sets from disparate disciplines and view the resulting figures and tables in similar formats. Easy access to large Earth Science data sets adds a new dimension to the way students can learn about the Earth and requires certain data analysis skills. The educational value of acquiring and using such skills is beyond dispute, for they teach how science is done and are applicable to both scientific and nonscientific inquiry. Nevertheless, learning directly from data is a little explored activity, below the graduate level, and much needs to be learned to maximize the gain from this form of pedagogy.

During the past decades, a variety of transient tracers have been used to derive information on pathways and mean residence times of oceanic water masses. Here, we discuss how information obtained in such studies can be applied to studying the spreading of dissolved pollutants in the ocean. The discussion focuses on the transient tracers tritium/3He and the H218O/H216O ratio of water. These tracers are used in combination with CFCs and 14C in a case study of Arctic Ocean contaminant transport to: (1) separate the freshwater components contained in the near-surface waters; (2) infer mean pathways of freshwater and associated contaminants from the H218O/H216O distribution in the surface waters; and (3) determine mean residence times of the surface, intermediate, deep and bottom waters.

Export of sea ice from the Kara Sea may redistribute contaminants entrained from atmospheric, marine and riverine sources. Ice exiting the Kara Sea ice to the north, will influence the Fram Strait, Svalbard and Barents Sea regions. Kara Sea ice may also be exported to the Barents Sea through straits north and south of Novaya Zemlya. Some ice from the Kara Sea makes its way into the Laptev Sea to the north and south of Severnaya Zemlya. Data on ice exchange and contaminant levels are not adequate to assess contaminant flux.

Sea ice has been reported to contain contaminants from atmospheric and nearshore sediment resuspension processes. In this study successive passive microwave images from the 85.5 GHz channels on the Special Sensor Microwave Imager (SSM/I) were merged with drifting buoy trajectories from the International Arctic Buoy Program to compute Arctic sea ice motion in the Russian Arctic between 1988 and 1994. Smooth daily motion fields were averaged to prepare monthly maps making it possible to compute the 7-year mean and mean seasonal ice motions as well as principal components of directional variability of sea ice motion for the entire Arctic and surrounding basins. These mean motion vectors are used to simulate the advection of contaminants deposited on or contained within the sea ice and subsequently transported into the Arctic Ocean in order to predict both their mean trajectories and dispersal over time. The 3-year displacement of contaminants from a number of Russian sites and one American site display various behaviours from substantial displacement and dispersal to almost no movement. This computational procedure could be applied to realtime SSM/I and ice buoy data to provide detailed, all-weather, vector motion maps of ice circulation to predict the path and dispersal of any new substance introduced to the sea ice and transported into the Arctic or Antarctic ocean surface.

The key features of the large-scale circulation of the Arctic Ocean are reviewed based on distributions of hydrographic parameters and natural and anthropogenic trace substances. Salinity and mass balances, as well as a combination of the tracers tritium and δ 18 O, suggest a mean residence time of the shelf waters in the Siberian seas of about 3 years. Potential pathways of pollutants released to the Siberian shelf seas from the dumpsites or from river runoff are inferred from the distributions of δ 18 O and salinity. Transit times needed for dissolved contaminants to cross the central Arctic basins (several years to one or two decades in near-surface waters) and mean residence times of contaminants in the intermediate (several decades) and deep waters (several centuries) are estimated from the distribution of transient tracers (tritium and its radioactive decay product, 3 He) and “steady-state” tracers ( 14 C and 39 Ar).

Nuclear activity on land and dumping of waste in the Siberian shelf seas mean that the Kara Sea is most likely to experience inputs of radioactivity. Industrial and other anthropogenic activities in the expansive Ob' and Yenisey watersheds also contribute organochlorines, heavy metals and oil to this region. Contaminant fate is influenced by the distribution of the river discharge and processes associated with ice formation and ocean currents. Although average conditions are important in the transport of pollutants, events such as storms and iceberg gouging may be critical in deciding the ultimate fate of dumped and released contaminants.

