THE LATE PLEISTOCENE HISTORY OF SURFACE-WATER DELTA-C-13 IN THE SULU SEA - POSSIBLE RELATIONSHIP TO PACIFIC DEEP-WATER DELTA-C-13 CHANGES

A reconstruction of late Pleistocene surface water carbon isotopic (deltaC-13) 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 (deltaO-18) of Globigerinoides ruber at site 769 shows a strong correlation with the SPECMAP stacked deltaO-18 record, attesting to the continuity of sediment archive at the site. SurfaCe deltaC-13 displays consistent glacial-interglacial variability which averages approximately 0.9 parts per thousand and has varied from 0.75 to 1.1 parts per thousand over the last 800 kyr. Comparison to surface water deltaC-13 records in the South China Sea and western tropical Pacific suggests that the glacial-interglacial surface deltaC-13 variability is regional in scale. Planktonic deltaC-13 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 deltaC-13 record is coherent at periods of 100 and 41 kyr with deepwater deltaC-13 records from the Pacific. The highest correlation occurs with the deep eastern Pacific, where benthic deltaC-13 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 deltaC-13 in the Sulu Sea that may explain the coherent timing with Pacific deepwater deltaC-13 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 deltaC-13 CoMposition of certain Pacific surface water locations. Future reconstructions of late Pleistocene surface water deltaC-13 variability in the western Pacific and Indonesian seas will be required to further evaluate the source of the glacial-interglacial surface water deltaC-13 change.