Radio telescope is a reflector antenna for receiving radio signals radiated by cosmic celestial bodies. After assembling phased array feed, continuous beam coverage can be formed, which greatly improves the observation efficiency. In this paper, the performance analysis of the reflector antenna after the assembly of the above systems is carried out by establishing the 0.7-1.8GHz metal Vivaldi antenna PAF array and the numerical model of the 25-meter aperture radio telescope. After the final optimization, the system temperature of the whole radio telescope is about 30K, and the antenna efficiency of the final optimization can reach 75% in the whole frequency band under different distances. The next step needs to be verified by full-wave simulation.

Seamount and the oxygen minimum zone (OMZ) are often two typical habitats coexisting in the deep sea, and studying the relationship between the “seamount effect” and OMZ is of great significance to improve the cognitive level of the two typical deep-sea habitats. Based on the investigation of the two cruises in the M4 seamount of the Western Pacific, this study revealed the “seamount effect”, explored the impact of seamount and environmental parameters on OMZ. The results showed that the uplifts of the isohaline, isotherm and isopycnal occurred near the summit in the two cruises, and the isolines of NO3-N, PO4-P and NO2-N were also elevated near the summit. Meanwhile, the ratio of the average concentration of POC near the summit for cruise 1 to cruise 2 can reach up to about 2 times. This may indicate that there was a “seamount effect” in both cruises, and it was stronger in cruise 1. The range and intensity of OMZ in both cruises were similar, with the range of 550–1100 m and (330–380, 850–1100) m, respectively. The impact of seamount on OMZ may be reflected in two aspects. One possible mechanism was that the hydrological phenomena such as upwelling near the summit may raise the isolines of low concentration DO in 200–300 m, increasing the range of the upper boundary of OMZ; Another possibility was that the biological activities of seamount sediments continuously may consume DO, such as in 1000 m at station A7 of cruise 1, increasing the intensity of OMZ. In addition, the temperature below 1000 m directly controlled the upper boundary of OMZ, while the decomposition of organic matter in 75–300 m above the OMZ consumed DO, which also had an important impact on the range and intensity of the OMZ.

As a water layer with significantly reduced dissolved oxygen (DO) in the ocean, the oxygen minimum zone (OMZ) plays a crucial role in regulating marine organism distribution, global material cycles, and climate change. Based on a systematic review of recent studies on OMZ, this paper summarizes the DO thresholds, structural characteristics, distribution patterns, formation and maintenance mechanisms, and driving factors of OMZ in the ocean in the context of global change. The DO thresholds of OMZ typically range from 20 to 100 µmol L−1. Specifically, the threshold is mostly 20 µmol L−1 in regions with intense OMZ, such as the Eastern Pacific and Northern Indian Oceans, while it is mostly 100 µmol L−1 in regions with mild OMZ, including the Western Pacific and Atlantic. In terms of structure, the OMZ is mainly composed of three parts: the upper oxycline, the lower oxycline, and the OMZ core. Significant differences exist in the horizontal and vertical distributions of OMZ across different regions. OMZ is mainly concentrated in tropical and subtropical regions, with the widest distribution in the eastern tropical North Pacific. The upper boundary of OMZ is shallower (50–150 m) in significantly affected regions, whereas it is below 200 m in less affected regions. The formation of OMZ is governed by the continuous consumption of DO in the ocean interior, and the water exchange restriction caused by seawater stratification, whereas the maintenance of the hypoxic state of OMZ relies on two positive feedbacks: increased microbial oxygen consumption due to reduced animal feeding, and increased oxygen consumption by anaerobic metabolic products. In the context of global change, rising temperature is the main driver of OMZ expansion, reducing O2 solubility, increasing respiration and decomposition rates, and enhancing seawater stratification. Additionally, the structure and evolution of OMZ is also profoundly affected by ocean circulation such as thermohaline circulation, wind-driven circulation, and upwelling, as well as changes in wind stress, mesoscale eddies and freshwater flux. Future research should focus on establishing OMZ gradient thresholds and classification criteria based on the law of deoxygenation, improving the systematic understanding of the temporal and spatial variations of OMZ, and continuously strengthening studies on OMZ in the Western Pacific.

