[M-IS16] Paleoclimatology and paleoceanography

[MIS16-P15] A paleoclimatic reconstruction of the southeastern Pacific last deglacial using geochemical proxies obtained from offshore Chile

*Karin Nemoto^1,2, Yusuke Yokoyama^1,2, Adam David Sproson², Yosuke Miyairi², Takahiro AZE², Hiroyuki Matsuzaki^3,4, Yair Rosentha⁵, Samantha Bova⁵ (1.Department of Earth and Planetary Science, The University of Tokyo, 2.Atmosphere and Ocean Research Institute, The University of Tokyo, 3.The University Museum,The University of Tokyo, 4.School of Engineering, The University of Tokyo, 5.Department of Marine and Coastal Sciences, School of Environmental and Biological Sciences, Rutgers University)

Keywords:paleoclimate, westerly, beryllium

The southeastern Pacific is a key location to understand the relationship between global climate change and Southern Ocean condition. The coast of Chile is ideally located to clarify the mechanisms behind local climate change. The Southern Westerly Wind belt (SWW) blows over central Chile and interacts with the Southern Annular Mode, the El Niño-Southern Oscillation (ENSO) and the Atlantic Meridional Overturning Circulation (AMOC). The Antarctic Circumpolar Current (ACC) diverts to the north and the south, causing steep latitudinal gradients off the coast of Chile.

A marine sediment core recovered from offshore Chile (44°S, 75°W) was used in this study. The age model of this core is based on 14C Accelerator Mass Spectrometry (AMS) dates. The 10Be and 9Be abundances were measured by AMS and High Resolution Inductively Coupled Plasma Mass Spectrometry, respectively. The organic elemental analyzer was used to measure organic C, N and S.

The variation in 10Be may reflect atmospheric conditions such as the location of the SWW and associated precipitation since 10Be is produced in the atmosphere. The amount of 10Be and 9Be are affected not only by the source but also by delivery. When 10Be is normalized by 9Be, the latter effect can be offset (Simon et al., 2016). The 10Be/9Be may reflect atmospheric processes since the ratio is highly controlled by 10Be. The results of 10Be/9Be and 10Be indicates the intensity of the SWW became stronger and the amount of precipitation was increased from 12 ka to 3 ka, which is antiphase to those in the core zone of the SWW (Lamy et al., 2010).

Most of the records from both this and previous research fluctuate around 12 ka, 8 ka and 3 ka. Climatic changes off the coast of Chile are associated with changes in the ACC and the SWW. The changes observed in this study clearly suggests close relationship with global climate indicating importance of coupling between atmosphere and ocean in this region.

References

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Pike J., Swann G.E.A., Leng M.J. & Snelling A.M. Glacial discharge along the west Antarctic Peninsula during the Holocene. Nat. Geosci. 6, 199-202 (2013).

Simon Q. etal. Authigenic ¹⁰Be /⁹Be ratios and ¹⁰Be-fluxes (²³⁰Th_xs-normalized) in central Baffin Bay sediments during the last glacial cycle: Paleoenvironmental implications. Quat. Sci. Rev. 140, 142-162 (2016).