Abstract The spatial and temporal variability of winter coccolithophore blooms in the Black Sea is studied using satellite measurements for 2003–2017 and Bio-Argo buoys data. Analysis shows that such blooms can occupy the entire upper 60-m layer with satellite-derived estimates of surface cell concentration reaching in some years 3.0·106 cells l−1. On average, winter coccolithophore blooms start in November–December, peak in the first decade of January, and terminate in February. They are characterized by significant interannual variability. Blooms in different years can be “basin-wide” covering most of the sea (2004–2005, 2005–2006, 2006–2007, 2012–2013) and “local” when they are observed only in certain areas of the Black Sea, most often in its southern part. A detailed analysis of the evolution of winter blooms has shown that they are usually triggered by intense storms, which are followed after 1–2 weeks by the initial growth of coccolithophores in the zone of storm-driven upwelling. Cross-shelf nutrients exchange may contribute to the coccolithophore growth over the continental slope. Intense winter coccolithophore blooms are observed in years with low autumn concentrations of chlorophyll-a, i.e., during periods of weakening of the typical diatom blooming autumn-winter. The strongest correlation on annual time scales is found between bloom intensity and decrease of the autumn-winter wind curl. We suggest that low wind curl causes a weakening of the basin-scale cyclonic circulation and intensifies the cross-shelf exchange, impacting the Black Sea trophic structure in the preceding summer period and may promote the winter bloom of coccolithophores in such years.

中文翻译：

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黑海冬季颗石藻开花：年际变化和驱​​动因素

摘要 使用 2003-2017 年的卫星测量和 Bio-Argo 浮标数据研究了黑海冬季颗石藻开花的时空变异性。分析表明，这种水华可以占据整个上层 60 米层，卫星得出的表面细胞浓度估计在某些年份达到 3.0·106 个细胞 l-1。平均而言，冬季颗石藻开花始于 11 月至 12 月，在 1 月的第一个十年达到高峰，并在 2 月结束。它们的特点是显着的年际变化。不同年份的水华可以是“全流域”覆盖大部分海域（2004-2005、2005-2006、2006-2007、2012-2013），也可以是“局部”的，仅在黑海的某些区域观察到，最常见的是在其南部。对冬季水华演化的详细分析表明，它们通常是由强烈风暴引发的，随后 1-2 周后，风暴驱动的上升流区域中的球石藻开始生长。跨大陆架的营养交换可能有助于大陆坡上的颗石藻生长。在秋季叶绿素-a 浓度较低的年份，即在典型的硅藻秋冬季开花减弱的时期，观察到强烈的冬季颗石藻开花。在年度时间尺度上发现最强的相关性是在开花强度和秋冬季风卷度的减少之间。我们认为低风旋会导致盆地规模的气旋环流减弱并加剧跨陆架交换，