2023 130 ENV

Investigating the Role of Marine Sediments as Sources of 14C-depleted Dissolved Organic Carbon in the Deep Ocean

By: Chelsea Allen

Departments: Biology, Chemistry & Biochemistry

Faculty Advisors: Dr. Tomoko Komada, Dr. William Cochlan, Dr. José De La Torre

It is widely accepted that marine sediments are sources of dissolved organic carbon (DOC) to the water column. However, the sources of 14C-depleted, refractory DOC to the deep ocean, is unknown. While it has been proposed that sediments are sources of refractory DOC to the water column, the fate of pore water DOC after exportation from the sediment remains unclear. To address this, we conducted a year-long, laboratory-based experiment in which pore water, harvested from anoxic marine sediment, was incubated under oxic conditions with seawater containing endemic microbes. We monitored ∆14C-DOC values, DOC concentration and cell density to determine what roles indigenous microbes play in the accumulation of refractory DOC in the deep ocean. Results show that flasks with higher cell densities had greater decreases in DOC concentration and smaller changes in ∆14C-DOC compared to flasks with lower cell densities. Solid-phase extracted ∆14C-DOC (SPE-DOC), which tends to be enriched in more refractory portions of DOC, showed similar ∆14C values across all flasks. Moreover, the concentration of SPE-DOC increased with time, suggesting higher relative concentration of refractory DOC with increased exposure to microbes. These findings are consistent with the hypothesis that microbial activity plays a role in the accumulation of refractory DOC in the ocean.