Ocean Conditions Research Articles

Turbulent Ice–Ocean Boundary Layers in the Well-Mixed Regime: Insights from Direct Numerical Simulations

Abstract The meltwater mixing line (MML) model provides a theoretical prediction of near-ice water mass properties that is useful to compare with observations. If oceanographic measurements reported in a temperature–salinity diagram overlap with the MML prediction, then it is usually concluded that the local dynamics are dominated by the turbulent mixing of an ambient water mass with near-ice meltwater. While the MML model is consistent with numerous observations, it is built on an assumption that is difficult to test with field measurements, especially near the ice boundary, namely, that the effective (turbulent and molecular) salt and temperature diffusivities are equal. In this paper, this assumption is tested via direct numerical simulations of a canonical model for externally forced ice–ocean boundary layers in a uniform ambient. We focus on the well-mixed regime by considering an ambient temperature close to freezing and run the simulations until a statistical steady state is reached. The results validate the assumption of equal effective diffusivities across most of the boundary layer. Importantly, the validity of the MML model implies a linear correlation between the mean salinity and temperature profiles normal to the interface that can be leveraged to construct a reduced ice–ocean boundary layer model based on a single scalar variable called thermal driving. We demonstrate that the bulk dynamics predicted by the reduced thermal driving model are in good agreement with the bulk dynamics predicted by the full temperature–salinity model. Then, we show how the results from the thermal driving model can be used to estimate the interfacial heat and salt fluxes and the melt rate. Significance Statement We investigate the turbulent dynamics and thermodynamical properties of water masses below ice shelves using new data from high-resolution simulations. This is important because there are currently too few observations of ice–ocean boundary layer dynamics to construct reliable models of ice-shelf melting as a function of ocean conditions. Our results demonstrate that the turbulent diffusivities of salt and temperature are approximately equal in the well-mixed regime. This implies a linear correlation between the mean temperature and salinity profiles, consistent with the meltwater mixing line prediction that is often used to interpret polar observations. We take advantage of this correlation to propose a reduced model of ice–ocean boundary layers that can predict ice-shelf melt rates at relatively low computational cost.

High infectivity and waterborne transmission of seagrass wasting disease.

Pathogen transmission pathways are fundamental to understanding the epidemiology of infectious diseases yet are challenging to estimate in nature, particularly in the ocean. Seagrass wasting disease (SWD), caused by Labyrinthula zosterae, impacts seagrass beds worldwide and is thought to be a contributing factor to declines; however, little is known about natural transmission of SWD. In this study, we used field and laboratory experiments to test SWD transmission pathways and temperature sensitivity. To test transmission modes in nature, we conducted three field experiments out-planting sentinel Zostera marina shoots within and adjacent to natural Z. marina beds (20 ± 5 and 110 ± 5 m from bed edge). Infection rates and severity did not differ among outplant locations, implicating waterborne transmission. The infectious dose of L. zosterae through waterborne exposure was assessed in a controlled laboratory experiment. The dose to 50% disease was 6 cells ml-1 and did not differ with the temperatures tested (7.5°C and 15°C). Our results show L. zosterae is transmissible through water without direct contact with infected plants. Understanding the transmission dynamics of this disease in the context of changing ocean conditions will improve Z. marina protection and restoration in critical coastal habitats worldwide.

Short Communication: Calcareous nannofossil assemblages and age determination in Leuwi Kenit, Ciletuh Palabuhanratu Geopark, Indonesia