Drifting sea ice in the Arctic may transport contaminants from coastal areas across the pole and release them during melting far from the source areas. Arctic sea ice often contains sediments entrained on the Siberian shelves and receives atmospheric deposition from Arctic haze. Elevated levels of some heavy metals (e.g. lead, iron, copper and cadmium) and organochlorines (e.g. PCBs and DDTs) have been observed in ice sampled in the Siberian seas, north of Svalbard, and in Baffin Bay. In order to determine the relative importance of sea ice transport in comparison with air/sea and oceanic processes, more data is required on pollutant entrainment and distribution in the Arctic ice pack.

Satellite images from the Kara Sea show that, until July, fast-ice extends along the coast and Fills the estuaries of the Ob' and Yenisey rivers. It is separated from offshore drift-ice by a region of open water, comprising a flaw lead/polynya. By August, much of the fast and drift-ice has melted and retreated from the southwestern Kara Sea, leaving behind a persistent patch of sea-ice east of Novaya Zemlya. Because both the OF and Yenisey rivers discharge water throughout the winter, the fast-ice is likely to incorporate river-borne contaminants by bottom adfreezing. During peak river discharge in June, the fast-ice remains in place, and is potentially influenced by the river outflow throughout the length of the estuary. Breakup and melting of the fast-ice in July could release contaminants to the surface waters. By late July and August, when the fast-ice has disappeared, the river discharge is observed primarily along the shore in a zone that extends offshore more than 100 km. In fall, newly-forming ice may incorporate contaminants from the river plume, while in late winter, convection penetrating to the sea floor may allow resuspended sediments to be entrained in ice forming in the flaw lead/polynya. Drift-ice formed in this region could then advect contaminants offshore. The potential for exchange of water, ice and contaminants with the Barents Sea through Karskiye Vorota, south of Novaya Zemlya, is discussed in the context of the temperature and turbidity distribution observed in the satellite images.

Polar bears and other ice-dependent species could survive in northern extremes provided we act now to limit the impact of human activity in the Arctic

Present conditions and sedimentary evolution of the shallow offshore region near Nauset Inlet on Cape Cod, Massachusetts were clarified using high-resolution seismic-reflection profiles, sidescan-sonar records, surface grab samples and current meter measurements. The study area contains three provinces: (1) a nearshore province (shallower than 18 m) with a relatively steep slope (0.6°) and a cover of medium sand; (2) a northern offshore province covered with coarse sand, gravel, and boulders, interpreted to be glacial drift; and (3) a southern offshore province with a gentle seaward-dipping slope (0.3°) and a surface sediment of coarse sand. The glacial drift exposed in the northern offshore province can be traced southward under the coarse sand province. The overlying fill is comprised of either outwash sediment derived from the Pleistocene South Channel ice lobe to the east or Holocene-aged marine sediments eroded from seacliffs to the north. Latest Holocene sediment appears to be limited to the zone shoreward of 18 m where the medium sand occurs. Near-bottom mean flows (measured over two winter months in 10 m water depth) average 6 cm sec −1 to the south. Mean flows exceeded 20 cm sec −1 approx. 23% of the time. Ninety percent of the flows exceeding 20 cm sec −1 were directed to the south, reflecting the dominant atmospheric forcing during these winter months. Waves had an average variance of 650 cm 2 with variance exceeding 5000 cm 2 , 3% of the time, indicating moderate wave activity. Present processes are actively reshaping the nearshore province, which is characterized by many east to northeast-trending shore-oblique channels that do not extend seaward of the 18-m contour. Coarse sand in the floors of these channels suggests they may be erosional features, and the presence of megaripples oriented perpendicular to the channel axes indicates active transport in these channels. Megaripple orientation and the current and wave regime of the study area support a rip-current origin for these channels.

