Oxygen minimum zones in the eastern tropical Atlantic and Pacific oceans

• Published in: Progress in Oceanography
• Main Authors: Karstensen, Johannes, Stramma, Lothar, Visbeck, Martin
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2008
• Subjects: Pacific; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/7187/; https://oceanrep.geomar.de/id/eprint/7187/1/95_Karstensen_2008_OxygenMinimumZonesInThe_Artzeit_pubid9275.pdf; https://oceanrep.geomar.de/id/eprint/7187/3/1-s2.0-S0079661108000670-main.pdf; https://doi.org/10.1016/j.pocean.2007.05.009

Within the eastern tropical oceans of the Atlantic and Pacific basin vast oxygen minimum zones (OMZ) exist in the depth range between 100 and 900 m. Minimum oxygen values are reached at 300–500 m depth which in the eastern Pacific become suboxic (dissolved oxygen content <4.5 μmol kg−1) with dissolved oxygen concentration of less than 1 μmol kg−1. The OMZ of the eastern Atlantic is not suboxic and has relatively high oxygen minimum values of about 17 μmol kg−1 in the South Atlantic and more than 40 μmol kg−1 in the North Atlantic. About 20 (40%) of the North Pacific volume is occupied by an OMZ when using 45 μmol kg−1 (or 90 μmol kg−1, respectively) as an upper bound for OMZ oxygen concentration for ocean densities lighter than σθ < 27.2 kg m−3. The relative volumes reduce to less than half for the South Pacific (7% and 13%, respectively). The abundance of OMZs are considerably smaller (1% and 7%) for the South Atlantic and only ∼0% and 5% for the North Atlantic. Thermal domes characterized by upward displacements of isotherms located in the northeastern Pacific and Atlantic and in the southeastern Atlantic are co-located with the centres of the OMZs. They seem not to be directly involved in the generation of the OMZs. OMZs are a consequence of a combination of weak ocean ventilation, which supplies oxygen, and respiration, which consumes oxygen. Oxygen consumption can be approximated by the apparent oxygen utilization (AOU). However, AOU scaled with an appropriate consumption rate (aOUR) gives a time, the oxygen age. Here we derive oxygen ages using climatological AOU data and an empirical estimate of aOUR. Averaging oxygen ages for main thermocline isopycnals of the Atlantic and Pacific Ocean exhibit an exponential increase with density without an obvious signature of the OMZs. Oxygen supply originates from a surface outcrop area and can also be approximated by the turn-over time, the ratio of ocean volume to ventilating flux. The turn-over time corresponds well to the average oxygen ages for the well ...