A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem ????¹³C-¹⁴C analysis
The Younger Dryas (YD, 12,900-11,700 years BP) is characterized by a return to near-glacial conditions in the northern hemisphere during the last deglacial period. Texas moisture proxy records support a general regional warming/drying trend from the YD through the Holocene, however, the timing and m...
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ftunivtexas:oai:repositories.lib.utexas.edu:2152/64615 2023-05-15T16:30:43+02:00 A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem ????¹³C-¹⁴C analysis A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem [delta] ¹³C-¹⁴C analysis James, Christina Danielle Banner, Jay L. Breecker, Daniel Miller, Nathan 2017-12 application/pdf http://hdl.handle.net/2152/64615 https://doi.org/10.15781/T2FT8F253 unknown doi:10.15781/T2FT8F253 http://hdl.handle.net/2152/64615 Speleothem Paleoclimate Central Texas Carbon isotope Thesis text 2017 ftunivtexas https://doi.org/10.15781/T2FT8F253 2020-12-23T22:00:40Z The Younger Dryas (YD, 12,900-11,700 years BP) is characterized by a return to near-glacial conditions in the northern hemisphere during the last deglacial period. Texas moisture proxy records support a general regional warming/drying trend from the YD through the Holocene, however, the timing and magnitude of changes in regional moisture and temperature conditions are poorly constrained. We use moisture proxies from a central Texas stalagmite record (McN-1) collected in the Edwards aquifer (an important human and ecological groundwater resource in central Texas) to assess how epikarst moisture conditions varied in the region during the YD-Holocene transition. The relatively high concentrations of ²³²Th (>1 ppb) in several horizons in this sample resulted in McN-1 U-series ages with high uncertainties (>10% of measured age). We use two isochrons and measured ²³⁰Th/²³²Th ratios from modern calcite grown in central Texas caves to estimate the McN-1 initial ²³⁰Th/²³²Th ratio and develop an age model with better constrained uncertainties. Strong correlations between speleothem ????¹³C and ¹⁴C activities can result from changes in epikarst carbonate dissolution due to variable CO2 ventilation or pore space moisture. A decrease in the proportion of ¹⁴C-free carbon (the dead carbon proportion, DCP) to 0% is interpreted as a change from partial dissolution in a water-saturated closed system to dissolution in an open system, where carbon from limestone has no measurable effect on dissolved inorganic carbon ¹⁴C activities. A negative shift in ????¹³C values of 2.8‰ coincident with a decrease in DCP from 7.5 to 0% occurs in McN-1 at the Younger Dryas-Holocene boundary in less than 230 years (as little as 50 years given age constraints). We attribute these parallel declines in ????¹³C and DCP to changes in the epikarst dissolution system. If changes in the dissolution system are controlled by pore space moisture, the change to an open system at the YD-Holocene boundary indicates a rapid regional drying event. Application of a calcite dissolution model indicates that 25% of the negative ????¹³C shift can be explained by change from a more closed to an open system in the epikarst dissolution region above the cave. We attribute the remaining shift in ????¹³C values to reduced drip water pH, associated with an increased contribution of respired CO₂ to epikarst pCO₂. Speleothem growth rates decrease at the YD-Holocene boundary, consistent with our interpretation that carbon isotopes record a decrease in vadose zone moisture. This epikarst moisture interpretation is consistent with other Texas paleoclimate records, indicating a climate transition to drier early Holocene conditions. Compared with existing regional proxy records, the relatively high temporal resolution of the McN-1 ????¹³C record (inter-annual) indicates a rapid drying event concurrent with Greenland temperature increases, suggesting a contemporaneous climate response between regional and high latitude climate at end of the YD. Geological Sciences Thesis Greenland The University of Texas at Austin: Texas ScholarWorks Greenland |
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Open Polar |
collection |
The University of Texas at Austin: Texas ScholarWorks |
op_collection_id |
ftunivtexas |
language |
unknown |
topic |
Speleothem Paleoclimate Central Texas Carbon isotope |
spellingShingle |
