Multi-proxy comparative analyses of sediment from Eagle Lake, including TOC, δ13C and δ15N composition of bulk organic material, n-alkane distribution, and biogenic silica, was used to document hydroclimatic changes during the early and late Holocene. Eagle Lake is currently located near the transition zone of the North American Precipitation Dipole, with the timing of precipitation showing a winter-wet scenario common to the Pacific Northwest, but overall precipitation (e.g. aridity) showing a Pacific Southwest pattern. The width and position of this transition is poorly constrained during the Holocene and is hypothesized to have migrated, particularly in response to the North American Monsoon. Eagle Lake is thus ideal in providing insights to the past positions of the dipole. Multi-proxy analyses results in differences between the early and late Holocene at Eagle Lake. TOC is lower in the early Holocene, however C:N ratios are much more variable indicating a transition from algal source material to terrestrial and back to algal material prior to the Mazama ash. There are also greater fluctuations of biogenic silica during the early Holocene, suggesting rapid changes in productivity.
To place these Holocene changes within the context of known climatic and anthropogenic conditions of the 20th century, a ~100 year record of hydrologic change is compared to drought and lake-level drops induced by the formation of the Bly Tunnel. Importantly, the effects of the tunnel on lake level is superimposed on the 1930s drought, making it difficult to disentangle the two impacts. However, the TOC and C:N ratios clearly mirror variations in lake level suggesting that they are effective indicators of Holocene variations.
|Commitee:||Hagedorn, Benjamin, Onderdonk, Nathan|
|School:||California State University, Long Beach|
|School Location:||United States -- California|
|Source:||MAI 57/02M(E), Masters Abstracts International|
|Subjects:||Geology, Paleoclimate Science|
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