ABSTRACT

Satellite-derived estimates of sea surface temperature (SST), chlorophyll (Chl), and fluorescence line height (FLH), from 22 sites ∼20 km offshore from the West Coast of the South Island, New Zealand (WCSI) are used to investigate long-term trends in SST, the frequency and magnitude of cool and warm events, and their impacts on SSC and FLH. WCSI trends have been towards higher temperature and less chlorophyll, with a 0.83°C rise in mean along-shore SST since 1982, and a 0.1 mg Chl m⁻³ drop in mean along-shore SSC since 2002. With respect to the trend, there were 13 extreme cool and 14 extreme warm events between 1982 and 2019, with mean values of −2.55 and 2.62°C, respectively. There was no measurable change in the frequency of extreme events, but there is a suggestion that extreme events are becoming warmer. During extreme events, Chl and FLH show inverse relationships with SST, suggesting that there is an underlying response of increased primary production to lower temperatures. Likely mechanisms are that upwelling brings nutrients up from depth, or that Ekman flow forces freshwater farther offshore, simultaneously introducing nutrients into the offshore region and providing a more stable water column allowing production.

摘要

卫星得出的估计值是从新西兰南岛西海岸约20 km离岸的22个站点的海面温度（SST），叶绿素（Chl）和荧光线高度（FLH）进行的，用于调查SST的长期趋势，冷热事件的频率和强度及其对SSC和FLH的影响。WCSI趋势是向高温，叶绿素减少的方向发展，自1982年以来平均沿海SST升高0.83°C，Chl m ^-3升高0.1 mg自2002年以来，沿海平均SSC下降。就这一趋势而言，1982年至2019年之间发生了13次极端凉事件和14次极端温暖事件，平均值分别为-2.55和2.62°C。极端事件的发生频率没有可测量的变化，但是有迹象表明，极端事件正在变暖。在极端事件中，Chl和FLH与SST呈反比关系，这表明初级产量增加对低温存在潜在的响应。可能的机制是上升流使营养物从深处上升，或者埃克曼流动迫使淡水移至更远的海上，同时将营养物引入海上区域并提供更稳定的水柱以进行生产。