Global lake-level variations from 18,000 to 0 years ago: A palaeoclimate analysis

Street-Perrott, F. Alayne; Marchand, Delphine; Roberts, N.; Harrison, S. P.

doi:10.2172/5609291

Cited by 77 publications

(17 citation statements)

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“…The greater presence of surface water in the form of lakes and wetlands during the AHP has been documented by numerous studies (Holmes & Hoelzmann, 2017; Lézine et al, 2011; Pachur & Kröpelin, 1987; Street‐Perrott et al, 1989). Modeling efforts have sought to understand the influence of these additional local sources of moisture on the climate (Coe & Bonan, 1997; Carrington et al, 2001; Contoux et al, 2013; Krinner et al, 2012).…”

Section: Methodsmentioning

confidence: 89%

“…Several lines of evidence such as paleo‐lake‐level reconstructions (Holmes & Hoelzmann, 2017; Lézine et al, 2011; Street‐Perrott et al, 1989), vegetation reconstructions (Hoelzmann et al, 1998; Harrison & Bartlein, 2012; Prentice et al, 2000), eolian (deMenocal et al, 2000) and leaf wax (Tierney et al, 2017) deposits in sedimentary cores in the Eastern Atlantic, observations of cave paintings depicting a lush landscape (Almásy, 1934; Barth, 1857; di Lernia, 2017), and other archaeological findings supporting human habitation (Cremaschi & Di Lernia, 1999; Dunne et al, 2012; Gabriel, 1987; Hoelzmann et al, 2001; Manning & Timpson, 2014; Kröpelin, 2004; Sereno et al, 2008) have led to compelling and undisputed understanding that northern Africa was considerably wetter and greener than today during an interval stretching from the end of the Younger‐Dryas at 11,500 to roughly 5,000 years before present (BP). This interval, which has come to be referred to as the African Humid Period (AHP) or the Green Sahara Period, was just the most recent in several precessionally forced wet‐dry cycles (Larrasoaña et al, 2013) through the Sahara desert's long, at least 2.5 Myr, but contested age (Kröpelin, 2006; Schuster et al, 2006; Zhang et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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African Humid Period Precipitation Sustained by Robust Vegetation, Soil, and Lake Feedbacks

Chandan

Peltier

2020

Geophysical Research Letters

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The African Humid Period (∼11,000-5,000 years before present) was the most recent of several precessionally paced wet intervals during which an increase in the Northern Hemisphere summer incoming solar radiation intensifies the West African Monsoon leading to dramatic changes over northern Africa. However, insolation anomaly alone is not sufficient and feedbacks are essential for further amplification of the monsoon. The most significant feedbacks derive from the land surface, arising from changes to vegetation, soil properties, and distribution of surface water. We show that in contrast to previous studies that have explored the individual impacts of these feedbacks, a modern climate model yields a much greater increase in precipitation in response to their collective effect. Agreement with proxies is improved while the desert-steppe transition is pushed further northward than in any previous study. In the West African Sahel, intensities of summer daily mean and extreme precipitation increase by 150% and 90%, respectively. Plain Language Summary From approximately 11,000 to 5,000 years before present, the summer monsoon over northern Africa was considerably stronger than what it is today and as such this period has come to be called the African Humid Period. As a result of this, lakes, wetlands, and rivers sprung up in the now arid regions of northern Africa and made it possible for vegetation to migrate northward which "greened the Sahara." It is widely understood that the greater amount of summer solar radiation impinging on this region, arising from a modest variation in the Earth's orbital configuration at that time, kick-started this intensification. However, while this may have triggered the strengthening of the monsoon, it was not by itself sufficient to intensify it to the degree suggested by proxies that register the strength of palaeomonsoons. The interaction between the atmosphere and the greener and wetter land surface could have further invigorated the monsoon, but based on the results from modeling experiments performed thus far, it has been thought that even this additional interaction is not sufficient. Here, we show that land-atmosphere interaction does however have the potential to strengthen the monsoon sufficiently to obtain agreement with proxy estimates.

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Section: Methodsmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

African Humid Period Precipitation Sustained by Robust Vegetation, Soil, and Lake Feedbacks

Chandan

Peltier

2020

Geophysical Research Letters

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“…At the centennial timescale, the lake level fluctuations could also be a result of the solar activity and atmospheric radiocarbon ( 14 C) production (cf. Street-Perrott et al, 1989;Jouzel et al, 1993;Olago, 1995). The latter phenomena are negatively linked because solar activity (as measured by reduced sunspot numbers) increases cosmic ray bombardment in the upper atmosphere, which enhances 14 C production.…”

Section: Synthesismentioning

confidence: 99%

Late Quaternary paleoenvironmental changes in East Africa: a review of multiproxy evidence from palynology, lake sediments, and associated records

