1. Examining the biogeochemistry behind the organic rich sediments of Guaymas Basin, Gulf of California
Rebecca S. Robinson, Graduate School of Oceanography
University of Rhode Island, Narragansett, RI
Nitrogen (N) is an essential nutrient. High productivity systems lose N from their bottom waters through denitrification in response to the depletion of oxygen associated with the oxidation of sinking organic matter. N losses may be countered through nitrogen fixation, the formation of bioavailable-N from atmospheric N2 by cyanobacteria. This study aims to test the utility of novel N isotopic tools for evaluating the significance of N- fixation in high productivity settings such as the Guaymas Basin.
Preliminary Findings
• Both sub-annual and decadal scale variability is apparent in the biogenic opal and N isotope data from Guaymas sediments.
Across the annual cycle, opal-rich layers tend to record a lower bulk sediment 15N.
Diatom bound 15N of the larger diatoms (≥63µm) is
~4‰ lower than of the fine fraction (<63µm).
The isotopic composition of N bound within fossil diatoms reflects the 15N of the source nitrogen.