9:35 AM - 10:15 AM

<aside> <img src="/icons/map-pin_purple.svg" alt="/icons/map-pin_purple.svg" width="40px" /> DPB Seminar Room + Zoom (DGE Conference Room, Solarium, DGE Lobby, Library)

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<aside> <img src="/icons/megaphone_purple.svg" alt="/icons/megaphone_purple.svg" width="40px" /> Chair by: Andrea Nebhut

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<aside> <img src="/icons/music-artist_purple.svg" alt="/icons/music-artist_purple.svg" width="40px" /> Structural complexity biases vegetation greenness measures

Yelu Zeng - China Agricultural University

9:35 AM - 9:48 AM

Vegetation ‘greenness’ characterized by spectral vegetation indices (VIs) is an integrative measure of vegetation leaf abundance, biochemical properties and pigment composition. Surprisingly, satellite observations reveal that several major VIs over the US Corn Belt are higher than those over the Amazon rainforest, despite the forests having a greater leaf area. This contradicting pattern underscores the pressing need to understand the underlying drivers and their impacts to prevent misinterpretations. Here we show that macroscale shadows cast by complex forest structures result in lower greenness measures compared with those cast by structurally simple and homogeneous crops. The shadow-induced contradictory pattern of VIs is inevitable because most Earth-observing satellites do not view the Earth in the solar direction and thus view shadows due to the sun–sensor geometry. The shadow impacts have important implications for the interpretation of VIs and solar-induced chlorophyll fluorescence as measures of global vegetation changes. For instance, a land-conversion process from forests to crops over the Amazon shows notable increases in VIs despite a decrease in leaf area. Our findings highlight the importance of considering shadow impacts to accurately interpret remotely sensed VIs and solar-induced chlorophyll fluorescence for assessing global vegetation and its changes.

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<aside> <img src="/icons/music-artist_purple.svg" alt="/icons/music-artist_purple.svg" width="40px" /> Disentangling the roles of CO2 and climate in the accelerating terrestrial carbon cycle

Eren Bilir - JPL/UCLA

9:48 AM - 10:00 AM

Rising atmospheric CO₂ and associated climate change trajectories interactively regulate the land carbon sink, and disentangling their effects is essential for assessing present and future sensitivities to global change. To reduce uncertainty in our estimate of these land sink sensitivities, and to increase consistency with the Earth Observation record, we synthesized a range of satellite and in-situ data with the ecological theory and physics constraints of mechanistic modeling in a Bayesian framework (CARDAMOM). Observational constraints include land-atmosphere CO₂ and CH4 fluxes, biomass distribution and trends, soil organic carbon distribution, fire burned area and CO fluxes, photosynthesis and leaf area index, terrestrial water storage anomalies, river runoff, snow cover, and deforestation disturbance. The resulting reanalysis shows that, over 2001–2021, CO₂ fertilization is the dominant driver: CO₂-driven gains, primarily in live biomass, outweigh climate-driven losses, concentrated in dead organic carbon, by a factor of 4. It also identifies rising CO₂ and climate trends as drivers of an accelerating terrestrial carbon cycle, in which carbon is cycling faster through shorter-lived pools rather than accumulating in stable, long-lived ones.

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<aside> <img src="/icons/music-artist_purple.svg" alt="/icons/music-artist_purple.svg" width="40px" /> Reconciling carbonyl sulfide budget estimates to advance understanding of the global carbon cycle

Wu Sun - Carnegie Science

10:00 AM - 10:15 AM

Carbonyl sulfide (OCS) is an airborne tracer for terrestrial carbon and water cycling. Globally, OCS is produced from ocean and human activities and consumed by terrestrial ecosystems. However, global OCS budget estimates are highly uncertain due to the persistent gap between a large estimated land sink and a small estimated ocean source, hindering our ability to infer biospheric changes from atmospheric OCS observations. In this talk, I will present several recent advances on both ocean and land OCS processes to show a path toward reconciling OCS budget estimates. I will discuss what a balanced OCS budget means for the terrestrial carbon cycle and how we improve model representations of land and ocean OCS processes for advancing OCS as a global tracer for carbon and water cycling.

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