Late slowdown of the Atlantic Meridional Overturning Circulation during the Last Glacial Inception: New constraints from sedimentary (231Pa/230Th)

Guihou, Abel; Pichat, Sylvain; Nave, Silvia Osorio; Govin, Aline; Labeyrie, Laurent D; Michel, Élisabeth; Waelbroeck, C.

doi:10.1016/j.epsl.2009.11.045

Cited by 34 publications

(47 citation statements)

References 53 publications

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“…Furthermore, a slowdown of the AMOC at the MIS 5-4 transition, with relatively constant NADW export during MIS 5, has been reported from a sediment core in the deep northeastern Atlantic (Fig. 3F) (30). Taken together, these records indicate that at the MIS 5-4 transition deep ocean circulation in the Atlantic changed significantly from a modern-like situation, where NADW flows southward at depth to the southern Atlantic and then partly into the Indian Ocean, to a glacial situation with a slower AMOC and a shallower Glacial North Atlantic Intermediate Water (GNAIW) cell lying on top of an increased Antarctic Bottom Water (AABW) mass extending into the North Atlantic (Fig.…”

Section: Discussionmentioning

confidence: 99%

Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Bereiter

Lüthi

Siegrist

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

151

188

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Important elements of natural climate variations during the last ice age are abrupt temperature increases over Greenland and related warming and cooling periods over Antarctica. Records from Antarctic ice cores have shown that the global carbon cycle also plays a role in these changes. The available data shows that atmospheric CO 2 follows closely temperatures reconstructed from Antarctic ice cores during these variations. Here, we present new high-resolution CO 2 data from Antarctic ice cores, which cover the period between 115,000 and 38,000 y before present. Our measurements show that also smaller Antarctic warming events have an imprint in CO 2 concentrations. Moreover, they indicate that during Marine Isotope Stage (MIS) 5, the peak of millennial CO 2 variations lags the onset of Dansgaard/Oeschger warmings by 250 AE 190 y. During MIS 3, this lag increases significantly to 870 AE 90 y. Considerations of the ocean circulation suggest that the millennial variability associated with the Atlantic Meridional Overturning Circulation (AMOC) undergoes a mode change from MIS 5 to MIS 4 and 3. Ocean carbon inventory estimates imply that during MIS 3 additional carbon is derived from an extended mass of carbon-enriched Antarctic Bottom Water. The absence of such a carbon-enriched water mass in the North Atlantic during MIS 5 can explain the smaller amount of carbon released to the atmosphere after the Antarctic temperature maximum and, hence, the shorter lag. Our new data provides further constraints for transient coupled carbon cycleclimate simulations during the entire last glacial cycle.abrupt climate change | CO2-temperature phasing | ice age variability | paleoclimate | greenhouse gas T he climate of the last glacial period is characterized by low global mean temperatures and a number of interhemispheric variations on time scales of several millennia. In the northern hemisphere, in particular on the Greenland ice sheet, large and very rapid temperature jumps of up to 15°C within a few decades, followed by more steady decreases of temperature, have been identified from ice core analyses (1, 2). 25 of these so-called Dansgaard-Oeschger (DO) events have been found during the last glacial period. For each of these events, an associated Antarctic temperature variation has been also documented in Antarctic ice cores (Antarctic Isotope Maximum [AIM] events) (3). Antarctic temperatures increase siteadily when Greenland is in the cold phase and slowly decrease following the abrupt temperature increase in Greenland during a DO event. This behavior is explained by the concept of an oceanic thermal bipolar seesaw, where variations in the Atlantic Meridional Overturning Circulation (AMOC) and associated changes in heat transport across the equator to the North Atlantic modulate the southern and northern hemisphere temperatures during each of these events (4).Previous reconstructions of atmospheric CO 2 concentrations during these millennial-scale variations show that CO 2 varies largely in parallel with the major AIM events (...

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Section: Discussionmentioning

confidence: 99%

Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Bereiter

Lüthi

Siegrist

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

151

188

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“…Data from twenty-seven of these cores come from the thesis of Yu [1994]. For the other twelve cores, data come either from more recent studies Gherardi et al, 2005;Hall et al, 2006;Bradtmiller et al, 2007; or are unpublished (L. Bradtmiller, unpublished data, 2009). For these twelve cores, Holocene is defined as the time interval 0-6 kyr B.P.…”

Section: Resultsmentioning

confidence: 99%

“…[48] The 231 Pa/ 230 Th data for the Heinrich Event 1 (H1) from fifteen cores are used Gherardi et al, 2005;Hall et al, 2006;Bradtmiller et al, 2007;. For four of these cores, unpublished data are provided by L. Bradtmiller (unpublished data, 2009).…”

