Atmospheric response to Ice Age conditions: Climatology near the Earth's surface

Lautenschlager, Michael; Herterich, Klaus

doi:10.1029/jd095id13p22547

Cited by 95 publications

(28 citation statements)

References 22 publications

(16 reference statements)

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“…Averaged over the globe, the LGM experiment cooling is 3.2 ЊC, with more intense cooling in the Northern Hemisphere (where there is also more land) than in the Southern Hemisphere, yielding a pronounced asymmetry about the Equator. Cooling of 3.2 ЊC is slightly less than found in some AGCM studies [16][17][18] , although it is similar to the amount found in others 37,38 . In the Northern Hemisphere maximum winter-mean cooling of 14.4 ЊC is found in the North Atlantic; this weakens to about 6.8 ЊC in the summer.…”

Section: Simulations Of the Lgm And The Present Daysupporting

confidence: 75%

“…In the first, ocean-only models have been used in which surface forcing consists of restoring temperature and salinity to LGM reconstructions with specified atmospheric general circulation model (AGCM) LGM surface wind stress fields [12][13][14] . The second class of studies involves the integration of AGCMs with either fixed SST or mixed-layer ocean models at the lower boundary [15][16][17][18][19] . Many of these modelling studies have found tropical SSTs consistent with CLIMAP, although this often (but not always; see, for example, ref.…”

mentioning

confidence: 99%

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Simulated influence of carbon dioxide, orbital forcing and ice sheets on the climate of the Last Glacial Maximum

Weaver

Eby

Fanning

et al. 1998

Nature

216

138

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A coupled atmosphere-ocean-sea-ice model is used to investigate the climate of the Last Glacial Maximum (ϳ21,000 years ago) and the relative climate-forcing effects of atmosphere CO 2 , the Earth's orbital parameters and ice-sheet albedo. Tropical temperatures are found to be ϳ2.2 ЊC less than today's-slightly colder than indicated by the CLIMAP palaeoclimate reconstruction. This result is consistent with a low to medium climate sensitivity to radiative perturbations. Temperatures are colder still in the northern North Atlantic region, owing to a weakening and shallowing of the thermohaline circulation. A sensitivity analysis suggests that changes in ocean circulation since the Last Glacial Maximum have not contributed directly to the global-mean temperature change since that time.Early CLIMAP 1,2 attempts to reconstruct sea surface temperature (SST) for the Last Glacial Maximum (LGM), around 21 kyr ago, have suggested that relative to the present, global SSTs were on average 1.7 ЊC cooler in August and 1.4 ЊC cooler in February. These reconstructions further suggested that tropical SSTs were similar to those of the present climate whereas in the North Atlantic, SSTs were much colder. Although recent alkenone evidence 3-6 also supports tropical SSTs having been only slightly cooler at the LGM, additional evidence is contradictory. For example, coral records form Barbados 7 and the southwest Pacific 8 , ice-core records from Peru 9 , noble-gas measurements in Brazil 10 and ocean core records from the western equatorial Atlantic 11 suggest that LGM tropical temperatures were significantly below the present-day values.Most previous modelling studies of the LGM have fallen into two categories. In the first, ocean-only models have been used in which surface forcing consists of restoring temperature and salinity to LGM reconstructions with specified atmospheric general circulation model (AGCM) LGM surface wind stress fields 12-14 . The second class of studies involves the integration of AGCMs with either fixed SST or mixed-layer ocean models at the lower boundary 15-19 . Many of these modelling studies have found tropical SSTs consistent with CLIMAP, although this often (but not always; see, for example, ref. 15) reflects the fact that CLIMAP data were used as a boundary condition. Webb et al. 20 on the other hand obtained relatively cool tropical SSTs using an AGCM in which present-day oceanic heat transports were maintained. They argued that reduced evaporation in the subtropics with present-day oceanic heat transport led to reduced water vapour in the atmosphere, and hence reduced absorption of outgoing longwave radiation. These workers also suggested that this cooling mechanism was amplified by other processes in the system.Until recently, it has not been possible to run coupled atmosphere-ocean GCM experiments to equilibrium for LGM scenarios owing to the necessity of applying explicit flux adjustments to keep stable the present-day climate. Any meaningful comparison between the simulated present-day and LGM clima...

