| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | September 7, 2017 |
| Latest Amendment Date: | August 1, 2019 |
| Award Number: | 1736677 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Henrietta Edmonds
hedmonds@nsf.gov (703)292-7427 OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | November 1, 2017 |
| End Date: | October 31, 2022 (Estimated) |
| Total Intended Award Amount: | $389,400.00 |
| Total Awarded Amount to Date: | $389,400.00 |
| Funds Obligated to Date: |
FY 2018 = $185,758.00 FY 2019 = $181,868.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
2221 UNIVERSITY AVE SE STE 100 MINNEAPOLIS MN US 55414-3074 (612)624-5599 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
310 Pillsbury Dr Se Minneapolis MN US 55455-0231 |
| 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): | Chemical Oceanography |
| Primary Program Source: |
01001819DB NSF RESEARCH & RELATED ACTIVIT 01001920DB 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
The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. Many trace elements are essential for life and their extremely low concentrations in seawater are thought to limit biological productivity (fertility) throughout much of the ocean. This limitation, in turn, partially constrains the level of fisheries that can be supported by marine ecosystems as well as the ocean's capacity to absorb carbon dioxide from the atmosphere. Whereas the importance of these trace-element micronutrients is well established, many basic features of their ocean distribution remain unknown. Measurements of other elements and isotopes can be used to understand the processes that influence the distributions of the micronutrient elements. Two naturally-occurring radioactive isotopes that are particularly important in this regard are thorium-230 and protactinium-231, which have been designated as key parameters to be measured as part of GEOTRACES. This project will focus on the measurement of these two isotopes in order to provide critical information about the processes that supply iron to the Pacific Ocean, as well as the rates of those processes. The project will support an early career investigator, a postdoctoral researcher, and students at the undergraduate and graduate levels.
Samples of seawater and of suspended particulate material will be collected along a north-south transect between Alaska and Tahiti to examine the processes that supply and remove trace elements. These samples will be analyzed for naturally-occurring radionuclides thorium-232, thorium-230 and protactinium-231. Aerosol samples and sediments collected along the transect will be analyzed as well. In collaboration with other investigators involved in the expedition, this project will:
1) Interpret the distributions of thorium-232 and thorium-230 to quantify the supply of iron and other trace elements delivered by dust as well as the trace elements supplied by chemical reactions in volcanic sediments along the Alaskan margin,
2) Determine the sinking flux of major particulate phases and of particulate trace elements throughout the water column to quantify their rate of removal from the ocean, and
3) Compare the rate of trace element removal among contrasting environmental regimes to be encountered along the Alaska to Tahiti transect to identify the key physical, chemical and biological factors, such as dust supply and biological productivity, that regulate the rate of trace element removal from the ocean.
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.
In this study we collected seawater samples in a transect across a broad swath of the Pacific Ocean, from the surface to the seafloor. Samples were filtered so that each seawater sample was divided into water that was truly dissolved, the large particles (>55 micrometers) and the small particles (1 to 55 micrometers). We then measured extremely rare forms of the elements thorium and protactinium in these different portions of the collected waters. Notably, we were able to measure the extremely low levels of these rare forms of these elements in the large particles. The Minnesota laboratory is currently the only laboratory in the world that makes these extremely sensitive measurements. These measurements in turn allow us to more fully characterize the processes discussed below. We and our collaborators have used these measurements to calculate the flux of airborne dust (from sites in Asia), the effects of ocean ridge hotsprings on the chemistry of that portion of the ocean, and the flux of carbon-bearing particles from the surface ocean to the seafloor.
All of these calculations are part of the intellect merit of the project, that is the main scientific conclusions of our work.
In terms of the broader impacts of our work, that is the ramifications of our work beyond the specific scientific findings, the latter finding is perhaps the most important in this regard. Knowledge of the flux of carbon to the deep ocean is critical to our understanding of the carbon cycle within the ocean and atmosphere, which, of course, involves carbon dioxide in the atmosphere, which in turn is important as carbon dioxide levels affect the earth's climate.
Last Modified: 06/24/2023
Modified by: R. Lawrence Edwards
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