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1. Matrix Approach to Land Carbon Cycle Modeling

   https://doi.org/10.1029/2022MS003008  

   Luo, Yiqi; Huang, Yuanyuan; Sierra, Carlos A.; Xia, Jianyang; Ahlström, Anders; Chen, Yizhao; Hararuk, Oleksandra; Hou, Enqing; Jiang, Lifen; Liao, Cuijuan; et al (July 2022, Journal of Advances in Modeling Earth Systems)
2. The Ocean Carbon Cycle

   https://doi.org/10.1146/annurev-environ-120920-111307  

   DeVries, Tim (October 2022, Annual Review of Environment and Resources)

   The ocean holds vast quantities of carbon that it continually exchanges with the atmosphere through the air-sea interface. Because of its enormous size and relatively rapid exchange of carbon with the atmosphere, the ocean controls atmospheric CO 2 concentration and thereby Earth's climate on timescales of tens to thousands of years. This review examines the basic functions of the ocean's carbon cycle, demonstrating that the ocean carbon inventory is determined primarily by the mass of the ocean, by the chemical speciation of CO 2 in seawater, and by the action of the solubility and biological pumps that draw carbon into the ocean's deeper layers, where it can be sequestered for decades to millennia. The ocean also plays a critical role in moderating the impacts of climate change by absorbing an amount of carbon equivalent to about 25% of anthropogenic CO 2 emissions over the past several decades. However, this also leads to ocean acidification and reduces the chemical buffering capacity of the ocean and its future ability to take up CO 2 . This review closes with a look at the uncertain future of the ocean carbon cycle and the scientific challenges that this uncertainty brings. 

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3. Modeling the Effects of Increased Hurricane Frequency on the Tropical Forest Carbon Cycle

   https://doi.org/10.1007/s10021-024-00937-6  

   Gutiérrez_del_Arroyo, Omar; Hartman, Melannie_D; Silver, Whendee_L (October 2024, Ecosystems)

   Abstract Models project that climate change is increasing the frequency of severe storm events such as hurricanes. Hurricanes are an important driver of ecosystem structure and function in tropical coastal and island regions and thus impact tropical forest carbon (C) cycling. We used the DayCent model to explore the effects of increased hurricane frequency on humid tropical forest C stocks and fluxes at decadal and centennial timescales. The model was parameterized with empirical data from the Luquillo Experimental Forest (LEF), Puerto Rico. The DayCent model replicated the well-documented cyclical pattern of forest biomass fluctuations in hurricane-impacted forests such as the LEF. At the historical hurricane frequency (60 years), the dynamic steady state mean forest biomass was 80.9 ± 0.8 Mg C/ha during the 500-year study period. Increasing hurricane frequency to 30 and 10 years did not significantly affect net primary productivity but resulted in a significant decrease in mean forest biomass to 61.1 ± 0.6 and 33.2 ± 0.2 Mg C/ha, respectively (p < 0.001). Hurricane events at all intervals had a positive effect on soil C stocks, although the magnitude and rate of change of soil C varied with hurricane frequency. However, the gain in soil C stocks was insufficient to offset the larger losses from aboveground biomass C over the time period. Heterotrophic respiration increased with hurricane frequency by 1.6 to 4.8%. Overall, we found that an increasing frequency of tropical hurricanes led to a decrease in net ecosystem production by − 0.2 ± 0.08 Mg C/ha/y to − 0.4 ± 0.04 Mg C/ha/y for 30–10-year hurricane intervals, respectively, significantly increasing the C source strength of this forest. These results demonstrate how changes in hurricane frequency can have major implications for the tropical forest C cycle and limit the potential for this ecosystem to serve as a net C sink. 

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4. Closing the geologic carbon cycle

   https://doi.org/10.1073/pnas.2409333121  

   Derry, Louis A (October 2024, Proceedings of the National Academy of Sciences)

   Estimates of sedimentary organic carbon burial fluxes based on inventory and isotope mass balance methods have been divergent. A new calculation of the isotope mass balance using a revised assessment of the inputs to the ocean-atmosphere system resolves the apparent discrepancy. Inputs include weathering of carbonate and old kerogen, geogenic methane oxidation, and volcanic and metamorphic degassing. Volcanic and metamorphic degassing comprise ≈23% of the total C input. Inputs from isotopically lightOCpetroandCH_4-geodrive the mean δ¹³C of the input to =−8.0 ± 1.9‰, notably lower than the commonly assumed volcanic degassing value. The isotope mass balance model yields a modern burial flux =15.9 ± 6.6 Tmol y⁻¹. The impact of the mid-Miocene Climatic Optimum isotope anomaly is an integrated excess deposition ≈ 4.3 × 10⁶Tmol between 18 and 11 Ma, which is both longer and larger than estimates for the total degassing by the Columbia River Basalt eruptions, implying a complex carbon system response to large eruptive events. Monte Carlo evaluation finds that late Cenozoic net growth of the carbonate reservoir is very likely while net growth of theC_orgreservoir is less certain but more likely than not. At present, subduction does not appear to keep up with net sedimentation and the overall masses of sedimentary carbonate and organic carbon are likely increasing. Growth in the sedimentaryC_orgreservoir implies oxidation of the surface environment and likely increases in atmospheric pO₂. 

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5. The land–ocean Arctic carbon cycle

   https://doi.org/10.1038/s43017-024-00627-w  

   Vonk, Jorien E; Fritz, Michael; Speetjens, Niek J; Babin, Marcel; Bartsch, Annett; Basso, Luana S; Bröder, Lisa; Göckede, Mathias; Gustafsson, Örjan; Hugelius, Gustaf; et al (February 2025, Nature Reviews Earth & Environment)