Evidence from "Köppen signatures" of fossil plant assemblages for effective heat transport of Gulf Stream to subarctic North Atlantic during Miocene cooling

[摘要] Shallowing of the Panama Sill and the closure of the Central American Seawayinitiated the modern Loop Current–Gulf Stream circulation pattern during theMiocene, but no direct evidence has yet been provided for effective heattransport to the northern North Atlantic during that time. Climatic signalsfrom 11 precisely dated plant-bearing sedimentary rock formations in Iceland,spanning 15–0.8 million years (Myr), resolve the impacts of the developingMiocene global thermohaline circulation on terrestrial vegetation in thesubarctic North Atlantic region. "Köppen signatures" were implementedto express climatic properties of fossil plant taxa and their potentialmodern analogues using the principal concept of the generic Köppen–Geigerclimate system, which is based on plant distribution patterns. UsingKöppen signatures and the correlation between Köppen climate zonesand major global vegetation zones, fossil assemblages were used to tracemajor vegetation shifts. This evidence was combined with evidence fromtectonics and palaeoceanography. In contrast to the global climatic trend,the vegetation record reveals no cooling between ~ 15 and 12 Myr,whereas periods of climatic deterioration between 12 and 10 Myr, 8 and 4 Myr, andin the Pleistocene are in phase with increased pulses of ice-rafted debris inthe Northern Hemisphere. The observed sequence of climate change in thenorthern North Atlantic can most likely be explained by an effective GulfStream-mediated heat transport from the middle Miocene onwards.

[学科分类] 地球化学与岩石