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| Registros recuperados: 12 | |
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| Dyez, Kelsey A.; Zahn, Rainer; Hall, Ian R.. |
| New high-resolution sea surface temperature (SST) and sea surface salinity (SSS) estimates are presented from the Agulhas Bank slope in the Atlantic sector of the Agulhas Corridor using planktic foraminiferal (Globigerinoides ruber) O-18 and Mg/Ca-derived SST. By focusing on the last 80,000years, this is the first fine-scale Agulhas leakage record that overlaps in time with much of the Greenland ice core record of abrupt climate changes in the North Atlantic region. The multicentennial profiles indicate instances of warm SST and/or increased SSS coincident with Northern Hemisphere cool periods, followed by Northern Hemisphere warming. These periods of enhanced SST and SSS in the Agulhas Corridor occur at the last glacial termination (T1) and during North... |
| Tipo: Text |
Palavras-chave: Agulhas leakage; SST. |
| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00289/40041/39390.pdf |
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| Jimenez-amat, Patricia; Zahn, Rainer. |
| Multidecadal to centennial planktic O-18 and Mg/Ca records were generated at Ocean Drilling Program Site 976 (ODP976) in the Alboran Sea. The site is in the flow path of Atlantic inflow waters entering the Mediterranean and captured North Atlantic signals through the surface inflow and the atmosphere. The records reveal similar climatic oscillations during the last two glacial-to-interglacial transitions, albeit with a different temporal pacing. Glacial termination 1 (T1) was marked by Heinrich event 1 (H1), post-H1 BOlling/AllerOd warming, and Younger Dryas (YD) cooling. During T2 the H11 O-18 anomaly was twice as high and lasted 30% longer than during H1. The post-H11 warming marked the start of MIS5e while the subsequent YD-style cooling occurred during... |
| Tipo: Text |
Palavras-chave: Last interglacial; Ocean perturbation; Heinrich event H11; Climate instability. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00351/46261/46066.pdf |
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| Maria Mejia, Luz; Ziveri, Patrizia; Cagnetti, Marilisa; Bolton, Clara; Zahn, Rainer; Marino, Gianluca; Martinez-mendez, Gema; Stoll, Heather. |
| Modern primary productivity on the Agulhas Bank, off South Africa, has been proposed to be linked to the midlatitude westerlies. A paleoproductivity record from this area may therefore resolve temporal changes in the westerly dynamics. Accordingly, we produced a coccolith Sr/Ca-based paleoproductivity record from core MD96-2080 (Agulhas Bank slope) during the penultimate glacial-interglacial cycle. Deriving the productivity signal from Sr/Ca requires a correction for a temperature effect, here constrained using Mg/Ca sea surface temperatures from the foraminifer Globigerina bulloides from core MD96-2080. Phases of depressed productivity coincided with periods of stratification in the same core, indicated by high relative abundances of the coccolithophore... |
| Tipo: Text |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00290/40116/39135.pdf |
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| Marino, Gianluca; Zahn, Rainer; Ziegler, Martin; Purcell, Conor; Knorr, Gregor; Hall, Ian R.; Ziveri, Patrizia; Elderfield, Henry. |
| An ensemble of new, high-resolution records of surface ocean hydrography from the Indian-Atlantic oceanic gateway, south of Africa, demonstrates recurrent and high-amplitude salinity oscillations in the Agulhas Leakage area during the penultimate glacial-interglacial cycle. A series of millennial-scale salinification events, indicating strengthened salt leakage into the South Atlantic, appear to correlate with abrupt changes in the North Atlantic climate and Atlantic Meridional Overturning Circulation (AMOC). This interhemispheric coupling, which plausibly involved changes in the Hadley Cell and midlatitude westerlies that impacted the interocean transport at the tip of Africa, suggests that the Agulhas Leakage acted as a source of negative buoyancy for... |
| Tipo: Text |
Palavras-chave: Agulhas Leakage; Abrupt climate change; Millennial-scale variability; AMOC; Bipolar seesaw; Southern Hemisphere atmospheric circulation. |
| Ano: 2013 |
URL: https://archimer.ifremer.fr/doc/00264/37493/35791.pdf |
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| Knutz, Paul C.; Zahn, Rainer; Hall, Ian R.. |
| Evidence from paleoclimatic archives suggests that Earth's climate experienced rapid temperature changes associated with pronounced interhemispheric asymmetry during the last glacial period. Explanations for these climate excursions have converged on nonlinear interactions between ice sheets and the ocean's thermohaline circulation, but the driving mechanism remains to be identified. Here we use multidecadal marine records of faunal, oxygen isotope, and sediment proxies from the northeast Atlantic proximal to the western margins of the last glacial British Ice Sheet (BIS) to document the coupling between ice sheet dynamics, ocean circulation, and insolation changes. The core data reveal successions of short-lived (80-100 years), high-amplitude ice-rafted... |
| Tipo: Text |
Palavras-chave: Ice sheet variability; Rapid climate change; North Atlantic overturning circulation. |
| Ano: 2007 |
URL: https://archimer.ifremer.fr/doc/00233/34437/32940.pdf |
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| Martinez-mendez, Gema; Zahn, Rainer; Hall, Ian R.; Peeters, Frank J. C.; Pena, Leopoldo D.; Cacho, Isabel; Negre, Cesar. |
