An evaluation of benthic foraminiferal U/Ca and U/Mn proxies for deep ocean carbonate chemistry and redox conditions

The deep ocean is thought to have played a crucial role in modulating atmospheric CO2 changes, and thus reconstructions of deep ocean conditions can place important constraints on the past global carbon cycle. Some previous studies suggested that foraminiferal U/Ca could be used to infer seawater ca...

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Bibliographic Details
Published in:Geochemistry, Geophysics, Geosystems
Main Authors: Chen, Pujiao, Yu, Jimin, Jin, Zhangdong
Format: Article in Journal/Newspaper
Language:English
Published: 2017
Subjects:
Science & Technology
Physical Sciences
LAST GLACIAL MAXIMUM
RICH CONTAMINANT PHASES
NORTH-ATLANTIC OCEAN
ATMOSPHERIC CO2
PLANKTONIC-FORAMINIFERA
SOUTHERN-OCEAN
BORON ISOTOPE
ICE-AGE
MG/CA PALEOTHERMOMETRY
INTERGLACIAL CHANGES
Geochemistry & Geophysics
Southern Ocean
North Atlantic
Planktonic foraminifera
Online Access:http://ir.ieecas.cn/handle/361006/5513
https://doi.org/10.1002/2016GC006730
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Summary:The deep ocean is thought to have played a crucial role in modulating atmospheric CO2 changes, and thus reconstructions of deep ocean conditions can place important constraints on the past global carbon cycle. Some previous studies suggested that foraminiferal U/Ca could be used to infer seawater carbonate chemistry changes, but others showed complications from diagenesis and temperature. A recent downcore study suggested that foraminiferal U/Mn may be used for sedimentary redoxconditions, but no core-top work has been done to investigate factors affecting U/Mn. We investigate controlling factors on U/Ca and U/Mn in two benthic foraminiferal species from 120 global core-tops and three Atlantic sediment cores. Our core-top data reveal no significant correlation between core-top benthic U/Ca and carbonate system parameters. The lack of an influence of deep-water [CO22-] on U/Ca is further supported by our downcore results. Together, our data highlight complications to use benthic U/Ca for deep-water carbonate chemistry reconstructions. Although no correlation is found between core-top U/Mn and hydrographic data, high-resolution U/Mn and U/Ca in core TNO57-21 show similar patterns to authigenic U (aU) and vary in tandem with atmospheric CO2 on millennial timescales. Changes in U/Mn, U/Ca and aU in TNO57-21 may reflect postdepositional diagenesis linked to sedimentary oxygen, which is controlled by subantarctic surface productivity and ventilation of deep South Atlantic in the past. We suggest that benthic U/Mn and U/Ca may be used as auxiliary indicators for past sedimentary redox-conditions and along with other proxies could reflect deep-water oxygenation.

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