Pervasive multidecadal variations in productivity within the Peruvian Upwelling System over the last millennium

Abstract

There is no agreement on the pluri-decadal expression of El Niño–Southern Oscillation (ENSO) in the Pacific over the last millennium. Marine records from the Peruvian margin indicate humid conditions (El Niño-like mean conditions) over the Little Ice Age, while precipitation records from the eastern equatorial Pacific infer arid conditions (La Niña-like mean conditions) for the same period. We here studied diatom assemblages, nitrogen isotopes, and major and minor elements at the lamination level in three laminated trigger cores located between 11°S and 15°S on the Peruvian shelf within the oxygen minimum zone (OMZ) to reconstruct precipitation and ocean productivity at the multiannual to multidecadal timescales over the last millennium. We respected the sediment structure, thus providing the first records of the mean climatic conditions at the origin of the lamination deposition, which ones represent several years. Light laminations were deposited under productive and dry conditions, indicative of La Niña-like mean conditions in the system, while dark laminations were deposited under non-productive and humid conditions, representative of El Niño-like mean conditions. La Niña-like mean conditions were predominant during the Medieval Warm Period (MWP; 1000–600 years BP) and Current Warm Period (CWP; 150 years BP to present), while El Niño-like mean conditions prevailed over the Little Ice Age (LIA; 600–150 years BP). We provide evidence for persistent multidecadal variations in productivity over the last millennium, which were disconnected from the mean climate state. Multidecadal variability has been stronger over the last 450 years concomitantly to increased variability in the NAO index. Two intervals of strong multidecadal variability were also observed over the MWP, congruent to decreased solar irradiance and increased volcanic activity.