Hydrographic observations of the flow in the vicinity of a shallow seamount top in the Gulf of California

An interdisciplinary study of the El Bajo de Espiritu Santo (EBES) seamount in the Gulf of California leads to a number of conclusions on the interaction between the dynamics and the biology on a shallow seamount. The EBES seamount is a mid-latitude, shallow seamount where the frequency of the tidal forcing (K1+M2) is superinertial. It is a place of high concentration of zooplankton, fish larvae and pelagic fish. A number of processes identified here are capable of locally enhancing productivity at very different time scales. Entrainment induced by vertical shear of the currents generates mixing on its summit. Three-dimensional tidal advection is important during spring tides. Surface hydrographic fields change quickly due to common, short-lived wind bursts, which force current jets out of the neighboring Bay of La Paz. Impinging large-scale flows perturb the vertical structure along the flanks of the seamount. Low frequency (1–3 weeks) cool and warm events, consequence of the large-scale dynamics in the Gulf of California, also reach the seamount. Recent consecutive El Nin˜ o y La Nin˜ a events produced large (2–3 C) interannual temperature differences. Not only biomass but diversity is also high, 104 different species of fish larvae have been identified here. This is thought to be due to the specific geographical location of the seamount. Outflows from the Bay of La Paz (and the variability observed in near-surface temperature record suggests that there are other phenomena) promote higher diversity of species by carrying larvae and zooplankton from regions biologically different to the EBES seamount.