988 resultados para October 17
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Vol. 20, Issue 17, 8 pages
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Vol. 24, Issue 17, 8 pages
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Anticyclonic mesoscale eddies (ACME) have been proposed as a mechanism by which new nutrients are episodically delivered into the euphotic zone, thereby enhancing new production as well as shifting phytoplankton community structure. In this paper, we report on a 34-month sediment trap experiment at the Cape Verde Ocean Observatory (CVOO; ca. 18°N, 24°E; December 2009-October 2012), occasionally influenced by ACME passages. The typically oligotrophic, weakly seasonal particle flux pattern at the CVOO is strongly modified by the appearance of a highly productive and low oxygen ACME. Out of four recorded diatom flux maxima at CVOO, three were associated with the passage of ACMEs. The recorded diatom maxima events support the view that local ACME dynamics promotes upward nutrient supply into the euphotic zone leading to a rapid response of diatoms. This response is clearly reflected by the flux seasonality: between 40% and 60% of the total annual diatom flux at the CVOO site was intercepted in a relatively short time interval (<60 days). A highly diverse diatom community characterized the diatom fluxes throughout. Along with the ACME passages, small species of the genus Nitzschia, and Thalassionema nitzschioides var. parva dominated and delivered a major portion of the opal and organic carbon into deeper waters at site CVOO. Several pelagic, warm-water background species became dominant during intervals with low nutrient availability in the euphotic zone. Results of our interannual time-series suggest that ACMEs impact on total diatom production and the species-specific composition of the assemblage north of the Cave Verde Islands, and can strengthen the biological pump in open-ocean, oligotrophic subtropical regions of the world ocean. Our observations are useful for testing biogeochemical ocean models and will also help in improving the knowledge of processes and mechanisms behind interannual time-series of bulk components and microorganisms in pelagic and hemipelagic ocean areas.
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The cores and dredges described in this report were taken during the Vema 17 Expedition from December 1960 until October 1961 by the Lamont Geological Observatory, Columbia University from the R/V Vema. An approximate total of 210 cores, dredges and camera stations were recovered and are available at Lamont-Doherty Earth Observatory for sampling and study.
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The Arctic sea-ice extent reached a record minimum in September 2012. Sea-ice decline increases the absorption of solar energy in the Arctic Ocean, affecting primary production and the plankton community. How this will modulate the sinking of particulate organic carbon (POC) from the ocean surface remains a key question. We use the 234Th/238U and 210Po/210Pb radionuclide pairs to estimate the magnitude of the POC export fluxes in the upper ocean of the central Arctic in summer 2012, covering time scales from weeks to months. The 234Th/238U proxy reveals that POC fluxes at the base of the euphotic zone were very low (2 ± 2 mmol C/m**2/d) in late summer. Relationships obtained between the 234Th export fluxes and the phytoplankton community suggest that prasinophytes contributed significantly to the downward fluxes, likely via incorporation into sea-ice algal aggregates and zooplankton-derived material. The magnitude of the depletion of 210Po in the upper water column over the entire study area indicates that particle export fluxes were higher before July/August than later in the season. 210Po fluxes and 210Po-derived POC fluxes correlated positively with sea-ice concentration, showing that particle sinking was greater under heavy sea-ice conditions than under partially ice-covered regions. Although the POC fluxes were low, a large fraction of primary production (>30%) was exported at the base of the euphotic zone in most of the study area during summer 2012, indicating a high export efficiency of the biological pump in the central Arctic. This article is protected by copyright. All rights reserved.
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A journal of commercial voyages and domestic life on the Tigris River from February 1899 to October 1899. jms_049_02_1899_010_xml.xml
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A journal of commercial voyages and domestic life on the Tigris River from February 1899 to October 1899. jms_049_02_1899_020_trf.txt
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Joseph Mathia Svoboda's journal of commercial voyages, travel, and domestic life on the Tigris River from February 1899 to October 1899. Diary 49, HTML Version. jms_049_02_1899_030_htm.html
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A journal of commercial voyages and domestic life on the Tigris River from February 1899 to October 1899. jms_049_02_1899_040_sum.html
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A journal of commercial voyages and domestic life on the Tigris River from February 1899 to October 1899. jms_049_02_1899_050_tex.tex
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Joseph Mathia Svoboda's 19th century journal of commercial voyages, travel, and domestic life on the Tigris River from February 1899 to October 1899. Diary 49, PDF Version. jms_049_02_1899_060_pdf.pdf
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A journal of commercial voyages and domestic life on the Tigris River from February 1899 to October 1899. jms_049_02_1899_110_arb.xlsx
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A journal of commercial voyages and domestic life on the Tigris River from February 1899 to October 1899. Arabic translations. jms_049_02_1899_120_arb.html