Measuring carbon’s impact in our ocean

A new Antarctic experiment seeks answers to one of the biggest questions about our planet: how will acidifying ocean waters affect marine life? [22 October 2013 | Peter Boyer]

Antarctic coastal sea-floor community. PHOTO JONNY STARK

Mutual dependence is a common thread running through the story of life on Earth. To take just our own kind, we need other species for food, shelter, aiding digestion and fighting infection. And company.

A healthy life system is a diverse one, and the loss of any species is a loss to all. We don’t seem to have caught on yet, but the mass extinctions happening around us today are a monumental disaster, a huge and growing threat to our future in this age of the human, or anthropocene.

The bottom line is that all species need others to survive. The living part of Earth, its biosphere, is essentially a single community of billions of inter-dependent individuals. Within the biosphere are countless smaller communities sharing a habitat: river, pond and swamp communities, forest and grassland communities, mountaintop communities, coastal communities and even communities living within individual plants and animals, including us.

And then there are the communities of the sea, where all life originated. Our thoughts about extinction tend to exclude the life that inhabits ocean waters, which is a big oversight. Life on land is confined pretty much to its surface, but there’s depth as well as width to the oceans, which make up more than 95 per cent of the living space on the planet.

Some more reasons for focusing on the ocean: It provides half of the oxygen we breathe. It’s an important source of protein for humans. And it shields us from the worst effects of climate change by taking up heat and excess carbon dioxide from the air.

But the benefits come at a price for the millions of species living under the waves, and ultimately, for the rest of life on Earth. I recently looked at how plastic waste is affecting marine life, but human impact on the oceans goes much further than that.

Last week, microbial ecologist Andrew Davidson left Hobart on a sea voyage to Davis, Antarctica, where he will continue a five-year study of how the Southern Ocean’s rapidly changing chemistry — a direct result of human carbon emissions — will affect ocean-dwelling microbes.

The chemistry in question is a shift in the acid-alkaline balance in ocean waters resulting from the ocean’s increased uptake of carbon dioxide from the air, a direct outcome of emissions from fossil-fuel burning and other human activities. Over the past 250 years ocean waters have become 30 per cent more acidic. We’ve already locked in a further increase of 30 per cent by 2050, and our current carbon emission trajectory points to an even steeper rise after that.

Oceans change slowly, normally taking centuries or millennia to reflect shifts in the carbon balance of the atmosphere. But combing through proxy records of ancient climates going back 60 million years, scientists can find no sea change that has happened as quickly as today’s.

If this process continues, it will affect many corals, shellfish and other marine calcifiers — species which form shells or skeletons from calcium carbonate. The signs are already there in abundant prey species called pteropods, whose shells have been found to be corroded by more acidic water.

But that’s just one small group of species. Davidson’s work in Antarctic waters is part of a much broader study that seeks to know how whole communities of plants, animals and microbes living on the Antarctic sea floor respond to higher acid levels in the seawater around them.

Donna Roberts is a senior scientist at the Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, whose quest for knowledge about the problem of ocean acidification has led her to an innovative engineer based at Monterey, California, named Bill Kirkwood.

Kirkwood’s employer is the Monterey Bay Aquarium Research Institute (MBARI), founded and funded by the late David Packard, of Hewlett-Packard fame. There, he and a team of marine scientists and engineers produced the unique research tool that caught Roberts’s attention.

FOCE, for Free Ocean Carbon dioxide Experiment, is the name of a system to enable scientists to study benthic (sea-floor) communities where they occur naturally, without removing specimens to a laboratory. In effect it makes a laboratory within the coastal sea floor environment.

Clever design enables users of the FOCE system to study the response of living communities to different chemical properties of sea water, such as lower pH levels (or higher acidity). So far the system has been deployed in US waters, in the Mediterranean Sea and on the Great Barrier Reef.

The system involves placing an upside-down glass box around a coastal sea-floor community so that carbon dioxide in the water can be regulated and oxygen and carbonate chemistry measured, along with the respiration, growth and calcification of the organisms living within the chamber.

Roberts has persuaded Kirkwood to join a team of mainly Tasmanian-based scientists and technicians who will set up the first Antarctic FOCE experiment, just offshore from Australia’s Casey station, due south of Western Australia. Kirkwood will join Martin Riddle, a senior ecologist with the Australian Antarctic Division, AAD engineers Glenn Johnstone and Andrew Cawthorn, and University of Tasmania student volunteer Lucy Quayle aboard Aurora Australis in late December for a month at Casey.

The team will establish the best site for the study, within a few hundred metres of the shore in a bay free of human contamination, offload equipment from the ship, and test it in preparation for the 2014-15 summer, when the main part of the experiment will get under way.

Acidification of the oceans is most advanced in colder waters, which are more able to retain dissolved carbon dioxide than temperate or tropical waters. A successful FOCE experiment in Antarctic waters will yield critical data on how marine communities might cope with this hugely important part of climate change. It’s a real win for Roberts, co-investigator and AAD ecologist Jonny Stark, and their team.

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