Increased aridity in southwestern Africa during the warmest periods of the last interglacial

Abstract

Abstract. Terrestrial and marine climatic tracers from marine core MD96-2098 were used to reconstruct glacialinterglacial climate variability in southwestern Africa between 194 and 24 thousand years before present. The pollen record documented three pronounced expansions of Namakaroo and fine-leaved savanna during the last interglacial (Marine Isotopic Stage 5 -MIS 5). These Nama-karoo and fine-leaved savanna expansions were linked to increased aridity during the three warmest substadials of MIS 5. Enhanced aridity potentially resulted from a combination of reduced Benguela Upwelling, expanded subtropical highpressure cells, and reduced austral-summer precipitation due to a northward shift of the Intertropical Convergence Zone. Decreased austral-winter precipitation was likely linked to a southern displacement of the westerlies. In contrast, during glacial isotopic stages MIS 6, 4 and 3, fynbos expanded at the expense of Nama-karoo and fine-leaved savanna indicating a relative increase in precipitation probably concentrated during the austral winter months. Our record also suggested that warm-cold or cold-warm transitions between isotopic stages and substages were punctuated by short increases in humidity. Increased aridity during MIS 5e, 5c and 5a warm substages coincided with minima in both precessional index and global ice volume. On the other hand, austral-winter precipitation increases were associated with precession maxima at the time of well-developed Northern Hemisphere ice caps.

Impact of precession on the climate, vegetation and fire activity in southern Africa during MIS4

“…Past, 10, 1165-1182, 2014 www has become too dry and grasses decline, leading to smaller amounts of light fuel and a decrease of fire. At the scale of the whole southern Africa, the dominant signal is the regression of grass-fueled fires in response to the precipitation decrease in the summer rainfall area, in qualitative agreement with Daniau et al (2013). The simulations confirm the link between precession and fire activity, inferred from the microcharcoal record.…”

“…By contrast, only few empirical data on past environmental changes from the Southern Hemisphere are available and paleoclimatic records from southern Africa are particularly rare. Data from Partridge et al (1997), Kristen et al (2007), and Daniau et al (2013) suggest an anticorrelation between the southern African monsoon and the northern African monsoon. To our knowledge no modeling study has yet been undertaken to investigate this hypothesis, neither has the link between precipitation, biomass burning and precession in southern Africa, in particular during glacial times, when the presence of Northern Hemisphere ice sheets and lower levels of greenhouse gases might have changed the sensitivity of the monsoons to precession changes.…”

“…In their simulations, forests cover the eastern part of southern Africa if fire disturbance is not taken into account. Daniau et al (2013) have analyzed microcharcoal concentrations in a marine sediment core off southwestern Africa and interpreted this marker as a record of past fire activity. The record, which covers the period from 170 to 30 kyr BP (before present), exhibits a tight correlation between grassfueled fires and the precessional cycle, with maximum fire activity occurring during maxima of the climatic precession index (e sin ω, with e the eccentricity and ω the longitude of the perihelion), when the boreal winter solstice occurs near the perihelion.…”

“…The record, which covers the period from 170 to 30 kyr BP (before present), exhibits a tight correlation between grassfueled fires and the precessional cycle, with maximum fire activity occurring during maxima of the climatic precession index (e sin ω, with e the eccentricity and ω the longitude of the perihelion), when the boreal winter solstice occurs near the perihelion. Daniau et al (2013) hypothesized that the variations in fire activity reflect precipitation changes in the grassy regions of eastern southern Africa, i.e., in the summer rainfall area. The decrease in solar radiation during austral summer associated with a low precession index would weaken the ITCZ convection and bring less rainfall over southern Africa.…”

Shifting Climates, Foods, and Diseases: The Human Microbiome through Evolution

“…Between 190 and 130 thousand years ago (often referred to as MIS 6), severe glaciation affected vast regions across the globe (including the Sahara) and triggered aridification of the African continent, where most human ancestors resided. [2,3] Repeated glaciation events over the next 100 thousand years (MIS 4, 3, 2) drastically altered the earth's climate, isolating human populations from each other for brief periods, then allowing reintroduction, and, in many cases, various amounts of admixture. Fluctuations in mean annual temperatures and rainfall, seasonality, and day length likely modified floral and faunal communities as well as local pathogen reservoirs.…”