ANALYSIS OF ORGANIC CARBON AND N-ALKANES IN THE GUAYMAS BASIN

The Guaymas Basin is tectonically active with sediment enriched in organic matter due to extreme hydrothermal-heating, producing petroleum-like compounds, like n-alkanes. The sediment is highly heterogeneous and ideal for studying organic carbon (OC) and n-alkanes and their interactions with microbial communities. In this study, four shallow sediment cores (<20 cm) were collected across three sites in the Guaymas Basin area, including Sonora Margin, Cathedral Hill, and Tay Mpaan. We analyzed OC content and its del¹³C percent, and concentrations of C₉-C₃₉ n-alkanes in the sediment samples. Our results showed that the Carbon Preference Index (CPI), derived from the n-alkane data, was close to 1.0 in these sediment samples, suggesting the key contribution of pyrolytic processes in modifying or transforming the sedimentary organic matter. There was an inverse relationship between del¹³C and OC content among the surveyed sites, with the most pronounced correlation found in the Sonora Margin depth profile. The Sonora Margin samples generally had depleted del¹³C values of OC (about -40 ‰) compared to the other sites (-25.7 to -21.5‰), suggesting a contribution by methanotrophs to the organic matter in this location. Furthermore, the high concentrations of short-chain n-alkanes (C₁₃-C₁₆) in some cores may have resulted from active microbial degradation. Ongoing metagenomic analyses targeting the microbial community and rate measurements, such as sulfate reduction, will provide more information on the interactions between the microbial community and sedimentary organic matter.

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Primary Presenter: Kylee Hutchinson, UT Marine Science Institute (khutchi585@gmail.com)

Authors:

Kylee Hutchinson, UT Marine Science Institute  (khutchi585@gmail.com)

Kaijun Lu, UT Marine Science Institute  (kaijun.lu@utexas.edu)

Brett Baker, UT Austin, Department of Marine Science, Department of Integrative Biology  (Brett_baker@austin.utexas.edu)

Samantha Joye, University of Georgia, Marine Science Department  (mjoye@uga.edu)

Zhanfei Liu, UT Marine Science Institute  (zhanfei.liu@utexas.edu)