Carbon Dynamics of the Deglacial and Contemporary Ocean Inferred from Radiocarbon Measurements in Foraminifera, Seawater and Atmospheric Carbon Dioxide
Late Pleistocene atmospheric CO2 concentrations varied by ~90 ppm, rising with Antarctic and global temperatures during deglaciations. These natural variations were smaller and slower than the present CO2 increase, caused by anthropogenic emissions, which is driving the current transition to the war...
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ftunicolboulder:oai:scholar.colorado.edu:geol_gradetds-1110 2023-05-15T13:49:40+02:00 Carbon Dynamics of the Deglacial and Contemporary Ocean Inferred from Radiocarbon Measurements in Foraminifera, Seawater and Atmospheric Carbon Dioxide Lindsay, Colin Metz 2016-01-01T08:00:00Z application/pdf https://scholar.colorado.edu/geol_gradetds/107 https://scholar.colorado.edu/cgi/viewcontent.cgi?article=1110&context=geol_gradetds unknown CU Scholar https://scholar.colorado.edu/geol_gradetds/107 https://scholar.colorado.edu/cgi/viewcontent.cgi?article=1110&context=geol_gradetds Geological Sciences Graduate Theses & Dissertations carbon cycle foraminifera marine geochemistry paleoceanography radiocarbon southern ocean Climate Geology Paleontology text 2016 ftunicolboulder 2018-10-07T08:58:27Z Late Pleistocene atmospheric CO2 concentrations varied by ~90 ppm, rising with Antarctic and global temperatures during deglaciations. These natural variations were smaller and slower than the present CO2 increase, caused by anthropogenic emissions, which is driving the current transition to the warm Anthropocene. Because the ocean is the largest carbon reservoir that exchanges readily with the atmosphere, most explanations of the glacial-interglacial variations and predictions of future CO2 concentrations involve mechanisms that mediate that exchange. A critical region for such exchange is the Southern Ocean (SO), where carbon-rich deep water is upwelled to the surface by westerly winds that may be responsive to past and present warming. In this dissertation, I use radiocarbon (14C) measurements as a tracer to investigate the ocean’s role in controlling atmospheric CO2 during the last deglaciation and the past two decades. Previously documented intervals of anomalously low 14C activity (Δ14C) in the deglacial (18-11 ka BP) mid-depth ocean coincide with rising CO2 and decreasing Δ14C in the atmosphere, possibly tracing the re-emergence of aged carbon sequestered in the deep ocean during the preceding glacial period. I combined new 14C measurements in foraminifera from marine sediment cores near Baja California with published data to reconstruct regional gradients of Δ14C during deglaciation. The results appear to constrain the source of aged carbon to the SO, via the Equatorial Pacific. I also present new 14C measurements in air sampled since 2006 from Drake Passage in the SO. Transiently high CO2 concentrations correlate with low Δ14C and dominant modes of atmospheric variability, suggesting that increases in wind-driven upwelling drive more deep ocean carbon into the atmosphere, temporarily reducing the local net ocean carbon sink. Finally, I estimate rates of surface ocean Δ14C change since the 1990s using published datasets. The results imply that anthropogenic carbon, previously absorbed at high southern latitudes, is now re-emerging in the low latitude ocean. In summary, evidence presented in this dissertation suggests that SO upwelling, during both deglacial and contemporary periods of global warming, can act as a positive feedback in the coupled climate-carbon system by shifting deep ocean carbon into the atmosphere. Text Antarc* Antarctic Drake Passage Southern Ocean University of Colorado, Boulder: CU Scholar Antarctic Southern Ocean Baja Drake Passage Pacific |
institution |
Open Polar |
collection |
University of Colorado, Boulder: CU Scholar |
op_collection_id |
ftunicolboulder |
language |
unknown |
topic |
carbon cycle foraminifera marine geochemistry paleoceanography radiocarbon southern ocean Climate Geology Paleontology |
spellingShingle |
carbon cycle foraminifera marine geochemistry paleoceanography radiocarbon southern ocean Climate Geology Paleontology Lindsay, Colin Metz Carbon Dynamics of the Deglacial and Contemporary Ocean Inferred from Radiocarbon Measurements in Foraminifera, Seawater and Atmospheric Carbon Dioxide |
