Thermohaline Circulation and Prolonged Interglacial Warmth in the North Atlantic

2002 ◽  
Vol 58 (1) ◽  
pp. 17-21 ◽  
Author(s):  
Jerry F. McManus ◽  
Delia W. Oppo ◽  
Lloyd D. Keigwin ◽  
James L. Cullen ◽  
Gerard C. Bond
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Thermohaline Circulation ◽  
Regional Climate ◽  
Sediment Cores ◽  
Glacial Cycle ◽  
Deep Sea Sediment ◽  
The North ◽  
Global Ice Volume ◽  
The Last Glacial

AbstractDeep-sea sediment cores provide spatially coherent evidence for the climatic and hydrographic conditions in the subpolar North Atlantic during the last interglaciation. Taken together with similarly high-resolution terrestrial sequences, these records indicate a regional climatic progression, beginning with the extreme and variable climate late in the penultimate glaciation, continuing through a relatively stable climatic optimum during the interglaciation, and concluding with the reestablishment of the markedly variable regime that characterized the last 100,000-yr glaciation. Relatively mild conditions in much of the subpolar region significantly outlasted the minimum in global ice volume, despite declining summer insolation and the cooling influence of incipient proximal glaciers. These effects were partially offset by enhanced thermohaline circulation that paradoxically increased heat transport into the region while simultaneously providing the likely moisture source for the growth of large northern ice sheets. The inception of the last glacial cycle thus provides an example of the influence of ocean circulation on regional climate. In contrast to the apparent orbital pace of the ongoing ice-sheet growth, the subsequent deterioration of surface conditions was abrupt and dramatic.

scholarly journals Relative timing of precipitation and ocean circulation changes in the western equatorial Atlantic over the last 45 kyr

2018 ◽  
Vol 14 (9) ◽  
pp. 1315-1330 ◽  
Author(s):  
Claire Waelbroeck ◽  
Sylvain Pichat ◽  
Evelyn Böhm ◽  
Bryan C. Lougheed ◽  
Davide Faranda ◽  
...  
Keyword(s):  
Mass Transport ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Wavelet Transforms ◽  
Water Mass ◽  
Sediment Cores ◽  
Equatorial Atlantic ◽  
The North ◽  
Atmospheric Changes ◽  
Circulation Changes

Abstract. Thanks to its optimal location on the northern Brazilian margin, core MD09-3257 records both ocean circulation and atmospheric changes. The latter occur locally in the form of increased rainfall on the adjacent continent during the cold intervals recorded in Greenland ice and northern North Atlantic sediment cores (i.e., Greenland stadials). These rainfall events are recorded in MD09-3257 as peaks in ln(Ti ∕ Ca). New sedimentary Pa ∕ Th data indicate that mid-depth western equatorial water mass transport decreased during all of the Greenland stadials of the last 40 kyr. Using cross-wavelet transforms and spectrogram analysis, we assess the relative phase between the MD09-3257 sedimentary Pa ∕ Th and ln(Ti ∕ Ca) signals. We show that decreased water mass transport between a depth of ∼1300 and 2300 m in the western equatorial Atlantic preceded increased rainfall over the adjacent continent by 120 to 400 yr at Dansgaard–Oeschger (D–O) frequencies, and by 280 to 980 yr at Heinrich-like frequencies. We suggest that the large lead of ocean circulation changes with respect to changes in tropical South American precipitation at Heinrich-like frequencies is related to the effect of a positive feedback involving iceberg discharges in the North Atlantic. In contrast, the absence of widespread ice rafted detrital layers in North Atlantic cores during D–O stadials supports the hypothesis that a feedback such as this was not triggered in the case of D–O stadials, with circulation slowdowns and subsequent changes remaining more limited during D–O stadials than Heinrich stadials.

scholarly journals Evidence for Two Distinct Modes of Large-Scale Ocean Circulation Changes over the Last Century

2010 ◽  
Vol 23 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Mihai Dima ◽  
Gerrit Lohmann
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Large Scale ◽  
Climate Changes ◽  
Thermohaline Circulation ◽  
Conveyor Belt ◽  
The North ◽  
Symmetric Pattern ◽  
The North Atlantic ◽  
Circulation Changes

