Supporting data set for article 'Submarine Groundwater Discharge Is an Unignorable Component in the Estuarine Dissolved Carbon Cycle'

Submarine groundwater discharge (SGD) is frequently neglected in the development of carbon budgets for estuarine system. However, SGD can carry substantial quantities of dissolved carbon from terrestrial environments and coastal sediments into the estuary. Here, we conducted a comprehensive study of SGD and dissolved carbon budgets in the Pearl River Estuary (PRE), the largest estuary in Southern China and highly populated estuarine region. Results shown that broadly-defined SGD contributes 89.4–96.2% to the dissolved inorganic carbon (DIC) pool of the PRE, which is 2–4 times higher than that carried by rivers. Moreover, SGD contributes comparably to the dissolved organic carbon (DOC) pool at 20–70%, similar to rivers. SGD transports DIC to the PRE at levels exceeding total alkalinity (TAlk) by 2.7–7 times, and the SGD-derived DOC entering the PRE can cause a daily decrease in estuary seawater pH by 0.02–0.18, indicating its potential to acidify PRE seawater. The <i>p</i>CO2 in groundwater samples is 10–36 times higher than that in estuary seawater, serving as a source of CO₂. Furthermore, the decomposition of DOC carried by SGD can lead to a daily increase in bottom seawater CO₂ concentrations by 0.001–0.015 mol L^-1, potentially affecting coral populations in the PRE. The DOC carried by SGD can result in a daily decline in bottom seawater oxygen levels by 0.002–0.025 mol L^-1, potentially fostering the development of hypoxia zones. Our findings indicate that SGD-carried dissolved carbon entering the ocean may lead to the co-occurrence of hypoxia zones, seawater acidification, and coral bleaching. This study highlights that SGD should be considered when constructing land-ocean continuum carbon cycling models and conducting estuarine ecological studies.