【科技日报】海水硫酸盐含量揭开5600万年前北极海洋加剧全球变暖谜底

Core Insights - The research reveals that subtle changes in ocean sulfate concentrations during the Paleocene-Eocene Thermal Maximum (PETM) 56 million years ago acted as a "chemical switch" that altered methane consumption, significantly impacting global climate change [1][2] Group 1: Methane Dynamics - Methane, the second-largest greenhouse gas after carbon dioxide, is primarily stored in the ocean floor as hydrates [1] - In modern oceans, approximately 90% of methane is utilized by microorganisms in sediments under anoxic conditions, using sulfate as a "fuel" to efficiently convert methane while producing alkaline substances that mitigate ocean acidification [1][4] - During the PETM, the concentration of sulfate in Arctic seawater was less than one-third of modern levels, leading to a shift in methane oxidation pathways [2][4] Group 2: Microbial Activity - A significant increase in the activity of methane-oxidizing bacteria that prefer oxygen was observed during the PETM, indicating a transition from slow combustion to rapid burning of methane [2] - The research team successfully reconstructed the methane oxidation process from 56 million years ago by detecting specific molecular traces left by ancient bacteria [2] Group 3: Carbon Cycle Implications - The study found that CO2 levels in Arctic seawater during the PETM were 200-700 ppm higher than the global average, indicating a shift from being a carbon sink to a carbon source [4] - Geological activities such as tectonic movements and volcanic eruptions directly influence ocean sulfate levels, which in turn determine methane decomposition methods [4] Group 4: Modern Relevance - The research highlights the potential for similar methane oxidation mechanisms to be reactivated due to rapid warming and freshening of modern Arctic waters, which could lead to a shift from efficient methane utilization to rapid burning [4] - This study serves as a crucial warning regarding the potential risks of greenhouse gas emissions in the context of modern Arctic climate changes [4]