scholarly journals Mid-depth South Atlantic Ocean circulation and chemical stratification during MIS-10 to 12: implications for atmospheric CO<sub>2</sub>

2008 ◽  
Vol 4 (4) ◽  
pp. 333-344 ◽  
Author(s):  
A. J. Dickson ◽  
M. J. Leng ◽  
M. A. Maslin
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Sediment Cores ◽  
Convective Cell ◽  
Ocean Ventilation ◽  
Cape Basin ◽  
Northern Atlantic ◽  
Glacial Periods ◽  
Atlantic Margin

Abstract. A detailed record of benthic foraminifera carbon isotopes from the intermediate-depth South East Atlantic margin shows little glacial-interglacial variability between MIS-12 to MIS-10, suggesting that Northern Atlantic deepwaters consistently penetrated to at least 30° S. Millennial-scale increases in either the mass or flux of northern-sourced deepwaters over the core site occurred alongside reductions in Lower North Atlantic Deep Water recorded in North Atlantic sediment cores and show that the lower and intermediate limb of the Atlantic deepwater convective cell oscillated in anti-phase during previous glacial periods. In addition, a 500 yr resolution record of the Cape Basin intermediate-deep δ13C gradient shows that a reduction in deep Southern Ocean ventilation at the end of MIS-11 was consistent with a modelled CO2 drawdown of ~21–30 ppm. Further increases in the Southern Ocean chemical divide during the transition into MIS-10 were completed before minimum CO2 levels were reached, suggesting that other mechanisms such as alkalinity changes were responsible for the remaining ~45 ppm drawdown.

scholarly journals Mid-depth South Atlantic ocean circulation and chemical stratification during MIS-10 to 12: implications for atmospheric CO<sub>2</sub>

2008 ◽  
Vol 4 (3) ◽  
pp. 667-695 ◽  
Author(s):  
A. J. Dickson ◽  
M. J. Leng ◽  
M. A. Maslin
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Sediment Cores ◽  
Convective Cell ◽  
Intermediate Water ◽  
Ocean Ventilation ◽  
Cape Basin ◽  
Glacial Periods ◽  
Atlantic Margin

Abstract. A detailed record of benthic foraminifera carbon isotopes from the South East Atlantic margin shows little glacial-interglacial variability between MIS-12 to MIS-10, suggesting that Glacial North Atlantic Intermediate Water (GNAIW) consistently penetrated to at least 30° S. Millennial-scale increases in either the mass or flux of GNAIW over the core site occur alongside reductions in Lower North Atlantic Deep Water recorded in North Atlantic sediment cores and show that the lower and intermediate limb of the Atlantic deepwater convective cell oscillated in anti-phase during previous glacial periods. In addition, a 500 yr resolution record of the Cape Basin intermediate-deep δ13C gradient shows that a reduction in deep Southern Ocean ventilation at the end of MIS-11 was consistent with a modelled CO2 drawdown of ~21–30 ppm. Further increases in the Southern Ocean chemical divide during the transition into MIS-10 were completed before minimum CO2 levels were reached, suggesting that other mechanisms such as alkalinity changes were responsible for the remaining ~45 ppm drawdown.

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 Deep ocean ventilation, carbon isotopes, marine sedimentation and the deglacial CO<sub>2</sub> rise

2011 ◽  
Vol 7 (3) ◽  
pp. 771-800 ◽  
Author(s):  
T. Tschumi ◽  
F. Joos ◽  
M. Gehlen ◽  
C. Heinze
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Isotope Composition ◽  
Deep Ocean ◽  
Atmospheric Co2 ◽  
Carbon Cycle Model ◽  
Ocean Ventilation ◽  
Marine Sedimentation ◽  
Sediment Formation ◽  
Ocean Carbon

Abstract. The link between the atmospheric CO2 level and the ventilation state of the deep ocean is an important building block of the key hypotheses put forth to explain glacial-interglacial CO2 fluctuations. In this study, we systematically examine the sensitivity of atmospheric CO2 and its carbon isotope composition to changes in deep ocean ventilation, the ocean carbon pumps, and sediment formation in a global 3-D ocean-sediment carbon cycle model. Our results provide support for the hypothesis that a break up of Southern Ocean stratification and invigorated deep ocean ventilation were the dominant drivers for the early deglacial CO2 rise of ~35 ppm between the Last Glacial Maximum and 14.6 ka BP. Another rise of 10 ppm until the end of the Holocene is attributed to carbonate compensation responding to the early deglacial change in ocean circulation. Our reasoning is based on a multi-proxy analysis which indicates that an acceleration of deep ocean ventilation during early deglaciation is not only consistent with recorded atmospheric CO2 but also with the reconstructed opal sedimentation peak in the Southern Ocean at around 16 ka BP, the record of atmospheric δ13CCO2, and the reconstructed changes in the Pacific CaCO3 saturation horizon.

scholarly journals What Fraction of the Pacific and Indian Oceans' Deep Water is formed in the North Atlantic?

