Under global climate change, water flow and related nutrient biogeochemistry in the Arctic are changing at an unprecedented rate, and potentially affect nutrient cycling in the Arctic Ocean. However, nutrient fluxes via submarine groundwater discharge (SGD) are potentially important yet poorly understood in the Arctic. Here we quantified that nutrient fluxes through radium-derived SGD were three orders of magnitude higher than those from the local river and constituted 25%−96% of the total nutrient inputs into the Kongsfjorden. These large groundwater nutrient fluxes with high NIN/DIP molar ratio (average 99) may change the biomass and community structure of phytoplankton. Meanwhile, combining other SGD study cases around the Arctic region, SGD rates tend to increase over the past three decades, possibly on account of the effects of global warming. The SGD-derived nutrient may cause the increase of net primary productivity in the Arctic Ocean. The results will provide important basic data for land-ocean interactions in the typical fjord of the Arctic under the influence of global warming.

Ny-Ålesund, located in Arctic Svalbard, is one of the most sensitive areas on Earth to global warming. In recent years, accelerated glacier ablation has become remarkable in Ny-Ålesund. Glacial meltwaters discharge a substantial quantity of materials to the ocean, affecting downstream ecosystems and adjacent oceans. In August 2015, various water samples were taken near Ny-Ålesund, including ice marginal meltwater, proglacial meltwater, supraglacial meltwater, englacial meltwater, and groundwater. Trace metals (Al, Cr, Mn, Fe, Co, Cu, Zn, Cd, and Pb), major ions, alkalinity, pH, dissolved oxygen, water temperature and electric conductivity were also measured. Major ions were mainly controlled by chemical weathering intensity and reaction types, while trace metals were influenced by both chemical weathering and physicochemical control upon their mobility. Indeed, we found that Brøggerbreen was dominated by carbonate weathering via carbonation of carbonate, while Austre Lovénbreen and Pedersenbreen were dominated by sulfide oxidation coupled with carbonate dissolution with a doubled silicate weathering. The higher enrichment of trace metals in supraglacial meltwater compared to ice marginal and proglacial meltwater suggested anthropogenic pollution from atmospheric deposition. In ice marginal and proglacial meltwater, principal component analysis indicated that trace metals like Cr, Al, Co, Mn and Cd were correlated to chemical weathering. This implies that under accelerated glacier retreat, glacier-derived chemical components are subjected to future changes in weathering types and intensity.

The biogeochemical processes of marine sediments are influenced by bioturbation and organic carbon decomposition, which is crucial for understanding global element cycles and climate change. Two sediment cores were acquired in 2017 from abyssal basins in the central-eastern tropical Pacific to determine the bioturbation and organic carbon degradation processes. The radioactivity concentrations of ²¹⁰Pb and ²²⁶Ra in the sediment cores were measured, indicating the presence of significant excess ²¹⁰Pb (²¹⁰Pb_ex) signals in the sediment cores. Besides, a manganese nodule was discovered in one core, which had a substantial influence on the distribution of ²¹⁰Pb_ex. With the exception of this anomalous finding, the bioturbation coefficients in the remaining core were estimated to be 10.6 cm²/a using a steady-state diffusion model, greater than most of the deep-sea sediments from the equatorial eastern Pacific. By using a bio-diffusion model, we further calculated the degradation rates of organic carbon (8.02 ka⁻¹), which is also higher than other areas of the Pacific. Our findings displayed the presence of a biologically active benthic ecosystem in the central-eastern tropical Pacific.

