Chronology of Sediment Deposition in Upper Klamath Lake, Oregon

Abstract

A combination of tephrochronology and 14 C, 210 Pb, and 137 Cs measurements provides a robust chronology for sedimentation in Upper Klamath Lake during the last 45 000 years. Mixing of surficial sediments and possible mobility of the radio-isotopes limit the usefulness of the 137 Cs and 210 Pb data, but 210 Pb profiles provide reasonable average sediment accumulation rates for the last 100-150 years. Radiocarbon ages near the top of the core are somewhat erratic and are too old, probably as a result of detrital organic carbon, which may have become a more common component in recent times as surrounding marshes were drained. Below the tops of the cores, radiocarbon ages in the center of the basin appear to be about 400 years too old, while those on the margin appear to be accurate, based on comparisons with tephra layers of known age.Taken together, the data can be combined into reasonable age models for each site. Sediments have accumulated at site K1, near the center of the basin, about 2 times faster than at site CM2, on the margin of the lake. The rates are about 0.10 and 0.05 cm/yr, respectively. The chronological data also indicate that accumulation rates were slower during the early to middle Holocene than during the late Holocene, consistent with increasing wetness in the late Holocene.

Changes in benthic nutrient sources within a wetland after hydrologic reconnection

“…Based on the results of laboratory experiments by Aldous et al [72], they also hypothesized that the benthic source of dissolved phosphorus would be short term (i.e., constrained to the initial months after the wetlands were flooded due to rapid reequilibration of pore waters with overlying water-column concentrations). In contrast, sediment-deposition rates for adjacent Upper Klamath Lake were an order of magnitude lower over the past century (0.05-0.1 cm/year [31]). Our direct measurements of the porewater concentration profiles that drive diffusive flux indicate a similar multiyear response (Fig.…”

Record of Late Pleistocene Glaciation and Deglaciation in the Southern Cascade Range. I. Petrological Evidence from Lacustrine Sediment in Upper Klamath Lake, Southern Oregon

“…Descriptions of coring, as well as the age control, lithology, and geochemistry of the core are given by Colman et al (2004). Here we summarize aspects of these descriptions (with ages in calendar years) that are essential background for this paper.…”

“…Here we summarize aspects of these descriptions (with ages in calendar years) that are essential background for this paper. The age model for the 12.86-m core is controlled by tephra layers and 17 radiocarbon dates (Colman et al 2004). Intervals of tephra, including the bottom of the core (sediment below 1190 cm; older than 37.5 ka), are discounted from our paleoenvironmental analysis, because the tephra affects magnetic properties and particle-size results.…”

Volcanic eruptions in the Longgang volcanic field, northeastern China, during the past 15,000 years

“…The eruption history of the LVF is still, however, poorly understood, due in part to the limit of 14 C dating of young deposits (e.g. Davies et al, 2004;Colmam et al, 2004;Guilderson et al, 2005;Oswald et al, 2005), as well as the paucity of historical documents relating to this remote area.…”