Sahel megadroughts triggered by glacial slowdowns of Atlantic meridional overturning

Mulitza, Stefan; Prange, Matthias; Stuut, Jan‐Berend; Zabel, Matthias; Dobeneck, Tilo von; Itambi, Achakie C; Nizou, Jean; Schulz, Michael; Wefer, Gerold

doi:10.1029/2008pa001637

Cited by 243 publications

(283 citation statements)

References 73 publications

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“…Although it is probably not a driver of abrupt climate change, the tropical climate may react very sensitively to changes in the AMOC and act as an amplifier (Chiang, 2009). The climatic shifts around the tropical North Atlantic Ocean are associated with large changes in the vegetation distribution, which is likely the result of a southward shift of the tropical rainbelt, as indicated by records from the Cariaco Basin (Hughen et al, 2004;Gonzalez et al, 2008), Northeast Brazil (Behling et al, 2000;Ledru et al, 2006;Dupont et al, 2010), and North West Africa (Mulitza et al, 2008;Hessler et al, 2010). These data emphasize the importance of the tropics and the changes in tropical vegetation during periods of abrupt climate change.…”

Section: Handiani Et Al: Tropical Climate and Vegetation Changes mentioning

confidence: 77%

“…The position of the ITCZ over the tropical Atlantic Ocean is, in turn, linked to North Atlantic sea surface temperatures (SSTs) over the last glacial period, as suggested by several proxy studies (e.g. Peterson et al, 2000;Mulitza et al, 2008). During HE1, the northernmost position of the ITCZ likely shifted southward leading to a drier climate in West Africa and northern South America (e.g.…”

Section: Handiani Et Al: Tropical Climate and Vegetation Changes mentioning

confidence: 99%

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Tropical climate and vegetation changes during Heinrich Event 1: a model-data comparison

2012

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Abstract. Abrupt climate changes from 18 to 15 thousand years before present (kyr BP) associated with Heinrich Event 1 (HE1) had a strong impact on vegetation patterns not only at high latitudes of the Northern Hemisphere, but also in the tropical regions around the Atlantic Ocean. To gain a better understanding of the linkage between high and low latitudes, we used the University of Victoria (UVic) Earth System-Climate Model (ESCM) with dynamical vegetation and land surface components to simulate four scenarios of climate-vegetation interaction: the pre-industrial era, the Last Glacial Maximum (LGM), and a Heinrich-like event with two different climate backgrounds (interglacial and glacial). We calculated mega-biomes from the plantfunctional types (PFTs) generated by the model to allow for a direct comparison between model results and palynological vegetation reconstructions.Our calculated mega-biomes for the pre-industrial period and the LGM corresponded well with biome reconstructions of the modern and LGM time slices, respectively, except that our pre-industrial simulation predicted the dominance of grassland in southern Europe and our LGM simulation resulted in more forest cover in tropical and sub-tropical South America.The HE1-like simulation with a glacial climate background produced sea-surface temperature patterns and enhanced inter-hemispheric thermal gradients in accordance with the "bipolar seesaw" hypothesis. We found that the cooling of the Northern Hemisphere caused a southward shift of those PFTs that are indicative of an increased desertification and a retreat of broadleaf forests in West Africa and northern South America. The mega-biomes from our HE1 simulation agreed well with paleovegetation data from tropical Africa and northern South America. Thus, according to our model-data comparison, the reconstructed vegetation changes for the tropical regions around the Atlantic Ocean were physically consistent with the remote effects of a Heinrich event under a glacial climate background.

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Section: Handiani Et Al: Tropical Climate and Vegetation Changes mentioning

confidence: 77%

Section: Handiani Et Al: Tropical Climate and Vegetation Changes mentioning

confidence: 99%

Tropical climate and vegetation changes during Heinrich Event 1: a model-data comparison

2012

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“…Most of the GCMs in this model inter-comparison (CCSM3, KCM and MPI-UW) simulate a MWT in the Indian and African monsoon regions which is delayed with respect to the insolation forcing. This can be explained by strong feedbacks between the insolation, land evapotranspiration and cloudiness as described by Mulitza et al (2008). In the MPI-UW simulation this negative feedback related to clouds and precipitation is partly compensated by the positive vegetation-albedo feedback in these regions as savanna is partly replaced by tropical and temperate forests (not shown).…”

