Time scales and magnitudes of environmental responses to volcanic activity in the deep-time record

Volcanism has played a key role in the evolution of Earth’s ecosystem, causing changes in the surface environments of the atmosphere, oceans, and land. Volcanic activity is intimately linked to environmental perturbations such as ocean anoxia, global warming, glaciation, and toxic inputs, but the magnitudes and time scales of the impacts of volcanism on the environment are not clear. We analyzed 608 research results from 42 volcanic events in geologic history and 26 time-scale results from laboratory analyses, combined with the changes in geochemical indicators such as Hg, Zr, Hg/total organic carbon, Hg/total sulfur, Cu, Mo, Sr/Cu, Sr/Ba, U/Th, and V/Cr contents at meter-scale and centimeter-scale intervals during the Ordovician−Silurian transition (Yangtze region, South China block) and changes in the mineral contents on the micrometer scale. The results showed that the time scale required for the sedimentary environment to reach a new stable state in terms of the vertical distribution of bentonite layers was 1947.42 k.y. The time scale for the deterioration of the sedimentary environment following volcanic activity in terms of the geochemistry of the sedimentary environment was 0.328−0.984 k.y. The time scale for the deterioration of the sedimentary environment after volcanic activity in terms of the change in mineral content was 0.029−0.082 k.y. The long-term climate response time scales for volcanism were within 2000 k.y., and silicate weathering processes mainly lasted between 100 k.y. and 10,000 k.y. Most of the response time scales for ocean anoxia caused by volcanism were within 3000 k.y., and the response time scales for primary productivity lasted for a minimum of 7 yr, but were mostly in the range of 100−4000 k.y. The larger volume and area of volcanism below the scale of the Karoo-Ferrar large igneous province resulted in greater amounts of CO2 released and rates of input to the environment, in turn resulting in greater magnitudes and rates of the resulting temperature change. Volcanic events with small eruption areas/volumes could trigger ocean anoxia events of more than 500 k.y. Volcanic activity in the Late Ordovician−early Silurian Period, lasting ∼10 m.y., caused rapid ecological changes and the disappearance of numerous species, resulting in the Late Ordovician mass extinction.