P2C2: Hydroclimatic response of the tropical Pacific to past changes in mean state: Observations and synthesis

厄尔尼诺现象如何随着气候变化而变化？ 对于这个问题的答案，目前还没有从对21世纪世纪气候变化的预测中得出共识。 然而，即使厄尔尼诺事件强度、持续时间或频率的微小变化，也会对美国和国际上的水资源、野火、农业和生态系统产生重大影响。 该项目将对过去两个时期的厄尔尼诺/南方涛动活动进行新的观测和分析，在这两个时期，热带太平洋的数据很少，但据认为全球气候分别相对温暖和相对寒冷。结果将与同期的气候模拟进行比较，以便我们能够更好地了解全球气候变化是否、如何以及为什么会导致厄尔尼诺活动的变化。 该项目还将为一名博士生和一名本科生研究员提供有指导的国际合作和多学科培训，包括教育、外联和传播活动。 它将为模拟具有丰富的前现代定居，航行和探索考古历史的地点和地区的人，渔业和气候之间的相互作用提供投入。 这些研究超出了本项目的范围，最终可能帮助我们了解社会如何适应过去和未来的气候变化，具体而言，将从库克群岛南部Aitutaki小冰期（LIA）和中世纪气候异常（MCA）时间窗的现有和成岩筛选珊瑚样本中开发成对氧同位素和Sr/Ca数据系列（18.85S，159.79W）。初步分析表明，从该地区的现今（PD）珊瑚氧同位素组成的年际变化主要反映了海表盐度（SSS）的变化所造成的位置和强度的变化与ENSO活动的南太平洋辐合带。 结合这些时间窗和PD的其他水文气候和海洋古气候数据，研究小组将测试LIA和MCA相对于PD的年际事件幅度和复发间隔是否存在差异。 该团队将把结果与从类似采样的PMIP 3物理气候模拟中获得的结果进行比较，包括完整的和单一的外部辐射强迫。 将在其不确定性的范围内对观测和模拟进行比较，以评估观测到的水文气候反应是否是被迫的或非被迫的，以及在多大程度上是被迫的，以及通过何种机制。

How will El Niño events change as the climate changes? There is currently no consensus on the answer to this question from climate change projections for the 21st century. Yet even small changes in El Niño event strength, duration or frequency have significant effects, both in the US and internationally, on water resources, wildfires, agriculture and ecosystems. This project will contribute new observations and analysis of El Niño/Southern Oscillation (ENSO) activity during two past time intervals for which there are very few data from the tropical Pacific, yet for which the global climate is thought to have been relatively warm and relatively cold, respectively. Results will be compared to climate simulations for the same periods, so that we can better understand if, how and why global climate change can cause changes in El Niño activity. The project will also provide mentored, international, collaborative, and multidisciplinary training for a PhD student and an undergraduate researcher, including educational, outreach and dissemination activities. It will contribute inputs for modeling the interactions between people, fisheries and climate in a location and region with a rich archaeological history of pre-modern settlement, voyaging and exploration. These studies, which are beyond the scope of this project, may ultimately help us understand how societies have and may adapt to past and future climate change.Specifically, paired oxygen isotope and Sr/Ca data series will be developed from existing and diagenetically screened coral samples dating to the Little Ice Age (LIA) and Medieval Climate Anomaly (MCA) time windows from Aitutaki, southern Cook Islands (18.85S, 159.79W). Preliminary analysis suggests interannual variations in present day (PD) coral oxygen isotopic composition from the region primarily reflect sea surface salinity (SSS) variability resulting from changes in the position and strength of the South Pacific Convergence Zone associated with ENSO activity. In conjunction with other hydroclimatic and oceanographic paleoclimate data available for these time windows and the PD, the research team will test whether there were differences in interannual event amplitude and recurrence interval in the LIA and MCA relative to the PD. The team will compare the results to those obtained from similarly sampled, PMIP3-compliant physical climate simulations with both complete and single external radiative forcings. Comparison of observations and simulations, within the context of their uncertainties, will be used to assess if and the extent to which the observed hydroclimatic response is forced or unforced, and by what mechanisms.