Pacific Southwest United States Holocene Droughts and Pluvials Inferred From Sediment δ18O(calcite) and Grain Size Data (Lake Elsinore, California)

Matthew Edward Christopher Kirby,Kevin Nichols,William Paul Patterson,Michael A Anderson,Matthew Lachniet,James A Noblet,Judith Avila

doi:10.3389/feart.2019.00074

Abstract

Records of past climate can inform us on the natural range and mechanisms of climate change. In the arid Pacific southwest United States (PSW), which includes southern California, there exist a variety of Holocene records that can be used to infer past winter conditions (moisture and/or temperature). Holocene records of summer climate, however, are rare from the PSW. In the future, climate changes due to anthropogenic forcing are expected to increase the severity of drought in the already water stressed PSW. Hot droughts are of considerable concern as summer temperatures rise. As a result, understanding how summer conditions changed in the past is critical to understanding future predictions under varied climate forcings. Here, we present a c. 10.9 kcal BP 18O(calcite) record from Lake Elsinore, California, interpreted to reflect 18O(lake water) values as controlled by over-water evaporation from summer-to-early fall. Our results reveal three millennial scale intervals: 1) the highly evaporative Early Holocene (10.55-6.65 kcal BP), 2) the less evaporative Mid-Holocene (6.65-2.65 kcal BP); and, 3) the evaporative Late Holocene (2.65-0.55 kcal BP). These results are coupled with an inferred winter precipitation runoff (sand content) record from Kirby et al. (2010). Using these data together, we estimate the duration and severity of centennial-scale Holocene droughts and pluvials (e.g., high 18O(calcite) values plus low sand content = drought and vice versa). Furthermore, the coupled 18O(calcite) and sand data provide a generalized Holocene lake level history. The most severe, long-lasting droughts (i.e., maximum summer-to-early fall evaporation and minimum winter precipitation runoff) occur in the Early Holocene. Fewer, less severe, and shorter duration droughts occurred during the Mid-Holocene as pluvials became more common. Droughts return with less severity and duration in the Late Holocene. Notably, the Little Ice Age is characterized as the wettest period during the Late Holocene.

Highlights

Extracting seasonality from climatic archives is a major challenge in the field of paleoclimatology (Anderson et al, 1987; Leavitt and Long, 1991; Wurster and Patterson, 2001; Miller et al, 2010; Labotka et al, 2016)
In the winter precipitation dominated, Pacific southwestern United States (PSW), for example, most previous Holocene-length work infers some component of past winter hydroclimates, without any significant insight to summer conditions (Enzel and Wells, 1997; McDonald et al, 2003; Wells et al, 2003; Bird and Kirby, 2006; Bird et al, 2010; Kirby et al, 2010, 2012, 2014, 2015; Pigati et al, 2011)
The preservation of warm season precipitated CaCO3 is favored by a warmer water column and the associated decrease in CaCO3 solubility at higher water temperatures. The latter relationship is apparent in Lake Elsinore via the presence and near absence of CaCO3 during the warmer Holocene versus the colder Glacial, respectively (Kirby et al, 2007, 2013, 2018)

Summary

INTRODUCTION

Extracting seasonality from climatic archives is a major challenge in the field of paleoclimatology (Anderson et al, 1987; Leavitt and Long, 1991; Wurster and Patterson, 2001; Miller et al, 2010; Labotka et al, 2016). There is, only one Holocene summer paleotemperature reconstruction from the study region – a July temperature pollen-reconstruction for the San Jacinto Mountains (headwaters to Lake Elsinore) (Wahl, 2002; Ohlwein and Wahl, 2012). We use a lacustrine sediment δ18O(calcite) archive from Lake Elsinore, California to infer centennial to multi-centennial scale changes in Holocene summer-to-early fall δ18O(lake water) values (i.e., period of maximum CaCO3 precipitation). These changes are interpreted to reflect summer-to-early fall over-water evaporation. We compare our results to a pollen-based, July temperature anomaly reconstruction from the San Jacinto Mountains – the headwater catchment area for Lake Elsinore (Wahl, 2002; Ohlwein and Wahl, 2012)

BACKGROUND

MATERIALS AND METHODS

RESULTS AND ISOTOPIC

DISCUSSION

CONCLUSION