Evaluation of methodologies for inferring temporal changes of oceanic respiration and ventilation under changing climate

Observations suggest that the dissolved oxygen inventory in the ocean has declined by over 2% since the middle of the 20th century. Such rapidly ongoing ocean deoxygenation raises concerns of widespread ocean anoxia associated with major mass extinction under a warming climate. Mechanistically understanding ocean deoxygenation requires quantifying the temporal change of ocean ventilation and respiration. However, direct measurements of these processes are very sparse due to methodological limitations. Therefore, indirect measurements based on available measurements are commonly used to estimate the aerobic respiration rates (oxygen utilization rate, OUR) and ventilation strength (Inverse Gaussian Transit Time Distribution, IG-TTD) in the real ocean.  This thesis evaluates their reliability in detecting temporal changes.

The results discussed in this thesis lead to the overall conclusion that in regions where different water masses mix, both OUR and IG-TTD cannot estimate robust mean state and temporal change of respiration rates and seawater age due to inherent imperfect assumptions. However, in the North Atlantic, OUR and the mean age of IG-TTD robustly reconstruct the temporal change of respiration rates and seawater age as inferred from model results. Current analysis of water age from decades of measurements suggests that intermediate water has become younger while the deep ocean has become older. Models suggest the slowing-down ventilation in the deep ocean will continue for centuries even if carbon dioxide emission stops today, and deep ocean deoxygenation seems unavoidable.

Rights

Use and reproduction:


CC BY 4.0

Please note that individual components of the publication may be subject to other licensing or copyright conditions.

Cite

Citation style:
Could not load citation form.