“ENSO-Modoki” on the rise under global warming conditions? A view from the past

在全球变暖的情况下，“ENSO-Mo​​doki”正在上升？

• 批准号: 467356352
• 负责人: Privatdozent Dr. André Bahr
• 金额: --
• 依托单位: Institut für Geowissenschaften
• 依托单位国家: 德国
• 项目类别: Infrastructure Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/467356352?language=en
• 关键词: ENSO; Modoki; rise; under; global

Recent observational studies have shown that aside of the “classical” El Niño Southern Oscillation (ENSO), which is characterized by anomalous sea surface temperature (SST) warming and thermocline deepening either in the Eastern Equatorial Pacific (EEP) or Western Equatorial Pacific (WEP), a third type of ENSO has become more prominent. During these events SST anomalies are located in the Central Equatorial Pacific (CEP) leading to alternate ENSO states coined “El Niño/La Niña Modoki” (or “Central Pacific ENSO”). During El Niño Modoki events, warming and thermocline deepening occurs in the CEP, while the cooling is centered in the CEP and WEP (vice versa for La Niña Modoki events). This leads to twin Walker circulation cells with their common updraft branch centered over the CEP causing anomalously arid conditions in both tropical South America and the western Pacific realm. Related global consequences include a higher frequency of hurricanes hitting the Gulf of Mexico as well increased warming in the subpolar realms of both hemispheres potentially accelerating high latitude ice sheet demise.To shed light onto the potential further evolution of ENSO Modoki, the proposed project aims to provide insights from a paleo-perspective. This will be done via assessing the occurrence of ENSO Modoki-like climatic states during varying climatic background states regarding (i) pCO2, (ii) global ice volume and (iii) insolation, factors with a well-documented impact on classical ENSO as well as ENSO Modoki dynamics. For this purpose, we will generate high-resolution proxy records of sea surface temperature (SST) and subsurface temperature (subT) variability on ODP/IODP Sites from the WEP (Site U1488), CEP (Site 871), and EEP (Site 846) covering 300 kyr-long time slices with distinctly different climatic background conditions: (i) the mid-Pleistocene to Holocene (0–300 ka) with relatively low pCO2 concentrations and high Northern Hemisphere ice volume, and (ii) the Early Pliocene (4.85–5.15 Ma) with pCO2 conditions similar to modern and largely absent Northern Hemisphere ice sheets.These SST and subT records will be based on Mg/Ca analysis of surface and deep dwelling planktic foraminifera as well as alkenone-based SST estimates (depending upon the method used on each site during previous studies to ensure consistency). The SST records will be used to compute an index of the past El Nino Modoki variability while the subT data will inform about associated thermocline variability. In the context with published reference records for pCO2, ice volume, and insolation our proxy data will be evaluated utilizing statistical methods (linear models). The results of this project will provide new insights into the drivers of El Nino Modoki variability and aid the predictions of its variability in response to future global warming.

最近的观测研究表明，除了以异常海表面温度(SST)变暖和赤道东太平洋(EEP)或西赤道太平洋(WEP)温跃层加深为特征的“经典”厄尔尼诺南方涛动(ENSO)外，第三种类型的ENSO变得更加突出。在这些事件期间，SST异常位于中赤道太平洋(CEP)，导致交替的ENSO状态，即“El Niño/La Niña Modoki”(或“中太平洋ENSO”)。在厄尔尼诺-莫多基事件期间，增温和温跃层加深发生在CEP，而冷却集中在CEP和WEP(拉尼娜-莫多基事件则相反)。这导致了双子Walker环流圈，它们共同的上升气流分支以CEP为中心，在热带南美洲和西太平洋地区都造成了异常干旱的条件。相关的全球后果包括飓风袭击墨西哥湾的频率更高，以及两个半球亚极区变暖的加剧，可能会加速高纬度冰盖的消失。为了阐明ENSO Modoki的潜在进一步演化，拟议中的项目旨在从古生物学角度提供见解。这将通过评估在关于(I)二氧化碳、(Ii)全球冰量和(Iii)日照、对经典ENSO以及ENSO Modoki动力学有充分记录的影响的因素的不同气候背景状态期间出现类似ENSO Modoki的气候状态来实现。为此，我们将从WEP(U1488站)、CEP(871站)和EEP(846站)覆盖300 KYR长时间片的WEP(U1488站)、CEP(871站)和EEP(846站)的ODPIODP站点上生成高分辨率的海表面温度(SST)和次表层温度(SUT)变率记录，这些切片具有明显不同的气候背景条件：(I)中更新世至全新世(0-300ka)，二氧化碳浓度相对较低，北半球冰量较高，和(Ii)上新世早期(4.85-5.15 Ma)，其二氧化碳条件与现代北半球冰盖相似，基本上没有北半球冰盖。这些SST和SubT记录将基于对表层和深层浮游有孔虫的镁/钙分析以及基于烯酮的SST估计(取决于先前研究期间每个地点使用的方法，以确保一致性)。海温记录将用于计算过去厄尔尼诺莫多基变率的指数，而SubT数据将提供有关温跃层变率的信息。在已公布的二氧化碳浓度、冰量和日照强度的参考记录的背景下，我们的替代数据将使用统计方法(线性模型)进行评估。该项目的结果将对厄尔尼诺莫多基变率的驱动因素提供新的见解，并有助于预测其变异性以应对未来的全球变暖。