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Deep Ocean Argo Floats, New Approach Yield New Insights into Ocean Acidification

The ongoing rise in atmospheric CO2 is paralleled by a rise in CO2 levels and acidity in the oceans. Ocean acidification is a growing concern in the marine and climate science communities, as well as more broadly speaking, as it could wreak havoc in the marine food web. Rising ocean acidity weakens coral, shellfish and plankton populations, many of which are directly or indirectly crucial for commercial fisheries, as these marine life forms manufacture less calcium carbonate for their skeletons and shells.

Thanks to the National Oceanic & Atmospheric Administration (NOAA) and a joint US-Canadian research team, it is now possible for marine scientists to use satellite data from five-foot-tall Argo floats that drift with deep ocean currents to remotely monitor ocean acidity (pH) and the total carbon dioxide (CO2) content of seawater to better understand changes in ocean chemistry.

The research team has determined the relationships between seawater temperature, oxygen, pH and CO2 from observations collected on previous ship-based expeditions in the last five years, NOAA announced on September 2. The relationships were then applied to high-resolution observations of temperature and oxygen collected by an Argo float released in the North Pacific in early 2010.

“Most observations have been taken by scientists aboard specialized research ships, so this represents a major step forward in the ability to monitor ocean chemistry at higher frequency and lower cost,” said Dr. Lauren Juranek, an oceanographer at the University of Washington Joint Institute for the Study of Atmosphere and Ocean (JISAO) the lead author of the research study.

Some 10% of the international Argo observing network of floats are equipped to measure dissolved oxygen concentrations, which are needed to use the new model. Argo floats have been deployed by researchers in 30 countries. There are approximately 3,000 active floats distributed throughout the global ocean at any time.

Argo floats ride ocean currents, descend down to 3,000 or as much as 6,000 feet. After about ten days, they rise to the surface, collecting temperature, salinity and other data that are transmitted via satellite when the float reaches the surface. Each float acquires 200 profiles over a 5-year life cycle, NOAA explains.

“These measurements can be used to complement traditional ship-based observations, not replace them. Because we can’t sample as frequently as we would like to, this approach allows us to provide repeat data on 10-day intervals,” said Richard Feely, a NOAA senior scientist and a co-author of the study.

Ship-based work is still essential for calibrating the Argo float data for pH and total CO2 concentrations, he noted.

“Autonomous profiling systems, such as the Argo floats, give us a new perspective on ocean physics and chemistry, and a more comprehensive deployment of chemical sensors in the ocean interior will provide a much more complete view of the ocean carbon system,” Feely explained.

Image credit: NOAA

 

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