Ocean Park Conservation Foundation

Abstract The position uncertainty of tropical cyclones (TCs) may stretch along specific directions, yet the global pattern of the dominant direction of uncertainty remains unclear. This study proposes an analogous ensemble algorithm based on historical best-track data to quantify TC track uncertainties in the along-track (AT) and cross-track (CT) directions. The results reveal a strong latitudinal variation in the dominant direction of uncertainty: AT uncertainty is larger near the equator and within the mid-latitude westerlies, whereas CT uncertainty increases in recurvature zones. Moreover, the ratio of CT to AT uncertainty exhibits a negative correlation with TC translation speed. A comparable anisotropic pattern of track uncertainty is also identified in multi-model ensemble forecasts, indicating that the state-dependent preferred direction of position variability is a natural characteristic of TC track predictions. These findings provide the global-scale quantification of intrinsic anisotropic TC track uncertainty and highlight the importance of representing anisotropic uncertainty in probabilistic risk assessment and operational forecasting.

Marine heterotrophic bacteria produce polyphosphate (polyP) ubiquitously, yet their polyP functions and ecological significance are rarely studied. We investigated polyP dynamics of three common marine bacteria under phosphorus (P) and organic carbon limitations. Our results show that these bacteria accumulate varying levels of polyP: Alteromonas sp. accumulates up to 87% of polyP in total biomass P, Photobacterium ganghwense accumulates up to 35%, and Vibrio sp. accumulates less than 16%. This variability appears linked to differences in polyP functions. Under P limitation, polyP supports the growth of the two high-polyP-accumulating species, but not in Vibrio sp. with a low polyP level. Under organic carbon limitation, P. ganghwense uniquely degrades polyP for energy and survival. However, this mechanism is not observed under P limitation, despite similar levels of polyP accumulation in the bacteria. The phosphate produced from polyP degradation in P. ganghwense under organic carbon limitation is recycled within cells rather than released into the environment. Overall, our findings suggest that polyP enables some marine heterotrophic bacteria to cope with P and organic carbon limitations, potentially enhancing their competitiveness against phytoplankton for the common limiting nutrient phosphorus in marine ecosystems.

Marine dissolved organic matter (DOM) is one of Earth’s largest long-term carbon reservoirs, critical to the global carbon cycle. A key breakthrough in understanding this pool is the identification of biorefractory carboxyl-rich alicyclic molecules (CRAM). Recent studies have challenged the biorecalcitrance of CRAM but lacked detailed molecular evidence. Using advanced online countergradient liquid chromatography–Fourier transform ion cyclotron resonance mass spectrometry to track microbial incubation, we revealed a wide spectrum of CRAM bioavailability regulated by molecular polarity. CRAM with lower polarity were preferentially degraded, whereas microbial reworking led to production of higher-polarity CRAM, characterized by increased oxidation state, nitrogen content, and aromaticity. Some microbially transformed CRAM were frequently detected in a global DOM dataset of 1485 seawater samples, suggesting their potential persistence in marine environments. This study provides molecular insights into the biorecalcitrance and transformation pathway of CRAM, underscoring the complexity and dynamic nature of marine organic carbon cycling.

Drastic riverbed deformation caused by intensive human activities will change river hydraulics which may impact the fluvial inundation. The Beijiang River has undergone severe downward incisions due to in-channel human activities, greatly increasing its discharge capacity. This study analyzed flood loss of life induced by dike breaches considering the effects of riverbed deformation. The hydrodynamic model coupled with the embankment failure model was established to simulate floods and provide the basis for mortality evaluation under different scenarios. The results show that the maximum inundation depth decreased by approximately 2 m and the flood arrival time was also delayed due to riverbed undercutting. The flood mortality in most areas in 2020 has decreased by approximately 0.2 compared with that in 1999. The changes in flood hydrodynamics contributed over 80% to the decline in mortality rate in the areas near the breach, while the mortality in the remaining zone that far away from the breach was more sensitive to the flood arrival time. Early warning is an effective measure to reduce loss of life during flood disasters, and a 12-hour advance warning may reduce the mortality rate by more than 50%. This study provides a reference for evaluating the impact of riverbed evolution on flood risk and mitigating losses of flood disasters. • Riverbed deformation and stage-discharge in the past two decades are analyzed. • This study establishes a fluvial inundation model coupled with a parametrized breach development model for hydrodynamic simulations. • The flood characteristics and life loss induced by dike breaches are quantitatively estimated. • The effect of flood arrival time and hydrodynamic parameters on flood mortality is investigated. • The contribution of early evacuation warnings to flood mortality decreasing is explored.

Iron separation from different solid phases is essential for evaluating the environmental function of iron in sediments. Oxalate is a commonly used extractant that effectively extract iron(hydro)oxides in sediments by complexation. However, when using spectrophotometry method, excess oxalate will interfere the complexation of iron with 1,10-phenanthroline resulting in the failure of iron measurement. In this study, we discovered an effective method for spectrophotometric analysis of iron samples with oxalate by adjusting the pH to 7-9, which changes the structure of the Fe-oxalate complexes and ensured the complexation of iron with 1,10-phenanthroline. Further exploration indicates that photolysis and heating also decompose Fe-oxalate complexes, but the performance is not as good as pH adjustment. The standard solution exhibits a strong linear relationship between absorbance (Abs) and concentration (Con): Abs = 0.1934 × Con + 0.1360, with a R2 of 0.9997, accuracy of 97.1%, and precision of 98.6%, which demonstrate the reliability of this method. Overall, the pretreatment is simple, and the influence of the organic solvent (oxalate) is diminished after pH adjustment. This method is expected to contribute to community by providing a new reliable, effective, less pre-treatment, costive, and sensitive testing approach and hopefully assist in the investigation on environmental function of iron minerals.

<strong class="journal-contentHeaderColor">Abstract.</strong> The South China Sea (SCS) is the largest semi-enclosed marginal sea in western Pacific. It exhibits a unique vertically rotating cyclonic, anticyclonic, and cyclonic circulation in its upper, middle, and deep layers. Over slope topography, these layered currents interact and significantly shape the structure and intensity of the basin circulation. In this study, we employ process-oriented numerical simulations to investigate how upper-layer processes, characterized by greater magnitude and variability, influence the layered circulation over the irregular topographic slope. The simulations reveal that stronger upper intrusion from open ocean directly enhances upper layer circulation, which subsequently strengthens the middle and the deep slope currents. Vorticity dynamics illustrate that changes in the middle and deep slope current are largely related to the vertical stretching (&zeta;_DIV) induced by bottom geostrophic cross-isobath transport (<em>CGT_b</em>). As the upper-layer cyclonic slope current intensifies, it modulates the bottom pressure distribution, resulting in stronger negative &zeta;_DIV predominantly over the northwestern slope to intensify the middle anticyclone slope current. Similarly, for the deep cyclonic slope current, the <em>CGT</em>_<em>b</em>maintains downward cascading in the northern part and upwelling over the southern slope. Over the southern slope, the strengthening of the positive _&nbsp;is induced by the increment of the advection of relative vorticity and planetary vorticity in water column, in which the middle layer provides approximately 40 % of the total strengthening trend, but the upper layer has a minimal impact. Conversely, on the northern slope, the strengthening of the negative <em>CGT</em>_<em>b</em>is primarily influenced by the upper layer.&nbsp;