| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
|
| Initial Amendment Date: | July 13, 2015 |
| Latest Amendment Date: | July 13, 2015 |
| Award Number: | 1537314 |
| 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: | August 1, 2015 |
| End Date: | July 31, 2019 (Estimated) |
| Total Intended Award Amount: | $300,971.00 |
| Total Awarded Amount to Date: | $300,971.00 |
| Funds Obligated to Date: |
|
| History of Investigator: |
|
| Recipient Sponsored Research Office: |
874 TRADITIONS WAY TALLAHASSEE FL US 32306-0001 (850)644-5260 |
| Sponsor Congressional District: |
|
| Primary Place of Performance: |
FL US 32306-4166 |
| Primary Place of
Performance Congressional District: |
|
| Unique Entity Identifier (UEI): |
|
| Parent UEI: |
|
| NSF Program(s): | Chemical Oceanography |
| Primary Program Source: |
|
| Program Reference Code(s): | |
| Program Element Code(s): |
|
| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
The availability of nitrogen in the surface ocean plays a critical role regulating rates of primary productivity in the ocean, and thus through modification of the carbon cycle, nitrogen has the capacity to influence climate. The dominant source of biologically available nitrogen to the ocean is through a process known as di-nitrogen (N2) fixation, which involves the reduction of N2 gas dissolved in seawater to ammonium by microbes referred to as diazotrophs. While significant progress has been made identifying a diversity of marine diazotrophs in recent years using molecular tools, quantifying global rates of N2 fixation, and identifying which ocean basin supports the highest fluxes, has remained a vexing question. This research will quantify rates of N2 fixation as well as its importance for supporting production in the southwest Pacific Ocean. Results from this research will shed light on the sensitivities of N2 fixation (temperature, iron concentrations) as well as the extent of spatial and temporal coupling of nitrogen sources and sinks in the ocean. The work will be carried out by an early career scientist, and involve mentoring of young women, middle school girls and minorities, training of undergraduate and graduate researchers, and international collaborations.
Identifying the spatial distribution of the largest di-nitrogen (N2) fixation fluxes to the ocean remains a critical goal of chemical oceanography. The spatial distribution can inform our understanding of the environmental sensitivities of N2 fixation and the capacity for the dominant marine nitrogen (N) source and sink processes to respond to each other and thus influence the global carbon cycle and climate. In addition to temperature, two factors are at the heart of the current debate over what influences the spatial distribution of N2 fixation in the ocean: 1) the presence of adequate iron to meet the needs of N2 fixing microbes, and, 2) the absolute concentrations as well as ratios of surface ocean nitrate and phosphate concentrations that are low relative to the "Redfield" ratio, which are thought to favor N2 fixing microbes. This project will test the effects of gradients in atmospheric dust deposition on N2 fixation rates when surface waters have relatively constant but favorable nitrate to phosphate concentrations. The work will be carried out in the southwest Pacific, a region highlighted by new modeling work for its unique geochemical characteristics that are expected to favor significant N2 fixation fluxes. Nitrate+nitrite d15N as well as total dissolved nitrogen (TDN) concentration and d15N will be measured in water column samples collected on a French cruise and sediment traps were deployed to capture the sinking particulate N flux. The results will be compared with published work to evaluate which ocean regions support the largest N2 fixation fluxes.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
Note:
When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external
site maintained by the publisher. Some full text articles may not yet be available without a
charge during the embargo (administrative interval).
Some links on this page may take you to non-federal websites. Their policies may differ from
this site.
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.
The outcomes from this project are primarily a better understanding of the magnitude and spatial distribution of biological di-nitrogen (N2) fixation in the southwest Pacific Ocean. This project confirmed the hypothesis that N2 fixation supports a significant fraction of export production in the southwest Pacific Ocean (Knapp et al., 2018, Biogeosciences). This finding is significant because placing better quantitative constraints on the spatial distribution of N2 fixation in the ocean helps identify the chemical and physical sensitivities of this process in the ocean. In this case, little prior work had been done quantifying the role of N2 fixation for supporting export production in this region. However, the results from this project support the hypotheses of recent modeling work which suggests that the southwest Pacific Ocean, which is relatively warm, has favorable macro-nutrient concentrations (i.e., nitrate and phosphate), and appears to have sufficient sources of iron to surface waters, supports rates of N2 fixation comparable to or greater than those found in the tropical North Atlantic. Indeed, results from this project found that N2 fixation supported the highest fraction (>50%) of export production ever measured in the global ocean when evaluated using modern methods (Knapp et al., 2018, Biogeosciences). Consequently, this project has shifted our understanding of where the highest global rates of N2 fixation are occurring and suggests than in addition to the tropical North Atlantic, the southwest Pacific Ocean supports significant global rates of N2 fixation.
Additional outcomes from this work include evidence for low-d15N release by N2 fixing organisms in a large volume mesocosm experiment that subsequently supported export production by non-N2 fixing organisms (Knapp et al., 2016). This result was particularly exciting because it provided the first geochemical evidence for this process that has been hypothesized to occur based on biological evidence. Other work supported by this project includes participation by the PI in the Future of Chemical Oceanography (?COME ABOARD?) meeting, which produced a paper summarizing the discussions at this meeting (Fassbender et al., 2017, Marine Chemistry). Other outcomes include papers constraining nitrogen cycling in the Gulf of Mexico (Redalje et al., 2019, in the Gulf of Mexico Origin, Waters, and Biota, Vol. 5, Chemical Oceanography), the North Atlantic (Marconi et al., 2017, Global Biogeochemical Cycles) and North Pacific (Wilson et al., 2019, Science) Oceans. In particular, this project supported the rapid-response analysis of samples collected in response to a lava-induced phytoplankton bloom observed after the lava from the Kilauea eruption of 2018 entered the ocean, with the key interpretation that the nitrate supporting the phytoplankton bloom originated from upwelling and not N2 fixation (Wilson et al., 2019, Science).
Finally, additional outcomes from this work that are soon to be submitted for publication include a manuscript describing the first measurements of the isotopic composition of water column nitrate from the Gulf of Mexico (Howe et al., in preparation). This manuscript concludes that nitrate from the Mississippi and Atchafalaya River Systems is not entrained in the Loop Current, nor is it exported from the Gulf of Mexico. This finding is consistent with recent modeling work indicate >90% of riverine nutrients are retained in the near-shore region. Additionally, a paper will soon be submitted that describes methods for isolating dissolved organic nitrogen for chemical characterization using solid phase extraction (SPE) for Fourier Transform-Ion Cyclotron Resonance analysis.
The Broader Impacts from this project include that this project supported one early-career faculty member, and the sole-PI NSF grant was cited as a reason for granting the PI tenure. Additionally, this project supported one female graduate student and four undergraduates, one of whom is currently in medical school and another, who completed her undergraduate honors thesis on the isotopic composition of nitrate in the Gulf of Mexico, is applying to graduate schools in earth sciences. All datasets generated by this project have been archived at the Biological and Chemical Oceanography Data Management Office (BCO DMO). Further outreach activities supported by this award included speaking with Florida State University?s ?Women in Math, Science, and Engineering? undergraduate scholars, who toured the PI?s lab and learned about the science conducted as part of this project. The PI also visited local summer camps and K-12 classrooms in association with this project, as well as a middle school ?Sci Girls? group.
Last Modified: 10/29/2019
Modified by: Angela N Knapp
Please report errors in award information by writing to: awardsearch@nsf.gov.