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Section: Simulations Of the Lgm And The Present Daysupporting

confidence: 75%

mentioning

confidence: 99%

Simulated influence of carbon dioxide, orbital forcing and ice sheets on the climate of the Last Glacial Maximum

Weaver

Eby

Fanning

et al. 1998

Nature

216

138

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“…There is a large number of other model simulations of the LGM ocean based on a wide variety of OGCMs, which for example employ air temperature and freshwater flux from an atmospheric model (Lautenschlager and Herterich 1990;Bigg et al 1998), reconstructions of SST and SSS (Seidov et al 1996;Winguth et al 1999) or an energy balance model for the temperature boundary condition (Fieg and Gerdes 2001). Two coupled model studies were carried out with intermediate complexity models (Ganopolski et al 1998;Weaver et al 1998).…”

Section: Comparison To Climapmentioning

confidence: 99%

The Atlantic Ocean at the Last Glacial Maximum: 2. Reconstructing the Current Systems with a Global Ocean Model

Paul

Schäfer-Neth

2003

The South Atlantic in the Late Quaternary

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Abstract:We use a global ocean general circulation model (OGCM) with low vertical diffusion and isopycnal mixing to simulate the circulation in the Atlantic Ocean at present-day and the Last Glacial Maximum (LGM). The OGCM includes δ 18 O as a passive tracer. Regarding the LGM sea-surface boundary conditions, the temperature is based on the GLAMAP reconstruction, the salinity is estimated from the available δ 18 O data, and the wind-stress is derived from the output of an atmospheric general circulation model. Our focus is on changes in the upper-ocean hydrology, the large-scale horizontal circulation and the δ 18 O distribution. In a series of LGM experiments with a step-wise increase of the sea-surface salinity anomaly in the Weddell Sea, the ventilated thermocline was colder than today by 2-3°C in the North Atlantic Ocean and, in the experiment with the largest anomaly (1.0 beyond the global anomaly), by 4-5°C in the South Atlantic Ocean; furthermore it was generally shallower. As the meridional density gradient grew, the Antarctic Circumpolar Current strengthened and its northern boundary approached Cape of Good Hope. At the same time the southward penetration of the Agulhas Current was reduced, and less thermocline-to-intermediate water slipped from the Indian Ocean along the southern rim of the African continent into the South Atlantic Ocean; the 'Agulhas leakage' was diminished by up to 60% with respect to its modern value, such that the cold water route became the dominant path for North Atlantic Deep Water (NADW) renewal. It can be speculated that the simulated intensification of the Benguela Current and the enhancement of NADW upwelling in the Southern Ocean might reduce the import of silicate into the Benguela System, which could possibly resolve the 'Walvis Opal Paradox'. Although δ 18 O w was restored to the same surface values and could only reflect changes in advection and diffusion, the resulting δ 18 O c distribution came close to reconstructions based on fossil shells of benthic foraminifera.

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“…Hyde et al 1989) and AGCMs (e.g. Lautenschlager & Herterich 1990). 3 Models that asynchronously couple a climate model to one or several ice sheet models (Marsiat 1994).…”

Section: Cryospherementioning

confidence: 99%

Climate Modeling

Lahoz¹

2003

Handbook of Atmospheric Science

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Atmospheric response to Ice Age conditions: Climatology near the Earth's surface

Cited by 95 publications

References 22 publications

Simulated influence of carbon dioxide, orbital forcing and ice sheets on the climate of the Last Glacial Maximum

Simulated influence of carbon dioxide, orbital forcing and ice sheets on the climate of the Last Glacial Maximum

The Atlantic Ocean at the Last Glacial Maximum: 2. Reconstructing the Current Systems with a Global Ocean Model

Climate Modeling

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