Carbon and oxygen isotopic composition and age dating of sediments from ODP Leg 170 sites and Hole 205-1253A

In this data report we present results from stable isotope measurements (d13C and d18O) on bulk sediment at several sites located on a transect along a subduction margin offshore Costa Rica (Ocean Drilling Program Sites 1039, 1040, and 1253). Comparison of stable isotope compositions (d13C and d18O) of the pelagic carbonates Subunit U3C between the reference sites (Site 1039 and 1253) and the underthrust section (Site 1040) reveals similar d13C values and minor differences in d18O values within four specific intervals. Isotope stratigraphy was then used to further constrain the shipboard age models based on bio- and magnetostratigraphy. The resulting age models are in agreement with those derived from biostratigraphy and confirm that the sedimentation rate of the lower Subunit 3C is roughly constant on the order of 50 m/m.y. This is in contrast with the postulated very high sedimentation rates at ~12.7 Ma and lower sedimentation rates (~18 m/m.y.) in the lower part of the section between 16 and 13 Ma, as suggested by shipboard magnetostratigraphic datums

Oxygen and carbon isotopes for foraminifers at DSDP Leg 73 Holes

We carried out oxygen and carbon isotope studies on monospecific foraminifer samples from DSDP Sites 522, 523, and 524 of Leg 73 in the central South Atlantic Ocean. The oxygen isotope ratios show a warming of 2 to 3 °C in bottom water and 5°C in surface water during the Paleocene and early Eocene. The carbon isotope values indicate strong upwelling during the early Eocene. The 1% increase in the d18O values of benthic and planktonic foraminifers at Site 523 in the later middle Eocene we ascribe to changes in the pattern of the evaporation and precipitation. The changes may be due to the worldwide Lutetian transgression. The oxygen ratios for the benthic and planktonic foraminifers indicate a cooling at the Eocene/Oligocene transition. The maximum temperature drop (5°C for benthic and 3°C for planktonic foraminifers) is recorded slightly beyond the Eocene/Oligocene boundary and took place over an interval of about 100,000 yr. The pattern of currents in the Southern Hemisphere was mainly structured by a precursor of the subtropical convergence during the Paleocene to late Eocene. The cooling at the Eocene/Oligocene transition led to drastic changes in the circulation pattern, and a precursor of the Antarctic convergence evolved