A New Profiling Float for Coastal and Upper Water Column Applications

Gene Massion, Kenneth S Johnson, Eric J Martin, Ed Mellinger, Paul McGill and Paul Coenen, Monterey Bay Aquarium Research Institute, Moss Landing, CA, United States
Abstract:
Here we present the initial work and results from the development of a biogeochemical profiling float optimized to operate on the continental shelf and upper slope. The continental shelves and slopes comprise only 5 to 10% of the ocean, but they contribute as much as half of the global new primary production (Jahnke, 2010). As a result, one of the key recommendations in the CCARS Science Plan for Carbon Cycle Research in North American Coastal Waters (Benway et al., 2016) is “Further development of event-scale observing capacity (e.g., novel autonomous platforms) in all continental margin systems to better quantify impacts of episodic events on coastal carbon budgets”. The Coastal Profiling Float (CPF) targets this recommendation with the specific goal of supporting coastal zone ecosystem observing missions using a large array of CPFs over spatial scales from 10s to 1000s of kilometers and time scales on the order of years at an economically sustainable cost. The CPF carries a suite of biogeochemical instruments (CTD, Oxygen, pH, Nitrate, Optical Radiometer, Fluorometer and backscatter) and can follow a user specified depth and sampling profile from 500 meters deep to the surface including the capability to park on the seabed or at a user specified depth. The results of each CPF profile are transmitted back to shore in near real time using the Iridium satellite network. Working in the coastal zone presents a variety of challenges that drove the need for significantly better buoyancy control in the CPF. The CPF can change its displacement by 3.5 liters allowing it to anchor (and more importantly de-anchor) on the seabed and profile through pycnoclines from almost any ocean density through freshwater. The large displacement allows for profiling velocities in excess of 50 cm/sec and minimizes the need for precise ballasting. In addition, the CPF supports user defined profile trajectories requiring precise depth and velocity control with minimal depth overshoot enabling missions in a few 10s of meters of water depth. The current CPF design is relatively configurable and we have run missions with a variety of other instruments including a large sediment trap. In addition, the CPF has the potential to operate in Arctic waters where large density gradients require the large displacement change capability of the CPF buoyancy engine.