Section: Analysis Of Sedimentmentioning

confidence: 99%

“…They claimed that constraining past changes in the MOC from 231 Pa/ 230 Th at one site is "impossible." [10] Although past changes in particle composition may be an important control on sediment 231 Pa/ 230 Th [Hall et al, 2006;Gil et al, 2009;Lippold et al, 2009], these changes remain poorly understood. For example, most of the biogenic silica produced in the sunlit layers of the ocean is dissolved in the water column or near the seafloor [e.g., Nelson et al, 1995], suggesting that past changes in opal production may not be recorded in the sedimentary column.…”

Section: Introductionmentioning

confidence: 99%

“…[3] Recently, downcore records of the ratio of two radioisotopes in sediment, protactinium-231 and thorium-230, have been used to infer past changes in the strength or structure of the meridional overturning circulation (MOC) in the Atlantic Ocean [e.g., Yu et al, 1996;Gherardi et al, 2005;Hall et al, 2006;Guihou et al, 2010;Negre et al, 2010]. 231 Pa and 230 Th are produced in seawater in a nearly constant ratio (0.093) from the radioactive decay of 235 U and 234 U, respectively [Yu et al, 1996].…”

Section: Introductionmentioning

confidence: 99%

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Constraining circulation changes through the last deglaciation with deep-sea coral radiocarbon and sedimentary 231Pa/230Th

Burke¹

2012

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Radioactive isotopes can be used in paleoceanography both for dating samples and as tracers of ocean processes. Here I use radiocarbon and uranium series isotopes to investigate the ocean's role in climate change over the last deglaciation. I present a new method for rapid radiocarbon analyses as a means of age-screening deep-sea corals for further study. Based on age survey results, I selected forty corals from the Drake Passage and thirteen from the Reykjanes Ridge off Iceland and dated them with uranium series isotopes. The uranium series dates give independent ages that allow radiocarbon to be used as a tracer of circulation and carbon cycle changes. The radiocarbon records generated from the Drake Passage corals show increased stratification in the Southern Ocean during the last glacial maximum (LGM) that disappeared during the start of the deglaciation as atmospheric CO 2 began to rise during Heinrich Stadial 1 (H1). Considering these data and using a simple mass budget calculation, I show that the drop in atmospheric radiocarbon activity during H1 can be explained given direct carbon exchange between the radiocarbon-depleted deep ocean and atmosphere, e.g. through the Southern Ocean. The Drake Passage radiocarbon records also show evidence for decreased air-sea gas exchange in the Southern Ocean during the Antarctic Cold Reversal/Bølling-Allerød coincident with the hiatus in the deglacial CO 2 rise. During this time period in the North Atlantic, radiocarbon reconstructions from deep-sea corals collected from off Iceland show a similar ventilation rate to that observed today and during the Holocene. To further investigate changes in North Atlantic ventilation over the last deglaciation, I used an inverse model to assess the consistency of sedimentary 231 Pa/ 230 Th ratios from the Holocene, H1, and the LGM with the modern circulation. Although sedimentary 231 Pa/ 230 Th has been used to infer changes in the strength of the meridional overturning circulation in the past, I find that published data are consistent with the modern circulation during the LGM and H1. These findings highlight the importance of giving due regard to the uncertainties in the behavior and spatial distribution of paleoceanographic tracers.

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Atlantic Ocean circulation changes preceded millennial tropical South America rainfall events during the last glacial

Bürckel

Waelbroeck

Gherardi

et al. 2015

Geophysical Research Letters

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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 231 Pa/ 230 Th 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 of the large precipitation events observed in tropical South America during Heinrich stadials. In addition, we propose a mechanism explaining the differences in the extent and timing of AMOC slowdowns associated with shorter and longer stadials.

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Late slowdown of the Atlantic Meridional Overturning Circulation during the Last Glacial Inception: New constraints from sedimentary (231Pa/230Th)

Cited by 34 publications

References 53 publications

Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Constraining circulation changes through the last deglaciation with deep-sea coral radiocarbon and sedimentary 231Pa/230Th

Atlantic Ocean circulation changes preceded millennial tropical South America rainfall events during the last glacial

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Late slowdown of the Atlantic Meridional Overturning Circulation during the Last Glacial Inception: New constraints from sedimentary (231Pa/230Th)

Cited by 34 publications

References 53 publications

Mode change of millennial CO 2 variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Mode change of millennial CO 2 variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Constraining circulation changes through the last deglaciation with deep-sea coral radiocarbon and sedimentary 231Pa/230Th

Atlantic Ocean circulation changes preceded millennial tropical South America rainfall events during the last glacial

Contact Info

Product

Resources

About

Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw