| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | August 7, 2015 |
| Latest Amendment Date: | August 7, 2015 |
| Award Number: | 1528733 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Enriqueta Barrera
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2015 |
| End Date: | August 31, 2018 (Estimated) |
| Total Intended Award Amount: | $60,597.00 |
| Total Awarded Amount to Date: | $60,597.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
501 E HIGH ST OXFORD OH US 45056-1846 (513)529-3600 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
OH US 45056-3653 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Geobiology & Low-Temp Geochem |
| Primary Program Source: |
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| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Land snails are one of the most common fossils in the terrestrial geologic record of North America. Their shells are composed of calcium carbonate and the oxygen isotopic composition of their shells record climatic conditions during growth. Therefore, the oxygen isotopic composition of land snails has the potential to reconstruct past climates on broad spatial and temporal scales. To date, however, there is a little understanding on the kinds of climatic information that can be inferred from the snails, and therefore, their current use as paleoclimatic archives is limited. This proposal will develop, test, and calibrate the oxygen isotope systematics of small land snails for use as a paleoclimatic proxy in terrestrial settings across North America. The modern calibration of this proxy will benefit society through the development of a terrestrial paleoclimatic proxy that is capable of reconstructing past climate over broad spatial and temporal scales and also will improve our understanding of the taxonomic diversity and spatial distribution of land snails, a fauna that is decreasing at an alarming rate globally. This project will teach and train future scientists, from high school to PhD candidates, integrate scientists from multiple fields (paleontology, biology, Quaternary geology), and broaden the participation of diverse and underrepresented groups. Dissemination of results will include a diverse audience (specialists and general public), in English and Spanish to reach the Hispanic community in USA and elsewhere. This project will establish linkages between underrepresented groups and STEM disciplines at research-intensive universities.
To calibrate the oxygen isotope systematics of modern land snails in North America, investigators will analyze the oxygen isotope composition of approximately 1,000 shell samples from modern snails collected along two selected transects that cross North America from southern Texas to Canada. They will identify the primary climatic controls on shell ä18O values by quantifying the relation between shell ä18O and relevant climatic variables (temperature, ä18O of precipitation, precipitation amount, relative humidity) using an evaporative steady-state flux balance-mixing model developed for land snails. Researchers hypothesize that: (1) the oxygen isotope composition of small land snails in temperate environments (latitudes of 26 to 48 degrees N) primarily will reflect the oxygen isotope composition of precipitation, and therefore can be used to infer past changes in precipitation oxygen isotope values; and (2) shell oxygen isotope values of snails living in arid to semi-arid environments will yield higher values than predicted because of low relative humidity values. After calibration of the oxygen isotope systematics for living specimens, investigators will conduct two case studies to determine how well the oxygen isotope values of small snails track the oxygen isotope records of speleothems or other proxy records. The proposed work will allow better quantification of past climate change over broad areas of North America, and from many different types of deposits.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
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This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Shells of small land snails, or terrestrial gastropods, are one of the most common types of fossils in the terrestrial geologic record of North America. They are found in lacustrine, fluvial, alluvial, loess, and wetlands deposits. In a sense, they are the foraminifera of the terrestrial realm. Like foraminifera, gastropod shells are composed of calcium carbonate and the oxygen isotopic composition of the carbonate record climatic and environmental information during their formation. Therefore, the oxygen isotopic composition of terrestrial gastropod shells has the potential to reconstruct past climate over broad spatial and temporal scales, much like how foraminifera have been used in marine settings. Unlike foraminifera, however, little research has been directed at understanding the environmental and climatic controls on the oxygen isotopic composition of terrestrial gastropods, limiting their potential use as a paleoclimatic proxy.
Over the duration of this proposal we conducted a variety of modern calibration studies including a latitudinal transect across North America to understand the key hemispheric controls on the oxygen isotopic composition of terrestrial gastropod shells. We also conducted detailed regional studies to identify more local-scale controls. Key findings include the dominant role of the oxygen isotopic composition of meteoric water – as opposed to temperature or relative humidity – on the oxygen isotopic composition of shell material, as well as significant (up to 3 per mil) disparities between the average oxygen isotopic composition of shell material between some taxa.
After calibrating the modern controls on the oxygen isotopic composition of small land snails in North America, we analyzed a sequence of fossil gastropod shells (n=456) from late Pleistocene and Holocene marls (calcareous muds) from wetland deposits in the San Pedro Valley of Arizona. We identified disparities between fossil shells of different taxa that were similar to what we found between modern taxa in our calibration studies, indicating the importance of separating results by taxon. When systematic differences among taxa were accounted for, a combined oxygen isotopic record that spans from 28,000 years ago to ~10,000 years ago was constructed from the San Pedro wetland deposits and compared to regional speleothem records that track changes in the oxygen isotope composition of meteoric water. The San Pedro gastropod oxygen isotope record showed a similar trend in oxygen isotopes over time as key speleothem records from the region (e.g., Ft. Stanton, NM), indicating that fossil gastropod shells in wetlands are capable of tracking changes in the oxygen isotopic composition of meteoric water linked to different moisture sources. The fossil gastropod record, however, is at a much coarser temporal resolution. A key question that remains is ‘What is the temporal, and spatial, resolution capable of fossil gastropod oxygen isotope records?’
The Broader Impacts Program of this program was multi-faceted and integrated among all primary investigators. The project trained several undergraduate and graduate students from under-represented groups at Miami University, Ohio and results of this work were disseminated broadly.
Last Modified: 02/15/2019
Modified by: Jason A Rech
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