Marine particles are a critical contributor to carbon export, food webs, and the sedimentary record, but uncertainties remain in the origins and composition of this material. Variations over depth in both &delta¹³C values of particulate organic carbon (POC) and ratios of POC to particulate nitrogen (PN) have previously been interpreted as a degradative signal. However, we have found that photosynthesis is responsible for relatively low &delta¹³C values in the deeper, low-light portions of the euphotic zone during stratified conditions at the Bermuda Atlantic Time-series Study site. Here, we additionally describe differences in POC:PN between the upper and lower euphotic zones in POM size fractions ranging between 0.3 to >20 µm, suggesting that variations in the biochemical composition of particulate organic matter (POM) may coincide with differences in photosynthetic &delta¹³C values. We will discuss how variations in POC:PN and the relative proportions of amino acids and carbohydrates relate to differences in heterotrophic bacterial activity and community composition over the same depths. The composition of POM may also influence the labile pool of dissolved organic matter via exudation, viral lysis, and extracellular hydrolysis. Lastly, because the lower euphotic zone is an important contributor to integrated euphotic zone POC, variations in organic matter composition over depth may affect the &delta¹³C values and chemical composition of material passed up marine food webs and exported to the deep ocean.

Primary Presenter: Lillian Henderson, University of Miami (lch39@miami.edu)

Authors:

Lillian Henderson, University of Miami  (lch39@miami.edu)

Dailen Jeng, University of Miami  (dlj73@earth.miami.edu)

Chance English, University of California, Santa Barbara  (cje@ucsb.edu)

Jacqueline Comstock, University of California, Santa Barbara  (jcomstock@ucsb.edu)

Craig Carlson, University of California, Santa Barbara  (craig_carlson@ucsb.edu)

Hilary Close, University of Miami  (hclose@miami.edu)