Understanding the dynamics of phytoplankton communities in coastal zones is crucial for the management and conservation of coastal ecosystems. Previous research indicated that the phytoplankton community structure and dominant taxa in the Bohai Sea (BHS) have exhibited significant shifts from the 1990s to the early 2010s in response to environmental changes, especially the change in nutrient structure. This study comprehensively investigated the variations in net-collected phytoplankton (>76 μm) community structure, diversity, and environmental factors in the BHS during the late summers of 2011−2020, aiming to understand the recent trend in phytoplankton community structure and to explore the interactions between the communities and the environment. During the study period, the nutrient status in the BHS was characterized by a decrease in dissolved inorganic nitrogen (DIN) concentration, an increase in dissolved inorganic phosphorus (DIP) concentration, and a return of the nitrogen-to-phosphorus (N/P) molar ratio (hereinafter referred to as N/P ratio) to the Redfield ratio since 2016. The eutrophication index (EI) in the BHS remained stable and was generally at a low level (<1). The Dia/Dino index fluctuated but did not show an obvious trend. Overall, the eutrophication, the imbalance in nutrient ratio, and the shift in phytoplankton community structure did not continue during the study period. The increased abundance of phytoplankton was strongly associated with elevated concentrations of DIN, as well as higher N/P and nitrogen-to-silicon (N/Si) ratios, whereas the greater diversity was strongly linked to higher concentrations of DIP. Diatoms and dinoflagellates showed significant differences in their interactions with the environment, and their relative dominance was related to water column depth and stratification intensity; their impacts on the phytoplankton community diversity were also significantly different. The variations of certain dominant species, i.e., Skeletonema costatum, Paralia sulcata, and Tripos longipes, exhibited strong links to the changes in nutrient structure in the BHS. The findings of this study contribute to understanding the regional environmental changes and provide insights into the adaptive strategies of coastal ecosystems in response to environmental shifts and fluctuations.

The tide plays a pivotal role in the ocean, affecting the global ocean circulation and supplying the bulk of the energy for the global meridional overturning circulation. To further investigate internal tides and their impacts on circulation, it is imperative to incorporate tidal forcing into the eddy-resolving global ocean circulation model. In this study, we successfully incorporated explicit tides (eight major constituents) into a global eddy-resolving general ocean circulation model and evaluated its tidal simulation ability. We obtained harmonic constants by analyzing sea surface height through tidal harmonic analysis and compared them with the analysis data Topex Poseidon Cross-Overs v9 (TPXO9), the open ocean tide dataset from 102 open-ocean tide observations, and tide gauge stations from World Ocean Circulation Experiment. The results demonstrated that the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics/Institute of Atmospheric Physics (LASG/IAP) Climate System Ocean Model 3.0 (LICOM3.0) effectively simulated tides, with errors predominantly occurring in nearshore regions. The tidal amplitude simulated in LICOM3.0 was greater than that of TPXO9, and these high-amplitude areas exhibited greater errors. The amplitude error of the M₂ constituent was larger, while the phase error of the K₁ constituent was more significant. Furthermore, we further compared our results with those from other models.

The three-dimensional displacements caused by ocean loading effects are significant enough to impact spatial geodetic measurements on sub-daily or longer timescales, particularly in the vertical direction. Currently, most tide models incorporate the distribution of vertical displacement loading tides; however, their accuracy has not been assessed for the equatorial and Indian Ocean regions. Global Positioning System (GPS) observations provide high-precision data on sea-level changes, enabling the assessment of the accuracy and reliability of vertical displacement tide models. However, because the tidal period of the K₂ constituent is almost identical to the orbital period of GPS constellations, the estimation of the K₂ tidal constituent from GPS observations is not satisfactory. In this study, the principle of smoothness is employed to correct the systematic error in K₂ estimates in GPS observations through quadratic fitting. Using the adjusted harmonic constants from 31 GPS stations for the equatorial and Indian Ocean, the accuracy of eight major constituents from five global vertical displacement tide models (FES2014, EOT11a, GOT4.10c, GOT4.8, and NAO.99b) is evaluated for the equatorial and Indian Ocean. The results indicate that the EOT11a and FES2014 models exhibit higher accuracy in the vertical displacement tide models for the equatorial and Indian Ocean, with root sum squares errors of 2.29 mm and 2.34 mm, respectively. Furthermore, a brief analysis of the vertical displacement tide distribution characteristics of the eight major constituents for the equatorial and Indian Ocean was conducted using the EOT11a model.

The frontogenetic processes of a submesoscale cold filament driven by the thermal convection turbulence are studied by a non-hydrostatic large eddy simulation. The results show that the periodic changes in the direction of the cross-filament secondary circulations are induced by the inertial oscillation. The change in the direction of the secondary circulations induces the enhancement and reduction of the horizontal temperature gradient during the former and later inertial period, which indicates that the frontogenetical processes of the cold filament include both of frontogenesis and frontolysis. The structure of the cold filament may be broken and restored by frontogenesis and frontolysis, respectively. The magnitude of the down-filament currents has a periodic variation, while its direction is unchanged with time. The coupling effect of the turbulent mixing and the frontogenesis and frontolysis gradually weakens the temperature gradient of the cold filament with time, which reduces frontogenetical intensity and enlarges the width of cold filament.