Abstract Through its nonlinear dynamics and involvement in past abrupt climate shifts the thermohaline circulation (THC) represents a key element for the understanding of rapid climate changes. The expected THC weakening under global warming is characterized by large uncertainties, and it is therefore of significant importance to identify ocean circulation changes over the last century. By applying various statistical techniques on two global sea surface temperature datasets two THC-related modes are separated. The first one involves relatively slow adjustment of the whole conveyor belt circulation and has an interhemispherically symmetric pattern. The second mode is associated with the relatively fast adjustment of the North Atlantic overturning cell and has the seesaw structure. Based on the separation of these two patterns the authors show that the global conveyor has been weakening since the late 1930s and that the North Atlantic overturning cell suffered an abrupt shift around 1970. The distinction between the two modes provides also a new frame for interpreting past abrupt climate changes.

scholarly journals Effect of vegetation on the Late Miocene ocean circulation

2006 ◽  
Vol 2 (4) ◽  
pp. 605-631 ◽  
Author(s):  
G. Lohmann ◽  
M. Butzin ◽  
A. Micheels ◽  
T. Bickert ◽  
V. Mosbrugger
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Late Miocene ◽  
Land Surface ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
The North ◽  
The North Atlantic

Abstract. A weak and shallow thermohaline circulation in the North Atlantic Ocean is related to an open Central American gateway and exchange with fresh Pacific waters. We estimate the effect of vegetation on the ocean general circulation using the atmospheric circulation model simulations for the Late Miocene climate. Caused by an increase in net evaporation in the Miocene North Atlantic, the North Atlantic water becomes more saline which enhances the overturning circulation and thus the northward heat transport. This effect reveals a potentially important feedback between the ocean circulation, the hydrological cycle and the land surface cover for Cenozoic climate evolution.

North Atlantic salinity oscillations linked to atmospheric and ocean circulation changes over the last glacial cycle

PAGES news ◽  
2008 ◽  
Vol 16 (1) ◽  
pp. 23-25 ◽  
Author(s):  
Matthew Schmidt ◽  
Howard Spero
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Glacial Cycle ◽  
Last Glacial ◽  
Circulation Changes ◽  
The Last Glacial

scholarly journals Ice-sheet modelling characteristics in sea-level-based temperature reconstructions over the last glacial cycle

2006 ◽  
Vol 52 (176) ◽  
pp. 149-158 ◽  
Author(s):  
Frank Wilschut ◽  
Richard Bintanja ◽  
Roderik S.W. Van De Wal
Keyword(s):  
Sea Level ◽  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Cores ◽  
Glacial Cycle ◽  
Deep Sea Sediment ◽  
Last Glacial ◽  
Proxy Records ◽  
Temperature Reconstructions ◽  
The Last Glacial

AbstractA widely used method for investigating palaeotemperatures is to analyze local proxy records (e.g. ice cores or deep-sea sediment cores). The interpretation of these records is often not straightforward, and global or hemispheric means cannot be deduced from local estimates because of large spatial variability. Using a different approach, temperature changes over the last glacial cycle can be estimated from sea-level observations by applying an inverse method to an ice-sheet model. In order to understand the underlying physical mechanisms, we used a 1-D ice-sheet model and a 3-D coupled thermodynamic ice-sheet–ice-shelf–bedrock model to investigate the importance of several physical processes for the inverse temperature reconstructions. Results show that (i) temperature reconstructions are sensitive to the employed formulation of mass balance, (ii) excluding thermodynamics in the ice sheet leads to a smaller temperature amplitude in the reconstruction and (iii) hysteresis in the non-linear relation between sea level and temperature occurs as a consequence of ice redistribution in the process of merging and separation of ice sheets. The ice redistribution does not occur if the geometry does not support the formation of a relatively flat dome, which tends to be preserved in warming conditions.

