Marine heatwave (MHW) events have led to acute decreases in primary production and phytoplankton biomass in the surface ocean, particularly at the mid latitudes. In the Northeast Pacific, these anomalous events have occasionally encroached onto the Oregon shelf during the ecologically important summer upwelling season. Increased temperatures reduce the density of offshore waters, and as a MHW is present offshore, coincident downwelling or relaxation may transport warmer waters inshore. As an event persists, new upwelling‐driven blooms may be prevented from extending further offshore. This work focuses on MHWs and coincident events that occurred off Oregon during the summers of 2015–2023. In late summer 2015 and 2019, both documented MHW years, coastal phytoplankton biomass extended on average 6 and 9 km offshore of the shelf break along the Newport Hydrographic Line, respectively. During years not influenced by anomalous warming, coastal biomass extended over 34 km offshore of the shelf break. Reduced biomass also occurs with reduced upwelling transport and nutrient flux during these anomalous warm periods. However, the enhanced front associated with a MHW aids in the compression of phytoplankton closer to shore. Over shorter events, heatwaves propagating far inshore also coincide with reduced chlorophyll a and sea‐surface density at select cross‐shelf locations, further supporting a physical displacement mechanism. Paired with the physiological impacts on communities, heatwave‐reinforced physical confinement of blooms over the inner‐shelf may have a measurable effect on the gravitational flux and alongshore transport of particulate organic carbon.

中文翻译：

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水华压缩与海洋热浪一起与俄勒冈州上升流季节当代


海洋热浪 （MHW） 事件导致表层海洋的初级生产和浮游植物生物量急剧下降，尤其是在中纬度地区。在东北太平洋，这些异常事件偶尔会在具有重要生态意义的夏季上升流季节侵占俄勒冈大陆架。温度升高会降低近海水域的密度，并且由于 MHW 存在于近海，同时发生的下降流或松弛可能会将较温暖的海水输送到近海。随着事件的持续存在，可能会阻止新的上升流驱动的水华进一步延伸到近海。这项工作的重点是 2015 年至 2023 年夏季在俄勒冈州附近发生的 MHW 和巧合事件。在 2015 年夏末和 2019 年，这两个年份都记录了 MHW 年，沿海浮游植物生物量分别沿着纽波特水文线向大陆架断裂近海平均延伸 6 公里和 9 公里。在不受异常变暖影响的年份，沿海生物量延伸到大陆架断裂近海 34 公里以上。在这些异常温暖的时期，生物量的减少也发生在上升流运输和营养通量的减少。然而，与 MHW 相关的增强锋面有助于在靠近海岸的地方压缩浮游植物。在较短的事件中，向近海传播的热波也与选定的跨大陆架位置的叶绿素 a 和海面密度减少相吻合，进一步支持了物理位移机制。再加上对群落的生理影响，热浪强化了水华在内陆架的物理限制，可能对重力通量和颗粒有机碳的沿岸运输产生可测量的影响。