989 resultados para Alaska-Bering-Chukchi_Sea


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Esta es una traducción al francés de la obra Travel and Adventure in the Territory of Alaska publicada en Londres en 1868. El libro describe los viajes llevados a cabo en Alaska por el explorador y artista británico Frederick Whymper entre 1865 y 1867. Desde 1862 Whymper venía participando en distintas proyectos exploratorios de la Columbia Británica, como la expedición de exploración de la Isla de Vancouver (Vancouver Island Exploring Expedition, 1864), y el proyecto del telégrafo ruso americano, que buscaba unir a San Francisco y Moscú, por el estrecho de Bering (Western Union Telegraph Expedition 1865-1867), pasando por los territorios estadounidenses, británicos y rusos de Norte América

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Between 1991 and 1993, Alaska harbor porpoise (Phocoena phocoena) abundance was investigated during aerial surveys throughout much of the coastal and offshore waters from Bristol Bay in the eastern Bering Sea to Dixon Entrance in Southeast Alaska. Line-transect methodology was used, and only those observations made during optimal conditions were analyzed. Survey data indicated densities of 4.48 groups/100 km2, or approximately 3,531 harbor porpoises (95% C.I. 2,206-5,651) in Bristol Bay and 0.54 groups/100 km2, or 136 harbor porpoises (95% C.I. 11-1,645) for Cook Inlet. Efforts off Kodiak Island resulted in densities of 1.85 groups/100 km2, or an abundance estimate of 740 (95% C.I. 259-2,115). Surveys off the south side of the Alaska Peninsula found densities of 2.03 groups/100 km2 and an abundance estimate of 551 (95% C.I. 423-719). Surveys of offshore waters from Prince William Sound to Dixon Entrance yielded densities of 4.02 groups/100 km’ and an abundance estimate of 3,982 (95% C.I. 2,567-6,177). Combining all years and areas yielded an uncorrected density estimate of 3.82 porpoises per 100 km2, resulting in an abundance estimate of 8,940 porpoises (CV = 13.8%) with a 95% confidence interval of 6,746-11,848. Using correction factors from other studies to adjust for animals missed by observers, the total number of Alaska harbor porpoises is probably three times this number.

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The known summer feeding range of the North Pacific humpback whale (Megaptera novaeangliae) extends from California, along the coasts of Oregon, Washington, and Alaska, into the Bering Sea, along the Aleutian Islands, the Sea of Okhotsk (Tomilin 1957), and to northern Japan (Rice 1977). In feeding areas of the northeastern Pacific Ocean, humpback whale photoidentification research has been concentrated off California (Calambokidis et al. 1993), southeastern Alaska (Darling and McSweeney 1985, Baker et al. 1986, 1992; Perry et al. 1990), Prince William Sound in Alaska (von Ziegesar 1992), the Oregon and Washington coasts (Calambokidis et al. 1993), and British Columbia (Darling and McSweeney 1985; Graerne Ellis, unpublished data). Results of these photoidentification studies have documented that individual whales tend to return to the same general areas in subsequent years (Darling and McSweeney 1985, Baker et al. 1986, Calambokidis et a(. 1996, von Ziegesar et al. 1994).

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Arctic Ocean freshening can exert a controlling influence on global climate, triggering strong feedbacks on ocean-atmospheric processes and affecting the global cycling of the world's oceans. Glacier-fed ocean currents such as the Alaska Coastal Current are important sources of freshwater for the Bering Sea shelf, and may also influence the Arctic Ocean freshwater budget. Instrumental data indicate a multiyear freshening episode of the Alaska Coastal Current in the early 21st century. It is uncertain whether this freshening is part of natural multidecadal climate variability or a unique feature of anthropogenically induced warming. In order to answer this, a better understanding of past variations in the Alaska Coastal Current is needed. However, continuous long-term high-resolution observations of the Alaska Coastal Current have only been available for the last 2 decades. In this study, specimens of the long-lived crustose coralline alga Clathromorphum nereostratum were collected within the pathway of the Alaska Coastal Current and utilized as archives of past temperature and salinity. Results indicate that coralline algal Mg/Ca ratios provide a 60 year record of sea surface temperatures and track changes of the Pacific Decadal Oscillation, a pattern of decadal-to-multidecadal ocean-atmosphere climate variability centered over the North Pacific. Algal Ba/Ca ratios (used as indicators of coastal freshwater runoff) are inversely correlated to instrumentally measured Alaska Coastal Current salinity and record the period of freshening from 2001 to 2006. Similar multiyear freshening events are not evident in the earlier portion of the 60 year Ba/Ca record. This suggests that the 21st century freshening of the Alaska Coastal Current is a unique feature related to increasing glacial melt and precipitation on mainland Alaska.

