Carbon dioxide emission to Earth’s surface by deep-sea volcanism

Abstract

Large amounts of CO 2 are transferred from Earth's interior to the surface by volcanism. On a geological time scale, the rate of CO 2 emission has controlled the evolution of Earth's atmosphere and climate, as well as the dynamic processes that take place in the mantle and core. The total rate of natural CO 2 emission from Earth has been estimated on the basis of CO 2 fl ux from arc, mid-ocean-ridge, and hotspot volcanism. However, previous estimates have overlooked the CO 2 emitted from a recently discovered type of volcanism-petit-spot volcanism-that occurs on the deep-sea fl oor. Here, we measure the CO 2 and H 2 O contents of glassy basalts produced by petit-spot volcanism and estimate the initial contents to be >5 wt% and 1.0-1.1 wt%, respectively. Based on these values and magma fl ux of petitspot volcanism, we show that the rate of CO 2 emission from petitspot volcanoes (2.7-5.4 × 10 11 g CO 2 yr -1 ) is a few percent of the CO 2 emissions from arc and mid-ocean-ridge volcanism, and up to ~14% of that from hotspot volcanism. Thus, the contribution to the carbon cycle on Earth of the large amounts of CO 2 that have been emitted from the deep-sea fl oor by petit-spot volcanism has not previously been recognized.

Petit-spot geology reveals melts in upper-most asthenosphere dragged by lithosphere

“…Previous experimental studies (e.g., Takahashi and Kushiro, 1983;Hirose and Kushiro, 1993;Kushiro, 1994;Baker and Stolper, 1994;Robinson et al, 1998;Hirschmann, 2000) have shown that major element composition, in particular for primary magma, is controlled mainly by melting conditions such as temperature and pressure. However, this is only applicable to magma suites derived from a single homogeneous source.…”

“…Thus, Machida et al (2009) proposed that melting of small-scale recycled plate material produces petit-spot magma. Moreover, Okumura and Hirano (2013) suggest that petit-spot volcanism plays an important role in Earth's CO 2 emission because of the enrichment of CO 2 in the primary magma. To achieve the further understanding of petit-spot geology, six sampling cruises were conducted over three petit-spot volcanic fields (Fig.…”

Electrical conductivity of old oceanic mantle in the northwestern Pacific I: 1-D profiles suggesting differences in thermal structure not predictable from a plate cooling model

“…Preliminary results of 3-D inversion analysis of the MT data from Area D revealed a conductive anomaly in the lithospheric mantle beneath the petit-spot field, which suggested melt accumulation and migration to the surface (Baba et al 2013b). Because carbon dioxide-rich melt is expected from the highly vesicular petit-spot basalt samples (Okumura and Hirano 2013), the mantle beneath the petit-spot field may be relatively enriched in carbon, which may be one of the causes of the difference in the electrical structure of Area D from that of Area C. For Area A and Area B, the plume associated with the formation of the Shatsky Rise may have affected the initial state of the temperature and/or composition of the mantle, although the two areas are located outside of the topographic anomaly of the Shatsky Rise itself. Ohira et al (2017) found that along the spreading direction southeast of Area B, there are areas where the Moho is diffuse, weak, or absent, and are thus characterized by the presence of a gradual crust-mantle transition in seismic velocity.…”

The behavior and concentration of CO2 in the suboceanic mantle: Inferences from undegassed ocean ridge and ocean island basalts

“…Here we present new CO2 and trace element data from additional ultradepleted midocean ridge basalts (UD-MORBs) to determine how variable the CO2/trace element ratios are regionally and locally. In addition, we also consider highly vesicular rocks from the North Arch region of the Hawaiian swell (Dixon et al, 1997;Yang et al, 2003), and petit spot volcanoes near Japan (Okumura and Hirano, 2013;Hirano et al, 2006) in order to determine if there are consistent relationships between incompatible elements and CO2 for enriched rocks. We discuss the question of bubble accumulation and loss in such rocks, and in MORBs in general.…”