Thermal cameras could measure ocean temperatures, while microwave sensors could measure ocean salinity, say scientists
By Tim Radford
Climate scientists are looking for a new perspective on the increasingly acidic oceans through a suite of satellites 700 km out in space, watching over parts of the seas that research ships cannot reach.
They report in the journal Environmental Science and Technology that thermal cameras could measure ocean temperatures, while microwave sensors could measure ocean salinity.
Together, the two sets of data could help answer, cheaply and easily, questions about the chemistry of the oceans – and in particular changes in pH, the index of acidity.
Until now, researchers have depended on specialist instruments or shipboard samples to provide answers to huge questions about the oceans’ increasing uptake of carbon dioxide. Such research is costly and limited.
But ocean science has become ever more important. Each year, 36 billion tonnes of CO2 are released into the atmosphere, and about a quarter of this gets into the oceans.
That’s a good thing: if it did not, global warming would accelerate at an even greater rate. But the same global transfer of greenhouse gas also delivers a stronger solution of carbonic acid to the oceans, and ocean acidity levels have risen by 26% over the last 200 years.
The consequences for all those sea creatures that evolved to exploit ocean chemistry to build shells or skeletons are uncertain, but the evidence so far is that changes can affect fish behaviour, shellfish reproduction, and coral growth.
The changes could almost certainly affect fisheries in the short term, and in the long term could possibly alter the continuous and vital exchanges between atmosphere and ocean that controls the climates of continents.
So marine scientists launched a Global Ocean Acidification Observing Network to assemble worldwide expertise and find new ways to monitor change.
“Satellites are likely to become increasingly important for the monitoring of ocean acidification especially in remote and dangerous waters like the Arctic,” says one of the report’s authors, Jamie Shutler, an oceanographer at the University of Exeter. UK.
“It can be difficult and expensive to take year-round direct measurements in such inaccessible locations. We are pioneering these techniques so that we can monitor large areas of the Earth’s oceans, allowing us to quickly and easily identify those areas most at risk from the increasing acidification.”
The new approach will exploit a number of existing satellites, along with the European Space Agency’s Soil Moisture and Ocean Salinity sensor (SMOS), launched in 2009, and the US space agency NASA’s Aquarius satellite, launched in 2011.
The satellites cannot, of course, directly measure ocean pH values, but the capacity of CO2 to dissolve in water is controlled by ocean temperatures.
On the other hand, salinity levels play into the capacity to form carbonates. Chlorophyll levels in the oceans also indicate the rates at which biology can exploit any of the dissolved carbon dioxide.
If the scientists have temperature and air pressure data as well, they have enough to begin to calculate the rates at which any stretch of sea might be acidifying.
Although such measurements are indirect, and involve complex mathematical calculation, the results can be checked in some places against real-time data from a network of autonomous instruments called Argo, and by shipboard laboratory studies.
But satellites are about the only way of making consistent measurements of the desolate and hostile Arctic and Indian Oceans. They could also help researchers understand the changes taking place in complex stretches of sea such as the Bay of Bengal and the Greater Caribbean.
The research is in its infancy. But the authors say that satellite studies − supported by good measurements taken directly at sea − could become a key element in understanding and assessing the acidification of the oceans.
This article was produced by the Climate News Network