The sensitivity of a phased array receiver can be enhanced by cryogenically cooling either its low-noise amplifiers or its front-end antenna array.This study addresses the cryogenic cooling requirements of phased array receivers.Based on a laboratory-based prototype broadband Vivaldi antenna array,we have designed a Dewar system adopting a full-array integrated cooling approach.Through thermal load analysis of the internal cryogenic structure and comparison with measured cooling temperatures from a prototype,we have validated a structural design while identifying areas for improvement.This work provides valuable insights for future integrated cooling and sensitivity optimization of phased array receivers equipped with cryogenic low-noise amplifiers.

Abstract In recent decades, global warming‐driven ocean stratification has profoundly affected nutrient cycling. As the largest marginal sea in the northwestern Pacific, the South China Sea (SCS) provides a representative setting to examine these responses. Based on two decades of temperature, salinity, and nutrient datasets, we quantified the evolution of stratification in the SCS, its impacts on the upward transport of deep‐water phosphate (PO 4 3− ), and the resulting changes in carbon sink. Results show an increasing intensification of stratification, with an upward shift of the thermocline's upper boundary, a downward shift of its lower boundary, increased thickness, and weakened vertical mixing. Despite enhanced external inputs from rivers and atmospheric deposition and reduced phytoplankton consumption of PO 4 3− in the mixed layer, PO 4 3− concentrations have declined persistently, indicating a substantial reduction in nutrient flux from the deep water across the thermocline into the surface layer. The minimum net reduction of PO 4 3− in the upper water column (mixed layer plus thermocline) was −0.047 Gmol·yr −1 . This decline in PO 4 3− supply constrained primary production and reduced CO 2 uptake, leading to an estimated carbon sink reduction of 2.21 × 10 5 t CO 2 ·yr −1 in the SCS.

Sediment microorganisms play important roles in coastal biogeochemical cycling, yet how sediment heterogeneity and coupled environmental gradients shape benthic microbial communities in marginal seas remains insufficiently understood. Here, we examined microbial communities in two contrasting sediment types from the East China Sea: fine-grained, organic-rich sediments (E1) and coarse-grained, organic-poor sediments (E2). We used an integrated approach to explore the relationships between sediment heterogeneity and microbial community composition, assembly processes, co-occurrence network organization, and functional potential. E2 showed higher α-diversity, broader niche breadth, and greater community heterogeneity than E1. Microbial community differentiation was jointly associated with sediment physicochemical properties, water-column conditions, and spatial/depth-related gradients. Community assembly analysis indicated that dispersal limitation was an important process in both sediment types, whereas E1 was more strongly influenced by drift and other stochastic processes and E2 exhibited relatively stronger heterogeneous selection. Co-occurrence network analysis revealed distinct network topologies: the E1 network was more modular and fragmented, whereas the E2 network was more connected and more dependent on connector nodes. PICRUSt2-inferred functional profiles suggested that core carbon-, nitrogen-, and sulfur-related pathways were broadly similar between E1 and E2, indicating potential functional redundancy. Meanwhile, E1 was associated with greater carbon-transformation potential, whereas E2 showed slightly higher potential for oxidative nitrogen transformation, particularly nitrification- and comammox-related pathways. Overall, sediment heterogeneity and coupled environmental gradients jointly shape benthic microbial community structure, assembly processes, network organization, and inferred functional potential in the East China Sea.

Abstract Estuaries and associated shelf deposits, which bury 70%–90% of global marine organic carbon, making them key sites for marine carbon burial. Variations in total organic carbon (TOC) content and the organic carbon burial rate (OCBR) in these sediments strongly influence carbon sequestration dynamics. Using the Yellow River Estuary as a representative case, this study assessed the impact of watershed damming on estuarine organic carbon burial based on 2023 field data and records from 1984 to 2023. Following the construction of the Xiaolangdi Reservoir, sediment TOC and OCBR in the Yellow River Estuary decreased by 46% (from 0.55% ± 0.08%–0.30% ± 0.12%) and 58% (from 155.0 ± 22.0 to 66.0 ± 25.0 g m−2 yr−1), respectively. This change was primarily attributed to a nearly 90% decline in sediment flux to the sea following reservoir construction, accompanied by significant sediment coarsening. Similar reservoir‐induced declines in estuarine carbon sinks have been widely observed in big estuaries such as the Mekong, Mississippi, and Nile rivers. Extrapolating from the empirical relationship between sediment flux and OCBR in the Yellow River Estuary, global damming is estimated to have reduced estuarine OCBR by approximately 33.6%, equivalent to an annual loss of about 23.5 Tg C in organic carbon burial. Collectively, sediment depletion and grain‐size coarsening are identified as major drivers of estuarine OCBR decline. These findings underscore the need to incorporate evolving estuarine carbon burial “hotspots” into global carbon cycle models.

