Hypoxic Zone Research Articles

Spatial Distribution and Seasonal Variation of Hypoxic Zone in the Eastern Equatorial Indian Ocean

Spatial Distribution and Seasonal Variation of Hypoxic Zone in the Eastern Equatorial Indian Ocean

Macrozoobenthic Diversity along an Oxygen Gradient in the Deep Trough of the Gulf of St. Lawrence (Canada)

In 2015, we studied the macrozoobenthic community composition along a dissolved oxygen gradient in the deep trough of the Gulf of St. Lawrence (Canada). We sampled the seabed at nine stations using box corers (three replicates per station), starting in the outer Gulf and ending in the Lower St. Lawrence River Estuary. We found four different communities dominated by polychaetes, crustaceans, and molluscs, with the emphasis shifting from mollusc to polychaete communities as oxygen saturation decreased. Contrary to our expectations, the stations furthest upstream in the estuary with the lowest oxygen saturation levels had the highest species diversity, and also the highest density and biomass values. Key genera of the hypoxic zone included bivalves (Thyasira), cumaceans (Diastylis), amphipods (Harpinia), and polychaetes such as Ampharete, Ceratocephale, Galathowenia, and Trochochaeta. We attribute this to the stability of the environmental conditions and the absence of stress, where the constant supply of oxygen, even at low concentrations, seems to be more important than the absolute oxygen concentration.

Hypoxic niches attract and sequester tumor-associated macrophages and cytotoxic T cells and reprogram them for immunosuppression

Glioblastoma (GBM), a highly lethal brain cancer, is notorious for immunosuppression, but the mechanisms remain unclear. Here, we documented a temporospatial patterning of tumor-associated myeloid cells (TAMs) corresponding to vascular changes during GBM progression. As tumor vessels transitioned from the initial dense regular network to later scant and engorged vasculature, TAMs shifted away from perivascular regions and trafficked to vascular-poor areas. This process was heavily influenced by the immunocompetence state of the host. Utilizing a sensitive fluorescent UnaG reporter to track tumor hypoxia, coupled with single-cell transcriptomics, we revealed that hypoxic niches attracted and sequestered TAMs and cytotoxic T lymphocytes (CTLs), where they were reprogrammed toward an immunosuppressive state. Mechanistically, we identified chemokine CCL8 and cytokine IL-1β as two hypoxic-niche factors critical for TAM trafficking and co-evolution of hypoxic zones into pseudopalisading patterns. Therefore, perturbation of TAM patterning in hypoxic zones may improve tumor control.

Modelling effects of nutrients and hypoxia on Lake Erie's central basin foodweb

Abstract Hypoxia (dissolved oxygen <2 mg l-1) has long been a prevalent feature of the central basin of Lake Erie. Studies of the sublethal impacts of hypoxia on fishes have focused on individual species feeding rates, behavior and spatial distributions over short time periods, but the long-term effects on the fish community and its foodweb are poorly known. Sublethal effects of hypoxia on fish include: interrupting their vertical migration, displacing them from bottom habitats either up into the water column or away from the hypoxic zones, altering predator-prey relationships by segregation or aggregation of predators and their prey, and increasing fishing mortality by concentrating fish at the edge of hypoxic zones. We used the Ecopath with Ecosim foodweb model to investigate the singular and combined effects of nutrient concentration and hypoxia on the foodweb structure in Lake Erie's central basin. Our model tracked predator-prey interactions and population biomass of 33 model groups. We balanced the model in Ecopath and calibrated it against biomass time series data from 1996 up to 2020. Model simulations were run with varied nutrients (from 20 to 220% of the previous nutrient loading target level) and hypoxia (none, average summer value from 1996 to 2017, historical high) as forcing variables on the foodweb. Model results suggested that nutrients had positive, non-linear effects on foodweb biomass, while hypoxia decreased biomass of benthos, benthivorous fishes, and some omnivores, but increased biomass of plankton and planktivorous fishes. Nutrient effects were greater than hypoxia effects on the foodweb. Results of the foodweb model analysis may inform water quality and fisheries management strategies for Lake Erie's central basin.

