CENOZOIC DEEP-SEA CIRCULATION: EVIDENCE FROM DEEP- SEA BENTHIC FORAMINIFERA
CENOZOIC DEEP-SEA CIRCULATION: EVIDENCE FROM DEEP- SEA BENTHIC FORAMINIFERA
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新生代深海环流：来自深海底栖有孔虫的证据
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发表时间：
2013
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通讯作者：
Ellen Thomas
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作者：
Ellen Thomas
深海底栖有孔虫动物群反映了深海环境，其特征是由深水环流模式、深水源区表层水的理化参数和上覆表层水初级生产力的养分流入的相互作用决定的。在新生代序列中可以识别深海底栖有孔虫组合的三个更替期：（1）在古新世晚期快速（<10 4 年）全球灭绝，随后迁移和多样化； (2) 中始新世晚期到渐新世早期的逐渐更替，其特征是多样性下降，Nuttallides truempyi 的相对丰度减少，随后灭绝，以及下深海到上深海带的 Bulimina 物种相对丰度减少或消失； (3)早中新世晚期逐渐更替，其特征是单系列物种从深海下游到深海的相对丰度减少或消失，miliolid物种迁移到这些地区，以及Cibicidoides wuellerstorfi的进化。古新世末期深海底栖有孔虫的快速大规模灭绝（35-50%的物种）与底栖和浮游有孔虫的氧和碳同位素比率短暂下降1-2%同时发生，叠加在长期变化之上。这次灭绝可能是由于主要的深水地层从高纬度地区向低纬度地区的转变造成的。这种转变将改变中层水域到深层水域的温度和氧气含量，但它也会通过改变营养丰富的水域上升到地表从而改变高生产力地区的全球模式来改变当地的营养输入。动物证据表明，这种“逆转”的海洋环流模式持续的时间不会超过始新世早期，也可能不会超过大约50万年。两个逐渐的底栖动物区系变化时期在时间上重叠，在最早的渐新世和中中新世，有两个相对快速（大约105年）的底栖有孔虫氧同位素值向较重的转变。动物区系的变化在同位素变化之前就开始了，而且更加渐进。动物区系的变化可能反映了深水地层源区地表水的物理化学特征逐渐变化的时期（例如温度下降）以及海洋生产力的变化。氧同位素值的快速变化并不直接反映在底栖有孔虫组合的变化中，并且可能至少部分地代表陆地上冰量的快速积累，这一过程无法反映在底栖有孔虫动物群中。
Deep-sea benthic foraminiferal faunas reflect the deep oceanic environment, the character of which is determined by interaction of deepwater circulation patterns, physicochemical parameters of the surface waters in the deepwater source areas, and nutrient influx from primary productivity in overlying surface waters. Three periods of turnover in deep-sea benthic foraminiferal assemblages can be recognized in Cenozoic sequences: (1) rapid (<10 4 yr), global extinction in the latest Paleocene, followed by migration and diversification; (2) gradual turnover in the late middle Eocene through early Oligocene, characterized by a decrease in diversity, a decrease in relative abundance of Nuttallides truempyi followed by its extinction, and a decreasing relative abundance or disappearance of Bulimina species in the lower bathyal to upper abyssal zones; and (3) gradual turnover in the late early through middle Miocene, characterized by the decrease in relative abundance or disappearance of uniserial species from the lower bathyal to abyssal reaches, the migration of miliolid species into these regions, and the evolution of Cibicidoides wuellerstorfi. The rapid mass extinction (35-50% of species) of deep-sea benthic foraminifera in the latest Paleocene was coeval with a transient 1-2%o decrease in oxygen and carbon isotope ratios in benthic as well as planktonic foraminifera, superimposed on longer-term changes. The extinction could have resulted from a shift in dominant deepwater formation from high to low latitudes. Such a shift would change temperature and oxygen content of the intermediate to deep waters, but it would also change local nutrient input by changing global patterns of upwelling of nutrient-rich waters to the surface and thus of high-productivity areas. Faunal evidence suggests that this "reversed" pattern of oceanic circulation persisted no longer than the early Eocene, and possibly not more than about half a million years. The two periods of gradual benthic faunal changes overlap in time with two relatively rapid (of the order of 105 years) shifts toward heavier oxygen isotopic values of benthic foraminifera, in the earliest Oligocene and middle Miocene. Faunal changes started before the isotopic changes and were more gradual. The faunal changes might reflect periods of gradual change in the physicochemical character of surface waters in the source areas of deepwater formation (e.g., decrease in temperature), as well as changes in oceanic productivity. The more rapid changes in oxygen isotopic values are not directly reflected in benthic foraminiferal assemblage changes and might represent, at least in part, a rapid buildup of ice volume on land, a process that cannot be reflected in the benthic foraminifera faunas.