Publicación:

Millennial variability of terrigenous transport to the central-southern Peruvian margin during the last deglaciation (18-13 kyr BP)

Resumen

Reconstructing precipitation and wind from the geological record could help researchers understand the potential changes in precipitation and wind dynamics in response to climate change in Peru. The last deglaciation offers natural experimental conditions to test the response of precipitation and wind dynamics to high-latitude forcing. While considerable research has been done to reconstruct precipitation variability during the last deglaciation in the Atlantic sector of South America, the Pacific sector of South America has received little attention. This work aims to fill this gap by reconstructing types of terrigenous transport to the central-southern Peruvian margin (12 and 14deg; S) during the last deglaciation (18-13 kyr BP). For this purpose, we used grain-size distribution in sediments of marine core M77/2-005-3 (Callao, 12deg; S) and core G14 (Pisco, 14deg; S). We analyzed end-members (EMs) to identify grain-size components and reconstruct potential sources and transport processes of terrigenous material across time.We identified four end-members for both Callao and Pisco sediments. In Callao, we propose that the changes in the contributions of EM4 (101 μm) and EM2 (58 μm) mainly reflect the hydrodynamic energy and diffuse sources, respectively, while the variations in EM3 (77 μm) and EM1 (11 μm) reflect changes in the eolian and fluvial inputs, respectively. In Pisco, where there are strong winds and an extensive coastal desert, changes in the contribution of EM1 (10 μm) reflect changes in river inputs, while EM2 (52 μm), EM3 (75 μm), and EM4 (94 μm) reflect an eolian origin. At millennial scale, our record shows an increase in the fluvial inputs during the last part of Heinrich Stadial 1 (~ 16-14.7 kyr BP) at both locations. This increase was linked to higher precipitation in the Andes related to a reduction of the Atlantic Meridional Overturning Circulation and meltwater discharge in the North Atlantic. In contrast, during the Bølling-Allerød interstadial (~ 14.7-13 kyr BP), there was an eolian input increase, associated with stronger winds and lower precipitation that indicate an expansion of the South Pacific Subtropical High. These conditions would correspond to a northern displacement of the Intertropical Convergence Zone-South Pacific Subtropical High system associated with a stronger Walker circulation. Our results suggest that variations in river discharge and changes in surface wind intensity in the western margin of South America during the last deglaciation were sensitive to Atlantic Meridional Overturning Circulation variations and the Walker circulation on millennial timescales. In the context of global warming, large-scale increases in precipitation and fluvial discharge in the Andes as a result of a declining Atlantic Meridional Overturning Circulation and southward displacement of the Intertropical Convergence Zone should be considered.