Section: The Monsoon and The Simulated Lig Temperature Evolutionmentioning

confidence: 99%

Last interglacial temperature evolution – a model inter-comparison

Bakker¹,

et al. 2013

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Abstract. There is a growing number of proxy-based reconstructions detailing the climatic changes that occurred during the last interglacial period (LIG). This period is of special interest, because large parts of the globe were characterized by a warmer-than-present-day climate, making this period an interesting test bed for climate models in light of projected global warming. However, mainly because synchronizing the different palaeoclimatic records is difficult, there is no consensus on a global picture of LIG temperature changes. Here we present the first model inter-comparison of transient simulations covering the LIG period. By comparing the different simulations, we aim at investigating the common signal in the LIG temperature evolution, investigating the main driving forces behind it and at listing the climate feedbacks which cause the most apparent inter-model differences. The model inter-comparison shows a robust Northern Hemisphere July temperature evolution characterized by a maximum between 130–125 ka BP with temperatures 0.3 to 5.3 K above present day. A Southern Hemisphere July temperature maximum, −1.3 to 2.5 K at around 128 ka BP, is only found when changes in the greenhouse gas concentrations are included. The robustness of simulated January temperatures is large in the Southern Hemisphere and the mid-latitudes of the Northern Hemisphere. For these regions maximum January temperature anomalies of respectively −1 to 1.2 K and −0.8 to 2.1 K are simulated for the period after 121 ka BP. In both hemispheres these temperature maxima are in line with the maximum in local summer insolation. In a number of specific regions, a common temperature evolution is not found amongst the models. We show that this is related to feedbacks within the climate system which largely determine the simulated LIG temperature evolution in these regions. Firstly, in the Arctic region, changes in the summer sea-ice cover control the evolution of LIG winter temperatures. Secondly, for the Atlantic region, the Southern Ocean and the North Pacific, possible changes in the characteristics of the Atlantic meridional overturning circulation are crucial. Thirdly, the presence of remnant continental ice from the preceding glacial has shown to be important when determining the timing of maximum LIG warmth in the Northern Hemisphere. Finally, the results reveal that changes in the monsoon regime exert a strong control on the evolution of LIG temperatures over parts of Africa and India. By listing these inter-model differences, we provide a starting point for future proxy-data studies and the sensitivity experiments needed to constrain the climate simulations and to further enhance our understanding of the temperature evolution of the LIG period.

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“…While millennial-scale hydroclimatic variations in northwest Africa are commonly linked to atmospheric processes involving latitudinal migrations of the intertropical convergence zone (ITCZ) related to North Atlantic climate anomalies (Dahl et al, 2005;Stouffer et al, 2006;Tjallingii et al, 2008;Mulitza et al, 2008;Itambi et al, 2009, Penaud et al, 2010Bouimetarhan et al, 2012;Kageyama et al, 2013), the mechanisms responsible for tropical southeastern African climate fluctuations remain a matter of debate. While it has been suggested that Indian Ocean sea surface temperatures (SST) influence eastern African rainfall variability on longer timescales (Tierney et al, 2008Tierney and deMenocal, 2013;Stager et al, 2011), other studies suggest that eastern African rainfall variations were atmospherically linked to North Atlantic climate fluctuations through a southward shift of the ITCZ (Johnson et al, 2002;Broccoli et al, 2006;Brown et al, 2007;Castañeda et al, 2007;Schefuß et al, 2011;Chiang and Friedman, 2012;.…”

Section: Introductionmentioning

confidence: 99%

Northern Hemisphere control of deglacial vegetation changes in the Rufiji uplands (Tanzania)

et al. 2015

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Abstract. In tropical eastern Africa, vegetation distribution is largely controlled by regional hydrology, which has varied over the past 20 000 years. Therefore, accurate reconstructions of past vegetation and hydrological changes are crucial for a better understanding of climate variability in the tropical southeastern African region. We present high-resolution pollen records from a marine sediment core recovered offshore of the Rufiji River delta. Our data document significant shifts in pollen assemblages during the last deglaciation, identifying, through changes in both upland and lowland vegetation, specific responses of plant communities to atmospheric (precipitation) and coastal (coastal dynamics and sea-level changes) alterations. Specifically, arid conditions reflected by a maximum pollen representation of dry and open vegetation occurred during the Northern Hemisphere cold Heinrich event 1 (H1), suggesting that the expansion of drier upland vegetation was synchronous with cold Northern Hemisphere conditions. This arid period is followed by an interval in which forest and humid woodlands expanded, indicating a hydrologic shift towards more humid conditions. Droughts during H1 and the shift to humid conditions around 14.8 kyr BP in the uplands are consistent with latitudinal shifts of the intertropical convergence zone (ITCZ) driven by high-latitude Northern Hemisphere climatic fluctuations. Additionally, our results show that the lowland vegetation, consisting of well-developed salt marshes and mangroves in a successional pattern typical for vegetation occurring in intertidal habitats, has responded mainly to local coastal dynamics related to marine inundation frequencies and soil salinity in the Rufiji Delta as well as to the local moisture availability. Lowland vegetation shows a substantial expansion of mangrove trees after ∼ 14.8 kyr BP, suggesting an increased moisture availability and river runoff in the coastal area. The results of this study highlight the decoupled climatic and environmental processes to which the vegetation in the uplands and the Rufiji Delta has responded during the last deglaciation.

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Sahel megadroughts triggered by glacial slowdowns of Atlantic meridional overturning

Cited by 243 publications

References 73 publications

Tropical climate and vegetation changes during Heinrich Event 1: a model-data comparison

Tropical climate and vegetation changes during Heinrich Event 1: a model-data comparison

Last interglacial temperature evolution – a model inter-comparison

Northern Hemisphere control of deglacial vegetation changes in the Rufiji uplands (Tanzania)

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