Abstract. Pratiwi SD, Nurdrajat, Pratiwy FM, Chiyonobu S. 2024. Short Communication: Calcareous nannofossil assemblages and age determination in Leuwi Kenit, Ciletuh Palabuhanratu Geopark, Indonesia. Biodiversitas 25: 3200-3207. Our meticulous and comprehensive investigation of nannofossil diversity in Leuwi Kenit, Sukabumi District, West Java Province, Indonesia, a part of the Ciletuh Palabuhanratu UGG, where the study of nannofossils is limited, is of significant importance their implications for age determination and clarifying the geological history of the region. The initial documentation of calcareous nannofossils in the Leuwi Kenit traverse of the Cikarang Member within the Jampang Formation resulted in the identification of thirty-three species from 62 samples. The studied section reveals seven nannofossil biozones, arranged from oldest to youngest as follows: LO Sphenolithus ciperoensis; LO Cyclicargolithus abisectus; FO Sp. disbelemnos; FCO Helicosphaera carteri; FO Sp. belemnos; LCO Sp. belemnos; LO Sp. conicus and FCO Sp. heteromorphus. Notably, the abundance of Coccolithus pelagicus, Cyclicargolithus floridanus, Reticulofenestra spp., and Sphenolithus spp. characterized their occurrence throughout the section. The diversity and preservation of nannofossils were found to be good, and based on nannofossil biohorizons, the age of Leuwi Kenit spans from 24.3 million years ago to around 17.7 million years ago at Paleogene (Oligocene age) to Neogen Periode (Early Miocene age). Based on the nannofossils assemblages, results show that the area has many important indicator species, making it essential for future research on ancient ocean conditions and past climate changes within this geopark.

Performance analysis of Sinh and Cosh Gaussian vortex beam in vertical underwater optical communication

The performance analysis of Sinh Gaussian vortex beam (ShGvB) and Cosh Gaussian vortex beam (ChGvB) in oceanic turbulence is established by employing an anisotropic spatial power spectrum that considers the influence of the ocean depth to mimic the actual oceanic conditions. Since the salinity and temperature variations along depth are not linear, the actual data of temperature and salinity measured from the tropical region of the ocean is used for the current study. The propagation properties of the ShGvB are studied by deriving the cross-spectral density of the beam, and the average intensity of the beam is plotted over depth and studied in both isotropic and anisotropic oceanic turbulence systems. The analysis of the beam spot radius shows that the beam degrades faster in anisotropic media than in isotropic media. Quantitative estimation of the detection probability, channel capacity and bit error rate (BER) have been made to evaluate the beam's performance for vertical underwater optical communication. The BER may be improved by enlarging the detector aperture radius and signal-to-noise ratio. The ShGvB performs effectively in vertical underwater optical communication compared to the ChGvB.

Increased threat of strong typhoons along the Pacific coast of Japan: Combined effect of track change and seasonal advance

AbstractThis study analyses the landfall intensity of tropical cyclones (TCs) affecting the Pacific coast of Japan and found that the proportion of strong typhoons increased significantly in the second 22 years from 1977 to 2020. With an objective cluster analysis of TC tracks, one could isolate a cluster of TCs originating from the southeastern part of the western North Pacific (WNP), which plays a dominant role in increasing landfalls of strong typhoons. These TCs are characterized by a long‐recurving track and could achieve significantly higher intensity and larger size. Further analysis of TC trajectories and the environmental steering flow show a greater tendency for TCs originating from the southeastern WNP to approach the Pacific coast of Japan, even though there was a dramatic decrease in TC genesis number during autumn. Meanwhile, a notable earlier onset of strong typhoons occurred within this cluster of TCs due to more favorable atmospheric and oceanic conditions in summer. The results of this study emphasize the impacts of TC track change and seasonal advance of strong typhoons on the variation of intensity and potential destructiveness of landfalling TCs.

Mixotrophic growth of a ubiquitous marine diatom.

