THE FIDELITY OF BENTHIC MARINE OXYGEN ISOTOPE PALEOCLIMATE PROXY RECORDS

Oxygen isotopic compositions of benthic foraminifera have long been utilized as proxies of paleoclimate variation. The fidelity of paleoclimate records can be defined as the degree to which changes in the Earth’s climate are faithfully recorded by a proxy. A high fidelity record accurately captures both large-scale and long-term changes in climate as well as the statistical characteristics of variation within those longer trends. It will be shown that relationships between sample density and spacing relative to variation in the deep ocean’s isotopic composition play a critical role in determining the fidelity of preserved records.

ODP Site 1090 preserves a high-resolution stable isotopic record that extends from the late Oligocene through the early Miocene. The site was sampled in 2002 and resampled in 2004 by Billups and others. Analysis of inter-sample variation as well as the identification of local extrema illustrates that resampling has not fully defined potential variation within the climate signal.

Reliability of traditional sampling techniques to accurately characterize down core isotopic variation is tested by an analysis of those benthic marine records that contain multiple sampling. Additionally, the impact of sampling density, inter-sample variability, and sample averaging is explored through an analysis of nine benthic marine δ¹⁸O records (as well as the LR04 stack they define) over the time interval 4.0 Ma to 3.0 Ma.

Together these analyses highlight complexities and limitations in the interpretation of benthic marine oxygen isotopes as high fidelity proxies of ancient climate.