Atmosphere‐Ocean CO2 Exchange Across the Last Deglaciation From the Boron Isotope Proxy. Issue 10 (29th October 2019)

• Record Type: Journal Article
• Authors: Shao, Jun; Stott, Lowell D.; Gray, William R.; Greenop, Rosanna; Pecher, Ingo; Neil, Helen L.; Coffin, Richard B.; Davy, Bryan; Rae, James W.B.
• Is Part Of: Paleoceanography and paleoclimatology. Volume 34:Issue 10(2019)
• Page Start: 1650
• Page End: 1670
• Publication Date: 2019-10-29
• Subjects: Paleoceanography -- Periodicals; Paleoclimatology -- Periodicals; 551.46
• DOI: 10.1029/2018PA003498
• Languages: English
• ISSNs: 2572-4517

Abstract

Abstract: Identifying processes within the Earth System that have modulated atmospheric pCO2 during each glacial cycle of the late Pleistocene stands as one of the grand challenges in climate science. The growing array of surface ocean pH estimates from the boron isotope proxy across the last glacial termination may reveal regions of the ocean that influenced the timing and magnitude of pCO2 rise. Here we present two new boron isotope records from the subtropical‐subpolar transition zone of the Southwest Pacific that span the last 20 kyr, as well as new radiocarbon data from the same cores. The new data suggest this region was a source of carbon to the atmosphere rather than a moderate sink as it is today. Significantly higher outgassing is observed between ~16.5 and 14 kyr BP, associated with increasing δ 13 C and [CO3 ] 2− at depth, suggesting loss of carbon from the intermediate ocean to the atmosphere. We use these new boron isotope records together with existing records to build a composite pH/pCO2 curve for the surface oceans. The pH disequilibrium/CO2 outgassing was widespread throughout the last deglaciation, likely explained by upwelling of CO2 from the deep/intermediate ocean. During the Holocene, a smaller outgassing peak is observed at a time of relatively stable atmospheric CO2, which may be explained by regrowth of the terrestrial biosphere countering ocean CO2 release. Our stack is likely biased toward upwelling/CO2 source regions. Nevertheless, the composite pCO2 curve provides robust evidence that various parts of the ocean were releasing CO2 to the atmosphere over the last 25 kyr. Key Points: Boron‐isotope‐based pH reconstructions indicate that the subtropical/subpolar Southwest Pacific was a source of CO2 during the last 19 ka Major CO2 outgassing from the Southwest Pacific was associated with enhanced ventilation of intermediate waters between 16.5 and 14 kyr BP A surface pH/pCO2 composite derived from 12 planktic δ 11 B records shows widespread CO2 release from the ocean during the last deglaciation