It is found that the winter (December–February) barrier layer (BL) in the Bay of Bengal (BoB) acts as a dynamical thermostat, modulating the subsequent summer BoB sea surface temperature (SST) variability and potentially affecting the Indian summer monsoon (ISM) onset and associated rainfall variability. In the years when the prior winter BL is anomalously thick, anomalous sea surface cooling caused by intensified latent heat flux loss appears in the BoB starting in October and persists into the following year by positive cloud-SST feedback. During January–March, the vertical entrainment of warmer subsurface water induced by the anomalously thick BL acts to damp excessive cooling of the sea surface caused by atmospheric forcing and favors the development of deep atmospheric convection over the BoB. During March–May, the thinner mixed layer linked to the anomalously thick BL allows more shortwave radiation to penetrate below the mixed layer. This tends to maintain existing cold SST anomalies, advancing the onset of ISM and enhancing June ISM precipitation through an increase in the land-sea tropospheric thermal contrast. We also find that most of the coupled model intercomparison project phase 5 (CMIP5) models fail to reproduce the observed relationship between June ISM rainfall and the prior winter BL thickness. This may be attributable to their difficulties in realistically simulating the winter BL in the BoB and ISM precipitation. The present results indicate that it is important to realistically capture the winter BL of the BoB in climate models for improving the simulation and prediction of ISM.

Shipboard radiosonde soundings are important for detecting and quantifying the multiscale variability of atmosphere-ocean interactions associated with mass exchanges. This study evaluated the accuracies of shipboard Global Positioning System (GPS) soundings in the eastern tropical Indian Ocean and South China Sea through a simultaneous balloon-borne inter-comparison of different radiosonde types. Our results indicate that the temperature and relative humidity (RH) measurements of GPS-TanKong (GPS-TK) radiosonde (used at most stations before 2012) have larger biases than those of ChangFeng-06-A (CF-06-A) radiosonde (widely used in current observation) when compared to reference data from Vaisala RS92-SGP radiosonde, with a warm bias of 5℃ and dry bias of 10% during daytimes, and a cooling bias of –0.8℃ and a moist bias of 6% during nighttime. These systematic biases are primarily attributed to the radiation effects and altitude deviation. An empirical correction algorithm was developed to retrieve the atmospheric temperature and RH profiles. The corrected profiles agree well with that of RS92-SGP, except for uncertainties of CF-06-A in the stratosphere. These correction algorithms were applied to the GPS-TK historical sounding records, reducing biases in the corrected temperature and RH profiles when compared to radio occultation data. The correction of GPS-TK historical records illustrated an improvement in capturing the marine atmospheric structure, with more accurate atmospheric boundary layer height, convective available potential energy, and convective inhibition in the tropical ocean. This study contributes significantly to improving the quality of GPS radiosonde soundings and promotes the sharing of observation in the eastern tropical Indian Ocean and South China Sea.

Typhoons in the western Pacific have a significant impact on the transport of heat, salt and particles through the Luzon Strait. However, there are very limited field observations of this impact because of extreme difficulties and even dangers for ship-based measurements during the rough weather. Here, we present the preliminary results from analyzing a dataset collected by a glider deployed west of the Luzon Strait a few days prior to the arrival of typhoon MITAG. The gilder data revealed an abnormally salinity (>34.8) subsurface water apparently sourced from Kuroshio intrusion during the typhoon. When typhoon MITAG traveled on the east of the Luzon Strait, the positive wind stress curl strengthened the cyclonic eddy and weakened the anti-cyclonic eddy. This led to a slowdown of Kuroshio and made its intrusion easier. The main axis of the Kuroshio at the northern part of the strait shifted westward after the typhoon and did not return to its original position until a week later. The Ekman transport from persistent northerly wind of typhoon MITAG was significant, but its importance in enhancing the Kuroshio intrusion is only secondary relative to the eddies variations.