https://doi.org/10.14379/iodp.sp.385.2018

International Ocean Discovery Program
Expedition 385 Scientific Prospectus

Guaymas Basin Tectonics and Biosphere: feedbacks between continental rifting, magmatism, sedimentation, thermal alteration of organic matter, and microbial activity¹

Published November 2018

Abstract

The Guaymas Basin in the Gulf of California is a young marginal rift basin characterized by active seafloor spreading and rapid deposition of organic-rich sediments from highly productive overlying waters. The high sedimentation rates in combination with an active spreading system produce distinct oceanic crust where the shallowest magmatic emplacement occurs as igneous intrusion into overlying sediments. The intrusion of magma into organic-rich sediments creates a dynamic environment where tightly linked physical, chemical, and biological processes regulate the cycling of sedimentary carbon and other elements, not only in a narrow hydrothermal zone at the spreading center but also in widely distributed off-axis venting. Heat from magmatic sills thermally alters organic-rich sediments, releasing CO₂, CH₄, petroleum, and other alteration products. This heat also drives advective flow, which distributes these alteration products in the subsurface and may also release them to the water column. Within the sediment column, the thermal and chemical gradients created by this process represent environments rich in chemical energy that support microbial communities at and below the seafloor. These communities may play a critical role in chemical transformations that influence the stability and transport of carbon in crustal biospheres. Collectively, these processes have profound implications for the exchange of heat and mass between the lithosphere and overlying water column and may determine the long-term fate of carbon accumulation in organic-rich sediments.

The fate of carbon deposited in Guaymas Basin, throughout the Gulf of California, and more broadly within similar marginal seas throughout the world, depends on the relative efficiencies of interacting physical, chemical, and microbial processes, some working to sequester carbon and others working to release carbon back to the ocean and the atmosphere. Drill core samples from Expedition 385 to Guaymas Basin will enable us to study these processes, their interactions, and their ultimate effects on carbon cycling. Samples obtained from scientific drilling are crucial to these goals, which include

• Quantifying the sedimentary and elemental inputs to the system through time and their variation with oceanographic and climatic conditions;
• Sampling igneous sills and the surrounding sediments to determine the products and efficiency of alteration and key hydrologic factors such as sediment type, faulting, and permeability evolution; and
• Studying subsurface microbial communities hosted by alteration products to determine their efficiency at capturing carbon-bearing alteration products and to further our understanding of the conditions that limit life in the deep biosphere.

¹Teske, A., Lizarralde, D., and Höfig, T.W., 2018. Expedition 385 Scientific Prospectus: Guaymas Basin Tectonics and Biosphere. International Ocean Discovery Program. https://doi.org/​10.14379/​iodp.sp.385.2018

This work is distributed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license.