Indo-Pacific Walker circulation drove Pleistocene African aridification

The Indian Ocean provides a source of salt for North Atlantic deep-water convection sites, via the Agulhas Leakage (AL), and may thus drive changes in the ocean's overturning circulation 6,7,8 . However, little is known about salt content variability of Indian Ocean and AL waters during past glacial cycles, and how this may influence circulation. Here we show that the glacial Indian Ocean surface salt budget was notably different from the modern, responding dynamically to changes in sea level.Indian Ocean surface salinity increases during glacial intensification peaking in glacial maxima. We find that this is due to rapid land exposure in the Indonesian archipelago induced by glacial sea level lowering, and we suggest a mechanistic link via reduced input of relatively fresh Indonesian throughflow (ITF) waters into the Indian Ocean.Using new climate model results, we show that the release of this glacial Indian Ocean salinity via the Agulhas Leakage during deglaciation can directly impact the Atlantic meridional overturning circulation and global climate.

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“…The age model for U1476 was taken from ref. 51 who aligned U1476 δ 18 Obenthic to the δ 18 Obenthic probability stack 52 .…”

Section: Age Modelmentioning

confidence: 99%

Indian Ocean salinity build-up primes deglacial ocean circulation recovery

Nuber

Rae

Zhang

et al. 2023

Nature

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“…Furthermore, if the ∼3 Ma changepoints in eastern Africa and western Australia were the result of permanent ITF restriction, IO Walker Circulation should have been permanently affected, but several measures of SST and hydroclimate rebound within ∼500 kyr (Figure S8 in Supporting Information ). Finally, late Pliocene

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SSTs at ODP Site 722 exhibit no trend (Herbert et al., 2015), suggesting that changes in the Leeuwin Current do not necessarily propagate across the entire IO (van der Lubbe et al., 2021).…”

Section: Discussionmentioning

confidence: 99%

High‐Latitude, Indian Ocean, and Orbital Influences on Eastern African Hydroclimate Across the Plio‐Pleistocene Boundary

Mitsunaga,

Lupien,

Ouertani

et al. 2023

Paleoceanog and Paleoclimatol

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Terrestrial‐marine dust fluxes, pedogenic carbonate δ13C values, and various paleovegetation proxies suggest that Africa experienced gradual cooling and drying across the Pliocene‐Pleistocene (Plio‐Pleistocene) boundary (2.58 million years ago [Ma]). However, the timing, magnitude, resolution, and relative influences of orbitally‐driven changes in high latitude glaciations and low latitude insolation differ by region and proxy. To disentangle these forcings and investigate equatorial eastern African climate across the Plio‐Pleistocene boundary, we generated a high‐resolution (∼3,000‐year) data set of compound‐specific n‐alkane leaf wax δ2H values—a robust proxy for atmospheric circulation and precipitation amount—from the HSPDP‐BTB13‐1A core, which spans a ∼3.3–2.6 Ma sequence in the Baringo‐Tugen Hills‐Barsemoi Basin of central Kenya. In combination with the physical sedimentology, our data indicate that precipitation varied strongly with orbital obliquity, not precession, during the late Pliocene, perhaps imparted by variations in the cross‐equatorial insolation gradient. We also observe a marked shift toward wetter conditions beginning ∼3 Ma that corresponds with global cooling, drying in western Australia, and a steepening of the west‐east zonal Indian Ocean (IO) sea surface temperature (SST) gradient. We propose that northward migration of the Subtropical Front reduced Agulhas current leakage, warming the western IO and causing changes in the IO zonal SST gradient at 3 Ma, a process that has been observed in the latest Pleistocene‐Holocene but not over longer timescales. Thus, the late Cenozoic moisture history of eastern Africa is driven by a complex mixture of low‐latitude insolation, the IO SST gradient, and teleconnections to distal high‐latitude cooling.

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“…These types of climatic changes were prevalent throughout the volatile climate in the Pleistocene, in which tropical Africa alternated between wet pluvials and dry interpluvials 30,31 . Accordingly, the eastern edge of the Rift Valley is associated with a rain shadow so prominent that it is known in biogeography as 'Kingdon's Line' 32,33 . During dry periods of the Pleistocene, very little free surface water would have been available along this rain shadow 34 , which could therefore have been the immediate agent of vicariance between the two waterbuck lineages.…”

Section: Discussionmentioning

confidence: 99%

Persistent gene flow suggests an absence of reproductive isolation in an African antelope speciation model

Wang

Pedersen

Athanasiadis

et al. 2022

Preprint

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African antelope diversity is a globally unique vestige of a much richer world-wide Pleistocene megafauna. Despite this, the evolutionary processes leading to the prolific radiation of African antelopes are not well understood. Here, we sequenced 145 whole genomes from both subspecies of the waterbuck, an African antelope believed to be in the process of speciation. We investigated genetic structure and population divergence and found evidence of a mid-Pleistocene separation on either side of the eastern Great Rift Valley, consistent with vicariance caused by a rain shadow along the so-called 'Kingdon's Line'. However, we also found pervasive evidence of not only isolated and recent, but also widespread historical gene flow across the Rift Valley barrier. By inferring the genome-wide landscape of variation among subspecies, we found 14 genomic regions of elevated differentiation, including a locus that may be related to each subspecies' distinctive coat pigmentation pattern. We investigated these regions as candidate speciation islands. However, we observed no significant reduction in gene flow in these regions, nor any indications of selection against hybrids. Altogether, these results suggest a pattern whereby climatically driven vicariance is the most important process driving the African antelope radiation, and suggest that reproductive isolation may not set in until very late in the divergence process.

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Indo-Pacific Walker circulation drove Pleistocene African aridification

Cited by 21 publications

References 72 publications

Indian Ocean salinity build-up primes deglacial ocean circulation recovery

Indian Ocean salinity build-up primes deglacial ocean circulation recovery

High‐Latitude, Indian Ocean, and Orbital Influences on Eastern African Hydroclimate Across the Plio‐Pleistocene Boundary

Persistent gene flow suggests an absence of reproductive isolation in an African antelope speciation model

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