Sea surface micro layer

The boundary between the ocean and the atmosphere, where the air and sea interact, is known as the sea surface microlayer. Understanding how nutrients, pollutants and organic matter are exchanged between the air and the sea also is vital for better understanding the role they play in regulating carbon cycles and climate. The problem, however, is that studying the sea surface microlayer is an extremely time-intensive undertaking that can present many challenges.

To better understand the air-sea interactions of biogeochemically important constituents such as gases and different particles, researchers from the University of Delaware and the University of Georgia (UGA) recently conducted a research cruise aboard UD's Research Vessel Hugh R. Sharp to study the sea surface microlayer in the North Atlantic Ocean.

The research is funded by the National Science Foundation and the research team has taken two prior cruises that were cut short due to stormy weather and the COVID-19 pandemic.

Andrew Wozniak, associate professor in the School of Marine Science and Policy (SMSP), is the UD project lead while the project lead for UGA is Amanda Frossard, associate professor in the Department of Chemistry at UGA.

Wozniak said the sea surface microlayer is a unique micro-environment.

"It accumulates organic material of a certain kind and then it reaches the air-sea interface and accumulates there, and that creates interesting physical properties that influence the exchange of materials back and forth," said Wozniak. "We thought that if we can do a better job of understanding how the chemistry of the organic matter changes in space and time due to the ocean processes and biology, then we'll have a better understanding of how these gases exchange and how the particles that are emitted to the atmosphere can influence atmospheric chemistry."

Frossard explained that the research team is interested in studying what are known as surfactants, compounds that reduce the surface tension of a liquid such as seawater and accumulate in surface waters and the sea surface microlayer due to their affinity for surfaces and interfaces, such as rising bubbles in the ocean.

One of the main goals of the project is to look at and better understand these surfactants.

"We want to understand what surfactants are in the ocean, how they partition to the microlayer and what affects their concentration and their composition," said Frossard. "We're collecting samples here, some that we're processing on the ship, but we're taking all of them back to the lab to do different analyses. We'll use these results to understand the sea surface microlayer and further understand air-sea gas exchange as well as the emission of particles from the ocean into the atmosphere."

Glass Panels

Researching the sea surface microlayer is anything but easy. As seen from the previous cruises which ran into unforeseen complications, oceanography work requires persistence amidst a sea of challenges.

For the experiment, researchers on board the ship conducted a suite of biological and chemical analyses which requires a lot of material.

The surface microlayer is incredibly thin, on the order of 100 micrometers thick, which is approximately the thickness of a piece of copy paper. One of the ways the researchers collect the material is by dipping a glass plate into the water and then taking a squeegee to scrape the water that stuck to the plate into a bottle.

"As you can imagine, that takes a really long time," said Wozniak. "What we want is about one and a half liters of water, and every time you do that, you collect about seven milliliters."

Working with the crew aboard the R/V Sharp-Jon Swallow, Timothy Deering and James Warrington-the team refined their collection technique to help improve upon their method of sampling.