Out of oxygen: Stratification and loading drove hypoxia during a warm, wet, and productive year in a Great Lakes estuary

Hypolimnetic hypoxia, or low oxygen in bottom waters, impairs ecosystem services of freshwater lakes and estuaries globally. Both hypoxia incidence and intensity are increasing around the world due to eutrophication and climate change. As the hypolimnion becomes hypoxic and ultimately anoxic, sediment-bound legacy phosphorus is released. Water column mixing due to large storm events or fall turnover entrains these nutrients to the surface, causing harmful algal blooms. To assess the dynamics of hypoxia throughout the growing season, we evaluated Muskegon Lake, where hypoxia recurs annually, utilizing high-frequency time-series data from the Muskegon Lake Observatory (MLO) buoy (https://www.gvsu.edu/wri/buoy/), biweekly nutrient sampling, and seasonal respiration experiments during 2021. While water-column stratification set the stage for hypolimnetic hypoxia, frequent wind-mixing events, and episodic intrusions of cold, oxygenated, upwelled Lake Michigan waters intermittently reduced the thickness or intensity of the hypoxic zone. Respiration experiments revealed that riverine and surface organic matter inputs contributed most to hypolimnetic hypoxia in the spring, whereas surface inputs did so during summer, and riverine inputs during fall, indicating seasonally variable sources drive hypoxia. Biweekly measurements indicated increased soluble reactive phosphorus in the hypolimnion during anoxia via internal phosphorus loading from the sediment with the potential for fueling surface blooms with net export of soluble reactive phosphorus and total phosphorus to nearshore Lake Michigan. Our findings on the role of seasonally changing temperature, loading, phytoplankton production, hypolimnetic respiration, and internal phosphorus loading in shaping hypoxia dynamics have relevance to similarly afflicted ecosystems in the Great Lakes Basin.

Hypoxia in the Bohai Bay, China: distributions, causes and mechanisms

The Haihe River system is a major conduit of land-based pollution into the Bohai Sea in North China, This study presented the first-ever observation of hypoxia in the Haihe River estuary, providing valuable insights into the complex interplay between physical and biochemical factors influencing hypoxia in estuarine systems. The research found seasonal variations in DO distribution in the estuaries of the Haihe and Yongdingxin Rivers. Hypoxia emerged in summer at the bottom of the Haihe River estuary and dissipated in autumn, with the minimum DO concentration of 1.85 mg/L recorded at the bottom of the HH-2 station. Within the hypoxic zone, the average DO concentration was 4.02 mg/L, and the average of DO saturation was less than 0.4. This study also identified the primary drivers of summer hypoxia as a combination of physical and biochemical factors, with water stratification due to hydrodynamic factors limiting exchange and reoxygenation between different water layers. In addition, the decomposition of organic matter in the bottom consumed a significant amount of dissolved oxygen.The significantly higher DO concentration and saturation in autumn compared to summer suggested the possible existence of seasonal hypoxia in the Haihe estuary. This study of hypoxia in the Haihe River estuary contribute to a better understanding of the factors that influence seasonal hypoxia. The findings have important implications for the management and remediation of hypoxia in the Haihe estuary and other estuarine systems.

Intercomparison of three spatially-resolved, process-based Lake Erie hypoxia models

Lake Erie hypoxia models have been developed for multiple objectives, including 1) to support development of phosphorus loading targets, and 2) to provide a real-time forecast of hypoxic zone location and movement. Nutrient management objectives have focused on spatially-averaged metrics, including the mean August-September hypoxic area or mean hypolimnetic dissolved oxygen (DO). However, the ability to model spatial patterns of bottom DO is also important for predicting impacts on drinking water intakes, benthic habitat, and biogeochemical cycling of nutrients. A previous binational effort used multiple models to develop load-response curves to guide setting phosphorus load reduction targets to achieve ecosystem objectives under the Great Lakes Water Quality Agreement. Models were assessed individually, using different sets of observations, obscuring differences in modeled spatial patterns of hypoxia. In a first binational effort, we compared three previously developed Lake Erie hypoxia models in terms of predicted hypoxic area, as well as spatial patterns of hypoxia. All models were similar in prediction of hypoxic area in 2012, but differed in 2013. Several differences in model constructs likely contributed to varying predictions of hypoxia spatial patterns, including sources and sinks of DO in the water column, parameterization of sediment oxygen demand, simulation of vertical mixing, and representation of atmospheric and riverine forcing. This study underscores the importance of comparing models, with various representations of ecological processes, using a common set of visualizations, metrics, and observations before generating ensemble modeling load-response curves to better inform lake management applications.

