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The multi-proxy study of Chilean fjord sediments: a high-resolution record of climate variability in South America since the end of the last glacial maximum

Final Activity Report Summary - CLIVASA (The multi-proxy study of Chilean fjord sediments: a high-resolution record of CLImate VAriability in South America since the end of the Last Glacial Maximum)

Reconstructing the nature, timing and amplitude of past climate and environmental changes at various geographical locations is of primordial importance to constrain the physics of the climate system and to learn how the environment adapts to a rapidly changing climate. To this end, the CLIVASA project aimed at generating new proxy records of climate and environmental change at the mid- and high-latitudes of the Southern Hemisphere, which play an important role in our understanding of Earth's climate variability but have been relatively understudied. We were particularly interested in sediment archives from the fjords of Chilean Patagonia, which contain high-resolution records of precipitation, glacier activity, and aquatic productivity during the Holocene.

During CLIVASA, we investigated the geochemistry, mineralogy and grain-size distributions of surface sediment samples and sediment cores from the fjords of Northern (44-47 S) and Southern (53-55 S) Chilean Patagonia. Results obtained on the surface samples demonstrate that the sediment composition in the fjords primarily reflects the distance from the main tributaries, and therefore mirrors the nature and degree of terrestrial sediment discharge. Proximal locations are characterised by high contents in dense minerals such as amphibole, and high Zr/Ti, Ti/Fe, Zr/Al, Fe/Al and C/N ratios, while more distal locations are enriched in biogenic particles and have high Na/Al, Sr/Al and low C/N ratios. These proxies are therefore well suited for estimating changes in the energy of terrestrial sediment supply into the fjords through time.

The application of these proxies to a 2-m long sediment core from the Quitralco fjord (PC29A, 46 S, 1400 years) shows an increased river runoff between ~1400 and 1900 AD, most likely linked to an increase in precipitation intensity and/or wetter climate conditions between ~1400 AD and the beginning of the 20th century. This wet period is coeval with a 1 C decrease in sea surface temperature, and is therefore believed to represent a northward shift of the Southern Westerlies over Northern Patagonia during the Little Ice Age.

The same proxies applied to a 15-m long sediment core collected in front of the Gualas glacier (Northern Patagonian Ice Cap, 46 S) clearly show alternations between sediment supplied by pro-glacial rivers, and slow sub-glacial sedimentation during the last 6000 years, reflecting variations in the dynamics of the Gualas Glacier. These data provide a unique high-resolution record of glacier variability in Northern Patagonia during the Holocene. They are currently used to assess the influence of climate and ocean circulation on the variability of Patagonian glaciers during the Holocene.