Hines, Sophia K. V. and Southon, John R. and Adkins, Jess F. (2015) A high-resolution record of Southern Ocean intermediate water radiocarbon over the past 30,000 years. Earth and Planetary Science Letters, 432 . pp. 46-58. ISSN 0012-821X. http://resolver.caltech.edu/CaltechAUTHORS:20151106-150028884
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The circulation of intermediate waters plays an important role in global heat and carbon transport in the ocean and changes in their distribution are closely tied to glacial–interglacial climate change. Coupled radiocarbon and U/Th measurements on deep-sea Desmophyllum dianthus corals allow for the reconstruction of past intermediate water ventilation. We present a high-resolution time series of Antarctic Intermediate Water radiocarbon from 44 corals spanning 30 ka through the start of the Holocene, encompassing the transition into the Last Glacial Maximum (LGM) and the last deglaciation. Corals were collected south of Tasmania from water depths between 1430 and 1950 m with 80% of them between 1500 and 1700 m, giving us a continuous record from a narrow depth range. The record shows three distinct periods of circulation: the MIS 3–2 transition, the LGM/Heinrich Stadial 1 (extending from ∼22 to 16 kyr BP), and the Antarctic Cold Reversal (ACR). The MIS 3–2 transition and the ACR are characterized by abrupt changes in intermediate water radiocarbon while the LGM time period generally follows the atmosphere at a constant offset, in support of the idea that the LGM ocean was at steady state for its ^(14)C distribution. Closer inspection of the LGM time period reveals a 40‰ jump at ∼19 ka from an atmospheric offset of roughly 230‰ to 190‰, coincident with an observed 10–15 m rise in sea level and a southward shift of the Subantarctic and Polar Fronts, an abrupt change not seen in deeper records. During the ACR time period intermediate water radiocarbon is on average less offset from the atmosphere (∼110‰∼110‰) and much more variable. This variability has been captured within the lifetimes of three individual corals with changes of up to 35‰ over ∼40 yr, likely caused by the movement of Southern Ocean fronts. This surprising result of relatively young and variable intermediate water radiocarbon during the ACR seems to go against the canonical idea of reduced circulation and ventilation in the south during this time period. However comparisons with other records from the Southern Ocean highlight zonal asymmetries, which can explain the deviation of our Tasmanian record from those in Drake Passage and the eastern Pacific. These signals seen in Tasmanian intermediate water Δ^(14)C can also be found in Greenland ice core δ^(18)O and East Asian monsoon strength. Throughout the LGM and the deglaciation, our Tasmanian intermediate water record is sensitive to times when the upper and lower cells of the meridional overturning circulation are more or less interconnected, which has important implications for the global climate system on glacial–interglacial time scales.
|Additional Information:||© 2015 Elsevier B.V. Received 5 February 2015, Revised 8 September 2015, Accepted 24 September 2015, Available online 3 November 2015. We would like to thank Heather Stoll, the editor of this paper, and three reviewers for their helpful comments. We would also like to acknowledge analytical help from Guillaume Paris. This work was funded by NSF P2C2 grant OCE-1204211.|
|Subject Keywords:||Southern Ocean; radiocarbon; glacial–interglacial climate change; meridional overturning circulation; Southern Ocean fronts; intermediate water|
|Official Citation:||Sophia K.V. Hines, John R. Southon, Jess F. Adkins, A high-resolution record of Southern Ocean intermediate water radiocarbon over the past 30,000 years, Earth and Planetary Science Letters, Volume 432, 15 December 2015, Pages 46-58, ISSN 0012-821X, http://dx.doi.org/10.1016/j.epsl.2015.09.038. (http://www.sciencedirect.com/science/article/pii/S0012821X15006135)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||07 Nov 2015 00:00|
|Last Modified:||07 Nov 2015 00:00|
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