Isotopic Analysis of Carbonate and Organic Matter Sediment from Morrison Lake, Montana; Implications for Hydroclimate of the Northern Rocky Mountains
Abstract
Hydroclimatic variability in high elevation, headwater environments of the northern Rocky Mountains has significant implications on downstream ecosystems. Current knowledge of precipitation variability is limited to data collections over the last several decades by SNOTEL, weather stations, and precipitation-sensitive tree ring records. Paleoclimatic proxies that span the Holocene are necessary to better develop our understanding of multidecadal to centennial scale hydroclimatic variability, and frame modern weather trends. Knowledge of mean drought duration and periodicity in northern Rocky Mountain headwater environments is currently spatially limited due to a lack of available climatic proxies. Isotopic analysis has been conducted on both the inorganic carbonate mineral fraction and the bulk organic fraction of sediment cores collected at Morrison Lake, Montana. This headwater lake is characterized by significant authigenic calcite production, allowing its sediments to record oxygen isotopic variability of the lake water, which is strongly modified by evaporation. Isotopic values from both the inorganic and organic fractions, over the past 7,500 yrs BP, show both multidecadal and centennial scale variability. Carbon to nitrogen mass ratios indicate shifts between an organic fraction dominated by a mix of terrestrial and aquatic plants, to one that is primarily aquatic by the mid Holocene. Nitrogen isotopes show significant multi-centennial scale variability with increasing δ15N values in the early Holocene, shifting to near atmospheric values throughout the mid Holocene, and then shifting back to enriched values in the late Holocene. Over the past 7,500 years, δ18O values are increasingly lower, with punctuations of increases of up to 8‰. Overall, this data indicates that the Morrison Lake region was characterized by an increasingly wetter and cooler climate over the past 7,500 years with a notable shift around 3,000 yrs BP. This record is punctuated by several multidecadal drought events. The lacustrine sediment record of Morrison Lake can assist in the development of a regional framework of Holocene hydroclimatic variability in the northern Rocky Mountains due to its unique characteristics and location.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP21B..05T
- Keywords:
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- 3335 North American Monsoon;
- ATMOSPHERIC PROCESSESDE: 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCESDE: 4914 Continental climate records;
- PALEOCEANOGRAPHYDE: 4938 Interhemispheric phasing;
- PALEOCEANOGRAPHY