Award: OCE-2123997

The Central Baltic Sea Air-Sea Exchange Experiment (CenBASE) was an international mission bringing together scientists from the US, Germany, and the UK. The team spent weeks aboard the German research vessel R/V Elisabeth Mann Borgese to solve a puzzle: how do gases like carbon dioxide (CO₂​ ) move between the atmosphere and the water in semi-enclosed inland seas compared to the open ocean?

The Challenge

We know that the ocean acts as a giant sponge, absorbing about a quarter of the CO₂​  that human activities have released. However, most of our formulas for calculating this "sponge effect" come from the deep, open ocean. Inland seas like the Baltic are different: they are less salty, have smaller waves because there is less room for wind to blow (limited "fetch"), and are often "oily" due to high levels of surfactants (natural organic substances produced by plankton).

What We Did

To get the most accurate picture possible, the team used two state-of-the-art techniques simultaneously:

• The Dual-Tracer Method: We released tiny, harmless amounts of two gases (³He and SF_6​) into the water and tracked how fast they escaped into the air.
• Eddy Covariance: We used a mast on the bow of the ship to "sniff" the air and measure the direct upward and downward movement of CO₂​ molecules in real-time.

By combining these with measurements of wave height and the "slickness" of the water surface, we could see exactly what was slowing down or speeding up the gas exchange.

What We Learned

1. The "Oily" Barrier: We found that natural surfactants in the Baltic Sea significantly "dampen" the water surface. These substances change the physical properties of the water surface and slow down the rate at which gases pass through.

2. Size Matters: Because the Baltic is smaller than an ocean, the wind doesn't have enough distance to build up the massive, breaking waves that typically help gases move into the water.

3. A New Formula: We discovered that standard global formulas were overestimating how fast gas moves in the Baltic. We developed a new, "Baltic-specific" formula that accounts for wind stress and surface slicks.

Why It Matters to You

When we applied our new formula to the entire Baltic Sea, we found that the seasonal cycle of $\text{CO}2$ than previously estimated.

This research is a major step forward for environmental research. As the world looks toward marine carbon dioxide removal (mCDR) to fight climate change, we must have accurate ways to measure how much carbon the ocean is actually taking up. CenBASE provides the math needed to make those accounts accurate for coastal and inland waters, ensuring that climate policies are based on real-world physics rather than open-ocean assumptions.

 

Last Modified: 12/19/2025
Modified by: David T Ho