Temporal variations of chemical and isotopic compositions in the river draining the Changbaishan volcanic area: The role of hydrological changes and volcanic activities

Abstract

Volcanic activities are known to release a substantial amount of deep carbon to the Earth's surface, thereby influencing the global carbon cycle on geological timescales.It is crucial to clarify the contribution of deep carbon and its changes under hydrological variations in rivers draining volcanic areas. This study reported the temporal variations of chemical compositions and isotopic compositions (δ 13 C and Δ 14 C) of dissolved inorganic carbon (DIC) from the Erdaobai River, which drains the Changbaishan volcanic area. The results showed that hydrothermal fluids had a considerable impact on the chemical and carbon isotopic compositions in this study area. The chemical mass balance model indicated that hydrothermal fluids composed 4.6 ± 0.7% of the water budget for the Erdaobai River. Additionally, the isotopic mixing model of Δ 14 C DIC showed that hydrothermal DIC accounted for 83.6 ± 1.9% and 40.8 ± 3.7% of the DIC budget for the upstream and downstream, respectively, and the proportion of hydrothermal contribution also varied in a narrow range in response to hydrological changes. However, the DIC and dissolved organic carbon fluxes showed significant seasonal variations, verifying the controlling role of hydrological processes. This study highlighted the impact of hydrological processes and deep carbon release on the carbon budget in the volcanic catchment, which is of great significance for understanding atmospheric CO 2 balance and climate change. K E Y W O R D S carbon isotopes, Changbaishan volcanic area, deep carbon, dissolved inorganic carbon, hydrological variations 1 | INTRODUCTION Climate change is controlled by the balance between carbon release from volcanic degassing and CO 2 consumption by silicate weathering on geological time scales (Berner & Caldeira, 1997; Penman et al., 2020). Silicate weathering consumes atmospheric CO 2 and stores it in the ocean as carbonate deposits (Frings & Buss, 2019), constituting a principal sink in the long-term (50-100 Ma) carbon cycle (Liu et al., 2011; Maher & Chamberlain, 2014). Volcanic degassing is considered the main way for transferring deep carbon to the Earth's surface (Aiuppa et al., 2019), and therefore, represents an essential regulator of global climate (Dasgupta, 2013;Maclennan et al., 2002).The discharge of hydrothermal fluids altered solute fluxes and carbon cycle in volcanic catchments (Chiodini et al., 2004;