A. Sathy Naidu

WISCONSIN--HOLOCENE PALEOENVIRONMENT OF THE BERING SEA: EVIDENCE FROM DIATOMS, POLLEN, OXYGEN ISOTOPES AND CLAY MINERALS

Abstract A core from the southeastern Bering Sea contains a depositional record of the Wisconsin glacial interval and the Holocene. Four lithologic units show distinctive changes in diatom species, palynomorphs, oxygen isotopes in diatom silica, and clay minerals. Unit 4, the oldest, probably represents the glacial advance of the early Wisconsin and records extensive sea ice cover and a soggy, herbaceous tundra on the exposed continental shelf. Unit 3 represents the stades and interstades of the middle Wisconsin, including an early period of high seasonal variability and a later period with expansion of winter sea ice in the basin and of tundra onshore. Unit 2 represents the late Wisconsin glacial maximum and subsequent deglaciation with a tundra-covered shelf. Sea ice cover increased to a maximum, during which the surface waters were probably covered by sea ice throughout the year. Subsequent to the sea ice maximum the isotope ratios record a major meltwater event. Unit 1 represents the Holocene, with expansion of shrub tundra or scrub forest in the coastal upland and waters of increased temperature and salinity in the Bering Sea.

Comparison of mercury and methylmercury in northern pike and Arctic grayling from western Alaska rivers

In western Alaska, mercury (Hg) could be a potential health risk to people whose diet is primarily fish-based. In 2000, total Hg (THg) and methylmercury (MeHg) were examined in northern pike (Esox lucius) and Arctic grayling (Thymallus arcticus) from two watersheds in western Alaska, the Yukon and Kuskokwim rivers. Whitefish (Coregonus sp.) were also examined from the Kuskokwim River. Pike from the Yukon and Kuskokwim rivers had mean concentrations of THg in muscle of 1.506 and 0.628 mg/kg wet wt, respectively. The mean concentrations of THg in grayling muscle from these rivers were 0.264 and 0.078 mg/kg, respectfully. Whitefish had a mean THg concentration in muscle of 0.032 mg/kg. MeHg, in pike and grayling constituted nearly 100% of the THg concentrations; the proportion was less in whitefish. A significant positive correlation between Hg levels and fish length was also found. Generally, there were no changes in Hg concentrations in pike or grayling over the last several years. Only pike from theYukon River had THg concentrations that exceeded the USFDA action level for human consumption of edible fish (1 mg/kg). Human hazard index for pike was > or = 1 for both adults and children, indicating a potential for toxic concern, especially among children. Further studies are needed to determine the environmental and human health impacts associated with these Hg concentrations in western Alaska, especially in the context of potentially increased consumption of resident fishes when anadromous salmon catches are reduced.

Character, paleoenvironment, rate of accumulation, and evidence for seismic triggering of Holocene turbidites, Canada Abyssal Plain, Arctic Ocean

Abstract Four box cores and one piston core show that Holocene sedimentation on the southern Canada Abyssal Plain for the last 8010 ± 120 yr has consisted of a continuing rain of pelagic organic and ice-rafted clastic sediment with a net accumulation rate during the late Holocene of ⩽10 mm/1000 yr, and episodically emplaced turbidites 1–5 m thick deposited at intervals of 830 to 3450 yr (average 2000 yr). The average net accumulation rate of the mixed sequence of turbidites and thin pelagite interbeds in the cores is about 1.2 m/1000 yr. Physiography suggests that the turbidites originated on the Mackenzie Delta or its clinoform, and δ13C values of −27 to −25%. in the turbidites are compatible with a provenance on a delta. Extant displaced neritic and lower slope to basin plain calcareous benthic foraminifers coexist in the turbidite units. Their joint occurence indicates that the turbidites originated on the modern continental shelf and entrained sediment from the slope and rise enroute to their final resting place on the Canada Abyssal Plain. The presence of Middle Pleistocene diatoms in the turbidites suggests, in addition, that the turbidites may have originated in shallow submarine slides beneath the upper slope or outer shelf. Small but consistent differences in organic carbon content and δ13C values between the turbidite units suggest that they did not share an identical provenance, which is at least compatible with an origin in slope failures. The primary provenance of the ice-rafted component of the pelagic beds was the glaciated terrane of northwestern Canada; and the provenance of the turbidite units was Pleistocene and Holocene sedimentary deposits on the outer continental shelf and upper slope of the Mackenzie Delta. Largely local derivation of the sediment of the Canada Abyssal Plain indicates that sediment accumulation rates in the Arctic Ocean are valid only for regions with similar depositional sources and processes, and that these rates cannot be extrapolated regionally. The location of an elliptical zone of active seismicity over the inferred provenance of the turbidites suggests that they were triggered by large earthquakes. Distal turbidite sediment accumulation rates were more than two orders of magnitude greater than pelagic sediment accumulation rates on the Canada Abyssal Plain during the last 8000 years. This disparity reconciles the discrepancy between the high accumulation rates assumed by some for the Arctic Ocean because of the numerous major rivers and large ice sheets that discharge into this small mediterranean basin and the low pelagic sedimentation rates that have been reported from the Arctic Ocean.

