Variability in diatom contributions to biomass, organic matter production and export across a frontal gradient in the California Current Ecosystem

Abstract

In the offshore waters of Southern California, submesoscale processes associated with fronts may stimulate phytoplankton blooms and lead to biomass shifts at multiple trophic levels. Here we report the results of a study on the cycling of biogenic silica (bSiO 2 ) with estimates of the contributions of diatoms to primary and new production in water masses adjacent to (i.e., coastal or oceanic) and within an offshore front in the Southern California Current Ecosystem (CCE). The coastal and oceanic water were sampled in cyclonic and anticyclonic eddies, respectively, with the frontal water being an interaction region between the eddy types. Concentrations of bSiO 2 varied by 25-fold across the front, with concentrations in frontal waters 20-25% of those in coastal waters. Rates of biogenic silica production spanned an equally large range, with rates within the frontal region that were half those in the coastal regions. Contributions of diatoms to primary and new production were disproportionately higher than their contribution to autotrophic biomass in all areas, ranging from 5-8%, 19-30%, and 32-43% for both processes in the oceanic, frontal and coastal waters, respectively. Across the frontal area, diatoms could account for <1.0%, 6-8%, and 44-72% of organic matter export in the oceanic, frontal and coastal waters, respectively. The results suggest that the regions of frontal interactions between eddies in the southern CCE can account for variability in diatom biomass, productivity and export over very short spatial scales that is comparable to the variability observed across the Pacific basin.

Iron-Binding Ligands in the Southern California Current System: Mechanistic Studies

“…This cruise was a CCE-LTER process cruise, which uses drifters in a Langrangian platform to follow distinct water masses (Landry et al, 2009;Krause et al, 2015). Each series of stations sampled within the same water mass were denoted as a "cycle" Krause et al, 2015).…”

“…However, only one station from each cycle was sampled in this particular study, so sampling locations will simply be referred to as stations. Each station has been given the same number as the cycle to which it belongs (for example, station 1 was part of cycle 1) in order to compare to other studies from the same cruise (e.g., Brzezinski et al, 2015;Krause et al, 2015).…”

“…Stations were sampled in the coastal (3, 4), frontal (1, 6), and oceanic (2) side of a distinct frontal feature Krause et al, 2015) shown over the averaged chlorophyll a (chl-a; mg m −3 ) for the month of July in 2011.…”

Phytoplankton Stimulation in Frontal Regions of Benguela Upwelling Filaments by Internal Factors

“…Krause et al, 2015). The optimal DIN:DSi ratios for diatoms are variable (Brzezinski, 1985), but for rough estimates a molar ratio of DIN:DSi = 1.25 is applicable (Sarthou et al, 2005).…”

“…Also on the worldwide scale, studies undertaken in frontal areas detected enhanced phytoplankton production and biomass, primarily in a subsurface maximum. These patterns are mainly explained by physical forcing, for example by wind events that cause vertical nutrient transport especially in these physically dynamic regions (Traganza et al, 1987;Franks, 1992;Largier, 1993;Claustre et al, 1994;Franks and Walstad, 1997;Allen et al, 2005;Landry et al, 2012;Li et al, 2012;Taylor et al, 2012;Krause et al, 2015;Nagai et al, 2015). Correspondingly, also the zooplankton concentration is enhanced .…”