Variable ecosystem response to climate change during the Holocene in northern Minnesota, USA.

Both terrestrial and aquatic ecosystems should respond to abrupt climate changes such as those that affected the midcontinent of North America during the Holocene. A variety of paleorecords indicate that the onset of prolonged dry conditions in this region occurred as rapidly as 300 yr during the early Holocene, with a subsequent increase in moisture occurring rapidly in the late Holocene. Here, we report a 9500 yr multiproxy sediment record from Deming Lake, Minnesota, USA, that demonstrates only subtle dynamics during rapid climate changes that caused vegetation in the catchment to shift among pine forest, open grassland, and deciduous forest. The most substantial changes in ecosystem properties immediately followed deglaciation of the landscape, formation of the lake, and initial development of pine forests. In contrast, there were only muted responses to pronounced mid-Holocene climate changes that caused vegetation in the catchment to switch from pine forest to open grassland (ca. 8000 yr B.P.), and then deciduous forest (ca. 5400 yr B.P.). The flux of organic and inorganic terrigenous material, the processing of carbon, and catchment erosion changed rapidly during the most recent shift at 3300 yr B.P. to the modern pine forest. These changes coincided with the onset of meromictic conditions that influenced internal lake dynamics. However, the terrestrial influence on the lake sedimentary record gradually diminished over time, indicating a trajectory of increasing catchment stabilization that was relatively impervious to dramatic regional climate changes. The relative complacency of the Deming Lake record during the late Holocene indicates relative resistance to abrupt climate change at later stages of eco-system development. [ABSTRACT FROM AUTHOR]