0 cm 120 cm 270 cm 420 cm 460 cm 550 cm Figure 1. Photographs of the 5 drives from the Max Lake sediment core. The first 2 drives were largely uniform in color and mucky in texture. The third drive displayed more banding. The fourth drive was composed largely of clay material and was reddish brown in color. The fifth drive was composed largely of sand with some silt near the top and likely consists of material deposited as the glacier receded.

Figure 2. Loss on ignition values are typical for many lakes in northern Wisconsin. Silicates/ash are high in the Late Glacial and Early Holocene due to detrital siliciclastics material in glacial meltwater and outwash. Ameliorating temperatures circa 11,000 yr BP resulted in increased in lake productivity and an elevated proportion of organic matter in the lake sediment throughout the Holocene.

Figure 3. Loss on ignition values for the last two centuries, like the CHAR records for this period, also reflect an anthropogenic pattern of activity. An increase in silicates/ash are the likely result of land-disturbing activities that contribute slope- wash and soil to the lake basin. The decrease in organic matter is likely just relative to the increase in siliciclastic material and not reflective of reduced primary productivity in the lake.

Group 1 Group 2 Group 3 Group 4 Figure 4. Cluster analysis of the diatom samples in the sediment core. The analysis used the Ward’s clustering method with squared chord distance. The scale is the square root of the squared chord distance. The table on the right indicates calibrated 14 C dates BP.

pHTP Group Group Group Group pH Phosphorus Group 1 Group 2 Group 4 Group = 2 = Figure 5. Principal Components Analysis ordination plot of downcore samples. Circled samples correspond with the 4 groups identfied with the cluster analysis. Groups 1 and 2 have higher pH and phosphorus values. The ordination plot shown in the inset is a Redundancy Analysis (RDA) illustrating the relationship between two environmental variables, pH and phosphorus.

Figure 6. Relative abundance of common diatom taxa. The four color groups are the 4 groups identified in the cluster analysis.

Calculated 14 C BP pH Calculated 14 C BP (µg L -1) Phosphorus Figure 7. Diatom inferred pH and phosphorus for the portion of the core that was dated. Both pH and phosphorus levels declined after the mid-Holocene warming period.

Figure 8. Charcoal accumulation rates (CHAR) for Max Lake from the Late Glacial to the present. CHAR values are are lowest in the late-Glacial and early Holocene and highest in the last 2000 years.

Figure 9. Max Lake CHAR record excluding the last 2000 years to better illustrate charcoal variability in the early and mid-Holocene. The largest charcoal accumulation rates in the Holocene are centered on 10,000 years ago, 7000 years ago and 4000 years ago.

Figure 10. Max Lake CHAR values for the last 2000 years. During this interval the most wildfire activity in the Max Lake basin occurred between 1100 and 550 yrs BP, concurrent with the Medieval Warm Period and likely reflecting regional drought.

Figure 11. Max Lake CHAR values for the same period of record as (previous figure) illustrating the relative contribution of charcoal pieces >250 μm and those between 125μm and 250μm in diameter. An elevation of the finer charcoal during the Medieval Warm Period suggests that fires were regional in nature and consistent with drought, versus local, isolated phenomena.

Figure 12. Max Lake CHAR values for the same period of record as (previous two figures) showing the contribution charcoal derived from arboreal/canopy component of vegetation and charcoal from grasses and understory vegetation. During the Medieval Warm Period (1100 and 550 yrs BP) charcoal in Max Lake suggests fires were larger arboreal/canopy events.

Figure 13. In the last 200 years CHAR in Max Lake reflects human activities in the area. In the early and middle parts of the 19 th Century very little charcoal accumulated in the lake, but logging at the turn of the 20 th Century as well as settlement in the area has resulted in increased fire frequencies and elevated CHAR. A rise in CHAR values in the last two decades may reflect a period of sustained drought in the region.

Figure 14. Annual PDSI Index for the instrumental record for northern Wisconsin. Negative PDSI values represent drought conditions. Years with low regional precipitation and low PDSI values occur in the early 1930's and mid-1970's, both corresponding to episodes of increased CHAR (Figure 12).

Figure 15. Hypothesized extent of lake basin that Max Lake was a part of prior to the mid-Holocene warming period. At the present time most of this historical lake basin is a wetland.