Geology Reports⌕ Search
Home/Archive/USGS

USGS · 70127985

Vegetation response to southern California drought during the Medieval Climate Anomaly and early Little Ice Age (AD 800–1600)

Linda E. Heusser·Ingrid L. Hendy·John A. Barron
View original source ↗Export metadata ↓

Abstract

High-resolution studies of pollen in laminated sediments deposited in Santa Barbara Basin (SBB) core SPR0901-02KC reflect decadal-scale fluctuations in precipitation spanning the interval from AD 800–1600. From AD 800–1090 during the Medieval Climate Anomaly (MCA) SBB sediments were dominated by xeric vegetation types (drought-resistant coastal sagebrush and chaparral) implying reduced precipitation in the southern California region. Drought-adapted vegetation abruptly decreased at AD 1090 and was rapidly replaced by mesic oak ( Quercus ) woodlands associated with an increased pollen flux into the basin. After a mesic interval lasting ∼100 years, pollen flux and the relative abundance of Quercus pollen dropped abruptly at AD 1200 when the rapid rise of chaparral suggests a significant drought similar to that of the MCA (∼AD 800–1090). This brief resurgence of drought-adapted vegetation between AD 1200–1270 marked the end of the MCA droughts. A gradual increase in mesic vegetation followed, characterizing cool hydroclimates of the Little Ice Age (LIA) in coastal southern California. The presence of xeric vegetation in SBB coincides with major drought events recorded in tree rings and low lake levels elsewhere in California except for the brief drought between AD 1130–1160. Correlative diatom and terrigenous sediment input proxy records from SBB are largely supportive of the pollen record predominantly linking the MCA with drought and La Niña-like conditions and the LIA with wetter (more El Niño-like) conditions. Differences between paleoclimate proxies (pollen, diatoms, and terrigenous sediment) in SBB exist, however, possibly reflecting the temporal and spatial differences in the generation of each proxy record, as well as their individual sensitivity to climate change.

Explore related subjects

Quaternary InternationalArticle

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Linda E. Heusser, Ingrid L. Hendy, John A. Barron. 2015. Vegetation response to southern California drought during the Medieval Climate Anomaly and early Little Ice Age (AD 800–1600). https://doi.org/10.1016/j.quaint.2014.09.032

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2024

Revisiting the physical processes controlling the tropical atmospheric circulation changes during the Mid-Piacenzian Warm Period

The Mid-Piacenzian Warm Period (MPWP; 3.0–3.3 Ma), a warm geological period about three million years ago, has been deemed as a good past analog for understanding the current and future climate change. Based on 12 climate model outputs from Pliocene Model Intercomparison Project Phase 2 (PlioMIP2), we investigate tropical atmospheric circulation (TAC) changes under the warm MPWP and associated underlying mechanisms by diagnosing both atmospheric static stability and diabatic processes. Our findings underscore the advantage of analyzing atmospheric diabatic processes in elucidating seasonal variations of TAC compared to static stability assessments. Specifically, by diagnosing alterations in diabatic processes, we achieve a quantitative understanding and explanation the following TAC changes (incl. Strength and edge) during the MPWP: the weakened (annual, DJF, JJA) Northern Hemisphere and (DJF) Southern Hemisphere Hadley circulation (HC), reduced (annual, DJF) Pacific Walker circulation (PWC) and enhanced (annual, JJA) Southern Hemisphere HC and (JJA) PWC, and westward shifted (annual, DJF, JJA) PWC. We further addressed that the increasing bulk subtropical static stability and/or decreasing vertical shear of subtropical zonal wind - two crucial control factors for changes in subtropical baroclinicity - may promote HC widening, and vice versa. Consequently, our study of spatial diabatic heating and cooling, corresponding to upward and downward motions within the TAC, respectively, provides a new perspective for understanding the processes controlling seasonal TAC changes in response to surface warming.

Quaternary International↗
USGS2023

Luminescence ages and new interpretations of the timing and deposition of Quaternary sediments at Natural Trap Cave, Wyoming

Natural Trap Cave, located in the Big Horn Mountains of north-central Wyoming, has a history of trapping and preserving a range of North American fauna that plummeted into the deep vertical entrance. These animal remains were buried and preserved within sediments of the main chamber and, in turn, have helped elucidate the procession of faunal dynamics during the latest glacial cycle. The cave location, south of the Laurentide and Cordilleran Ice Sheets, and proximal to Yellowstone, is at an ideal geographical juncture to provide insights to ecological changes in North America. The sediments that the animals are buried in inform us about transport and deposition both inside and outside of the cave that relate to catchment dynamics. We report on a series of optically stimulated luminescence (OSL) ages derived from samples obtained within the cave during excavation work in 2014 and in 2018. We also examine chronology produced by argon, tephrochronology, fission track, and luminescence techniques that have been used for understanding the infilling of the cave. The cave sediment ages and in situ measured gamma spectroscopy as measured in this study helped resolve an improved chronological age model when combined with previous data. The suite of OSL ages is interpreted through the stratigraphic relationships (and vertebrates contained within) which requires the use of an adequate age model; we use either the central age model or minimum age model where appropriate and with justification. Lowest sediments are dated to ∼150 ka with a hiatus at ∼130 to 52 ka. Above this, sediment deposition and entrainment of paleontological materials are representative of Pleistocene and early Holocene times, between 37 ± 6 ka and 7.6 ± 0.5 ka. The stratigraphic architecture suggests that deposition of materials into the cave is episodic and rapid, followed by quiescent periods where hydrologic scour, heavy overland flow , or possibly a cryo-hydrologic process may have altered unit relationships. Thus, the complementary geochronometers and the characteristics of quartz versus feldspar luminescence signals improve temporal interpretations of these complex deposits. This adapted understanding of mixing also sets the stage for future work with the aim to improve our understanding of ages and sources for ash units within these cave deposits. The three ash units recognized in the cave may represent an in-situ reworking of the same ash or may be representative of previously undocumented eruptions from the Yellowstone Caldera.

Wyoming↗
USGS2022

An 11,300 yr record of paleoclimatology and paleoceanography of the central California coast in a gravity core from Pioneer Seamount

Diatom, pollen, silicoflagellate, and biogenic opal analyses from a 155 cm-long gravity core from Pioneer Seamount, offshore Santa Cruz, California (PS1410-06 GC, latitude 37.3°N, longitude 123.4°W, water depth 2165 m) are compiled for the last ~11,300 years and compared with those of ODP 1019 and TN062-O550 from northern California. The relative abundance record of the subtropical diatom Fragilariopsis doliolus has similar bimodal Holocene patterns in all three cores, suggesting that sea surface temperatures (SST) were lower during the middle part of the Holocene than they were during the later and earlier parts. The relative abundance of coastal redwood ( Sequoia sempervirens ) pollen, a proxy for fog and coastal upwelling, displays stepwise increases in ODP 1019 and TN062-O550 between ~ 4000 and 3000 cal yr. BP, but its relative abundance in PS1410-06 GC increases gradually throughout the past 10,200 yr without any major steps. Similarly, biogenic silica (opal) displays stepwise increases at ~3600 and 2900 cal yr. BP in ODP 1019 and TN062-O550, respectively, whereas opal increases more gradually in PS1410-06 GC during the past 10,100 yr with relatively minor steps at ~3100 and ~2600 cal yr. BP. Together, coastal redwood and opal argue for a more gradual late Holocene increase in coastal upwelling along the coast of central California compared with that off northern California, where onshore-offshore gradients are more distinct.

California↗