[21-1] Deglacial and Holocene variations of the southern westerly wind belt and sea surface temperatures as recorded in Chilean margin sediments

• Main Authors: Societa Geologica Italiana 2021, Lamy, Frank
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Underline Science Inc. 2021
• Subjects: Antarctic; Austral; Pacific; Antarc*
• Online Access: https://dx.doi.org/10.48448/8xg7-cg94; https://underline.io/lecture/33928-21-1-deglacial-and-holocene-variations-of-the-southern-westerly-wind-belt-and-sea-surface-temperatures-as-recorded-in-chilean-margin-sediments

Abstract: The westerlies are major zonal atmospheric circulation systems in both northern and southern hemispheres. The southern westerly wind belt (SWW) substantially contributes to the forcing of the deep and vigorous Antarctic Circumpolar Current (ACC). Wind-induced upwelling raises large amounts of deep water to the ocean’s surface in this circumpolar belt affecting the global thermohaline circulation and atmospheric carbon dioxide contents. Therefore, the southern westerlies exert a strong control on global climate and oceanography. The SE Pacific off southern Chile, where the SWW and ACC intersect with South America, represents an important area for understanding the behavior of southern hemisphere mid- and high-latitude climate. Chile is ideally located to reconstruct past variability of the SWW since the westerlies nearly entirely control precipitation on the western side of the Andes in southern South America, with an extreme north-south rainfall gradient. In present-day austral winters, the SWW extends northward providing rainfall to central Chile (33-40°S) and occasionally northern Chile (up to ~27°S) but zonal winds and rainfall are reduced in its core zone in southernmost Chile (50-55°S). During austral summer, the zonal wind pattern shows a latitudinally more confined and intensified SWW with maximum rainfall over southernmost Chile. Paleo-precipitation estimates based on terrigenous sediment input changes off northern and central Chile agree with terrestrial records that glacial rainfall was higher in the semiarid part of Chile suggesting stronger glacial westerlies at the northern margin of the SWW. Less is known on glacial precipitation in the present core zone in southernmost Chile because this region was largely glaciated during that time. Holocene records suggest, however, a distinct latitudinal anti-phasing of precipitation/wind changes between the southern core zone of the SWW and the northern margin in central Chile. During the early Holocene, the core westerlies were enhanced and the northern margin was reduced, whereas the opposite pattern is observed in the late Holocene. These Holocene changes resemble modern seasonal SWW variations and can be best explained by varying sea-surface temperature (SST) fields in the Pacific. The analogy to modern seasonal changes implies that a latitudinal expansion of the SWW during cold phases (“winter-like”) and contraction during warm climate conditions (“summer-like”) may have been likewise important for the behavior of the SWW on glacial/interglacial time-scales and over the glacial millennial-scale fluctuations. For the late Holocene, detailed temperature reconstructions are important for contextualizing modern climate change in the SE Pacific. Superimposed on the late Holocene cooling, we observe multicentennial-scale SST variability, including relatively cool SSTs corresponding to the Medieval Climate Anomaly, and warmer SSTs corresponding to the Little Ice Age. Authors:* Lamy F.*