Wind-driven coastal upwelling can be compensated by onshore geostrophic flow, and river plumes are associated with such flow. We investigate possible limitation of the northeast Gulf of Guinea upwelling by the Niger River plume, using regional ocean model simulations with or without river and dynamical upwelling indices. Here, the upwelling is weakened by 50% due to an onshore geostrophic flow equally controlled by alongshore thermosteric and halosteric sea-level changes. The river contributes to only 20% of this flow, as its plume is shallow while upwelling affects coastal temperature and salinity over a larger depth. Moreover, the river-induced mixed-layer thinning compensates the current increase, with no net effect on upwelling. The geostrophic compensation is due to an abrupt change in coastline orientation that creates the upwelling cross-shore front. The river nonetheless warms the upwelling tongue by 1°C, probably due to induced changes in horizontal advection and/or stratification.

中文翻译：

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尼日尔河羽流周围几内亚湾陆上地转流对海岸上升流的限制

风驱动的沿海上升流可以通过陆上地转流来补偿，河流羽流与这种流有关。我们研究了尼日尔河羽流对几内亚湾东北部上升流的可能限制，使用区域海洋模型模拟，有或没有河流和动力上升流指数。在这里，由于陆上地转流同时受到沿海温控和海平面海平面变化的控制，上升流减弱了 50%。这条河流仅占该流量的 20%，因为它的羽流较浅，而上升流会影响更大深度的沿海温度和盐度。此外，河流引起的混合层变薄补偿了当前的增加，对上升流没有净影响。地转补偿是由于海岸线方向的突然变化造成了上升流的跨海岸锋。尽管如此，这条河还是使上升流的舌头变暖了 1°C，这可能是由于水平对流和/或分层的诱发变化。