Sea Surface Temperature Variability During the Past 2000 Years in Santa Barbara Basin, California

Abstract:

An understanding of the spatial and temporal variability of late Holocene climate events is necessary to decipher natural climate variability from anthropogenic influence. At present, few North Pacific high-resolution marine records of the last 2000 years of temperature exist. High quality box and kasten cores from Santa Barbara Basin provide an opportunity to link foraminiferal proxy records to the instrumental sea surface temperature record over the past 200 years, to extend these proxy temperature records back over the last 2000 years, and to compare them with marine and continental records of temperature from other regions.

We present an approximately annual to decadal record of planktonic foraminiferal proxies of temperature, including Mg/Ca, calcite δ¹⁸O and size-normalized shell weight of the near-subsurface dwelling planktonic foraminifera Globigerina bulloides, and Neogloboquadrina pachyderma coiling in Santa Barbara Basin, California (34° 16.847’ N, 120° 02.268’ W), over the past 2000 years. G. bulloides Mg/Ca temperatures exhibit a long-term cooling trend of approximately 2°C that ended in the early 18^th century. Similarly, G. bulloides calcite δ¹⁸O and shell weight gradually increased from 0 to 1000 AD indicating long-term cooling. However, the cooling trend was followed by a calcite δ¹⁸O decrease from 1000 to 1700 AD, indicating either warming or freshening of surface water through the Little Ice Age (ca. 1400 to 1850 AD). After the early nineteenth century, G. bulloides calcite δ¹⁸O, Mg/Ca and shell weight trends are again broadly similar and correlate with historical sea surface temperature since 1850, and indicate that near surface temperatures have warmed by approximately 2°C since ~1920.