-1 An alpine lacustrine record of early Holocene North American Monsoon dynamics from Dry Lake, southern California (USA) Broxton W. Bird * and Matthew E. Kirby Department of Geological Sciences, California State University, Fullerton, Fullerton, California 92834 USA; *Author for correspondence (broxton.bird@gmail.com) Received 21 February 2005; accepted in revised form 31 May 2005 Key words: Climate change, Dry Lake, Early Holocene, North American Monsoon, Southern California Abstract Dry Lake (2763 m), located in the San Bernardino Mountains of southern California, USA, provides a high-resolution climate record from the coastal southwest depicting early Holocene terrestrial climate. 27 AMS 14 C dates and multi-proxy analyses, including magnetic susceptibility, total organic mater, microfossil counts, and grain size, suggest the early Holocene was significantly wetter then present, due to an enhanced North American Monsoon (NAM). Elevated insolation at 9000 cal year B.P., raised summer sea surface temperatures in the Gulf of California and the eastern tropical Pacific, as well as land surface temperatures, extending the NAM into southern California. The data also provide evidence of the 8.2 ka event, which registers as a 300-year cool period characterized by reduced monsoonal precipitation, depressed basin productivity, and increased erosion. We suggest this event is the most likely period for the early to middle Holocene (9000–5000 cal year B.P.) glacial advance in the San Bernardino Mountains proposed by Owen et al. (2003, Geology 31: 729–732). Introduction The nature of early Holocene (defined for this paper as the period from 9000 to 7500 cal year B.P.) terrestrial climate change in the coastal southwest is not well characterized. This problem arises mainly from the fact that long-term (>5000- years), regional records of terrestrial climate are scarce. Furthermore, the resolution of the scarce early Holocene records are limited to millennial- scale climate interpretations (e.g., Enzel et al. 1992; Kirby et al. 2005). These records, however, indicate that the coastal southwest was signifi- cantly wetter during the early Holocene in re- sponse to varied seasonal insolation. Notably, these findings are in agreement with the results from recent climate modeling studies, which sug- gest that the early Holocene summer insolation maximum strengthened the North American Monsoon (NAM), resulting in greater effective moisture in the southwestern United States (Webber 2001; Liu et al. 2003). While these studies are insightful, important questions still remain concerning higher-frequency early Holocene cli- mate variability in the coastal southwestern Uni- ted States. In order to address these questions, we present a well-dated, high-resolution lacustrine record of early Holocene climate from Dry Lake in the San Bernardino Mountains of southern California, USA (Figure 1). This study is part of a larger re- search initiative to understand terrestrial Holocene climate in the coastal southwest using the rare, but natural, lakes of southern California. In this paper we focus on the interval from 9000 and 6500 cal year B.P. in order to explore two main issues: (1) Journal of Paleolimnology (2006) 35: 179–192 Ó Springer 2006 DOI 10.1007/s10933-005-8514-3