Algorithm finds missing phytoplankton in Southern Ocean

NASA satellites may have missed more than 50% of the phytoplankton in the Southern Ocean, making it far more difficult to estimate the carbon capture potential of this vast area of sea.

But now, new research published in the Journal of Geophysical Research, Three improved satellite chlorophyll algorithms for the Southern Ocean, has led to the development of an algorithm that produces substantially more accurate estimates of Southern Ocean phytoplankton populations.

That research from the University of Tasmania's Institute for Marine and Antarctic Studies (IMAS) was led by PhD student Rob Johnson and Associate Prof Peter Strutton

"This new algorithm allows us to detect changes in plankton numbers that have previously gone unnoticed," said Mr Johnson.

"This better understanding of the phytoplankton population will, in turn, allow us to gain a much more accurate idea of how much carbon this ocean can take up."

The importance of phytoplankton and their role in our planetary ecosystem cannot be underestimated. They form the base of the marine food chain, produce half the oxygen on Earth and are partly responsible for the ocean uptake of at least a third of total human induced CO2 emissions.

So it was important to understand why existing ocean colour satellites systematically underestimated the chlorophyll concentration (a proxy for phytoplankton biomass) of the Southern Ocean and Antarctica.

To get the observations needed to make valid comparisons and develop the algorithm, the researchers used more than 1000 Southern Ocean phytoplankton samples collected over 10 years and compared these to satellite measurements.

The majority of the samples used in this study were collected by the French Antarctic vessel MV L'Astrolabe through a collaborative and long-term monitoring program between the CSIRO, the Australian Antarctic program, and the French Antarctic Program.

Once this observational data was collected, the new algorithm was used to process satellite data and make comparisons. It quickly became clear that the algorithm produced a much closer estimate of phytoplankton numbers than past satellite measurements.

"Our improved satellite chlorophyll algorithms will be used to produce higher-accuracy observations on the vitally important phytoplankton of the Southern Ocean and Antarctica," said Assoc Prof Peter Strutton.

"This will go a long way towards improving our understanding of how the Southern Ocean works and how the movement of carbon is changing in these remote waters."

The improved data will also be made freely available to the global research community through the Integrated Marine Observing System (IMOS).