Phytoplankton is at the base of the ocean food chain and this coupled with the fact that it provides more than half our oxygen supply means it has an integral role in the control of global warming.
Annually, phytoplankton are responsible for converting a massive 45 gigatons of atmospheric carbon dioxide to organic carbon, and some 16 gigatons of this is transferred into the deep ocean – a process known as a "biological carbon pump."
As one of Earth’s natural carbon "sinks", the deep ocean can hold carbon sequestered from the atmosphere for hundreds of years. The biological carbon pump controls the amount of carbon dioxide held in the upper ocean, which regulates atmospheric carbon dioxide levels – and, subsequently, climate change.
One limiting factor of phytoplankton growth is iron concentrations and in iron-limited environments (approximately 30% of the global ocean), the biological pump becomes inefficient and there is a reduction in carbon dioxide absorbed from the atmosphere.
Maria Maldonado, Canada Research Chair in Phytoplankton Trace Metal Physiology at The University of British Columbia, has made understanding the intricacies of marine phytoplankton her life's work, and for the past 20 years she has been examining how phytoplankton adapt to and survive in, these iron-limited environments.
"In essence, what we are illustrating is that they have evolved to deal with iron limitation, and we are trying to figure out how they have adapted to take up iron more efficiently," she says.
"In the process of answering these questions, what we have seen is the importance of other trace metals. For example, copper for many years has been thought of as a toxic trace metal for phytoplankton," says Maldonado. "We know that phytoplankton need a little bit of copper...but what we have discovered is that phytoplankton that are iron-limited need more copper than normal. Iron-limited phytoplankton have a very good transport system for iron, and in order for this transport system to operate properly they need copper. So we are discovering uses of these other metals that we didn't know of."
It’s not just copper either, Maldonado and her team have uncovered how the intracellular iron content of phytoplankton affects their ability to acquire other elements, such as nitrate and cadmium.
These findings on cadmium helped British Columbia's oyster aquaculture industry, which was suffering great losses from elevate level of cadmium in ocean waters. By developing guidelines for the best culture depth, seed size and site selection in conjunction with a model to schedule harvests against – when cadmium levels are at their lowest – the oyster industry in British Columbia has seen higher yields and healthier oysters.
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