Premium
Deepwater Expansion and Enhanced Remineralization in the Eastern Equatorial Pacific During the Last Glacial Maximum
Author(s) -
Umling N. E.,
Thunell R. C.,
Bizimis M.
Publication year - 2018
Publication title -
paleoceanography and paleoclimatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.927
H-Index - 127
eISSN - 2572-4525
pISSN - 2572-4517
DOI - 10.1029/2017pa003221
Subject(s) - radiocarbon dating , last glacial maximum , oceanography , benthic zone , glacial period , geology , isotopes of carbon , authigenic , paleoceanography , carbon cycle , remineralisation , dissolved organic carbon , holocene , total organic carbon , environmental chemistry , paleontology , chemistry , sediment , ecosystem , ecology , inorganic chemistry , fluoride , biology
Abstract Published estimates of the radiocarbon content of middepth waters suggest a decrease in ventilation in multiple locations during the last glacial maximum (LGM; 24.0–18.1 ka). Reduced glacial ventilation would have allowed respired carbon to accumulate in those waters. A subsequent deglacial release of this respired carbon reservoir to the atmosphere could then account for the observed increases in atmospheric CO 2 and decline in atmospheric radiocarbon content. However, age model error and a release of 14 C‐depleted mantle carbon have also been cited as possible explanations for the observed middepth radiocarbon depletions, calling into question the deep ocean's role in storing respired carbon during the LGM. Joint measurements of benthic foraminiferal carbon isotope values (δ 13 C) and cadmium/calcium (Cd/Ca) ratios provide a method for isolating the air‐sea component of a water mass from changes in remineralization. Here we use benthic foraminiferal δ 13 C and Cd/Ca records from the eastern equatorial Pacific to constrain changes in remineralization and water‐mass mixing over the last glacial‐interglacial transition. These records are complemented with elemental measurements of the authigenic coatings of foraminifera to monitor postdepositional changes in bottom water properties. Our results suggest an increase of deep waters at midwater depths consistent with a shoaling of the boundary between the upper and lower branches of Southern Ocean overturning circulation. Additionally, our records demonstrate increased organic matter remineralization in middepth waters during the LGM, suggesting that respired carbon did accumulate in middepth waters under periods of reduced ventilation.