A multi-proxy stalagmite record from northwestern Namibia of regional drying with increasing global-scale warmth over the last 47 kyr: The interplay of a globally shifting ITCZ with regional currents, winds, and rainfall
Railsback, L. Bruce | Brook, George A. | Liang, Fuyuan | Marais, Eugene | Cheng, Hai | Edwards, R. Lawrence
Stalagmite Orum-1 from a cave near Orumana in northwestern Namibia provides a multi-proxy record of regional drying with increasing global-scale warmth over the last 47 kyr, in a region with few long well-dated location specific paleoclimate records. Data from Stalagmite Orum-1 include carbon and oxygen stable isotope ratios, proportions of aragonite and calcite, pronouncedly differing petrographic fabrics, positions of layer-bounding surfaces, variation in layer-specific width, and changes in layer thickness, all of which combine to support change from wetter to drier conditions. Combined with fourteen U-Th ages, they suggest that climate was wetter in northwestern Namibia during globally cold MIS 3 than it is today, and with more grass than is present today. The climate at Orumana became drier during the deglacial transition after the Last Glacial Maximum, but carbon isotope data indicate that C-4 grasses persisted. In the Holocene, even greater aridity led to a reduction in grass cover and to the present C-3-dominated vegetation. Hiatuses in Stalagmite Orum-1 suggest even drier conditions during the Bolling-Allerod and during the early Holocene thermal maximum. Wetter conditions at Orumana during glacial times may have resulted from movement of the Intertropical Convergence Zone southward, in a shift that was significant west of longitude 13 degrees E but perhaps less significant east of that line. It may have been accompanied by a lesser southward shift of the Angola-Benguela Front at sea and/or the Inter-Ocean Convergence Zone on land, leading to increased rainfall in northern Namibia (but perhaps not farther south). Extrapolation from the present to warmer conditions in the next century would suggest that further drying in northern Namibia and southern Angola may occur.
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