Diatoms are major players in the global carbon cycle, and their metabolism is affected by ocean conditions. Understanding the impact of changing inorganic nutrients in the oceans on diatoms is crucial, given the changes in global carbon dioxide levels. Here, we present a genome-scale metabolic model (iMK1961) for Cylindrotheca closterium, an in silico resource to understand uncharacterized metabolic functions in this ubiquitous diatom. iMK1961 represents the largest diatom metabolic model to date, comprising 1961 open reading frames and 6718 reactions. With iMK1961, we identified the metabolic response signature to cope with drastic changes in growth conditions. Comparing model predictions with Tara Oceans transcriptomics data unraveled C. closterium's metabolism in situ. Unexpectedly, the diatom only grows photoautotrophically in 21% of the sunlit ocean samples, while the majority of the samples indicate a mixotrophic (71%) or, in some cases, even a heterotrophic (8%) lifestyle in the light. Our findings highlight C. closterium's metabolic flexibility and its potential role in global carbon cycling.

Modelling the multiple action pathways of projected climate change on the Pacific cod (Gadus macrocephalus) early life stages

Understanding how future ocean conditions will impact early life stages and population recruitment of fishes is critical for adapting fisheries communities to climate change. In this study, we incorporated projected changes in physical and biological ecosystem dynamics from an oceanographic model into a mechanistic individual-based model for larval and juvenile stages of the Pacific cod (Gadus macrocephalus) in the eastern Bering Sea. We particularly investigated the impacts of ocean currents, temperature, prey density, and pCO2 on the hatching success, growth, survival, and spatial distribution of this species during 2021–2100. We evaluated two CO2 emission scenarios: RCP8.5 (high CO2 emissions, low mitigation efforts) and RCP4.5 (medium CO2 emissions and mitigation efforts). We found that the increase in temperature and decrease in prey density were the main drivers of faster growth rates and lower survival through increased starvation by the end of the century. Conversely, pCO2 had negligible impacts, which suggests that this species might be resilient to ocean acidification. The largest effects were observed under the high CO2 emission scenario, while the RCP4.5 projections displayed minimal impacts. We also identified an area with favourable conditions in the southeastern Bering Sea that will likely persist in future decades. This study provides relevant information on the future impacts of climate change on Pacific cod, and our results can be used to implement and inform climate-ready management for this important stock in Alaska.

Assessing the global distribution and risk of harmful microalgae: A focus on three toxic Alexandrium dinoflagellates

Harmful dinoflagellates and their resulting blooms pose a threat to marine life and human health. However, to date, global maps of marine life often overlook harmful microorganisms. As harmful algal blooms (HABs) increase in frequency, severity, and extent, understanding the distribution of harmful dinoflagellates and their drivers is crucial for their management. We used MaxEnt, random forest, and ensemble models to map the habitats of the representative HABs species in the genus Alexandrium, including A. catenella, A. minutum, and A. pacificum. Since species occurrence records used in previous studies were solely morphology-based, potentially leading to misidentifications, we corrected these species' distribution records using molecular criteria. The results showed that the key environmental drivers included the distance to the coastline, bathymetry, sea surface temperature (SST), and dissolved oxygen. Alexandrium catenella thrives in temperate to cold zones and is driven by low SST and high oxygen levels. Alexandrium pacificum mainly inhabits the Temperate Northern Pacific and prefers warmer SST and lower oxygen levels. Alexandrium minutum thrives universally and adapts widely to SST and oxygen. By analyzing the habitat suitability of locations with recorded HAB occurrences, we found that high habitat suitability could serve as a reference indicator for bloom risk. Therefore, we have proposed a qualitative method to spatially assess the harmful algae risk according to the habitat suitability. On the global risk map, coastal temperate seas, such as the Mediterranean, Northwest Pacific, and Southern Australia, faced higher risks. Although HABs currently have restricted geographic distributions, our study found these harmful algae possess high environmental tolerance and can thrive across diverse habitats. HAB impacts could increase if climate changes or ocean conditions became more favorable. Marine transportation may also spread the harmful algae to new unaffected ecosystems. This study has pioneered the assessment of harmful algal risk based on habitat suitability.

