资源环境科技发展态势分析平台

The mechanisms controlling the variability of oxygen levels in the ocean are poorly quantified. I focus here on the impact of wind synoptic variability associated with tropical convective regions and extratropical storms. Removing the wind higher frequencies of variability (2 days to 1month) in an atmosphere reanalysis used to force an ocean model decreases wind stress by up to 20% in the tropics and 50% in the midlatitudes, weakening wind-driven ocean circulation by 20%. Oxygen levels decrease by up to 10 mmol/m(3) in tropical oceans and 30 mmol/m(3) in subtropical gyres mainly due to changes in advective processes. While a large part of the tropical oxygen anomaly has local origins, changes in oxygen levels in the subtropical gyres modulate tropical oxygen distribution. This study suggests that the "storminess" of the ocean is an important parameter that could determine the future evolution of poorly oxygenated regions.

Plain Language Summary A number of studies reported a strong decrease in marine oxygen levels during the last decades, threatening marine life and ecosystems. The mechanisms responsible of the variability of oxygen in the oceans are still not completely understood, hampering reliable future projections. It is however well known that upper oceanic currents, driven by the wind, play a major role in transporting oceanic properties at basin scale. The wind strength is strongly dependent of the day-to-day weather. For instance, precipitations, storms, cyclones, are responsible for a strong variability of the order of a few days (so called "synoptic variability"). I assess here the impact of the synoptic activity, or in other words the integrated impact of the weather phenomenons, on the mean oxygen levels in numerical, idealized, experiments. I show that "switching off" the synoptic variability is responsible of a decrease of oxygen in the ocean by about 20 %. This study suggests that a future increase of the frequency of storms or cyclones (so called "storminess"), hence enhancing the synoptic variability, may impact oceanic oxygen levels.