| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | August 14, 2018 |
| Latest Amendment Date: | June 1, 2021 |
| Award Number: | 1829431 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Henrietta Edmonds
hedmonds@nsf.gov (703)292-7427 OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | November 1, 2018 |
| End Date: | April 30, 2023 (Estimated) |
| Total Intended Award Amount: | $350,280.00 |
| Total Awarded Amount to Date: | $378,244.00 |
| Funds Obligated to Date: |
FY 2021 = $27,964.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
266 WOODS HOLE RD WOODS HOLE MA US 02543-1535 (508)289-3542 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
266 Woods Hole Rd. Woods Hole MA US 02543-1050 |
| 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 |
| 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
Iron is one of the most abundant elements in fluids released from mid-ocean ridges, yet it has been thought to be mostly removed from seawater near to its hydrothermal vent source. Recent evidence has emerged showing this hydrothermally-derived iron can be transported great distances in the ocean, including toward the sunlit surface layer where it is an essential nutrient for phytoplankton growth. This study will use naturally-occurring radium isotopes, which are also enriched in hydrothermal fluids but are non-reactive compared to iron, as tracers of hydrothermal iron in the deep ocean. With a range of half-lives from days to centuries, radium isotopes can be used as "clocks" to measure the precise rates at which hydrothermal iron is carried by ocean currents toward the ocean interior. Such information can be incorporated into ocean models designed to determine the role of hydrothermal iron on ocean productivity, which has societal relevance due to its role in regulating the carbon dioxide concentrations of Earth's atmosphere. This project will support research opportunities for two students through the Woods Hole Partnership in Education Program, which seeks to increase diversity in ocean and environmental science by inviting college juniors and seniors to gain practical experience through a summer of classroom study and hands-on research activities.
A scientist from Woods Hole Oceanographic Institution will quantify rates of iron (Fe) transport above a major ocean spreading center to evaluate the role of hydrothermal venting in supplying this essential micronutrient to the surface ocean. Special attention will be paid to the role of low-temperature hydrothermal Fe fluxes, which are hypothesized to arrive at the seafloor in a stable form that mitigates significant removal during transport. If true, low-temperature fluids may supply a disproportionate amount of the "transportable" dissolved Fe that has not been observed in large-scale deep ocean plumes. Assessment of process rates will be accomplished through concurrent measurements of Fe concentration and speciation and the radium (Ra) "quartet" (224Ra, 223Ra, 228Ra, 226Ra) during an expedition along the southern East Pacific Rise (EPR; 15-18 degrees South). Autonomous underwater vehicle and towed-CTD surveys will be used to identify locations of low- and high-temperature discharge. At selected target areas, the investigators will test the hypotheses that low-temperature hydrothermal inputs have a distinct radium isotopic ratio fingerprint, and that the relative rate of Fe scavenging removal is lower in low-temperature sources. Given their wide ranging half-lives, Ra isotopes have the unique ability to integrate over biogeochemically-relevant time scales of Fe transport in the deep ocean. The combination of concurrent Ra isotope and total dissolved Fe measurements will allow the investigators to quantify Fe residence time for any Fe phase that is transported on large horizontal scales, as has been observed previously along the EPR. Together, Fe loss and transport from Ra measurements will lead to improvements in the predictive capabilities of ocean circulation and biogeochemistry models that assess the importance of hydrothermal Fe in supporting primary productivity and carbon drawdown in overlying surface waters.
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.
Iron (Fe) is a common element found in hot fluids coming out of the seafloor at places like mid-ocean ridges. Scientists used to think that most of this iron stayed close to these hydrothermal vents and didn't travel far in the ocean. However, new evidence suggests that some of this iron can actually travel long distances in the ocean and even reach the top layer where sunlight reaches, which is important for the growth of microscopic plants called phytoplankton.
In our research, we wanted to figure out how fast this iron moves away from a major undersea mountain range called the southern East Pacific Rise. To do this, we used naturally occuring radioactive materials called radium isotopes, which are also found in the hydrothermal fluids but don't react like iron does. We used underwater robots and measurements taken from instruments towed behind ships to locate two types of hydrothermal discharges - high and low temperature - then, we measured the levels of both iron and radium isotopes.
We found that the hot water coming out of the seafloor had slightly more radium isotopes than the normal seawater, but the cold water had a lot more of a specific radium isotope called 223-Ra. This is similar to what another study found near Hawaii, where they thought this specific radium isotope came from a process involving seawater circulating through rocks.
Our data used these measurements of radium isotopes and iron to figure out how fast the fluids are moving and how long the iron stays near the southern East Pacific Rise. This will help us improve our computer models that predict how important this hydrothermal iron is for the growth of phytoplankton and in turn their abiliyt to remove carbon dioxide from the surface of the ocean.
Last Modified: 09/26/2023
Modified by: Matthew A Charette
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