Much of what we know about the ocean in those early years of modern science is thanks to the presence of the merchant marine on the high seas. This came about through the organizing efforts of Matthew Fontaine Maury, who arranged for ships to file reports on weather, winds, currents and sea surface temperatures. Charts of prevailing winds based on these reports led to much improved shipping times. Similarly, what we know about sea surface temperature 150 years ago is thanks to the reports from those vessels. Why do I make this point?
Merchant marine vessels have a presence on the high seas second to none. I like to think of them as satellites orbiting earth at sea level. They are platforms from which we can peer into the ocean. Ships operate thermosalinographs that record surface water properties, tow Hardy plankton recorders to collect information on plankton species and their distributions, and release XBTs that profile upper ocean temperatures. A very few ships also operate acoustic Doppler current profilers (ADCP) that scan upper ocean currents along their routes. What makes these operations so valuable is that they are sustained over long periods of time, from years to decades, enabling us to study how water properties and currents vary and trend over time. These are questions we cannot address with our present arsenal of observational tools, research vessels, profiling floats, gliders, and moored instrumentation for they are not cost-effective for sustained observation. Profiling floats give us terrific information on the large-scale hydrographic state of the ocean, but little about what it is doing. So why is it that we don’t include the merchant marine in our planning of long-term observational activities?
The reasons are many and complex, but an overarching reason is that we have yet to develop a policy or culture, if you will, for sustained observation; it is not in our DNA. We all agree on the importance of sustained observation, but sustained observation is costly with the tools we normally work with. In addition, it is poorly aligned with the expectations of professional careers within academic institutions. Even in public institutions it can be difficult to be a champion for and maintain sustained observation. There are of course exceptions: the Sir Alistair Hardy Foundation has been operating continuous plankton recorders on various ships across the Atlantic since the 1930s. NOAA has been working with the merchant marine for decades taking XBTs on select routes in the Atlantic and Pacific oceans. Some ships operate thermosalinographs, and/or are also equipped to measure dissolved CO2. A few ships have been measuring upper ocean currents for years to decades. What is common to all of the above activities is that they have relied upon the sustained interest of a few individuals operating independently.
My own experience, together with Charlie Flagg at Stony Brook University, operating ADCPs on merchant marine vessels has been overwhelmingly positive, vessel owners and operators have been uniformly receptive to our entreaties. Problems notwithstanding, there is no question that the data from these sustained ADCP operations have opened up new and exciting areas of study about oceanic variability.
The value of scanning ocean currents is enormous: first, scanning ocean currents at high resolution gives us directly measured transport(!); second, real time data can be assimilated into future ocean circulation models, alternatively they can be used to assess the accuracy of current operational models; third, archived data enable us to determine space-time variability along the routes, fourth, they can inform us on the presence or absence long-term trends; and fifth, reverse geostrophy can be used to construct density fields at high horizontal resolution. This might be of interest for density may be easier to assimilate into operational models than the velocity field. The ADCP on a ship in regular traffic is a remarkably cost-effective and accurate means by which to keep tabs on the action of the subsurface ocean, what the ocean is doing, if you will. But satellites orbiting at sea level can do so much more. By combining velocity with temperature and salinity we can determine their fluxes, from the ADCP acoustic backscatter we can get measures of biomass, by towing photometers (away from the shadow of the ship) we can accurately determine upwelling light, with lidars we can measure particulate loading in the photic zone, with a little imagination we could develop probes that reach deeper into the water column. All this is possible were the merchant marine to become part of our thinking, culture, or DNA if you will.
In today’s rapidly warming world we badly need to improve our coverage of the high seas, not just of the surface but of the water column as well. This is why I think the merchant marine should be a natural partner in ocean observation for they can with modest effort be equipped to scan the water column along their routes. Further, they also provide valuable ground truth data to remote sensing. I don’t know what we might call it or what it would look like, but we need something akin to an ‘international merchant marine’ UNOLS, a private-public partnership for ocean observation. The Science RoCS initiative (https://sciencerocs.org) is taking the first steps to develop such a partnership and several shipping companies are keen to be involved. Just imagine what might be possible!