Right after we moved the Exploratorium to its new waterfront location, we got a gift from NOAA’s Pacific Marine Environmental Lab in Seattle: a beautiful red-and-white ocean buoy. Normally, these buoys are deployed out at sea to measure dissolved and atmospheric carbon dioxide, but we got to put one right in the lagoon between piers 15 and 17.
Since the beginning of May, the buoy has been collecting CO2 data from the bay waters and the atmosphere in San Francisco and we’ve noticed some interesting patterns in the read-outs. First, it might help to know why we care about dissolved CO2. Carbon dioxide is constantly exchanged between air and water; when atmospheric CO2 levels increase, more of the gas is absorbed by ocean. The increase in dissolved CO2 is increasing the acidity of the ocean, an effect called ocean acidification. Since the start of the industrial age, the ocean has absorbed 30% of the CO2 produced by the burning of fossil fuels, changing the chemistry of the ocean. These chemical changes can have harmful effects on the biology of marine organisms that build shells, including oysters, plankton, and a marine snail called a pteropod, which in turn affect food webs and marine ecosystems.
We see higher levels of dissolved carbon dioxide in San Francisco Bay than offshore in part because urban areas are sources of atmospheric CO2 but also because our location is influenced by both the open ocean outside the Golden Gate and the freshwater estuary in the South Bay. Estuaries typically contain more dissolved CO2 because they have higher levels of organic matter than the open ocean. When organic matter decomposes, it releases CO2 into the water. At Pier 15, we see a decrease in the dissolved CO2 and sea surface temperature (SST) and an increase in salinity as the tide rises and brings in cold salty and less acidic water from the Pacific. As the tide falls, estuary waters flow in from the south bay and the CO2 levels go up, while temperature increases and the salinity goes down. That’s why you see this daily zig-zag in the data.
The data also shows a longer two-week pattern of decreased levels of dissolved CO2 corresponding to an increase in dissolved oxygen. We think the increased oxygen is from a bloom of phytoplankton which take up carbon dioxide (decreasing the dissolved CO2 levels) and release oxygen (increasing the O2 levels) as they grow. I heard from scientists at Bodega Marine lab that this bloom also corresponded to an upwelling event off the coast which brings cold, nutrient-rich waters from the deep up to the surface feeding the phytoplankton bloom. This is similar to what happens with atmospheric carbon dioxide in the summer. As plant life grows in the summer it absorbs CO2, causing a temporary dip in the levels of atmospheric carbon dioxide. In the winter, plants shed their leaves which decay and release CO2 into the atmosphere, creating a yearly zig-zag in the gas levels.
The CO2 buoy is part of our Wired Pier project which places scientific instruments and sensors in the water and on the roof of Pier 15. In the coming months we’ll post more of these data stories, but you can access the current real-time feeds and other locations at