| Planktonic delta(18)O and Mg/Ca-derived sea surface temperature (SST) records from the Agulhas Corridor off South Africa display a progressive increase of SST during glacial periods of the last three climatic cycles. The SST increases of up to 4 degrees C coincide with increased abundance of subtropical planktonic foraminiferal marker species which indicates a progressive warming due to an increased influence of subtropical waters at the core sites. Mg/Ca-derived SST maximizes during glacial maxima and glacial Terminations to values about 2.5 degrees C above full-interglacial SST. The paired planktonic delta(18)O and Mg/Ca-derived SST records yield glacial seawater delta(18)O anomalies of up to 0.8%, indicating measurably higher surface salinities during... |
| Tipo: Text |
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| Ano: 2010 |
URL: https://archimer.ifremer.fr/doc/00230/34134/32779.pdf |
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| Rodriguez-sanz, Laura; Graham Mortyn, P.; Herguera, Juan C.; Zahn, Rainer. |
| Fine-scale, paired Mg/Ca-O-18 profiles (Globigerinoides ruber white, sensu lato) from the San Lazaro Basin (SLB) at 25 degrees N in the Northeast Pacific reveal a transition from a predominant presence of tropical/subtropical waters during the last glacial termination (T1) to an increasing influence of fresh and cold California Current waters toward the Holocene. Changing atmospheric circulation patterns over the Northeast Pacific in step with the demise of the Northern Hemisphere ice sheets and/or with a shift from El Nino- to La Nina-like conditions toward the Holocene are prime candidates to explain this water mass change. O-18(SW-IVC) increases of similar to 0.5-0.7 during the Younger Dryas (YD) and Heinrich stadial 1 (HS1) at the SLB are observed in a... |
| Tipo: Text |
Palavras-chave: SST; California margin; Last deglaciation. |
| Ano: 2013 |
URL: https://archimer.ifremer.fr/doc/00264/37491/35812.pdf |
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| Caley, Thibaut; Peeters, Frank J. C.; Biastoch, Arne; Rossignol, Linda; Van Sebille, Erik; Durgadoo, Jonathan; Malaize, Bruno; Giraudeau, Jacques; Arthur, Kristina; Zahn, Rainer. |
| The Indian-Atlantic water exchange south of Africa (Agulhas leakage) is a key component of the global ocean circulation. No quantitative estimation of the paleo-Agulhas leakage exists. We quantify the variability in interocean exchange over the past 640,000 years, using planktic foraminiferal assemblage data from two marine sediment records to define an Agulhas leakage efficiency index. We confirm the validity of our new approach with a numerical ocean model that realistically simulates the modern Agulhas leakage changes. Our results suggest that, during the past several glacial-interglacial cycles, the Agulhas leakage varied by ~10 sverdrup and more during major climatic transitions. This lends strong credence to the hypothesis that modifications in the... |
| Tipo: Text |
Palavras-chave: Quantitative palaeo Agulhas leakage; Planktic foraminiferal; Numerical ocean model; Overturning circulation. |
| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00291/40172/39028.pdf |
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| Koutsodendris, Andreas; Pross, Joerg; Zahn, Rainer. |
| The transport of warm and saline surface water from the Indo-Pacific Ocean into the South Atlantic (Agulhas leakage) influences the Atlantic Meridional Overturning Circulation (AMOC), which in turn exerts control on European climate. Paleoceanographic data document a remarkably strong Agulhas leakage at the end of marine isotope stage (MIS) 11c interglacial (similar to 400ka B.P.), which is one of the best orbital analogues for the Holocene. Here we assess the potential influence of this exceptional Agulhas leakage on North Atlantic climate based on a compilation of marine and terrestrial proxy records from the Iberian margin and continental Europe. We show that a similar to 5ka long warm period persisted across Europe beyond the MIS 11c climatic optimum.... |
| Tipo: Text |
Palavras-chave: Agulhas leakage; Interhemispheric teleconnection; MIS 11c; Iberian margin; Central European climate. |
| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00289/40056/39273.pdf |
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| Molyneux, Elizabeth G.; Hall, Ian R.; Zahn, Rainer; Diz, Paula. |
| Sortable silt mean grain sizes together with oxygen and carbon isotopic data produced on the benthic foraminiferal species Fontbotia wuellerstorfi are used to construct high-resolution records of near-bottom flow vigour and deep water ventilation at a core site MD02-2589 located at 2660 m water depth on the southern Agulhas Plateau. The results suggest that during glacial periods ( marine oxygen isotope stages 2 and 6, MIS 2 and MIS 6, respectively), there was a persistent contribution of a well-ventilated water mass within the Atlantic to Indian oceanic gateway with a delta(13)C signature similar to present-day Northern Component Water (NCW), e. g., North Atlantic Deep Water (NADW). The records of chemical ventilation and near-bottom flow vigor reflect... |
| Tipo: Text |
Palavras-chave: Benthic isotopes; Sortable silt mean grain size; North Atlantic Deep Water. |
| Ano: 2007 |
URL: https://archimer.ifremer.fr/doc/00233/34459/32867.pdf |
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| Registros recuperados: 12 | |
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