COMPARISONS OF THE ECOLOGY AND STABLE ISOTOPIC COMPOSITIONS OF LIVING(STAINED) BENTHIC FORAMINIFERA FROM THE SULU AND SOUTH CHINA SEAS

Significant differences are observed between living (Rose Bengal stain ed) deep-sea benthic foraminifera found in 14 box cores (510-4515m) fr om the thermospheric (>10 degrees C) environments of the Sulu Sea and the psychrospheric (<10 degrees C) conditions in the South China Sea. Gavelinopsis Bolivinopsis, Astrononion, Osangularia and Ceratobulimina are common taxa in the South China Sea, but are rare to absent in the Sulu Sea; Siphonina and Valvulineria are dominant genera at certain d epths in the Sulu Sea, but are rare to absent in the South China Sea. Faunal differences appear to result from large differences of the bott om-water temperatures (differences from about 6 to 8 degrees C) betwee n these basins. Faunal abundance patterns within each basin are sugges ted to be related to the organic carbon contents in the sediments, sin ce temperatures, salinities and dissolved oxygen levels of the bottom- waters are relatively uniform The delta(18)O values show a >2 parts pe r thousand range and are similar to those presented by previous worker s, but have no consistent relationship with microhabitat preferences. Vertical distribution patterns and carbon isotope compositions of spec ies, however, reflect microhabitat preferences and are consistent with previous observations from other regions. Epifaunal species (0-1 cm i nterval) such as Cibicidoides pachyderma, Cibicidoides wuellerstorfi, Hoeglundina elegans and Anomalinoides colligera have higher delta(13)C values than taxa which have the ability to live deeper within the sed iments. Infaunal taxa that live in the upper 2-3 cm, including Uvigeri na peregrina, Uvigerina proboscidea, and Bulimina mexicana, have lower delta(13)C values than epifaunal species, and the deep infaunal speci es, Chilostomella oolina, has the lowest delta(13)C. Cibicidoides brad yi and Oridorsalis umbonatus are found between 0 and similar to 4 cm a nd have lower carbon isotope values (by > 1.4 parts per thousand in so me cores) than epifaunal Cibicidoides species. Exceptions to this patt ern include the aragonitic species, Gavelinopsis lobatulus, (0-4 cm) w hich produces significantly lower delta(13)C values than deep infaunal taxa, and the shallow infaunal species, Ceratobulimina pacifica (also aragonitic) and Bolivinopsis cubensis (deep infaunal), which yield hi gher carbon isotopic values than epifaunal taxa. These exceptions are found primarily in only one core, and additional samples are needed to confirm the relationship between their distribution patterns and isot opic compositions. Each of the species examined has a relatively consi stent delta(13)C value throughout its distribution within the sediment s that may result from heterogeneity of microhabitats within the inter vals sampled. Intrageneric differences in delta(13)C of Cibicidoides, and possibly Uvigerina and Bulimina, are evident. The isotopic differe nces between C. bradyi and many other Cibicidoides species are related to differences in microhabitat preferences between species. The delta (13)C results confirm the influence of microhabitat preferences on the carbon isotopic composition of deep-sea benthic foraminifera and reaf firm the importance of assessing the microhabitat preferences of speci es used for isotopic analyses. Copyright (C) 1996 Elsevier Science Ltd