Equatorial convergence of India and early Cenozoic climate trends

Abstract

India's northward flight and collision with Asia was a major driver of global tectonics in the Cenozoic and, we argue, of atmospheric CO 2 concentration (pCO2) and thus global climate. Subduction of Tethyan oceanic crust with a carpet of carbonate-rich pelagic sediments deposited during transit beneath the high-productivity equatorial belt resulted in a component flux of CO 2 delivery to the atmosphere capable to maintain high pCO 2 levels and warm climate conditions until the decarbonation factory shut down with the collision of Greater India with Asia at the Early Eocene climatic optimum at Ϸ50 Ma. At about this time, the India continent and the highly weatherable Deccan Traps drifted into the equatorial humid belt where uptake of CO 2 by efficient silicate weathering further perturbed the delicate equilibrium between CO 2 input to and removal from the atmosphere toward progressively lower pCO 2 levels, thus marking the onset of a cooling trend over the Middle and Late Eocene that some suggest triggered the rapid expansion of Antarctic ice sheets at around the Eocene-Oligocene boundary.CO2 ͉ Deccan ͉ Tethys ͉ Himalaya ͉ Eocene M odern-day glacial climate, characterized by polar ice at sea level, is the long-term cooling derivative of a Cretaceousearly Cenozoic world dominated by warm conditions and the general absence of ice sheets (1, 2). The zenith of global warmth in the Cenozoic (0-65 Ma) was reached at Ϸ50 Ma during the Early Eocene climatic optimum (EECO) as the culmination of a Late Paleocene-Early Eocene (Ϸ60-50 Ma) warming trend in oceanic bottom waters (3) (Fig. 1A). The EECO was characterized by the widespread occurrence of cherts (4) (Fig. 1B) and reflected in warm climate conditions at even extreme high latitudes (5, 6). A persistent cooling trend ensued over the Middle and Late Eocene that eventually plummeted into a glacial climate mode with the inception of major Antarctic ice sheets at Oi-1 near the Eocene-Oligocene boundary at Ϸ34 Ma (7). Changes in ocean circulation and heat transport related to the opening of Southern Ocean gateways (8) occurred well after the start of the cooling trend at Ϸ50 Ma and do not seem to adequately account for inception of Antarctic glaciation according to recent climate models (e.g., refs. 9 and 10). Instead, reduction in greenhouse gas concentrations is the more likely fundamental cause of Antarctic freezing and global cooling (10). This is supported by the occurrence of high (albeit highly scattered) pCO 2 estimated values of Ͼ1,000 ppm at around the EECO (e.g., 11, 12; see also ref. 13) and generally low (Ͻ500 ppm) pCO 2 estimated values after Oi-1 that followed a decline that more or less parallels the long-term temperature record (14, 15) (Fig. 1 A). However, what triggered the global cooling from the EECO to Oi-1 (and thus the cause of the long-term decrease in pCO 2 ) is unclear (16).The BLAG model (17, 18) postulates that long-term changes in pCO 2 and resulting climate were driven primarily by variations in mantle outgassing tied to global seafloor prod...

Equatorial heat accumulation as a long-term trigger of permanent Antarctic ice sheets during the Cenozoic

“…It is well established that the decrease in global temperatures that occurred during the Eocene and more broadly in the Cenozoic arose, in part, from declining pCO 2 concentrations (28,38). However, in terms of rate, our Late Eocene pCO 2 record does not depart from this long-term overarching trend (Fig.…”

Continental erosion and the Cenozoic rise of marine diatoms

“…The physical removal of soils continuously refreshes mineral surfaces and increases the rate of chemical weathering. Ultimately, continental weathering fluxes depend on runoff, lithology (29), topographic relief (18,31), and geographic location with respect to large-scale persistent climate belts (32,33) that are a function of Hadley circulation. To the extent that this relationship between physical erosion and chemical weathering extends over geological time, the lithium isotope record suggests substantial increase in H 4 SiO 4 flux to the oceans across the E/O transition and through the Miocene (Fig.…”

Climate modelling and deep-time climate change

“…Plate tectonics can aff ect both source and sink: increased seafl oor spreading rates or the subduction of carbonate-rich sediments will lead to increased outgassing, while the breakup of a supercontinent, continental drift from a temperate to a tropical zone and mountain uplift will all increase weathering rates and lead to reduced CO 2 levels. As a specifi c example, Kent and Muttoni ( 2008 ) suggest that high CO 2 during the early Cenozoic was due to the closing of Tethys (see Rodríguez-Sánchez and Arroyo, Chapter 13 ), a relatively shallow tropical ocean with a deep carpet of carbonate sediments, whose subduction led to a period of increased outgassing. Th is period ended with the collision of India and Asia , which also brought the highly weatherable Deccan Traps into the equatorial humid belt, explaining the subsequent decline in CO 2 through the Eocene and Oligocene .…”