Lora Stevens

California State University, Long Beach

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Morteza Djamali

Institut Méditerranéen de Biodiversité et d'Ecologie Marine et Continentale

Jacques‐Louis de Beaulieu

Institut Méditerranéen de Biodiversité et d'Ecologie Marine et Continentale

Varenka Lorenzi

California State University, Long Beach

Valérie Andrieu‐Ponel

Aix-Marseille Université

Kelsey E. Doiron

International Ocean Discovery Program

Sherilyn C. Fritz

University of Nebraska–Lincoln

Mitchell J. Power

University of Utah

A.J. White

California State University, Long Beach

Samuel E. Muñoz

Northeastern University

Cathy Whitlock

Montana State University

Cooperative Institutions

Centre National de la Recherche Scientifique

Institut de Recherche pour le Développement

Aix-Marseille Université

Centre de Recherche et d’Enseignement de Géosciences de l’Environnement

Institut Méditerranéen de Biodiversité et d'Ecologie Marine et Continentale

Laboratoire Méditerranéen de Préhistoire Europe Afrique

University of Minnesota

United States Geological Survey

California State University, Long Beach

University of Nebraska–Lincoln

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Increased effective moisture in northern Vietnam during the Little Ice Age

Palaeogeography Palaeoclimatology Palaeoecology (2018)

Lora Stevens Brendan M. Buckley Sung Hoon Kim Pam Hill Kelsey E. Doiron

Ice core

δ18O

Paleoclimatology

Centennial

10.1016/j.palaeo.2018.09.011

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Citations (12)

Holocene seasonal variability inferred from multiple proxy records from Crevice Lake, Yellowstone National Park, USA

Palaeogeography Palaeoclimatology Palaeoecology (2012)

Cathy Whitlock Walter E. Dean Sherilyn C. Fritz Lora Stevens Jeffery R. Stone

Varve

10.1016/j.palaeo.2012.03.001

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Citations (73)

A comparative analysis of Holocene monsoon precipitation in the central highlands of Vietnam using hydrogen isotopic analyses of leaf wax n-alkanes

Linda Pineda Kelsey E. Doiron Lora Stevens Simon C. Brassell

<p>Understanding the effects of current climate change on water resources is of critical importance particularly in tropical regions where water availability is reliant on both the timing and intensity of monsoon precipitation. &#160;Summer rainfall in Southeast Asia is directly influenced by the Bay of Bengal arm of the Indian Summer Monsoon. Based on numerous speleothem records, prevailing theory argues that compared with the late Holocene, the early Holocene experienced enhanced monsoon strength and thus greater rainfall due to greater summer insolation. However, recent modeling work and one preliminary multi-proxy record from Ia M&#8217;He, Vietnam suggest that monsoon rainfall in parts of mainland southeast Asia may be out of phase with monsoon trends in eastern Asia. The results of the modeling work and multi-proxy record suggest that unlike eastern Asia, monsoon precipitation in Vietnam is greater in the late Holocene relative to the early Holocene. To confirm the results of these data, a lake sediment core from the Central Highlands of Vietnam was used to reconstruct a record of precipitation using the hydrogen-isotopic values of n-alkanes in terrestrial leaf waxes. The objective of this research is to provide the first well-dated hydroclimate record for Vietnam and to test the proposed model of an out-of-phase relationship between SE Asia and surrounding monsoon trends.</p>

East Asian Monsoon

Tropical monsoon climate

Paleoclimatology

10.5194/egusphere-egu23-205

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EARLY HOLOCENE CLIMATE CHANGE AT EAGLE LAKE, CA LOCATED IN THE TRANSITION ZONE OF THE NORTH AMERICAN DIPOLE

Abstracts with programs - Geological Society of America (2016)

Mounga Nonu Lora Stevens Varenka Lorenzi

10.1130/abs/2016cd-274606

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Timing of Atmospheric Precipitation in the Zagros Mountains Inferred from a Multi-Proxy Record from Lake Mirabad, Iran

Quaternary Research (2006)

Lora Stevens Emi Ito Antje Schwalb Herbert E. Wright

Abstract A sediment core 7.2 m long from Lake Mirabad, Iran, was examined for loss-on-ignition, mineralogy, oxygen-isotopic composition of authigenic calcite, and trace-element composition of ostracodes to complement earlier pollen and ostracode-assemblage studies. Pollen, ostracode-inferred lake level, and high Sr/Ca ratios indicate that the early Holocene (10000 to 6500 cal yr BP) was drier than the late Holocene. Low δ 18 O values during this interval are interpreted as resulting from winter-dominated precipitation, characteristic of a Mediterranean climate. Increasing δ 18 O values after 6500 cal yr BP signal a gradual increase in spring rains, which are present today. A severe 600-yr drought occurred at ca. 5500 cal yr BP, shortly after the transition from pistachio-almond to oak forest. During the late Holocene, two milder droughts occurred at about 1500 and 500 cal yr BP. Within the resolution of the record, no drought is evident during the collapse of the Akkadian empire (4200–3900 cal yr BP). Rather, a decrease in δ 18 O values to early-Holocene levels may indicate the return to a Mediterranean precipitation regime.