Microbe, climate change and marine environment: Linking trends and research hotspots

Microbes, or microorganisms, have been the foundation of the biosphere for over 3 billion years and have played an essential role in shaping our planet. The available knowledge on the topic of microbes associated with climate change has the potential to reshape upcoming research trends globally. As climate change impacts the ocean or marine ecosystem, the responses of these “unseen life” will heavily influence the achievement of a sustainable evolutionary environment. The present study aims to identify microbial-related research under changing climate within the marine environment through the mapping of visualized graphs of the available literature. We used scientometric methods to retrieve documents from the Web of Science platform in the Core Collection (WOSCC) database, analyzing a total of 2767 documents based on scientometric indicators. Our findings show that this research area is growing exponentially, with the most influential keywords being “microbial diversity,” “bacteria,” and “ocean acidification,” and the most cited being “microorganism” and “diversity.” The identification of influential clusters in the field of marine science provides insight into the hot spots and frontiers of research in this area. Prominent clusters include “coral microbiome,” “hypoxic zone,” “novel Thermoplasmatota clade,” “marine dinoflagellate bloom,” and “human health.” Analyzing emerging trends and transformative changes in this field can inform the creation of special issues or research topics in selected journals, thus increasing visibility and engagement among the scientific community.

Small-scale oxygen distribution patterns in a coral reef

One mechanism giving fleshy algae a competitive advantage over corals during reef degradation is algal-induced and microbially-mediated hypoxia (typically less than 69.5 µmol oxygen L−1). During hypoxic conditions oxygen availability becomes insufficient to sustain aerobic respiration in most metazoans. Algae are more tolerant of low oxygen conditions and may outcompete corals weakened by hypoxia. A key question on the ecological importance of this mechanism remains unanswered: How extensive are local hypoxic zones in highly turbulent aquatic environments, continuously flushed by currents and wave surge? To better understand the concert of biological, chemical, and physical factors that determine the abundance and distribution of oxygen in this environment, we combined 3D imagery, flow measurements, macro- and micro-organismal abundance estimates, and experimentally determined biogenic oxygen and carbon fluxes as input values for a 3D bio-physical model. The model was first developed and verified for controlled flume experiments containing coral and algal colonies in direct interaction. We then developed a three-dimensional numerical model of an existing coral reef plot off the coast of Curaçao where oxygen concentrations for comparison were collected in a small-scale grid using fiberoptic oxygen optodes. Oxygen distribution patterns given by the model were a good predictor for in situ concentrations and indicate widespread localized differences exceeding 50 µmol L-1 over distances less than a decimeter. This suggests that small-scale hypoxic zones can persist for an extended period of time in the turbulent environment of a wave- and surge- exposed coral reef. This work highlights how the combination of three-dimensional imagery, biogenic fluxes, and fluid dynamic modeling can provide a powerful tool to illustrate and predict the distribution of analytes (e.g., oxygen or other bioactive substances) in a highly complex system.

