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  1. Abstract

    Perspectives on past climate using lake sediments are critical for assessing modern and future climate change. These perspectives are especially important for water-stressed regions such as the western United States. One such region is northwestern California (CA), where Holocene-length hydroclimatic records are scarce. Here, we present a 9000-year, relative lake level record from Maddox Lake (CA) using a multi-indicator approach. The Early Holocene is characterized by variably low lake levels with a brief excursion to wetter climates/relative highstand ca. 8.4–8.06 cal ka BP, possibly related to the 8.2 ka cold event and changing Atlantic Meridional Overturning Circulation (AMOC). From 5.2–0.55 cal ka BP, Maddox Lake experienced a long-term regression, tracking changes in summer-winter insolation, tropical and northeast Pacific SSTs, and the southward migration of the ITCZ. This gradual regression culminated in a pronounced relative lowstand during the Medieval Climatic Anomaly (MCA). A marked relative highstand followed the MCA, correlative to the Little Ice Age. The latter reflects a far-field response to North Atlantic volcanism, solar variability, and possibly changes in AMOC and Arctic sea ice extent. Our results further confirm the hydroclimatic sensitivity of northwest California to various forcings including those emanating from the North Atlantic.

     
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    Free, publicly-accessible full text available September 1, 2024
  2. Abstract

    This study examines the relationship between water depth and diatom assemblages from lake-sediment-surface samples at Kelly Lake, California. A total of 40 surface-sediment samples (integrated upper 5 cm) were taken at various depths within the small (~ 3.74 ha) 5.7 m-deep lake. Secchi depths, water temperature, pH, salinity, conductivity, and total dissolved solids were also measured. Some diatom species showed distinct association with depth (e.g.,Fragilaria crotonensis, Nitzschia semirobusta). The relationship between the complete diatom assemblages and water depth was analyzed and assessed by depth-cluster analysis, a one-way analysis of similarity, principal components analysis and canonical correspondence analysis. Statistically significant differences were found between the assemblages associated with shallow depth (0–1.25 m), mid-depth (1.25–3.75 m), and deep-water (3.75–5.2 m) locations. The relationship between diatom assemblages and lake depth allowed two transfer models to be developed using the Modern Analogue Technique and Weighted Averaging Partial Least Squares. These models were compared and assessed by residual scatter plots. The results indicate that diatom-inferred transfer models based on surface-sediment samples from a single, relatively small and shallow lake can be a useful tool for studying past hydroclimatic variability (e.g., lake depth) from similar lakes in California and other regions where the large number of lakes required for traditional transfer-function development may not exist.

     
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