Kiage

Liu

2006

Progress in Physical Geography: Earth and Environment

112

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This paper presents an overview of paleoenvironmental changes in East Africa during the late Quaternary based on evidence from pollen, diatoms, microscopic charcoal, and lake level records and associated proxies. The paleoenvironmental records derived from different proxies complement each other to provide a more accurate and complete assessment of the paleoenvironmental changes in East Africa. The records show that the period prior to c. 42,000 14C yr BP was characterized by warm climatic conditions similar to the present. This was followed by a change to cold dry conditions from 42,000 to 30,000 14C yr BP, and cold and moist conditions from 30,000 to 21,000 14C yr BP. Temperatures during the latter period leading to the Last Glacial Maximum (LGM) were probably 2 to 4.1°C lower than the present. Between c. 21,000 and 12,500 14C yr BP East Africa's environment was generally cool, punctuated by two significant episodes of prolonged desiccation. Warm and moist conditions punctuated by rapid climatic changes prevailed in the region during the deglacial and middle Holocene period. Ice core records document two significant and abrupt drought events in the region, one at 8300 14C yr BP and the other at 5200 14C yr BP. The onset of a longer and more extensive desiccation period commencing 4000 14C yr BP was registered in nearly all sites. The climate of East Africa was generally drier than present during the Medieval Warm Period (MWP) while fairly wet conditions prevailed during the Little Ice Age (LIA) interrupted by three episodes of aridity, more severe than those of more recent times. Whereas this review advances our understanding of climate and vegetational changes in East Africa beyond the Last Glacial Maximum, it also highlights limitations of the paradigms that explain the forcing mechanisms behind the changes. However, unequivocal interpretation of the multiproxy data from East Africa with respect to paleoenvironmental changes becomes extremely complex and challenging especially when the anthropogenic input is considered.

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“…Subsequent geological and archaeological investigations, coupled with numerical modeling experiments (Claussen et al, this volume), have established an understanding of the nature and timing of climatic changes associated with the AHP, as well as the response of ecosystems and human populations to those changes (Drake et al, 2011;Manning and Timpson, 2014). Geological investigations have included studies of lake and wetland sediments (Street-Perrott et al, 1989;Gasse, 2000), dune fields (Sarnthein, 1978) and marine sediments from the oceans adjacent to the African continent (McGee and deMenocal, this volume). The last of these sources provides information about changing vegetation (Lézine et al, 2005;Hooghiemstra et al, 2011) and land surface conditions (deMenocal et al, 2000a) on the African continent and can also provide information about potential links between ocean circulation and African climate (deMenocal et al, 2000b;liu et al, 2007;Chang et al, 2008) and so is important for our understanding of the causes of change.…”

Section: Introductionmentioning

confidence: 99%

The Late Pleistocene-Holocene African Humid Period as Evident in Lakes

Holmes¹,

Hoelzmann²

2017

Oxford Research Encyclopedia of Climate Science

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From the end of the last glacial stage until the mid-Holocene, large areas of arid and semi-arid North Africa were much wetter than present, during the interval that is known as the African Humid Period (AHP). During this time, large areas were characterized by a marked increase in precipitation, an expansion of lakes, river systems, and wetlands, and the spread of grassland, shrub land, and woodland vegetation into areas that are currently much drier. Simulations with climate models indicate that the AHP was the result of orbitally forced increase in northern hemisphere summer insolation, which caused the intensification and northward expansion of the boreal summer monsoon. However, feedbacks from ocean circulation, land-surface cover, and greenhouse gases were probably also important.Lake basins and their sediment archives have provided important information about climate during the AHP, including the overall increases in precipitation and in rates, trajectories, and spatial variations in change at the beginning and the end of the interval. The general pattern is one of apparently synchronous onset of the AHP at the start of the Bølling-Allerød interstadial around 14,700 years ago, although wet conditions were interrupted by aridity during the Younger Dryas stadial. Wetter conditions returned at the start of the Holocene around 11,700 years ago covering much of North Africa and extended into parts of the southern hemisphere, including southeastern Equatorial Africa. During this time, the expansion of lakes and of grassland or shrub land vegetation over the area that is now the Sahara desert, was especially marked. Increasing aridity through the mid-Holocene, associated with a reduction in northern hemisphere summer insolation, brought about the end of the AHP by around 5000–4000 years before present. The degree to which this end was abrupt or gradual and geographically synchronous or time transgressive, remains open to debate. Taken as a whole, the lake sediment records do not support rapid and synchronous declines in precipitation and vegetation across the whole of North Africa, as some model experiments and other palaeoclimate archives have suggested. Lake sediments from basins that desiccated during the mid-Holocene may have been deflated, thus providing a misleading picture of rapid change. Moreover, different proxies of climate or environment may respond in contrasting ways to the same changes in climate. Despite this, there is evidence of rapid (within a few hundred years) termination to the AHP in some regions, with clear signs of a time-transgressive response both north to south and east to west, pointing to complex controls over the mid-Holocene drying of North Africa.

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Global lake-level variations from 18,000 to 0 years ago: A palaeoclimate analysis

Cited by 77 publications

References 0 publications

African Humid Period Precipitation Sustained by Robust Vegetation, Soil, and Lake Feedbacks

African Humid Period Precipitation Sustained by Robust Vegetation, Soil, and Lake Feedbacks

Late Quaternary paleoenvironmental changes in East Africa: a review of multiproxy evidence from palynology, lake sediments, and associated records

The Late Pleistocene-Holocene African Humid Period as Evident in Lakes

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