Timing of the Younger Dryas event in East Africa from lake-level changes

Roberts, N.; Taieb, Maurice; Barker, Philip A.; Damnati, Brahim; Icole, Michel; Williamson, David

doi:10.1038/366146a0

Cited by 212 publications

(72 citation statements)

References 18 publications

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“…Surface water information is vital for water resources, climate, and agriculture studies [1]. Surface water change is critically important for studies on the land use/cover (LULC), climate, and other forms of environmental change in the world.…”

Section: Introductionmentioning

confidence: 99%

Target Detection Method for Water Mapping Using Landsat 8 OLI/TIRS Imagery

Geng

Sun

et al. 2015

Water

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Extracting surface water distribution with satellite imagery has been an important subject in remote sensing. Spectral indices of water only use information from a limited number of bands, thus they may have poor performance from pixels contaminated by ice/snow, clouds, etc. The detection algorithms using information from all spectral bands, such as constrained energy minimization (CEM), could avoid this problem to some extent. However, these are mostly designed for hyperspectral imagery, and may fail when applied to multispectral data. It has been proved that adding linearly irrelevant data to original data could improve the performance of CEM. In this study, two kinds of linearly irrelevant data are added for water extraction: the spectral indices and the spectral similarity metric data. CEM is designed for targets with low-probability distribution in an image, but water bodies do not always satisfy this condition. We thereby impose a sensible coefficient for each pixel to form the weighted autocorrelation matrix. In this study, the weight is based on the orthogonal subspace projection, so this new method is named Orthogonal subspace projection Weighted CEM (OWCEM). The newly launched Landsat 8 images over two lakes, the Hala Lake in China with ice/snow distributed in the north, and the Huron Lake in OPEN ACCESSWater 2015, 7 795North America, a lake with a very large surface area, are selected to test the accuracy and robustness of our algorithm. The Kappa coefficient and the receiver operating characteristic (ROC) curve are calculated as an accuracy evaluation standard. For both lakes, our method can greatly suppress the background (including ice/snow and clouds) and extract the complete water surface with a high accuracy (Kappa coefficient > 0.96).

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Section: Introductionmentioning

confidence: 99%

Target Detection Method for Water Mapping Using Landsat 8 OLI/TIRS Imagery

Geng

Sun

et al. 2015

Water

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“…The main period of transition may have occupied as little as 50 years [Alley et al, 1993;Björck et al, 1996;Severinghaus et al, 1998;Alley, 2000;Lotter et al, 2000]. It is now becoming clear that the YD event also had a significant impact on tropical Africa [e.g., Roberts et al, 1993;Beuning et al, 1998;Stager et al, 2002;Barker et al, 2004;Johnson et al, 2004;Schefuss et al, 2005;Weldeab et al, 2005;Garcin et al, 2006]. Here, using high-resolution (typically <100-to 300-year sample spacing) paleoenvironmental data from cores from African lakes, we show that within the limits of available dating methods, there was an apparently contemporaneous, abrupt change in the climate of tropical Africa at the end of the YD, a change that seems to have involved reorganization of monsoonal circulation across the continent and adjacent oceans.…”

Section: Introductionmentioning

confidence: 99%

An abrupt change in the African monsoon at the end of the Younger Dryas

Talbot

Filippi

Jensen

et al. 2007

Geochem Geophys Geosyst

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[1] High-resolution studies of variations in the elemental and stable carbon-and nitrogen-isotope composition of organic matter in cores from Lakes Malawi, Tanganyika, and Bosumtwi (tropical Africa) indicate an abrupt change in the wind-driven circulation of these lakes that, within the limits of available chronologies, was contemporaneous with the end of the Younger Dryas in the northern hemisphere. The change was also coincident with shifts in surface winds recorded in cores from off the west and northeast coasts of Africa. A range of other proxies indicate that these changes in wind regime were accompanied by a marked increase in precipitation in the northern tropics. Africa south of 5°-10°S, on the other hand, initially suffered drought conditions. Together, the evidence suggests an abrupt northward translation of the African monsoon system at circa 11.5 ± 0.25 ka B.P. The data assembled here contribute to a growing body of work showing that the Younger Dryas was a major climatic excursion in tropical Africa. Furthermore, they add substance to recent suggestions that climatic events in the southern hemisphere may have played a significant role in the abrupt demise of the Younger Dryas.

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“…This taxon is followed by another sun-loving species, Ilex mitis, and finally by Olea capensis, Podocarpus and Schefflera. This phase culminates in a very short period between 13,800 and 13,700 cal yrs BP, corresponding to the beginning of the warm Alleröd in high latitudes (Roberts et al, 1993(Roberts et al, , 2010. This increase of forest cover at Bambili is coeval with the start of the African Humid Period dated to 15,500 cal yrs BP by DeMenocal et al (2000).…”

Section: Chronology Of Colonization Forestmentioning

confidence: 98%

“…The permanence of steppe elements reflects the importance of continued northeasterly circulation. This phase corresponds to the YD (Younger Dryas) in the high latitudes (Roberts et al, 1993). As mentioned earlier, the YD is generally dry in tropical North Africa, reflected in the general lowering of lake levels (Gasse, 2000).…”

Section: Chronology Of Colonization Forestmentioning

confidence: 99%

Vegetation Evolution in the Mountains of Cameroon During the Last 20 000 Years: Pollen Analysis of Lake Bambili Sediments

Assi-Kaudjhis¹

2012

Forest Ecosystems - More Than Just Trees

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Timing of the Younger Dryas event in East Africa from lake-level changes

Cited by 212 publications

References 18 publications

Target Detection Method for Water Mapping Using Landsat 8 OLI/TIRS Imagery

Target Detection Method for Water Mapping Using Landsat 8 OLI/TIRS Imagery

An abrupt change in the African monsoon at the end of the Younger Dryas

Vegetation Evolution in the Mountains of Cameroon During the Last 20 000 Years: Pollen Analysis of Lake Bambili Sediments

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