Abstract
The eastern South Pacific (ESP) oxygen minimum zone (OMZ) is a permanent hydrographic feature located directly off the coasts of northern Chile and Peru. The ESP OMZ reaches from coastal waters out to thousands of kilometers offshore, and can extend from the near surface to depths greater than 700 m. Oxygen minimum zones support unique microbial assemblages and play an important role in marine elemental cycles. We present results from two autonomous profiling floats that provide nine months of time-series data on temperature, salinity, dissolved oxygen, chlorophyll a, and particulate backscattering in the ESP OMZ. We observed consistently elevated backscattering signals within low-oxygen waters, which appear to be the result of enhanced microbial biomass in the OMZ intermediate waters. We also observed secondary chlorophyll a fluorescence maxima within low-oxygen waters when the upper limit of the OMZ penetrated the base of the photic zone. We suggest that autonomous profiling floats are useful tools for monitoring physical dynamics of OMZs and the microbial response to perturbations in these areas.
Highlights
Despite their small volume (1% of the global ocean [1]), oxygen minimum zones (OMZ) contribute to about one-third of the oceanic nitrogen loss via denitrification [2]
A strong backscattering signal associated with the oxygen minimum zone was observed in 82.7% of all profiles
Our preliminary results indicate that optical methods could yield important information about spatio-temporal distributions of microbial assemblages in the eastern South Pacific (ESP) OMZ at relevant scales
Summary
Despite their small volume (1% of the global ocean [1]), oxygen minimum zones (OMZ) contribute to about one-third of the oceanic nitrogen loss via denitrification [2]. The world’s largest oxygen minimum zone stretches from the eastern subtropical North Pacific (ESTNP) to the eastern South Pacific (ESP) [6,1,7]. We focus on the eastern South Pacific oxygen minimum zone, which is a permanent hydrographic feature located directly off the coasts of northern Chile and Peru. It reaches from coastal waters to thousands of kilometers offshore, and can extend from the near surface to depths greater than 700 meters. It is maintained by a combination of low oxygen source waters (Equatorial Subsurface Water, ESSW) and high coastal productivity with subsequent bacterial respiration [3,8]
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