| NSF Org: |
OPP Office of Polar Programs (OPP) |
| Recipient: |
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| Initial Amendment Date: | July 27, 2015 |
| Latest Amendment Date: | March 6, 2017 |
| Award Number: | 1504307 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Marc Stieglitz
mstiegli@nsf.gov (703)292-4354 OPP Office of Polar Programs (OPP) GEO Directorate for Geosciences |
| Start Date: | December 1, 2015 |
| End Date: | November 30, 2018 (Estimated) |
| Total Intended Award Amount: | $405,188.00 |
| Total Awarded Amount to Date: | $477,988.00 |
| Funds Obligated to Date: |
FY 2017 = $72,800.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
1375 GREATE RD GLOUCESTER POINT VA US 23062-2026 (804)684-7000 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
P.O. Box 1346 Gloucester Point VA US 23062-1346 |
| 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): | ANS-Arctic Natural Sciences |
| 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): | 47.078 |
ABSTRACT
The extent of summer Arctic sea ice loss is increasing and now occurs earlier in the year. As a result, it is predicted that the rate of growth of phytoplankton, the base of the marine food web that sustains subsistence marine harvests by native populations, will increase within the Arctic seas. The limited amount of available nitrogen, a required nutrient for phytoplankton, eventually will restrict the level of growth. Nitrogen gas dissolved in the ocean can be converted to a form readily utilizable by phytoplankton, but this has been considered primarily a warm-water process. The principal investigators of this project recently have observed this process in the Arctic Ocean, but there is so little data that its extent remains highly speculative. If it is widespread, it will change the way we think about future scenarios for the changing Arctic marine ecosystem, subsistence fishing, and, potentially, commercial fishing in the Arctic. The project will also contribute to workforce development. The principal investigator is an early-career, female scientist. She will use the project as a mechanism to entrain an undergraduate student into research. She will also use the project to sustain an existing educational collaboration between the Virginia Institute of Marine Sciences and Hampton University, a historically black university.
It is hypothesized that microorganisms capable of fixing N2 (diazotrophs) are present in the Chukchi and Beaufort Seas, that they produce measurable rates of N2 fixation in near shore and offshore Arctic marine waters and that diazotroph community composition will differ between coastal sites, which are influenced by terrestrial inputs, versus open water sites. The Chukchi and Beaufort Seas will be sampled during a cruise in late summer 2016, when hydrographic and nutrient conditions are likely to favor diazotrophic populations. The impact that N2 fixation will have on Arctic ecosystems is dependent on its rate, spatial extent and the conditions that favor it. As a consequence, on each cruise the PIs propose to determine diazotroph community composition, examine their distributions based on the presence of the nitrogenase gene (nifH), measure rates of primary productivity and uptake of inorganic and organic N and C substrates using 15N and 13C tracer techniques, and to compare these to hydrographic, nutrient, and overall microbial community composition profiles made along cruise transects. The proposed work will determine the extent of active N2 fixation within the region in the context of other key biogeochemical and microbial community parameters.
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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.
Nitrogen fixation is the source of all biologically usable nitrogen on earth. In the ocean, specialized microorganisms take nitrogen gas from the atmosphere and convert it into forms of nitrogen that other organisms use to grow. In the Arctic, the limited amount of available nitrogen, an essential nutrient for phytoplankton and all life on earth, will eventually limit the level of growth, which will then affect the organisms preying on them and so on up the Arctic food chain. Nitrogen fixation helps to prevent systems from running out of nitrogen. Much of what we know about what conditions promote and inhibit nitrogen fixation in marine systems comes from studies in temperate and tropical waters. Until 2012, many scientists did not think that nitrogen fixation could even occur in the Arctic Ocean. As a result of this recent discovery, scientist are still learning about the extent and importance of nitrogen fixation in the Arctic and its role cold ocean productivity now and in the future.
Our research investigates the extent of nitrogen fixation in the coastal Alaskan Arctic and compares the rate of nitrogen fixation to uptake (use) rates of other nitrogen compounds including ammonium, nitrate, urea and amino acids. Samples were collected over two consecutive summers in 2016 and 2017. The effort encompassed coastal regions in the Bering, Chukchi and Beaufort Seas with a specific interest in the areas of high productivity surrounding the Hanna Shoal region of the Chukchi Sea. In general, phytoplankton (algae) abundance (as Chlorophyll a) was lower in the Beaufort than in the Chukchi Sea, which is typical for the region. Inorganic nutrient concentrations (ammonium, nitrate, nitrite and phosphate) were generally low after already being depleted in the system by algal growth earlier in the season. Nitrogen uptake rates, how fast a nitrogen sources is used, were higher in the Beaufort Sea than in the Chukchi Sea. Of the nitrogen sources assessed (ammonium, nitrate, urea, amino acids and nitrogen fixation, ammonium had the highest specific uptake rates generally followed by urea, nitrate, amino acids and nitrogen fixation in that order.
Nitrogen fixation was not detected at all sites or depths but was detected in each the Bering, Chukchi and Beaufort Seas indicating that while not ubiquitous in the Arctic, nitrogen fixation is occurring in each region of the Alaskan Arctic Ocean. Nitrogen fixation was the highest in the Bering Sea where an endosymbiont, uncultured cyanobacteria (UCYN-A) was confirmed, using high-resolution nanoscale secondary ion mass spectrometry, as the main nitrogen fixer in that system. The rate of nitrogen fixation was far lower than other substrates (ammonium, nitrate, urea and amino acids) indicating that while it is present it was likely not the dominant source of nitrogen supporting late summer productivity in the region. The degradation of organic matter and the release of ammonium from degradation was likely the most important process during that time for many of our sample sites.
Our study serves as the largest and most complete assessment of nitrogen fixation in the Alaskan Arctic to date. This research provides a critical baseline for a process that is new to this system or has been present but remained undetected. While nitrogen fixation was not the most critical nitrogen source in the Arctic in late summer, its presence means that there is potential of fixation rates to change in the future and our study will serve as benchmark for these future comparisons.
Last Modified: 10/07/2020
Modified by: Rachel E Sipler
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