Dating rapid climate change in the North Atlantic during Heinrich Stadial 1

2020 ◽  
Author(s):  
Andrea Burke ◽  
Rosanna Greenop ◽  
James Rae ◽  
Rhian Rees-Owen ◽  
Paula Reimer ◽  
...  
Keyword(s):  
Climate Change ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Sediment Cores ◽  
Last Deglaciation ◽  
Large Reservoir ◽  
The North ◽  
The Last Deglaciation ◽  
The North Atlantic ◽  
Reservoir Age

<p>Paleoclimate records from the North Atlantic show some of the most iconic signals of abrupt climate change during the ice ages. Here we use radiocarbon as a tracer of ocean circulation and air-sea gas exchange to investigate potential mechanisms for the abrupt climate changes seen in the North Atlantic over the last deglaciation. We have created a stack of North Atlantic surface radiocarbon reservoir ages over the past 20,000 years, using new synchronized age models from thirteen sediment cores refined with thorium normalization between tie-points. This stack shows consistent and large reservoir age increases of more than 1000 years from the LGM into HS1, dropping abruptly back to approximately modern reservoir ages before the onset of the Bolling-Allerod. We use the intermediate complexity earth system model cGENIE to investigate the potential drivers of these reservoir age changes. We find that sea ice, circulation and CO<sub>2</sub> all play important roles in setting the reservoir age. We use these coherently dated records to revisit the sequence and timing of climatic events during HS1 and the last deglaciation, and show that Laurentide Heinrich Events are a response to stadial conditions, rather than their root cause.</p>

scholarly journals Modelling ocean circulation, climate and oxygen isotopes in the ocean over the last 120 000 years

2006 ◽  
Vol 2 (5) ◽  
pp. 657-709 ◽  
Author(s):  
R. Marsh ◽  
M. P. L. M. Smith ◽  
E. J. Rohling ◽  
D. J. Lunt ◽  
T. M. Lenton ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Oxygen Isotopes ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Dominant Role ◽  
Sediment Cores ◽  
Co2 Concentration ◽  
Ocean Drilling Program ◽  
The North ◽  
The North Atlantic

Abstract. A new Earth System Model of Intermediate Complexity, GENIE-1, is used to simulate the most recent glacial-interglacial cycle by prescribing orbital forcing, atmospheric CO2 concentration, and the time evolution of ice sheet extent and orography. A series of experiments investigates uncertainty in the amplitude, frequency and location of prescribed meltwater pulses (MWPs) associated with Heinrich events in the North Atlantic and layers enriched in ice rafted debris around Antarctica. Associated with each MWP is a flux into the ocean of very light glacial oxygen isotope ratios, which serve as a tracer of the melt water. Additionally accounted for are temperature-related changes in the fractionation of stable oxygen isotopes between water and calcite. Modelled forwards from 120 000 years ago, simulated oxygen isotope records can thus be directly compared with measurements in calcite taken from International Marine Global Change Study (IMAGES) and Ocean Drilling Program (ODP) sediment cores at three locations representative of the North and South Atlantic, and the South Pacific. During the period of simulation corresponding to Marine Isotope Stage 3, the best agreement between the simulated oxygen isotope record in the North Atlantic and core measurements is found in the experiment that includes MWPs around Antarctica as well as into the North Atlantic. This challenges previous assumptions about the dominant role of northern ice sheets in glacial sea-level variability.

Contour currents of the North Atlantic during the last glacial cycle

Oceanology ◽  
2015 ◽  
Vol 55 (6) ◽  
pp. 899-905 ◽  
Author(s):  
V. V. Sivkov ◽  
E. V. Dorokhova ◽  
L. D. Bashirova
Keyword(s):  
North Atlantic ◽  
Glacial Cycle ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
The Last Glacial

scholarly journals Sedimentary record of rapid climatic variability in the North Atlantic Ocean during the Last Glacial Cycle

1995 ◽  
Vol 10 (5) ◽  
pp. 911-926 ◽  
Author(s):  
Elsa Cortijo ◽  
Pascal Yiou ◽  
Laurent Labeyrie ◽  
Michael Cremer
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Climatic Variability ◽  
Glacial Cycle ◽  
Sedimentary Record ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
The Last Glacial
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