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Glacier advances in the southern mid-latitudes during the last glacial cycle ( ca . 110–10 ka) were controlled by changes in temperature and precipitation linked to several important ocean-climate systems. As such, the timing of glacial advance and retreat can yield important insights into the mechanisms of Southern Hemisphere climate change. This is particularly important given that several recent studies have demonstrated significant glacial advances prior to the global Last Glacial Maximum (gLGM) in Patagonia and New Zealand, the cause of which are uncertain. The recent increase in chronological studies in these regions offers the opportunity to compare regional trends in glacial activity. Here, we compile the first consistent 10 Be exposure-dating chronologies for Patagonia and New Zealand to highlight the broad pattern of mid-latitude glacial activity over the last glacial cycle. Our results show that advances or still stands culminated at 26–27 ka, 18–19 ka and 13–14 ka in both Patagonia and New Zealand and were broadly synchronous, but with an offset between regions of up to 900 years that cannot be explained by age calculation or physically plausible erosion differences. Furthermore, there is evidence in both regions for glacial advances culminating from at least 45 ka, during the latter half of Marine Isotope Stage (MIS) 3. Glacial activity prior to the gLGM differed from the large Northern Hemisphere ice sheets, likely due to favourable Southern Hemisphere conditions during late MIS 3: summer insolation reached a minimum, seasonality was reduced, winter duration was increasing, and sea ice had expanded significantly, inducing stratification of the ocean and triggering northward migration of oceanic fronts and the Southern Westerly Winds. Glacial advances in Patagonia and New Zealand during the gLGM were probably primed by underlying orbital parameters. However, the precise timing is likely to have been intrinsically linked to migration of the coupled ocean-atmosphere system, which may account for the small offset between Patagonia and New Zealand due to differences in oceanic frontal migration. During deglaciation, advances or still stands occurred in both regions during the southern Antarctic Cold Reversal ( ca . 14.5–12.9 ka) rather than the northern Younger Dryas ( ca . 12.9–11.7 ka). Our findings suggest that major rearrangements of the Southern Hemisphere climate system occurred at various times during the last glacial cycle, with associated impacts on the position and intensity of the Southern Westerly Winds and oceanic fronts, as well as wind-driven upwelling and degassing of the deep Southern Ocean. Thus, reconstructing the timing of glacial advance/retreat using our compilation is a powerful way to understand the mechanisms of past interhemispheric climate change. [ABSTRACT FROM AUTHOR]

Abstract: As part of a wider study of last glacial and deglacial climates in the Southern Hemisphere continents, we here review terrestrial and near-shore marine records from equatorial and southern Africa between 30,000 and 10,000years ago (30–10ka). This time interval covers the lead-up to the Last Glacial Maximum (LGM; 21±2ka), the LGM proper, and the ensuing deglacial. Records selected for review needed to meet three requirements: continuity or near continuity over the period; a well-established chronology; and at least one but preferably several unambiguous proxy(ies). We aim to show how regional climates of the sub-continent have responded to orbital forcing as opposed to other global glacial-interglacial boundary conditions, and how they are related to high latitude climates, sea and land surface conditions, positions of the Intertropical Convergence Zone (ITCZ) and of the westerly belt. Evidence of past climates derived from many independent proxies is given from west to southwest Africa (moisture from the Atlantic Ocean), then from equatorial East Africa to the southern subtropical summer rainfall domain (moisture mainly from the Indian Ocean). The LGM was cooler than today, and generally drier in the tropics. North of 8–9°S, glacial to Holocene increase in monsoonal precipitation, primarily related to orbitally-induced summer insolation in the northern hemisphere, occurred by steps of increasing amplitude (∼17–16, 14.5, 11.5ka). Major wet–dry spells coincide with abrupt warm–cold events in high northern latitudes and related ITCZ migrations. In the southern tropics, the main post-glacial increase in tropical rainfall generally appears more gradual and in phase with Antarctic warming. Data suggest a restricted northward migration of the ITCZ and concentration of tropical rainfall well south of the Equator during the LGM and the Younger Dryas. Drier glacial conditions prevailed in southeastern Africa, while parts of southwestern Africa point to enhanced humidity during the LGM, suggesting that the winter westerly belt was either stronger than today or displaced further north possibly as a result of more extensive Antarctic sea-ice. Inferred African climatic fluctuations show the competing influences of tropical and high latitude climates of both hemispheres, and suggest changes in both meridional and zonal circulation modes. This review also reveals major geographical and methodological gaps, and a number of unresolved issues providing pointers for future research. [Copyright &y& Elsevier]

Recent paleoclimate reconstructions have challenged the traditional view that Northern Hemisphere insolation and associated feedbacks drove synchronous global climate and ice-sheet volume during the last glacial cycle. Here we focus on the response of the Patagonian Ice Sheet, and demonstrate that its maximum expansion culminated at 28,400 ± 500 years before present (28.4 ± 0.5 ka), more than 5,000 years before the minima in 65°N summer insolation and the formally-defined Last Glacial Maximum (LGM) at 21,000 ± 2,000 years before present. To investigate the potential drivers of this early LGM (eLGM), we simulate the effects of orbital changes using a suite of climate models incorporating prescribed and evolving sea-ice anomalies. Our analyses suggest that Antarctic sea-ice expansion at 28.5 ka altered the location and intensity of the Southern Hemisphere storm track, triggering regional cooling over Patagonia of 5°C that extends across the wider mid-southern latitudes. In contrast, at the LGM, continued sea-ice expansion reduced regional temperature and precipitation further, effectively starving the ice sheet and resulting in reduced glacial expansion. Our findings highlight the dominant role that orbital changes can play in driving Southern Hemisphere glacial climate via the sensitivity of mid-latitude regions to changes in Antarctic sea-ice extent. [ABSTRACT FROM AUTHOR]