Paper No. 192-6
Presentation Time: 9:30 AM
FORAMINIFERAL STABLE ISOTOPE RECORDS ACROSS THE PETM ONSET AT MILLVILLE, NJ: IMPLICATIONS FOR CARBON RELEASE RATE
The onset of the PETM was rapid (<10 kyr), precluding traditional paleoceanographic tools (magneto-biostratigraphy, orbital cycles) to assign rates to the initial release of carbon. The ODP Leg 174AX Millville, NJ PETM section (70 m paleodepth) provides a greatly expanded section relative to open ocean sites, with 12 m of the “core” versus 1.2 m at Site 690. Bulk carbonate ð13C values from Millville decrease by 3.5‰ across 25 cm interval, offering a potential record for the onset interval. Two groups used Millville to constrain the timing for the initial pulse of carbon. Wright and Schaller (2013) focused on the differential responses in ð13C and %CaCO3 concluding that the release was fast (<1 year). Zeebe et al. (2016) instead assumed equilibrium conditions, concluding a 4 kyr duration for the release. We generated planktonic and benthic foraminiferal stable isotope records across the onset of the PETM CIE at Millville. Most of the ð13C change recorded by foraminifera occurred over the 25 cm interval where bulk sediment ð13C decreased. However, foraminiferal ð18O values continue to decrease for another 1.5 m above the initial ð13C decrease suggesting that Zeebe et al.’s assumption of equilibrium conditions is incorrect. The foraminiferal stable isotope pattern is similar to the modeled response following a large, instantaneous release of light carbon to the atmosphere, that produces a rapid (decadal) scale warming in the surface air masses followed by continued warming but at a slower rate. Fitting the Millville isotope records to the models constrains of the initial sedimentation rate of on the order of 1 cm/yr for the Marlboro Formation deposited at Millville. The mid-shelf location of Millville a made it responsive to atmospheric changes unlike open ocean sites where thermal inertia dampens the larger atmosphere changes. Differential responses in ð13C, ð18O, and %CaCO3 at the onset of the PETM are consistent with an instantaneous initial release of carbon with centennial-scale warming that continued well after the initial carbon pulse similar to that predicted by climate models.