NOAA/WDS Paleoclimatology - Tropical Pacific benthic isotope record for 0-5 Ma

Benthic foraminifer and δ13C data from Site 849, on the west flank of the East Pacific Rise (0° 11 'N, 110°3 l'W; 3851 m), give relatively continuous records of deep Pacific Ocean stable isotope variations between 0 and 5 Ma. The mean sample spacing is 4 k.y. Most analyses are from Cibicides wuellerstorfi> but isotopic offsets relative to Uvigerina peregrina appear roughly constant. Because of its location west of the East Pacific Rise, Site 849 yields a suitable record of mean Pacific Ocean δ'3C, which approximates a global oceanic signal. The ~l00-k.y.-period climate cycle, which is prevalent in δ18θ does not dominate the long-term δ13C record. For δ13C, variations in the -400- and 41-k.y. periods are more important. Phase lags of δ13C relative to ice volume in the 41- and 23-k.y. bands are consistent with δ13C as a measure of organic biomass. A model-calculated exponential response time of 1-2 k.y. is appropriate for carbon stored in soils and shallow sediments responding to glacial-interglacial climate change. Oceanic δ13C leads ice volume slightly in the 100-k.y. band, and this suggests another process such as changes in continental weathering to modulate mean river δ13C at long periods. The δ13C record from Site 849 diverges from that of Site 677 in the Panama Basin mostly because of decay of 13C-depleted organic carbon in the relatively isolated Panama Basin. North Atlantic to Pacific δ13C differences calculated using published data from Sites 607 and 849 reveal variations in Pliocene deep water within the range of those of the late Quaternary. Maximum δ13C contrast between these sites, which presumably reflects maximum influx of high-δ13C northern source water into the deep North Atlantic Ocean, occurred between 1.3 and 2.1 Ma, well after the initiation of Northern Hemisphere glaciation. Export of high-δ13C North Atlantic Deep Water from the Atlantic to the circumpolar Antarctic, as recorded by published δ13C data from Subantarctic Site 704, appears unrelated to the North Atlantic-Pacific δ13C contrast. To account for this observation, we suggest that deep-water formation in the North Atlantic reflects northern source characteristics, whereas export of this water into the circumpolar Antarctic reflects Southern Hemisphere wind forcing. Neither process appears directly linked to ice-volume variations.