https://repository.kopri.re.kr/handle/201206/11591 2026-04-17T18:15:59Z 2026-04-17T18:15:59Z Joo, Young Ji Sim, Min Sub Madden, Megan E. Elwood Soreghan, Gerilyn S. https://repository.kopri.re.kr/handle/201206/12446 2022-03-24T07:15:33Z 2019-01-01T00:00:00Z

Title: The biogeochemical cycle of sulfur in a glacial meltwater stream in Jostedalsbreen of Songefjord, Norway Authors: Joo, Young Ji; Sim, Min Sub; Madden, Megan E. Elwood; Soreghan, Gerilyn S. Abstract: It is widely accepted that chemical weathering of silicate minerals consumes atmospheric CO2, regulating the carbon cycle over geologic time scales; however, the role of sulfuric acid produced from weathering of sulfide minerals has only recently received attention as a potential source of CO2. Some evidence suggests that physical erosion enhanced by glaciers imparts a greater impact on the chemical weathering of relatively labile minerals such as sulfides and carbonates compared to silicates, raising the hypothesis of a negative feedback between glacial weathering and pCO2. Yet, our understanding of the biogeochemical sulfur cycle in glacial drainages remains incomplete. This study investigates the fate of sulfur in a proglacial stream system fed by the Jostedal Glacier of Norway, which overlies a granitic gneiss complex. The area has a low-temperature (MAT = 4.5°C) and high-humidity (MAP = 1769 mm) climate, and the melt season generally extends from May to September. Considering that sulfur isotope compositions of meltwater sulfate and other sulfur reservoirs may reflect the sulfur budget and biogeochemical processes in the drainage, we collected stream water, atmospheric wet deposition (rain and snow), basement rocks, sediments, and plant debris to analyze their sulfur isotope compositions. Riverine sulfate is enriched in heavy sulfur isotopes relative to the bedrock in the study area, regardless of the correction for atmospheric deposition; it is consistent with previous studies on the glacier meltwater streams in Svalbard and the Himalayas. Two hypotheses have been suggested for this enrichment: (1) sulfur isotope fractionation during pyrite oxidation under anaerobic conditions, and (2) dissimilatory sulfate reduction in freshwater wetland soils. Interestingly, in the Jostedal Glacier, the most 34S-enriched sulfur reservoir is plant debris. Since plants assimilate sulfate from soil water without significant isotope effects, 34S/32S fractionation during the release of pyrite sulfur to solution (first hypothesis) cannot solely explain the sulfur isotopic offset between plant debris and riverine sulfate. Instead, plant debris isotopically heavier than both atmospheric deposition and basement rock suggests the activity of sulfate reducers in the soil. Dissimilatory sulfate reduction is seemingly more likely here, because this drainage basin is heavily vegetated and hosts abundant organic matter to drive sulfate reduction especially during the melt season, when bioessential nutrients are released from fresh rock surfaces produced by glacier abrasion. Although comparative studies in glacial catchments with minimal vegetation are essential to test this hypothesis, it is noteworthy that some sulfate produced by pyrite oxidation can be reduced back to sulfide at the expense of organic carbon oxidizing back to CO2. Perhaps the fraction of sulfate consumed by dissimilatory reduction in rivers might have changed over geologic time as well, in response to major events such as terrestrial afforestation.

2019-01-01T00:00:00Z Joo, Young Ji Sageman, Bradley Hurtgen, Matthew https://repository.kopri.re.kr/handle/201206/12449 2022-03-24T07:15:34Z 2019-01-01T00:00:00Z

Title: Data-model comparison reveals key environmental changes leading to Cenomanian-Turonian Oceanic Anoxic Event 2 Authors: Joo, Young Ji; Sageman, Bradley; Hurtgen, Matthew Abstract: The middle Cretaceous (Cenomanian Turonian) was a period characterized by major environmental changes, including elevated sea-floor spreading rates, enhanced volcanism, high atmospheric CO2 levels, warming terrestrial and marine temperatures, and the peak eustatic highstand of the Mesozoic. Two well-known perturbations in the global carbon cycle, that are recognized in various depositional settings, mark this interval the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2) and the Mid-Cenomanian Event (MCE). Although studies of OAE2 during the past two decades have arrived at consensus that the Caribbean Large Igneous Province (LIP) likely played a key role in triggering OAE2, the details of environmental developments during the Mid-Late Cenomanian leading up to this event, arguably the most significant biogeochemical perturbation of the Late Cretaceous, have only recently been the focus of investigations. This study employs a simple box model, based on previous studies of mid-Cretaceous climate, tectonism, and sea-level change, to test plausible environmental scenarios to explain the behavior of the Middle Cenomanian to Early Turonian carbon cycle. A compilation of published δ13C datasets of carbonates and organic carbon is used to constrain the timing and magnitude of key excursions in δ13C curves as tiepoints for the carbon cycle isotope-mass balance calculation. The model experiments based on our hypotheses successfully reproduce two distinctive features observed in the Mid-Late Cenomanian δ13C curves - 1) decoupling of δ13Ccarb and δ13Corg reflecting increasing carbon isotope fractionation in response to steadily rising pCO2, driven by enhanced volcanic degassing of mantle-derived CO2, which likely proceeded the presumed peak volcanism of the Caribbean LIP; and 2) a long-lived, secondary positive δ13C excursion that documents enhanced organic carbon burial in shallow shelf areas, which expanded during global sea-level rise and highstand. Our results demonstrate a plausible combination of environmental forcings that pre-conditioned the mid-Cretaceous ocean-atmosphere system for a massive perturbation, the Cenomania-Turnonian OAE2.

2019-01-01T00:00:00Z