Qinghua Yang

Estuaries play a crucial role in the transport and cycling of particulate organic carbon (POC) from terrestrial ecosystems to the ocean. However, an understanding of the processes controlling POC dynamics under extreme weather conditions is still lacking. In this study, we established a high‐resolution, coupled atmosphere–ocean–biogeochemistry modeling system for the Pearl River Estuary to investigate the mechanisms controlling POC dynamics during a strong successive typhoon event (Hato and Pakhar, 2017). Our simulation results show that before the typhoons, the POC distribution was characterized by two distinct maxima, sustained by terrestrial inputs and marine production, respectively. However, during the typhoons, strong hydrodynamic conditions and reduced light availability suppressed local primary production, leading to an increase in the dominance of terrestrial POC. In Lingding Bay (LB) and the Western Four Outlets (WFO), POC was mainly supported by regenerated production, whereas in the shallow coastal region (SCR) outside the estuarine, new and regenerated production played an equal role. Regarding POC sinks, zooplankton excretion served as the dominant sink in the outer LB and SCR regions, while sediment denitrification played an equally significant role in the inner LB and WFO. Budget analysis revealed that although the estuary acted as a weak carbon source on an annual basis, successive typhoons can transform it into a weak carbon sink. Our simulation provides novel insights into the impact of extreme weather on POC within estuaries, benefiting the maintenance of ecological health and the development of effective water quality management strategies under global warming.

Snow depth on Antarctic sea ice is a critical climate variable affecting energy and mass balance, yet its observation and modeling remain challenging. We present a systematic intercomparison of snow depth from six ocean reanalysis products, two satellite retrievals, and ship‐based and airborne observational constraints. Results indicate that reanalysis and satellite products show consistent large‐scale climatological snow depth patterns, with the highest depths in the Weddell Sea. However, substantial differences remain in magnitude, seasonal phasing, spatial variability, and trends. The multi‐model mean agrees with satellite‐derived products in some integrated metrics, but tends to smooth regional features and may reflect compensation among reanalysis members. The sensitivity of simulated snow depth to atmospheric forcing and simplified snow processes highlights current limitations in representing wind redistribution and snow‐to‐ice conversion. Improved observations and model physics are needed to better constrain Antarctic sea‐ice snow depth.

With the recent popularity of the tide‐resolving and submesoscale‐admitting numerical simulations, there is an increasing interest in separating vortical and wavy motions in the ocean. The recently‐proposed dynamics‐based decomposition exploits the relative magnitude of the relative vorticity and horizontal divergence in Fourier space and proves efficient. In this decomposition, physical variables over non‐water regions (e.g., coasts, islands, seamounts) are filled with zeros following standard practice. This zero‐filling would adversely affect the accuracy of vortical‐wavy separation, however. To mitigate this effect, this study adopts a streamline‐following perspective. With physical variables projected along the streamline and dynamics‐based decomposition adjusted accordingly, we get a boundary‐aware separation of vortical and wavy motions. The potential usefulness of this approach is demonstrated through its application to data from a high‐resolution numerical simulation.

Sea spray generated by wave breaking under high wind speeds strongly influences air-sea turbulent heat exchange. Nowhere is this process more critical than the Southern Ocean where the most extreme wave climate on Earth is located. However, current existing gridded air-sea heat flux datasets lack representation of sea spray-mediated component, which lead to a major problem in assessing and understanding the role of sea spray in the Southern Ocean. Here, we present a new gridded dataset of spray-mediated latent and sensible heat fluxes over the Southern Ocean that incorporates a full sea spray microphysical model, which considers spray generation that depends on regional wind and wave states. Our data allows a quantitative assessment of the spray-mediated contribution to the total air-sea heat flux exchange. Climatologically, spray-mediated heat fluxes range from 0.04 to 39.6 W m-2, with large fluxes in the circumpolar region (50° S–60° S), especially in the Indian sector during austral winter. Validation of an extreme cyclone shows that, within the high wind sector of the cyclone, spray-mediated heat fluxes double the regional fluxes compared to conventional bulk algorithm estimates. This dataset serves a critical foundation for examining the Southern Ocean’s role in the global energy budget.

The ocean is a crucial sink for anthropogenic CO ₂ and experiences various biogeochemical extremes, yet it is not clear whether and to what extent such extreme events occur in air–sea CO ₂ fluxes. Here, we established a framework to define oceanic carbon uptake extremes (CUXs) and release extremes (CRXs) using daily air–sea CO ₂ flux from both an observational‐based product and a state‐of‐the‐art Earth system model. Globally, cumulative CUX and CRX intensity over 1982–2022 were −0.14 and 0.14 Pg C yr ⁻¹ , respectively, each accounting for ∼10% of the total oceanic CO ₂ uptake. The number of annual days and the absolute mean intensity of CUXs (CRXs) increase at rates of 1.22 d dec ⁻¹ (2.23 d dec ⁻¹ ) and 0.08 mol C m ² yr ⁻¹ dec ⁻¹ for both events. Under the high‐warming future scenario, these increasing trends are projected to accelerate, leading to a nearly five‐fold rise in the global cumulative intensity of CUXs and CRXs compared to the past four decades. After the 2050s, CRXs increase more rapidly than CUXs, especially in the Southern Ocean and North Atlantic, due to a reduced oceanic buffering capacity. Thermally driven seawater pCO ₂ dominates over half of the projected global CUX and CRX days, primarily in temperate oceans. The model also indicates shifts from nonthermal to thermal dominance in the tropical Pacific and Atlantic, the Indian Ocean, and the sporadic high‐latitude Southern Ocean, while the North Atlantic shows an opposite pattern. Our study shows that more frequent CRXs would further exacerbate the projected weakening in ocean carbon sinks.

