Glacial-to-deglaical changes in South Pacific surface water oceanography - centennial-scale age control -

Glacial-to-interglacial changes in atmospheric pCO2 are considered as largely controlled by processes in the Southern Ocean. In particular, upwelling both near coastlines and along the Polar Front is regarded as a major pathway of old CO2 from the deep ocean up to the sea surface and atmosphere, hence plays an important role in regulating the CO2 exchange between ocean and atmosphere. At the beginning of the last glacial termination, changes in ocean overturning circulation in the Southern Ocean probably triggered two huge events of CO2 outgassing from a deep-ocean reservoir into the atmosphere as revealed by Antarctic ice core records 1. They parallel two intervals of rapidly decreasing atmospheric 13C 2 and ∆14C 3. They probably concurred with two intervals of enhanced ocean upwelling, directly linking increased ventilation of the deep ocean to the deglacial rise in atmospheric CO2. To constrain the precise timing and origin of released CO2 we used paired records of marine 14C reservoir ages from the Pacific sector of the Southern Ocean, established by means of the 14C Plateau Tuning method 4. High surface ocean reservoir ages serve as tracer for upwelled old water masses. They were obtained from our centennial-scale resolution planktonic radiocarbon records of sediment cores off southern New Zealand and southern Chile. During the last peak glacial our 14C ages reveal planktonic reservoir ages of 1600 - 2200 yr exceeding previous estimates 5,6 by 400-1200 yr, but well agree to the previously reported high value of 1970 yr 7. Right at the onset of the last deglacial our records suggest an extreme drop down to a very low reservoir age of 200-400 yr matching the low estimates of 300-400 yr by 5,6,7,8. During terminal Heinrich-1 times, the values once more reached 1100 yr. This pattern of increased reservoir ages during peak glacial times (and the B/A) and strongly reduced values during the early deglacial parallels and precedes the 13C trends of atmospheric CO2 each and may have great implications for both constraining the history of past deep-water ages and related changes in the CO2 (1‰ 14C -1.22 μmol DIC kg−1) 4 storage of South Pacific deep waters. (1) Marcott et al. 2014, Nature Vol. 514, 616 (2) Schmitt et al. 2013, Science Vol. 336, 711 (3) Bronk Ramsey et al. 2012, Science Vol. 338, 370 (4) Sarnthein et al. 2013, Clim. Past Vol. 9, 2595 (5) Pahnke et al. 2005, Science Vol. 307, 1741 (6) Ronge et al. 2016, Nature Comm. Vol. 7, 11487 (7) Sikes et al. 2000, Nature Vol. 405, 555 (8) Siani et al. 2013, Nature Comm. Vol. 4. 275