Physical drivers of chlorophyll and nutrients variability in the Southern-Central Arabian Gulf

The southern-central Arabian Gulf demonstrates a poor understanding of nutrients and chlorophyll dynamics in physical-biogeochemical settings. Here, using data of chlorophyll, nutrients and hydrographic parameters collected in two cruises in summer 2019 and winter 2020, we examined variability in nutrients and chlorophyll concentrations, and the driving mechanisms. Summer thermal stratification enhanced by intrusion of fresher surface water plume from the Arabian Sea developed a hypoxic zone (DO < 2.0 mL/L) below the thermocline. Nitrate and ammonium summer concentrations (2.24 ± 0.36, 1.70 ± 0.17 μM) were about 3 times the winter concentrations. Nutrient stoichiometry showed a Redfield-like nitrogen/phosphorus (N:P) ratio in summer (15.9:1) and a nitrogen limitation in winter (N:P = 4:1). Chlorophyll-a content in summer (mean = 0.80 mg/m3) was about 1.4 times the winter concentration (mean = 0.58 mg/m3) (p > 0.05). Photo-protective carotenoids content in summer (0.59 mg/m3) was about 2.7 times their winter concentration. Winter cooling resulted in downwelling of dense water on the shallow coastal banks, which enhanced near bottom oxygen concentrations and swept away nutrient-rich water resulting in lower winter chlorophyll. This research features aspects of the physical and biogeochemical drivers underpinning the dynamics of nutrients and chlorophyll in the central Gulf.

Dissolved oxygen shapes the archaeal communities in the seawater of Changjiang Estuary

Archaea play a significant role in regulating the biogeochemical processes of marine ecosystems. In this study, the high-throughput sequencing was used to explore the archaeal communities in the seawater from the hypoxic and non-hypoxic zones of the Changjiang Estuary. Thaumarchaeota dominated the archaeal communities in the hypoxic zones (bottom water), and Euryarchaeota were mainly distributed in the non-hypoxic zones (surface water). However, the diversity and richness of the archaeal communities showed no obvious difference in the hypoxic and non-hypoxic zones. Moreover, Thaumarchaeota and Nitrosopumilales were positively correlated with salinity, but negatively correlated with dissolved oxygen (DO) and temperature. Temperature, phosphorus, and dissolved oxygen had significant correlations with archaeal richness, while ammonia nitrogen was correlated with archaeal diversity. The networks of archaeal communities possessed a high proportion of positive interspecific interaction and revealed that the Marine Group II species may play distinct roles in both hypoxic and non-hypoxic zones. The current work assessed the influence of dissolved oxygen on the archaeal community patterns and network interaction, thereby illumining the community structure shift of archaea caused by the hypoxia phenomenon in the Changjiang Estuary, which laid a foundation for the future studies on the ecological functions of archaea in estuary ecosystems.

Evaluation of long-term impact of cereal rye as a winter cover crop in Illinois

Extensive tile drainage usage combined with excess nitrogen fertilization has triggered nutrient loss and water quality issues in Illinois, which over time endorsed the hypoxia formation in the Gulf of Mexico. Past research reported that the use of cereal rye as a winter cover crop (CC) could be beneficial in reducing nutrient loss and improving water quality. The extensive use of CC may aid in reducing the hypoxic zone in the Gulf of Mexico. The objective of this study is to analyze the long-term impact of cereal rye on soil water‑nitrogen (N) dynamics and cash crops growth in the maize-soybean agroecosystem in the state of Illinois. A gridded simulation approach was developed using the DSSAT model for the CC impact analysis. The CC impacts were estimated for the last two decades (2001–2020) for two fertilization scheduling (FA-SD = Fall and side-dress N and SP-SD = Spring pre-plant and side-dress N) comparing between CC scenario (FA-SD-C/SP-SD-C) with no CC (NCC) scenario (FA-SD-N/SP-SD-N). Our results suggest that the nitrate-N loss (via tile flow) and leaching reduced by 30.6 % and 29.4 %, assuming extensive adaptation of cover crop. The tile flow and deep percolation decreased by 20.8 % and 5.3 %, respectively, due to cereal rye inclusion. The model performance was relatively poor in simulating the CC impact on soil water dynamics in the hilly topography of southern Illinois. Generalizing changes in the soil properties (due to cereal rye inclusion) from the field scale to whole state (regardless of soil type) could be one of the possible limitations in this research. Overall, these findings substantiated the long-term benefits of cereal rye as a winter cover crop and found the spring N fertilizer application reduced nitrate-N loss compared to fall N application. These results could be helpful in promoting the practice in the Upper Mississippi River basin.

