Consulta: subjectFacets:"AMOC"
Registros recuperados: 11
Data/hora: 09/06/2024 04:34:32

Coherent Response of Antarctic Intermediate Water and Atlantic Meridional Overturning Circulation During the Last Deglaciation: Reconciling Contrasting Neodymium Isotope Reconstructions From the Tropical Atlantic
Provedor de dados: 5
Autores: Gu, Sifan; Liu, Zhengyu; Zhang, Jiaxu; Rempfer, Johannes; Joos, Fortunat; Oppo, Delia W.
Antarctic Intermediate Water (AAIW) plays important roles in the global climate system and the global ocean nutrient and carbon cycles. However, it is unclear how AAIW responds to global climate changes. In particular, neodymium isotopic composition (epsilon(Nd)) reconstructions from different locations from the tropical Atlantic have led to a debate on the relationship between northward penetration of AAIW into the tropical Atlantic and the Atlantic meridional overturning circulation (AMOC) variability during the last deglaciation. We resolve this controversy by studying the transient oceanic evolution during the last deglaciation using a neodymium-enabled ocean model. Our results suggest a coherent response of AAIW and AMOC: when AMOC weakens, the...
Tipo: Text
Palavras-chave: AAIW; AMOC; Deglacial; Neodymium isotope; Paleocirculation tracer.
Ano: 2017
URL: https://archimer.ifremer.fr/doc/00495/60709/65334.pdf

Climate variability and ice-sheet dynamics during the last three glaciations
Provedor de dados: 5
Autores: Obrochta, Stephen P.; Crowley, Thomas J.; Channell, James E. T.; Hodell, David A.; Baker, Paul A.; Seki, Arisa; Yokoyama, Yusuke.
A composite North Atlantic record from DSDP Site 609 and IODP Site U1308 spans the past 300,000 years and shows that variability within the penultimate glaciation differed substantially from that of the surrounding two glaciations. Hematite-stained grains exhibit similar repetitive down-core variations within the Marine Isotope Stage (MIS) 8 and 4-2 intervals, but little cyclic variability within the MIS 6 section. There is also no petrologic evidence, in terms of detrital carbonate-rich (Heinrich) layers, for surging of the Laurentide Ice Sheet through the Hudson Strait during MIS 6. Rather, very high background concentration of iceberg-rafted debris (IRD) indicates near continuous glacial meltwater input that likely increased thermohaline disruption...
Tipo: Text
Palavras-chave: Insolation; IRD; Heinrich Event; MIS 6; MIS 8; AMOC.
Ano: 2014
URL: https://archimer.ifremer.fr/doc/00289/40050/38793.pdf

Impact of deglacial and Holocene AMOC changes on the mixed layer and deepwater hydrography of the subtropical North Atlantic
Provedor de dados: 5
Autores: Respschläger, Janne.
The Atlantic meridional overturning circulation (AMOC) transports warm saline water from low to high northern latitudes where it cools, sinks down and returns southward as deepwater flow. By the heat transfer from low to high latitudes, AMOC contributes in balancing the global energy budget and thus is an important part of global climate system. Within this study the impact of AMOC changes on surface and deepwater hydrography of the subtropical North Atlantic is investigated by the use of high-resolution sediment cores from a coring site located south of the Azores at the eastern flank of the Mid Atlantic Ridge. The Azores coring site is situated in the subtropical eastern North Atlantic (NA) at the boundary between warm Subtropical Gyre Water (STG) and...
Tipo: Text
Palavras-chave: Paleoceanography; AMOC; Subtropical gyre; Deglacial; Multiproxy SST; BWT; Stable isotopes; Planktonic and benthic foraminifera.
Ano: 2013
URL: https://archimer.ifremer.fr/doc/00493/60444/63889.pdf