2018 ◽  
Author(s):  
James W. B. Rae ◽  
Wally Broecker
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Deep Water ◽  
Bottom Water ◽  
Ocean Bottom ◽  
The North ◽  
Water Value ◽  
The Pacific ◽  
Northern Atlantic ◽  
The North Atlantic

Abstract. In this contribution we explore constraints on the fractions of deep water present in Indian and Pacific Oceans which originated in the northern Atlantic and in the Southern Ocean. Based on PO4* we show that if ventilated Antarctic shelf waters characterize the Southern contribution, then the proportions are close to 50–50. If instead a Southern Ocean bottom water value is used, the Southern contribution is increased to 75 %. While this larger estimate may characterize the volume of water entering the Indo-Pacific from the Southern Ocean, it contains a significant portion of entrained northern water. We also note that ventilation may be highly tracer dependent: for instance Southern Ocean waters may contribute only 35 % of the deep radiocarbon budget, even if their volumetric contribution is 75 %. In our estimation, the most promising approaches involve using CFC-11 to constrain the amount of deep water formed in the Southern Ocean.

scholarly journals Rapid shifts in circulation and biogeochemistry of the Southern Ocean during deglacial carbon cycle events

2020 ◽  
Vol 6 (42) ◽  
pp. eabb3807
Author(s):  
Tao Li ◽  
Laura F. Robinson ◽  
Tianyu Chen ◽  
Xingchen T. Wang ◽  
Andrea Burke ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Deep Sea ◽  
Deep Ocean ◽  
Biological Pump ◽  
Last Deglaciation ◽  
Proxy Data ◽  
Ocean Ventilation ◽  
Carbon Release ◽  
The Last Deglaciation

The Southern Ocean plays a crucial role in regulating atmospheric CO2 on centennial to millennial time scales. However, observations of sufficient resolution to explore this have been lacking. Here, we report high-resolution, multiproxy records based on precisely dated deep-sea corals from the Southern Ocean. Paired deep (∆14C and δ11B) and surface (δ15N) proxy data point to enhanced upwelling coupled with reduced efficiency of the biological pump at 14.6 and 11.7 thousand years (ka) ago, which would have facilitated rapid carbon release to the atmosphere. Transient periods of unusually well-ventilated waters in the deep Southern Ocean occurred at 16.3 and 12.8 ka ago. Contemporaneous atmospheric carbon records indicate that these Southern Ocean ventilation events are also important in releasing respired carbon from the deep ocean to the atmosphere. Our results thus highlight two distinct modes of Southern Ocean circulation and biogeochemistry associated with centennial-scale atmospheric CO2 jumps during the last deglaciation.

Late glacial and Holocene glacier fluctuations at the Sub-Antarctic Island Kerguelen in the Southern Indian Ocean

2020 ◽  
Author(s):  
Jostein Bakke ◽  
Fabien Arnaud ◽  
Philip Deline ◽  
Charline Guiguet-Covex ◽  
Henriette Linge ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Sediment Cores ◽  
Critical Role ◽  
Late Glacial ◽  
Global Ocean ◽  
Exposure Dating ◽  
Temperature And Precipitation ◽  
Late Glacial And Holocene ◽  
Do So

&lt;p&gt;The Southern Hemisphere`s westerly winds play a critical role in regulating Earth`s climate by shielding Antarctica from low-latitude heat, driving global ocean circulation and regulate the uptake of CO2 in the Southern Ocean. Both strength and position of this globally significant atmospheric pattern are rapidly shifting in the face of ongoing global warming. A string of recent studies links these developments to dramatic coupled changes in temperature, precipitation, sea-ice coverage and glacier extent that unfold across the Southern Ocean region. Critically, a lack of baseline information restricts our ability to understand the causes and patterns of these shifts and represent them robustly in the future projections that underpin climate policies. To help do so, we utilize the sensitivity of glaciers to atmospheric climate change and the potential of glacier-fed lake sediments to record this signal through time. For this purpose, we integrate emerging sedimentological, geochemical and glacier modelling tools in a new method framework to reconstruct changes in glacier extent, temperature and precipitation on human-relevant timescales. To do so, we rely on a number of novel sedimentological and geochemical approaches. These include biomarker-based temperature reconstructions, exposure dating of moraines and the use emerging non-destructive scanning techniques (e.g. Computed Tomography &amp;#8211; CT) to fingerprint depositional pathways. Our study area in this cross-disciplinary project is the poorly investigated sub-Antarctic Kerguelen Archipelago, well-situated in the core southern westerly wind belt. During an extensive 2019 field campaign, we collected 130 meters of sediment cores from six lakes, 110 rock samples for exposure dating and numerous catchment samples.&amp;#160;&lt;/p&gt;

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

&lt;p&gt;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&lt;sub&gt;2&lt;/sub&gt; 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.&lt;/p&gt;

North Atlantic versus Southern Ocean contributions to a deglacial surge in deep ocean ventilation

Geology ◽  
2013 ◽  
Vol 41 (6) ◽  
pp. 667-670 ◽  
Author(s):  
L.C. Skinner ◽  
A.E. Scrivner ◽  
D. Vance ◽  
S. Barker ◽  
S. Fallon ◽  
...  
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Deep Ocean ◽  
Ocean Ventilation

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 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.

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