Deep-water foraminifera of the Kerguelen Plateau: Responses to climate in the late Neogene.

摘要

During the Pliocene-Pleistocene climate oscillated between glacial and interglacial extremes. The Kerguelen Plateau, located within the southern Indian Ocean, was an important location during the late Neogene due to critical bottom water production and extreme polar conditions around Antarctica.;This research focused on using benthic foraminiferal assemblages from Ocean Drilling Program Leg 119 and 120 Sites (747A, 748B, 751A, and 744B) to interpret changing Pliocene-Pleistocene paleoclimate and paleoceanography. The stratigraphic record of hiatuses and ice-rafted debris at Kerguelen Plateau during the late Neogene was probably due to changing glacial dynamics of the East Antarctic Ice Sheet.;Pliocene Dissolution Events (PDEs) at the Southern Kerguelen Plateau (748, 751, and 744) were deciphered with low carbonate values, rare foraminiferal test abundances and low benthic foraminiferal species diversity. These PDEs were due to a shoaling of the carbonate critical depth possibly caused by oscillation of the Antarctic Polar Front, upwelling of deep waters and resulting biosiliceous productivity, and/or advection of carbonate-corrosive waters into the Circumpolar Deep Water system. Pliocene Warming Events were documented in the Kerguelen Plateau region using planktonic organisms. Higher carbonate values may be the only expression of these events preserved at the seafloor.;Benthic foraminifera at the Kerguelen Plateau offer limited biostratigraphic utility during the Pliocene-Pleistocene due to the persistent occurrence of long-ranging, cosmopolitan deep-sea assemblages. However, they are very useful for characterizing paleoenvironmental change. The major driving factors in maintaining these benthic assemblages during the late Neogene were seasonal flux of phytodetritus, reflected in the dominance of Epistominella exigua and the availability of carbonate for test construction and preservation.;Milankovitch-scale cyclicity (105 years) is evident in the biostratigraphic record of species diversity at Site 744B. Both lower and higher frequency cycles are recognized. The lower frequency cycles appear to be correlated with fluctuations in carbonate values. The higher frequency cycles are correlated with abundance of unilocular calcareous benthic foraminiferal species (in the families Lagenidae and Ellipsolagenidae). The factor(s) responsible for the higher frequency fluctuations in species abundance is currently unknown. Variations in bottom current velocities and lateral transport of the microscopic tests may be related to the cycles.