Some places experience double high tides, where the tide starts to ebb for a short while, only to briefly flood again before finally receding. The result is a very long high tide with weak currents, and is important for navigational purposes. The existing theory for when and where double high tides occur does not always capture them, and it can only be applied to double highs occurring on a twice-daily tide. Here, the criterion has been generalized to capture all double high or low tides.

A new method of observing ocean heat content throughout the entire ocean depth is provided. The new method is compared with simulated ocean heat content changes from climate models. The comparisons are carried out in various depth layers of the ocean waters. It is found that there is excellent agreement between the models and the observations. Furthermore, we propose that changes to ocean heat content be used as a fundamental metric to evaluate climate models.

Lee waves play a significant role in ocean mixing but are difficult to study with traditional casts, moorings, and tows due to their stationary nature and limited spatial extent. We develop a new method to estimate turbulent diffusivity from seismic data and find elevated levels of turbulence associated with lee waves in the mid-water and around the seafloor that are 5 times greater than surrounding waters and 50 times greater than open-ocean diffusivities.

Regional sea surface height (SSH) changes due to an abrupt weakening of the Atlantic meridional overturning circulation (AMOC) are simulated with a high- and low-resolution model. A rapid decrease of the AMOC in the high-resolution version induces shorter return times of several specific regional and coastal extremes in North Atlantic SSH than in the low-resolution version. This effect is caused by a change in main eddy pathways associated with a change in separation latitude of the Gulf Stream.

We use ocean bottom-pressure measurements from 17 tropical sites to determine the annual cycle of ocean mass. We show that such a calculation is robust, and use three methods to estimate errors in the mass determination. Our final best estimate, using data from the best sites and two ocean models, is that the annual cycle has an amplitude of 0.85 mbar (equivalent to 8.4 mm of sea level, or 3100 Gt of water), with a 95% chance of lying within the range 0.61–1.17 mbar.