TheVertical flow in the tropical Pacific Ocean plays a crucial role in vertical exchange of oceanic heat and mass, biogeochemical cycling, and climate change. However, due to observational limitations, the spatiotemporal characteristics of vertical velocity in this region remain poorly understood. Here we present vertical velocity estimates from continuous velocity measurements from Acoustic Doppler Current Profilers (ADCPs), which were mounted on a triangular array of four subsurface moorings in the North Equatorial Countercurrent (NECC) region centered near 4.7°N, 142°E and sustained for 40 months from December 2017 to March 2021. The vertical velocity was calculated from the continuity equation using the horizontal velocity components measured by the ADCPs. Upwelling was observed in the mean vertical velocity at and above the NECC core, peaking at 1.2×10−5 m s−1 at 70 m, in contrast to the basin-averaged near-surface downwelling typical for this latitude. Below 110 m, the flow transitioned to downwelling, with a peak velocity of −2.5×10−5 m s−1 observed near 240 m. Significant fluctuations in vertical velocity were observed, with alternating upwelling and downwelling episodes driven primarily by zonal divergence and convergence associated with NECC acceleration and deceleration. The dominant seasonal variability of the vertical velocity was linked to fluctuations in the depth of the 20 °C isotherm driven by remotely forced Rossby waves, whereas interannual variability was governed by local wind stress curl through Ekman pumping. Vertical velocity substantially modulated subsurface water properties, driving fluctuations in potential temperature and density—manifested as isotherm shoaling during upwelling and deepening during downwelling. In contrast, near-surface temperature was considerably less affected. Intense vertical motion was spatially confined to the 3°–6°N latitude band, with no concurrent signals at adjacent latitudes, suggesting a mechanism distinct from equatorial upwelling systems.
Iron minerals are ubiquitous in Earth’s surface waters and soils, serving as effective adsorbents for phosphorus (P) removal. However, the underlying mechanism linking P removal efficiency to the crystallinity and Lewis acidity of iron minerals remains unclear under varying hydrogeochemical conditions. Therefore, this study reveals the intrinsic relationship between crystallinity and Lewis acidity for ferrihydrite110, goethite110, and hematite 001, as well as their impact on P adsorption. Mechanisms insights were obtained using X-ray absorption spectroscopy (XAS), in situ Raman spectroscopy, and density functional theory (DFT) calculations. Results demonstrate that reduced crystallinity correlates with enhanced Lewis acidity. This crystallinity-dependent Lewis acidity originates from Fe-O orbital coupling: high crystallinity strengthens Fe-O orbital coupling, whereas low crystallinity weakens this process, resulting in more unsaturated Fe sites with available empty orbitals. Consequently, differences in Lewis acidity directly govern P adsorption efficiency, with the adsorption capacities following the order: ferrihydrite>goethite>hematite. These findings suggest that the effect of iron mineral crystallinity on Lewis acidity should not be overlooked, which has important implications for P cycling in soil and water ecosystems.
The onset timing of tropical Asian summer monsoon (TASM) was observed to have experienced two pronounced interdecadal shifts during 1979–2024. Specifically, remarkable advancement of the monsoon onset occurred around the late 1990s, while significant delay appeared at the beginning of the 2010s. In this study, the two interdecadal shifts are proposed to be influenced by different warming patterns of sea surface temperature (SST) in the Indo-Pacific Ocean. For the advanced onset of the TASM after 1998, an intensified La Niña-like SST warming pattern in the Pacific played a crucial role. The corresponding positive SST anomalies in the western North Pacific enhanced atmospheric convective heating, which consequently induced an anomalous lower-level cyclonic circulation in the TASM region through a westward Rossby wave response. Meanwhile, the La Niña-like SST pattern can strengthen the Walker circulation, further intensifying convection over the western North Pacific and the aforesaid Rossby wave response, and then advancing the TASM onset. However, since the beginning of the 2010s, the Pacific La Niña-like SST warming pattern has weakened, accompanied by a rapid warming in the tropical Indian Ocean (TIO). The TIO warming exerted a growing negative influence on the TASM onset by strengthening local convection that forced an eastward atmospheric Kelvin wave. The associated tropical lower-level easterly anomalies postponed the monsoon onset. The above diagnostic results are well verified by numerical simulations. Our findings underscore the significant contribution of different Indo-Pacific SST warming patterns to the two interdecadal shifts of the TASM onset timing in recent decades.
