Variability of internal tide energy, mixing and nitrate fluxes in response to changes in stratification on the northeast New Zealand continental shelf
Variability of internal tide energy, mixing and nitrate fluxes in response to changes in stratification on the northeast New Zealand continental shelf
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DOI：
10.1080/00288330.2019.1705357
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发表时间：
2019-12
影响因子：
1.6
通讯作者：
J. Sharples;J. Zeldis
中科院分区：
文献类型：
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作者：
J. Sharples;J. Zeldis
摘要 利用新西兰北岛陆架 4 个月的水柱温度结构时间序列来计算春季和夏季之间分层演变时内潮汐的能量。内潮波的平均总能量为200 J·m−2，峰值达到600 J·m−2。波浪能与层结（r = 0.2）和潮流的春潮周期（r = 0.17）呈弱相关。总体而言，内潮汐行为对物理环境的响应几乎没有可预测性。波浪能的减少与有利于下涌的风事件有关，风事件通过混合和去除陆架上更深的水来减少分层。由内部波耗散驱动的垂直涡流扩散率范围在 5.6 × 10−5 和 3.2 × 10−4 m2 s−1 之间。结合硝酸盐数据，这种扩散率导致向海面的二重硝酸盐通量为 1.6–2.2 mmol m−2 day−1。夏季强烈的层结降低了涡流扩散率，但对硝酸盐通量影响不大，因为加强的垂直硝酸盐梯度补偿了扩散率的降低。当预测温暖气候中更强的分层可能如何改变上层海洋的二密营养物供应时，这种补偿非常重要。
ABSTRACT A 4-month time series of water column temperature structure on the shelf of North Island New Zealand is used to calculate the energy in the internal tide as stratification evolved between spring and summer. Average total energy in the internal tidal wave was 200 J m−2, with peaks reaching 600 J m−2. Wave energy was weakly correlated with stratification (r = 0.2) and with the spring-neap cycle of tidal currents (r = 0.17). Overall there was little predictability in internal tide behaviour in response to the physical environment. Reduction in wave energy was associated with a downwelling-favourable wind event which reduced stratification by mixing and by removing deeper water off the shelf. Vertical eddy diffusivity driven by internal wave dissipation ranged between 5.6 × 10−5 and 3.2 × 10−4 m2 s−1. Combined with nitrate data this diffusivity resulted in diapycnal nitrate fluxes towards the sea surface of 1.6–2.2 mmol m−2 day−1. Strong stratification in summer reduced the eddy diffusivity but had little effect on nitrate flux as a strengthened vertical nitrate gradient compensated for the reduced diffusivity. This compensation will be important when predicting how stronger stratification in a warmer climate might alter diapycnal nutrient supplies to the upper ocean.