Evidence for a bathyal front at 2000‐M depth in the glacial Pacific, based on a depth transect on Ontong Java Plateau

Abstract

Data on oxygen and carbon isotope compositions of the benthic foraminifer Planulina wüllerstorfi 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 δ 18 O profile during glacial time shows an increased gradient at a depth near 2000 m. The corresponding δ 13 C data suggest that a bathyal nutricline existed close to the same depth level. The δ 13 C 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 CO 2 content of glacial deep waters, which is reflected in the more negative δ 13 C 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 in the upper waters, above 2000 m, may have been more vigorous than today.