Deoxygenation & N cycle

(Andreas Oschlies)

We study causes, impacts and threats of the ongoing loss of oxygen from the ocean, called ocean deoxygenation. The marine oxygen and N cycles are tightly linked through oxygen minimum zones (OMZs), which are sites of major fixed-N losses and hence exert a strong control on the oceanic N inventory. While global warming by anthropogenic greenhouse gas emissions, and pollution by nutrients and organic wastes particularly in coastal waters, are considered main drivers of deoxygenation, a quantitative mechanistic understanding of the physical and biological processes involved is still lacking. Numerical models are used to investigate impacts of changes in temperature-driven solubility, circulation, biological production and respiration, and coastal processes. Feedbacks in the Earth system are examined for the current situation, for possible future scenarios and for past deoxygenation events in the Earth’s history.

Contributors:

  • Andreas Oschlies (co-chair Global Ocean Oxygen Decade, GOOD, and Global Ocean Oxygen Network, GO2NE; Earth system modeling with intermediate complexity models)
  • Wolfgang Koeve (UVic model development, experiments and publications to disentangle quantitatively drivers of transient changes in global oxygen on centennial to millennial time scales; co-supervisor of Doctoral student Haichao Guo)
  • Haichao Guo (quantitatively disentangle drivers of ocean deoxygenation in perspective of ocean ventilation and ocean respiration using high-complexity Earth system model; doctoral student)
  • Julia Getzlaff (disentangling processes, biogeochemical and physical, that impact global oxygen inventory as well as those affecting shape and size of the OMZ. As part of CO2Meso: impact of vertical migration of zooplankton and mesopelagic fish on oxygen)
  • Iris Kriest (co-chair SCOR WG 161 ReMO: Respiration in the Mesopelagic Ocean; testing sensitivities of simulated present-day oxygen and nitrogen to various model parameterisations; global model optimisation against observed oxygen and nitrogen)
  • Ivy Frenger (resetting nitrate of water masses - physical versus biological contributions in the Southern Ocean; using oxygen utilization in the interior ocean as a proxy to estimate carbon of biological origin)
  • Markus Pahlow (mechanistic descriptions of marine biogeochemistry for Earth system models: primary production with optimality-based variable stoichiometry for decoupli​​ng the biogeochemical cycles of nutrients, carbon and oxygen)
  • Chia-Te Chien (evaluating homeostasis of the marine nitrogen cycle and the dependence between oxygen level, nitrogen inventory, primary production, and iron supply using an optimality-based ecosystem mode (OPEM) within the UVic-ESCM)