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| Registros recuperados: 11 | |
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| Peck, V. L.; Hall, I. R.; Zahn, R.; Elderfield, H.. |
| We present high-resolution records of upper ocean temperatures derived from Mg/Ca ratios of surface-dwelling Globigerina bulloides and subsurface-dwelling Neogloboquadrina pachyderma sinistral and the relative abundance of N. pachyderma sinistral for the period 55-8 ka BP from NE Atlantic sediment core MD01-2461. Millennial-scale temporal variability and longer-term trends in these records enable us to develop a detailed picture of past ocean conditions such as a weakening of thermocline intensity from marine isotope stage 3 (MIS 3) to the last glacial maximum (LGM). The correspondence of all temperature proxies and convergence of paired oxygen isotope (delta O-18) records from both planktonic species implies a breakdown in the thermocline and year-round... |
| Tipo: Text |
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| Ano: 2008 |
URL: https://archimer.ifremer.fr/doc/00237/34797/33340.pdf |
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| Evans, H. K.; Hall, I. R.; Bianchi, G. G.; Oppo, D. W.. |
| Records from Ocean Drilling Program Sites 1057 and 1059 (2584 m and 2985 m water depth, respectively) have been used to reconstruct the behavior of the Deep Western Boundary Current (DWBC) on the Blake Outer Ridge (BOR) from 130 to 60 kyr B. P. (marine isotope stage (MIS) 5 and the 5/4 transition). Site 1057 lies within Labrador Sea Water (LSW) but close to the present-day boundary with Lower North Atlantic Deep Water (LNADW), while Site 1059 lies within LNADW. High-resolution sortable silt mean ((SS) over bar) grain size and benthic delta C-13 records were obtained, and changes in the DWBC intensity and spatial variability were inferred. Comparisons are made with similar proxy records generated for the Holocene from equivalent depth cores on the BOR.... |
| Tipo: Text |
Palavras-chave: Sortable silt; Deep Western Boundary Current; Marine isotope stage 5. |
| Ano: 2007 |
URL: https://archimer.ifremer.fr/doc/00238/34930/33251.pdf |
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| Mccave, I. N.; Hall, I. R.. |
| The basis for, and use of, fine grain size parameters for inference of paleoflow speeds is reviewed here. The basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field, experimental data on suspended sediment transport and deposition, and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed. In the deep sea, sorting events occur under resuspension/deposition events in benthic storms. At flow speeds below 10 - 15 cm s(-1), size in the noncohesive "sortable silt'' ( 10 - 63 mm) range is controlled by selective deposition, whereas above that range, removal of finer material by winnowing also plays a role. The best... |
| Tipo: Text |
Palavras-chave: Sortable silt; Grain size; Paleocurrent; Flow speed; Ocean circulation; Contourite; Sediment drift. |
| Ano: 2006 |
URL: https://archimer.ifremer.fr/doc/00234/34515/33417.pdf |
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| Boessenkool, K. P.; Hall, I. R.; Elderfield, H.; Yashayaev, I.. |
| Variations in the near-bottom flow speed of Iceland-Scotland Overflow Water (ISOW) are documented in a 230-year-long deep-sea sediment record from the eastern flank of Reykjanes Ridge in the subpolar North Atlantic at (sub) decadal time scales. For recent decades, the ISOW palaeocurrent reconstructions show similarities with observational hydrographic data. Furthermore, recent ISOW flow changes fall mostly within the range of its variability of the past 230 years. The record also reveals a hitherto unrecognized coupling of deep flow speeds in the subpolar North Atlantic with the North Atlantic Oscillation (NAO) index, with more (less) vigorous ISOW flow during negative (positive) phases of the NAO. Our results suggest that the changes in ISOW vigor are... |
| Tipo: Text |
Palavras-chave: Deep ocean circulation; North Atlantic Oscillation; Drift sediments. |
| Ano: 2007 |
URL: https://archimer.ifremer.fr/doc/00235/34646/33007.pdf |
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| Sicre, M. -a.; Hall, I. R.; Mignot, J.; Khodri, M.; Ezat, U.; Truong, M. -x.; Eiriksson, J.; Knudsen, K. -l.. |
| A decadal resolution time series of sea surface temperature (SST) spanning the last two millennia is reconstructed by combining a proxy record from a new sediment sequence with previously published data from core MD99-2275, north of Iceland. The alkenone based SST reconstruction is validated with historic observational data and compared to a new similar temporal resolution reconstruction obtained from sediment core RAPiD21-3K, in the subpolar North Atlantic. The two SST paleorecords show consistent multidecadal scale coolings throughout the interval and similar expressions during the contrasted climatic periods 'colloquially known' as the Medieval Climatic Anomaly (MCA) and Little Ice Age (LIA). In order to further understand the temporal and spatial SST... |
| Tipo: Text |
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| Ano: 2011 |
URL: https://archimer.ifremer.fr/doc/00227/33776/32585.pdf |
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| Hall, I. R.; Colmenero-hidalgo, E.; Zahn, R.; Peck, V. L.; Hemming, S. R.. |
| In order to monitor the evolution of the British-Irish Ice Sheet (BIIS) and its influence in surface ocean structure during marine isotopic stages (MIS) 2 and 3, we have analyzed the sediments recovered in core MD04-2829CQ (Rosemary Bank, north Rockall Trough, northeast Atlantic) dated between similar to 41 and similar to 18 ka B.P. Ice-rafted debris flux and composition, Ar-40/Ar-39 ages of individual hornblende grains, multispecies planktonic stable isotope records, planktonic foraminifera assemblage data and faunal-based sea surface temperatures (SSTs) demonstrate a close interaction between BIIS dynamics and surface ocean structure and water properties in this region. The core location lies beneath the North Atlantic Current (NAC) and is ideal for... |
