Tuesday, December 21, 2010

Crossing the final ecological threshold: some Arctic lakes are disappearing.

My friend John Smol is a noted paleolimnologist (lake historian) at Queen's University, Kingston, Ontario, who has a knack for finding dramatic stories to investigate with sediment corer and microscope.  But this story may top them all.

Normally, paleolimnologists reconstruct human impacts on lakes that have changed them from a clear, clean-looking condition to a silty or algae-choked state, or that make them more or less deep, acidic, or salty.  Such changes occur along spectra that range from low to high intensity, but John and his colleagues have recently found a situation among certain lakes and ponds of the Canadian High Arctic that pushes them completely off the scale of relative environmental impact. 

He calls it "crossing the final ecological threshold," and describes it in detail on his lab's website (http://post.queensu.ca/~pearl/Threshold.htm) and in several high-profile papers, but there's a simpler way to put it. 

The shallow ponds are disappearing.

Here's a photo of what used to be one of his larger ponds at Cape Herschel on Ellesmere Island, taken from the lab website.

And here's another photo that he sent to me recently, showing some of his colleagues collecting the last water sample from a vanishing pond in the same locale.

We often hear that most of the Arctic is warming faster than the global average, that ice is retreating on the Arctic Ocean, and that  melting of the Greenland ice sheet is speeding up.  But the lakes, ponds, and wetlands up there are also changing, though we rarely hear about it.  They're losing ice, as well, and it's making many of them more prone to evaporation and drying out.

Smol told me, "Until recently, the Ellesmere ponds remained frozen until July in some cases, and some of the deeper lakes would maintain at least a partial cover throughout the summer, with only a narrow moat of open water around the edges." Now that it's getting so much warmer up there, the ice shrinks enough seasonally to let larger and larger amounts of water evaporate from the lakes' exposed blue surfaces under the 24-hour daylight of summer.  There are no major rivers feeding most of them, and they aren't replenished by groundwater because they sit in depressions in solid bedrock.  As a result of the new boost in annual evaporation, many of them now lose more water than they gain.  In more and more cases, that imbalance is driving them over the edge into what amounts to hydrological bankruptcy.

Is it just part of some repetitive "natural cycle?" 

Being lake historians, John and his colleagues are well qualified to adress that question, which often remains unanswered when it's raised in discussions about human-driven climate change. 

The sediment cores that they've collected there over the years show that these lakes have existed for thousands of years with no sign of desiccation, which would show up clearly in the sediment record.  The remains of diatom algae in the cores also show that the ice cover has been shrinking for the last century or so, another change that is unique in their long history and that can only be logically attributed to warming (see the papers posted on the lab's website if you'd like more technical info in support of that claim).

How does John feel about watching his study lakes vanish before his eyes?  "Depressed," he says. "But not quite despairing, either. I still rage about what's going on, but that's because I still have hope than we can stop things from getting a lot worse."

1 comment:

  1. John sounds like another one of those Democrat scientists. Oh, but I see he's actually just a Canadian. :-)