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The clay mineral composition at IODP Exp. 323 Site U1343 in the Bering Sea was analyzed so as to unravel their provenance over glacial-interglacial cycles for the last 2.4 Ma. Smectite was negatively correlated with the sum of illite and chlorite; therefore, their ratio [S/(I + C)] was used as an indicator of clay mineral composition changes. In general, the S/(I + C) ratio was rather similar for glacial and interglacial periods during most of the last 2.4 Ma. In addition, these results overlap with those of surface sediments in the modern East Aleutian Basin, which suggests that smectite-rich clay particles are delivered from the Aleutians by the northward Bering Slope Current (BSC) rather than from rivers in western Alaska. However, some clay mineral compositions of the glacial periods after the Mid-Pleistocene Transition (MPT: 1.25-0.7 Ma) were characterized by low illite and relatively high smectite. During this period, extensive ice-rafting might have transported the smectite-rich clay particles to Site U1343 from the glacial shelf off Alaska and/or from glacial rivers from that area.

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Analysis of lithology, grain-size composition, clay minerals, and geochemistry of Upper Pleistocene bottom sediments from the submarine Shirshov Ridge (Bering Sea) showed that the Yukon-Tanana terrane of the Central Alaska was main source area of the sediments. Sedimentary material was transported by the Yukon River through Beringia up to the shelf break, where they were entrained by a strong north-west sea current. Lithological data revealed several pulses of ice-rafted debris deposition roughly synchronous with Heinrich events and periods of weaker bottom current intensity. Based on geochemical results we distinguished intervals of an increase in paleoproductivity and extension of the oxygen minimum zone. Our results suggest that there were three stages of deposition driven by glacioeustatic sea-level fluctuations and glacial cycles in Alaska.

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Increasing atmospheric CO2 concentrations are potentially affecting marine ecosystems twofold, by warming and acidification. The rising amount of CO2 taken up by the ocean lowers the saturation state of calcium carbonate, complicating the formation of this key biomineral used by many marine organisms to build hard parts like skeletons or shells. Reliable time-series data of seawater pH are needed to evaluate the ongoing change and compare long-term trends and natural variability. For the high-latitude ocean, the region facing the strongest CO2 uptake, such time-series data are so far entirely lacking. Our study provides, to our knowledge, the first reconstruction of seasonal cycle and long-term trend in pH for a high-latitude ocean obtained from 2D images of stable boron isotopes from a coralline alga.

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Atmospheric deposition of mercury to remote areas has increased threefold since pre-industrial times. Mercury deposition is particularly pronounced in the Arctic. Following deposition to surface oceans and sea ice, mercury can be converted into methylmercury, a biologically accessible form of the toxin, which biomagnifies along the marine food chain. Mass-independent fractionation of mercury isotopes accompanies the photochemical breakdown of methylmercury to less bioavailable forms in surface waters. Here we examine the isotopic composition of mercury in seabird eggs collected from colonies in the North Pacific Ocean, the Bering Sea and the western Arctic Ocean, to determine geographical variations in methylmercury breakdown at northern latitudes. We find evidence for mass-independent fractionation of mercury isotopes. The degree of mass-independent fractionation declines with latitude. Foraging behaviour and geographic variations in mercury sources and solar radiation fluxes were unable to explain the latitudinal gradient. However, mass-independent fractionation was negatively correlated with sea-ice cover. We conclude that sea-ice cover impedes the photochemical breakdown of methylmercury in surface waters, and suggest that further loss of Arctic sea ice this century will accelerate sunlight-induced breakdown of methylmercury in northern surface waters.

