An Annual Cycle of Upper Ocean Salinity Captured by High-Resolution Glider Surveys

PI: Luc Rainville, Craig M. Lee, Charles Eriksen, Kyla Drushka
Sponsor: NASA

We are using Seagliders to provide long-term and high-resolution measurements of the upper ocean in the SPURS region. Gliders maintain a persistent presence though a complete annual cycle, repeatedly occupying survey patterns to resolve the mixed layer and upper pycnocline. Over deployments lasting an entire year, the main objectives of the SPURS Seaglider program are to

  1. Resolve the salinity, temperature, density, and velocity fields in the upper 1000 m of the water column in 200 km by 200 km boxes centered on the two flux mooring sites, over temporal scales of 14 days and spatial scales of ~50 km.
  2. Measure the rates of turbulent dissipation in the thermocline and at the base of the mixed layer in the two 200 km by 200 km boxes. Mixing measurements will be made on all gliders sampling near the moorings (3 gliders each), to resolve vertical mixing term with the same temporal and spatial scales as for the scalar and velocity fields.
  3. Provide the large context of the two sites by repeating a long meridional section across the subtropical gyre and the salinity maximum. Two gliders will complete a full 1100-km section in one month or less.

With these measurements, we will be able to resolve the salt storage and the horizontal and vertical advection of salt, and quantify diapycnal mixing of salt by small-scale turbulence around the moorings, therefore providing a direct estimate of the main terms of the salt budgets in the mixed layer and in the whole upper ocean.

The glider surveys characterize the upper ocean in a consistent, reapeatable manner at temporal and spatial scales that are well matched to the Aquarius footprint and repeat cycle. The year-long time series will capture an annual cycle to provide ample data for direct comparison with satellite measurements. These data will also be used to assess the ability (and limitations) of using remotely-­‐sensed measurements to quantify selected terms of the large-scale salinity budget.