Last Glacial Maximum and Holocene Climate in CCSM3

Otto‐Bliesner, Bette L.; Brady, Esther C.; Clauzet, Gabriel; Tomas, Robert A.; Levis, Samuel; Kothavala, Zavareh

doi:10.1175/jcli3748.1

Cited by 571 publications

(465 citation statements)

References 61 publications

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“…Coupled LGM climate simulations using the Community Climate System Model (CCSM)1.4 and CCSM3 show a strongly increased abyssal stratification and shallower NADW (7,23,24). Consistent with the results discussed here, these changes have been attributed to enhanced sea-ice export around Antarctica (7) and ultimately reduced CO2 concentrations (8).…”

Section: Discussionsupporting

confidence: 81%

Glacial ocean circulation and stratification explained by reduced atmospheric temperature

Jansen

2016

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

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Earth's climate has undergone dramatic shifts between glacial and interglacial time periods, with high-latitude temperature changes on the order of 5-10 • C. These climatic shifts have been associated with major rearrangements in the deep ocean circulation and stratification, which have likely played an important role in the observed atmospheric carbon dioxide swings by affecting the partitioning of carbon between the atmosphere and the ocean. The mechanisms by which the deep ocean circulation changed, however, are still unclear and represent a major challenge to our understanding of glacial climates. This study shows that various inferred changes in the deep ocean circulation and stratification between glacial and interglacial climates can be interpreted as a direct consequence of atmospheric temperature differences. Colder atmospheric temperatures lead to increased sea ice cover and formation rate around Antarctica. The associated enhanced brine rejection leads to a strongly increased deep ocean stratification, consistent with high abyssal salinities inferred for the last glacial maximum. The increased stratification goes together with a weakening and shoaling of the interhemispheric overturning circulation, again consistent with proxy evidence for the last glacial. The shallower interhemispheric overturning circulation makes room for slowly moving water of Antarctic origin, which explains the observed middepth radiocarbon age maximum and may play an important role in ocean carbon storage.LGM | AMOC | stratification | cooling | sea-ice T he deep ocean today is ventilated mainly by two water masses. North Atlantic deep water (NADW) is formed in the North Atlantic before flowing southward at a depth of about 2-3 km and eventually rising back up to the surface in the Southern Ocean. Antarctic bottom water (AABW) is formed around Antarctica and spreads northward into the abyssal basins. The AABW that makes it into the Atlantic then slowly upwells into the lower NADW before returning southward and resurfacing again around Antarctica (1, 2). The glacial equivalent of NADW was likely confined to shallower depths, leaving more of the deep Atlantic filled with water masses originating primarily from around Antarctica (3-5). Moreover, the two water masses appear more distinct, with less mixing between them (6).Multiple studies have pointed toward the potential importance of sea ice and surface buoyancy fluxes around Antarctica in controlling changes in the deep ocean stratification and circulation between the present and Last Glacial Maximum (LGM) (7-11). Specifically, we recently showed that enhanced buoyancy loss around Antarctica is expected to lead to an increase in the abyssal stratification, an upward shift of NADW, and a clearer separation between NADW and southward-flowing AABW (11)-all in agreement with inferences made for differences in circulation and stratification between the present and LGM (3,6,12,13). This gives rise to the hypothesis that strong cooling around Antarctica led to an increased net freezing...

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Section: Discussionsupporting

confidence: 81%

Glacial ocean circulation and stratification explained by reduced atmospheric temperature

Jansen

2016

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

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“…The classical 'linear' model links ENSO variability with the zonal gradient through the 'destabilizing' effect of cold thermocline waters of the Eastern Pacific but produced the opposite relationship [10][11][12] (for example, positive instead of negative correlation) compared with the results of our study. Another mechanism linking ENSO variability and SST zonal gradient is based on external forcing of one of several feedbacks within the ENSO system during a particular season 13,14 .…”

Section: Discussioncontrasting

confidence: 66%

Palaeoclimate reconstructions reveal a strong link between El Niño-Southern Oscillation and Tropical Pacific mean state

et al. 2013

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The El Niño-Southern Oscillation (ENSO) is one of the most important components of the global climate system, but its potential response to an anthropogenic increase in atmospheric CO 2 remains largely unknown. One of the major limitations in ENSO prediction is our poor understanding of the relationship between ENSO variability and long-term changes in Tropical Pacific oceanography. Here we investigate this relationship using palaeorecords derived from the geochemistry of planktonic foraminifera. Our results indicate a strong negative correlation between ENSO variability and zonal gradient of sea-surface temperatures across the Tropical Pacific during the last 22 ky. This strong correlation implies a mechanistic link that tightly couples zonal sea-surface temperature gradient and ENSO variability during large climate changes and provides a unique insight into potential ENSO evolution in the future by suggesting enhanced ENSO variability under a global warming scenario.

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“…Pendleton et al (2015) suggested that early deglaciation in the Brooks Range may have also been related to the impact that the expanded Laurentide Ice Sheet had on atmospheric circulation. Indeed, simulations by global climate models show that the Laurentide Ice Sheet caused significant warming and drying in the Alaska-Yukon region during the LGM (Roe and Lindzen, 2001;Otto-Bliesner et al, 2006), which agrees with very little LGM temperature depressions based on chironomids (Kurek et al, 2009) and pollen (Bartlein et al, 2011). Regardless, among the eight sites in Alaska reviewed here that have sufficient existing chronology to address this question, data from seven sites support significant glacier recession prior to ~18 ka.…”

Section: How Did the Timing Of Glacier Recession Relate To Buildup Ofsupporting

confidence: 67%

The last deglaciation of Alaska

Briner

Tulenko

Kaufman

et al. 2017

CIG

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Last Glacial Maximum and Holocene Climate in CCSM3

Abstract: The climate sensitivity of CCSM3 is studied for two past climate forcings, the Last Glacial Maximum (LGM) and the mid-Holocene. The LGM, approximately 21,000 years ago, is a glacial period with large changes in the greenhouse gases, sea level, and ice sheets.

Cited by 571 publications

References 61 publications

Glacial ocean circulation and stratification explained by reduced atmospheric temperature

Glacial ocean circulation and stratification explained by reduced atmospheric temperature

Palaeoclimate reconstructions reveal a strong link between El Niño-Southern Oscillation and Tropical Pacific mean state

The last deglaciation of Alaska

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