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This layer is a georeferenced raster image of the historic paper map entitled: Behring's Sea and Arctic Ocean : from surveys of the U.S. North Pacific Surveying Expedition in 1855, Commander John Rodgers U.S.N. commanding and from Russian and English authorities, J.C.P. de Kraft, commodore U.S.N. Hydrographer to the Bureau of Navigation ; compiled by E.R. Knorr ; drawn by Louis Waldecker. Corr. & additions to Jan. 1882. It was published by U.S. Navy, Hydrographic Office in 1882. Scale [ca. 1:4,400,000]. Covers the Bering Sea and Arctic Ocean region. The image inside the map neatline is georeferenced to the surface of the earth and fit to a non-standard 'Mercator' projection with the central meridian at 180 degrees west. All map collar and inset information is also available as part of the raster image, including any inset maps, profiles, statistical tables, directories, text, illustrations, index maps, legends, or other information associated with the principal map. Note: The central meridian of this map is not the same as the Prime Meridian and may wrap the International Date Line or overlap itself when displayed in GIS software. This map shows features such as drainage, cities and other human settlements, territorial boundaries, expedition routes, shoreline features, bays, harbors, islands, rocks, and more. Relief shown by hachures and spot heights. Depths shown by soundings. Includes drawing of Wrangel Island "as seen from Bark Nile of New London ... ; 15 to 18 miles distant". This layer is part of a selection of digitally scanned and georeferenced historic maps from the Harvard Map Collection and the Harvard University Library as part of the Open Collections Program at Harvard University project: Organizing Our World: Sponsored Exploration and Scientific Discovery in the Modern Age. Maps selected for the project correspond to various expeditions and represent a range of regions, originators, ground condition dates, scales, and purposes.

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Mode of access: Internet.

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"Handbook no. 84."

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During the last glacial termination, the upper North Pacific Ocean underwent dramatic and rapid changes in oxygenation that lead to the transient intensification of oxygen minimum zones (OMZs), recorded by the widespread occurrence of laminated sediments on circum-Pacific continental margins. We present a new laminated sediment record from the mid-depth (1100 m) northern Bering Sea margin that provides insight into these deglacial OMZ maxima with exceptional, decadal-scale detail. Combined ultrahigh-resolution micro-X-ray-fluorescence (micro-XRF) data and sediment facies analysis of laminae reveal an alternation between predominantly terrigenous and diatom-dominated opal sedimentation. The diatomaceous laminae are interpreted to represent spring/summer productivity events related to the retreating sea ice margin.We identified five laminated sections in the deglacial part of our site. Lamina counts were carried out on these sections and correlated with the Bølling-Allerød and Preboreal phases in the North Greenland Ice Core (NGRIP) oxygen isotope record, indicating an annual deposition of individual lamina couplets (varves). The observed rapid decadal intensifications of anoxia, in particular within the Bølling-Allerød, are tightly coupled to short-term warm events through increases in regional export production. This dependence of laminae formation on warmer temperatures is underlined by a correlation with published Bering Sea sea surface temperature records and d18O data of planktic foraminifera from the Gulf of Alaska. The rapidity of the observed changes strongly implies a close atmospheric teleconnection between North Pacific and North Atlantic regions.We suggest that concomitant increases in export production and subsequent remineralization of organic matter in the Bering Sea, in combination with oxygen-poor waters entering the Being Sea, drove down oxygen concentrations to values below 0.1ml/l and caused laminae preservation. Calculated benthic-planktic ventilation ages show no significant variations throughout the last deglaciation, indicating that changes in formation rates or differing sources of North Pacific mid-depth waters are not prime candidates for strengthening the OMZ at our site. The age models established by our correlation procedure allow for the determination of calendar age control points for the Bølling-Allerød and the Preboreal that are independent of the initial radiocarbon-based chronology. Resulting surface reservoir ages range within 730-990 yr during the Bølling-Allerød, 800-1100 yr in the Younger Dryas, and 765-775 yr for the Preboreal.

