X-ray computed tomograms (CAT-scans) of bedding-parallel ichnofabrics in a marine sediment core from ODP Site 1017, offshore of Point Conception, CA, exhibit trends in burrow orientation which correlate with global climatic fluctuation during the past 160,000 years. This study suggests that local changes in intermediate water oxygenation are represented by synchronous burrow ellipticity trends. These ichnofabric shifts reflect the margin-wide extent of paleoceanographic changes found at ODP Site 893 in the semi-restricted Santa Barbara Basin.

CAT-scans were taken of the recovered 96% of the 25.5 m core at 5 cm increments, revealing a series of ichnofabric ‘snapshots' spaced at <300 year intervals. Digital image analysis was used to quantify ellipticity and size trends in the bedding parallel ichnofabrics. Our model proposes that as porewater oxygenation increases, mean burrow orientations shift to become increasingly vertical. Alternately, as dissolved O₂ levels decline, the habitable zone of oxygenation is compressed toward the sediment-water interface; organisms are restricted to less vertical burrow orientations on average, resulting in higher ellipticities in cross-section.

The correlation of mean burrow ellipticity at Site 1017 with the ichnofabrics and oxygen isotope records of the Santa Barbara Basin, 100 km to the east, suggests a synchronous shift between Pacific Ocean intermediate waters and global temperature events. This study correlates the bioturbation indices of the sediments in the semi-restricted Santa Barbara Basin with burrow ellipticity data in sediments exposed on the open slope, extending the ability to document large-scale oceanographic changes along the California margin. This supports the hypothesis that mean burrow ellipticity is an effective proxy for porewater oxygenation levels. The results also illustrate the viability of using x-ray computed tomography to nondestructively reveal subtle density features and to quantify ichnofabrics for paleoceanographic or paleoclimatic investigation.