| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | July 23, 2020 |
| Latest Amendment Date: | July 23, 2020 |
| Award Number: | 2002444 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Jonathan G Wynn
jwynn@nsf.gov (703)292-4725 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | October 1, 2020 |
| End Date: | May 31, 2024 (Estimated) |
| Total Intended Award Amount: | $173,502.00 |
| Total Awarded Amount to Date: | $173,502.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
874 TRADITIONS WAY TALLAHASSEE FL US 32306-0001 (850)644-5260 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1017 Academic Way Tallahassee FL US 32306-4520 |
| 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): | GLOBAL CHANGE |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
A catastrophic outburst of glacial meltwater into the Labrador Sea 8,200 years ago disrupted Atlantic Ocean circulation, plunging the North Atlantic region into cold conditions for more than a century and impacting climate globally. Some climate models indicate that the vast tropical rain bands may shift south in response to such a perturbation, which has important implications for understanding how the climate might change in the future if a warming ocean disrupts ocean circulation. Yet few reconstructions of rainfall exist from the tropics that span the 8,2000-year-ago time interval, making it difficult to confirm the model-based predictions. To remedy this data gap this project will reconstruct rainfall changes in the tropical Pacific from chemical variations in lake sediments in Palau and the Galápagos that lie on the northern and southern edges of the modern tropical rain band. The research will include climate model simulations elucidating the rainfall changes expected in Palau and the Galápagos in response to a meltwater addition to the North Atlantic similar in size to that estimated during the 8,200-year-ago event. A workshop will be held for Micronesian high school teachers along with an experiential learning coarse in Kosrae (Micronesia). Students from the University of Washington will work with high school teachers and conduct field exercises and create curricular activities based on their experiences.
Rainfall will be reconstructed from hydrogen isotope ratios of the microalgal lipid dinosterol in radiocarbon-dated sediments from lakes in Palau and the Galápagos. Confidence in the regional nature of the hydrogen isotope signals will be achieved through replication of measurements, sediment cores, lakes, and islands. All nine sediment cores, which range in length from 2-15 m, have been collected, and most have initial radiocarbon chronologies. A temporal resolution of 25-40 yr is proposed for the 7,000-9,000-year-ago interval of each core, which ranges in thickness from 50-250 cm. The remainder of the Holocene period in each core will have hydrogen isotope data produced at 250-500-yr resolution in order to place any of the 8,200-yr-ago excursions in the context of the full Holocene. Interpretations of these rainfall reconstructions, including their global context, will be aided by simulations with the isotope-enabled Community Earth System Model forced with realistic meltwater fluxes to the Labrador Sea. Because models diverge widely in their response of tropical Pacific rainfall to freshwater forcing, our rainfall reconstructions will provide a critical benchmark for these models and help constrain the mechanisms by which the tropics respond to abrupt AMOC disruptions.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
PROJECT OUTCOMES REPORT
Disclaimer
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.
Around 8,200 years ago, Earth experienced an abrupt climate event when glacial meltwater disrupted the Atlantic Ocean circulation, triggering rapid global changes. Such abrupt climate change events are important to examine in the context of evaluating future climate change risk, as we have no modern analogue with which to study these events, and we cannot rule out the possibility of such events occurring in the future. The most recent period of abrupt climate change occurred around 8,200 years before present day (the 8.2ka Event), during the otherwise stable Holocene epoch. It was driven by a large outburst of glacial meltwater into the Labrador Sea that disrupted the Atlantic Meridional Overturning (AMOC), plunging the North Atlantic region into cold conditions and impacting climate globally. Proxy data and theory link the widespread cooling of the Northern Hemisphere to a southward shift in tropical rainfall, with hydroclimate anomalies lasting decades to centuries.
In this project, we investigated the spatial and temporal patterns in the tropical hydroclimate response to the 8.2ka Event based on a multi-proxy compilation of 61 tropical hydroclimate records and assessed the consistency between the reconstructed hydroclimate changes and those simulated by a new state-of-the-art climate model simulation of the 8.2ka Event. This work is the first to explicitly account for age uncertainty in the proxy records through the event detection analysis. When age uncertainties are accounted for, significant hydroclimate anomalies associated with the 8.2ka Event were detected in 30% of the records in the compilation, with a mean onset age of 8.28ka, mean termination age of 8.11ka, and mean duration of 152 years (range of 50-289 years). These results indicate a regionally variable tropical hydroclimate response to the 8.2ka Event, with events spanning decades to centuries. Notably, the hydroclimate changes varied widely in different regions of the tropics. Notable signatures of the 8.2ka Event were found in East Asia, South Asia, and the Arabian Peninsula, as well as Central America and central/eastern Brazil. In contrast, no signatures of the 8.2ka Event were found over Indonesia and the Western Pacific Ocean.
Many of these rainfall patterns agree well with our new set of climate model simulations of the 8.2ka Event. In the model, the North Atlantic meltwater pulse led to a large-scale cooling of the Northern Hemisphere, warming of the Southern Hemisphere, and a broad southward shift in tropical rainfall, resulting in a generally drier Northern Hemisphere and wetter Southern Hemisphere, but with large regional variations. Major rainfall features included drying in the monsoon regions of South Asia and West Africa, and a southward shift of the tropical ocean rain bands in the Atlantic, Eastern Pacific, and Indian Oceans, accompanied by drying in Central America and northern South America and wetting in northeastern Brazil. In contrast, the Western Pacific Ocean experienced a muted rainfall response compared to the other ocean basins.
The model simulations also included water isotope tracers to facilitate data-model comparisons, as many of the proxy records included in this study were based on the isotopic composition of precipitation. In some places, including the South Asian monsoon region, the isotopic response was large and did not always follow changes in rainfall amount, indicating that other processes like changes in the source and pathway of the atmospheric moisture dominated the isotopic signal in those regions.
These results have advanced our understanding of the tropical hydroclimate response to the 8.2ka Event, demonstrating that the tropical hydroclimate response to the 8.2ka Event cannot be described as a simple hemispheric dipole pattern, especially over continental regions, and that the rich regional structure of both the precipitation response and the isotopic composition of precipitation must be considered in order to understand the full picture of the tropical hydroclimate response to this event. The study also highlighted the importance of accounting for age uncertainty in detecting events in the proxy record and the value of using isotope-enabled model simulations for data-model intercomparison.
The impacts of this work extend beyond paleoclimate research. As AMOC is projected to weaken under continued anthropogenic warming of the climate system, the findings of this study are relevant to future climate change risk and impact assessment. The proxy synthesis in this study may also aid in model development efforts by providing a test environment that can be directly compared with output from global climate models driven by prescribed forcings over the early Holocene. The project supported the training of a graduate student in climate science, data analysis, and climate modeling, preparing her for a career in academia, government, or industry, thus enhancing the workforce with expertise in climate science research. The PI also engaged in public outreach in association with the project, making presentations to the general public and engaging with lawmakers and the media on climate science topics.
Last Modified: 11/11/2024
Modified by: Alyssa Atwood
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