Chemical conditions in autumn after the 2017 coastal El Niño during the 2017-0506 Research Cruise for demersal resources

Abstract

Our work presents the results of the distribution of oxygen, chlorophyll-a, and nutrient along the Peruvian coast, obtained in autumn 2017 (May 27 to June 15) within 100 nm. We aimed to evaluate the chemical conditions during the research cruise targeting demersal resources after the occurrence of the 2017 coastal El Niño (cEN). Upwelling cells were found off Talara, Paita, Punta la Negra, in an extensive region between Mórrope and Salaverry and off Chicama, resulting from oxygen contents below 4.0 mL.L-1 within 20 to 40 nm, approximately. Off Puerto Pizarro, the oxygen content exceeded 0.5 mL.L-1 in the water column over 300 m deep, while off Paita, the upper edge of the Oxygen Minimum Zone (< 0.5 mL.L-1) was located below 200 m deep. In the northern zone, these oxygenation conditions would correspond to the remnant effects of the final phase of the 2017 cEN. Regarding Chicama, a shallower OMZ was observed, covering part of the shelf above 50-100 m, with some oxygenation between 20 and 50 nm, while in Chimbote it covered the shelf up to 25 m deep. The chlorophyll-a concentrations, on average, were higher than 2.5 μg.m-3, with one cell off Paita with more than 5.0 μg.m-3, and a maximum value of 23.08 μg.m-3 off Chimbote. The latter was associated with a Nitrogen/Phosphorus (N/P) ratio of 4.81, a non-redfieldlian behavior, due to high nitrate consumption.