Abstract.

"Quantification of oxygen uptake at the ocean surface and its surface-to-interior pathways is crucial for understanding oxygen concentration change in a warming ocean. We investigate the mean meridional global oxygen transport between 1950 and 2009 using coupled physical-biogeochemical model output. We introduce a streamfunction in latitude-oxygen coordinates to reduce complexity in the description of the mean meridional oxygen pathways. [...]".

Source: Wiley Online Library
Authors: Esther Portela et al.
DOI: https://doi.org/10.1029/2023JC020259

Read the full article here.

"The satellite event 'New approaches to combat eutrophication and hypoxia' brought together partners under the GEF-8 Clean and Healthy Ocean Integrated Program (CHO-IP) for introductions and to begin the next phase of tackling eutrophication and hypoxia in 14 national child projects.

Representatives of partner organisations, the Food and Agriculture Organization of the United Nations (FAO), Asian Development Bank (ADB), Development Bank for Latin America (CAF), European Bank for Reconstruction and Development (EBRD), together with the  IOC-UNESCO Global Ocean Oxygen Network (GO₂NE) and the Global Water Partnership (GWP) discussed the program aims and objectives over the course of a 90 minute deoxygenation primer, panel discussion and Q&A session.

Keys points expressed by participants included that:

• Partners across scales and sectors must be involved early, with appropriate financing mechanisms, and engaged throughout to foster project ownership and outcome longevity.
• Scientific data, and methods of access, must be shared openly.
• Science will be unheeded unless it is delivered in a manner that is clear, timely, intelligible, and contextualised and translated to those who have, or will have, the capacity to use it.
• Collaboration with regional actors must be enhanced to aid identification of the most effective science-based actions that will have the highest impact in regional contexts, rather than following global trends.
• International institutions must be encouraged to identify and engage with initiatives of actors in their networks that may already be addressing or adapting to hypoxic conditions.
• Scientifically well-versed personnel are needed in Development Banks and other institutions positioned to leverage existing networks to tackle deoxygenation and other marine issues.

Partners will now move ahead with the program's Global Coordination Project and begin to make connections to national actors and networks working to address eutrophication and hypoxia and implement the program in the 14 participating countries.

The program will synergise with the Global Ocean Oxygen Database and Atlas (GO₂DAT), an endorsed action under the UN Ocean Decade of Ocean Science for Sustainable Development and may lead to the development of new Actions as the program is implemented."

Contact: go2ne-secretariat@unesco.org

More information:

The 'New approaches to combat eutrophication and hypoxia' event

The GEF Clean and Healthy Ocean Program

IOC-UNESCO program announcement

Abstract.

"In the tropical Pacific, weak ventilation and intense microbial respiration at depth give rise to a low dissolved oxygen (O2) environment that is thought to be ventilated primarily by the equatorial current system (ECS). The role of mesoscale eddies and vertical mixing as potential pathways of O2 supply in this region, however, remains poorly known due to sparse observations and coarse model resolution. Using an eddy resolving simulation of ocean circulation and biogeochemistry, we assess the contribution of these processes to the O2 budget balance and find that vertical mixing of O2 [...]".

Source: Wiley Online Library
Authors: Yassir A. Eddebbar et al.
DOI: https://doi.org/10.1029/2023JC020588

Read the full article here.

Abstract.

"The largest continental shelf Oxygen Minimum Zone (OMZ) in the world is formed along the Indian western shelf in the eastern Arabian Sea during the Southwest Monsoon [(SWM); June–September], which is a natural pollution event associated with the coastal upwelling. This study examines the composition, abundance, and distribution of copepods during the Northeast Monsoon [(NEM); November to February] and SWM in 50 m depth zones along the Indian western shelf in the eastern Arabian Sea. [...]".

Source: Science Direct
Authors: Vidhya Vijayasenan et al.
DOI: https://doi.org/10.1016/j.marenvres.2024.106380

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Abstract.

