About this Research Topic
Deoxygenation of the ocean is a key stressor of marine ecosystems and biogeochemical cycles. Climate projections based on earth system models (ESMs) suggest a significant decline in global oxygen inventory during the next century under the persistent emission of greenhouse gases. Oxygen minimum zones (OMZs), located close to the productive eastern boundary upwelling systems (EBUSs) and the Arabian Sea, may dramatically expand, impacting regional marine habitats and ecosystem services. However, coupled ocean-biogeochemical models still struggle to reproduce the observed oxygen trends and variability of the past decades, indicating that key physical and biogeochemical processes are still poorly represented. Therefore, the scientific community urgently needs to identify and reduce the uncertainties related to the key physical and biogeochemical processes governing the oxygen budget in order to improve our confidence in predicting climate change impact on marine ecosystems and biogeochemical cycles.
ESMs and coupled ocean-biogeochemical simulations have difficulties in reproducing the correct magnitude and spatial patterns of observed oxygen trends. Oxygen concentration is difficult to accurately simulate, as the determination of the oxygen budget involves a wide range of mechanisms acting at different temporal and spatial scales. These mechanisms are related to both ocean circulation (strength of wind driven circulation, meridional overturning, water mass formation rate, and mesoscale activity) and biogeochemical cycles (export production, remineralization rate, ecological communities, microbial loop, and anaerobic N-cycle processes). Uncertainties accumulate and, consequently, the models participating in the Coupled Model Intercomparison Project Phase 5 and 6 (CMIP5 / CMIP6) effort do not agree on the magnitude of the oxygen decline and the OMZ expansion. However, the CMIP6 dataset has not been fully exploited as yet. Several CMIP6 models include large ensembles, allowing robust separation of natural variability and forced response, time of emergence, as well as exploring predictability of oxygen from seasonal to decadal timescales. Single model experiments can be performed to understand the importance of specific processes. Recent advances in eddy resolving and regional model simulations coupled to ocean biogeochemistry provide new research avenues to explore the effects of the mesoscale and submesoscale processes on the oxygen cycle and identify the role of model resolution in improving the model biases and model-observation discrepancies. Accumulated observations from the last several decades along with recent deployment of BGC-Argo floats could be exploited to estimate interannual variability and multi-decadal trends, as well as validate model hindcasts. This Research Topic aims to assess and quantify simulated uncertainties in order to produce more robust future oxygen level projections.
This Research Topic includes original research, perspectives, and reviews, and welcomes studies that investigate and discuss the following aspects:
- Model validation and observational analyses (time series, floats, historical measurements)
- Near term predictions and projections of dissolved oxygen levels at temporal scales ranging from interannual to centennial and spatial scales from regional to global
- Analysis of model ensembles and robustness
- Model sensitivity to biogeochemical or physical parameters or their processes
- Impact of model resolution and role of mesoscale and submesoscale processes on oxygen cycling
- Disentangling natural variability and anthropogenic trends in models or observations
Keywords: deoxygenation, oxygen minimum zones, model uncertainty, ocean biogeochemical model, climate projection, climate change, hindcast
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