HF-ND ISOTOPES OF EQUATORIAL PACIFIC OXYHYDROXIDE LEACHATES ACROSS THE EOT

The presence of continental ice on Antarctica has been documented in recent decades using near and far field proxies of continental ice production. Moreover, these proxies denote a prolonged episode in which short glaciations flickered in and out of existence until the formation of the continental scale ice sheet during the Eocene Oligocene Transition (EOT; ~34Ma). This period is also marked by pCO₂ declining below a critical threshold for the existence of an Antarctic continental ice sheet. Preliminary oxyhydroxide hafnium (Hf) and neodymium (Nd) leachate data from IODP Site U1411 on the Newfoundland Ridge indicate increased weathering intensities coinciding with the EOT, denoted by less radiogenic hafnium isotopic composition.

Hf-Nd isotopic composition of sediment on the Newfoundland ridge indicates a shift from incongruous chemical weathering to a more congruous mechanical weathering regime (i.e. glaciers). Data from U1411 could suggest a glaciation of the Northern hemisphere (e.g. Greenland). This would indicate a bipolar glaciation (northern and southern hemisphere) during this time interval. However, the pCO­2­ threshold for the development of ice on Greenland is not obtained until the late Oligocene. As such, it could be suggested that the observed congruous Hf-Nd signal originates in the southern ocean and has propagated north from the Antarctic.

Here we are using equatorial Pacific IODP Site U1333 to determine if the glacial weathering signal could be transmitted through deep waters from Antarctica. Site U1333 is positioned far from either pole thus, a shift towards congruous weathering would not be expected. Preliminary data shows Hf isotopic composition far more radiogenic than would be expected for Antarctic sourced water. Moreover, the data suggest a deep water Hf composition more radiogenic than previous observations.