Changes in diatom productivity and upwelling intensity off Peru since the Last Glacial Maximum: Response to basin‐scale atmospheric and oceanic forcing

New records of stable silicon isotope signatures (δ 30 Si) together with concentrations of biogenic opal and organic carbon from the central (9°S) and northern (5°S) Peruvian margin reveal changes in diatom productivity and nutrient utilization during the past 20,000 years. The findings are based on a new approach using the difference between the δ 30 Si signatures of small (11–32 µm) and large (>150 µm) diatom fractions (Δ 30 Si Coscino‐bSi ) in combination with the variance in diatom assemblages for reconstruction of past upwelling intensity. Combination of our records with two previously published records from the southern upwelling area off Peru (12–15°S) shows a general decoupling of the environmental conditions at the central and southern shelf mainly caused by a northward shift of the main upwelling cell from its modern position (12–15°S) toward 9°S during Termination 1. At this time only moderate upwelling intensity and productivity levels prevailed between 9°S and 12°S interpreted by a more northerly position of Southern Westerly Winds and the South Pacific Subtropical High. Furthermore, a marked decrease in productivity at 12–15°S during Heinrich Stadial 1 coincided with enhanced biogenic opal production in the Eastern Equatorial Pacific, which was induced by a southward shift of the Intertropical Convergence Zone and enhanced northeasterly trade winds. Modern conditions were only established at the onset of the Holocene. Past changes in preformed δ 30 Si signatures of subsurface waters reaching the Peruvian Upwelling System did not significantly affect the preserved δ 30 Si signatures.