Past Analogues of Deoxygenation Events in the Mediterranean Sea: A Tool to Constrain Future Impacts

Human-induced carbon emissions are altering the modern climate, with severe repercussions on ecosystems. Among others, anthropogenic pressure is causing deoxygenation of the bottom water, with the widespread establishment of hypoxic zones in several Mediterranean areas. The geological archives allow investigating past deoxygenation dynamics (sapropel events) and their impact on marine ecosystems. Here, we compare the causes and the evolution of deoxygenation dynamics which occurred during two different time periods (Messinian and Holocene) in different paleoceanographic settings based on their micropaleontological content. The Messinian sapropel events are the result of increased export productivity during a relatively cold and arid context, triggering bottom anoxic conditions. The Holocene sapropel formed in response to weakening/stopping of the thermohaline circulation due to increasing temperature and freshwater input. Our results suggest that the deoxygenation dynamics in the Mediterranean in the near future will not follow the trend characteristic of the Holocene deep-sea sapropel because of the predicted drying trend. Differently, the paleoceanographic setting triggering the Messinian shallow-sea sapropels is comparable with the modern situation in different Mediterranean areas, where human-induced eutrophication is promoting deoxygenation. Based on these results, we suggest that the patchy deoxygenation trend in the Mediterranean Sea caused by climate warming may lead to a drastic change in the ecosystem services which would likely impact human activities.

Bacteria-Driven Tumor Microenvironment-Sensitive Nanoparticles Targeting Hypoxic Regions Enhances the Chemotherapy Outcome of Lung Cancer.

Chemotherapy still plays a dominant role in cancer treatment. However, the inability of conventional chemotherapeutic drugs to reach the hypoxic zone of solid tumors significantly weakens their efficacy. Bacteria-mediated drug delivery systems can be an effective targeting strategy for improving the therapeutic outcomes in cancer. Anaerobic bacteria have the unique ability to selectively transport drug loads to the hypoxic regions of tumors. We designed a Bifidobacterium infantis (Bif)-based biohybrid (Bif@PDA-PTX-NPs) to deliver polydopamine (PDA)-coated paclitaxel nanoparticles (PTX-NPs) to tumor tissues. The self-driven Bif@PDA-PTX-NPs maintained the toxicity of PTX as well as the hypoxic homing tendency of Bif. Furthermore, Bif@PDA-PTX-NPs significantly inhibited the growth of A549 xenografts in nude mice, and prolonged the survival of the tumor-bearing mice compared to the other PTX formulations without any systemic or localized toxicity. The Bif@PDA-PTX-NPs biohybrids provide a new therapeutic strategy for targeted chemotherapy to solid tumors.

Transport of nutrients into the southern Gulf of Mexico by the Grijalva–Usumacinta rivers

AbstractNutrient transport by rivers strongly influences ecosystem productivity and hypoxia zone formation in coastal areas. In this study, we estimated the transport of nitrogen and phosphorus by the Grijalva and Usumacinta rivers that combined represent the second largest source of fresh water into the Gulf of Mexico. Water samples were collected monthly within an annual cycle at different sites (mainstem and tributaries) in the Lower Grijalva and Usumacinta basins to encompass the seasonal variation in discharge. Nitrogen (total nitrogen, nitrate‐N, ammonium‐N, and nitrite‐N), phosphorus (total phosphorus, soluble reactive phosphorus), and chlorophyll concentrations were determined, and annual loads estimated using the Beale ratio approach. Nutrient and chlorophyll concentrations were greater in the Grijalva than in the Usumacinta River. Stronger seasonal patterns in nutrient concentrations and discharge were identified in the Usumacinta, evincing the flow regulation experimented by the Grijalva. In the Grijalva, higher nutrient concentrations were measured at the De la Sierra and Pichucalco rivers, compared to the regulated Carrizal. TN:TP ratios were greater during the dry season in both rivers, and higher TN:TP occurred in the Usumacinta than in the Grijalva. The Usumacinta showed greater nutrient loads (nitrogen, 26790.6 × 103 kg year−1; phosphorus, 3056.9 × 103 kg year−1) than the Grijalva (nitrogen 19974.7 × 103 kg year−1; phosphorus, 1941.8 × 103 kg year−1). However, the Grijalva River showed higher soluble reactive phosphorus and ammonium‐N loads and yields than the Usumacinta, likely explained by greater delivery of urban wastewater in the lower Grijalva Basin. The Grijalva–Usumacinta represents an important source of nitrogen compared to other rivers draining into the Gulf of Mexico, even though more disturbed rivers can exceed the phosphorus load. This study can contribute to the modelling of nutrient delivery into the Gulf of Mexico and to better understand the influence of tropical rivers in the formation of coastal hypoxia.

