HIGH RESOLUTION MARINE, ESTUARINE, AND LACUSTRINE CLIMATE RECORDS FROM NORTHERN CALIFORNIA

In the comparison of marine, estuarine, and inland sites, multiple proxies (microfossils, alkenones, environmental magnetism, stable isotopes, and physical properties) are useful in unraveling the complex history of marine-atmospheric interactions in northern California and along the adjacent margin. Although each method by itself is limited, the combination of techniques has proven valuable in these regional climatic analyses.

The early Holocene (11,500-8,000 cal yr B.P.) is characterized by a transition from warmer and wetter to cooler and drier conditions along the coast and in inland areas, indicating declining July insolation. The early part of the middle Holocene (8,000-3,000 cal yr B.P.) was characterized by weaker, less regular El Niño events, and more sustained La Niña-like conditions resulting in lower coastal sea surface temperatures and drier conditions inland. Gradual strengthening of the California Current due to a stronger thermal gradient led to increased seasonal (spring-summer) coastal upwelling and associated fog along the coast during the latter half of this interval. The late Holocene (3,000-0 cal yr B.P.) is distinguished by increasing winter precipitation and enhanced ENSO cycles. During the last 3,000 years, multiproxy marine, estuarine, and lacustrine records all show several extended periods of lower precipitation, alternating with wetter periods.

Unraveling the complex history of regional variations and the diachroneity of specific events is frustrated by several factors. Age control at many sites is poor, with few dates or low carbon values requiring bulk samples extending over long core intervals. Sedimentation rates are often poorly constrained due either to a lack of age control or low sedimentation rates. Average marine sedimentation rates vary from 0.016-0.100 cm/yr depending on the amount of terrestrial input. Estuarine rates range from 0.06-0.16 cm/yr, and lacustrine rates vary from 0.10 cm/yr in eutrophic systems to 0.02 cm/yr in oligotrophic conditions. In some cases, environmental conditions limit site to site comparison of some chemical and biological proxies. A suite of coring techniques such as freeze coring, APC, and HPC combined with modern dating methods should provide improved age control and more accurate determination of sedimentation rates.