Enso-like cyclicity In Late Pleistocene varve thickness measurements from two alpine lakes, Wind River Range, Wyoming, USA
Abstract
Spectral analyses of varve thickness measurements in sediment cores from two moraine-dammed lakes in the Wind River Range of Wyoming, USA, reveal a 2.8-to-8-yr cyclicity consistent with that expressed by ENSO. The lakes [Louis Lake (42.596°N,108.846°W, 2610 m and nearby Fiddlers Lake 42.6312°N, 108.8786°W, 2868 m] and hold the possibility of longer records of mid-continental climate change even into the last interglacial. Nine macrofossil-based 14C ages (AMS) combined with varve thicknesses indicate the lakes were deep enough during the LGM to form and preserve varves and that the minimum age for the lacustrine sediments here is ~20 kyrs. The ENSO signal is most robust in the Louis Lake varves, displaying high spectral power across the entire band of frequencies associated with ENSO. Analysis of the Fiddlers Lake varves yield predictably less significant results, a consequence of the different geomorphic settings of these two lakes. Specifically, (1) Louis Lake has a large catchment and receives surface water input from a stream, which has delivered a large quantity of sediment to the lake margin and deposited a substantial delta. In this setting, variations in precipitation appear closely linked to sediment delivery to the lake, and are reflected in sediment distributions, while (2) Fiddlers Lake is located in a small re-entrant basin with a relatively insignificant catchment area and fed almost entirely by groundwater and direct rain/snow events, with little surface runoff; (3) the deeper water of Louis Lake aids in the formation and preservation of varves, while (4) lake level fluctuations in the shallower Fiddlers Lake directly affect varve creation and preservation (the onset of glaciation in the Fiddlers Lake core is represented by thick sediment packages that eventually thin to varves by ~1m up-core). The significant ENSO-like periodicities in the the varved sediments in these lakes suggests that the effects of ENSO forcing were felt far into the western interior of North America during the late Pleistocene, a result that accords with earlier work on lacustrine sediments of similar age in New England (Rittenour et al., 2000).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMGC51H1141D
- Keywords:
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- 1637 GLOBAL CHANGE / Regional climate change;
- 4522 OCEANOGRAPHY: PHYSICAL / ENSO;
- 4926 PALEOCEANOGRAPHY / Glacial;
- 4942 PALEOCEANOGRAPHY / Limnology