Sediments on high Arctic shelves result from modern processes and the effect of former glaciations. Based on data from the northern Barents Sea, an area with input from large and numerous surging glaciers, we define two principal zones with different environmental regimes and corresponding sedimentary facies: (1) a glacier-proximal zone influenced by grounding-line processes and the immediately adjacent areas affected by glacial sediment input, and (2) a glacier-distal, sea-ice and current-controlled zone, which also includes a wide sediment-starved region dominated by biogenic carbonate accumulation. Characteristic of the glacier-proximal zone are glacial surges which affect sedimentation rates and leave a diagnostic pattern of sea-floor morphologies. Extensive ice gouging causes a homogeneous sediment texture. In the glacier-distal zone, fine-grained mud supplied from sea ice and infrequent coarser material deposited from icebergs is reworked by modern oceanographic processes. On shallow banks, in 30–50 m of water, carbonates accumulate from a prolific bottom fauna formed in response to extensive reworking and nutrient supply.

Acoustical profiling and bottom photography reveal several different sea-floor morphological features adjacent to the grounded Brasvellbreen glacier on Svalbard, northwestern Barents Sea. Some of the features and their distribution may be closely related to a major glacial surge in 1936–1938, and as such are valuable in identifying former surges in other locations. A continuous, wide ridge with a characteristic asymmetrical cross-section, running subparallel to the glacier, is the end moraine defining the maximum extent of the surge. A large part of the material forming this ridge is most likely rapidly deposited from meltwater during the surge. A rhombohedral pattern of smaller mounds inside the ridge is probably an expression of relief in the glacier sole during the surge. Discontinuous arcuate ridges define local, minor oscillations during retreat of the ice at a later stage. Iceberg plough marks are most frequent seaward of the end moraine, their orientation is controlled by the combination of a coastal current, offshore katabatic winds and topography. Superimposed on plough marks are secondary features such as a “washboard pattern” and striae, most likely caused by push-up of overconsolidated material during gouging and multi-keel icebergs, respectively. Bottom sediments, observed in photographs and cores, are loose, pebbly muds with high variability in clast content, resting on overconsolidated material, probably basal till. Mud deposition presently prevails close to the glacier.

The ice-proximal environment of the Nordaustlandet tidewater ice cap, Svalbard Archipelago, is one of the best analogues for understanding glacial geologic processes of northern continental shelves during initial Pleistocene deglaciation. Investigations of the proglacial region in 1980–1983 showed that the sedimentary environment is dominated by numerous meltwater outflows which discharge sediment-laden water from subglacial meltwater streams during the summer. Two large, stable meltwater outflows were observed in embayments along the southern part of the ice front. Landsat images show that both outflows have been in approximately the same position since at least 1976. They are located at the intersection of glacial drainage basins and centered over depressions in the underlying bedrock. An “outflow valley” extending away from the ice front was observed in front of the western meltwater outflow. Sidescan sonar profiling along the glacier front showed a 200 m wide gap in acoustic reflection at the base of the western meltwater outflow, probably caused by meltwater effluence. Enhanced sediment accumulations in this region, observed as a ≈ 3 ms sediment drape in front of the outflow, and large arcuate ridges in the outflow valley, testify to the transport efficiency of the subglacial meltwater stream. Several mounds, up to about 25 m high and 200 m wide, are observed on sidescan and 3.5 kHz profiles directly in front of the outflow. Although samples from these structures are absent, they are most likely composed of sediment and are similar to beaded eskers observed in Pleistocene glacimarine sequences indicating locally very high sedimentation rates. Fine-grained components of the subglacial discharge incorporated in the buoyant meltwater plume are usually entrained in a westerly coastal current. Elevated suspended particulate material concentrations are observed within the coastal waters in a region extending about 15 km perpendicular to the glacier front and at least 60 km along the ice front extending into the northwestern Barents Sea.