EVIDENCE FOR A BATHYAL FRONT AT 2000-M DEPTH IN THE GLACIAL PACIFIC, BASED ON A DEPTH TRANSECT ON ONTONG JAVA']JAVA PLATEAU

Data on oxygen and carbon isotope composition of the benthic foraminifer Planulina wullerstorfi from 18 cores (17 box cores and one piston core) from Ontong Java Plateau provide proxy depth profiles for temperature, water mass, and nutrient content for the late Holocene, the last transition, and the last glacial. The delta O-18 profile during glacial time shows an increased gradient at a depth near 2000 m. The corresponding delta C-13 data suggest that a bathyal nutricline existed close to the same depth level. The delta C-13 values provide limits on the global change in carbon content of the glacial ocean, which may be estimated as distinctly less than 1 atmospheric carbon mass (1 ACM = 700 GtC). The greater CO2 content of glacial deep waters, which is reflected in the more negative delta C-13 values, may be at least in part due to a more sluggish renewal of (abyssal) deep waters. If so, the water of the deep Pacific was up to 400 years older than now. In turn, ventilation of the upper waters, above 2000 m, may have been more vigorous than today.