| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | August 6, 2021 |
| Latest Amendment Date: | August 6, 2021 |
| Award Number: | 2124317 |
| 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, 2021 |
| End Date: | August 31, 2024 (Estimated) |
| Total Intended Award Amount: | $139,554.00 |
| Total Awarded Amount to Date: | $139,554.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1200 E CALIFORNIA BLVD PASADENA CA US 91125-0001 (626)395-6219 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
MC 131-24 1200 E California Blvd Pasadena CA US 91125-0600 |
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Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Chemical Oceanography |
| Primary Program Source: |
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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
Nearly all of the photosynthesis in the oceans is carried out by microscopic, single-cell ?plants? called phytoplankton. The photosynthesis by phytoplankton forms the base of the food chain, supporting almost all life in the oceans. One of the key nutrients that phytoplankton need to grow is iron, which is often in short supply in ocean surface waters and can limit the phytoplankton growth and photosynthesis rates. This project seeks to better understand the cycling of iron in the oceans, focusing on the removal of iron from the oceans by particle scavenging. Particle scavenging refers to dissolved iron sticking to large, sinking particles, which ultimately remove iron to the sediments. This modeling study will simulate iron cycling in the oceans, along with the cycling of several different metal isotopes, that are also subject to removal by particles scavenging, but do not act as nutrients for phytoplankton. This will help separate the biological influences on iron distributions, from the impacts of particle scavenging and other physical processes. The external sources of iron to the oceans coming from dust deposition, ocean sediments, river runoff, and the seafloor hydrothermal vents will also be evaluated. This work is important for understanding how climate change and human activities will modify the iron cycle and impact biogeochemistry in the future. This project will also support two graduate students and an undergraduate student researcher.
The model simulations will be evaluated and constrained with extensive comparisons to field measurements of iron and the other key variables. The GEOTRACES program has recently produced a global set of ship measurement surveys, with full depth measures of numerous isotopes and trace elements, including iron, that are ideal for evaluating the prognostic ocean model (Community Earth System Model (CESM) ocean component). The GEOTRACES datasets are also ideal for incorporation into our offline, inverse model (OCIM, CYCLOCIM) which can interpret the still sparse observations in the context of 3D circulation and biogeochemistry. The simulations of 230Th, 232Th, 231Pa, and Fe cycling will improve mechanistic understanding of particle scavenging and place stronger observational constraints on the patterns and magnitude of external lithogenic sources of trace elements to the oceans. Results and products from this study, with the ocean model component of the Community Earth System Model (CESM), will be incorporated into future versions of CESM, to improve the current ability to predict how ocean biogeochemistry and marine ecosystems will respond to climate change along a range of potential future climate trajectories.
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.
We developed a new global model to simulate the distributions of the naturally-occurring radioactive isotopes 232Th, 230Th, and 231Pa in the global ocean. Over the past 15 years, globally distributed measurements of these isotopes have been made as part of the GEOTRACES program. Our modeling efforts were aimed at synthesizing our understanding of these isotopes and using them to improve the ways the biogeochemical processes were previously being modeled. We began simulating these isotopes using the existing dissolved iron model in the Community Earth System Model (CESM). We quickly realized that improvements needed to be made to the model. Namely, we needed to add enhanced removal of elements from the surface ocean by sinking particles to the model to accurately simulate the surface distributions of 230Th and 231Pa. Second, we needed to add enhanced removal of elements at depth by resuspension of bottom sediments to accurately simulate the deep distributions of 230Th and 231Pa.
Our newly developed model accurately simulates the global distributions of thorium and protactinium isotopes. In regions where inaccuracies persisted, we have been able to identify regional improvements that must be made to the broader CESM model (e.g. changes in particle flux) necessary for accurate simulations. By applying our 230Th model to the dust-borne isotope 232Th, we have identified regions where atmospheric dust deposition, something notoriously difficult to measure in the open ocean, is underestimated in current atmospheric dust models. We are able to use our coupled 230Th-232Th simulations to create optimized, data-constrained atmospheric dust deposition fields that can be used widely for studies of marine biogeochemical cycling and its response to past and future climate change.
Last Modified: 02/07/2025
Modified by: Jess F Adkins
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