Speleothem Paleoclimate Central Texas Carbon isotope James, Christina Danielle A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem ????¹³C-¹⁴C analysis |
topic_facet |
Speleothem Paleoclimate Central Texas Carbon isotope |
description |
The Younger Dryas (YD, 12,900-11,700 years BP) is characterized by a return to near-glacial conditions in the northern hemisphere during the last deglacial period. Texas moisture proxy records support a general regional warming/drying trend from the YD through the Holocene, however, the timing and magnitude of changes in regional moisture and temperature conditions are poorly constrained. We use moisture proxies from a central Texas stalagmite record (McN-1) collected in the Edwards aquifer (an important human and ecological groundwater resource in central Texas) to assess how epikarst moisture conditions varied in the region during the YD-Holocene transition. The relatively high concentrations of ²³²Th (>1 ppb) in several horizons in this sample resulted in McN-1 U-series ages with high uncertainties (>10% of measured age). We use two isochrons and measured ²³⁰Th/²³²Th ratios from modern calcite grown in central Texas caves to estimate the McN-1 initial ²³⁰Th/²³²Th ratio and develop an age model with better constrained uncertainties. Strong correlations between speleothem ????¹³C and ¹⁴C activities can result from changes in epikarst carbonate dissolution due to variable CO2 ventilation or pore space moisture. A decrease in the proportion of ¹⁴C-free carbon (the dead carbon proportion, DCP) to 0% is interpreted as a change from partial dissolution in a water-saturated closed system to dissolution in an open system, where carbon from limestone has no measurable effect on dissolved inorganic carbon ¹⁴C activities. A negative shift in ????¹³C values of 2.8‰ coincident with a decrease in DCP from 7.5 to 0% occurs in McN-1 at the Younger Dryas-Holocene boundary in less than 230 years (as little as 50 years given age constraints). We attribute these parallel declines in ????¹³C and DCP to changes in the epikarst dissolution system. If changes in the dissolution system are controlled by pore space moisture, the change to an open system at the YD-Holocene boundary indicates a rapid regional drying event. Application of a calcite dissolution model indicates that 25% of the negative ????¹³C shift can be explained by change from a more closed to an open system in the epikarst dissolution region above the cave. We attribute the remaining shift in ????¹³C values to reduced drip water pH, associated with an increased contribution of respired CO₂ to epikarst pCO₂. Speleothem growth rates decrease at the YD-Holocene boundary, consistent with our interpretation that carbon isotopes record a decrease in vadose zone moisture. This epikarst moisture interpretation is consistent with other Texas paleoclimate records, indicating a climate transition to drier early Holocene conditions. Compared with existing regional proxy records, the relatively high temporal resolution of the McN-1 ????¹³C record (inter-annual) indicates a rapid drying event concurrent with Greenland temperature increases, suggesting a contemporaneous climate response between regional and high latitude climate at end of the YD. Geological Sciences |
author2 |
Banner, Jay L. Breecker, Daniel Miller, Nathan |
format |
Thesis |
author |
James, Christina Danielle |
author_facet |
James, Christina Danielle |
author_sort |
James, Christina Danielle |
title |
A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem ????¹³C-¹⁴C analysis |
title_short |
A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem ????¹³C-¹⁴C analysis |
title_full |
A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem ????¹³C-¹⁴C analysis |
title_fullStr |
A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem ????¹³C-¹⁴C analysis |
title_full_unstemmed |
A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem ????¹³C-¹⁴C analysis |
title_sort |
central texas drying event identified at the younger dryas-early holocene transition using coupled speleothem ????¹³c-¹⁴c analysis |
publishDate |
2017 |
url |
http://hdl.handle.net/2152/64615 https://doi.org/10.15781/T2FT8F253 |
geographic |
Greenland |
geographic_facet |
Greenland |
genre |
Greenland |
genre_facet |
Greenland |
op_relation |
doi:10.15781/T2FT8F253 http://hdl.handle.net/2152/64615 |
op_doi |
https://doi.org/10.15781/T2FT8F253 |
_version_ |
1766020459266048000 |