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 13 C 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 (r 2 = 0.61), but when these data were separated into two periods, higher r 2 value was found during winter (r 2 = 0.70) with respect to the rest of the year (r 2 = 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.

Influence of coastal upwelling on micro-phytoplankton variability at Valparaíso Bay (~33ºS), Central Chile

“…Second, dinoflagellates are favoured under stratification (non-upwelling) and oligotrophic (low nutrient content) conditions during the autumn/winter period (Anabalón et al 2007. However, this seasonal pattern has showed temporal and spatial heterogeneity related to episodic wind-forcing regimes and other hydrographic factors (Thiel et al 2007, Anabalón et al 2016, Testa et al 2018.…”

“…However, nutrients from rivers in Central Chile can also impact the phytoplankton (Iriarte et al 2012, Anabalón et al 2016, Aparicio-Rizzo & Masotti 2019. Seasonal freshwater discharge can impact coastal systems during weak upwelling activity periods when nutrient input from rivers can help maintain basal phytoplankton biomass (Chl-a) and PP (Léniz et al 2012, Testa et al 2018. In these areas, with quasi-constant high nutrient concentrations year-round, changes in phytoplankton are not just linked to nutrients availability but also other factors (temperature, salinity, stratification/mixing conditions, or solar radiation).…”

“…During these months, upwelled nutrient-rich water fertilizes the photic layer in response to favourable S-SW wind intensification (Shaffer et al 1999, Sobarzo et al 2007, Pinochet et al 2019. This triggers the phytoplankton response via an increment in biomass and cell abundance and impulse the primary production (PP) (González et al 2007, Testa et al 2018.…”

The Influence of River Discharge on Nutrient Export and Phytoplankton Biomass Off the Central Chile Coast (33°–37°S): Seasonal Cycle and Interannual Variability

“…Off the Itata River, evidence suggests that nutrient inputs have a positive influence on the pico-nanophytoplankton community (Iriarte et al, 2012). Furthermore, Itata River discharge during austral winter may partially support basal productivity around the river mouth, as a result of nutrient input and the influence of the fresh water plume on water column stratification (Testa et al, 2018). Recently, salinity (measured by a SBE 37 MicroCAT) and chlorophyll data (measured by a C3 TM Submersible Fluorometer) was collected at approximately 1 m depth, taken from a coastal buoy located about 10 km off the mouth of the Itata River (Belmar et al, 2017).…”

“…In this region, recent studies have shown evidences of the impact of the nutrient export in these river plumes on the carbon biogeochemistry and phytoplankton community of coastal waters off Central Chile in winter (Iriarte et al, 2012;Léniz et al, 2012;Pérez et al, 2015;Yevenes et al, 2016) and its possible contribution in maintaining high primary productivity rates in coastal waters (Testa et al, 2018). Nonetheless, there is a lack of a systematic analysis into the regional scale influence of the river discharges variability on nutrient loading and phytoplankton biomass in coastal waters.…”