Washington: Marine phytoplankton – the tiny, single-celled algae, which act as a natural sponge for carbon dioxide and are a critical part of the global carbon cycle – may play a key role in ensuring the health of the planet, say a Canadian scientist.
According to Maria (Maite) Maldonado, Canada Research Chair in Phytoplankton Trace Metal Physiology at The University of British Columbia, phytoplankton form the base of the ocean food chain, have an integral role in controlling global warming and provide more than half of our oxygen supply.
Each year, phytoplankton are responsible for converting about 45 gigatons of carbon dioxide from the atmosphere to organic carbon. Of this, approximately 16 gigatons is transferred to the waters of the deep ocean in a process commonly referred to as a “biological carbon pump.”
The deep ocean is one of the Earth’s natural carbon “sinks” and will hold carbon from the atmosphere for centuries. The biological carbon pump controls the carbon dioxide content in the upper ocean, which in turn regulates atmospheric carbon dioxide levels—and, as a result, climate change.
Scientists have established that low iron concentrations in ocean water limit phytoplankton growth, since phytoplankton use iron to photosynthesize and grow. In these iron-limited environments (which make up approximately 30 per cent of the global ocean), the biological pump becomes inefficient and the ocean’s ability to absorb carbon dioxide from the atmosphere is reduced.
For the past 20 years, Maldonado 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 said.
“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.
“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,” explained Maldonado
In addition to copper, Maldonado and her team have also uncovered how the intracellular iron content of phytoplankton affects their ability to acquire other elements, such as nitrate and cadmium.
Maldonado’s findings on cadmium have already helped British Columbia``s oyster aquaculture industry, which had been suffering high losses because of elevated cadmium levels in ocean waters.
Her team developed specific guidelines on the best culture depth, seed size and site selection, and developed a model with indicators that farmers can routinely measure against to schedule their oyster harvests when cadmium levels are at their lowest. The result has been a more robust oyster industry in British Columbia—with higher yields and healthier oysters.
Maldonado described her research at Canada Press Breakfast on the Arctic and oceans held in Vancouver.