Anthropogenic CO2 emissions are intensifying climate change, creating an urgent need for scalable and efficient strategies to enhance the oceanic carbon sink. This study proposes and evaluates a new calcium-alkali coupling pathway in which the co-addition of Ca2+ and OH- promotes the conversion of seawater dissolved inorganic carbon (DIC) into solid CaCO3. This process perturbs carbonate-system equilibrium and subsequently drives additional atmospheric CO2 uptake during system re-equilibration. Unlike conventional alkalinity-enhancement approaches that mainly retain absorbed CO2 as dissolved bicarbonate and carbonate species, the pathway examined here emphasizes carbonate precipitation as a major mode of DIC removal. Laboratory experiments, mesocosm simulations, and a 1000 m3 offshore field demonstration in the southern Yellow Sea were conducted to assess carbon-removal efficiency and short-term environmental responses. Under a dosing scheme of 1.79 mmol Ca2+ and 3.58 mmol OH- per litre of seawater, DIC in the 1000 m3 field system decreased by 1763 μmol kg-1 and was converted into CaCO3, corresponding to an estimated uptake of 77.6 kg atmospheric CO2. During the observation period, the monitored physicochemical parameters and trace-metal indicators showed only limited and controllable perturbations. A first-order scaling estimate based on this single-application, dose-dependent capacity suggests a theoretical carbon-sink enhancement potential of 2.48 Pg C on the Chinese continental shelf and 74 Pg C across global continental shelves. Because the carbonate system tended to relax toward its near-initial state after intervention, repeated applications may be feasible in principle and could provide considerable carbon-sink enhancement potential, although their long-term effectiveness, ecological consequences, and practical scalability require further evaluation. Overall, these results indicate that calcium-alkali coupling provides an efficient and mechanistically distinct pathway for engineered enhancement of the oceanic carbon sink.

This study selected Jiaozhou Bay (JZB), a typical semi-enclosed urbanized bay in northern China, to collect carbonaceous aerosol samples. Using the benzene polycarboxylic acid (BPCA) method to quantify aerosol dissolved black carbon (DBC), we analyzed the seasonal variations in its abundance and deposition fluxes, as well as their driving factors. By integrating multiple input sources, we evaluated the critical role of atmospheric deposition in the allochthonous DBC input to the JZB and its contribution to the marine refractory dissolved organic carbon (RDOC) pool. Results indicate that aerosol DBC mainly originated from anthropogenic emissions in the Bohai Rim region and Yellow Sea coastal provinces, with fossil fuel combustion being the dominant source across all seasons. The DBC dry deposition flux peaked in winter, driven primarily by variations in concentration. Significant positive correlations were observed among DBC, water-soluble organic carbon (WSOC) and black carbon (BC). Based on these relationships, linear regression models were established to estimate the dry (6.08 t yr-1) and wet (21.96 t yr-1) DBC deposition fluxes in the JZB. Atmospheric deposition accounted for 25.11%-40.78% of the total allochthonous DBC input to the bay. Consequently, the global atmospheric DBC deposition flux to the ocean was estimated to reach 2.125 ± 0.128 Tg yr-1 (WSOC-based). These findings provide essential data for further refining global carbon cycle models and highlights the potential role of atmospheric DBC deposition in marine carbon sequestration.

