Recently, Yuntao Zhou’s research group has published a research paper entitled “Responses of Horizontally Expanding Oceanic Oxygen Minimum Zones to Climate Change Based on Observations” in Geophysical Research Letters.

Expanding oxygen minimum zones (OMZs, low dissolved oxygen [DO] zones) in the open ocean have been the topic of intense interest, which greatly affect marine organisms, community composition, habitats, as well as change biogeochemical cycles. Previous studies have examined the OMZ range on regional scales or vertical sections. However, annual OMZ areas, trends in OMZ areas, and causes of OMZ expansions remain unclear. Our paper explores the locations and annual areas of global and regional OMZ areas based on observations from 1960 to 2019.

Figure1 Mean DO_min (a), mean DO_min depth (b), temporal trend in DO_min (c), and temporal trend in DO_min depth (d) from 1960 to 2019.

We first calculated the minimum (DO_min) concentration within each DO profile and its depth (DO_min depth), and then obtained the OMZ areas using geostatistical regression. This study revealed that mean minimum DO concentration (DO_min) and its depth are nonuniformly distributed based on observations from 1960 to 2019 (Figure 1). DO_min is lowest in the equatorial oceans and NP, and is highest in the Arctic Ocean. Most oceans show decreasing trends in DO_min, except for the equatorial Pacific and Arabian Sea. Mean DOmin depths appear shallower in the equatorial and polar oceans than in the mid-latitude oceans. The largest increase in DOmin depths occurs in the mid-latitude Southern Hemisphere.

Figure 2 Annual OMZ20 (red) and OMZ60 (blue) areas in oceanic regions from 1960 to 2019.

Over the last six decades, annual global OMZ20 (DO < 20 μmol/kg) and OMZ60 (DO < 60 μmol/kg) areas cover 5%–14% and 15%–32% of the global ocean, respectively (Figure 2). The global OMZ areas show great interannual variability but remain stably large after the late 2000s. Most oceanic regions have experienced significant OMZ expansion, especially the North Pacific. In the North Pacific, OMZ60 and OMZ20 have the largest area expansion rate of 20×10⁴ km² per year and 11×10⁴ km² per year, respectively. Understanding how OMZs will change over the long-term due to climate change is beneficial for the protection of marine resources.

Linkage：

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL097724

References：

Gong, H., Li, C., & Zhou, Y. (2021). Emerging global ocean deoxygenation across the 21st century. Geophysical Research Letters, 48, e2021GL095370. https://doi.org/10.1029/2021GL095370

Zhou, Y., Gong, H., & Zhou, F. (2022). Responses of horizontally expanding oceanic oxygen minimum zones to climate change based on observations. Geophysical Research Letters, 49, e2022GL097724. https://doi.org/10.1029/2022GL097724