Influence Of Magmatism On Sediment Organic Matter Carbon Source In Guaymas Basin Since Middle Pleistocene

Earth is the only planet known to harbor life.Earth’s active internal dynamic processes drive multiple cycles of substances,including the carbon cycle,and the evolution of Earth’s climate and ecosystem,thereby significantly influencing the habitability of the Earth.Studying how the dynamical processes in the Earth’s interior affects the surface-earth carbon cycle is an important means to understand the changing Earth’s habitability over time.This paper aims to study the sediments since the Middle Pleistocene from the Guaymas Basin in the Gulf of California.Various geochemical proxies were measured,and comparative analyses were conducted to reconstruct change in the carbon source of the sedimentary organic matter in the Guaymas Basin under the influence of magmatic activities since middle Pleistocene.The research results help to explore the influence of the Earth’s deep dynamic process on its habitability.A total of 769 sediment samples from Site U1546 drilled during the International Ocean Discovery Program（IODP）Expedition 385 in the Guaymas Basin were selected to analyze the concentrations of carbonates（Ca CO₃%）,mercury（Hg）,total organic carbon（TOC）,total nitrogen（TN）,and measure the carbon/nitrogen ration（C/N）and stable carbon isotope composition(δ¹³C)of sediment organic matter.Combined with published calcareous nannofossil biostratigraphy,the variation history of sediment organic carbon sources in the Guaymas Basin since middle Pleistocene was revealed.The main results are as follows.1.By analyzing the positions of two calcareous nanofossil datums obtained in previous study,the first occurrent datum of Emiliania huxleyi（0.29 Ma）and the last occurrent datum of Pseudoemiliania lacunosa（0.44 Ma）,the 0–249.28 m interval was constrained to the Holocene to the middle Pleistocene（0–0.29 Ma）,and the 249–352.13 m interval to the middle Pleistocene（0.29–0.44 Ma）.Further comparison of Ca CO₃%variation with marine oxygen isotope stages（LR04）allowed to establish a high-resolution chronological framework and derive the average sedimentation rates of the two intervals（86 and 69 cm/kyr,respectively）.2.Sediment Hg concentration significantly increased during 301–241 ka interval,with high Hg/TOC values reaching a maximum of 230.This indicates that large-scale magmatic activity occurred in the Guaymas Basin during this period.3.TOC and TN show consistent variation.During the 301–241 ka interval,both TOC and TN decrease with increased C/N ratios,andδ¹³C shows a positive excursion.These changes suggests enhanced terrestrial input and increased marine primary productivity.4.The sediment organic matter in Guaymas Basin mainly originate from terrigenous input by large rivers such as Colorado River,and endogenous phytoplankton.Using the Bayesian mixture model,it is estimated that the contribution by Colorado River gradually increases over time,while the contribution of phytoplankton decreases over time.Especially since 300 ka,the contribution by the Colorado River has increased significantly.