Nutrient Replenishment by Turbulent Mixing in Suspended Macroalgal Farms

AbstractThis study uses large eddy simulations to investigate nutrient transport and uptake in suspended macroalgal farms. Various farm configurations and oceanic forcing conditions are examined, with the farm base located near the nutricline depth. We introduce the Damkohler number Da to quantify the balance between nutrient consumption by macroalgae uptake and supply by farm‐enhanced nutrient transport. Most cases exhibit low Da, indicating that farm‐generated turbulence drives sufficient upward nutrient fluxes, supporting macroalgae growth. High Da and starvation may occur in fully grown farm blocks, a configuration that generates the weakest turbulence, particularly when combined with densely planted macroalgae or weak flow conditions. Flow stagnation within the farm due to macroalgae drag may constrain the uptake efficiency and further increase the starvation risk. Mitigation strategies involve timely harvesting, avoiding dense macroalgae canopies, and selecting farm locations with robust ocean currents and waves. This study provides insights for sustainable macroalgal farm planning.

Highly Sensitive Hybrid Triboelectric Nanogenerator with Ferris‐Wheel‐Like Structure for Ocean Wave Energy Harvesting

AbstractOcean wave energy represents a widely distributed and abundant clean, renewable energy source. However, its efficient harnessing remains a challenge. In this study, a triboelectric‐electromagnetic hybrid generator of a Ferris‐wheel‐like structure (FWS‐TEHG) with magnetic repulsion assistance is proposed to effectively enhance the collection of low‐frequency and low‐amplitude water wave energy. The Ferris‐wheel shell and the internal rotator are designed with a phase difference to heighten the swing amplitude, while the introduction of magnetic repulsion augments the motion frequency. The device has demonstrated excellent performance in low‐frequency conditions, from laboratory to ocean wave tests. Operating at a frequency of 0.5 Hz and a swing angle of 12° on a six‐freedom platform, it lights up 64 LEDs with a power rating of 2 W. Triggered by simulated water waves with a frequency of 1 Hz, the FWS‐TEHG charges a 19 mF capacitor at an average charging rate of ≈0.58 W h−1, powering a water‐level alarm. In oceanic conditions, the FWS‐TEHG effectively harvests energy from water waves by exhibiting an output frequency approximately four to five times higher than that of the primary frequency of ocean waves, thus enabling it to power electrical devices such as temperature–humidity meters efficiently. This study provides a valuable reference for advancing the practical application of nanogenerators in natural ocean environments.

The State of Marine Social Science: Yesterday, Today, and into the Future.

Rapidly changing ocean conditions are resulting in changes in marine species and across entire ecosystems that, in turn, affect communities and individuals who rely on these resources for their livelihoods, culture, and sustenance. Marine social science, an emerging field that embraces diverse methods to understand human-ocean relationships, is increasingly called on to contribute to transdisciplinary ocean science that can inform the evidence-based policy and management needed to address these changes. Here, we review the state of marine social science as a growing field of study. First, we outline the history of marine social science, including the emergence of the field and the social science disciplines and community it encompasses. We then discuss current marine social science research themes as a framework to understand key ocean issues, which is followed by a commentary on the future of marine social science research.

Impact of ocean in-situ observations on ECMWF sub-seasonal forecasts

We assess for the first time the impact of in-situ ocean observations on European Centre for Medium-Range Weather Forecasts (ECMWF) sub-seasonal forecasts of both ocean and atmospheric conditions. A series of coupled reforecasts have been conducted for the period 1993-2015, in which different sets of ocean observations were withdrawn in the production of the ocean initial conditions. Removal of all ocean in-situ observations in the initial conditions leads to significant degradation in the forecasts of ocean surface and subsurface mean state at lead times from week 1 to week 4. The negative impact is predominantly caused by the removal of the Argo observing system in recent decades. Changes in the mean state of atmospheric variables are comparatively small but significant in the forecasts of lower and upper atmospheric circulation over large regions. Our results highlight the value of continuous, real-time in-situ observations of the surface and subsurface ocean for coupled forecasts in the sub-seasonal range.

