Insolation-driven changes in atmospheric circulation over the past 116,000 years in subtropical Brazil

Abstract

During the last glacial period, large millennial-scale temperature oscillations--the 'Dansgaard/Oeschger' cycles--were the primary climate signal in Northern Hemisphere climate archives from the high latitudes to the tropics. But whether the influence of these abrupt climate changes extended to the tropical and subtropical Southern Hemisphere, where changes in insolation are thought to be the main direct forcing of climate, has remained unclear. Here we present a high-resolution oxygen isotope record of a U/Th-dated stalagmite from subtropical southern Brazil, covering the past 116,200 years. The oxygen isotope signature varies with shifts in the source region and amount of rainfall in the area, and hence records changes in atmospheric circulation and convective intensity over South America. We find that these variations in rainfall source and amount are primarily driven by summer solar radiation, which is controlled by the Earth's precessional cycle. The Dansgaard/Oeschger cycles can be detected in our record and therefore we confirm that they also affect the tropical hydrological cycle, but that in southern subtropical Brazil, millennial-scale climate changes are not as dominant as they are in the Northern Hemisphere.

Mechanisms rectifying the annual mean response of tropical Atlantic rainfall to precessional forcing

“…Reconstructions of continental precipitation over Africa and South America confirm our finding that continental precipitation follows the warmer summer hemisphere (Gasse 2000;DeMenocal et al 2000;Fritz et al 2004;Wang et al 2004Wang et al , 2007Cruz et al 2005;Weldeab et al 2007;Tjallingii et al 2008). A sediment record from Cariaco Basin (Deplazes et al 2013) is interpreted as reflecting shifts in ITCZ, but these occur mostly on millennial timescales.…”

“…This enhancement is also found in records from northern Africa and South America and shown in Fig. 1a by the anti-phasing of the north African humidity index of Tjallingii et al (2008) and Gulf of Guinea sea surface salinity reconstruction of Weldeab et al (2007) with the South American cave records of Wang et al (2004Wang et al ( , 2007, Cruz et al (2005) and Bolivian salt flat sediment core of Fritz et al (2004). The much-studied African Humid Period, during which grass and low shrub vegetation expanded northward into the Sahel-Sahara region, coincides with a maximum in NH summer insolation (Gasse 2000;DeMenocal et al 2000).…”

“…Section 3.2 focuses on the Atlantic ITCZ and discusses how the continental response to precessional forcing rectifies the response of the Atlantic ITCZ. Our results are compared against paleoclimate reconstructions from Cariaco Basin (Deplazes et al 2013), Brazil (Wang et al 2004(Wang et al , 2007Cruz et al 2005), and the tropical Atlantic (Tjallingii et al 2008;Arbuszewski et al 2013) in Sect. 4, where we will also briefly touch on the role of eccentricity.…”

“…1 a Paleorecords of tropical hydroclimate against the precessional cycle (e sin(ω), see Sect. 2; grey); from top to bottom: composite of speleothem δ 18 O from Chinese caves (25°-32°N): Dongge (Dykoski et al 2005), Hulu (Wang et al 2004), Sanbao (Wang et al 2008); North African humidity index 20.8°N (Tjallingii et al 2008); sediment total reflectance in Cariaco Basin 10.7°N (Deplazes et al 2013); salinity reconstruction from Ba/Ca in Eastern Atlantic (2.5°N) (Weldeab et al 2007); ln(Ti/Ca) from West Pacific Warm Pool (2.5°S) (Tachikawa et al 2014); sediment gamma radiation from Bolivia (20.3°S) (Fritz et al 2004); speleothem δ 18 O from Botuvera cave (Brazil; 27.2°S) (Wang et al 2004(Wang et al , 2007Cruz et al 2005). Records are ordered from north to south, with inferred precipitation increasing along the y-axis; A 1000-year running mean was applied to each record.…”

Paleohydrological changes during the last deglaciation in Northern Brazil

“…Recent studies indicate that past variations in the water vapour cycle over tropical South America are closely related to oceanic and atmospheric circulation patterns at global scale (Peterson et al, 2000;Wang et al, 2004;Cruz et al, 2005). Nonetheless, there is not yet a clear consensus on the role of the tropics in driving global climate variability and on the possible extratropical feedbacks (Stoecker et al, 2003).…”