I first dipped into the ocean noise issue back in 1992, when the US Navy was funding a project that would ensonify a large portion of the Pacific Basin, purportedly to measure “ocean climate.” Without the benefit of more complete information, my suspicions were alerted.
By 1990 the public’s concerns about climate change began to seep into the collective discussion. This served as a backdrop for a range of responses – from serious conversations about how to stop it, to carpetbaggers using the public’s worries to provide justifications for various hair-brained proposals.
Probably the most audacious of these was flown by a big-thinking adman who proposed launching a geo-stationary reflective billboard that would float above the horizon throughout the global sunset announcing some product or other. Coca-Cola was one of the suggestions – thereby colonizing the sunsets of everybody on the planet with a singular consumer message.
The prospect was so outrageous and prompted so much public ire – which the company, Space Marketing Inc., attempted to ameliorate by suggesting that the 1km x .5km reflective billboard would be used as a platform for an advanced meteorological instruments to monitor climate change. Fortunately, the project didn’t fly, but it was one of many bad ideas lurking around at the time seeking cover under the ruse of addressing public concern about an existential threat.
So when the proposal to use sound to measure the ocean’s climate came up, I already had one eyebrow raised. Amplifying my concern was the argument that the program – called Acoustic Tomography of Ocean Climate (ATOC) – could settle the “global warming” question.
There is a direct correlation between ocean sound velocity and water density – the higher the density, the higher the velocity. There are three main variables in the density of seawater; temperature, salinity, and depth pressure. So knowing the salinity (typically 3.5%) and depth, you can figure out the temperature. If you average this velocity across ocean basins, you can get a pretty accurate measure of the mean temperature of the entire body of water.
There are other factors to consider: The ocean surface is subject to warming by the sun and turbulence mixing from wind, and thus the surface temperature is quite variable; from frozen cold to bathtub warm – depending on weather, solar exposure, season, and latitude.
But there is a deep isothermal layer in the ocean which is below the surface “mixing” area which has been thermally stable since the last ice age (between 0 and 3 degrees C, depending on the depth). So the reasoning was that if you could measure any warming of this isothermal layer we’d know for sure that “global warming” was happening. This was the foundation of the ATOC idea.
But there were two problems with this argument: First, we already knew the earth was warming, so fishing for additional data-points to “prove it” was just more procrastination. This was substantiated by the designer and key proponent of the scheme, Walter Munk (known as the “Einstein of the Ocean”) who was at the time suggesting that we needn’t act on “global warming” until we really knew for sure…
The second, and far more menacing problem was that, given that 90% of the ocean’s water is in this isothermal layer, an increase of 0.1° C would already indicate a state of ‘thermal runaway.’ So it was with some concern that last summer I read that this isothermal layer had increased in temperature by 0.3°C.
So it was ominous, but not entirely surprising that two recent articles appeared – one in the Washington Post, the other in the New York Times, about two scientific papers – one from Science and one from Nature, detailing the surprisingly rapid rise in ocean temperature.
Neither of these studies used ATOC; rather they used data from the Argo Float Program – with thousands of globally deployed buoys that sink down into the deep ocean and return with temperature, salinity, pH and other data that they beam up to satellites on their return to the surface. By averaging these thousands of data-points, average ocean temperature can be derived.
Perhaps we should re-deploy ATOC, just to make sure the Argo data are correct….
Michael, You write: “There is a direct correlation between ocean sound velocity and water density – the higher the density, the higher the velocity. There are three main variables in the density of seawater; temperature, salinity, and depth pressure. So knowing the salinity (typically 3.5%) and depth, you can figure out the temperature. If you average this velocity across ocean basins, you can get a pretty accurate measure of the mean temperature of the entire body of water.
There are other factors to consider: The ocean surface is subject to warming by the sun and turbulence mixing from wind, and thus the surface temperature is quite variable; from frozen cold to bathtub warm – depending on weather, solar exposure, season, and latitude.”
My question: is the microplastic now found in the ocean a factor?
Michael, You write: “There is a direct correlation between ocean sound velocity and water density – the higher the density, the higher the velocity. There are three main variables in the density of seawater; temperature, salinity, and depth pressure. So knowing the salinity (typically 3.5%) and depth, you can figure out the temperature. If you average this velocity across ocean basins, you can get a pretty accurate measure of the mean temperature of the entire body of water.
There are other factors to consider: The ocean surface is subject to warming by the sun and turbulence mixing from wind, and thus the surface temperature is quite variable; from frozen cold to bathtub warm – depending on weather, solar exposure, season, and latitude.”
My question: is the microplastic now found in the ocean a factor?