Plate tectonic controls on atmospheric CO₂levels since the Triassic

Abstract

Climate trends on timescales of 10s to 100s of millions of years are controlled by changes in solar luminosity, continent distribution, and atmosphere composition. Plate tectonics affect geography, but also atmosphere composition through volcanic degassing of CO 2 at subduction zones and midocean ridges. So far, such degassing estimates were based on reconstructions of ocean floor production for the last 150 My and indirectly, through sea level inversion before 150 My. Here we quantitatively estimate CO 2 degassing by reconstructing lithosphere subduction evolution, using recent advances in combining global plate reconstructions and present-day structure of the mantle. First, we estimate that since the Triassic (250-200 My) until the present, the total paleosubduction-zone length reached up to ∼200% of the present-day value. Comparing our subduction-zone lengths with previously reconstructed ocean-crust production rates over the past 140 My suggests average global subduction rates have been constant, ∼6 cm/y: Higher ocean-crust production is associated with longer total subduction length. We compute a strontium isotope record based on subduction-zone length, which agrees well with geological records supporting the validity of our approach: The total subduction-zone length is proportional to the summed arc and ridge volcanic CO 2 production and thereby to global volcanic degassing at plate boundaries. We therefore use our degassing curve as input for the GEOCARBSULF model to estimate atmospheric CO 2 levels since the Triassic. Our calculated CO 2 levels for the mid Mesozoic differ from previous modeling results and are more consistent with available proxy data.paleoclimate | carbon cycle | geodynamic V olcanism forms the most efficient mechanism to transfer carbon (C) from the mantle to the ocean-atmosphere system, the exogenic reservoir. At midocean ridges, mantle upwelling occurs between two diverging plates. At subduction zones, sinking oceanic plates lead to arc volcanism (1). A third type of volcanism, driven by mantle plumes, leads occasionally to large igneous provinces (LIPs) that typically last a few My (2, 3). Longterm (>>5 My) changes in volcanic output thus dominantly relate to the long-term plate tectonic processes. Constraints on volcanism-related degassing of CO 2 at subduction zones and midocean ridges hence derive from studies on lithosphere production/consumption (3-6). The quality of these constraints determines the mechanistic underpinning of climatic changes on timescales of 10 7 to 10 8 y. This is because on such timescales, volcanism is the major source of CO 2 to the atmosphere and thereby drives climate and the critical feedbacks in the carbon cycle, such as weathering. To date, estimates of CO 2 degassing through plate tectonic processes for the last 150 My are based on reconstructions of ocean-floor production (7), and for older periods indirect inferences were made through sea level inversion (8). An increasing body of work reveals major uncertainties in eustatic sea level reconstructi...

Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)

“…5 • 22 22 ). Palaeogeographical reconstruction based on comprehensive palaeomagnetic data, performed by Osete et al (2010), locates the Rodiles section studied at a latitude of approximately 32 • N for the Hettangian-Sinemurian interval, which is in good agreement with the calculations of Van Hinsbergen et al (2015) and at a latitude of almost 40 • N (the current latitude of Madrid) for the Toarcian-Aalenian interval. The section was deposited in an open marine external platform environment with sporadic intervals of oxygen deficiency.…”

“…The causes of this lowering of atmospheric pCO 2 are unknown but they might be favoured by elevated silicate weathering rates, nutrient influx, high primary productivity, and organic matter burial (Suan et al, 2010;Silva and Duarte, 2015). In addition, estimates of the mantle degassing based on the fit between the length of the subduction zones through time and the atmospheric CO 2 levels (Van Der Meer et al, 2014), taking into account the standard GEOCARSULF degassing parameters (Berner, 2006a, b), suggests that plate tectonics has exerted a fundamental role in the control on the climatic system of the Earth.…”

Arc volcanism, carbonate platform evolution and palaeo-atmospheric CO<sub>2</sub>: Components and interactions in the deep carbon cycle

“…the planetary cycling of carbon over million-year timescales) attributes fluctuations in the atmospheric carbon dioxide (CO2) to the realm of tectonic forces, where arc-volcanic emissions (Van Der Meer et al, 2014;Kerrick, 2001) and metamorphic decarbonation 10 (Lee et al, 2013) are major CO2 sources, and the processes of silicate weathering (Sundquist, 1991;Kent and Muttoni, 2008) and marine organic carbon burial (Berner and Caldeira, 1997;Ridgwell and Zeebe, 2005) are major sinks removing CO2 from the atmosphere. Subduction plays a critical role in this cycle.…”

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

“…Climatic modeling suggests that this cooling mainly results from decreasing seafloor spreading and subduction rates, as well as increasing CO 2 removal through silicate weathering (Park and Royer, 2011;Godderis et al, 2014;van der Meer et al, 2014). During the Cenozoic, CO 2 consumption was mainly governed by the erosion of the Tethyan orogenic belt, and by continental drift, responsible for the arrival of highly weatherable basaltic provinces in the equatorial belt (Raymo and Ruddiman, 1992;Kent and Muttoni, 2013;Lefebvre et al, 2013).…”

“…However, global cooling was interrupted by a long-term increase of global temperatures (+4 to +6 • C) and pCO 2 (∼ 450 to ∼ 1000 ppm) from 58 to 50.7 Ma, crowned by the Early Eocene Climate Optimum (EECO, 52.9-50.7 Ma), the warmest interval of the Cenozoic (Zachos et al, 2001;Beerling and Royer, 2011). Because conventional carbon cycle models compute important weathering rates at that time, they fail to reproduce this rise in temperature and atmospheric CO 2 without the addition of excess CO 2 compared to background CO 2 volcanic degassing rates (4-10 × 10 18 molCO 2 Ma −1 at present; Berner, 2004) (Lefebvre et al, 2013;Van der Meer et al, 2014). Carbonates also indicate that from ∼ 58.0 to 52.5 Ma this warming was characterized by a 2 per mil negative shift in marine and terrestrial δ 13 C, referred to as the Late Paleocene-Early Eocene (LPEE) by Komar et al (2013).…”