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Miocene Environmental Variability at the Antarctic Margin: Marine Productivity Changes Indicated by Biogenic Components in the ANDRILL Core AND‐2A, Ross Sea, Antarctica.

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Citation:
Kuhn, G. , Hoffmann, S. and von Eynatten, H. (2011): Miocene Environmental Variability at the Antarctic Margin: Marine Productivity Changes Indicated by Biogenic Components in the ANDRILL Core AND‐2A, Ross Sea, Antarctica. , 11th International Symposium of Antarctic Earth Sciences (ISAES), Edinburgh, July 2011 - unspecified .
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Abstract:

The content of biogenic opal, organic carbon (TOC) and inorganic carbon (TIC) in glaciomarine sediments could be an indicator for bio‐productivity and climate related signals in the sediment. Within the international Antarctic Geological Drilling Program (ANDRILL), core AND‐2A was drilled and recovered a 1138 m long core of early Miocene to Pleistocene age from the McMurdo Sound in the Ross Sea. The glaciomarine sequence is dominated by changes between glacially deposited diamictites, mud‐ and sandstones with variable amount of ice rafted clasts deposited under or in front of a floating ice shelf, and open marine deposits which are found only during the Middle Miocene Climate Optimum (MMCO). Sampling about every core meter, we analysed the contents of TOC and total carbon by burning and measuring CO2 contents with infrared cells in element analysers. TIC (Calcit, Mg‐, and Fe‐carbonates) was calculated from the difference between those two values. Biogenic opal was analysed by sequential leaching in an auto‐analyser device. Biogenic opal content has a mean of 9% (weight %). Mostly, the values vary between 0% and 20%. Peak values close to 60% were detected in the core from the Middle Miocene Climate Optimum, at 310 to 311 meters below the seafloor (mbsf). TOC is generally very low in AND‐2A glaciomarine sediment and has a mean of 0.14%. During times of less glacial and more marine influence, it has peaked up to 0.3%. Only from 283 to 293 (age: 15.9 Ma), 310 to 312 mbsf (16.0 Ma) and at 434 mbsf (16.5 Ma), values are above 0.5%. This corresponds to warmer climate phases and also to higher amounts of biogenic opal in the sediments. Both components are related to productivity in the surface water and proximity to sea‐ice or ice shelf conditions. Changing preservation conditions or reworking older material may alter the signals. The pattern of TIC concentration (mean 0.9%) is different. Carbonate skeletons and shells were found throughout the core and contribute to the productivity part of the signal, the background concentration with TIC values up to 2%. Diagenetic precipitations make up the peaks of the TIC pattern, with maxima between 2 and 9.6%. From these productivity proxies, we calculated a parameter for environmental changes for the entire core.

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