Authors: Tom Rippeth, Sijing Shen, Ben Lincoln, Brian Scannell, Xin Meng, Joanne Hopkins, and Jonathan Sharples
Journal: Nature Communications
Seasonally stratified shelf seas are amongst the most biologically productive on the planet. A consequence is that the deeper waters can become oxygen deficient in late summer. Predictions suggest global warming will accelerate this deficiency. Here we integrate turbulence timeseries with vertical profiles of water column properties from a seasonal stratified shelf sea to estimate oxygen and biogeochemical fluxes. The profiles reveal a significant subsurface chlorophyll maximum and associated mid-water oxygen maximum. We show that the oxygen maximum supports both upward and downwards O2 fluxes. The upward flux is into the surface mixed layer, whilst the downward flux into the deep water will partially off-set the seasonal O2 deficit. The results indicate the fluxes are sensitive to both the water column structure and mixing rates implying the development of the seasonal O2 deficit is mediated by diapcynal mixing. Analysis of current shear indicate that the downward flux is supported by tidal mixing, whilst the upwards flux is dominated by wind driven near-inertial shear. Summer storminess therefore plays an important role in the development of the seasonal deep water O2 deficit.
季节性层化陆架海是地球上最具生物生产力的海域之一。由此导致，较深的水域在夏末可能会发生缺氧。预测表明，全球变暖将加速这一缺陷。本文结合湍流时间序列与季节性层化陆架海水柱性状的垂直剖面，估算了氧通量和生物地球化学通量。剖面结果揭示了显著的次表层叶绿素最大值和相关的中层水氧最大值。本文发现，氧最大值同时支持向上及向下的氧通量。向上的通量进入表层混合层，而向下的通量进入深层水域，将部分抵消季节性缺氧。结果表明，通量对水柱结构和混合率都很敏感，表明季节性缺氧的形成是受跨等密度面混合调节。对海流切变的分析表明，向下的通量由潮汐混合支撑，向上的通量由风驱动的近惯性切变主导。因此，夏季风暴在季节性深水缺氧的形成中起重要作用。
（实习生许若橦编译）
