Advances in bio-optical sensing on robotic platforms to elucidate ecosystem production in the interior ocean

The global view of ocean productivity has been defined for the past three decades by satellite-derived images of optical properties of the ocean’s surface layer. Yet in most of the ocean, zones of enhanced phytoplankton production and nutrient recycling are located at depths below the view of optical satellites. In the subtropical gyres, the almost ubiquitous deep chlorophyll maximum is often located at depths exceeding 100m, along density interfaces at a boundary between the down welling light flux and upward transport of nutrients. Below the chlorophyll maximum heterotrophic production is the dominant process resulting in strong oxygen consumption and dissolved nutrient regeneration. Observing the physical forcing and biogeochemical dynamics that drive this system at the relevant time scales ranging from the diel to the seasonal has been a long-standing challenge in oceanography. In particular, measuring the processes occurring through perturbations to relaxation has often been more happenstance than design.

In this presentation we describe advances in sensor systems deployed on autonomous robotic profilers to quantify carbon, oxygen and nutrient cycling within the interior ocean and present examples from the subtropical Indian Ocean, western Mediterranean and Labrador Sea.