Authigenic

Loss on ignition

Sapropel

Paleoclimatology

10.1016/j.yqres.2006.06.008

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Citations (154)

Geochemical evidence for hydroclimatic variability over the last 2460 years from Crevice Lake in Yellowstone National Park, USA

Quaternary International (2007)

Lora Stevens Walter E. Dean

δ18O

Discharge

10.1016/j.quaint.2007.11.012

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Citations (14)

A 2200-yr record of hydrologic variability from Foy Lake, Montana, USA, inferred from diatom and geochemical data

Quaternary Research (2006)

Lora Stevens Jeffery R. Stone Joshua W. Campbell Sherilyn C. Fritz

Abstract A 2200-yr long, high-resolution (∼5 yr) record of drought variability in northwest Montana is inferred from diatoms and δ 18 O values of bio-induced carbonate preserved in a varved lacustrine core from Foy Lake. A previously developed model of the diatom response to lake-level fluctuations is used to constrain estimates of paleolake levels derived from the diatom data. High-frequency (decadal) fluctuations in the de-trended δ 18 O record mirror variations in wet/dry cycles inferred from Banff tree-rings, demonstrating the sensitivity of the oxygen-isotope values to changes in regional moisture balance. Low frequency (multi-centennial) isotopic changes may be associated with shifts in the seasonal distribution of precipitation. From 200 B.C. to A.D. 800, both diatom and isotope records indicate that climate was dry and lake level low, with poor diatom preservation and high organic carbon: nitrogen ratios. Subsequently, lake level rose slightly, although the climate was drier and more stable than modern conditions. At A.D. 1200, lake level increased to approximately 6 m below present elevation, after which the lake fluctuated between this elevation and full stage, with particularly cool and/or wetter conditions after 1700. The hydrologic balance of the lake shifted abruptly at 1894 because of the establishment of a lumber mill at the lake's outlet. Spectral analysis of the δ 18 O data indicates that severe droughts occurred with multi-decadal (50 to 70 yr) frequency.

Varve

10.1016/j.yqres.2005.08.024

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Citations (60)

A 1000-Year Record of Cahokia Region Population Change through Fecal Stanol Biomarker Analysis

The 81st Annual Meeting of the Society for American Archaeology (2017)

AJ White Lora Stevens Varenka Lorenzi

Source

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Citations (0)

Proposed changes in seasonality of climate during the Lateglacial and Holocene at Lake Zeribar, Iran

The Holocene (2001)

Lora Stevens H. E. Wright Emi Ito

Calcareous sediments spanning the last 13 ka from Lake Zeribar, western Iran, were sampled for stable-isotope analysis as a means of augmenting earlier climatic interpretations based on pollen and macrofossils. The Lateglacial period was cold and dry, supporting semi-desert vegetation and highly concentrated lake water. Low evaporation rates due to the cold resulted in long residence times and high lake stands. Durinig the early Holocene, the upland vegetation changed to a pistachio-oak savanna as low temperatures and aridity ameliorated. Lake level dropped in response to increased evapotranspiration. The low oxygen-isotope values of lacustrine calcite during this period are interpreted as a relative increase in the contributioni of winiter moisture rather than overall changes in effective moisture. A gradual increase in oak pollen at ∼7 ka BP signalled the increase in effective moisture to levels similar to those of today. At the same time the δ 18 O values increased. reflecting a greater percentage of 18 O-enriched spring rains. Modern values and seasonal distribution of precipitation were established by 6 ka BP. A short-lived return to winter-only precipitation occuiTed at ∼4.5 ka BP and resulted in a temporary increase in aridity. The covariance among δ 13 C, carbonate deposition and δ 18 O values suggests that lake productivity is linked to these seasonal climatic changes.

Meltwater

Macrofossil

Seasonality

10.1191/09596830195762

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Citations (224)

An evaluation of fecal stanols as indicators of population change at Cahokia, Illinois

Journal of Archaeological Science (2018)

A.J. White Lora Stevens Varenka Lorenzi Samuel E. Muñoz Carl P. Lipo

Proxy (statistics)

Before Present

10.1016/j.jas.2018.03.009

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Citations (43)