Temporal and spatial evolution of bottom-water hypoxia in the St Lawrence estuarine system

Abstract. Persistent hypoxic bottom waters have developed in the Lower St Lawrence Estuary (LSLE) and have impacted fish and benthic species distributions. Minimum dissolved oxygen concentrations decreased from ∼ 125 µmol L−1 (38 % saturation) in the 1930s to ∼ 65 µmol L−1 (21 % saturation) in 1984. Minimum dissolved oxygen concentrations remained at hypoxic levels (&lt; 62.5 µM = 2 mg L−1 or 20 % saturation) between 1984 and 2019, but in 2020, they suddenly decreased to ∼ 35 µmol L−1. Concurrently, bottom-water temperatures in the LSLE have increased progressively from ∼ 3 ∘C in the 1930s to nearly 7 ∘C in 2021. The main driver of deoxygenation and warming in the bottom waters of the Gulf of St Lawrence and St Lawrence Estuary is a change in the circulation pattern in the western North Atlantic, more specifically a decrease in the relative contribution of younger, well-oxygenated and cold Labrador Current Waters to the waters of the Laurentian Channel, a deep valley that extends from the continental shelf edge, through Cabot Strait, the gulf and to the head of the LSLE. Hence, the warmer, oxygen-depleted North Atlantic Central Waters carried by the Gulf Stream now make up nearly 100 % of the waters entering the Laurentian Channel. The areal extent of the hypoxic zone in the LSLE has varied since 1993 when it was first estimated at 1300 km2. In 2021, it reached 9400 km2, extending well into the western Gulf of St Lawrence. Severely hypoxic waters are now also found at the end of the two deep channels that branch out from the Laurentian Channel, namely, the Esquiman Channel and Anticosti Channel.

Ovarian masculinization and reproductive impairment in 3 species of groundfish in and around the hypoxic zone in the Gulf of Mexico

Ovarian masculinization and reproductive impairment in 3 species of groundfish in and around the hypoxic zone in the Gulf of Mexico

Metabolic Responses and Resilience to Environmental Challenges in the Sedentary Batrachoid Halobatrachus didactylus (Bloch &amp; Schneider, 1801)

In the context of climate change, warming of the seas and expansion of hypoxic zones are challenges that most species of fish are, or will be subjected to. Understanding how different species cope with these changes in their environment at the individual level can shed light on how populations and ecosystems will be affected. We provide first-time estimates on the metabolic rates, thermal, and oxygen-related limits for Halobatrachus didactylus, a coastal sedentary fish that lives in intertidal environments of the Northeast Atlantic. Using respirometry in different experimental designs, we found that this species is highly resistant to acute thermal stress (CTmax: 34.82 ± 0.66 °C) and acute hypoxia (Pcrit: 0.59-1.97 mg O2 L-1). We found size-specific differences in this stress response, with smaller individuals being more sensitive. We also quantified its aerobic scope and daily activity patterns, finding this fish to be extremely sedentary, with one of the lowest standard metabolic rates found in temperate fish (SMR: 14.96 mg O2 kg-1h-1). H. didactylus activity increases at night, when its metabolic rate increases drastically (RMR: 36.01 mg O2 kg-1h-1). The maximum metabolic rate of H. didactylus was estimated to be 67.31 mg O2 kg-1h-1, producing an aerobic scope of 52.35 mg O2 kg-1h-1 (77.8% increase). The metrics obtained in this study prove that H. didactylus is remarkably resilient to acute environmental variations in temperature and oxygen content, which might enable it to adapt to the extreme abiotic conditions forecasted for the world's oceans in the near future.

