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| Galbraith, Eric D.; Kienast, Markus; Jaccard, Samuel L.; Pedersen, Thomas F.; Brunelle, Brigitte G.; Sigman, Daniel M.; Kiefer, Thorsten. |
| [1] The open subarctic Pacific is, at present, a high nitrate low chlorophyll (HNLC) region, where nitrate is perennially abundant at the surface. Theoretically, the HNLC status of this region is subject to modification by ocean circulation and/or micronutrient supply, with implications for the effectiveness of the biological pump and hence carbon sequestration in the ocean interior. Records of biogenic detritus in sediments from throughout the subarctic Pacific indicate that export production was generally lower during glacial maxima, while nitrogen isotope measurements from the Bering Sea have shown that nitrate consumption there was more complete during the last glacial period than it is today. Here, nitrogen isotopic analyses of bulk sediments (delta... |
| Tipo: Text |
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| Ano: 2008 |
URL: https://archimer.ifremer.fr/doc/00237/34840/33281.pdf |
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| Chang, Alice S.; Pedersen, Thomas F.; Hendy, Ingrid L.. |
| Variations in chalcophile and redox-sensitive trace elements are examined at high-resolution intervals from a similar to 50 kyr long sediment core (MD02-2496) from the Vancouver Island margin. Enrichments of Ag, Cd, Re, U, and Mo above lithogenous levels, signifying sedimentary suboxia and anoxia, occurred during the early Holocene and Bolling/Allerod, and during warm interstadial events of Marine Isotope Stage (MIS) 3. Down-core trace element profiles co-vary with productivity proxy records (opal, CaCO3, and marine organic carbon), and with sedimentary nitrogen isotope ratios, which reflect variably enriched nitrate upwelled from intermediate waters that were transported northward from the Eastern Tropical North Pacific. The similarity of the MD02-2496... |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00290/40117/39132.pdf |
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| Ganeshram, Raja S.; Pedersen, Thomas F.; Calvert, Stephen E.; Mcneill, Gavin W.; Fontugne, Michel R.. |
| The late Quaternary history of water-column denitrification of the eastern Pacific margins and the Arabian Sea is reconstructed using sedimentary delta(15)N measurements. The delta(15)N values in six piston cores raised from these regions show remarkably similar cyclic variations, being heavy (9-10.5 parts per thousand) during the interglacials and 2-3 parts per thousand lighter during the glacials. This implies that denitrification in these regions decreased substantially during the glacial periods. The glacial decline in denitrification is attributed to reduced upwelling and flux of organic material through the oxygen minimum zone. Since water-column denitrification in these areas accounts for about half of the fixed-nitrogen loss in the modern ocean,... |
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| Ano: 2000 |
URL: https://archimer.ifremer.fr/doc/00220/33123/31655.pdf |
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| Price, Andrea M.; Mertens, Kenneth; Pospelova, Vera; Pedersen, Thomas F.; Ganeshram, Raja S.. |
| A high-resolution record of organic-walled dinoflagellate cyst production in Guaymas Basin, Gulf of California (Mexico) reveals a complex paleoceanographic history over the last similar to 40 ka. Guaymas Basin is an excellent location to perform high resolution studies of changes in late Quaternary climate and paleo-productivity because it is characterized by high primary productivity, high sedimentation rates, and low oxygen bottom waters. These factors contribute to the deposition and preservation of laminated sediments throughout large portions of the core MD02-2515. In this study, we document dinoflagellate cyst production at a centennial to millennial scale throughout the late Quaternary. Based on the cyst assemblages, three dinoflagellate cyst zones... |
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| Ano: 2013 |
URL: https://archimer.ifremer.fr/doc/00262/37306/35718.pdf |
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| Chang, Alice S.; Pichevin, Laetitia; Pedersen, Thomas F.; Gray, Victoria; Ganeshram, Raja. |
| A high-resolution, 55 kyr long record of chalcophile and redox-sensitive trace element accumulation (Ag, Cd, Re, and Mo) from MD02-2515, western Guaymas Basin, is investigated in conjunction with patterns in stratigraphy and productivity. High opal concentrations (~59 wt. %), representing increased diatom production, coincide with laminated sediments and dilute the concentrations of organic carbon (Corg) and metals. A similarity between opal and normalized Corg, Ag, and Cd concentrations suggests delivery to the sediments by diatom export production, while patterns in normalized Re and Mo accumulation suggest a different emplacement mechanism. Although Mo enrichment in organic-rich, laminated sediments typically represents anoxic conditions at other... |
| Tipo: Text |
Palavras-chave: Productivity; Redox; Trace elements; Laminated sediments; Guaymas Basin; Northeast Pacific Ocean. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00294/40566/39461.pdf |
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| Pichevin, Laetitia; Ganeshram, Raja S.; Reynolds, Ben C.; Prahl, Fredrick; Pedersen, Thomas F.; Thunell, Robert; Mcclymont, Erin L.. |
| Iron is considered to play a large role in the cycling of Si in Fe-limited regions of the ocean, but little is known about its role in Si biogeochemistry outside these areas. Here, we present published sediment trap data, new nutrient profiles and high resolution sedimentary records (Si isotopes, Biogenic silica%, N% and C%) from the Gulf of California, a non-Fe-limited region, to investigate the history of Si cycling in this highly productive basin. Modern nutrient profiles show that silicic acid in subsurface waters is in excess relative to nitrate and is therefore incompletely utilized during moderate winter upwelling events. Modern data, however, suggest that during intense upwelling episodes, silicic acid is preferentially utilized relative to nitrate... |
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| Ano: 2012 |
URL: https://archimer.ifremer.fr/doc/00265/37665/36967.pdf |
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