One of the great things about having gone to three different universities is that you get to meet a lot of people doing many interesting projects. A friend of mine, David Mazzucchi, was involved in a project that was published in the latest issue of Geology. National Geographic has a synopsis of the research with interviews of the authors.
The research group collected a sediment core from the northernmost lake in the world, Kaffeklubben Sø, located in northern Greenland. The sediment record spans the last 3500 years. The lake is located in a region where temperatures only reach above freezing point briefly during the summer, and the average annual temperature is a cold -18C.
The sediment record indicates that organic production (i.e. single celled lifeforms like diatoms) in the lake ceased at around 2400 years ago, reflecting a shift to colder temperatures that kept the lake from thawing in the summer to allow them to grow. Around the year 1920, diatoms began to grow in the lake again, and production reached unprecedented levels after 1980. The stability of nitrogen in the sediments since the reactivation of organic production indicates that the rise is most likely due to warming, rather than the introduction of materials that fertilize the lake.
Back in 2005, there was the revelation that over 100 lakes had disappeared in the Arctic over the preceding 30 year period. There is a great story about how researchers from Canada had been monitoring a lake in Ellesmere Island since 1983, only to come back in 2007 and find the lake had dried up. Clearly, the Arctic is warming up, allowing lakes to thaw for longer in the summertime, and it will have a dramatic effect on the ecosystem there.