Sensitivity of Southern Hemisphere circulation to LGM and 4 × CO2 climates

Rojas, Maisa

doi:10.1002/grl.50195

Cited by 47 publications

(50 citation statements)

References 32 publications

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“…Accordingly, the factor of SHW wind-driven evaporation would not be a determinant for the lake water balance, which is consistent with the hypothesis of an equatorward shift of 7-10 • latitude of the SHW belt during the LGM (Toggweiler et al, 2006). However, the changes in strength and latitudinal position of the SHW during the LGM relative to today are still in an open debate, as a consequence of uncertainties in modelling results (Chavaillaz et al, 2013;Pollock and Bush, 2013;Rojas, 2013;Sime et al, 2013) and ambiguities in proxy interpretations (Kohfeld et al, 2013).…”

Section: δ 18 O Lw−corr Of the Full Glacial (26 000-21 000 Cal Bp)supporting

confidence: 76%

Climate history of the Southern Hemisphere Westerlies belt during the last glacial–interglacial transition revealed from lake water oxygen isotope reconstruction of Laguna Potrok Aike (52° S, Argentina)

Zhu¹,

Lücke²,

Wissel³

et al. 2014

Clim. Past

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Abstract. The Southern Hemisphere Westerlies (SHW) play a crucial role in large-scale ocean circulation and global carbon cycling. Accordingly, the reconstruction of how the latitudinal position and intensity of the SHW belt changed during the last glacial termination is essential for understanding global climatic fluctuations. The southernmost part of the South American continent is the only continental mass intersecting a large part of the SHW belt. However, due to the scarcity of suitable palaeoclimate archives continuous proxy records back to the last glacial are rare in southern Patagonia. Here, we show an oxygen isotope record from cellulose and purified bulk organic matter of submerged aquatic moss shoots from Laguna Potrok Aike (52 • S, 70 • W), a deep maar lake located in semi-arid, extra-Andean Patagonia, covering the last glacial-interglacial transition (26 000 to 8500 cal BP). Based on the highly significant correlation between oxygen isotope values of modern aquatic mosses and their host waters and abundant well-preserved moss remains in the sediment record a high-resolution reconstruction of the lake water oxygen isotope (δ 18 O lw−corr ) composition is presented. The reconstructed δ 18 O lw−corr values for the last glacial are ca. 3 ‰ lower than modern values, which can best be explained by generally cooler air temperatures and changes in the moisture source area, together with the occurrence of permafrost leading to a prolonged lake water residence time. Thus, the overall glacial δ 18 O lw−corr level until 21 000 cal BP is consistent with a scenario of weakened or absent SHW at 52 • S compared to the present. During the last deglaciation, reconstructed δ 18 O lw−corr values reveal a significant two-step rise describing the detailed response of the lake's hydrological balance to this fundamental climatic shift. Rapid warming is seen as the cause of the first rise of ca. 2 ‰ in δ 18 O lw−corr during the first two millennia of deglaciation (17 600 to 15 600 cal BP) owing to more 18 O enriched precipitation and increasing temperature-induced evaporation. Following this interpretation, an early strengthening of the SHW would not be necessary. The subsequent decrease in δ 18 O lw−corr by up to 0.7 ‰ marks a millennial-scale transition period between 15 600 and 14 600 cal BP interpreted as the transition from a system driven by temperature-induced evaporation to a system more dominated by wind-induced evaporation. The δ 18 O lw−corr record resumes its pronounced increase around 14 600 cal BP. This further cumulative enrichment in 18 O of lake water could be interpreted as response to strengthened wind-driven evaporation as induced by the intensification and establishment of the SHW at the latitude of Laguna Potrok Aike (52 • S) since 14 600 cal BP.

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Section: δ 18 O Lw−corr Of the Full Glacial (26 000-21 000 Cal Bp)supporting

confidence: 76%

Climate history of the Southern Hemisphere Westerlies belt during the last glacial–interglacial transition revealed from lake water oxygen isotope reconstruction of Laguna Potrok Aike (52° S, Argentina)

Zhu¹,

Lücke²,

Wissel³

et al. 2014

Clim. Past

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“…LGM simulation ensembles show considerable inter-model disagreement in PI to LGM southern hemispheric jet changes (Rojas, 2013;Chavaillaz et al, 2013). This is despite the fact that nearly all CMIP5 models exhibit a poleward shift, and all models a strengthening, of the surface jet from 1900 to 2100 (Bracegirdle et al, 2013).…”

