Abstract
The temporal variability of Net Primary Production (NPP) off central Chile (36oS, 73oW), 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 Nino Southern Oscillation events do not appear to impact the NPP interannual variability.
Highlights
The Eastern Boundary Upwelling Systems (EBUS) are considered the most productive regions in the world’s oceans and sustain the greatest portion of global fishery production (Pauly and Christensen, 1995; Cubillos et al, 1998b)
A significant gap remains for understanding temporal Net Primary Production (NPP) dynamics and rates, which in turn limits the knowledge of how NPP rates and their variability are maintained
Cruises (R/V Kay-Kay II) visited the site to collect continuous profiles using a Conductivity Temperature Depth (CTD) probe (SeaBird 19 and SeaBird 25), along with discrete samples for O2, nutrients, Chlorophyll-a (Chl-a) and NPP rates at depths of 2, 5, 10, 15, 20, where τy (Pa; kg m−1 s−2) is the mean wind stress meridional component within the box 73–74◦W, 36–39◦S, ρ represents the mean density of the water column at ST18 (1026.21 kg m−3), and f indicates the Coriolis parameter corresponding to the latitude of ST18 (8.67 ∗10−5 s−1)
Summary
The Eastern Boundary Upwelling Systems (EBUS) are considered the most productive regions in the world’s oceans and sustain the greatest portion of global fishery production (Pauly and Christensen, 1995; Cubillos et al, 1998b). This high productivity is mainly the result of the coastal upwelling process by which subsurface, nutrient-rich waters ascend to the surface in response to wind stress on surface water, fertilizing waters in the photic zone and promoting phytoplankton blooms. Information on marine primary production has been centrally important in understanding the fluxes of energy and organic matter in the ocean and the major biogeochemical cycles (e.g., C, N, P)
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