Kevin G. Cannariato

Decline of surface temperature and salinity in the western tropical Pacific Ocean in the Holocene epoch

In the present-day climate, surface water salinities are low in the western tropical Pacific Ocean and increase towards the eastern part of the basin. The salinity of surface waters in the tropical Pacific Ocean is thought to be controlled by a combination of atmospheric convection, precipitation, evaporation and ocean dynamics, and on interannual timescales significant variability is associated with the El Niño/Southern Oscillation cycles. However, little is known about the variability of the coupled ocean–atmosphere system on timescales of centuries to millennia. Here we combine oxygen isotope and Mg/Ca data from foraminifers retrieved from three sediment cores in the western tropical Pacific Ocean to reconstruct Holocene sea surface temperatures and salinities in the region. We find a decrease in sea surface temperatures of ∼0.5 °C over the past 10,000 yr, whereas sea surface salinities decreased by ∼1.5 practical salinity units. Our data imply either that the Pacific basin as a whole has become progressively less salty or that the present salinity gradient along the Equator has developed relatively recently.

Biotic response to late Quaternary rapid climate switches in Santa Barbara Basin: Ecological and evolutionary implications

Benthic foraminiferal assemblages from Santa Barbara Basin exhibit major faunal and ecological switches associated with late Quaternary millennial- to decadal-scale global climate oscillations. Repeated turnovers of entire faunas occurred rapidly (<40--400 yr) without extinction or speciation in conjunction with Dansgaard-Oeschger shifts in thermohaline circulation, ventilation, and climate, confirming evolutionary model predictions of Roy et al. Consistent faunal successions of dysoxic taxa during successive interstadials reflect the extreme sensitivity and adaptation of the benthic ecosystem to the rapid environmental changes that marked the late Quaternary and possibly other transitional intervals in the history of the Earth`s ocean-atmosphere-cryosphere system. These data support the hypothesis that broad segments of the biosphere are well adapted to rapid climate change.

Structure of the penultimate deglaciation along the California margin and implications for Milankovitch theory

The detailed structure and timing of the penultimate deglaciation are insufficiently defined yet critical for understanding mechanisms responsible for abrupt climate change. Here we present oxygen isotope records (from planktonic and benthic foraminifera) at unprecedented resolution encompassing late marine oxygen isotope stage (MIS) 6 and Termination II (ca. 150–120 ka) from the Santa Barbara Basin, supported by additional southern California margin records, a region highly sensitive to millennial-scale climate oscillations during the last deglaciation. These records reveal millennial- and centennial-scale climate variability throughout the interval, including an interstadial immediately preceding the deglaciation, a brief warm event near the beginning of Termination II, and a Bolling-Allerod–Younger Dryas–like climate oscillation midway through the deglaciation. Recognition of these events in an oxygen isotope record from a 230Th-dated stalagmite allows the adoption of this radiometric chronology for the California margin records. This chronology supports the Milankovitch theory of deglaciation. The suborbital history of climate variability during Termination II may account for records of early deglaciation.

Santa Barbara basin study extends global climate record

A fundamental goal of Earth science is to understand the remarkable instability of late Quaternary global climate prior to the beginning of the Holocene, about 11,000 years ago. This unusual climate behavior was characterized by millennial-scale climate oscillations on suborbital timescales, and a distinctive ‘sawtooth’ pattern of very abrupt glacial and stadial terminations (within decades) followed by more gradual global cooling [e.g., Dansgaard et al., 1993; Hendy and Kennett, 1999]. The fact that both major (glacial) and minor (stadial) cooling periods in Earths climate were terminated by similar abrupt warming episodes suggests a common mechanism driving such rapid changes in global climate. Understanding the causes of this instability is crucial given developing concerns about global warming, yet knowledge about this climate behavior has been essentially confined to the last 150,000 years or so, owing to the absence of available sequences of sufficient age and chronological resolution. The high-resolution paleoclimate record from the Greenland ice cores is limited to about 110 thousand years ago (ka),and although Antarctic ice cores now extend back to more than 740 ka [European Project for Ice Coring in Antarctica, 2004], these latter cores primarily provide information about high-latitude conditions at much lower resolution than is required to address abrupt climate change.

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

Publisher Summary Linguistic diversity and the patchwork distribution of language groups in western North America reflect a complex history of early settlement, in situ development, and periodic population movement. Available climate records in western North America (7000–3800 cal yr BP) indicate a severe dry interval between 6300 and 4800 cal yr BP embedded within a generally warm and dry Middle Holocene. Dry conditions in western North America between 6300 and 4800 cal yr BP correlate with cold to moderate sea-surface temperatures (SST) and relatively high marine productivity along the Southern California Coast evident in Ocean Drilling Program (ODP) Core 893A/B (Santa Barbara Basin). Marine climate data from the Santa Barbara Basin indicates that SSTs oscillated during the Middle Holocene between warm and cold states. Based on archeological, linguistic, and genetic data, this chapter argues for a movement of Uto-Aztecan people from western desert environments to the Southern California Coast, including the southern Channel Islands, and into portions of the Central Valley by at least 5500–4500 cal yr BP. It hypothesizes that population dispersal from the desert interior was primarily in response to severe and prolonged drought and that people moved selectively to coastal and aquatic habitats because of the ameliorated effects of drought and their overall productivity. Furthermore, it suggests that some Uto-Aztecan groups were displaced as conditions in the southern California desert became dryer and less productive. Finally, it demonstrates the linkages between environmental change and human adaptive response during the arid Middle Holocene in western North America.