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| Titel |
Late Holocene subalpine lake sediments record a multi-proxy shift to increased aridity at 3.65 kyr BP, following a millennial-scale neopluvial interval in the Lake Tahoe watershed and western Great Basin, USA |
| VerfasserIn |
Paula Noble, Susan Zimmerman, Ian Ball, Kenneth Adams, Jillian Maloney, Shane Smith |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127637
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| Publikation (Nr.) |
 EGU/EGU2016-7533.pdf |
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| Zusammenfassung |
| A mid Holocene dry period has been reported from lake records in the Great Basin and Sierra
Nevada, yet the spatial and temporal extent of this interval is not well understood. We present
evidence for a millennial-scale interval of high winter precipitation (neopluvial) at the end of
the mid Holocene in the Lake Tahoe-Pyramid Lake watershed in the northern Sierra Nevada
that reached its peak ∼3.7 kcal yr BP. A transect of 4 cores recovered from Fallen Leaf
Lake in the Tahoe Basin were dated using AMS14C on plant macrofossils, and
analyzed using scanning XRF, C and N elemental and stable isotope measurements,
and diatoms as paleoclimate proxies. Fallen Leaf Lake is a deep glacially-derived
lake situated in the Glen Alpine Valley at an elevation of 1942m, ∼45 m above
the level of Lake Tahoe. In Fallen Leaf Lake, the end of the neopluvial is dated
at 3.65 ± 0.09 kcal yr BP, and is the largest post-glacial signal in the cores. The
neopluvial interval is interpreted to be a period of increased snowpack in the upper
watershed, supported by depleted g δ13Corg (-27.5) values, negative baseline shifts
in TOC and TN, lower C:N, and high abundances of Aulacoseira subarctica, a
winter-early spring diatom. Collectively, these proxies indicate cooler temperatures,
enhanced mixing, and/or shortened summer stratification resulting in increased algal
productivity relative to terrestrial inputs. The neopluvial interval ends abruptly at
3.65 ka, with a change from mottled darker opaline clay to a homogeneous olive
clay with decreased A. subarctica and opal, and followed by a 50% reduction in
accumulation rates. After this transition δ13Corg becomes enriched by 2‰ and
TOC, TN, and C:N all show the start of positive trends that continue through the
Holocene. Pyramid Lake is an endorheic basin situated at the terminal end of the
watershed, and inflow arrives from the Lake Tahoe basin via the Truckee River. At
Pyramid Lake, existing ages on paleo-shorelines indicate a significant lake-level rise
beginning at some point after 5 kcal yr BP and reaching a highstand of about 1186 m
between 3.8 – 4.1 kcal yr BP (Briggs et al., 2005), but new OSL ages on Holocene
shorelines are pending. In the Walker, Mono, and Owens lake basins, the neopluvial
shorelines represent the highest late Holocene shorelines (Stine, 1990; Adams et
al., 2014). Collectively, these studies indicate that the neopluvial and subsequent
aridification intervals preserved in Fallen Leaf Lake sediments were at least regional in
scale, affecting the watersheds in the northern Sierra Nevada-western Great Basin |
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