Surface nutrient enrichment in the California Current off Southern California: description and possible causes

摘要: Abstract Concentrations of inorganic plant nutrients in California Current waters are frequently greater near the surface than deeper euphotic zone. This nutrient enrichment (conversely, shallow subsurface minima) is poorly described. We used data from 1983–1995 quarterly Cooperative Oceanic Fisheries Investigations surveys to characterize better and examine causal hypotheses. Averaged over survey area, frequency occurrence (% stations) was: phosphate 28%; silicate 51%; nitrate 8%; nitrite 2%. Enrichment frequency, strength depth, thickness minima layers showed spatial (latitudinal, onshore-offshore) temporal (seasonal year-to-year) trends. Co-occurrence, at a given station, two was nearly random. Apparently, different driven by independent factors or may be out phase. Wind speed, wave height, cloud cover had little effect on strength, layers. Potential causes include atmospheric deposition, bubble concentration, vertical horizontal circulation, differences between rates uptake regeneration, photoinhibition, photochemistry, migrations. Relative importance these possible contributors unknown, but some appear minor based arguments using CalCOFI data. believe an imbalance consumption regeneration zone plankton most important factor producing enrichment; least bubbles, advection circulation.