Holocene climate and oceanography of the coastal Western United States and California Current System

Abstract

Examination of climatic and oceanographic changes through the Holocene (11.75 ka–present) allows for an improved understanding and contextualization of modern climate change. Climate records of the Holocene can be utilized as a “baseline” from which to compare modern climate and can also provide insights into how environments experience and recover from change. However, individual studies on Holocene climate in the literature tend to focus on a distinct geographic location, a specific proxy record, or a certain aspect of climate (e.g., upwelling or precipitation), resulting in localized, record-specific trends rather than a comprehensive view of climate variability through the Holocene. Here we synthesize the major oceanographic and terrestrial changes that have occurred in the Western United States (bounded by 30 to 52∘ N and 115 to 130∘ W) through the most recent 11.75 kyr and explore the impacts of these changes on marine and terrestrial ecosystems. We present a novel spatiotemporal analysis of Holocene marine and terrestrial temperature, hydroclimate, and fire activity across the Early, Middle, and Late Holocene using a coded analysis of over 40 published studies. Following coded analysis of temperature, hydroclimate, and fire activity in the paper, we include a broader literature review of environmental change through the Holocene, including an examination of the impacts of multi-millennial climate trends on ecological communities. We find that the Early Holocene is characterized by warming relative to pre-Holocene conditions, including warm sea surface conditions, a warm and dry Pacific Northwest, a warm and wet Southwest, and overall spatial and temporal stability. In the Middle Holocene, these patterns reverse; this interval is characterized by cool sea surface temperatures, a cool and wet Pacific Northwest and warm and dry Southwest. The Late Holocene is the most variable interval, both spatially and temporally, and a novel spatial trend appears in terrestrial climate with warmer coastal areas and cooler inland areas. Human communities interacted with the environment throughout the entire Holocene, as evidenced in archeological and paleoenvironmental records, yet the recent Era of Colonization (1850–present) represents an unprecedented environmental interval in many records. Broadly, our analysis shows linkages between terrestrial and oceanographic conditions, distinct environmental phases through time, and emphasizes the importance of local factors in controlling climate through the dynamic Holocene.