Inception of the Northern European ice sheet due to contrasting ocean and insolation forcing
Provedor de dados: 5
Autores: Risebrobakken, Bjorg; Dokken, Trond; Ottera, Odd Helge; Jansen, Eystein; Gao, Yongqi; Drange, Helge.
About 115,000 yr ago the last interglacial reached its terminus and nucleation of new ice-sheet growth was initiated. Evidence from the northernmost Nordic Seas indicate that the inception of the last glacial was related to an intensification of the Atlantic Meridional Overturning Circulation (AMOC) in its northern limb. The enhanced AMOC, combined with minimum Northern hemisphere insolation, introduced a strong sea-land thermal gradient that, together with a strong wintertime latitudinal insolation gradient, increased the storminess and moisture transport to the high Northern European latitudes at a time when the Northern hemisphere summer insolation approached its minimum.
Tipo: Text
Palavras-chave: Glacial inception; Nordic Seas; Northern European ice sheets; Palco-reconstruction; OGCM; AMOC; Insolation; Insolation gradient.
Ano: 2007
URL: https://archimer.ifremer.fr/doc/00233/34441/82768.pdf

Paleoceanographic and climatic teleconnections between the subarctic and subtropical North Atlantic during the last interglacial (MIS 5e)
Provedor de dados: 5
Autores: Zhuravleva, Anastasia.
The last interglacial, MIS (Marine Isotope Stage) 5e, lasting from about ~129 to 116 ka, holds important implications for the projected global warming, as this geological interval is believed to have been significantly warmer-than-preindustrial. This thesis refines the current understanding of the MIS 5e paleoceanography in the subarctic and subtropical North Atlantic, providing new insights into ice-sheets dynamics and cross-latitudinal climatic teleconnections. For this purpose, a multi-proxy dataset comprising stable isotope compositions, foraminiferal assemblages and lithic as well as X-ray fluorescence data was produced using marine sediments from the Nordic Seas and the Bahama region. Several lines of evidence from the Nordic Seas suggest a strong...
Tipo: Text
Palavras-chave: Last interglacial; MIS 5e; Greenland ice sheet; AMOC; ITCZ; Climatic variability letztes Interglazial; MIS 5e; Grönländisches Eisschild; AMOC; ITCZ; Klimatische Variabilität.
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00495/60640/64136.pdf

Exploring the oxygen isotope fingerprint of Dansgaard-Oeschger variability and Heinrich events
Provedor de dados: 5
Autores: Bagniewski, Witold; Meissner, Katrin J.; Menviel, Laurie.
We present the first transient simulations of Marine Isotope Stage 3 (MIS 3) performed with an oxygen isotope-enabled climate model. Our simulations span several Dansgaard-Oeschger cycles and three Heinrich stadials and are directly compared with oxygen isotope records from 13 sediment and 2 ice cores. Our results are consistent with a 30-50% weakening of the Atlantic Meridional Overturning Circulation during Dansgaard-Oeschger stadials and a complete shutdown during Heinrich stadials. We find that the simulated delta O-18 anomalies differ significantly between Heinrich stadials and non-Heinrich stadials. This difference is mainly due to different responses in ocean circulation, and therefore climate, impacting oceanic delta O-18, while the volume of...
Tipo: Text
Palavras-chave: MIS3; Model-data comparison; Heinrich events; Dansgaard-Oeschger cycles; Delta O-18; AMOC.
Ano: 2017
URL: https://archimer.ifremer.fr/doc/00420/53180/55067.pdf

Dynamical reconstruction of the global ocean state during the Last Glacial Maximum
Provedor de dados: 5
Autores: Kurahashi-nakamura, Takasumi; Paul, Andre; Losch, Martin.
The global ocean state for the modern age and for the Last Glacial Maximum (LGM) was dynamically reconstructed with a sophisticated data assimilation technique. A substantial amount of data including global seawater temperature, salinity (only for the modern estimate), and the isotopic composition of oxygen and carbon (only in the Atlantic for the LGM) were integrated into an ocean general circulation model with the help of the adjoint method, thereby the model was optimized to reconstruct plausible continuous fields of tracers, overturning circulation and water mass distribution. The adjoint-based LGM state estimation of this study represents the state of the art in terms of the length of forward model runs, the number of observations assimilated, and the...
Tipo: Text
Palavras-chave: Last Glacial Maximum; Ocean circulation; AMOC; Proxy records; Ocean general circulation model; Data assimilation.
Ano: 2017
URL: https://archimer.ifremer.fr/doc/00383/49466/49951.pdf

