During the next few days we will follow the path of the water as it flows away from South Georgia. As we move downstream following the currents, the blooming phytoplankton should take more and more carbon out of the water( plankton is 50 % carbon once you remove all the water) and this will drive the level of CO2 in the water lower and lower. Normally there is a rather similar level in seawater as in the atmosphere( about 390 ppm), as seen on the day that Mariana wrote her blog post about how we measure it on board. However, where the seas are especially productive this can drastically change. For instance, a few days ago in the middle of an intense bloom it fell to about 230 ppm, nearly half of its normal level. This uptake by phytoplankton is the opposite of ocean acidification( removing CO2 instead of adding it) and thus makes seawater more alkaline rather than more acidic. Over the next few days we are going to examine and measure organisms, ecosystems and processes in this naturally de-acidified environment.
Another benefit for us is that the phytoplankton impacts decouple the carbon chemistry from temperature. Across much of the ocean temperature and carbon chemistry vary together. If we see differences between one place and another, it then becomes hard to determine whether it is the temperature change or the carbon chemistry change that drives the difference. Around South Georgia the carbon chemistry changes strongly but the water temperature does not, which should help in disentangling the two effects.
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