Investigating the effects of sunlight and microbes on low molecular weight compounds in the surface ocean

The amount of dissolved organic carbon in the ocean is similar to the total amount of carbon dioxide (CO2) in the atmosphere. Some of this dissolved organic carbon includes small, rapidly cycling organic molecules that are not well-understood. The production, loss, and seawater concentrations of these molecules are influenced by sunlight-driven reactions, the activity of marine life, and exchange with the atmosphere. Rapid cycling keeps the concentration of these compounds low, making them difficult to measure, while allowing them to support carbon transfer through the surface ocean. This project will use an improved analytical approach to examine how sunlight and marine microorganisms control the production and loss of formaldehyde and acetaldehyde, two small organic molecules that contribute to surface-ocean carbon cycling. This work will provide new insight into ocean biogeochemistry and ocean-atmosphere connections, which are fundamental to environmental and economic well-being. The project will also support student training and public outreach activities that connect ocean carbon-cycle research with broader science education. Marine labile dissolved organic carbon (DOC), which encompasses hundreds to thousands of low-molecular-weight (LMW) organic compounds, mediates a major fraction of carbon flux through the DOC pool. These LMW organic compounds are present at low concentrations, often in the low- to sub-nanomolar range, and are rapidly produced and consumed on timescales of hours to days. This research project focuses on the cycling of two biologically labile compounds in the surface ocean: formaldehyde and acetaldehyde. These LMW aldehydes play important roles in the photochemical transformation of marine DOC, the microbial cycling of LMW organic compounds, and air-sea exchange. Despite the importance of formaldehyde and acetaldehyde in labile DOC cycling, the biogeochemical controls on their production and loss in seawater are poorly constrained. This gap is partly due to analytical challenges, including the potential for atmospheric contamination. To address this limitation, this project uses a closed system for formaldehyde and acetaldehyde sampling and analysis that minimizes atmospheric contamination. This three-year study aims to address three questions: (Q1) Do diel variations in formaldehyde and acetaldehyde concentrations in surface ocean waters reflect a balance among photochemical production, microbial cycling, air-sea exchange, and mixing? (Q2) How important are biological processes to the cycling of formaldehyde and acetaldehyde in the surface mixed layer relative to photochemical production? (Q3) How does seasonality influence the photochemical production and microbial cycling of formaldehyde and acetaldehyde at the Bermuda Atlantic Time-series Study station? Data obtained from underway measurements, hydrographic station sampling, and incubation experiments will allow the research team to investigate changes in formaldehyde and acetaldehyde concentrations in relation to their production and removal in seawater. As an interdisciplinary effort, this research project combines tools from chemical oceanography and atmospheric measurement. The closed-system sampling and analysis method developed and applied in this study can be broadly adapted to a wide range of LMW compounds for which atmospheric contamination is an issue. 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. NSF Award ID: 2547473 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Yuting Zhu | Institution: Old Dominion University Research Foundation, NORFOLK, VA | Award Amount: $632,896 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2547473 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2547473.html