Revisiting chlorophyll data along the coast in north-central Chile, considering multiscale environmental variability

Abstract

Phytoplankton abundance in the surface mixed layer of the coastal ocean responds to environmental changes at various time scales. Here the "warm", "cold" and "neutral" phases of "three environmental cycles" have been jointly considered to assess chlorophyll-a (Chl-a) biomass variability for both the active and relaxed phases of the local, wind-driven coastal upwelling: (i) the interannual ENSO cycle (ii) the annual (seasonal) cycle and (iii) the intraseasonal cycle associated with equatorially-sourced, ocean trapped-waves along the coast in northern Chile. The main goal of this study is to quantitatively assess the variability of the depthintegrated Chl-a biomass in the euphotic zone (∫Chl-a) in terms of an overall "environmental condition" over a 50 km upwelling sensitive coastal strip, revisiting published and unpublished Chl-a ship (C ship = Chl-a + Phaeopigments) data. All possible "environmental conditions" combinations were further ranked into seven "environmental indices" ranging from 0 ("absolutely cold") to 6 ("absolutely warm"). Out of 332 samples of ∫Chl-a, 198/134 were obtained during active/relaxed upwelling conditions from which 24/38 and 30/36 samples were associated with the simultaneous occurrence of at least two "cold"/"warm" phases of the three environmental cycles ("cold"/"warm" environmental conditions), respectively. Lower ∫Chl-a values during "cold" and "warm" environmental conditions relative to the "neutral" ones reached statistical significance for both active and relaxed conditions (144/60 samples respectively). Higher turbulent mixing during "cold" environmental conditions and a deeper nutricline during "warm" ones would explain lower ∫Chl-a-values. Satellite chlorophyll (C sat ) data obtained in clear skies (active upwelling only), showed a similar distribution to those of ∫Chl-a when classified into the corresponding "environmental indices". These results suggest that during "neutral" (transitional) "environmental conditions", nutrient supply, mean light exposure and mixing thresholds, including biological interactions, could be more effective in producing a higher phytoplankton biomass, in spite of a larger dispersion.Key words: ENSO, Coastal trapped waves, coastal upwelling, phytoplankton biomass, AntofagastaValparaíso, Chile. RESUMENLa abundancia de fitoplancton en la capa de mezcla superficial del océano costero responde a cambios ambientales en diferentes escalas de tiempo. Aquí se han considerado conjuntamente las fases "cálida", "fría" y "neutra" de "tres ciclos ambientales" para estimar la variabilidad de la biomasa de la clorofila (Chl-a) para las fases activa y relajada de la surgencia costera inducida por el viento local: (i) el ciclo interanual ENOS (ii) el ciclo anual (estacional) y (iii) el ciclo intraestacional asociado con ondas oceánicas atrapadas a lo largo de la costa en el norte de Chile. El objetivo principal de este estudio es estimar cuantitativamente la variabilidad de la Cl-a integrada en la zona eufótica (∫Chl-a) en términos de una "condición ambien...

The green ribbon: Multiscale physical control of phytoplankton productivity and community structure over a narrow continental shelf

“…The effect of coastally trapped waves on the character of the phytoplankton ecosystem has been demonstrated in the upwelling areas off Chile, where equatorially generated coastally trapped waves alter the efficacy of wind-forced nutrient upwelling by changing the depth of the nutricline. This remote modulation of locally driven nutrient fluxes in Chilean waters causes changes in both phytoplankton biomass and community composition and is thought to impact the Humboldt Current anchoveta fishery (Rutllant and Montecino 2002;Montecino et al 2006). In addition to coastally trapped waves, the mesoscale (, 50 km) eddy field is often energetic in the SSCB (DiGiacomo and Holt 2001;Bassin et al 2005;Todd et al 2009).…”

“…There is a growing body of research that indicates the importance of physical dynamics of different origins and scales acting in concert to structure phytoplankton ecosystems across a wide range of oceanographic settings, including wind-forced upwelling systems (Rutllant and Montecino 2002;Herrera and Escribano 2006;Montecino et al 2006), areas dominated by river plumes (Acha et al 2008;Hickey et al 2010), and continental shelf ecosystems inshore of western boundary currents . The fundamental message of such studies is that the longterm variability of oceanic ecosystems, oceanic biogeochemistry, and fisheries resources depends directly on the nuanced and detailed interplay between physical dynamics on widely disparate scales.…”

Intra- and interannual variability of nearshore phytoplankton biovolume and community changes in the northern Humboldt Current system

“…Fluctuations in phytoplankton biomass have been linked to both intra-and interannual environmental variability through direct observations of in situ samples (Montecino et al, 2006;Pennington et al, 2006;Echevin et al, 2008), remote sensing estimates (Thomas et al, 2001a, b;Carr et al, 2002) and modelling explorations (Chavez et al, 1989;Carr, 2002Carr, , 2003Carr and Kearns, 2003;Echevin et al, 2008). Apart from the modelling studies, descriptions of the phytoplankton community changes have been largely semi-quantitative through the recording of cell abundance changes for different taxonomic groups or the presence of indicator species associated with particular water masses.…”

Diatom blooms and primary production in a channel ecosystem of central Patagonia

“…Among the highly productive ecosystems found in the SE Pacific, the coastal upwelling system that spans the coast of central and northern Chile has been the focus of most research conducted over the past decades, although it is restricted to a relatively narrow coastal band (<50 km, Montecino et al, 2006). Patagonian fjords, on the other hand, comprises ca.…”