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.