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海洋纹层硅藻席古海洋学与生物地球化学研究进展
熊志方1,2,3, 李铁刚2,3
1.中国科学院海洋研究所 青岛 266071;2.国家海洋局第一海洋研究所 海洋沉积与环境地质重点实验室 青岛 266061;3.青岛海洋科学与技术国家实验室 海洋地质过程与环境功能实验室 青岛 266061
摘要:
海洋大型硅藻的勃发及其在海底的纹层硅藻席沉积代表大规模的有机碳和生物硅输出通量,该生物堆积事件或过程对海洋酸化和全球变暖产生负反馈,因而在气候变化中的地位不容小觑。本文在融入作者研究成果的基础上总结了国内外关于海洋纹层硅藻席的研究现状,认为大型硅藻勃发不能直接和上涌活动相关联,在热带海区一般与成层化相关,在亚热带海区总体上与锋面作用相关。大型硅藻勃发时,表层水不一定贫养,也可以是富养的,也不总是需要借助浮力下沉到营养跃层吸收营养物,可直接吸收海洋表层中的营养物(如风尘溶解来源的硅酸)。大型硅藻通过高的初级生产力吸收大气中的CO2,尔后在海洋深部降解形成的CO2在海洋成层化条件下以巨大“呼吸CO2库”得以封存,代表促使冰期大气pCO2降低的一种重要机制。海洋纹层硅藻席的保存环境由多种因素制约,可以是氧化的也可以是亚氧化的,因而对用纹层沉积物来指示缺氧底层水条件应持谨慎态度。另外,提出了解释大型硅藻勃发和硅藻席形成机制的新模式“风尘触发硅藻席沉积”,极大地促进了硅藻席沉积成因谜团的解决。最后,指出了目前海洋纹层硅藻席研究中存在的问题并阐述了未来可以开展的研究方向。
关键词:  大型硅藻  纹层沉积物  浮力策略  生产力  碳循环
DOI:10.11693/hyhz20170900225
分类号:P736.2+4
基金项目:国家自然科学基金面上项目,41576051号;中国科学院战略性先导科技专项(A类),XDA11030104号;国家自然科学基金重点项目,41230959号。
MARINE LAMINATED DIATOM MATS IN PALAEOCEANOGRAPHY AND BIOGEOCHEMISTRY: RETROSPECTIVE AND PROSPECTIVE
XIONG Zhi-Fang1,2,3, LI Tie-Gang2,3
1.Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;2.Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China;3.Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China
Abstract:
The blooms of giant diatoms and their deposits as laminated diatom mats (LDMs) at seafloor represent mass export fluxes of organic carbon and biogenic silicon, potentially acting as a negative feedback to ocean acidification and global warming and consequently playing a key role in climate changes. We review the progress on the study of marine LDMs, with an emphasis on our relevant research outcomes, in paleoceanography and biogeochemistry. The occurrences of giant diatoms cannot be seen as an indicator of upwelling. Their mass accumulations in tropical ocean sediments are generally related to strong oceanic stratification, while their oozes in subtropical marine sediments are mainly associated with frontal zones. Surface water is not always oligotrophic and also eutrophic when giant diatoms blooming. The buoyancy regulation with extraction of nutrients from below the nutricline is not the sole nutrient utilization pathway for giant diatoms. Giant diatoms can also utilize silicic acid generated through dissolution of eolian dust in surface water. The organic carbon is generated by the absorption of atmospheric CO2 by high primary production of giant diatoms, and then degraded into respired CO2 in deep ocean. The respired CO2 is sequestrated in deep ocean with the form of a deeper respired carbon pool under ocean stratification condition, representing an important force on atmospheric CO2 drawdown during the glaciation. Marine LDMs can accumulate in oxic and suboxic conditions, indicating that controls on the formation of laminated sediments are more complicated and varied than previously thought. Thus, caution needs to be taken in routinely correlating preservation of sedimentary lamination with anoxic bottom water conditions. The “eolian-silicon-induced blooms” model represents an important new addition to mechanisms of formation of marine LDMs. Finally, some existent problems and prospects in the field of marine LDMs are put forward.
Key words:  giant diatoms  laminated sediments  buoyancy strategy  productivity  carbon cycle
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