Timestamping seawater to improve climate modeling

The ocean absorbs about one quarter of carbon dioxide, a major greenhouse gas, emitted by humans into the atmosphere. Over the past 150 years, humans have emitted carbon dioxide into the atmosphere faster than the ocean can dissolve it into seawater. Scientists are studying the variables that prevent this air-to-ocean exchange of gases from reaching equilibrium. One major challenge is obtaining accurate measurements of dissolved carbon dioxide in seawater. To address this gap, electrical engineering professor Olav Solgaard of the School of Engineering and colleagues are developing a photonic sensor that can distinguish between the light signatures of two carbon isotopes, meaning they are chemically identical but have different physical properties. These two isotopes make up the majority of carbon on Earth and are found in carbon-containing compounds like carbon dioxide. One of these carbon isotopes is found in plants, which decompose and transform over millions of years to form fossil fuels. When humans burn fossil fuels, a trend documented in the atmosphere since the 1800s, the carbon dioxide they release has a distinct signature of the carbon isotope found in plants. By quantifying differences in carbon isotope concentrations between air and seawater, the researchers can estimate the last time an area of the ocean was in equilibrium with the atmosphere. This makes it possible to trace carbon sources, pathways, and storage timeframes to improve predictions of the ocean’s capacity to absorb carbon dioxide that would otherwise escape to the atmosphere and contribute to climate change.

Above: A silicon photonics chip used in spectrometers that can distinguish between carbon isotopes. Image credit: Stanford Engineering