| Tipo: Text |
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| Ano: 2011 |
URL: https://archimer.ifremer.fr/doc/00227/33835/32445.pdf |
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| Romero, O. E.; Kim, J. -h.; Barcena, M. A.; Hall, I. R.; Zahn, R.; Schneider, R.. |
| The hydrography of the Indian-Atlantic Ocean gateway has been connected to high-latitude climate dynamics by oceanic and atmospheric teleconnections on orbital and suborbital timescales. A wealth of sedimentary records aiming at reconstructing the late Pleistocene paleoceanography around the southern African continent has been devoted to understanding these linkages. Most of the records are, however, clustered close to the southern South African tip, with comparatively less attention devoted to areas under the direct influence of frontal zones of the Southern Ocean/South Atlantic. Here we present data of the composition and concentration of the diatom assemblage together with bulk biogenic content and the alkenone-based sea surface temperature (SST)... |
| Tipo: Text |
Palavras-chave: Agulhas; SST; Diatoms; Fronts; Silica; Southern Ocean. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00294/40555/39440.pdf |
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| Eynaud, F; Zaragosi, S; Scourse, J; Mojtahid, M; Bourillet, Jean-francois; Hall, I. R.; Penaud, A; Locascio, M; Reijonen, A. |
| [1] We have compiled results obtained from four high sedimentation rate hemipelagic sequences from the Celtic sector of the NW European margin ( NE Atlantic) to investigate the paleoceanographic and paleoclimatic evolution of the area over the last few climatic cycles. We focus on periods characteristic of deglacial transitions. We adopt a multiproxy sedimentological, geochemical, and micropaleontological approach, applying a sampling resolution down to ten microns for specific intervals. The investigation demonstrates the relationships between the Bay of Biscay hydrography and the glacial/deglacial history of both the proximal British-Irish Ice Sheet (BIIS) and the western European continent. We identify recurrent phases of laminae deposition concurrent... |
| Tipo: Text |
Palavras-chave: Paleoceanography : micropaleontology; Paleoceanography : abrupt/rapid climate change; Paleoceanography : glacial; Planktonic microfossils; Ice rafted detritus; Freshwater pulse/discharge; Laminated sediments; Glacial terminations; Celtic margin. |
| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-2606.pdf |
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| Thornalley, D. J. R.; Blaschek, M.; Davies, F. J.; Praetorius, S.; Oppo, D. W.; Mcmanus, J. F.; Hall, I. R.; Kleiven, H.; Renssen, H.; Mccave, I. N.. |
| The overflow of deep water from the Nordic seas into the North Atlantic plays a critical role in global ocean circulation and climate. Approximately half of this overflow occurs via the Iceland-Scotland (I-S) overflow, yet the history of its strength throughout the Holocene (similar to 0-11 700 yr ago, ka) is poorly constrained, with previous studies presenting apparently contradictory evidence regarding its long-term variability. Here, we provide a comprehensive reconstruction of I-S overflow strength throughout the Holocene using sediment grain size data from a depth transect of 13 cores from the Iceland Basin. Our data are consistent with the hypothesis that the main axis of the I-S overflow on the Iceland slope was shallower during the early Holocene,... |
| Tipo: Text |
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| Ano: 2013 |
URL: https://archimer.ifremer.fr/doc/00264/37571/35836.pdf |
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| Hall, I. R.; Boessenkool, K. P.; Barker, S.; Mccave, I. N.; Elderfield, H.. |
| The subpolar North Atlantic Ocean (SPNA) is of key importance for modulating the climate of NW Europe because of heat loss to the atmosphere from the North Atlantic Current. Although hydrographic properties of the surface SPNA vary on interannual to multidecadal timescales, hydrographic time series scarcely extend back beyond the 1950s. We present a 230 year long record of SPNA surface conditions reconstructed from a very high accumulation rate core that also registers changes in deep flow speed in the Iceland Basin. A lagged correlation is observed between the records of deep flow speed and stable oxygen isotopic composition of the surface SPNA (delta(18)O(w)), with strongest correlation when the paleoflow speed record leads by 15-20 years. This offset... |
| Tipo: Text |
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| Ano: 2010 |
URL: https://archimer.ifremer.fr/doc/00231/34203/32762.pdf |
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| Peck, V. L.; Hall, I. R.; Zahn, R.; Scourse, J. D.. |
| We present high-resolution benthic delta C-13 records from intermediate water depth core site MD01-2461 ( 1153 m water depth), from the Porcupine Seabight, NE Atlantic, spanning 43 to 8 kyr B. P. At an average proxy time step of 160 +/- 56 years this core provides information on the linkage between records from the Portuguese Margin and high-latitude North Atlantic basin, allowing additional insights into North Atlantic thermohaline circulation (THC) variability during millennial-scale climatic events of the last glacial. Together, these records document both discrete and progressive reductions in Glacial North Atlantic Intermediate Water (GNAIW) formation preceding Heinrich ( H) events 1, 2, and 4, recorded through the apparent interchange of glacial... |
| Tipo: Text |
Palavras-chave: Atlantic thermohaline circulation; Benthic carbon isotopes; Heinrich events; Meltwater forcing. |
| Ano: 2007 |
URL: https://archimer.ifremer.fr/doc/00238/34945/33241.pdf |
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| Registros recuperados: 11 | |
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