美国西北大学Jones Matthew M课题组在研究中取得进展。他们报道了由大规模火山活动引发的白垩纪中期海洋酸化的突然发生。这一研究成果发表在2023年1月19日出版的国际学术期刊《自然—地球科学》上。
课题组报告了国际海洋发现计划在澳大利亚西南海域钻探的两个地点，这些地点以缺乏碳酸盐矿物的地层间隔的形式，展示了受抑制的远洋碳酸盐沉积的明确证据，记录了事件期间的海洋酸化。然后，研究组将大块沉积物中锇同位素的组成与火山活动开始时，浅滩中约600kyr 海相方解石补偿深度的延长联系起来。
在高产区域，异养呼吸的增加增加了水体中的二氧化碳，生物地球化学反馈延长了海洋pH值的下降时间。白垩纪中期海相地层记录的汇编揭示了，在同一时期，全球大陆坡地区的沉积碳酸盐含量下降。因此，研究认为海洋碳酸盐化学的变化是地质历史上许多大火成岩省火山爆发期间二氧化碳快速排放的主要生态压力和重要后果。
据悉，白垩纪中期的大型火成岩省火山活动引发了大约9450万年前全球范围内海洋氧水平下降的事件，即海洋缺氧事件2。有人假设，火山二氧化碳在地质上的快速脱气改变了海水碳酸盐的化学性质，影响了海洋生态系统、地球化学循环和沉积。
附：英文原文
Title: Abrupt episode of mid-Cretaceous ocean acidification triggered by massive volcanism
Author: Jones, Matthew M., Sageman, Bradley B., Selby, David, Jacobson, Andrew D., Batenburg, Sietske J., Riquier, Laurent, MacLeod, Kenneth G., Huber, Brian T., Bogus, Kara A., Tejada, Maria Luisa G., Kuroda, Junichiro, Hobbs, Richard W.
Issue&Volume: 2023-01-19
Abstract: Large-igneous-province volcanic activity during the mid-Cretaceous triggered a global-scale episode of reduced marine oxygen levels known as Oceanic Anoxic Event 2 approximately 94.5 million years ago. It has been hypothesized that this geologically rapid degassing of volcanic carbon dioxide altered seawater carbonate chemistry, affecting marine ecosystems, geochemical cycles and sedimentation. Here we report on two sites drilled by the International Ocean Discovery Program offshore of southwest Australia that exhibit clear evidence for suppressed pelagic carbonate sedimentation in the form of a stratigraphic interval barren of carbonate minerals, recording ocean acidification during the event. We then use the osmium isotopic composition of bulk sediments to directly link this protracted ~600kyr shoaling of the marine calcite compensation depth to the onset of volcanic activity. This decrease in marine pH was prolonged by biogeochemical feedbacks in highly productive regions where elevated heterotrophic respiration added carbon dioxide to the water column. A compilation of mid-Cretaceous marine stratigraphic records reveals a contemporaneous decrease of sedimentary carbonate content at continental slope sites globally. Thus, we contend that changes in marine carbonate chemistry are a primary ecological stress and important consequence of rapid emission of carbon dioxide during many large-igneous-province eruptions in the geologic past.
DOI: 10.1038/s41561-022-01115-w
Source: https://www.nature.com/articles/s41561-022-01115-w