The ocean absorbs most of the excess heat induced by anthropogenic greenhouse gas emissions. Among the different processes, a key role has been attributed to the Atlantic Meridional Overturning Circulation (AMOC), both for heat uptake and redistribution among basins, yet a comprehensive view remains elusive. In this study, we investigate how a weakening of the AMOC would influence ocean heat storage in a warming climate by comparing two idealized experiments with two different AMOC evolutions from the global climate model EC-Earth3, after abrupt carbon dioxide quadrupling. We find that AMOC weakening influences both vertical and inter-basin heat redistribution. For a stronger AMOC decline, more heat is stored in the Indo-Pacific Ocean and in the intermediate ocean layers above 700 m, while less heat accumulates in the deeper ocean layers, especially in the Atlantic. Globally, we find a 3% increase in cumulated ocean heat uptake at the end of the simulations.
Nitrous oxide (N2O) is a potent greenhouse gas and major driver of stratospheric ozone depletion. Isotopic data constrain bottom-up models, yet global natural-abundance patterns remain poorly resolved. We compiled a global database of in situ soil-emitted N2O isotopes from chamber- or probe-based studies to examine the spatiotemporal variability and environmental controls. Croplands showed the greatest variability, with mean δ15Nbulk, δ18O, and δ15NSP values of −15.0‰, 35.3‰, and 13.7‰; natural soils were slightly 15N-enriched, consistent with less anthropogenic influence. Using the Time-resolved Fractionation and Mixing Evaluation (TimeFRAME) model, we estimated bacterial denitrification as the major N2O source process (45%–63%) and found a mean N2O reduction potential of 43%. Global distribution of isotope signatures reflected the edaphic drivers including positive δ15NSP–pH and negative δ15Nbulk–moisture relationship. Overall, this global inventory provides empirically constrained isotopic end-members for improved source–sink attribution, new insights into terrestrial N2O cycling, and a benchmark for model evaluation.
In India, over 200 million people live within 100 km of the coastline, and many reside in low-lying areas exposed to increasing flood risks associated with sea-level rise. However, the role of vertical land motion (VLM)—particularly land subsidence—in shaping this coastal exposure remains poorly quantified. Here we present the first assessment of VLM across India's coastal zone, using 8 years of Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) time series data (2016–2024). This comprehensive data set reveals widespread subsidence with several notable hotspots: Ahmedabad, Chennai, Amaravathi, Kochi, Kakinada, and Kolkata. The five major deltas along the east coast display extensive subsidence up to 20 mm/yr. Over 8.5 million residents live in coastal areas experiencing subsidence greater than 5 mm/yr. Our findings suggest that coastal subsidence in India is more extensive than previously recognized and poses a significant challenge for long-term land-use planning in coastal zones.
Coastal hypoxia is profoundly affected by sediment depletion of oxygen and recycling of nutrients—processes sustained by long-term accumulation of sediment organic matter. While sediment-water interactions are widely recognized, quantitative understanding of sediment legacy effects remains limited. To address this gap, we developed a two-layer sediment model integrated with a physical-biogeochemical framework for the Pearl River Estuary to elucidate how legacy organic matter perpetuates hypoxia via benthic-pelagic coupling. Results show that sediment oxygen consumption accounts for 44% of total oxygen depletion in low-oxygen zones, increasing to 81% in near-bottom waters. This oxygen demand is significantly supported by legacy organic matter, without which would reduce primary production by 68% and the hypoxic area by 53%. Furthermore, we demonstrate that sediment legacy effects amplify hypoxia sensitivity to nutrient loading and may lead to hysteresis and regime shifts if unaddressed. Therefore, effective hypoxia mitigation requires management strategies tailored to system-specific sediment-water coupling dynamics.
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