Award Abstract # 1155320
Collaborative Research: Dissolved organic carbon (DOC) transformations in deep sub-surface sediments and its role as a source of "old" DOC to the water column

NSF Org: OCE
Division Of Ocean Sciences
Recipient: FLORIDA STATE UNIVERSITY
Initial Amendment Date: March 9, 2012
Latest Amendment Date: March 9, 2012
Award Number: 1155320
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: March 15, 2012
End Date: February 29, 2016 (Estimated)
Total Intended Award Amount: $169,111.00
Total Awarded Amount to Date: $169,111.00
Funds Obligated to Date: FY 2012 = $169,111.00
History of Investigator:
  • Jeffrey Chanton (Principal Investigator)
    jchanton@fsu.edu
Recipient Sponsored Research Office: Florida State University
874 TRADITIONS WAY
TALLAHASSEE
FL  US  32306-0001
(850)644-5260
Sponsor Congressional District: 02
Primary Place of Performance: Florida State University
FL  US  32306-4320
Primary Place of Performance
Congressional District:
02
Unique Entity Identifier (UEI): JF2BLNN4PJC3
Parent UEI:
NSF Program(s): Chemical Oceanography
Primary Program Source: 01001213DB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s): 1389, EGCH
Program Element Code(s): 1670
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.050

ABSTRACT

Organic carbon (Corg) remineralization rates are typically highest near the sediment-water interface, and decrease with depth as labile substrates and strong oxidants are consumed. However, in many ocean margin sediments, at the depth interval where sulfate (SO4=) is exhausted and CH4 concentrations begin to increase (the sulfate-methane transition; SMT), SO4= reduction rates typically show strong sub-surface maxima, indicating locally-enhanced microbial activity and carbon turnover. These hot spots for SO4= reduction are generally attributed to anaerobic oxidation of CH4 by SO4=, but a number of studies have found an excess of SO4= reduction over CH4 oxidation, indicating the presence of a major additional SO4= sink in the SMT.

In this project a research team from San Francisco State University, Florida State University, and Old Dominion University will investigate the nature of this SO4= sink by combining cutting-edge porewater compositional analyses -- del-14C and del-13C of CH4, dissolved organic and inorganic carbon (DOC and DIC), and 1H-NMR on DOC -- with numerical reactive transport modeling. They will test the hypothesis that the SMT is an oxidation front for not just CH4, but also for DOC that is produced deeper in the sediment column, and transported upward into the SMT. They will also test the idea that not all of this DOC is oxidized in the SMT, and that some reaches the surface sediments, and represents a source of 14C-depleted (pre-aged) DOC to the oceans. The premise is that DOC production from Corg is enhanced in methanogenic sediments due to an uncoupling in the anaerobic food chain between terminal metabolism and fermentation reactions involved in the overall Corg remineralization process. The work will focus on two ocean margin sites, Santa Monica Basin and Santa Barbara Basin, which despite their geographic proximity, appear to have different CH4 dynamics in the deep sediments.

Intellectual Merit: This study should result in a greater understanding of the role of sub-surface sediments in the overall benthic Corg remineralization process, and in the exchange of major elements between the sea floor and the water column. It will also allow testing of the hypothesis that marine sediments are sources of 14C-depleted, recalcitrant DOC to the overlying water column, thereby addressing a problem that has perplexed chemical oceanography for several decades: what factors control the 14C signature of DOC in the deep oceans?

Broader Impacts: This work will integrate research and education in several ways. It will allow the 3 PIs to continue with their effort to incorporate their research activities into the classes they teach, which range from advanced graduate- to 100-level undergraduate courses intended for non-science majors. Second, it will directly impact the learning experiences of 2 Ph.D. and 2 M.S. candidates, and at least 2 undergraduate students who will receive training in key aspects of the proposed work, including the field, experimental and modeling components.

PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH

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Magen, C., Lapham, L.L., Pohlman, J.W., Marshall, K., Bossman, S., Casso, M. and Chanton, J.P. "A simple two-phase equilibration method for measuring dissolved methane." Limnology and Oceanography Methods , v.12 , 2014 , p.637
Komada, T. D. J Burdige; H.L. Li; C. Magen; J.P Chanton "Organic matter cycling across the sulfate-methane transition zone of the Santa Barbara Basin, California Borderland" Geochimica et Cosmochimica Acta, , v.176, , 2016 , p.259 doi:10.1016/j.gca.2015.12.022

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.

Methane is a greenhouse gas that has a global warming potential that is 45 times more powereful than carbon dioxide over a 100 year times scale.  In the ocean, methane is produced deep in the sea floor, and various transport processes move it towards the surface, towards the water column. As it is transported upwards, methane encounters sulfate, which is the second most abundant element in seawater.    Bacteria live at this interface, where methane intersects sulfate, and they essentially eat the methane and breath the sulfate.  In this sense, "food" is anything that donates electrons, and what is respired or "breathed" accepts the electrons.  This process is called anaerobic methane oxidation, and it "shields" the water column or acts as a biofilter for methane coming up from below.    The results of our study indcate that in this interfacial zone, there are other processes that use up the sulfate, interfering with this biofilter, so that the biofilter is only 55-65% effecient.   Part of this interferant is aged dissolved organic carbon which is also coming up from below and it encoutners the sulfate and is oxidized similarly to the methane.   Some 30% of this dissolve organic carbon is oxidized.   In addition to making these measureents we developed mathematical models of these processes which allow us to verify that we understand the chemistry.   These models are basically complex accounting that add the processes together to see if we can reproduce the outcome.  


Last Modified: 06/15/2016
Modified by: Jeffrey P Chanton

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