Dusting off a feast fit for a fish
Last month, the residents of Sydney awoke to a strange, apocalyptic landscape. Dawn had struggled to push its way through the ochre-coloured haze that had crept over the city during the night, washing everything in an eerie red light. Far from being the end of the world, this massive cloud of dust led to an explosion of life in nearby ocean waters and even contributed to the removal of a few million tonnes of carbon dioxide (CO2) from the atmosphere.
On most days, 20 micrograms of dust per cubic metre drifts through Sydney’s air. On 22 September, there were 15 400 micrograms. CSIRO estimates 16 million tonnes of topsoil were lifted from outback New South Wales and South Australia and carried east by strong winds. Such an unusual combination of factors occurs once every 70 years, although global warming could see it become a little more frequent.
In addition to weathered particles of rock, soil consists of the microscopic remains of dead organisms. As protein breaks down, it forms the chemical ‘urea’, which is a useful source of nitrogen for growing plants. Given such nutrients are usually rather scarce in Australia’s coastal waters, the tonnes of dust that fell into the water provided a feast for the phytoplankton.
These tiny plant-like microorganisms lie at the heart of the vast marine food web. More phytoplankton means more of the little fish that feed on them, leading to more big fish, and so on. Measurements made by the Sydney Institute of Marine Science showed microscopic plant life 10 kilometres off Australia’s east coast had tripled following the dust storm.
This is potentially useful information for those concerned about our ocean’s decreasing fish stocks. It is also interesting for those studying the effects of carbon dioxide on climate change. Like all plants, phytoplankton absorb CO2 as they grow, acting as a significant carbon sink.
Questions have been raised regarding the possibility of fertilising the ocean with nitrogen to artificially create similar blooms in phytoplankton, both as a way of stimulating an increase in fish numbers and as a means of reducing the amount of carbon in our atmosphere.