INTRODUCTION

One of the goals of Leg 165 was to sample deep-sea sediments to examine the nature of climate variability and changes in ocean circulation under a variety of boundary conditions present during the Cenozoic time. The late Oligocene-Miocene is a key interval in the global climatic evolution of the Cenozoic. The transition from relative global warmth of the late Oligocene-early Miocene to the Neogene "ice-house" world took place with a series of major changes in climate, polar ice volume, and ocean circulation. The middle Miocene ¹⁸O increase was a major step in this climate transition, reflecting a combination of Antarctic ice growth and deep-water cooling linked to circulation changes (Shackleton and Kennett, 1975; Woodruff et al., 1981; Miller et al., 1991; Woodruff and Savin, 1991; Wright et al., 1992). Paleoceanographic changes were accompanied by major variations in mean ocean ¹³C, reflecting redistribution of carbon between reservoirs and changes in global carbon cycling (Vincent and Berger, 1985; Miller and Fairbanks, 1985; Kennett, 1986). Possible factors contributing to this climate transition include tectonic events that altered atmospheric and oceanic circulation, such as the opening and closing of major oceanic gateways (Kennett, 1982), or forcing factors that contributed to cooling via reduced greenhouse effect, such as the uplift of major orogenies that increased weathering (Raymo and Ruddiman, 1992; Raymo, 1994), and/or organic carbon burial rates (Vincent and Berger, 1985).

Stable isotope records spanning from the latest Oligocene through the middle Miocene were generated for Sites 999 and 1000, respectively (Fig. 1).This study has two major objectives. (1) Because stable isotope records from the Caribbean region are sparse for this time interval, it was considered useful to generate a record from these two sites that can be compared with the chemostratigraphy already established from well-dated sections in other locations in the world. (2) To analyze over a time span of ~17 m.y. the detailed character of the carbon- and oxygen-isotope records and the relationships between these two climate proxies at this tropical location.