Arctic Plankton Sing the Global Warming Blues
The canary in the climate change mine is singing a new and slightly different tune.
Scientists say that the Arctic is to climate change as the canary is to the coal mine. Because the temperature changes caused by global warming tend to be most pronounced in the polar regions, especially the Arctic whose ecosystems are particularly sensitive to climate changes, scientists are watching the Arctic closely as the place to look for early warning signs of global warming’s effects.
This idea of the Arctic “canary” is not new. In 2006 the Arctic Council and the International Arctic Science Committee published a report detailing the rapid environmental changes the region has been undergoing. Now two new papers add to the evidence documenting puzzling and potentially disturbing trends in Arctic phytoplankton.
The Essential Phytoplankton: Small but Mighty
Phytoplankton are arguably the keystone organism of the oceans, if not the entire world. For one, they sit at the very bottom of the ocean’s food web, producing through photosynthesis the organic material that feeds essentially all marine fauna — and some billion or more people.
Moreover, phytoplankton help remove carbon dioxide (CO2) from the atmosphere into the deep ocean, thereby ameliorating the global warming impact of our CO2 pollution from fossil fuel burning and deforestation.
They achieve this through the so-called biological pump. During photosynthesis, phytoplankton remove dissolved CO2 from the surface ocean; when they eventually die, they sink into the deep ocean taking that CO2 with them.
It’s estimated that each year the biological pump moves about 10 gigatons of carbon into the intermediate and deep ocean depths, offsetting about 25 percent of the carbon dioxide we add to the atmosphere annually from fossil fuels and deforestation.
The Incredible Shrinking Phytoplankton
A new paper in Science by William Li of Canada’s Bedford Institute of Oceanography and colleagues suggests that the phytoplankton of the Arctic are changing in a fairly profound way.
Because melting glaciers and warming surface temperatures are adding lots of fresh water to the Arctic Ocean, the availability of nutrients in its surface waters has been diminished. The resulting competition for the remaining nutrients is leading to a growing abundance of tiny picoplankton at the expense of larger, arguably more important nanoplankton. Because picoplankton, sized at less than two micrometers, are more buoyant, they do not move carbon as effectively as nanoplantkon (which range in size from about two to 20 micrometers).
Lake Sediments Tell a Story
A similar story of change was recently reported by Yarrow Axford of the Institute of Arctic and Alpine Research at the University of Colorado in Boulder and colleagues in the early edition of the Proceedings of the National Academy of Sciences.
Their analysis of sediment cores taken from Lake CF8 on Baffin Island in the Eastern Canadian Arctic suggests that the lake’s current environmental regime is different from that of any other time over the past 200,000 years.
The 200,000-year sediment record studied by Axford et al. is dominated by glacial or ice-age conditions. But it also includes two periods when summertime temperatures at the lake were comparable to or even higher than they are currently:
- the last interglacial or warm period, about 115,000- to 130,000 years ago, and
- the so-called Holocene Climate Optimum, which occurred some 5,000 to 9,000 years ago during the early part of the current interglacial.
The waning days of a third interglacial period that ended about 190,000 years ago was also partially captured by the sediment cores.
The sediment record suggests that the lake’s biotic diversity and environmental conditions were similar during the three preceding warm periods. But this doesn’t appear to be true for the current warm period. For example, analyses of sediment from the last 40 to 50 years reveal unique changes in the populations of both phytoplankton and midge fly larvae:
- two cold-temperature midge larva species have apparently disappeared and
- at least one phytoplankton species that was previously only present intermittently has shown an “unprecedented increase.”
The authors conclude that their “study site has deviated from [the] recurring natural pattern and has entered an environmental regime that is unique within the past 200 millennia.” And, citing similar datasets from other Arctic lakes, the authors suggest that “conditions in many lakes and ponds in the Arctic may now be outside the range of natural … variability.”
What Do These Phytoplanktonic Shifts Mean for the Arctic Ocean and Beyond?
Do these changes presage more sweeping changes all the way up the food web? Because smaller phytoplankton sink more slowly, will the shrinking size of phytoplankton in the Arctic Ocean mean a slowing of the biological pump and an acceleration in global warming? Will the changes in Arctic phytoplankton spread to the rest of the ocean? And are there even more profound changes occurring with the oceanic phytoplankton that we have yet to uncover? Obviously, we don’t know, but it would appear that we are about to find out.