Cruising the Ocean’s Surface Microlayer

June 16, 2017 · 0 comments

Oceans are deep, and they are integral to the climate system. But the exchanges between ocean and atmosphere that preoccupy many scientists are not in the depths but instead in the shallowest of shallow layers.

A lot happens in the topmost millimeter of the ocean, a film of liquid called the “sea-surface microlayer that is, in many ways, a distinct realm. At this scale, exchanges with the atmosphere are more about diffusion, conduction, and viscosity than turbulence. But the layer is small and difficult to observe undisturbed and over sufficient areas. As a result, “it has been widely ignored in the past,” according to a new paper by Mariana Ribas-Ribas and colleagues in the Journal of Atmospheric and Oceanic Technology.

Nonetheless, Ribas-Ribas and her team, based in Germany, looked for a new way to skim across and sample the critical top 100 micrometers (one tenth of a millimeter) of the ocean. This surface microlayer (SML) “plays a central role in a range of global biogeochemical and climate-related processes.” However, Ribas-Ribas et al. add,

The SML often has remained in a distinct research niche, primarily because it was thought that it did not exist in typical oceanic conditions; furthermore, it is challenging to collect representative SML samples under natural conditions.

In their paper (now in early online release), the authors report on their solution to observing is a newly outfitted remote-controlled catamaran. A set of rotating glass discs with holes scoops up water samples. Pictured below are the catamaran and (at left, top) the glass discs mounted between the hulls and (bottom left) the flow-through system.

catamaran

Catamarans are not new to this research, but they were generally towed behind other vessels and subject to wake effects or were specialized. The new Sea Surface Scanner (S3) takes advantage of better remote control and power supply technology and can pack multiple sampling and sensors and controls onto one platform. Tests in the Baltic Sea last year showed the ability of S3 to track responses of organisms in the surface microlayer to ocean fronts, upwelling areas, and rainfall. The biological processes in turn affect critical geochemical processes like exchanges of gases and production of aerosols for the atmosphere.

The technology may be a fresh start for research looking in depth at the shallowest of layers. See the journal article for more details on the S3 and its performance in field tests.