Deep coalbed methane (CBM) development represents an important technological pathway for advancing China’s unconventional natural gas reserves and production while supporting the coordinated achievement of the “dual carbon” goals. Constrained by complex deep geological conditions, deep CBM wells commonly exhibit rapid production decline, substantial interwell productivity variability, and a high proportion of low-efficiency wells. Focusing on the multiscale gas-water two-phase flow mechanisms during deep CBM development, this paper systematically reviews recent domestic and international research progress in terms of reservoir conditions and depth effects, gas-water occurrence and transformation mechanisms, permeability evolution and multiphase multiscale flow mechanisms, and experimental characterization and numerical simulation methods. The synthesis indicates that deep coal seams are generally subjected to a “three-high” environment characterized by high temperature, high reservoir pressure, and high in situ stress. Depth-dependent effects continuously constrain multiscale gas-water flow processes by modifying coal-rock mechanical properties, pore-fracture structures, reservoir connectivity, and engineering stimulation responses. With increasing burial depth, CBM occurrence progressively evolves from an adsorption-dominated state to the coexistence of adsorbed and free gas, while the gas-water occurrence pattern and its dynamic evolution affect fluid mobility and continuous gas supply capacity. The dynamic conversion between adsorbed and free gas, together with diffusion-seepage coupling, is an important factor influencing the establishment of gas-flow pathways and production capacity. Permeability evolution in deep coal reservoirs is closely related to adsorption/desorption, effective stress, and the dynamic evolution of pore-fracture networks. Overall, multiscale gas-water two-phase flow in deep coal reservoirs is a continuous process involving the occurrence, transformation, diffusion, and seepage of multiphase fluids within hierarchical pore-fracture networks, and is jointly regulated by pore structure, gas-water occurrence characteristics, coal structural heterogeneity, and multifield coupling. This paper distills the major understandings in this field and identifies key issues and future research directions. These synthesized insights can provide theoretical support and a scientific basis for deepening research on multiscale gas-water two-phase flow mechanisms in deep CBM reservoirs and supporting efficient deep CBM development.
The Holocene is a critical interval for understanding natural climate variability and testing climate mechanisms relevant to future warming. However, reliable terrestrial temperature proxies remain a major bottleneck in palaeoclimate reconstruction. Soil microbial glycerol dialkyl glycerol tetraethers (GDGTs) have become important palaeotemperature indicators, but the conventional brGDGT-based MBT’5ME index often produces biased estimates in arid and semi-arid regions. Recent studies have addressed this limitation by optimizing brGDGT calibrations through data-driven approaches and extending the marine TEX86 proxy to soil systems. Focusing on the Pan-Third Pole region, this review synthesizes recent progress and common challenges in soil GDGT-based temperature reconstruction, and evaluates its application to Holocene loess-palaeosol records. Overall, the field is shifting from single empirical indices toward a dual-proxy framework that combines complementary GDGT indicators, improving the potential for reconstructing temperature in complex terrestrial settings. However, major uncertainties remain regarding the climatic meaning of GDGT signals, including their seasonal versus annual and air versus soil temperature sensitivities, the influence of non-thermal factors, and the applicability limits of different proxies. These uncertainties hinder comparisons among GDGT records and between proxy reconstructions and climate model simulations. Future work should strengthen coordinated observations of air and soil temperatures alongside GDGT distributions, advance the integrated analysis of microbial communities, key environmental factors, and lipid molecular responses, and incorporate palaeoclimate data assimilation to impose stronger mechanistic constraints on terrestrial GDGT-based temperature reconstructions. In particular, the temperature response of soil TEX86 should be continuously evaluated across broader spatial scales and environmental gradients, thereby providing more robust terrestrial evidence for understanding the record-model discrepancy underlying the Holocene temperature conundrum.