Expression of HIF-1α and markers of angiogenesis and metabolic adaptation in molecular subtypes of breast cancer

Hypoxic zones exist in solid tumors, where oxygen levels are significantly lower than in normal tissues. Hypoxia makes chemo-radiation therapeutics less effective and renders the metastatic potential more favorable. Emerging research has found that the transcriptional expression of hypoxia-inducible factor-1alpha (HIF-1α) promotes the transcription of vascular endothelial growth factor A (VEGF-A) and Hexokinase-I (HK-I), which are associated to cellular growth, angiogenesis, and metastatic invasion in many malignancies. However, it is still unclear whether VEGFA and HK-I expression has any influence on survival based on the intrinsic subtypes of breast cancer. Their prognostic significance remains a debatable topic. In the present study, quantitative Real-time polymerase chain reaction (qRT-PCR) was employed to check the relative expression of HIF-1α, VEGF-A and HK-I. The hazard ratios (HR) of breast cancer-specific and overall mortality were calculated using Cox proportional hazards model, which were adjusted for demographic, clinicopathological, and associated molecular variables, as well as the diagnosis year. The relative mRNA expression levels of HIF-1α (p = 0.0010) and VEGFA (p = 0.0119) were significantly higher in tumor tissues. The expression of both HIF-1α (p = 0.0111) and VEGFA (p = 0.0078) was higher in the TNBC group of breast cancers, while HK-I (p = 0.0106) was higher in ER/PR-positive, HER2-negative group. HIF-1α and HK-I overexpression were associated with a higher likelihood of survival, while overexpression of VEGFA was associated with a low survival rate, although it was not statistically significant.

North-south differences in hypoxia and nitrogen cycle of the East China Sea over the last century indicated by sedimentary bacteriohopanepolyols

Coastal hypoxic zones are expanding due to anthropogenic activities and climate changes. Increased hypoxia has greatly affected the marine nitrogen cycle. There are two typical seasonal hypoxic core areas in the north and south of the East China Sea (ECS). However, the interannual variations, north-south differences in hypoxia and their effects on the nitrogen cycle are still poorly understood. This study investigated bacteriohopanepolyols (BHPs), especially newly developed marine anammox bacteria and hypoxic biomarker bacteriohopanetetrol stereoisomer (BHT-x) and cyanobacterial nitrogen fixation biomarker 2-methyl BHT in two sediment cores, aiming to reconstruct hypoxia and nitrogen cycle records in the northern and southern hypoxic zones of the ECS over the last century. The results showed that BHT-x ratio in northern core 3100–2 presented higher values since 1960s (>0.2) and increased after 2000 (0.25–0.57), while it decreased in southern core DH6–1 after 2000 (0.03–0.11), indicating the continuously intensified hypoxia in the northern area and significantly weakened hypoxia in the southern area. Hypoxia is mainly associated with organic matter degradation and seawater stratification. The similar temporal increases of BHT-x ratios and marine-derived organic matter (MOM) contents in core 3100–2 suggest that eutrophication-driven MOM degradation is the main reason for hypoxia formation, which is exacerbated by strong water stratification there. Differently, although MOM contents still increased in core DH6–1 after 2000, the hypoxia weakened and even disappeared due to lessened stratification. In addition, the temporal variations of BHT-x and 2-methyl BHT in both cores indicated that anammox and nitrogen fixation simultaneously increased during periods of hypoxia. The co-variation suggests that hypoxia promotes anammox, and nitrogen loss may induce an increase in nitrogen fixation to compensate for nitrogen availability.