"Hypoxic zones and oceanic deoxygenation are spreading worldwide due to anthropogenic activities and climate change, greatly affecting marine organisms exposed to lowered O2. Yet, the effects of the lowered O2 on phytoplankton are often neglected when studying O2 effects as they are the O2 producers. Here we showed that low O2 (dissolved O2, 150 ± 10 μmol L−1) enhanced the growth of the marine diatom Thalassiosira pseudonana in limited light but reduced it in moderate to inhibitory light and that hypoxia (40 ± 7.5 μmol L−1) reduced its growth at any growth lights. [...]".

Source: Science Direct
Authors: Bokun Chen et al.
DOI: https://doi.org/10.1016/j.envexpbot.2024.105667

Read the full article here.

Abstract.

"Reef fishes in the California Current Ecosystem have evolved in habitats affected by seasonally variable, episodic upwelling of high pCO2 (acidified, low pH) and low dissolved oxygen (deoxygenated) water, which suggests that these fishes might exhibit resilience to ocean acidification (OA) and deoxygenation. Yet, how the fitness of these fish are affected by natural variability in pH and DO over short time scales remains poorly understood, as do the effects of longer-term trends in pH and DO driven by climate change. [...]".

Source: Science Direct
Authors: Corianna Flannery & Eric P. Bjorkstedt
DOI: https://doi.org/10.1016/j.jembe.2024.151993

Read the full article here.

Abstract.

"Ocean acidification and deoxygenation co-occur in marine environments, causing deterioration of marine ecosystems. However, effects of compound stresses on marine organisms and their physiological coping mechanisms are largely unknown. Here, we show how high pCO2 and low dissolved oxygen (DO) cause transcriptomic changes in eggs of a demersal fish (Sillago japonica), which are fully exposed to such stresses in natural environment. Overall gene expression was affected more strongly by low DO than by high pCO2. Enrichment analysis detected significant stress responses such as glycolytic processes in response to low DO. [...]".

Source: Science Direct
Authors: Akira Iguchi et al.
DOI: https://doi.org/10.1016/j.scitotenv.2023.169484

Read the full article here.

Abstract.

"Abrupt changes in ocean biogeochemical variables occur as a result of human-induced climate forcing as well as those which are more gradual and occur over longer timescales. These abrupt changes have not yet been identified and quantified to the same extent as the more gradual ones. We review and synthesise abrupt changes in ocean biogeochemistry under human-induced climatic forcing. We specifically address the ocean carbon and oxygen cycles because the related processes of acidification and deoxygenation provide important ecosystem hazards. [...]".

Source: Biogeosciences
Authors: Christoph Heinze et al.
DOI: https://doi.org/10.5194/bg-2023-182

Read the full article here.

Full title: "Marine anoxia initiates giant sulfur-oxidizing bacterial mat proliferation and associated changes in benthic nitrogen, sulfur, and iron cycling in the Santa Barbara Basin, California Borderland"

Abstract.

"The Santa Barbara Basin naturally experiences transient deoxygenation due to its unique geological setting in the southern California Borderland and seasonal changes in ocean currents. Long-term measurements of the basin showed that anoxic events and subsequent nitrate exhaustion in the bottom waters have been occurring more frequently [...]".

Source: Biogeosciences
Authors: David J. Yousavich et al.
DOI: https://doi.org/10.5194/bg-21-789-2024

Read the full article here.

Abstract.

"Accelerated Arctic warming has raised concerns about future environmental conditions in the Bering Sea, one of the world's most productive marine ecosystems. Marine Isotope Stage (MIS) 11 (424–374 ka), a period with orbital parameters similar to those of the current interglacial (Holocene), is thought to be a suitable analog to predict future marine environments. Here, we reconstruct paleoredox changes in the Bering Sea over the last 800 kyr using high-resolution U/Th ratios from four sites, which were sampled by the Integrated Ocean Drilling Program (IODP) Expedition 323. [...]".

Source: Science Direct
Authors: Xuguang Feng et al.
DOI: https://doi.org/10.1016/j.palaeo.2023.111982

Read the full article here.