Sampling the Sea Surface Microlayer

This is Jim Fiorendino, your host for On the Ocean.

Clouds form when water droplets or ice crystals grow on aerosols in the atmosphere. These aerosols may originate as organic material in the world’s oceans. Breaking waves and the bursting of bubbles propel droplets of water containing organic material into the atmosphere, which may become aerosolized and promote cloud formation. An important source of the organic material in droplets of seawater are marine phytoplankton, which leak exopolymers and organic matter into the surrounding water. Exopolymers are carried to the surface of the ocean by bubbles and become concentrated in the sea surface microlayer, which is a thin skin at the ocean’s surface roughly 50 micrometers thick.

Figure 1: Exopolymer concentration results from sea surface microlayer sampling.                   Thornton DCO, Brooks SD and Chen J (2016) Protein and carbohydrate exopolymer particles in the sea surface microlayer (SML). Frontiers in Marine Science 3:135.

Studying the sea surface microlayer is important in understanding the transfer of organic material and other particles to the atmosphere. The sea surface microlayer contains higher concentrations of organic material and exopolymers than the water beneath it, and is home to a unique microbial community capable of coping with high amounts of ultra-violet radiation from the sun. Sampling this thin layer of the ocean is difficult, and cannot be done from a research ship. Instead, scientists operate from rigid-hulled inflatable boats to avoid contamination from larger vessels. Sampling is conducted by dipping a large sheet of glass into the ocean. When the glass is pulled up, water from the sea surface microlayer clings to the glass and can be collected and stored for analysis. Results of sea surface microlayer sampling are shown in figure 1. Understanding the relationship between phytoplankton biology and cloud formation requires interdisciplinary research; Dr. Daniel Thornton of the Texas A&M University Department of Oceanography is currently collaborating with Dr. Sarah Brooks of the Department of Atmospheric Sciences on research regarding phytoplankton biology and cloud formation. Ultimately, through careful laboratory experiments and sampling in the field, Dr. Thornton and Dr. Brooks hope to link cloud formation processes to the biology of marine phytoplankton. The research being conducted by Dr. Thornton and Dr. Brooks is funded by the National Science Foundation.

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to and click On the Ocean.

Contributing Professor: Dr. Daniel Thornton