Temporal variability in net primary production in an upwelling area off central Chile (36°S)

Abstract

The temporal variability of Net Primary Production (NPP) off central Chile (36°S, 73°W), an area subjected to seasonal coastal upwelling, was analyzed using monthly in situ 13C incubations within the photic zone, along with bio-oceanographic variables from a fixed time series station; and satellite NPP estimations (NPPE) from the Vertically Generalized Production Model between 2006 and 2015. NPP and NPPE rates varied from 0.03 to 18.29 and from 0.45 to 9.07 g C m-2 d-1, respectively. Both rates were fairly well correlated with each other (r2 = 0.61), but when these data were separated into two periods, higher r2 value was found during winter (r2 = 0.70) with respect to the rest of the year (r2 = 0.24); the latter correlation was partially due to increased weekly NPPE variability during active and relaxed upwelling events. NPP rates along with other biophysical variables allowed for a division of the annual cycle into three distinct periods: September to January (high productivity, mean integrated NPP rates of 4.0 g C m-2 d-1), February to March (intermediate productivity, mean integrated NPP rates of 1.4 g C m-2 d-1), and May to August (basal level, mean integrated NPP rates of 0.5 g C m-2 d-1). NPP appeared to be partially controlled by nutrient inputs, either from upwelling (September-April) and river discharge (May-August), maintaining high NPP rates throughout the entire year, with an annual mean NPP rate of 1.1 kg C m-2 yr-1. In this region, El Niño Southern Oscillation events did not appear to impact the NPP interannual variability.