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Published September 15, 2013 | Supplemental Material
Journal Article Open

Responses of the deep ocean carbonate system to carbon reorganization during the Last Glacial–interglacial cycle


We present new deep water carbonate ion concentration ([CO_3^(2−)]) records, reconstructed using Cibicidoides wuellerstorfi B/Ca, for one core from Caribbean Basin (water depth = 3623 m, sill depth = 1.8 km) and three cores located at 2.3–4.3 km water depth from the equatorial Pacific Ocean during the Last Glacial–interglacial cycle. The pattern of deep water [CO_3^(2−)] in the Caribbean Basin roughly mirrors that of atmospheric CO_2, reflecting a dominant influence from preformed [CO_3^(2−)] in the North Atlantic Ocean. Compared to the amplitude of ∼65 μmol/kg in the deep Caribbean Basin, deep water [CO_3^(2−)] in the equatorial Pacific Ocean has varied by no more than ∼15 μmol/kg due to effective buffering of CaCO_3 on deep-sea pH in the Pacific Ocean. Our results suggest little change in the global mean deep ocean [CO_3^(2−)] between the Last Glacial Maximum (LGM) and the Late Holocene. The three records from the Pacific Ocean show long-term increases in [CO_3^(2−)] by ∼7 μmol/kg from Marine Isotope Stage (MIS) 5c to mid MIS 3, consistent with the response of the deep ocean carbonate system to a decline in neritic carbonate production associated with ∼60 m drop in sea-level (the "coral-reef" hypothesis). Superimposed upon the long-term trend, deep water [CO_3^(2−)] in the Pacific Ocean displays transient changes, which decouple with δ^(13)C in the same cores, at the start and end of MIS 4. These changes in [CO_3^(2−)] and δ^(13)C are consistent with what would be expected from vertical nutrient fractionation and carbonate compensation. The observed ∼4 μmol/kg [CO_3^(2−)] decline in the two Pacific cores at >3.4 km water depth from MIS 3 to the LGM indicate further strengthening of deep ocean stratification, which contributed to the final step of atmospheric CO_2 drawdown during the last glaciation. The striking similarity between deep water [CO_3^(2−)] and ^(230)Th-normalized CaCO_3 flux at two adjacent sites from the central equatorial Pacific Ocean provides convincing evidence that deep-sea carbonate dissolution dominantly controlled CaCO_3 preservation at these sites in the past. Our results offer new and quantitative constraints from deep ocean carbonate chemistry to understand roles of various mechanisms in atmospheric CO_2 changes over the Last Glacial–interglacial cycle.

Additional Information

© 2013 Elsevier Ltd. Received 25 March 2013; Received in revised form 23 June 2013; Accepted 24 June 2013; Available online 17 July 2013. We thank W.S. Broecker, P. De Deckker, and F.J. Ryerson for helpful discussion, Fei Zhang for assistance with sediment processing and foraminfera picking. Core materials are provided by D. McCorkle at WHOI (MW91-9 GGC15 and MW91-9 GGC48), LDEO core repository (VM28-122), and S. Carey at University of Rhode Island (TTO13 PC61; supported by NSF OCE-644625), and ODP/IODP. We thank the Editor (Dr. Hillaire-Marcel) for editorial handling, and two anonymous reviewers for constructive comments. This research is supported by NSF, LLNL Fellowship, startup fund at RSES-ANU (JY), and by CAS/SAFEA International Partnership Program for Creative Research Teams (JY/ZJ).

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