Quinolone antibiotics (QNs), owing to their persistence and capacity to promote antimicrobial resistance, have become emerging contaminants of global concern. This study systematically investigated 19 QNs in the North Yellow Sea (NYS) and South Yellow Sea (SYS) to characterize their spatial patterns, sources, and ecological risks. QNs were ubiquitously detected, with significantly higher concentrations in the NYS (60.3-206.8 ng L-1; mean: 136.5 ng L-1) than in the SYS (30.7-128.7 ng L-1; mean: 82.6 ng L-1), showing a distinct pattern of higher in the north, enriched nearshore, and decreasing offshore. Compositional differences revealed that ofloxacin, ciprofloxacin, and norfloxacin dominated in the NYS, reflecting inputs from municipal and hospital wastewater, whereas enrofloxacin, flumequine, and orbifloxacin were more prevalent in the SYS, indicating contributions from aquaculture and veterinary sources. Vertically, the NYS exhibited a profile of strong input and rapid attenuation, while the SYS displayed a pattern of diffuse input and middle layer buffering. Correlation identified salinity, nutrients, and carbonate buffering capacity as key regulators of QNs distribution. Principal Component Analysis (PCA) analyses collectively verified a dual-source fingerprint characterized by concurrent human and aquaculture inputs. Ecological risk assessment suggested algae as the most sensitive group, with ofloxacin identified as a priority pollutant for management. Antimicrobial resistance risk analysis further indicated that ciprofloxacin, ofloxacin, and enrofloxacin exerted major selective pressures, particularly pronounced in the NYS. Overall, this study reveals the dual-source fingerprints and coupled environmental controls of QNs in the Yellow Sea (YS), and proposes to enhance municipal and hospital wastewater treatment in the NYS and to regulate use of antibiotics in aquaculture within the SYS. These results may provide a reference basis and practical guidance for implementing risk-based monitoring and source-oriented management and control in the YS region.

The widespread presence of carbonaceous aerosols exerts profound impacts on global climate and human health. Furthermore, their deposition into coastal waters may effectively contribute to reducing atmospheric carbon levels and enhancing marine carbon inventory. However, the magnitude of carbonaceous aerosol deposition flux and its corresponding carbon sink potential remain poorly constrained. In this study, we examined the geochemical characteristics of carbonaceous aerosols in Jiaozhou Bay (JZB), a typical urbanized coastal bay in China, to identify their sources and sinks. The results show that the concentrations of organic carbon (OC) and black carbon (BC) in the JZB are strongly affected by anthropogenic emissions, exhibiting higher values in winter. The atmospheric total carbon (TC, OC + BC) deposition load to the JZB is 1153.4 t yr(-1), contributing up to 70% of the riverine input, which underscores the prominent role of atmospheric deposition in delivering exogenous carbon to the bay. The annual BC deposition load is 193 t yr(-1), representing a non-negligible marine carbon sink due to its refractory properties. Results from the Bayesian mixture model indicate that C3 plants are the dominant annual source of TC in the JZB (52.6%), followed by liquid fossil fuel and coal combustion. Atmospheric TC in the JZB is dominated by primary emissions, and the elevated TC concentrations in winter are mainly attributed to long-range transport from North China. Our study provides new insights into air quality in human-impacted coastal regions, as well as the transport dynamics and carbon sequestration potential of carbonaceous aerosols during atmosphere-ocean transfer.

Radio telescope is a reflector antenna for receiving radio signals radiated by cosmic celestial body, and microwave receiver is a signal receiving device placed at the focal position of radio telescope. Because of the limited beam width, single beam receiver can only observe the sky area with fixed field of view. In order to improve the observation efficiency of telescope, multi-beam receiver came into being, because it can apply multiple beams at the same time, especially for sky survey or mapping observation. Phased array receiver is a classification of multi-beam receiver. Compared with the traditional multi-beam receiver composed of discrete feed array, the adjacent beams formed by phased array receiver overlap each other, so the field of view of the telescope formed by combining with radio telescope is not only larger, but also more continuous, which can further improve the observation efficiency. Based on the beam width and equivalent field of view of the radio telescope with reflector antenna, combined with the definition of telescope beam deviation and simulation software, this paper analyzes and compares the beam performance of the telescope in the case of multiple continuous beams, and gives the design method of the field of view of phased array receiver. The above work has certain guiding significance for the realization of the front-end array size and field of view of phased array receiver used for reflector antenna, and the array design can be constrained in combination with the field of view requirements in the future.

