Analysis of oceanographic and biological conditions of the coastal upwelling off Callao in contrasting periods during 2018

Abstract

Graco M, Anculle T, Aramayo V, Bernales A, Carhuapoma W, Correa D, Fernández J, García W, Ledesma
J, Marquina R, Quipúzcoa L, Romero D, Sarmiento M, Solís J. 2019. Analysis of the oceanographic and biological
conditions of the coastal upwelling off Callao in contrasting periods during 2018. Bol. Inst Mar Peru. 34(2): 519-543.-
The coastal upwelling ecosystem off Peru is characterized by intense oceanographic variability that impacts
the Oxygen Minimum Zone (OMZ), on nutrient availability and the plantonic and benthic ecology. This work
presents the results of two Intensive Oceanographic Cruises (CRIO in Spanish) associated with one of the most
important upwelling areas of Peru, Callao (12°S), carried out in autumn (April) under higher productivity and in
winter (August) when the physical upwelling process predominated. In April and August 2018, the conditions can
be defined in two contrasting periods under the influence of different intensities of the upwelling events with the
associated chemical and biological responses. Both periods were characterized by an intense and shallow OMZ. In
the autumn, higher productivity and deficit of nitrates were observed, while in winter silicates and nitrates were
available throughout the study area. The phytoplankton community reflected the different conditions. Diatoms
were dominant in April and on the coast, while winter and the ocean side were dominated by the nanoplankton.
Changes in water masses gave the possibility of approaching ocean waters in winter increasing pH favorable for
coccolithophorid calcifying organisms. These organisms have been identified during El Niño Costero 2017. At the
benthos, the response indicates conditions that would still reflect aspects associated with El Niño and its impact
on oxygenation and organic matter. The predominance of polychaetes such as Mageloma phyllisae and the decrease
of microbial mats (Candidatus Marithioploca) was detected. Less reduced sediment with relatively low H2
S values
was present. For the foraminifer assemblage, a mixture of species was observed, some that appeared since El Niño
and others that reflect some normalization towards oxygen deficiency and the availability of organic matter.