Award Abstract # 1829834
Collaborative research: Using individual amino acids N isotopes in sinking particles and surficial sediments to reconstruct euphotic zone N sources and trophic structure

NSF Org: OCE
Division Of Ocean Sciences
Recipient: UNIVERSITY OF MASSACHUSETTS DARTMOUTH
Initial Amendment Date: August 30, 2018
Latest Amendment Date: August 30, 2018
Award Number: 1829834
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, 2018
End Date: August 31, 2022 (Estimated)
Total Intended Award Amount: $164,689.00
Total Awarded Amount to Date: $164,689.00
Funds Obligated to Date: FY 2018 = $164,689.00
History of Investigator:
  • Mark Altabet (Principal Investigator)
    maltabet@umassd.edu
Recipient Sponsored Research Office: University of Massachusetts, Dartmouth
285 OLD WESTPORT RD
NORTH DARTMOUTH
MA  US  02747-2356
(508)999-8953
Sponsor Congressional District: 09
Primary Place of Performance: University of Massachusetts, Dartmouth
706 S Rodney French Blvd
New Bedfore
MA  US  02744-2300
Primary Place of Performance
Congressional District:
09
Unique Entity Identifier (UEI): PMMKPCKNN9R2
Parent UEI:
NSF Program(s): Chemical Oceanography
Primary Program Source: 01001819DB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s): 8242
Program Element Code(s): 1670
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.050

ABSTRACT

Nitrogen is a limiting nutrient over most of the surface ocean. Fixed nitrogen (N) such as nitrate controls absorption of atmospheric carbon dioxide and production of organic matter by marine plants and algae. Nitrogen availability, use patterns, and biological community structure in the surface ocean help determine the amount of organic matter passed onto higher organisms. Nitrogen availability also controls how much organic matter sinks into deep waters. This project will reconstruct past sources of nitrogen, use patterns, and trophic structures in surface waters of the Gulf of California, equatorial Pacific, and Sargasso Sea. The tool employed by the principal investigators from Texas A&M University in Corpus Christi and University of Massachusetts Dartmouth is nitrogen isotope ratios of individual amino acids. The investigators will measure isotope ratios in sinking particle samples collected by sediment traps such as those used by the Ocean Flux Program in the Sargasso Sea. This study will train graduate students in stable isotope biogeochemistry and oceanography. This project will also provide research funds for students in the McNair program. McNair students come from underrepresented and economically challenged backgrounds to pursue degrees in STEM fields at Texas A&M University Corpus Christi, a Hispanic and Minority Serving Institution. Data from this project will be made available to the public through the Biological and Chemical Oceanography-Data Management Office (www.bco-dmo.org).

There is great interest in reconstructing past climate-forced variations in nitrogen sources, their patterns of utilization, and euphotic zone community structure using compound specific N isotope ratios in amino acids liberated from preserved proteinaceous materials in sediments and coral skeletons. However, it has not yet been verified whether 1) the nitrogen isotope ratios of individual amino acids produced in the euphotic zone are transported with fidelity by sinking particles to deep-sea corals and sediments and 2) the nitrogen isotope ratios of individual amino acids liberated from sedimentary organic matter have been altered by diagenesis. Through analysis of sediment trap material collected over time, this project seeks to verify that nitrogen isotope ratios in individual amino acids reflect the 1) overall spatial contrast in N sources, utilization patterns, and trophic structures among the Gulf of California, equatorial Pacific, and Sargasso Sea and 2) temporal variations in nitrogen sources, utilization patterns, and trophic structures within both the Gulf of California and equatorial Pacific due to seasonal upwelling and/or El Nino-Southern Oscillation. This study will also test if the nitrogen isotope ratios of total hydrolysable amino acids in sedimentary organic matter from the three locations retain the unaltered nitrogen isotope patterns carried by sinking particles. This project will, for the first time, compare nitrogen stable isotope ratios in amino acids collected from sediment trap samples with surficial sediments from deep-sea oxic sites to verify whether total hydrolysable amino acids in deep-sea sediments preserve unaltered nitrogen isotope signals produced in overlying euphotic zone, which can provide insights on addressing diagenetic alteration of bulk N isotope ratios that have hindered paleo-nitrogen cycle reconstruction.

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.

PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH

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Zhang, Lin and Lee, Wing?man (Charlotte) and Kreider?Mueller, Ava and Kuhnel, Evelyn and Baca, Jesus and Ji, Chongxiao and Altabet, Mark "High?precision measurement of phenylalanine and glutamic acid ? 15 N by coupling ion?exchange chromatography and purge?and?trap continuous?flow isotope ratio mass spectrometry" Rapid Communications in Mass Spectrometry , v.35 , 2021 https://doi.org/10.1002/rcm.9085 Citation Details

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.

Amino acids are an important component of all living things and the organic matter that is derived from them.  Natural variations in their nitrogen stable isotope ratio (15N/14N; δ15N) have been used as powerful tools to reconstruct food webs as well as the source and fate of organic matter produced from them.  However, methods used to date have been expensive and time consuming as well as limited in the kinds of amino acids that could be examined.  We have developed a new and easier method for δ15N analysis of individual amino acids that extends the number of amino acids that can be analyzed as well as has the potential for determining variations in δ15N between the N atoms within an amino acid. An optimal procedure was developed for separation and collection of individual amino acids using ion chromatography and pretreatment of biological samples. Separated amino acids are then converted via nitrite to nitrous oxide for isotope analysis. The reliability and robustness of this method were verified by testing standard mixtures with known δ15N values and various samples including fish (Striped Mullet), cyanobacteria (Spirulina Pacifica), and sediments (Gulf of California). 

 To apply these new methods, sinking/suspended particles and zooplankton samples were collected at the surface, deep chlorophyll maximum (DCM), anoxic core, and lower oxycline in the Eastern Tropical North Pacific in December 2020. These samples are analyzed for the δ15N of two amino acids (phenylalanine [Phe] and glutamic acid [Glu]) to retrieve information on both the base of the food web and number of trophic steps that produced the sample material. The preliminary results from suspended particles showed a low δ15NPhe which decreased to a minimum at the deep chlorophyll maximum (DCM), suggesting changes with depth in the phytoplankton communities contributing to these particles. δ15NPhe increased with depth below the DCM toward the lower oxycline. The vertical profile of δ15NGlu exhibited a similar trend to that of δ15NPhe, yielding relatively constant trophic stepping from DCM to the lower oxycline which suggests the planktonic origin of these suspended particles. The increasing trend in both δ15NPhe and δ15NGlu with depth implies that the protein materials in suspended particles experienced similar degradation processes, probably by heterotrophic microbes. The δ15NPhe and δ15NGlu data in sinking particles and zooplankton will further help elucidate the interactions between the two particle pools and zooplankton in the anoxic core.

 


Last Modified: 01/19/2023
Modified by: Mark A Altabet

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