Changes in silicate utilisation and upwelling intensity off Peru since the Last Glacial Maximum - insights from silicon and neodymium isotopes

The εNd signatures of the coatings extracted from sediment core SO147-106KL located in the present day centre of coastal upwelling near 12°S have been essentially constant (−1.5) throughout the past 20,000 years, while the detrital εNd (87Sr/86Sr) varied between values of −0.7 (0.70620) during the Last Glacial and −4.5 (0.70849) during the late Holocene reflecting changes in the origin of the sediment and current transport from a more northerly towards a more southerly source and from overall stronger to weaker upwelling. The δ30Si signature of both total biogenic opal (δ30Siopal) and of hand-picked diatoms (δ30Sidiatom) ranged from +0.3‰ (Last Glacial) to +1.4‰ (late Holocene) confirming large variations in upwelling intensity driving silicic acid utilisation by diatoms. Our combined bSiO2 MAR, δ30Siopal and detrital radiogenic isotope results demonstrate that the strongest El Niño-Southern Oscillation conditions off Peru of the past 20 ka have prevailed during the past 5 ka.