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Sand and sandstone compositions from different types of basins reflect provenance terranes governed by plate tectonics. One hundred and one thin sections of Upper Miocene to Holocene sand-sized material were examined from DSDP/IPOD Sites in the North Pacific Ocean and the Bering Sea. The Gazzi-Dickinson point-counting method was used to establish compositional characteristics of sands from different tectonic settings. Continental margin forearc sands from the western North America continental margin arc system are clearly different from backarc/marginal-sea sands from the Aleutian intraoceanic arc system. The forearc sands have average QFL percentages of 29-42-29, LmLvLst percentages of 32-34-34, 3 Fmwk%M and 0.82 P/F. Aleutian backarc sands have average QFL percentages of 8-22-69. LmLvLst percentages of 9-85-6, 0.5 Fmwk%M and 0.96 P/F. A trend of increasing QFL%Q and decreasing LmLvLst%Lv westward in the backarc region of the Aleutian Ridge reflects the influence of the Asiatic continental margin. Aleutian backarc sands without continental influence have average QFL percentages of 1-20-79, LmLvLst percentages of 1-98-1, 0 Fmwk%M and 0.99 P/F. Of the continental margin forearc samples, sands on the Astoria Fan (west of the Oregon-Washington trench) contain the highest LmLvLst%Lv and lowest P/F; sands from mixed transform-fault and trench settings (Delgada Fan and Gulf of Alaska samples) have slightly higher Qp/Q (0.03); and sands from the Pacific-Juan de Fuca-North America triple junction have the highest Fmwk%M. Delgada Fan and Gulf of Alaska sands have average QFL percentages of 27-38-35, LmLvLst percentages of 37-26-37, 2 Fmwk%M and 0.86 P/F. Astoria Fan sands have average QFL percentages of 35-41-24, LmLvLst percentages of 30-47-23, 3 Fmwk%M and 0.74 P/F. The triple-junction sands have average QFL percentages of 28-59-13, LmLvLst percentages of 25-26-49, 9 Fmwk%M and 0.87 P/F. The petrologic data from the modern ocean basins examined in this study can provide useful analogs for interpretation of ancient oceanic sequences. Our data suggest some refinements of, but generally substantiate, existing petrologic models relating sandstone composition to tectonic setting.

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Tsar Peter the Great ruled Russia between 1689 and 1725. Its domains, stretching from the Baltic Sea in the west to the Pacific Ocean in the east. From north to south, its empire stretching from the Arctic Ocean to the borders with China and India. Tsar Peter I tried to extend the geographical knowledge of his government and the rest of the world. He was also interested in the expansion of trade in Russia and in the control of trade routes. Feodor Luzhin and Ivan Yeverinov explored the eastern border of the Russian Empire, the trip between 1719 and 1721 and reported to the Tsar. They had crossed the peninsula of Kamchatka, from west to east and had traveled from the west coast of Kamchatka to the Kuril Islands. The information collected led to the first map of Kamchatka and the Kuril Islands. Tsar Peter ordered Bering surf the Russian Pacific coast, build ships and sail the seas north along the coast to regions of America. The second expedition found equal to those of the previous explorers difficulties. Two ships were eventually thrown away in Okhotsk in 1740. The explorers spent the winter of 1740-1741 stockpiling supplies and then navigate to Petropavlovsk. The two ships sailed eastward and did together until June 20, then separated by fog. After searching Chirikov and his boat for several days, Bering ordered the San Pedro continue to the northeast. There the Russian sailors first sighted Alaska. According to the log, "At 12:30 (pm July 17) in sight of snow-capped mountains and between them a high volcano." This finding came the day of St. Elijah and so named the mountain.