The Eurasian Arctic Ocean along the MOSAiC drift in 2019–2020: An interdisciplinary perspective on physical properties and processes

The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC, 2019–2020), a year-long drift with the Arctic sea ice, has provided the scientific community with an unprecedented, multidisciplinary dataset from the Eurasian Arctic Ocean, covering high atmosphere to deep ocean across all seasons. However, the heterogeneity of data and the superposition of spatial and temporal variability, intrinsic to a drift campaign, complicate the interpretation of observations. In this study, we have compiled a quality-controlled physical hydrographic dataset with best spatio-temporal coverage and derived core parameters, including the mixed layer depth, heat fluxes over key layers, and friction velocity. We provide a comprehensive and accessible overview of the ocean conditions encountered along the MOSAiC drift, discuss their interdisciplinary implications, and compare common ocean climatologies to these new data. Our results indicate that, for the most part, ocean variability was dominated by regional rather than seasonal signals, carrying potentially strong implications for ocean biogeochemistry, ecology, sea ice, and even atmospheric conditions. Near-surface ocean properties were strongly influenced by the relative position of sampling, within or outside the river-water influenced Transpolar Drift, and seasonal warming and meltwater input. Ventilation down to the Atlantic Water layer in the Nansen Basin allowed for a stronger connectivity between subsurface heat and the sea ice and surface ocean via elevated upward heat fluxes. The Yermak Plateau and Fram Strait regions were characterized by heterogeneous water mass distributions, energetic ocean currents, and stronger lateral gradients in surface water properties in frontal regions. Together with the presented results and core parameters, we offer context for interdisciplinary research, fostering an improved understanding of the complex, coupled Arctic System.

Rapid in-motion heading alignment using time-differenced carrier phases from a single GNSS antenna and a low-grade IMU

Abstract Despite advancements in global navigation satellite system/inertial navigation system (GNSS/INS) integrated systems, the challenge of achieving rapid and accurate initial heading alignment remains, particularly in low-grade IMUs and marine applications with swaying conditions. This study introduces an innovative in-motion heading alignment method utilizing time-differenced carrier phases (TDCP) from a single GNSS antenna and a low-grade IMU based on the fundamental principle of trajectory similarity. The heading angle is determined by comparing the dead reckoning (DR)-derived trajectory with the TDCP-derived trajectory. This is achieved using gyro measurements and the delta position from TDCP solutions. The proposed alignment method can be implemented in real-time and the alignment period is just 1s, which indicates that the method could continuously output heading when the carrier is in motion. We not only validate the effectiveness of the proposed alignment method in land vehicle applications, but also in maritime vessels, like unmanned surface vessels (USV), and unmanned underwater vehicles (UUV). In addition, we evaluated the impact of challenging ocean conditions and mounting angle errors on the proposed alignment method. Experimental results show that the heading could be determined with an accuracy of 0.49º, 3.10º, and 2.31º at a 95% confidence level for the land vehicle, USV, and UUV tests, respectively. Besides, the RMS of the alignment errors calculated by our method reaches 0.24º, 1.42º, and 1.19º for the land vehicle, USV, and UUV tests, respectively.

Suitability of the CICE sea ice model for seasonal prediction and positive impact of CryoSat-2 ice thickness initialization

