M. Elena Pérez

Relationships between the stable isotopic signatures of living and fossil foraminifera in Monterey Bay, California

[1] Fossil foraminifera are critical to paleoceanographic reconstructions including estimates of past episodes of methane venting. These reconstructions rely on benthic foraminifera incorporating and retaining unaltered the ambient isotopic compositions of pore fluids and bottom waters. Comparisons are made here of isotopic compositions of abundant live and fossil foraminifera (Uvigerina peregrina, Epistominella pacifica, Bulimina mexicana, and Globobulimina pacifica) collected in Monterey Bay, CA from two cold seeps (Clam Flats and Extrovert Cliffs) and from sediments � 5 m outside of the Clam Flats seep. Clam Flats has steep d 13 CDIC gradients (to <� 45%), but DIC at Extrovert Cliffs is less enriched in 12 C (to approximately � 22%). Oxygen isotope values of fossil foraminifera at Clam Flats are � 1.5% enriched in 18 O over the living foraminifera, as well as those of both live and fossil foraminifera at Extrovert Cliffs, suggesting they may have lived during the last glacial maximum. Statistical comparisons (Student’s t and Kolmogorov-Smirnov tests) of d 13 C and d 18 O values indicate that live and fossil foraminifera come from different populations at both Clam Flats and Extrovert Cliffs. At Clam Flats, the difference appears to result from alteration enriching some fossil foraminifera in 12 C over live foraminifera. At Extrovert Cliffs, the fossil foraminifera are enriched in 13 C over the live foraminifera, suggesting they lived prior to the onset of venting and thus that venting began recently. The short time of venting at Extrovert Cliffs may be responsible for the less alteration there compared with Clam Flats. These results indicate that preservation of foraminifera is likely to be poor within long-lived cold seeps, but that foraminifera living in the surrounding sediment may incorporate and preserve broad basin-wide changes in isotopic compositions of the ambient water.

Skeletal Extension Rates of Cenozoic Caribbean Reef Corals

Abstract There has been significant biological and environmental change in Caribbean coral reefs during the past 30 million years, including two periods of accelerated turnover of species in the zooxanthellate coral biota that may have been correlated with changes in regional sea-surface productivity during the Early Miocene and the Early Pleistocene. Skeletal extension rates measured on x-radiographs of 11 massive genera of fossil corals collected from Late Oligocene to Pleistocene units from across the Caribbean were analyzed to determine whether average coral growth responded to these regional environmental changes. The observed patterns were evaluated by comparisons with records of Recent coral growth rates taken from published literature. These analyses suggest that there is significant variation in average growth rate among corals living in the Recent Indo-west Pacific, eastern Pacific, and Caribbean, even when broad ranges of taxa and habitats are intermingled. When applied to fossils, a similar analysis suggests that rates of growth do not change overall through time. One exception is during the Late Miocene, when rates of growth were significantly lower than from other fossil units or for Recent colonies from the Caribbean. However, the Late Miocene colonies sampled for this study lived in relatively deep, turbid habitats, so the observed reduced growth rates may have resulted from local low availability of light. Similar facies were not sampled in other stratigraphic intervals, so there is no strong evidence for reduced regional average growth rates for Caribbean corals during the past 30 million years.