Great Lakes Climate ... getting warmer?
I think my Lake Erie mud cores have recorded a warm/dry climate event that peaked about 3,000 years ago (see earlier entries for details). NOW I'm trying to figure out how this might influence or fit into the bigger regional picture. Was Lake Erie warm while other lakes were cool? That seems odd, but that's what data from some other research papers suggests. Here are some of my thoughts on the relationship/similarities/differences between Lake Erie and Lake Ontario.
McFadden's Ontario paper shows that carbonate precipitation drops and then essentially stops in the Neoglacial (the period between ~5200 to 250 years ago), and they interpret it to indicate cool/dry climate conditions. They also see a dramatic increase in diatoms (little floaty organisms made of silica), and a dramatic (fivefold) decrease in sedimentation rates (mud building up on the lake floor) during this period.
I'm not sure their data is actually documenting a cool period ... a couple ideas:
1) I think biology could actually be really important here. A study on whitings in Fayetteville Green Lake, NY (Thompson 1997) shows a really strong correlation between abundance of cyanobacteria and whiting events. Cyanobacteria blooms, coupled with warm conditions, seems to be initiating/intensifying calcite precipitation in Fayetteville Green lake more than any other factor. The paper talks about competition between cyanobacteria and diatoms -- says that diatoms need lots of nutrients but cyanobacteria (because of their shape/size, ability to absorb) can out-compete diatoms in oligotrophic conditions (because Green Lake is oligotrophic, cyanobacteria dominate and there are lots of whitings). In Lake Ontario, Mullins and Halfman said there was more wind, upwelling, and thus more nutrients in the Neoglacial -- so maybe diatoms out-competed the cyanobacteria there, and thus made it much more difficult for whitings to occur? No carbonate precipitation is associated with diatoms.
2) Maybe there were whitings, but the carbonate dissolved? Maybe oxygen levels were higher in the lake and there was more dissolution in the sediment Today Ontario mixes almost continuously from late fall to early spring (says McFadden). Is there more mixing in Ontario than in Erie? It's much deeper than Erie, so that doesn't seem quite right. Also magnetic susceptibility drops low and stays low during the Hypsithermal in Ontario -- since magnetic susceptibility is correlated with carbonate in Erie's central and eastern basins, could low mag. sus. could be evidence that there weren't whitings in Ontario?
3) Or, maybe McFadden is right, and it is a cool/dry period. What would make Ontario cool and Erie warm at the same time? Air masses/jet stream shifts?
Too many possibilities ... don't know if I can investigate them all! I almost wish I had more than 3 weeks of school left ... Almost.