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Repeta, Daniel J. Granzow, Benjamin Nash Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences 2024-02-08T15:11:40Z 2024-02-08T15:11:40Z 2023-02 2024-02-01T14:00:40.503Z https://hdl.handle.net/1721.1/153470 0000-0001-5241-4254 Marine dissolved organic matter (DOM) is an actively cycling reservoir of carbon containing thousands of unique compounds. To describe the complex dynamics that govern the biological transformation and decomposition of compounds in this molecular black box, models of DOM reactivity use chemical characteristics, as well as environmental parameters, to describe trends in the turnover time of classes of DOM. In this thesis, I describe two projects that examine hypotheses regarding the turnover of two classes of DOM. In the 1st project, I test the assumption made by the size–reactivity continuum hypothesis that high molecular weight (> 1 kDa) DOM (HMWDOM) represents a diagenetic intermediate between large labile material and small recalcitrant compounds. Size-fractions of HMWDOM were collected using size-exclusion chromatography, and the changes in MW and chemical composition of the fractions were studied using diffusion-ordered spectroscopy. The size fraction carbon isotopic values were correlated with the proportion of humic substances in the fractions. Through linear modeling, the apparent radiocarbon ages of the two major components of HMWDOM were determined to be 1-3 yrs and 2-4 kyrs, respectively. Combined with the measurements of MW distribution this work demonstrates that HMWDOM is composed of two components that have contrasting decomposition pathways in the ocean. HMWDOM cannot be treated as a single DOM pool when incorporated into models of DOM diagenesis. The 2nd project in this dissertation examines the remineralization of phosphonates, compounds with a direct C-P bond, in the lower euphotic zone using a newly developed fluorescent assay, which measures the activity of carbon-phosphorus lyase. C-P lyase activity (CLA) profiles from the North Pacific Subtropical Gyre (NPSG) showed a sharp activity maximum near the deep-chlorophyll maximum (DCM). High-resolution nutrient measurements suggest that this subsurface CLA maximum is the result of a high nitrate flux at the top of the nitracline. The composition of particulate-P through the euphotic zone was also examined. While phosphonates were not detected in suspended particles, a significant amount of aminoethylphosphonate was measured in sinking material, suggesting eukaryotic material may be an important source of phosphonates to the ocean. Ph.D. Massachusetts Institute of Technology In Copyright - Educational Use Permitted Copyright retained by author(s) https://rightsstatements.org/page/InC-EDU/1.0/ Chemical Controls on the Cycling and Reactivity of Marine Dissolved Organic Matter Thesis application/pdf Doctoral Doctor of Philosophy Publication unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="226fa9f8-6193-4d76-b918-85c8ab248662"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Title>Chemical Controls on the Cycling and Reactivity of Marine Dissolved Organic Matter</Title> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>2023-02</PublicationDate> <Authors> <Author> <DisplayName>Granzow, Benjamin Nash</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>https://rightsstatements.org/page/InC-EDU/1.0/</License> <Abstract>Marine dissolved organic matter (DOM) is an actively cycling reservoir of carbon containing thousands of unique compounds. To describe the complex dynamics that govern the biological transformation and decomposition of compounds in this molecular black box, models of DOM reactivity use chemical characteristics, as well as environmental parameters, to describe trends in the turnover time of classes of DOM. In this thesis, I describe two projects that examine hypotheses regarding the turnover of two classes of DOM. In the 1st project, I test the assumption made by the size–reactivity continuum hypothesis that high molecular weight (&gt; 1 kDa) DOM (HMWDOM) represents a diagenetic intermediate between large labile material and small recalcitrant compounds. Size-fractions of HMWDOM were collected using size-exclusion chromatography, and the changes in MW and chemical composition of the fractions were studied using diffusion-ordered spectroscopy. The size fraction carbon isotopic values were correlated with the proportion of humic substances in the fractions. Through linear modeling, the apparent radiocarbon ages of the two major components of HMWDOM were determined to be 1-3 yrs and 2-4 kyrs, respectively. Combined with the measurements of MW distribution this work demonstrates that HMWDOM is composed of two components that have contrasting decomposition pathways in the ocean. HMWDOM cannot be treated as a single DOM pool when incorporated into models of DOM diagenesis. The 2nd project in this dissertation examines the remineralization of phosphonates, compounds with a direct C-P bond, in the lower euphotic zone using a newly developed fluorescent assay, which measures the activity of carbon-phosphorus lyase. C-P lyase activity (CLA) profiles from the North Pacific Subtropical Gyre (NPSG) showed a sharp activity maximum near the deep-chlorophyll maximum (DCM). High-resolution nutrient measurements suggest that this subsurface CLA maximum is the result of a high nitrate flux at the top of the nitracline. The composition of particulate-P through the euphotic zone was also examined. While phosphonates were not detected in suspended particles, a significant amount of aminoethylphosphonate was measured in sinking material, suggesting eukaryotic material may be an important source of phosphonates to the ocean.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>