The 2014–2015 warm anomaly (aka “the Blob”), the largest of periodic and intensifying marine heat wave (MHW) perturbations in the northeast Pacific, may provide some insight about the future warmer ocean. Here, we use mixed‐layer carbon estimates for total phytoplankton, major size classes and functional groups from 45 CalCOFI cruises to: (1) compare 2014–2015 MHW impacts in the southern California Current System to baseline estimates from 2004 to 2013 and (2) to test a space‐for‐time exchange hypothesis that links biomass structure to variability of nitracline depth (NCD). Seasonal and inshore‐offshore analyses from nine stations revealed almost uniform 2°C MHW warming extending 700 km seaward, fourfold to sixfold declines in nitrate concentration and 18‐m deeper NCDs. Phytoplankton C decreased 16–21% compared to 45–65% for Chl a, with the threefold difference due to altered C : Chl a. Among size classes, percent composition of nanoplankton decreased and picophytoplankton increased, driven by higher Prochlorococcus biomass, while Synechococcus and picoeukaryotes generally declined. Diatom and dinoflagellate C decreased in both onshore and offshore waters. Seasonally, the MHW delayed the normal winter refresh of surface nitrate, resulting in depressed stocks of total phytoplankton and nanoplankton, Synechococcus and picoeukaryotes during winter. Consistent with the space‐for‐time hypothesis, biomass variations for baseline and MHW cruises followed similar (not significantly different) slope relationships to NCD. All biomass components, except Prochlorococcus, were negatively related to NCD, and community biomass structure realigned according to regression slopes differences with NCD variability. Empirically derived biomass‐NCD relationships could be useful for calibrating models that explore future food‐web impacts in this coastal upwelling system.

中文翻译：

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浮游植物生物量对海洋热浪的响应与硝斜深度的改变一致


2014-2015年的温暖异常（又名“Blob”）是东北太平洋最大的周期性和强化海洋热浪（MHW）扰动，可能会为未来海洋变暖提供一些见解。在这里，我们使用来自 45 次 CalCOFI 航行的浮游植物总数、主要尺寸类别和功能组的混合层碳估算来：(1) 将 2014 年至 2015 年南加州洋流系统 MHW 影响与 2004 年至 2013 年基线估算进行比较，以及(2 ）来测试将生物量结构与硝斜深度（NCD）变化联系起来的时空交换假设。来自 9 个站点的季节性和近海分析显示，MHW 几乎均匀变暖 2°C，向海延伸 700 公里，硝酸盐浓度下降四到六倍，非传染性疾病深度加深 18 米。与叶绿素 a 的 45-65% 相比，浮游植物 C 减少了 16-21%，由于 C : 叶绿素 a 的改变，导致了三倍的差异。在大小类别中，由于原绿球藻生物量增加，纳米浮游生物的百分比组成下降，超微型浮游植物增加，而聚球藻和超微核生物普遍下降。陆上和近海水域的硅藻和甲藻碳含量均有所下降。从季节性来看，MHW 推迟了表面硝酸盐的正常冬季更新，导致冬季总浮游植物和纳米浮游生物、聚球藻和超微核生物的数量减少。与时空假设一致，基线和 MHW 巡航的生物量变化遵循与 NCD 相似（没有显着不同）的斜率关系。除原绿球藻外，所有生物量成分均与 NCD 呈负相关，并且群落生物量结构根据回归斜率差异与 NCD 变异性进行重新调整。 经验得出的生物量与非传染性疾病关系可用于校准探索沿海上升流系统中未来食物网影响的模型。