ALBERT

Description: A reconstruction of late Pleistocene surface water carbon isotopic (delta13C) variability is presented from Ocean Drilling Program (ODP) site 769 in the Sulu Sea in the western tropical Pacific. The Sulu Sea is a shallowly silled back arc basin with a maximum sill depth of 420 m. Site 769 was drilled on a bathymetric high in 3643 m of water and has average late Pleistocene sedimentation rates of 8.5 cm/kyr. The oxygen isotope record (delta18O) of Globigerinoides ruber at site 769 shows a strong correlation with the SPECMAP stacked delta18O record, attesting to the continuity of sediment archive at the site. Surface delta13C displays consistent glacial-interglacial variability which averages ~0.9 per mil and has varied from 0.75 to 1.1 per mil over the last 800 kyr. Comparison to surface water delta13C records in the South China Sea and western tropical Pacific suggests that the glacial-interglacial surface delta13C variability is regional in scale. Planktonic delta13C data from ODP site 677 in the eastern Pacific is also coherent with the site 769. Additionally, we have found that the site 769 surface delta13C record is coherent at periods of 100 and 41 kyr with deepwater delta13C records from the Pacific. The highest correlation occurs with the deep eastern Pacific, where benthic delta13C data from cores RC13-110 and ODP site 677 closely match the Sulu Sea surface water record. We evaluate several possible controls of surface water delta13C in the Sulu Sea that may explain the coherent timing with Pacific deepwater delta13C records. These include variations in terrestrial organic matter flux to the basin, the upwelling of subsurface water and productivity changes, and the influx of western Pacific intermediate water to the Sulu Sea. Our preferred explanation involves a region of upper intermediate water upwelling in the far western Pacific which has been shown to outgas CO2 from subsurface waters into surface waters. Upwelling also occurs in the area of Panama Basin site 677. These equatorial upwelling zones could potentially provide a route by which Pacific intermediate water can modulate the delta13C composition of certain Pacific surface water locations. Future reconstructions of late Pleistocene surface water delta13C variability in the western Pacific and Indonesian seas will be required to further evaluate the source of the glacial-interglacial surface water delta13C change.