Abstract. The Los Alamos Community Ice CodE (CICE) sea ice model is being tested in standalone mode to identify biases that limit its suitability for seasonal prediction, where it is driven by atmospheric forcings from the NCEP Climate Forecast System Reanalysis (CFSR) and a built-in mixed-layer ocean model in CICE. The initial conditions for the sea ice and mixed-layer ocean are also from CFSR in the control experiments. The simulated sea ice extent agrees well with observations during the warm season at all lead times up to 12 months, in both the Arctic and the Antarctic. This suggests that CICE is able to provide useful sea ice edge information for seasonal prediction. However, the model's initial conditions have ice that is too thick in the Beaufort Sea, resulting in excessive ice extent in the Arctic at 6-month lead forecasts and errors in ice volume at all lead times when compared to available observations. To address this limitation, additional CS2_IC experiments were conducted, where the Arctic ice thickness was initialized using CryoSat-2 satellite observations while keeping all other initial fields the same as in the control experiments. This reduced the positive bias in the ice thickness in the initial conditions, leading to improvements in both the simulated ice edge and the ice thickness at the seasonal timescale. This indicates that CICE has the potential to improve its seasonal forecast skill and provide more accurate predictions of sea ice extent and thickness when initialized with a more realistic sea ice thickness. This study highlights that the suitability of CICE for seasonal prediction depends on various factors, including initial conditions such as sea ice thickness, in addition to sea ice coverage, as well as oceanic and atmospheric conditions.

Real-time passive underwater localization using a compact acoustic sensor array

This paper proposes an underwater passive localization system that can be installed on remote platforms and can locate in real-time sound sources using a compact 4-element array. The localization system relies on both the Time Difference of Arrival (TDoA) algorithm to localize sources that are impulsive, and a low-complexity implementation of the matched field processing (MFP) algorithm for broadband continuous waves, such as propeller noise. The array is intended to be mounted on small platforms and compact geometries are investigated to optimize the localization accuracy. Figures of merit are defined to assess the accuracy and reliability of the algorithm as a function of the distance between the elements. The proposed algorithm is implemented on a System-on-Chip (SoC) which executes the algorithm on an embedded system for real-time operation. Finally, the performance is assessed in realistic ocean conditions in different environments. It is shown that the MFP provides an excellent angle estimate for broadband continuous sources, but TDoA is more reliable, particularly when the deployment is sensitive to the environment conditions.

Sea Ice Interannual Variability and Sensitivity to Fall Oceanic Conditions and Winter Air Temperature in the Gulf of St. Lawrence, Canada

AbstractThe Gulf of St. Lawrence has been nearly free of sea ice in the winter six times in its recorded history, four of which have occurred since 2010. This study examines the inter‐annual variability of sea ice cover characteristics (1969–2024) and winter mixed layer heat content (1996–2024), their sensitivity to fall oceanic conditions (since fall of 1995) and to winter air temperatures. The study finds no relationship between fall oceanic conditions with either the first occurrence of sea ice, maximum seasonal estimated volume or winter mixed layer heat content. However, it shows that the first occurrence of sea ice in the northwestern Gulf is related to the timing of sea surface temperature crossing the 1°C threshold with a lag time of 30–37 days, and with air temperature dropping below −2°C with a lag of 37–44 days; longer lags have weak correlations. The seasonal maximum conditions in area or estimated volume can be estimated by the preceding measurements of the same metrics with a lead time of only 29 days for volume and 36 days for area. The average air temperature over the Gulf between December and February or March is highly correlated to seasonal maximum sea ice area and estimated volume, as well as ice season duration. The six nearly ice‐free winters correspond to the warmest December to February (or December to March) average air temperatures over the Gulf. A warming of >1.9°C–2.4°C (DJFM) or >2.2°C–2.9°C (DJF) above the 1991–2020 climatology leads to nearly ice‐free conditions.

Gene networks governing the response of a calcareous sponge to future ocean conditions reveal lineage-specific XBP1 regulation of the unfolded protein response.

Marine sponges are predicted to be winners in the future ocean due to their exemplary adaptive capacity. However, while many sponge groups exhibit tolerance to a wide range of environmental insults, calcifying sponges may be more susceptible to thermo-acidic stress. To describe the gene regulatory networks that govern the stress response of the calcareous sponge, Leucetta chagosensis (class Calcarea, order Clathrinida), individuals were subjected to warming and acidification conditions based on the climate models for 2100. Transcriptome analysis and gene co-expression network reconstruction revealed that the unfolded protein response (UPR) was activated under thermo-acidic stress. Among the upregulated genes were two lineage-specific homologs of X-box binding protein 1 (XBP1), a transcription factor that activates the UPR. Alternative dimerization between these XBP1 gene products suggests a clathrinid-specific mechanism to reversibly sequester the transcription factor into an inactive form, enabling the rapid regulation of pathways linked to the UPR in clathrinid calcareous sponges. Our findings support the idea that transcription factor duplication events may refine evolutionarily conserved molecular pathways and contribute to ecological success.

