Myrbo, A. E. Limnological Research Center, amyrbo@umn.edu
Dean Jr., W. E. US Geological Survey, dean@usgs.gov
Kelts, K. R. Limnological Research Center, kkelts@umn.edu

 
INORGANIC-ORGANIC CARBON TRANSITIONS IN LACUSTRINE SEDIMENTARY RECORDS: A COMPARISON OF NATURAL AND ANTHROPOGENIC SHIFTS
 
The carbon cycle in lakes reflects a complex interplay of organic and inorganic landscape and aquatic processes. Although commonly CO2 sources, lakes are major sinks of both organic and carbonate forms of carbon. Surface sediments in most Minnesota lakes contain more than 30% calcium carbonate as low-Mg calcite, and less than 15% organic carbon. Sediments of some lakes, however, contain no carbonate, but contain >15% organic carbon (up to 35%). Cores from several high-low carbonate pairs of lakes in close proximity and with similar water chemistries show that they all buried up to 80% carbonate sediment during the early and middle Holocene. In those lakes with no carbonate in surface sediments, the threshold crossover from inorganic- to organic-carbon burial appears to be related to the end of mid-Holocene aridity (the hypsithermal, or "prairie period" in Minnesota). Sediments in lakes which continue to bury carbonate across this transition show a marked rise in organic carbon, and drop in carbonate, in response to European settlement and catchment clearance. Coulometric, mineral, geochemical, and isotopic analyses provide evidence of terrestrial and aquatic sources and processes as the basis of a model evaluation of the sensitivity of and controls on the systems.
 
Day: Friday, Feb. 5
Time: 02:30 - 02:45pm
Location: Sweeney Center
 
Code: CS63FR0230S