Chlorophyll a (Chl a) observations from satellites exhibit a unimodal seasonal variation in the open Black Sea that peaks during winter, which has led to the hypothesis that phytoplankton production is sustained by convective mixing of nitrate from deeper layers. We compiled in situ carbon‐to‐Chl a ratios for the entire year, displaying an expected seasonal pattern ranging from 46 in February to 195 mg C mg Chl⁻¹ in September. We combined monthly ratios with satellite Chl a to obtain a comprehensive proxy data set for phytoplankton carbon biomass, and used this to examine the seasonal variation in phytoplankton biomass and bloom occurrences. Contrary to current understanding, our results showed that phytoplankton accumulation is predominantly taking place from July to September, when biomass increased threefold despite nitrate transport from below being negligible. We hypothesize that nitrate harvesting at depths and endosymbiont nitrogen fixation by large diatoms could be important, albeit unexplored mechanisms.

中文翻译：

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重新考虑黑海中浮游植物的季节性

来自卫星的叶绿素 a（Chl  a）观测结果显示，在黑海的开放季节中，单峰季节性变化在冬季达到顶峰，这导致了这样一个假设，即对流混合深层硝酸盐可以维持浮游植物的产量。我们在原位的碳-叶绿素编译一个比整个年，显示预期的季节性模式范围从46日至195毫克ç毫克叶绿素^-1在九月。我们结合卫星叶绿素每月比 一以获得浮游植物碳生物量的全面代理数据集，并用它来检查浮游植物生物量和水华发生的季节变化。与目前的理解相反，我们的结果表明，浮游植物的积累主要发生在7月至9月，当时尽管从下面的硝酸盐迁移可以忽略不计，但生物量却增长了三倍。我们推测，尽管机制尚待探索，但在深处收获硝酸盐和大硅藻固定共生共生氮可能是重要的。