Paleoproductivity development during the last 350 ka in the Guaymas Basin, central of the gulf of California

Abstract

The biogenic silica content in the Guaymas Basin over the past ∼350 kyr exhibits a strong correlation with high XRF-based Si/Al ratios and low NGR total counts, utilizing biogenic silica as a proxy for paleoproductivity to infer past changes in the environmental conditions and productivity of the Gulf of California (GOC). Elevated bSi_acc and bulk_acc values, alongside fluctuations in %bSi content, were observed in the Guaymas Basin prior to the onset of MIS 6, suggesting an increased contribution of terrestrial input and enhanced stratification of surface and subsurface waters in the GOC during these periods. High %bSi values observed around ∼170 and 150 kyr during MIS 6 and the Last Glacial Maximum (LGM) indicate a strengthening of the winter monsoon in the GOC, which in turn promoted upwelling and productivity. The decline in %bSi content and XRF-based Si/Al ratios during the abrupt cold events of MIS 3 and MIS 2 suggests a reduction in upwelling intensity, likely driven by a shift in the position of the Intertropical Convergence Zone (ITCZ) and the North Pacific High (NPH), in response to the continued expansion of the Laurentide Ice Sheet until ∼16.5 kyr. This was also accompanied by reduced nutrient availability in subsurface waters due to a weakening of thermocline circulation. The elevated %bSi content during the Holocene reflects modern oceanographic conditions in the GOC, characterized by La Niña-like conditions that enhance upwelling and foster higher productivity in the central GOC during these intervals.