Wind on the Water

The world's oceans represent the major source of stored heat energy that helps to mediate Earth's climate. The ocean surface boundary layer, where the ocean and atmosphere meet, heat is exchanged, as are gasses like CO2. The rate at which these exchanges take place has major implications for the mechanisms controlling climate change. A soon to be published paper in the journal Science documents a new study of the ocean surface boundary layer and, to the investigators' surprise, reveals that the rate of energy dissipation within the boundary layer to be enhanced by 10 to 20 times. This indicates that the atmosphere does not supply the energy for the boundary turbulence, the ocean does. This contradicts the prevailing scientific wisdom and shows once again that computer climate models are constructed using false assumptions.

In the classical paradigm and in current climate models, turbulence at the ocean surface boundary layer is driven by atmospheric forcing. Using observations from a 1-km-wide front within the Kuroshio, a strong western boundary current in the northwestern Pacific Ocean, Eric D’Asaro et al. found the rate of energy dissipation within the boundary layer to be enhanced by 10-20 times. According to their paper, “Enhanced Turbulence and Energy Dissipation at Ocean Fronts,” this suggests that the front not the atmospheric forcing supplied the energy for the turbulence. The authors describe the situation in the paper's introduction:

Although the basic characteristics of the ocean circulation have been well known for many decades, a detailed understanding of its energetics has only emerged recently. The energy sources are well understood: wind stress acting on surface currents or “wind-work,” particularly in the Southern Ocean, is the dominant energy source, with little net input from heating/cooling or precipitation/evaporation. The energy sinks, however, are less well understood. Energy dissipation necessarily requires a cascade of energy through 9 orders of magnitude, from the size of the ocean to the centimeter scales of viscous dissipation. A cascade of processes supports this flux. Instabilities of the large-scale circulation lead to the generation of a rich field of eddies with typical scales of 100 km at mid-latitudes. The dynamics of these eddies is highly constrained by the Earth’s rotation such that their currents are nearly geostrophic (i.e., the flow is governed by a balance between Coriolis and horizontal pressure forces). A turbulent, geostrophic eddy field tends to flux energy to larger, rather than smaller scales, thus providing no obvious path to dissipation. Recent simulations with very high-resolution models suggest a new path from the eddy field toward dissipation through the formation of “submesocale” fronts, regions of strong lateral gradient in the upper ocean, with horizontal scales of 1-10 km. Instabilities of these fronts could then cascade energy from the frontal scale to dissipation.

The paper then goes on to explain that the boundary layer is stratified, not mixed, and deepens by the action of turbulent motions. These motions get at least part of their energy from the frontal circulation as opposed to atmospheric forcing, as commonly thought. “This is a shift from the classical paradigm of a surface boundary layer driven by the atmosphere, with implications for climate dynamics,” the authors state.

The surface boundary layer is the mediator for air-sea interaction and greatly influences “processes that play an integral role in the climate system such as the oceanic sequestration of carbon and the subduction, or transfer, of heat, salt, and dissolved gasses from the ocean’s surface to its interior.” Furthermore, sequestration of carbon and subduction occurs to a large degree in the proximity of the ocean’s main currents: the Gulf Stream, Antarctic Circumpolar Current, and Kuroshio, the subject of this study. This could, in part, help explain why ocean uptake of CO2 is not shrinking as predicted.


Diagram showing the forces affecting boundary layer turbulence.

The study found that a number of previously unexpected mechanisms were at work moving energy among layers in the ocean. These have significant, previously unsuspected impact on the upper ocean boundary layer. The authors conclude: “The observations presented here break from this paradigm by suggesting that lateral density gradients and their geostrophic currents can also play a role in boundary layer dynamics by supplying energy to turbulence at the expense of the circulation and permitting stratification and turbulence to coexist.”

While this finding is of interest for oceanographers there are wider implications for those trying to predict Earth's future climate. Modelers will say that the total amount of energy transferred to and from the Earth system isn't altered by these findings. Perhaps not, but having the transfer mechanism wrong means any prediction of change in that system cannot be relied upon to be accurate. And the Science paper claims that current estimates are off by a factor of 10 or 20 fold. Here are the authors' final conclusions:

[T]hese results are consistent with recent theory on submesoscale processes and thus encourage incorporation of this theory into boundary layer models. Such physics is not accounted for in present-day climate models. Fronts associated with the Kuroshio, Gulf Stream, and Antarctic Circumpolar Current are key players in the ocean-atmosphere climate system. Inaccurate representation of the boundary layer and flow energetics in frontal regions could thus significantly affect the predictive skill of climate models.

That is science speak for the models are wrong—they do not represent an accurate picture of how nature works. This means that the models' predictions are suspect. The study's findings affect both energy transfer and the sequestration and release of CO2, the climate lobby's favorite smoking gun. This bears repeating because, despite many such revelations, climate change catastrophists and ecological prophets of doom continue to base their case on outdated, disproven models. This is just the latest in a number of such findings, highlighting the inadequacy of climate models. Science moves on, the climate alarmists have not.

Be safe, enjoy the interglacial and stay skeptical.