We determined changes in equatorial Pacific P burial and barite concentrations across the P/E boundary in sediments from ODP Leg 199 Site 1221 (153.40–154.80 mbsf at 2 cm resolution). Reactive phosphorus (the sum of oxide-associated, authigenic, and organic P; sequentially extracted from bulk sediment) was used to distinguish the signal of P involved in biogeochemical cycling from detrital P, a measure that can be used for determining organic C delivery and burial in the sediment even when organic C is oxidized postdepositionally. On a CaCO3-free basis, reactive P concentrations are high but relatively constant at ~1 wt% and show little change across the section, with the exception of lower values from 154.2 to 154.0 mbsf. Barite concentrations for the sediments range from 0.05 to 5.6 wt% calculated on a CaCO3-free basis. Barite shows a distinct peak at 154.08 mbsf. Barite Ba/reactive P ratios in the sediments are low (average = 0.48 from 154.8 to 154.20 mbsf) before and immediately after the BEE and similar to or higher than modern values (average = 1.1 from 154.04 to 153.40 mbsf) after the BEE (Table T4; Fig. F4), even though both barite and reactive P concentrations are higher than modern core top values. Observed organic C to reactive P ratios (0.26 ± 0.34) (Table T4) are lower than the Redfield Ratio (117:1) (Anderson and Sarmiento, 1994) potentially suggesting organic C loss after burial.
Despite the lack of sedimentation rates, the use of CaCO3-free based calculations and elemental ratios (although not ideal) allow us to make preliminary conclusions about oxygenation, nutrient cycling and burial, and export productivity at this site across the PETM. The presence of Mn oxide nodules and the size, morphology, and sulfur isotopes of barite imply that these sediments were oxygenated or at least not sulfate reducing during the PETM. Relatively constant reactive P, organic C, and biogenic silica concentrations indicate little variation in organic C burial across the interval, whereas a peak in barite concentration indicates fluctuations in export productivity. Fluctuations in the barite/reactive P ratios along the interval may indicate changes in the efficiency of organic C export from the photic zone vs. nutrient and organic C burial in the sediments. Organic C must have been oxidized sometime after deposition to explain the low C to P and barite ratios. After the BEE, higher barite/reactive P ratios may indicate higher export productivity coupled with more efficient organic C and reactive P regeneration in the water column. Efficient organic matter recycling, despite high export productivity, indicates only short-term (timescale of deepwater mixing) drawdown of CO2 occurred as indicated by the low organic C burial in the sediments. Differences in export productivity and organic C burial and postdepositional alteration of sedimentary records may help explain discrepancies in productivity proxies from the same sites during the PETM and may be indicative of various water column and postdepositional biogeochemical processes.