Characterization of Refractory DOC in the Deep Pacific Ocean Using Polymer Theory

Monica Orellana, University of Washington, Applied Physics Laboratory Polar Science Center, Seattle, WA, United States, Jarod Koopman, University of Washington, Applied Physics Lab Polar Science Center, Seattle, WA, United States, Sarah Bercovici, University of Oldenburg, Oldenburg, Germany and Dennis A Hansell, University of Miami, Miami, United States
DOC is a massive carbon reservoir about which we know little mechanistically. Reports suggest that an important fraction of the DOC pool (10-30%) assembles to form a nutrient-rich pool of “microgels”, thereby converting dispersed recalcitrant DOC to a particulate form more directly accessible to the microbial loop. In this study we quantify the microgel reactivity in North Pacific waters, applying a gel conceptual framework as a predictive theory. The deep waters of the region contain a large pool of refractory DOC (RDOC) while the surface waters contain higher concentrations of more labile components. The deep ocean contains the lowest DOC concentrations (35 µM), oldest radiocarbon ages (up to 6000 years old) and with lowest bioreactivity. While the paradoxical persistence of RDOC in the ocean has been explained by its chemical stability, its low concentration and biologically recalcitrant nature, especially in the deep ocean, our knowledge on the transformation and removal of this refractory material is obscured by a lack of observable mechanisms. Here, we test the hypothesis that short polymer chain polymers do not assemble into microgels and we characterize the DOC reactivity of surface and deep waters by quantifying microgel gel assembly kinetics.