Section: Existing Analyses Of Pmip2 and Pmip3mentioning

confidence: 97%

“…All models use the PMIP3 LGM ice sheet or ICE5.2G ice sheet configurations (Chavaillaz et al, 2013). Simulations are run for long enough to allow the atmosphere and ocean to reach quasi-equilibrium (Braconnot et al, 2012;Rojas, 2013).…”

Section: Existing Analyses Of Pmip2 and Pmip3mentioning

confidence: 99%

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Sea ice led to poleward-shifted winds at the Last Glacial Maximum: the influence of state dependency on CMIP5 and PMIP3 models

et al. 2016

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Abstract. Latitudinal shifts in the Southern Ocean westerly wind jet could drive changes in the glacial to interglacial ocean CO 2 inventory. However, whilst CMIP5 model results feature consistent future-warming jet shifts, there is considerable disagreement in deglacial-warming jet shifts. We find here that the dependence of pre-industrial (PI) to Last Glacial Maximum (LGM) jet shifts on PI jet position, or state dependency, explains less of the shifts in jet simulated by the models for the LGM compared with future-warming scenarios. State dependence is also weaker for intensity changes, compared to latitudinal shifts in the jet. Winter sea ice was considerably more extensive during the LGM. Changes in surface heat fluxes, due to this sea ice change, probably had a large impact on the jet. Models that both simulate realistically large expansions in sea ice and feature PI jets which are south of 50 • S show an increase in wind speed around 55 • S and can show a poleward shift in the jet between the PI and the LGM. However, models with the PI jet positioned equatorwards of around 47 • S do not show this response: the sea ice edge is too far from the jet for it to respond. In models with accurately positioned PI jets, a +1 • difference in the latitude of the sea ice edge tends to be associated with a −0.85 • shift in the 850 hPa jet. However, it seems that around 5 • of expansion of LGM sea ice is necessary to hold the jet in its PI position. Since the Gersonde et al. (2005) data support an expansion of more than 5 • , this result suggests that a slight poleward shift and intensification was the most likely jet change between the PI and the LGM. Without the effect of sea ice, models simulate poleward-shifted westerlies in warming climates and equatorward-shifted westerlies in colder climates. However, the feedback of sea ice counters and reverses the equatorward trend in cooler climates so that the LGM winds were more likely to have also been shifted slightly poleward.

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“…Four major factors contribute to these changes. The lower greenhouse gas concentration and the presence of the ice sheets decrease air temperature and water vapor content, 1 3 2010), hemispheric (Li and Battisti 2008;Laine et al 2009;Rojas et al 2009;Chavaillaz et al 2013;Rojas 2013) and general climatologic features (Braconnot et al 2007a, b;Otto-Bliesner et al 2009;Wang et al (2013b)) responding to the LGM conditions using the PMIP datasets. However, little has been done concerning the changes of the monsoon precipitation during the LGM, especially in the global perspectives.…”

Section: Introductionmentioning

confidence: 99%

Global monsoon change during the Last Glacial Maximum: a multi-model study

2015

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resulting in a general weakening of the GM precipitation and reduction of GM domain. The reduced hemispheric difference in seasonal variation of insolation may contribute to the weakened GM intensity. The changed land-ocean configuration in the vicinity of the Maritime Continent, along with the presence of the ice sheets and lower greenhouse gas concentration, result in strengthened land-ocean and North-South hemispheric thermal contrasts, leading to the unique strengthened Australian monsoon. Although some of the results are consistent with the proxy data, uncertainties remain in different models. More comparison is needed between proxy data and model experiments to better understand the changes of the GM during the LGM.

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Sensitivity of Southern Hemisphere circulation to LGM and 4 × CO2 climates

Cited by 47 publications

References 32 publications

Climate history of the Southern Hemisphere Westerlies belt during the last glacial–interglacial transition revealed from lake water oxygen isotope reconstruction of Laguna Potrok Aike (52° S, Argentina)

Climate history of the Southern Hemisphere Westerlies belt during the last glacial–interglacial transition revealed from lake water oxygen isotope reconstruction of Laguna Potrok Aike (52° S, Argentina)

Sea ice led to poleward-shifted winds at the Last Glacial Maximum: the influence of state dependency on CMIP5 and PMIP3 models

Global monsoon change during the Last Glacial Maximum: a multi-model study

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