Trophic cycling and carbon export relationships in the California Current Ecosystem

Abstract

We constructed a simple non-steady-state model of trophic cycling relationships in the California Current Ecosystem and tested its predictions of mesozooplankton fecal-pellet export against vertical carbon-flux measurements by the 234 Th method taken during Lagrangian experiments. To assess trophic relationships, we simultaneously measured 14 C-primary production and chlorophyll-based rate estimates of phytoplankton growth, microzooplankton grazing, mesozooplankton grazing, and net phytoplankton growth. Study locations ranged from coastal upwelling to offshore oligotrophic conditions. E-ratios (carbon export : 14 C-primary production) predicted by the model ranged from 0.08 to 0.14, in good agreement with both the magnitude and the variability found in contemporaneous measurements of 234 Th export and C : 234 Th-ratios of sinking particles. E-ratios were strongly decoupled from new production estimates. The lowest measured and predicted e-ratios were associated with higher nutrient chlorophyll parcels with net accumulating phytoplankton in the inshore region. For our study sites, variability in export efficiency was determined by the local net balance of growth and grazing and the relative strengths of grazing pathways to microzooplankton and mesozooplankton. Despite very different plankton assemblages studied, the consistently good agreement between independently measured productiongrazing processes and biogeochemical rates suggest that zooplankton are the major drivers of vertical carbon-flux in this system during springtime.

Small time scale plankton structure variations at the entrance of a tropical eutrophic bay (Guanabara Bay, Brazil)

“…The phytoplankton export can be due to vertical transport (sinking), lateral transport (advection) or grazing (e.g. LEGENDRE; STUKEL et al, 2011;ADJOU et al, 2012;TORTAJADA et al, 2012). Small cells are able to remain in suspension longer due to their high surface/volume ratio (GUENTHER; BOZELLI, 2004), and lateral transport is not size selective.…”

“…Conversely, in shorter food chains (e.g., near the bottom: autotrophic microplanktonmesozooplankton), a greater amount of carbon is available for export (e.g. LEGENDRE; LE FEVRE, 1989;VARGAS et al, 2007;STUKEL et al, 2011). Since the bottom layer is moving towards the inner bay while the surface layer is flowing outwards, at least during neap tide periods, if the carbon balance at each of these layers is positive (i.e., export higher than regeneration), it will result in export in both directions .…”

Temporal variation of phytoplankton growth and grazing loss in the west coast of Peninsular Malaysia

“…Grazing loss is an important process in the classical pathway as the fate of phytoplankton 20 production not grazed is either through horizontal export into adjacent waters or sinking (Cloern et al 1985, Turner 2002, Stukel et al 2011. From a cross-compilation of 66 studies, Calbet and Landry (2004) revealed that grazing loss accounts for 60 -75% of daily phytoplankton production, and is higher in estuarine and coastal waters than in oceanic waters.…”

Biological production rates off the Southern California coast estimated from triple O2 isotopes and O2 : Ar gas ratios

“…Export production in the California Current EcosystemSeveral studies based on both in situ (Thunell 1998;Stukel et al 2011) and modeling (Olivieri and Chavez 2000) approaches suggest that POC export may be inversely related to PP in the California Current Ecosystem. These studies also suggest that much of the organic material fixed in high-productivity regions inshore of the California Current may be advected offshore in the Ekman layer.…”

“…Recent 14 C-PP estimates for the CalCOFI region using the same 24 h in situ methodology employed at HOT also suggest that on-deck incubations underestimate 14 C-PP. Stukel et al (2011) (where the CalCOFI 14 C-PP has been scaled to a 24 h rate using the factor of 1.81 discussed above). We also note that recent comparisons of mixed-layer 17 D-GOP and 14 C-PP off the central California coast (D. Munro unpubl.)…”