Deep ocean hydrographic heterogeneity inferred from offshore geodetic experiments

Observational evidence, supported by high resolution numerical model simulations, indicate that meso- and submesoscale dynamics exists in the deep ocean (>2000m). However, over most parts, observing the deep ocean is restricted to address either spatial but not temporal (ship surveys) or temporal but not spatial (moored sensors) scales of variability. The advent of a growing number of offshore geodesy experiments, conducted with networks of distributed sensor arrays, aiming to evaluate tectonic deformation through strain measurements can potentially provide new ways to observe deep sea hydrographic variability. Despite the different observing objectives of offshore geodetic and oceanographic experiments, a great overlap in the measured parameter space exists, which has motivated analyses exploring possible cross-benefits. Here we present the evaluation of temperature, pressure, and sound speed observations from a 2.5-year offshore geodesy experiment centered along the northern Chilean subduction zone (~21.5°S and ~71.5°W to ~70.5°W). Our analysis confirms multi-year warming trends that previous studies have reported for the deep ocean but shows an additional regionalization of warming trends. Superimposed onto the multi-year warming trend are temperature fluctuations that show multi-hourly to multi-weekly periods and amplitudes that show both spatial and depth/regional dependencies. Aside from a general decrease in energy levels of the fluctuations with depth, we see evidence of ocean-topography interactions through barotropic topography waves. Taken together, the observations reveal de-coupled dynamical regimes seaward and landward of the deep-sea trench that mark the extent of the abyssal part of the eastern boundary current off Chile and demonstrate the potential of time series from offshore geodetic surveys for hydrographic analyses.