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18 results on '"Lehmann, Sophie B."'

11. Andean drought and glacial retreat tied to Greenland warming during the last glacial period

Author

Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Woods, Arielle, Rodbell, Donald T, Abbott, Mark B, Hatfield, Robert G, Chen, Christine, Lehmann, Sophie B, Mcgee, David, Weidhaas, Nicholas C, Tapia, Pedro M, Valero-Garcés, Blas L, Bush, Mark B, Stoner, Joseph S, Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Woods, Arielle, Rodbell, Donald T, Abbott, Mark B, Hatfield, Robert G, Chen, Christine, Lehmann, Sophie B, Mcgee, David, Weidhaas, Nicholas C, Tapia, Pedro M, Valero-Garcés, Blas L, Bush, Mark B, and Stoner, Joseph S

Abstract

© 2020, The Author(s). Abrupt warming events recorded in Greenland ice cores known as Dansgaard-Oeschger (DO) interstadials are linked to changes in tropical circulation during the last glacial cycle. Corresponding variations in South American summer monsoon (SASM) strength are documented, most commonly, in isotopic records from speleothems, but less is known about how these changes affected precipitation and Andean glacier mass balance. Here we present a sediment record spanning the last ~50 ka from Lake Junín (Peru) in the tropical Andes that has sufficient chronologic precision to document abrupt climatic events on a centennial-millennial time scale. DO events involved the near-complete disappearance of glaciers below 4700 masl in the eastern Andean cordillera and major reductions in the level of Peru’s second largest lake. Our results reveal the magnitude of the hydroclimatic disruptions in the highest reaches of the Amazon Basin that were caused by a weakening of the SASM during abrupt arctic warming. Accentuated warming in the Arctic could lead to significant reductions in the precipitation-evaporation balance of the southern tropical Andes with deleterious effects on this densely populated region of South America.

Published
2021

12. Andean drought and glacial retreat tied to Greenland warming during the last glacial period

Author

Woods, Arielle, Rodbell, Donald T, Abbott, Mark B, Hatfield, Robert G, Chen, Christine Y, Lehmann, Sophie B, McGee, David, Weidhaas, Nicholas C, Tapia, Pedro M, Valero-Garcés, Blas L, Bush, Mark B, Stoner, Joseph S, Woods, Arielle, Rodbell, Donald T, Abbott, Mark B, Hatfield, Robert G, Chen, Christine Y, Lehmann, Sophie B, McGee, David, Weidhaas, Nicholas C, Tapia, Pedro M, Valero-Garcés, Blas L, Bush, Mark B, and Stoner, Joseph S

Abstract

© 2020, The Author(s). Abrupt warming events recorded in Greenland ice cores known as Dansgaard-Oeschger (DO) interstadials are linked to changes in tropical circulation during the last glacial cycle. Corresponding variations in South American summer monsoon (SASM) strength are documented, most commonly, in isotopic records from speleothems, but less is known about how these changes affected precipitation and Andean glacier mass balance. Here we present a sediment record spanning the last ~50 ka from Lake Junín (Peru) in the tropical Andes that has sufficient chronologic precision to document abrupt climatic events on a centennial-millennial time scale. DO events involved the near-complete disappearance of glaciers below 4700 masl in the eastern Andean cordillera and major reductions in the level of Peru’s second largest lake. Our results reveal the magnitude of the hydroclimatic disruptions in the highest reaches of the Amazon Basin that were caused by a weakening of the SASM during abrupt arctic warming. Accentuated warming in the Arctic could lead to significant reductions in the precipitation-evaporation balance of the southern tropical Andes with deleterious effects on this densely populated region of South America.

Published
2021

13. Corrigendum to “U–Th dating of lake sediments: Lessons from the 700 ka sediment record of lake Junín, Peru” [Quat. Sci. Rev. 244 (2020) 106422]

Author

Chen, Christine Y., McGee, David, Woods, Arielle, Pérez, Liseth, Hatfield, Robert G., Edwards, R. Lawrence, Cheng, Hai, Valero-Garcés, Blas L., Lehmann, Sophie B., Stoner, Joseph S., Schwalb, Antje, Tal, Irit, Seltzer, Geoffrey O., Tapia, Pedro Miguel, Abbott, Mark B., and Rodbell, Donald T.

Published
2020
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14. Comparative isotopic evidence from East Turkana supports a dietary shift within the genus Homo

Author

Patterson, David B., primary, Braun, David R., additional, Allen, Kayla, additional, Barr, W. Andrew, additional, Behrensmeyer, Anna K., additional, Biernat, Maryse, additional, Lehmann, Sophie B., additional, Maddox, Tom, additional, Manthi, Fredrick K., additional, Merritt, Stephen R., additional, Morris, Sarah E., additional, O’Brien, Kaedan, additional, Reeves, Jonathan S., additional, Wood, Bernard A., additional, and Bobe, René, additional

Published
2019
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18. THE IMPORTANCE OF LIGHT PENETRATION AND CHLOROPHYLL CONCENTRATION ON METALIMNETIC OXYGEN MAXIMA (MOM) DEVELOPMENT IN LAKE ERIE.

Author

Conroy, Joseph D., Dubelko, Gwen L., Lehmann, Sophie B., Kane, Douglas D., and Culver, David A.

Subjects
*DISSOLVED oxygen in water, *HYPOXIA (Water), *LIGHT, *GEOLOGICAL basins
Abstract

Recurring seasonal hypoxia (low dissolved oxygen DO concentration, < 4 mg O2 L-1) and anoxia (< 1 mg L-1) greatly affects pelagic and benthic biota in Lake Erie's central basin. Here, we report the presence of metalimnetic oxygen maxima (MOM) throughout the Sandusky subbasin, the southwest portion of the central basin during 2005, 2006, and 2007. Using weekly (or more frequent) vertical-profile sampling of water temperature (degrees Celsius) and DO at 0.5-m intervals at seven sites in the Sandusky subbasin during summer (June-August), we found that MOM frequently occurred (in 72 of 135 DO vertical profiles) during 2005-2007. We hypothesized that the shallow depth (mean depth = 13.3 m relative to the central basin mean depth = 18.5 m) and high productivity (as chlorophyll a concentration, Chl a) of the Sandusky subbasin permitted adequate light penetration (as Secchi Disk transparency, SD) facilitating metalimnetic phytoplankton growth. We tested this prediction in 2007 and found that deeper, eastern subbasin sites more frequently had DO profiles with MOM than shallower, western subbasin sites (about 67% of the profiles versus 33% for eastern and western sites, respectively). However, neither Chl a nor SD predicted MOM occurrence (P > 0.05, R² < 0.10). These results reveal that either light penetration or the presence of primary producers is unimportant for MOM occurrence or that our temporal and spatial scales of investigation did not appropriately identify effect scales. Nevertheless, occurrence of MOM in the Sandusky subbasin and possibly the rest of the central basin may ameliorate hypoxic and anoxic conditions. [ABSTRACT FROM AUTHOR]

Published
2008

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