Stephanie Pfirman

Reconstructing the origin and trajectory of drifting Arctic sea ice

Recent studies have indicated that drifting Arctic sea ice plays an important role in the redistribution of sediments and contaminants. Here we present a method to reconstruct the back- ward trajectory of sea ice from its sampling location in the Eurasian Arctic to its possible site of ori- gin on the shelf, based on historical drift data from the International Arctic Buoy Program. This method is verified by showing that origins derived from the backward trajectories are generally con- sistent with other indicators, such as comparison of the predicted backward trajectories with known buoy drifts and matching the clay mineralogy of sediments sampled from the sea ice with that of the seafloor in the predicted shelf source regions. The trajectories are then used to identify regions where sediment-laden ice is exported to the Transpolar Drift Stream: from the New Siberian Islands and the Central Kara Plateau. Calculation of forward trajectories shows that the Kara Sea is a major contributor of ice to the Barents Sea and the southern limb of the Transpolar Drift Stream.

The potential transport of pollutants by Arctic sea ice

Abstract 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.

The role of the large-scale Arctic Ocean circulation in the transport of contaminants

Abstract 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).

Methane-generated(?) pockmarks on young, thickly sedimented oceanic crust in the Arctic: Vestnesa ridge, Fram strait

Acoustic backscatter imagery in the Fram strait (between Greenland and Spitzbergen) reveals a 1-3-km-wide, 50-km-long belt of ∼50 pointlike backscatter objects decorating the ∼1300-m-deep crest of Vestnesa Ridge, a 1- >2 km thick sediment drift possibly underlain by a transform-parallel oceanic basement ridge (crustal ages ∼3-14 Ma). A 3.5 kHz seismic-reflection profile indicates that at least some objects are pockmarks ∼100-200 m in diameter and 10-20 m deep. The pockmarks (possibly also mud diapirs) may have been formed by evolution of methane generated by the decomposition of marine organic matter in the Vestnesa ridge sediment drift. The ridge may be underlain by an anticlinal carapace of methane-hydrate calculated to be 200-300 m thick, comparable to the hydrate thickness measured just to the south. The rising methane would collect in the ridge-crest trap, intermittently escaping to the sea floor. This hypothesis is supported by multichannel evidence for bright spots and bottom-simulating reflectors in the area. The pockmark belt may also be located above a transcurrent fault. Sediment slumps on the flanks of Vestnesa ridge and northeast of Molloy ridge may have been triggered by plate-boundary earthquakes and facilitated by methane hydrates.

Potential for rapid transport of contaminants from the Kara Sea

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.

Pathways and mean residence times of dissolved pollutants in the ocean derived from transient tracers and stable isotopes

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.

New satellite derived sea ice motion tracks Arctic contamination

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.

Tracer Studies of the Arctic Freshwater Budget

The freshwater lens covering the surface of the Arctic Ocean is roughly 50 to 150 meters thick and consists of river runoff, sea-ice meltwater, and low-salinity water of Pacific origin imported through Bering Strait. Whereas salinity data provide us with a good picture of the distribution and variability of the total freshwater contained in the Arctic Ocean, they cannot, in general, distinguish between the individual freshwater components. To obtain this information, measurements of additional water mass properties have to be performed.

Earth science instruction with digital data

Abstract 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 computers 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.

Righting the balance: Gender diversity in the geosciences

The blatant barriers are down. Women are now routinely chief scientists on major cruises, lead field parties to all continents, and have risen to leadership positions in professional organizations, academic departments, and funding agencies. Nonetheless, barriers remain. Women continue to be under-represented in the Earth, ocean, and atmospheric sciences. Lets do the numbers: As of 1997, women received 41% of all Ph.D.s in science and engineering, but only 29% of the doctorates in the Earth, atmospheric, and oceanographic sciences [NSF, 1999a]. Women were 23% of employed Ph.D.s across all fields of science, but only accounted for 13% in the geosciences. Womens salaries also lag: the median salary for all Ph.D. geoscientists was