Assessment of Heavy Metals in Red King Crabs Following Offshore Placer Gold Mining

Abstract Red king crabs, Paralithodes camtschaticus, with commercial and subsistence importance, seasonally occur nearshore in Norton Sound, north-eastern Bering Sea, Arctic Alaska. Since the end of the nineteenth century, the coastal area in the northern Sound has been intensively mined for placer gold. Mining was extended offshore in 1986–1990. Heavy metal concentrations in the crabs were monitored during 1987–1990 to assess the impact of offshore mining. Crabs were only present in the study area during ice-covered months when mining was seasonally suspended. Arsenic, Cd, Cr, Cu, Pb, Ni, Zn and Hg concentrations in muscle and hepatopancreas tissues were generally not different between mined and unmined reference (control) areas. Furthermore, concentrations of these metals were not different in similar surficial sediments upcurrent and downcurrent of mining. The concentrations of most metals in both tissues fluctuated over the study period, with no temporal trend. Exceptions were for Hg in muscle tissue and As in hepatopancreas tissue which showed progressive significant increases each year. Also, there was a fractionation of selected metals between the two tissues; Cr, Pb and Zn were greater in muscles, whereas Cd, Cu and Ni were greater in hepatopancreas. Arsenic and Hg had similar concentrations in both tissues. All elemental concentrations in the crab muscles from Norton Sound were below or within the range of concentrations observed in red king crabs from five other locations in the North Pacific, including a mined area. In Norton Sound, all metals, except Cd, were at least an order of magnitude below the US Food and Drug Administration guidance levels for contamination or human consumption. This investigation demonstrated that mining activities did not affect the concentrations of the heavy metals measured in red king crabs.

Recent Sediment Accumulation in a Mangrove Forest and Its Relevance to Local Sea-Level Rise (Ilha Grande, Brazil)

Abstract An accumulation rate in a well-developed mangrove forest has been associated with relative sea-level rise on an island off the coast of Rio de Janeiro State. This rate was calculated by 210Pb dating models from a single sediment core. Results indicate an accumulation rate of approximately 1.7 mm/y for the past approximately 100 years. This rate is almost identical to the ongoing eustatic mean rise in global sea level, indicating a tectonically stable mangrove habitat. Organic C (OC), total N, δ13C(OC), and δ15N values from selected core intervals suggest a constant source of accumulating vegetal debris, dominated by C3-type vegetation with insignificant input of marine-derived organic matter, and a stable subaerial mangal habitat.

Clay minerals as indicators of sources of terrigenous sediments, their transportation and deposition: Bering Basin, Russian-Alaskan Arctic

Abstract Cluster analysis of clay mineral abundances in surficial sediments from 52 stations revealed the presence of four station cluster groups within the Bering Basin and contiguous eastern Aleutian Trench/Forearc. These results can be explained using two end-members of terrigenous clay mineral sources, and their admixtures. The first end-member, Cluster Group I, consists of the highest (average) concentration of illite (48%) and chlorite plus kaolinite (40%) and lowest of expandable minerals (12%). In contrast, the second end-member, Cluster Group IV, has the highest concentration of expandable minerals (43%) and lowest concentrations of illite (30%) and chlorite plus kaolinite (27%). The Group I assemblages come from two regions: the eastern Aleutian Trench/Forearc and the northwestern margin of the Bering Basin off Koryak Mountains, east Siberia. Clays in the former region are derived primarily from the meta-sedimentary and meta-volcanic rocks of the Chugach Mountains with infiltrations from Alaska Peninsula, and are transported from the southeastern Kodiak Shelf of the Gulf of Alaska to the trench/forearc by the Alaska Current/Alaskan Stream. Similar clays are derived from the Koryak Mountains. Group IV clays, located within the Komandorsky and Bowers Basins and Unmak Plateau, originated from the Mio-Pliocene andesites and basalts of the eastern Kamchatka Peninsula and Aleutian Islands, respectively. It is postulated that Group II clays in the southcentral Aleutian Basin and Bowers Ridge/Basin area, and Group III clays in the northern Aleutian Basin, are mixtures obtained primarily from terrigenous sources of Group I and IV. The distribution patterns and boundaries of the cluster groups reflect the dispersal pathways of clays from the primary sources and the extent of their mixing by regional and local surface currents and mesoscale gyres/eddies. Presumably, the minor infiltration of Anadyr River clays into Group III is a result of clay transport by episodic turbidity currents. Most of the clays derived from the Alaska mainland and Russia proper do not reach the Bering Basin as these clays are trapped within the Bering Sea shelf.

Historical changes in trace metals and hydrocarbons in nearshore sediments, Alaskan Beaufort Sea, prior and subsequent to petroleum-related industrial development: Part II. Hydrocarbons

Concentrations of Fe, As, Ba, Cd, Cu, Cr, Pb, Mn, Ni, Sn, V and Zn in mud (<63μm size), and total and methyl Hg in gross sediment are reported for Arctic Alaska nearshore. Multivariate-PCA analysis discriminated seven station clusters defined by differences in metal concentrations, attributed to regional variations in granulometry and, as in Elson Lagoon, to focused atmospheric fluxes of contaminants from Eurasia. In Colville Delta-Prudhoe Bay, V increase was noted in 1985 and 1997 compared to 1977, and Ba increase from 1985 to 1997. Presumably the source of increased V is the local gas flaring plant, and the elevated Ba is due to barite accumulation from oil drilling effluents. In Prudhoe Bay, concentration spikes of metals in ∼1988 presumably reflect enhanced metals deposition following maximum oil drilling in 1980s. In summary, the Alaskan Arctic nearshore has remained generally free of metal contamination despite petroleum-related activities in past 40 years.