Hotspots and drivers of compound marine heatwaves and low net primary production extremes
Hotspots and drivers of compound marine heatwaves and low net primary production extremes
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DOI：
10.5194/bg-19-5807-2022
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发表时间：
2022-12
期刊：
影响因子：
4.9
通讯作者：
Natacha Le Grix;J. Zscheischler;K. Rodgers;R. Yamaguchi;T. Frölicher
中科院分区：
文献类型：
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作者：
Natacha Le Grix;J. Zscheischler;K. Rodgers;R. Yamaguchi;T. Frölicher
抽象的。极端事件会严重影响海洋生物和生态系统。特别令人关切的是多变量复合事件，即多个海洋生态系统压力源同时极端的情况。例如，在2013 - 2015年，一场被称为Blob的大范围海洋热浪（MHW）与极低的净初级生产力（NPPX）在当地同时发生，并对东北太平洋的海洋生物产生了负面影响。然而，很少有人知道这种多元复合MHW-NPPX事件的特征和驱动因素。使用五种不同的卫星衍生的净初级生产力（NPP）估计和两个广泛使用的综合地球系统模型，地球物理流体动力学实验室（GFDL）ESM2M-LE和社区地球系统模型版本2（CESM2-LE）的大型集合模拟输出，我们评估了当今复合MHW-NPPX事件的分布，并调查了其在全球范围内的潜在驱动因素。基于卫星的估计和两个模型揭示了赤道太平洋中心和副热带印度洋频繁发生复合事件的热点，其发生率至少是MHWs（温度高于季节变化的第90百分位阈值）和NPPX事件（NPP低于季节变化的第10百分位阈值）独立发生的3倍（超过10 d yr-1）。然而，这些模型显示了北方高纬度地区的差异，其中复合事件在基于卫星的估计和GFDL ESM 2M-LE（小于3 d yr − 1）中很少见，但在CESM 2-LE中相对频繁。在南大洋以南的60 ° S，低协议之间的观测为基础的估计，很难确定这两个模型更好地模拟MHW-NPPX事件。频率模式可以解释的驱动程序的复合事件，这两个模型和浮游植物类型之间的变化。在低纬度地区，MHWs与增强的营养盐限制浮游植物的生长，这导致频繁的复合MHW-NPPX事件在两个模式。在高纬度地区，GFDL ESM2M-LE中的NPPX事件是由增强的光限制驱动的，这很少与MHWs共同发生，导致罕见的复合事件。相反，在CESM 2-LE中，高纬度地区的NPPX事件是由营养供应减少驱动的，营养供应减少通常与MHWs共同发生，缓和浮游植物生长，并导致生物量减少。MHW-NPPX复合事件与大多数区域向较大浮游植物的相对转移有关，但两个模型中的东赤道太平洋以及CESM 2-LE中的北方高纬度和35至50 ° S之间除外，其中模型表明向较小浮游植物转移，对海洋生态系统有潜在影响。总体而言，我们的分析表明，复合MHW-NPPX事件的可能性取决于限制浮游植物生产的因素的模型表示。这确定了一个重要的需要，以改善过程的理解，在地球系统模型用于预测和预测复合MHW-NPPX事件及其影响。
Abstract. Extreme events can severely impact marine organisms and ecosystems. Of particular concern are multivariate compound events, namely when conditions are simultaneously extreme for multiple ocean ecosystem stressors. In 2013–2015 for example, an extensive marine heatwave (MHW), known as the Blob, co-occurred locally with extremely low net primary productivity (NPPX) and negatively impacted marine life in the northeast Pacific. Yet, little is known about the characteristics and drivers of such multivariate compound MHW–NPPX events. Using five different satellite-derived net primary productivity (NPP) estimates and large-ensemble-simulation output of two widely used and comprehensive Earth system models, the Geophysical Fluid Dynamics Laboratory (GFDL) ESM2M-LE and Community Earth System Model version 2 (CESM2-LE), we assess the present-day distribution of compound MHW–NPPX events and investigate their potential drivers on the global scale. The satellite-based estimates and both models reveal hotspots of frequent compound events in the center of the equatorial Pacific and in the subtropical Indian Ocean, where their occurrence is at least 3 times higher (more than 10 d yr−1) than if MHWs (temperature above the seasonally varying 90th-percentile threshold) and NPPX events (NPP below the seasonally varying 10th-percentile threshold) were to occur independently. However, the models show disparities in the northern high latitudes, where compound events are rare in the satellite-based estimates and GFDL ESM2M-LE (less than 3 d yr−1) but relatively frequent in CESM2-LE. In the Southern Ocean south of 60∘ S, low agreement between the observation-based estimates makes it difficult to determine which of the two models better simulates MHW–NPPX events. The frequency patterns can be explained by the drivers of compound events, which vary among the two models and phytoplankton types. In the low latitudes, MHWs are associated with enhanced nutrient limitation on phytoplankton growth, which results in frequent compound MHW–NPPX events in both models. In the high latitudes, NPPX events in GFDL ESM2M-LE are driven by enhanced light limitation, which rarely co-occurs with MHWs, resulting in rare compound events. In contrast, in CESM2-LE, NPPX events in the high latitudes are driven by reduced nutrient supply that often co-occurs with MHWs, moderates phytoplankton growth, and causes biomass to decrease. Compound MHW–NPPX events are associated with a relative shift towards larger phytoplankton in most regions, except in the eastern equatorial Pacific in both models, as well as in the northern high latitudes and between 35 and 50∘ S in CESM2-LE, where the models suggest a shift towards smaller phytoplankton, with potential repercussions on marine ecosystems. Overall, our analysis reveals that the likelihood of compound MHW–NPPX events is contingent on model representation of the factors limiting phytoplankton production. This identifies an important need for improved process understanding in Earth system models used for predicting and projecting compound MHW–NPPX events and their impacts.