{"id":{"repo_id":"texas","oai_identifier":"oai:repositories.lib.utexas.edu:2152/64615"},"canonical_url":"https://search.dev.ndltd.org/etd/texas/oai:repositories.lib.utexas.edu:2152/64615","repository":{"repo_id":"texas","name":"University of Texas","base_url":"https://repositories.lib.utexas.edu/server/oai/request"},"display":{"title":"A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem 𝛿¹³C-¹⁴C analysis","abstract":"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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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.","abstract_html":"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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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.","abstract_has_math":false,"creators":["James, Christina Danielle"],"institution":"The University of Texas at Austin","degree_name":"Master of Science in Geological Sciences","degree_level":"Masters","degree_discipline":"Geological Sciences","degree_department":null,"school":null,"contributors":[],"advisors":["Banner, Jay L."],"committee_chairs":[],"committee_members":["Breecker, Daniel","Miller, Nathan"],"year":2017,"date_issued":"2017-08-29","date_published":"2017-08-29","updated_at":"2026-07-24T05:01:20Z","subjects":["Speleothem","Paleoclimate","Central Texas","Carbon isotope"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["doi:10.15781/T2FT8F253"],"render_values":[{"text":"doi:10.15781/T2FT8F253","href":"https://doi.org/10.15781/T2FT8F253","code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2152/64615","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Banner, Jay L."]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Breecker, Daniel","Miller, Nathan"]},{"key":"dc:creator","label":"Author","values":["James, Christina Danielle"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2018-04-23T16:56:02Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2018-04-23T16:56:02Z"]},{"key":"dc:date.issued","label":"Date","values":["2017-08-29"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Geological Sciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Masters"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Master of Science in Geological Sciences"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["The University of Texas at Austin"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Speleothem","Paleoclimate","Central Texas","Carbon isotope"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["doi:10.15781/T2FT8F253"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/2152/64615"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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."]},{"key":"dc:format.mimetype","label":"Dc Format Mimetype","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem 𝛿¹³C-¹⁴C analysis"]}]}],"canonical_facts":{"dc:contributor.advisor":["Banner, Jay L."],"dc:contributor.committeemember":["Breecker, Daniel","Miller, Nathan"],"dc:creator":["James, Christina Danielle"],"dc:date.accessioned":["2018-04-23T16:56:02Z"],"dc:date.available":["2018-04-23T16:56:02Z"],"dc:date.issued":["2017-08-29"],"dc:description.abstract":["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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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 𝛿¹³C 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."],"dc:format.mimetype":["application/pdf"],"dc:identifier":["doi:10.15781/T2FT8F253"],"dc:identifier.uri":["http://hdl.handle.net/2152/64615"],"dc:subject":["Speleothem","Paleoclimate","Central Texas","Carbon isotope"],"dc:title":["A central Texas drying event identified at the Younger Dryas-early Holocene transition using coupled speleothem 𝛿¹³C-¹⁴C analysis"],"dc:type":["Thesis"],"thesis:degree_discipline":["Geological Sciences"],"thesis:degree_level":["Masters"],"thesis:degree_name":["Master of Science in Geological Sciences"],"thesis:institution_name":["The University of Texas at Austin"]},"updated_at":"2026-07-24T05:01:20Z"}