The joint effects of the El Niño-Southern Oscillation and Arctic Oscillation on tropical Indian Ocean heat flux during boreal winter

In this study, the joint effects of the El Niño-Southern Oscillation (ENSO) and Arctic Oscillation (AO) on winter net surface heat flux (Qnet) anomalies over the tropical Indian Ocean (TIO) are investigated for the 1979/1980–2017/2018 period. The results show that, in multisource datasets, the Qnet pattern for El Niño plus positive AO cases is the most robust. The major feature of Qnet is dominated by a significant dipole pattern, with oceanic heat gain anomalies appearing over the southeastern TIO and oceanic heat loss near the western TIO. Analysis of the flux components shows that the Qnet anomalies are mainly contributed by changes in latent heat flux and shortwave radiation (QLHF and QSWR), which are tightly associated with the regional atmospheric and oceanic conditions. In association with positive AO, northerly wind anomalies on the eastern flanks of a low-level anomalous anticyclone in the Arabian Sea enhance the intertropical convergence zone (ITCZ) in the western TIO. Meanwhile, the El Niño-related SST warming occurs in the western TIO. Both enhanced ITCZ and anomalous SST warming favour in situ increased low and middle cloud cover and a reduced QSWR. Furthermore, under El Niño's effect, a low-level anomalous anticyclone located in the southeastern TIO leads to a positive QLHF through decreased near-surface wind speed and increased near-surface air humidity. As a result, a dipole Qnet pattern tends to be observed for the combination of El Niño and positive AO.

Application of the Ocean Health Index to assess ocean and coastal conditions of the Tokyo Metropolitan area

Ocean ecosystem services are fundamental to coastal economic development and climate regulation. The Tokyo Metropolitan Area (TMA) is one of the world’s most significant bay areas, with its economic development and residents relying on a healthy ocean and diverse marine ecosystem services. Post-World War II, the coastal zones of TMA have suffered from various human-induced stresses and impacts, jeopardizing the capacity of ocean ecosystem services and sustainable development. Although recent years have seen improvements in basic marine water quality, other ecosystem health issue, such as biodiversity, carbon storage, coastal protection are remain limited and require comprehensive enhancement. To better understand the current state of ocean health, promote more comprehensive ocean management decisions and plans, and support sustainable development in the region, it is essential to evaluate the ocean’s condition in the TMA and to assess future trends and risks. The Ocean Health Index (OHI) offers a comprehensive framework to evaluate global and regional ocean health conditions and their ecosystem services. This study applies the OHI to assess the ocean and coastal health of TMA, with indicators and reference points adjusted based on local conditions. From 2014 to 2019, the OHI assessment results indicate that TMA obtained an overall OHI score of 49 (out of 100), with goals ranging from 13 to 87. The environmental and social goals, such as Tourism and Recreation (87), Clean Water (67), Coastal Livelihoods and Economies (62), Sense of Place (62), and Artisanal Fishery Opportunity (51), are relatively high. In contrast, the ecological goals, such as Biodiversity (14), Carbon Storage (13), Coastal Protection (38), and Food Provision (24), are relatively low. This case study highlights strategies for improving ocean health conditions in TMA from both OHI goals and management structure perspectives. The methods and results provide a quantitative tool for regional marine and coastal management in TMA, aiding regional management organizations to establish quantifiable objectives for actions that were previously difficult to quantify. These results can indirectly promote the establishment of more comprehensive and holistic regional management organizations in TMA, which is currently fragmented, thereby effectively enhancing ocean health in TMA.