Did high Neo-Tethys subduction rates contribute to early Cenozoic warming?

Abstract

Abstract. The 58–51 Ma interval was characterized by a long-term increase of global temperatures (+4 to +6 °C) up to the Early Eocene Climate Optimum (EECO, 52.9–50.7 Ma), the warmest interval of the Cenozoic. It was recently suggested that sustained high atmospheric pCO2, controlling warm early Cenozoic climate, may have been released during Neo-Tethys closure through the subduction of large amounts of pelagic carbonates and their recycling as CO2 at arc volcanoes ("carbonate subduction factory"). To analyze the impact of Neo-Tethys closure on early Cenozoic warming, we have modeled the volume of subducted sediments and the amount of CO2 emitted at active arc volcanoes along the northern Tethys margin. The impact of calculated CO2 fluxes on global temperature during the early Cenozoic have then been tested using a climate carbon cycle model (GEOCLIM). We first show that CO2 production may have reached up to 1.55 × 1018 mol Ma−1 specifically during the EECO, ~ 4 to 37 % higher that the modern global volcanic CO2 output, owing to a dramatic India–Asia plate convergence increase. In addition to the background CO2 degassing, the subduction of thick Greater Indian continental margin carbonate sediments at ~ 55–50 Ma may also have led to additional CO2 production of 3.35 × 1018 mol Ma−1 during the EECO, making a total of 85 % of the global volcanic CO2 outgassed. However, climate modelling demonstrates that timing of maximum CO2 release only partially fit with the EECO, and that corresponding maximum pCO2 values (750 ppm) and surface warming (+2 °C) do not reach values inferred from geochemical proxies, a result consistent with conclusions arise from modelling based on other published CO2 fluxes. These results demonstrate that CO2 derived from decarbonation of Neo-Tethyan lithosphere may have possibly contributed to, but certainly cannot account alone for early Cenozoic warming, including the EECO. Other commonly cited sources of excess CO2 such as enhanced igneous province volcanism also appear to be up to one order of magnitude below fluxes required by the model to fit with proxy data of pCO2 and temperature at that time.

Proxy evidence for state-dependence of climate sensitivity in the Eocene greenhouse

“…Light blue bar indicates the timing of temperature and CO 2 decline after the EECO. Green light bar indicates the timing of potential circulation changes in the early Eocene, as demonstrated in the δ 13 C record of f. Overlying solid black and yellow bars represent the timing of volcanism [21][22][23][24][25][26] .…”

Magmatic Forcing of Cenozoic Climate?

“…Similarly, Kerrick and Caldeira (1994) suggested that carbon degassing due to metamorphism of Indian margin rocks along the Himalayan belt enhanced paleoatmospheric carbon levels, although revised estimates point to a minor contribution to early Eocene warming (Kerrick & Caldeira, 1998). A reduction of carbon dioxide emissions is inferred between~50 and 40 Ma, synchronous with the observed phase of climate cooling, when Tibetan arc volcanism was waning after collision between India and Eurasia (Hoareau et al, 2015;Jagoutz et al, 2016; Figure 1).…”

“…The short‐lived magmatic flare‐up is in striking coincidence with the Early‐Eocene Climate Optimum, suggesting a cause‐effect relationship between the magmatic and climatic event, a possibility that was only marginally investigated thus far. Subduction of the carbonate‐rich Indian passive margin succession in the middle Paleocene may have enhanced carbon recycling at the Transhimalayan volcanic arc (e.g., Kent & Muttoni, ; van Hinsbergen et al, ; Hoareau et al, ). Hoareau et al () modeled the volume of subducted materials and the amount of CO 2 emitted along the northern Tethyan margin and the effects of estimated CO 2 fluxes on global climate.…”

“…Subduction of the carbonate‐rich Indian passive margin succession in the middle Paleocene may have enhanced carbon recycling at the Transhimalayan volcanic arc (e.g., Kent & Muttoni, ; van Hinsbergen et al, ; Hoareau et al, ). Hoareau et al () modeled the volume of subducted materials and the amount of CO 2 emitted along the northern Tethyan margin and the effects of estimated CO 2 fluxes on global climate. Enhanced CO 2 degassing due to subduction of thicker Indian continental margin sediments after ~60 Ma would raise surface temperatures to some extent, consistently with the observed early Eocene climate warming.…”

A sink- or a source-driven carbon cycle at the geological timescale? Relative importance of palaeogeography versus solid Earth degassing rate in the Phanerozoic climatic evolution

“…1992; Rowley, 2002; Hoareau et al . 2015), compilation of zircon age (McKenzie et al . 2016), and reconstruction of the subduction zone length as a function of age (Van der Meer et al .…”