The most significant distinction between Phased Array Feed(PAF) and traditional multi-beam receivers lies in its beamforming capability, where the purpose of beam calibration is to accurately determine the weighting information for each beam within the field of view. This paper first introduces the beamforming principles and algorithm classifications of PAF. Drawing on the successfully implemented PAF beam calibration schemes of Australian Square Kilometer Array Pathfinder and Aperture Tile in Focus in radio astronomy observations, we present a detailed explanation of the principles and procedures for beam calibration based on the Maximum Signal-to-Noise Ratio(Max-SNR) and Linear Constrained Minimum Variance(LCMV) algorithm. Based on the existing 1.25 GHz microstrip antenna PAF array, we designed a calibration grid comprising seven distinct directional beams and established an experimental platform for PAF array beam calibration based on an analog beamformer with the Max-SNR algorithm. Test results demonstrated a maximum gain fluctuation of 3.2 d B among the seven beams, and we further refined the weighting coefficients for each beam by selecting an appropriate gain target value and introducing a scaling factor, thereby reducing the maximum gain fluctuation between the seven beams to 1.5 dB. Building upon the Max-SNR measurements of the central axial beam's intersection points with adjacent beam patterns and their gain differentials, we implemented a recalibration of the central beam using the LCMV algorithm. This approach enforced gain consistency across predetermined directions, with test results demonstrating a reduction in the central beam's gain fluctuation from 1.6 to 0.9 dB.This research systematically validates the array-level beamforming algorithm and beam calibration scheme,offering significant guidance for future PAF receivers in areas such as beam calibration scheme selection and performance correction. Furthermore, it establishes a solid foundation for the development of advanced digital beamforming technologies with enhanced data processing ability and weighting accuracy.

Marine hypoxia, exacerbated by global warming, has led to the expansion of oxygen minimum zone (OMZ) in the ocean. Based on investigations across four sections in the Tropical Western Pacific Ocean, this study examines the characteristics and key controlling factors of OMZ in the region, with a focus on the interactions between organic matter and hypoxia, using particulate organic carbon (POC) as an example. Results indicate that OMZ are located at depths of 550-1380 m, 290-1120 m, 740-1380 m, and 730-1380 m across the four sections, with a dissolved oxygen threshold of 3.2 mg/L. Seawater stratification plays a crucial role in defining OMZ distribution, with OMZ upper boundaries occurring below the halocline and minimum oxygen levels found beneath the thermocline. Ocean circulation facilitates the westward expansion of the intense OMZ from the Eastern Pacific, influencing its extent in the study area. OMZ enhance the transport of POC to the deep sea, with decomposition rates within OMZ significantly lower than in overlying waters, 17.7 %, 3.1 %, 3.7 %, and 13.6 % in sections A, B, C, and D, respectively. These findings provide valuable insights into the fundamental characteristics, drivers, and biogeochemical implications of OMZ in the Western Pacific.

This study investigates the distribution, sources, and ecological risks of heavy metals (Cr, Cu, Zn, Cd, Pb, and Hg) and metalloid (As) in surface sediments of the Yellow River Estuary intertidal zone during the 2023 water-sediment regulation scheme (WSRS) period (summer) and the non-WSRS period (autumn). The results revealed that metal accumulation in both periods was primarily controlled by the co-adsorption of organic matter and fine particles. Hydrodynamic enhancement during the WSRS period reduced metal accumulation through sediment flushing and dilution, whereas weakened flows in the non-WSRS period promoted metal buildup. Assessment based on the geo-accumulation index (Igeo) and ecological risk index (RI) showed low risks for Cr, Cu, Zn, As, and Pb, while Cd and Hg posed moderate risks. Overall, the ecological risks in the study area remained within a low-risk range. The study highlights WSRS influences on heavy metal behavior and provides a basis for estuarine pollution assessment.

Radio astronomy is a science based on observation. Radio telescope is a reflector antenna used to receive radio signals radiated by cosmic celestial bodies in the field of radio astronomy, and microwave receiver is a signal receiving device placed at the focal position of radio telescope. Phased array receiver is a multi-beam technology, which places a small array antenna at the focal plane of the reflector and realizes the coverage of multiple continuous beams through the beam synthesis network. With the increasing demand for observation, the research and development of multi-beam and high-sensitivity phased array receiver is more extensive. In this paper, a large horn with flat microwave window is designed to provide a low-temperature environment for the front end of the existing phased array receiver. It is simulated and optimized by reflecting surface, and finally compared with the traditional plane microwave window and without any window. Because of its structure, it solves the disadvantage that the phase center of the array is lower than the upper edge of dewar, which is more conducive to the crgogenic design of the whole array refrigeration. It is hoped that the antenna efficiency can be improved, and at the same time, the noise temperature of the whole phased array receiver can be reduced and the sensitivity can be improved.

