Changes in Eastern Pacific ocean ventilation at intermediate depth over the last 150kyrBP

摘要

The circulation patterns of the deep glacial Pacific Ocean are still debated. Difficulties arise due to the scarcity of reliable paleoceanographic records that can document the past movements and properties of Pacific Ocean water masses. Here, we jointly use δ~(13)C and δ~(18)O measured on the epibenthic foraminifer Cibicidoides wuellerstorfi, from the MD02-2529 sediment core collected at 1619m water depth in the eastern equatorial Pacific, to monitor changes in water mass circulation spanning the past 150kyrBP. After the extraction of short-term (centennial to millennial-scale) δ~(13)C and δ~(18)O changes, which were ~1.0 and 0.5%, respectively, we observed that these rapid δ~(13)C and δ~(18)O shifts were closely interrelated during the last 150kyrBP. A comparison of MD02-2529 with other benthic δ~(13)C records localized to the north and south of the core location revealed that MD02-2529 was alternately bathed by a northern nutrient-rich and a southern nutrient-poor water mass. The comparison provided a diagnostic for the latitudinal movements of a sharp water mass front that was particularly evident during marine isotope stages 4 and 3 on the millennial timescale. By considering that δ~(13)C is an indicator of the northern vs. southern origin of the water that bathed the MD02-2529 coring site in the past, we found that a North Pacific water mass, that occasionally spreads to the eastern Pacific Ocean as deep as 1600m and as far south as 8°N, was responsible for shifts toward the positive δ~(18)O we observed in the past. We then used the δ~(13)C/δ~(18)O relationship to reconstruct latitudinal temperature and/or salinity gradients of the water mass that were linked to changes in the northern and/or the southern water mass end-members. Evolution of the δ~(13)C/δ~(18)O relationship spanning the past 150kyrBP has shed light on how hydrological processes occurring at northern and southern high latitudes are transmitted to the ocean's interior through water mass advection.