Abstract. Changes in the geometry of ocean meridional overturning circulation (MOC) are crucial in controlling past changes of climate and the carbon inventory of the atmosphere. However, the accurate timing and global correlation of short-term glacial-to-deglacial changes of MOC in different ocean basins still present a major challenge. The fine structure of jumps and plateaus in atmospheric and planktic radiocarbon (14C) concentration reflects changes in atmospheric 14C production, ocean–atmosphere 14C exchange, and ocean mixing. Plateau boundaries in the atmospheric 14C record of Lake Suigetsu, now tied to Hulu Cave U∕Th model ages instead of optical varve counts, provide a stratigraphic “rung ladder” of up to 30 age tie points from 29 to 10 cal ka for accurate dating of planktic oceanic 14C records. The age differences between contemporary planktic and atmospheric 14C plateaus record the global distribution of 14C reservoir ages for surface waters of the Last Glacial Maximum (LGM) and deglacial Heinrich Stadial 1 (HS-1), as documented in 19 and 20 planktic 14C records, respectively. Elevated and variable reservoir ages mark both upwelling regions and high-latitude sites covered by sea ice and/or meltwater. 14C ventilation ages of LGM deep waters reveal opposed geometries of Atlantic and Pacific MOC. Like today, Atlantic deep-water formation went along with an estuarine inflow of old abyssal waters from the Southern Ocean up to the northern North Pacific and an outflow of upper deep waters. During early HS-1, 14C ventilation ages suggest a reversed MOC and ∼1500-year flushing of the deep North Pacific up to the South China Sea, when estuarine circulation geometry marked the North Atlantic, gradually starting near 19 ka. High 14C ventilation ages of LGM deep waters reflect a major drawdown of carbon from the atmosphere. The subsequent major deglacial age drop reflects changes in MOC accompanied by massive carbon releases to the atmosphere as recorded in Antarctic ice cores. These new features of MOC and the carbon cycle provide detailed evidence in space and time to test and refine ocean models that, in part because of insufficient spatial model resolution and reference data, still poorly reproduce our data sets.
Plateaus and jumps in the atmospheric radiocarbon record -Potential origin and value as 1 global age markers for glacial-to-deglacial paleoceanography, a synthesis 2 3 4 ABSTRACT 27 Changes in the geometry of ocean Meridional Overturning Circulation (MOC) are crucial in 28 controlling changes of climate and the carbon inventory of the atmosphere. However, the precise 29 timing and global correlation of short-term glacial-to-deglacial changes of MOC in different ocean 30 basins still present a major challenge. A possible solution is offered by the fine structure of jumps 31 and plateaus in the record of radiocarbon ( 14 C) concentration of the atmosphere and surface ocean 32 that reflects changes in atmospheric 14 C production as well as in the 14 C exchange between air 33 and sea and within the ocean. Boundaries of atmospheric 14 C plateaus in the 14 C record of Lake 34 Suigetsu, now tied to Hulu U/Th model-ages instead of optical varve counts, provide a 35 stratigraphic 'rung ladder' of ~30 age tie points from 29 to 10 ka for correlation with and dating of 36 planktic oceanic 14 C records. The age difference between contemporary planktic and atmospheric 37 14 C plateaus gives an estimate of the global distribution of 14 C reservoir ages for surface waters of 38 the Last Glacial Maximum (LGM) and deglacial Heinrich Stadial 1 (HS-1), as shown by 19 planktic39 14 C records. Clearly elevated and variable reservoir ages mark both high-latitude sites covered by 40 sea ice and/or meltwater and upwelling regions. 14 C ventilation ages of LGM deep waters reveal 41 opposed geometries of Atlantic and Pacific MOC. Similar to today, Atlantic deep-water formation 42 went along with an estuarine inflow of old abyssal waters from the Southern Ocean up to the 43 northern North Pacific and an outflow of upper deep waters. Vice versa, 14 C ventilation ages 44 suggest a reversed MOC during early HS-1 and a ~1500 year long flushing of the deep North 45 Pacific up to the South China Sea, when estuarine circulation geometry marked the North Atlantic, 46 gradually starting near 19 ka. Elevated 14 C ventilation ages of LGM deep waters reflect a major 47 drawdown of carbon from the atmosphere. Inversely, the subsequent massive age drop and 48 change in MOC induced two major events of carbon release to the atmosphere as recorded in 49 Antarctic ice cores, shifts that highlight the significance of ocean MOC for atmospheric CO 2 and its 50 14 C inventory. These new features of MOC and the carbon cycle offer a challenge to model 51 simulations that, in part because of insufficient spatial model resolution and reference data for 52 testing the model results, still poorly reproduce them.
A multibarrel seabed drill rig was used for the first time to drill unconsolidated sediments and consolidated sedimentary rocks from an Antarctic shelf with core recoveries between 7% and 76%. We deployed the MARUM‐MeBo70 drill device at nine drill sites in the Amundsen Sea Embayment. Three sites were located on the inner shelf of Pine Island Bay from which soft sediments, presumably deposited at high sedimentation rates in isolated small basins, were recovered from drill depths of up to 36 m below seafloor. Six sites were located on the middle shelf of the eastern and western embayment. Drilling at five of these sites recovered consolidated sediments and sedimentary rocks from dipping strata spanning ages from Cretaceous to Miocene. This report describes the initial coring results, the challenges posed by drifting icebergs and sea ice, and technical issues related to deployment of the MeBo70. We also present recommendations for similar future drilling campaigns on polar continental shelves.
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