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. Changes in the geometry of ocean meridional overturning circulation (MOC)are crucial in controlling past changes of climate and the carbon inventoryof the atmosphere. However, the accurate timing and global correlation ofshort-term glacial-to-deglacial changes of MOC in different ocean basinsstill present a major challenge. The fine structure of jumps and plateaus inatmospheric and planktic radiocarbon (14C) concentration reflectschanges in atmospheric 14C production, ocean–atmosphere 14Cexchange, and ocean mixing. Plateau boundaries in the atmospheric 14Crecord of Lake Suigetsu, now tied to Hulu Cave U∕Th model ages instead of opticalvarve counts, provide a stratigraphic “rung ladder” of up to 30 age tiepoints from 29 to 10 cal ka for accurate dating of planktic oceanic 14C records. The age differences between contemporary planktic and atmospheric14C plateaus record the global distribution of 14C reservoir agesfor surface waters of the Last Glacial Maximum (LGM) and deglacial HeinrichStadial 1 (HS-1), as documented in 19 and 20 planktic 14C records, respectively. Elevatedand variable reservoir ages mark both upwelling regions and high-latitudesites covered by sea ice and/or meltwater. 14C ventilation ages of LGMdeep waters reveal opposed geometries of Atlantic and Pacific MOC. Liketoday, Atlantic deep-water formation went along with an estuarine inflow ofold abyssal waters from the Southern Ocean up to the northern North Pacificand an outflow of upper deep waters. During early HS-1, 14C ventilationages suggest a reversed MOC and ∼1500-year flushing ofthe deep North Pacific up to the South China Sea, when estuarine circulationgeometry marked the North Atlantic, gradually starting near 19 ka. High14C ventilation ages of LGM deep waters reflect a major drawdown ofcarbon from the atmosphere. The subsequent major deglacial age drop reflectschanges in MOC accompanied by massive carbon releases to the atmosphere asrecorded in Antarctic ice cores. These new features of MOC and the carboncycle provide detailed evidence in space and time to test and refine oceanmodels that, in part because of insufficient spatial model resolution andreference data, still poorly reproduce our data sets.

climate of the past

Plateaus and jumps in the atmospheric radiocarbon record – potential origin and value as global age markers for glacial-to-deglacial paleoceanography, a synthesis