Antarctic sea ice has undergone unprecedented changes in recent years, marked by a stepwise shift from long-term expansion to rapid decline since 2016. Yet the underlying processes remain poorly understood due to the complex interplay of dynamic and thermodynamic drivers. Using an ascendant data mining framework, we objectively classify sea ice into distinct process-based regimes during the growth season in the NEMO-SI³ model. Six robust regimes with unique combinations of dynamic and thermodynamic drivers are identified. We reveal that a coastal regime, characterized by strong dynamic divergence and compensating thermodynamic ice growth, has experienced significant area loss since 1979, accelerating after 2016, potentially reflecting weakened new ice formation. Meanwhile, sea ice extent anomalies closely correlate with both the coastal and a pack ice regime, highlighting their dominant role in overall sea ice variability. By capturing physically consistent sea ice regimes, our work offers a new process-based perspective for understanding Antarctic sea ice variability and its unprecedented recent changes.

Antarctic sea ice has undergone unprecedented changes in recent years, marked by a stepwise shift from long-term expansion to rapid decline since 2016. Yet the underlying processes remain poorly understood due to the complex interplay of dynamic and thermodynamic drivers. Using an ascendant data mining framework, we objectively classify sea ice into distinct process-based regimes during the growth season in the NEMO-SI³ model. Six robust regimes with unique combinations of dynamic and thermodynamic drivers are identified. We reveal that a coastal regime, characterized by strong dynamic divergence and compensating thermodynamic ice growth, has experienced significant area loss since 1979, accelerating after 2016, potentially reflecting weakened new ice formation. Meanwhile, sea ice extent anomalies closely correlate with both the coastal and a pack ice regime, highlighting their dominant role in overall sea ice variability. By capturing physically consistent sea ice regimes, our work offers a new process-based perspective for understanding Antarctic sea ice variability and its unprecedented recent changes.

Snow plays a critical role in the mass and energy balance of sea ice through its insulating properties and high albedo. Based on observations from the Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC) campaign, we assess the influence of snow redistribution on snow thickness simulations using the Icepack column model. Our results show that, without snow redistribution, snow thickness is overestimated in winter and spring. The bulk redistribution scheme slightly reduces snow accumulation, while the blowing snow scheme (snwITDrdg) further increases agreement with observations but still shows biases during snowfall events. Sensitivity experiments indicate that setting the ratio of snow mass on ridges to that on level ice to 4 in the bulk scheme yields the best agreement with snow observations (MAE = 6.2 mm). In the snwITDrdg scheme, the snow erosion coefficient is treated as an effective tuning parameter. When observed sea ice concentration is prescribed, setting the snow erosion coefficient to 2.4×10^-5 produces simulated accumulated snow loss to leads consistent with observations and improves the simulated snow thickness (MAE = 6.4 mm). This study provides new insights into snow thickness simulation and the parameterization of snow redistribution, offering valuable guidance for improving Arctic snow thickness modeling.

Antarctic sea ice projected to have large reduction associated with increasing greenhouse gases, with potential impacts extending beyond the Southern Hemisphere. However, its influence on East Asian climate is not fully understood. Using Earth system model experiments and multi‐model simulations, we show that Antarctic sea‐ice loss by the end of the 21st century leads to a significant increase in summer precipitation over central and southern China. This precipitation response is further amplified with enhanced sea‐ice loss under quadrupled CO ₂ forcing. Additional atmospheric model experiments indicate that atmospheric pathways alone cannot transmit the Antarctic signal to East Asia. Instead, Antarctic sea‐ice loss shapes a hemispherically asymmetric pattern of tropical sea surface warming through anomalous northward cross‐equatorial heat transport and southward of the intertropical convergence zone driven by interhemispheric energy imbalance, with the warming further amplified by positive low‐cloud shortwave feedbacks. The resulting warming in the tropical Atlantic and Indian Oceans induces anomalous northeasterly winds over eastern China and southwesterly flow over southern China through Rossby wave trains and modulation of the Hadley circulation. These circulation changes enhance upward motion and precipitation over central and southern China. Antarctic sea‐ice loss accounts for roughly 40% of the projected summer precipitation increase in this region under the high‐emission scenario, highlighting its potential role in shaping future East Asian climate.