Abstract

This paper presents a summary of paleoclimate and vegetation studies in western Oregon during the late Quaternary. The Willamette Valley climate is dominated by mild winters with massive accumulation of precipitation. In the summer months rains begin to disappear and we are dominated by warm, dry high pressure systems. In the Cascades and Coast Range we see a similar pattern, but there is a slight variation. The winter variation brings snowfall to higher elevations and short lived, intense thunderstorms in the summer.

The vegetation, in association with the law of uniformitarianism, helps us unravel the past climate. Different plant assemblages occurred in the Willamette Valley and surrounding mountain regions during the past 100,000 years. Since plants are extremely sensitive to even minimal climate changes, we can determine relatively precise climate variations over time, based on the sedimentary record.

Introduction

• Took samples of sediment from specific areas in Oregon to show Climate change between about 13,000 years and 7,000 years.

• The first area examined was Little Lake.• The second area was Gordon Lake.

Methods and Techniques

1 – Methods included taking core samples for Little Lake (15,700 and 10,200 B.P.) and Gordon lakes (15,500 and 8,500 B.P.). 2 – Taking soil samples and calculating the pollen concentration and charcoal concentrations.3 – Thus determining the specific plants found in that area during a specific time period. 4- Then relating climate to vegetation with the law of uniformitarianism.5- Drawing conclusions about the past climate associated with the vegetation found.

Conclusions

(1) With the vegetation changes we can infer a climate change, since vegetation is extremely climate sensitive.

(2) A period of Picea, Pinus, and subalpine vegetation in association with the law of uniformitarianism, tells us the climate was cold and dry.

(3) This occurred in both tables during the same time frame so we can conclude this is true.

(4) As the vegetation begins to shift to Pseudotsuga about 10,000 years before present, by the same principles can infer climate is warming and receiving more precipitation.

(5) Finally this tells us that the sea as climate warms is rising because warmer global temperature means less global ice.

(6) Since the last glacial period was about 20,000 years before present, this makes sense.

References Cited

Laurie D. Grigg and Cathy Whitlock (1998) Late-Glacial Vegetation and Climate Change in Western Oregon Quaternary Research 49, Figure 2 p.288.Laurie D. Grigg and Cathy Whitlock (1998) Late-Glacial Vegetation and Climate Change in Western Oregon Quaternary Research 49, Table 1 p.291.Laurie D. Grigg and Cathy Whitlock (1998) Late-Glacial Vegetation and Climate Change in Western Oregon Quaternary Research 49, Table 2 p.293.Laurie D. Grigg and Cathy Whitlock (1998) Late-Glacial Vegetation and Climate Change in Western Oregon Quaternary Research 49, Figure 3 p.294.Taylor, S.B., 2008 website Hydrology http://www.wou.edu/las/physci/taylor/hydro/water_budget_files/frame.htm (2008)

Table 2 Gordon Lake Analysis

• This table is similar to table 3, but shows samples taken from Gordon Lake.• Between 7,760 and 13,040 years before present similar trends are shown in this table.•A dominance of Picea and Pinus shifts to Pseudotsuga as you approach 8,000 years before present.

Figure 3 Vegetation and climate changes by Grigg and Whitlock (1998)

Figure 2 Location of two areas studied by Grigg and Whitlock (1998).

Table 1 Little Lake Analysis

• This table shows the time frame in which specific vegetation was found throughout this area.• Carbon 14 samples are able to give us a relatively precise dating systems (half-life).• 13,170 before present the most dominant species is Pinus and subalpine forest plants, then around 10,000 before present it begins to shift to Pseudotsuga.

Figure 1 Climate and Vegetation relationship (Taylor 2008). Table 1 Little Lake vegetation samples by Grigg and Whitlock (1998)

Table 2 Gordon Lake vegetation samples by Grigg and Whitlock (1998).

Prepared By: Bobby KelsoES 473 Environmental Geology