Regulation of phytoplankton communities by physical processes in upwelling ecosystems

Abstract

Sinking rates of particles were superimposed on the x-z-t current field observed at 15S off the coast of San Juan, Peru in March-May, 1977 to calculate particle trajectories in the upwelling circulation. Vertical velocities were calculated by a modified variational objective analysis technique using the measured onshore and longshore currents in conjunction with the physical constraint of mass continuity. The calculated vertical flow showed considerable temporal and spatial variability, with the mean vertical transport varying by two orders of magnitude over the 16 km wide continental shelf. Changes in direction occurred rapidly (within 24 h) as has been observed for horizontal circulation in this region. The vertical velocity of water was much greater than the sinking rates of particles during the 52 day period, so that the net vertical transport of particles was controlled by the vertical velocity of the water. Reseeding of sinking particles from the surface offshore-flowing layer into the deeper onshore flow could not be demonstrated for this period, which may explain why the measured biomass and primary productivity were anomalously low in 1977. Vertical mixing greatly increased the possibility of reseeding by transporting material downward into the onshore flow. We suggest that recirculation of particles may normally occur in the Peruvian upwelling system, but that the continuity probably involves movement in the longshore as well as the cross-shelf direction.

Benthic community structure and spatiotemporal thermal regimes in two upwelling ecosystems: Comparisons between South Africa and Chile

“…On a global scale, these similar physical characteristics appear to drive similar biological processes, and one of the consequences is that EBCEs account for a disproportionate amount of primary and secondary production in the world (Chavez and Toggweiler 1995;Pauly and Christensen 1995) and support similar assemblages of zooplankton and pelagic fish (Parrish et al 1983). Likewise, similarities have been observed in seasonal succession of phytoplankton, from diatoms to dinoflagellates (Smith et al 1983) and interdecadal shifts in dominance of fish species, anchovy or anchoveta alternating with sardine (Lluch-Belda et al 1989;Cury et al 2000). Relative to nonupwelling regions, rocky intertidal communities of EBCEs appear to have higher primary productivity and greater biomass and abundance, but lower diversity (Bustamante et al 1995;Bustamante and Branch 1996;Menge et al 2003).…”

Primary production enhancement by artificial upwelling in a western Norwegian fjord

“…In many coastal waters primary production rates benefit from upwelling of deep water. In this process surface waters are displaced offshore by a one-sided horizontal divergence caused by surface Ekman transport and are replaced by nutrient-rich deep water (Smith et al 1983). The upwelling circulation operates on a wide range of time scales, which include short (hours), intermediate (days) and long (seasonal and inter-annual) scales.…”

Diatom dynamics in a coastal ecosystem affected by upwelling: coupling between species succession, circulation and biogeochemical processes

“…Fluctuation in diatom composition and number has been correlated with changes in the circulation of water bodies associated with upwelling events (Huntsman & Barber 1977, Margalef 1978, Barber & Smith 1980, Jones & Halpern 1981. The temporal evolution of upwelling to stratification is marked by a change from small-celled diatoms to a community of medium-sized mixed diatoms and culminates in flagellates which are better adapted at maintaining buoyancy under low mixing conditions (Smith et al 1983, Mann 1993. Changes in nutrient regime are associated with upwelling/stratification cycles and have been correlated with species succession (e.g.…”