HOW OLD IS THE HUMBOLDT CURRENT SYSTEM?

Nowadays, about 20% of the world’s marine fish catch comes from the Peru-Chile area in the southeastern Pacific Ocean. The high productivity and biomass abundance of these waters reflect coastal upwelling in the framework of the Humboldt Current System (HCS). The latter includes surface and subsurface currents that bring deep, cold, nutrient-rich waters from Antarctica to Peru. Despite its ecological significance, the age and origin of the HCS remain poorly constrained. Here, we present a comprehensive review of previous works on the deep past of the HCS and coastal upwelling off Peru, with a special focus on the Cenozoic succession of the southern Peruvian Pisco Basin. The Paleogene biogenic portion of the basin fill indicates warm-water conditions for the middle Eocene and an incipit of coastal upwelling before the latest Eocene, hinting at the existence of a “proto-Humboldt current”. A late Eocene age is also attributed to the establishment of the Antarctic Circumpolar Current following the opening of the Drake Passage and Tasmanian Gateway. Although diatomaceous sediments have occurred since the late Eocene, the main diatom genera indicate seasonal rather than year-round upwelling. Warm/temperate taxa in the LowerMiddle Miocene, and paleotemperature estimates as well as diatom assemblages in the Upper Miocene point to a moderate upwelling during the Early-Middle Miocene that strengthened in Late Miocene times. Likewise, neodymium isotope ratios of fossil shark teeth show an overall Miocene-Pleistocene trend similar to that of the deep equatorial Pacific, with increasing contribution of Antarctic waters since ca. 6 Ma.