Experimentally capturing microbial drivers of POM chemical transformations at BATS

The sinking of particulate organic matter (POM) acts as the primary pathway of the biological carbon pump. However, only a fraction of POM that exits the upper euphotic reaches the base of the mesopelagic due to a variety of food web processes that remineralize, transform, and solubilize particles. Systematic changes in POM isotopic and carbohydrate composition, as well as particle-associated prokaryotes, have been resolved over depth at the Bermuda Atlantic Time-series Study site (BATS). However, both photosynthetic and heterotrophic processes can affect POM composition, making it difficult to differentiate factors driving transformation over depth.  Here we aimed to experimentally capture the transformation of naturally occurring POM under heterotrophic control in the euphotic and upper twilight zone to better constrain the relative role microbes play in POM transformation. We collected naturally occurring POM and resuspended it in unfiltered water from depths in the euphotic and twilight zone at BATS. We then monitored chemical and biological transformations within POM over 6-day dark incubations. We observed transformations of POM carbohydrate composition and microbial communities over time that were remarkably similar to those observed across depth in previous in situ measurements. Additionally, the particle-associated prokaryotic taxa that proliferated during the incubation matched those found on naturally occurring mesopelagic particles at BATS. Our results directly tie naturally occurring particle-associated prokaryotes to observed transformations in POM.

Presentation Preference: Oral

Primary Presenter: Jacqueline Comstock, UC Santa Barbara (jcomstock@ucsb.edu)

Authors:

Lillian Henderson, Department of Ocean Sciences, Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami, Miami, FL, USA  (lillianhenderson05@gmail.com)

Chance English, Marine Science Institute, Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106, US  (cje@ucsb.edu)

Holger Buchholz, Department of Microbiology, Oregon State University  (Buchholh@oregonstate.edu)

Hilary Close, Department of Ocean Sciences, Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami,  (hclose@miami.edu)

Craig Carlson, Department of Ecology, Evolution and Marine Biology, Marine Science Institute, University of California, Santa Barbara, CA, USA  (craig_carlson@ucsb.edu)