Sustainable observations of the AMOC: Methodology and Technology
Provedor de dados: 5
Autores: Mccarthy, G.d.; Brown, P.j.; Flagg, C.n.; Goni, G.; Houpert, L.; Hughes, C.w.; Hummels, R.; Inall, M.; Jochumsen, K.; Larsen, K.m.h.; Lherminier, Pascale; Meinen, C.s.; Moat, B.i.; Rayner, D.; Rhein, M.; Roessler, A.; Schmid, C.; Smeed, D.a.
The Atlantic Meridional Overturning Circulation (AMOC) is a key mechanism of heat, freshwater, and carbon redistribution in the climate system. The precept that the AMOC has changed abruptly in the past, notably during and at the end of the last ice age, and that it is ‘very likely’ to weaken in the coming century due to anthropogenic climate change is a key motivation for sustained observations of the AMOC. This paper reviews the methodology and technology used to observe the AMOC and assesses these ideas and systems for accuracy, shortcomings, potential improvements and sustainability. We review hydrographic techniques and look at how these traditional techniques can meet modern requirements. Transport mooring arrays provide the ‘gold standard’ for...
Tipo: Text
Palavras-chave: Ocean Observing; AMOC; Ocean Circulation.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00595/70674/68872.pdf

Atlantic Ocean circulation changes preceded millennial tropical South America rainfall events during the last glacial
Provedor de dados: 5
Autores: Burckel, Pierre; Waelbroeck, Claire; Gherardi, Jeanne Marie; Pichat, Sylvain; Arz, Helge; Lippold, Joerg; Dokken, Trond; Thil, Francois.
During the last glacial period, Greenland's climate shifted between cold (stadial) and warm (interstadial) phases that were accompanied by ocean circulation changes characterized by reduced Atlantic Meridional Overturning Circulation (AMOC) during stadials. Here we present new data from the western tropical Atlantic demonstrating that AMOC slowdowns preceded some of the large South American rainfall events that took place during stadials. Based on 231Pa/230Th and Ti/Ca measurements in the same sediment core, we determine that the AMOC started to slowdown 1420 ± 250 and 690 ± 180 (1σ) years before the onset of two large precipitation events associated with Heinrich stadials. Our results bring unprecedented evidence that AMOC changes could be at the origin...
Tipo: Text
Palavras-chave: Heinrich stadials; Dansgaard-Oeschger stadials; AMOC; ITCZ; Pa; Th.
Ano: 2015
URL: https://archimer.ifremer.fr/doc/00296/40711/39709.pdf

Atlantic Ocean ventilation changes across the last deglaciation and their carbon cycle implications
Provedor de dados: 5
Autores: Skinner, L. C.; Freeman, E.; Hodell, D.; Waelbroeck, C.; Vazquez Riveiros, Natalia; Scrivner, A.e.
Changes in ocean ventilation, controlled by both overturning rates and air‐sea gas exchange, are thought to have played a central role in atmospheric CO2 rise across the last deglaciation. Here we constrain the nature of Atlantic Ocean ventilation changes over the last deglaciation using radiocarbon and stable carbon isotopes from two depth transects in the Atlantic basin. Our findings broadly cohere with the established pattern of deglacial Atlantic overturning change, and underline the existence of active northern sourced deep‐water export at the Last Glacial Maximum (LGM). We find that the western Atlantic was less affected by incursions of southern‐sourced deep water, as compared to the eastern Atlantic, despite both sides of the basin being strongly...
Tipo: Text
Palavras-chave: Air&amp;#8208; Sea exchange; AMOC; Carbon cycle; Deglaciation; Radiocarbon; Ventilation.
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00665/77717/79810.pdf

Agulhas salt-leakage oscillations during abrupt climate changes of the Late Pleistocene
Provedor de dados: 5
Autores: 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