Changes in biological productivity and ocean-climatic fluctuations during the last similar to 1.5 kyr in the Humboldt ecosystem off northern Chile (27 degrees S): A multiproxy approach

A sedimentary box core (BIAC072014) collected in a coastal environment in the Humboldt Current Ecosystem (HCE, Inglesa Bay, similar to 27 degrees S, northern Chile) was used to reconstruct the changes in biological productivity and ocean-climate fluctuations during the last similar to 1.5 kyr via geochemical, mineralogical and micropaleontological analyses. From similar to 510 CE to similar to 930 CE, 'El Nifio-like' conditions prevailed, while during the Medieval Climate Anomaly (MCA, similar to 950 CE to similar to 1450 CE), 'La Nifia-like' conditions predominated. This pattern might have resulted from weakening/strengthening of the Walker cell, contraction/expansion of the South Pacific Sub-tropical High (SPSH) and a predominance of warm/cold phases of the Pacific Decadal Oscillation (PDO). Between similar to 1820 CE and the present Inglesa Bay experienced a reduction in the Oxygen Minimum Zone (OMZ) intensity and biological productivity, an increase in the detritic input and a decrease in sea surface temperature (SST). Despite the regional intensification and secular cooling (similar to 14 degrees S and similar to 27 degrees S) of coastal upwelling, the similarity between the reduction in biological productivity and OMZ intensity in this region and that in the central zone of Chile (36 degrees S) suggests that Inglesa Bay acts a transition zone in relation to the oceanographic behaviour of the HCE. The reduction in the OMZ intensity and biological productivity during the last similar to 200 years could be explained by greater subsurface ventilation in intermediate depths due to more northward displacement of the subduction region of the Eastern South Pacific Intermediate Water (ESPIW) near similar to 30 degrees S in response to the strengthening of the circulation of the Subtropical Gyre. The coastal cooling observed in the northern section of HCE during the current Warm Period suggests that it is not possible to demonstrate that El Nino-like conditions promoted the reduction in biological productivity and OMZ intensity in Inglesa Bay