Jim Zachos - UC Santa Cruz

Feb. 12, 2019, 3:30 p.m. - 4:30 p.m.
3656 Geology

Presented By:
Jim Zachos,
UC Santa Cruz

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Intensification of the hydrological cycle during Early Eocene Hyperthermals: Theory versus observations

The early Eocene hyperthermals, a series of transient global warming events (∆T=+2 to +6°C), provide a unique opportunity to assess the sensitivity of the hydrologic cycle to the scale of greenhouse forcing expected over the next several centuries. A growing body of evidence from the most prominent of the hyperthermals, the Paleocene Thermal Maximum (PETM; ~56 Ma), points toward a major mode shift in the intensity and patterns of precipitation. Regionally, the shift in hydrology differs notably, with some regions becoming drier, others wetter. In many regions both sedimentologic and paleontologic evidence indicate that precipitation became much more seasonal or episodic in character. In continental fluvial and coastal sections, changes in siliciclastic depositional facies reflect on increased frequency of high-energy events (e.g., extreme flooding), possibly from monsoon-like seasonal rains, and/or from unusually intense and/or sustained extra-tropical storms. In the open ocean, geochemical data, though still relatively sparse, suggests that the sub-tropical ocean became saltier as a consequence of locally reduced precipitation and/or increased evaporation suggestive of increased meridional vapor transport from low to high latitudes. Indeed evidence, from high latitude oceans suggests reduced salinity. New data emerging for subsequent smaller hyperthermals (ie., Eocene Thermal Maximum 2) show similar patterns. Such observations are consistent with and thus support general theory on the sensitivity of large-scale vapor transport and regional cycle of precipitation to extreme greenhouse warming.