
NSF Org: |
OCE Division Of Ocean Sciences |
Recipient: |
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Initial Amendment Date: | June 29, 2020 |
Latest Amendment Date: | May 11, 2023 |
Award Number: | 2023046 |
Award Instrument: | Standard Grant |
Program Manager: |
Elizabeth Canuel
ecanuel@nsf.gov (703)292-7938 OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
Start Date: | September 1, 2020 |
End Date: | August 31, 2024 (Estimated) |
Total Intended Award Amount: | $370,684.00 |
Total Awarded Amount to Date: | $394,376.00 |
Funds Obligated to Date: |
FY 2023 = $23,692.00 |
History of Investigator: |
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Recipient Sponsored Research Office: |
8622 DISCOVERY WAY # 116 LA JOLLA CA US 92093-1500 (858)534-1293 |
Sponsor Congressional District: |
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Primary Place of Performance: |
CA US 92093-0210 |
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): |
SPECIAL EMPHASIS PROGRAM, Chemical Oceanography |
Primary Program Source: |
01002021DB NSF RESEARCH & RELATED ACTIVIT |
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
Collaborative Proposal: Unravelling the Oceanic Dimethylmercury Cycle
This project will study how dimethylmercury is formed and removed in the oceans. Dimethylmercury is a naturally occurring compound. It is thought to be formed when man-made mercury is converted into monomethylmercury, a toxin that accumulates in fish. Despite representing a large fraction of mercury in the oceans, the origin and fate of dimethylmercury is not known. This research will use state-of-the-art analytical, genomic and modeling tools to address this information gap. It will also train graduate and undergraduate students to use field, experimental, and modeling methods. The results will be used in predictive models to forecast future trends in the oceanic mercury cycle. These models are needed to evaluate the effectiveness of international actions that seek to reverse increasing trends in the bioaccumulation of monomethylmercury in fish.
Methylated mercury species in the ocean are formed in sediment and the water column from inorganic divalent mercury delivered from the atmosphere and rivers. The putative mechanism is a two-step process during which monomethylmercury is formed first, followed by slow methylation into dimethylmercury. The first step, biomethylation of divalent mercury into monomethylmercury, is relatively well-studied in sediment and known to be driven by sulfate- and iron-reducing bacteria and methanogens. The mechanism for monomethylmercury formation in the water column is less well understood, and the process of dimethylmercury formation in sediment or seawater is essentially unknown. Until recently, it was assumed that dimethylmercury represented a small enough fraction of the methylated and total mercury (the sum of all mercury species) pools to be insignificant in the global mercury cycle. Recent measurements, however, show that dimethylmercury levels in seawater can be in the same range as the other mercury species. This project will identify the biological and chemical methylating agents involved in the formation of dimethylmercury. Further, it will test the impact of varying biogeochemical conditions on dimethylmercury production. Results will be used to update the mercury module of the MIT General Circulation Model (MITgcm, a global biogeochemical model, and analyze the impacts of dimethylmercury production and degradation on monomethylmercury concentrations.
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.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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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.
Intellectual Merit. This project significantly advanced our understanding of dimethylmercury (DMHg), a naturally occurring form of mercury, and its role in the global mercury cycle. DMHg, a relative of the neurotoxic monomethylmercury, often dominates in deep ocean waters but was poorly understood due in part to a lack of reliable analytical methods. Also traditional sampling techniques often lack the ability to track changes over time, making it difficult to study how DMHg is formed and broken down in seawater. To address these gaps, the project developed new, highly accurate methods for measuring DMHg. These were applied alongside innovative sampling strategies, such as tracking water parcels over time and establishing a long-term sampling program at the Scripps Pier in California. After over four years of weekly sampling, we discovered seasonal patterns in mercury levels influenced by rainfall, wave activity, and biological processes like phytoplankton growth. By studying upwelled water masses, we found that DMHg breaks down in surface waters and serves as a major source of monomethylmercury in the California Current System. This challenges prior assumptions about the sources of monomethylmercury in upwelling regions and highlights DMHg’s critical role in mercury cycling.
Broader Impacts. Mercury pollution poses significant risks to human health and marine ecosystems through its conversion into monomethylmercury, the neurotoxic form that accumulates in fish and enters the food chain. Human activities have disrupted the global mercury cycle, leading to increased monomethylmercury levels in seafood. International efforts aim to reduce mercury pollution, but a deeper understanding of the mercury cycle is essential to assess the effectiveness of these actions. This project identified a previously underestimated source of monomethylmercury in regions where it bioaccumulates in marine food webs. The findings provide essential insights for environmental monitoring and policy development, particularly in areas where mercury pollution poses significant risks. The project also supported the professional development of graduate students, contributing to three published manuscripts and several in progress. Students presented their findings at conferences, trained peers in advanced sampling techniques, and gained valuable research experience that will shape their careers.
This project expanded our knowledge of DMHg in marine systems, developed tools to improve mercury research, and supported the training of future environmental scientists. These findings will inform research and policies aimed at mitigating mercury’s harmful effects on ecosystems and human health.
Last Modified: 01/13/2025
Modified by: Amina B Schartup
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