1,721,135 research outputs found
Trace element and stable isotope data analyzed in core topes and a core sediment from the eastern equaterial Atlantic
No full textThe foraminiferal trace element and carbon and oxygen isotope were analyzed in core tops and core sediment from the eastern equatorial Atlantic. The down core analyses were carried out to reconstruct climatic conditions during Eemian
Spatio-temporal evolution of the West African monsoon during the last deglaciation
No full textOn the basis of a multi-proxy data set from the Gulf of Guinea (eastern equatorial Atlantic) we reconstruct the spatio-temporal evolution of the West African monsoon (WAM) and present evidence for a decoupling between latitudinal shifts of the rain belt and WAM intensification. The onset of deglacial monsoon invigoration at ∼16,600 years before present lagged northward migration of a weak rainfall zone by ∼2800 years. Conversely, during the Younger Dryas (YD) time interval, WAM precipitation was severely reduced but we find no evidence for a large-scale retreat of the rainfall front. This observation is not in agreement with the hypothesis of a large-scale shift of the intertropical convergence zone south of the tropical WAM region during the YD. Our results can be better reconciled with the newly emerging concept of a strong influence of Tropical Easterly and African Easterly Jets on modern WAM
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Hydroclimate Reconstruction of Semi-Arid Central Asia: Insights from a Kyrgyz Speleothem
Full text linkSemi-arid Central Asia has been identified as a particularly vulnerable region to global climate change. However, model projections for the region have relatively high uncertainty and there is a lack of absolutely dated records to establish the region’s climatic history. In an effort to better understand Central Asia’s hydroclimate response to changes in radiative and freshwater forcings, this study focuses on a Kyrgyz speleothem (Central Asia) that spans late Marine Isotope Stage (MIS) 10 (343–358 kyr before present). Trace element, fluorescence, and calcite fabric analysis are employed to provide insights into orbital- to decadal-scale Central Asian climate history. We find that fluorescent banding is exclusively present in columnar microcrystalline calcite and interpret these intervals to be wetter than average. Furthermore, changes in calcite fabrics correspond to shifts in trace element concentrations and correlation coefficients. The correlation between Mg and Sr varies from positive to negative depending on fabric type, whereas Mg and P concentrations are negatively correlated throughout the investigated stalagmite. These results are consistent with the concept of prior calcite precipitation (PCP), which predicts high (low) Mg and low (high) P concentrations during relatively dry (wet) periods. Following the concept of PCP, we interpret Mg and P oscillations as shifts in hydroclimate and find that MIS 10 is characterized by precipitation variability at the multiannual, decadal, centennial, and millennial scale. The short-term oscillations are superimposed on an orbital-scale aridification trend observed in the Mg signal. Comparing our records with those from northern high latitude (north of our study area) and Asian monsoon regions, a consistent picture emerges; an episode of relatively strong Siberian High (cold high latitude) from mid to late MIS 10 most likely caused a southward shift of the Westerlies and intertropical convergence zone (ITCZ), resulting in decreasing precipitation over the cave site and a weak Asian Monsoon respectively. In contrast, millennial-scale episodes of ice rafted debris (IRD) deposition in the North Atlantic correspond with wet phases in Central Asia. In conclusion, a strengthening of the Siberian High and resulting southward shift of the Westerlies and ITCZ provides a consistent and viable mechanism that reconciles northern high latitude, mid latitude (this study), and low latitude (Asian Monsoon) records. The forcings of the documented millennial-scale changes in Central Asian hydroclimate require further investigation but may be associated with the effects of North Atlantic freshwater perturbations on atmospheric circulation. On the other hand, multidecadal-scale oscillations in Central Asian precipitation may be linked to climate mode variability analogous to the modern North Atlantic Oscillation (NAO) and El Niño Southern Oscillation (ENSO)
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Southern African Monsoon strengthening and weakening of Mozambique Channel through flow during Heinrich events
Full text linkThe Mozambique Channel is a conduit of trade wind-driven, warm and salty throughflow that is a key component of the Agulhas Current and Agulhas leakage. Agulhas leakage is a flux of warm and salty water from the tropical Indian to the Atlantic Ocean and is thought to strengthen the Atlantic meridional overturning circulation (AMOC). Previous studies from the Agulhas region suggest that enhanced Agulhas leakage, driven by shift and intensification of the southern hemisphere westerlies, played an important role in accelerating glacial terminations. The southeastern monsoon response to freshwater-induced climate instabilities that punctuated the last deglaciation and its impact on the Mozambique Channel through flow and, by extension, on the Agulhas leakage is not well understood. Here we present a high-resolution hydroclimate and mixed layer temperature reconstruction using three sediment cores collected from the runoff-influenced eastern Mozambique Channel, off northwestern Madagascar, in the core region of the southern hemisphere monsoon domain. Local δ18O seawater time-series, obtained by removing the calcification temperature and ice volume imprints on δ18O of Globigerinoides ruber tests, is used as a proxy of river runoff and, by extension, precipitation changes over northwestern Madagascar. Superimposed on orbital scale climate trend that indicates a humid glacial, the proxy record reveals precipitation increases centered at 11-13 thousand years before present (kyr BP), 14-18 kyr BP, and 23-25 kyr BP. Considering age model uncertainty, this is the first strong and consistent evidence for southern African monsoon strengthening in response to freshwater forcing during Younger Dryas (YD), Heinrich Event 1 (H1), and Heinrich Event 2 (H2). Furthermore, our study shows a reversal of mixed layer temperature gradient between the west and east Mozambique Channel during H1 and YD. Consistent with the results of climate simulation, we suggest that the gradient reversal indicates a weakening of the trade wind-driven South Equatorial Current and Mozambique Channel throughflow that weakens the Agulhas leakage. In conclusion, the results of this study indicate that millennial scale weakening of Mozambique Channel through flow is strongly linked to the changes in the southern hemisphere monsoon wind fields over the Tropical Indian Ocean. As shown in this study, the latter is sensitive to northern high latitude freshwater forcing, potential creating a positive feedback that contributes to the weakening of the AMOC by reducing the amount of heat and salt leakage into the Atlantic
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Central Asia’s hydroclimate response to Heinrich events 4 and 5
Full text linkDocumentation of mid-latitude hydroclimate responses to late Pleistocene North Atlanticclimate change is sparse and fragmented due to a lack of continuous and well dated
reconstructions. Here we analyze the remote effects of Heinrich events to understand the
relationship between periods of North Atlantic climate changes and Central Asia’s
precipitation variability. We analyzed trace element, δ18O and δ13C data as proxies for
precipitation variability. Comparison of these proxies with climate records of northern
hemisphere high and low latitude climate changes reveals several episodes of
increased precipitation over Central Asia that coincide with cooling of the northern high
latitude and weakening of northern hemisphere monsoon. We propose two atmospheric links
between the North Atlantic and Central Asia which likely brought increased moisture to the
region during Heinrich events 4 and 5: the Westerly Jet and Siberian High
Stable carbon and oxygen isotope ratios of Uvigerina peregrina of sediment core MD03-2707
No full textStable carbon isotope ratios of benthic foraminifera in Eastern Equatorial Atlantic surface sediments
No full textStable carbon and oxygen isotope ratios of Globorotalia truncatulinoides of sediment core MD03-2707
No full textStable carbon and oxygen isotope ratios of Neogloboquadrina dutertrei of sediment core MD03-2707
No full textStable carbon and oxygen isotope ratios of benthic foraminifera of sediment core MD03-2707 (120-138 ka)
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