Lien, Wan‐YinWan‐YinLienChen, RickRickChenTsai, Jui‐FenJui‐FenTsaiChen, Jhen‐NienJhen‐NienChenLin, Li‐HungLi‐HungLinWang, Pei‐LingPei‐LingWang2025-12-192025-12-192025-04-29https://www.scopus.com/pages/publications/105004196243https://scholars.lib.ntu.edu.tw/handle/123456789/734801The oxidation of petrogenic organic carbon contributes a large CO2 flux to the atmosphere, regulating the geological carbon cycle. While few in situ fluxes have been measured in near-surface sedimentary rocks, deep fracture-controlled metamorphic terranes remain unexplored. Here, we present a novel design for continuous in situ measurements of subsurface CO2 flux feasible for metamorphic rocks. The accumulative CO2 measurements were performed by either the passive mode or active recirculation on an 80-m deep borehole in eastern Taiwan. Measurements in the passive mode yielded stepwise CO2 releases in the fractured zone and steady accumulation in the pulverized zone at rates (18.9–132 mgC m−2 day−1) resembling those for other active orogens. By contrast, the active recirculation produced an overestimation of CO2 flux. The high flux combined with variation patterns highlights heterogeneous metamorphic terranes as an important CO2 source and the necessities of extended monitoring using the passive mode.TaiwanCarbon cyclesContinuous measurementsMeasurements ofNear surfacesNovel designOrganicsPassive modePetrogenicRecirculationsRemineralizationboreholecarbon dioxidecarbon fluxmetamorphic rockorganic carbonpetrogenesisremineralization[SDGs]SDG6[SDGs]SDG13[SDGs]SDG14journal article10.1002/vzj2.70020