WAS THE EOCENE ARCTIC MONSOONAL?

The hydrological cycle was significant for maintaining high latitude Eocene warmth. The early Eocene featured 3 hyperthermals; PETM/ETM1, ETM2 and EECO. Warm climates extended into the Arctic with substantive paleobotanical data for high Arctic precipitation (MAP > 150cm/yr) – an Arctic rainforest, contradicting climate models that show low Arctic precipitation. Analysis of spore-pollen and other proxies from the Lomonosov Ridge showed significant warming and changes in hydrology consistent with high precipitation during the PETM and later hyperthermals. Arctic early Eocene wood stable isotope chemistry however, showed a summer peak in precipitation, with modern analogs best sought on the summer-wet east coasts (e.g., China, Japan, South Korea) not the winter-wet west coasts of present-day northern temperate continents (e.g., Pacific northwest, North America). Highly seasonal ‘monsoon-type’ summer-wet precipitation regimes (i.e., summer/winter precip. > 3.0) seem to characterize Eocene hyperthermals in several regions, including the Arctic and Antarctic, based on both climate model and paleoclimate proxy data. Presented here are new analyses from work with 3 sets of collaborators based on macrofloras from Ellesmere Island and spore-pollen from marine sediment cores from the Arctic basin and North Sea. The Ellesmere floras are analyzed using leaf physiognomy of 3 early Eocene (likely ETM1 &/or ETM2) leaf macrofloras from the Margaret Formation (Split Lake, Stenkul Fiord and Strathcona Fiord). Spore-pollen is analyzed using bioclimatic analysis, a NLR approach, from sediments from the ACEX core as well as from the North Sea. High summer precipitation is estimated in the Arctic during the early Eocene, including ETM1, corroborating Eocene wood chemistry data. Monsoonal conditions however, are not indicated by this present analysis. High summer precipitation (i.e., light-season = wet-season) in Eocene Arctic hyperthermals would have contributed to regional warmth.