Increased northeast Pacific climatic variability during the warm middle Holocene

Abstract

We use a pair of decadally resolved planktonic foraminiferal δ18O records from Santa Barbara Basin (SBB) to show that the warmest interval of the current interglacial, the middle Holocene, was characterized by increased decadal‐ to centennial‐scale climatic variability. Modern relationships between the Pacific Decadal Oscillation (PDO), the El Niño‐Southern Oscillation (ENSO), and upper water conditions in SBB also suggest a preference of the northeast (NE) Pacific climate during the warm mid‐Holocene toward the warm phase of the PDO and more intense ENSO warm events (“El Niños”). In the context of future climate, this study suggests increasing decadal‐ to centennial‐scale climatic variability in a globally warmed world.

Middle Holocene climate change and human population dispersal in western North America

“…The warmest Middle Holocene interval occurred between 4500 and 4000 cal yr BP ($151C), in agreement with Friddell et al (2003). SSTs between 5800 and 5200 cal yr BP were relatively moderate compared to these warm and cold episodes.…”

“…In general, SSTs were relatively warm during the Middle Holocene, supporting interpretations of Friddell et al (2003), except for one distinct cold interval between about 6300 and 5800 cal yr BP. More moderate SSTs are evident in this record from 5800 to 5000 cal yr BP.…”

“…During the Middle Holocene dry conditions throughout western North America (Antevs, 1948;Benson et al, 2002) correspond to warm SSTs in Santa Barbara Basin. Similarly warm SSTs through the Middle Holocene recorded in another Santa Barbara Basin sequence have been interpreted as evidence for stronger El Nin˜o-Southern Oscillation (ENSO) activity in the Pacific and implied generally wetter conditions in western North America (Friddell et al, 2003). This, however, is inconsistent with indications of widespread Middle Holocene aridity in western North America.…”

Post-glacial redistribution and shifts in productivity of giant kelp forests

“…Analysis of southern California kelp canopy area and biomass records from 1968 to 2002 reveals predictably higher biomass density during periods of high productivity potential (La Niñ a) versus low productivity potential (El Niñ o; figure 3a), presumably owing to nutrient deficiency during El Niñ o events (Zimmerman & Robertson 1985;Tegner et al 1997). Furthermore, recently published palaeooceanographic records (Hendy et al 2002(Hendy et al , 2004Friddell et al 2003) for the last 20 000 years reveal an abrupt shift in late Quaternary oceanographic productivity potential, from cold unproductive conditions at the LGM to warmer, more productive conditions from 15 600 yr BP to present (figure 3b). The low productivity potential of the LGM may be analogous to long-term El Niñ o conditions (Ortiz et al 2004).…”

“…Thus, to estimate late Quaternary changes in giant kelp productivity potential we chose proxies for three environmental variables: sea surface temperature (SST), presence of nutrient-rich sub-photic water (d 15 N) and surface water productivity (%C org ) from the varved sediments of the Santa Barbara Basin, one of the best-known regional records of late Quaternary climate change (Kennett & Ingram 1995). Data from two well-studied sediment cores in the Santa Barbara Channel region, Hole 1017E and Hole JPC76, were used to reconstruct periods of low or high productivity potential since the LGM (SST: Friddell et al 2003;Hendy et al 2004;d 15 N: Hendy et al 2004;%C org : Hendy et al 2002). These proxies provided independent measures of relative changes in temperature, nutrient delivery and productivity, three processes that are highly coupled at daily to decadal scales but may be decoupled at centennial to millenial and longer time scales.…”