Sulfonamides (SAs), widely used in human and veterinary medicine, enter the environment through metabolism and accumulate in marine ecosystems, affecting both marine ecosystems and human health. However, there is a lack of systematic research in China regarding the relationship between the usage inputs of SAs and their marine fate. This study presented a comprehensive analysis of data regarding SAs in the marginal seas of China and the usage of SAs from 2009 to 2020 what we can collect, focusing on the distribution and fate of SAs in China's marginal seas. Results supported by restrictive data indicated 22 types of SAs in seawater and 17 in sediments, with sulfamethoxazole and trimethoprim being the two primary SAs. Total SAs concentration in seawater ranged from 0.12 ng/L to 309.71 ng/L, while in sediments it ranged from 0.07 ng/g to 360.4 ng/g, with the Bohai Sea being the most severely polluted marine area by SAs in China. SAs residues varied significantly by year, ranging from 3 tons to 242 tons in the Bohai Sea and from 7 tons to 316 tons in the Yellow Sea. It is noteworthy that the residues of SAs in both the Bohai Sea and Yellow Sea have markedly decreased in recent years, reflecting reduced pollution levels likely attributed to factors such as reduced usage of SAs due to national regulatory measures. This study holds significant scientific value for systematically understanding the status of SAs in China's marginal seas, as well as for formulating strategies for the use, emission, and pollution management of emerging contaminants including SAs.

A significant issue in estimating sea-air CO2 flux (FCO2) in marginal seas is the reliance on single-survey data, ignoring significant diurnal variations and causing large uncertainties. Here, we analyzed 12 days of observations from March to September 2012 near Xiaomai Island in the Southern Yellow Sea to investigate the factors influencing FCO2 and identified wind speed (WS10m) and surface seawater CO2 partial pressure (pCO2,sw) as the primary sources of uncertainty. Based on these, we used the monthly average WS10m instead of real-time WS10m to calculate CO2 flux, significantly reducing the standard deviation (sigma) of FCO2 from 2.58 to 0.53 mmolCm-2d-1. In addition, the pronounced diurnal variation in pCO2,sw introduces considerable uncertainty in CO2 flux observations. Meanwhile, we found that photosynthetically active radiation (PAR) is a major factor controlling the diurnal variation of pCO2,sw. Therefore, we developed a PAR-based correction method for pCO2,sw, which further lowered the sigma of FCO2 to 0.32 mmolCm-2d-1. These improvements provide a new method to reduce uncertainties in FCO2 estimates derived from single-survey data in marginal seas.

This paper achieves indirect monitoring and prediction of the working conditions of the refrigeration system by monitoring the temperature of the receiver Dewar, thereby ensuring that the radio telescope can maintain its optimal operating state continuously and thus guarantee its observational sensitivity. This goal is achieved by fully utilizing existing temperature monitoring data, without the need for additional hardware investment, thus reducing costs and enhancing practicality. By setting thresholds and identification factors, this paper employs the K-means++ clustering algorithm to process the temperature data of the receiver Dewar. The algorithm classifies the data into four categories, representing normal, temperature rise, temperature drop, and ambient temperature states. The results indicate that by monitoring the temperature characteristics of the receiver Dewar, this paper can conduct in-depth analysis of key information such as the refrigeration conditions of the receiver and the gas tightness of the Dewar container, thereby providing a solid basis for fault prediction and maintenance. Furthermore, the K-means++ algorithm exhibits good performance and applicability when processing such data, providing strong support for subsequent research and applications in this paper. This research finding is of great significance for improving the observational sensitivity and stability of radio telescopes.

In recent years, as the ocean absorbs increasing amounts of atmospheric CO2, ocean acidification has intensified. Simultaneously, global warming and enhanced ocean stratification have led to the continuous expansion of the oceanic oxygen minimum zone (OMZ). Under the combined effects of these processes, a key question arises: How will the transport of particulate organic carbon (POC) to the deep ocean (>1,000 m) be affected? Analysis of POC flux data from 547 stations, collected via global sediment traps since the 1980s, reveals that POC flux has increased only in the shallow ocean (<300 m) but has significantly decreased in the deep ocean. These findings suggest that the expansion of the OMZ has not led to more carbon being transported to the deep ocean. Instead, more POC is being retained in the mid-upper ocean (<1,000 m), where its degradation results in significant consumption of dissolved oxygen, contributing to the expansion of the OMZ.