topic_facet |
carbon cycle foraminifera marine geochemistry paleoceanography radiocarbon southern ocean Climate Geology Paleontology |
description |
Late Pleistocene atmospheric CO2 concentrations varied by ~90 ppm, rising with Antarctic and global temperatures during deglaciations. These natural variations were smaller and slower than the present CO2 increase, caused by anthropogenic emissions, which is driving the current transition to the warm Anthropocene. Because the ocean is the largest carbon reservoir that exchanges readily with the atmosphere, most explanations of the glacial-interglacial variations and predictions of future CO2 concentrations involve mechanisms that mediate that exchange. A critical region for such exchange is the Southern Ocean (SO), where carbon-rich deep water is upwelled to the surface by westerly winds that may be responsive to past and present warming. In this dissertation, I use radiocarbon (14C) measurements as a tracer to investigate the ocean’s role in controlling atmospheric CO2 during the last deglaciation and the past two decades. Previously documented intervals of anomalously low 14C activity (Δ14C) in the deglacial (18-11 ka BP) mid-depth ocean coincide with rising CO2 and decreasing Δ14C in the atmosphere, possibly tracing the re-emergence of aged carbon sequestered in the deep ocean during the preceding glacial period. I combined new 14C measurements in foraminifera from marine sediment cores near Baja California with published data to reconstruct regional gradients of Δ14C during deglaciation. The results appear to constrain the source of aged carbon to the SO, via the Equatorial Pacific. I also present new 14C measurements in air sampled since 2006 from Drake Passage in the SO. Transiently high CO2 concentrations correlate with low Δ14C and dominant modes of atmospheric variability, suggesting that increases in wind-driven upwelling drive more deep ocean carbon into the atmosphere, temporarily reducing the local net ocean carbon sink. Finally, I estimate rates of surface ocean Δ14C change since the 1990s using published datasets. The results imply that anthropogenic carbon, previously absorbed at high southern latitudes, is now re-emerging in the low latitude ocean. In summary, evidence presented in this dissertation suggests that SO upwelling, during both deglacial and contemporary periods of global warming, can act as a positive feedback in the coupled climate-carbon system by shifting deep ocean carbon into the atmosphere. |
format |
Text |
author |
Lindsay, Colin Metz |
author_facet |
Lindsay, Colin Metz |
author_sort |
Lindsay, Colin Metz |
title |
Carbon Dynamics of the Deglacial and Contemporary Ocean Inferred from Radiocarbon Measurements in Foraminifera, Seawater and Atmospheric Carbon Dioxide |
title_short |
Carbon Dynamics of the Deglacial and Contemporary Ocean Inferred from Radiocarbon Measurements in Foraminifera, Seawater and Atmospheric Carbon Dioxide |
title_full |
Carbon Dynamics of the Deglacial and Contemporary Ocean Inferred from Radiocarbon Measurements in Foraminifera, Seawater and Atmospheric Carbon Dioxide |
title_fullStr |
Carbon Dynamics of the Deglacial and Contemporary Ocean Inferred from Radiocarbon Measurements in Foraminifera, Seawater and Atmospheric Carbon Dioxide |
title_full_unstemmed |
Carbon Dynamics of the Deglacial and Contemporary Ocean Inferred from Radiocarbon Measurements in Foraminifera, Seawater and Atmospheric Carbon Dioxide |
title_sort |
carbon dynamics of the deglacial and contemporary ocean inferred from radiocarbon measurements in foraminifera, seawater and atmospheric carbon dioxide |
publisher |
CU Scholar |
publishDate |
2016 |
url |
https://scholar.colorado.edu/geol_gradetds/107 https://scholar.colorado.edu/cgi/viewcontent.cgi?article=1110&context=geol_gradetds |
geographic |
Antarctic Southern Ocean Baja Drake Passage Pacific |
geographic_facet |
Antarctic Southern Ocean Baja Drake Passage Pacific |
genre |
Antarc* Antarctic Drake Passage Southern Ocean |
genre_facet |
Antarc* Antarctic Drake Passage Southern Ocean |
op_source |
Geological Sciences Graduate Theses & Dissertations |
op_relation |
https://scholar.colorado.edu/geol_gradetds/107 https://scholar.colorado.edu/cgi/viewcontent.cgi?article=1110&context=geol_gradetds |
_version_ |
1766251933143662592 |