Analysis: low oxygen concentrations and biogenic elements associated with Equatorial Subsurface water, and variability in Humboldt Current System off Chile

Analysis of the distribution of low oxygen concentrations and
biogenic elements associated with the Equatorial Subsurface water
and characterization of seasonal and inter-annual variability in the
Humboldt Current System off Chile.

The Equatorial Subsurface Water (ESSW), which is characterized by low
dissolved oxygen content (<2 ml l-1) and high nutrient concentrations,
is one of the main sources of upwelling water in the area. It is
noticeable that the upper boundary of the oxygen minimum layer (OML)
is found at shallower depths in the coastal zone (25-50m) than in the
adjacent oceanic waters (50-100m), both off northern Chile and Peru.
This is a special feature of the Humboldt Current Eastern Boundary
System and is associated with an important de-nitrification regime in
the water column. Before this work was completed, information on the
sources of variability associated with the distribution of the ESSW
OML, the impact of these changes upon pelagic productivity in the
region and biogeochemical cycling was very limited.

The study was focused on three main areas:

- The distribution of low oxygen concentrations in the HCS
- Biogeochemical cycling in relation to the OML in the ESSW
- Biological/ecological effects upon pelagic organisms of the
OML in the ESSW