Abstract

Little is known on the El Nino-related impacts affecting the CO2 dynamic and fluxes in productive Eastern Boundary Upwelling Systems (EBUS). Through 35 oceanographic campaigns conducted between January 2015 and April 2016 in the Humboldt EBUS (23 degrees S), intraseasonal (i.e., daily-to-bimonthly) hydrographic variations and nearshore changes in surface carbonates system were assessed during the 2015 El Nino event. Collected hydrographic and carbonates system data (sea surface temperature (SST), subsurface temperature, salinity, oxygen, chlorophyll a, pH, total alkalinity (A(T)) and pCO(2)), were analyzed and interpreted considering local (i.e., satellite winds and tide gauge sea level) and remote (i.e., equatorial Kelvin waves) forcing. Permanent alongshore wind conditions prompted a relatively deep mixed layer favoring elevated acidity (7.8-7.9 pH(T)) and CO2 saturated (>450 mu atm) conditions throughout most of the study period. Between austral summer-fall and fall-winter transitions, intermittent warm events increased water temperature (SST) above the long-term climatological state (2000-2010), and gave rise to high acidity-warm conditions. However, despite warm water particularly high in salinity (>35) and A(T) (>2,300 mu mol kg(-1)) associated with downwelling Kelvin waves activity observed during the developing phase of the 2015 El Nino event, phytoplankton production and CO2 uptake were favored because of the maintenance of mean upwelling conditions. These results are discussed in terms of data limitations, coastal processes adding variability to carbonates system variability, and requirements for a better understanding of hydrographic forcing and responses in the Humboldt EBUS.