We present two hypotheses regarding the evolution of Holocene climate in the Northern Rocky Mountains that stem from a previously unpublished environmental magnetic record from Jones Lake, Montana. First, we link two distinct intervals of fining magnetic grain size (documented by an increasing ratio of anhysteretic to isothermal remanent magnetization) to the authigenic production of magnetic minerals in Jones Lake bottom waters. We propose that authigenesis in Jones Lake is limited by rates of groundwater recharge and ultimately regional hydroclimate. Second, at ~8.3 ka, magnetic grain size increases sharply, accompanied by a drop in concentration of magnetic minerals, suggesting a rapid termination of magnetic mineral authigenesis that is coeval with widespread effects of the 8.2 ka event in the North Atlantic. This association suggests a hydroclimatic response to the 8.2 ka event in the Northern Rockies that to our knowledge is not well documented. These preliminary hypotheses present compelling new ideas that we hope will both highlight the sensitivity of magnetic properties to record climate variability and attract more work by future research into aridity, hydrochemical response, and climate dynamics in the Northern Rockies.
Bibliographical noteFunding Information:
We thank the research staff at both the National Lacustrine Core Facility (LacCore) and Institute for Rock Magnetism (IRM) for long-standing support and the landowners and community members from Ovando, MT, for permission to access field sites and for interest in this work. The complete dataset reported here and updated age modeling for Jones Lake are available online as supplemental materials that accompany this paper. Nina Berglund contributed analyses under CEG?s supervision during a summer internship at the LacCore. This is IRM contribution 1905. The author(s) received no financial support for the research, authorship, and/or publication of this article.
© The Author(s) 2019.
- 8.2 ka
- Rocky Mountains
- environmental magnetism
- lake sediments