全球变化知识资源中心

Sediment records from Lake Pallcacocha, Ecuador, have been interpreted as proxies of El Nino-Southern Oscillation (ENSO) variability, owing to increased precipitation in the area during El Nino events. However, the lake's watershed receives precipitation from processes arising from both the eastern and western Andes, where ENSO has different impacts; this has led to ambiguity in observed regional ENSO signals and has consequently challenged the suitability of the lake's records as ENSO proxies. Here, a mesoscale weather prediction model is used to investigate the regional circulation dynamics and precipitation response during different ENSO events, namely, Eastern Pacific (EP), Central Pacific (CP), coastal El Nino (COA), and La Nina (LN). The region receives more accumulated precipitation during COA and LN compared to EP and CP events. However, during EP and COA events, the region is prone to extreme precipitation associated with convective bursts originating from the Pacific. During CP and LN, moisture originates from the Atlantic and may reach the area as broader-scale less-intense precipitation. Statistical analysis of modeled precipitation reveals consistency between the number of threshold-exceeding precipitation events in the high Andean elevations and the number of events identified in the late Holocene Pallcacocha record. These results illustrate the importance of considering ENSO flavors when interpreting paleoclimate proxies, highlight the role of COA events in understanding eastern Pacific proxy records, and support the hypothesis that Holocene changes in the number of events recorded in the lake sediment may indicate a change in the relative frequency of ENSO flavors.

Plain Language Summary El Nino-Southern Oscillation (ENSO) events strongly impact weather and climate; therefore, there is much impetus to understand changes in ENSO in the future. To study ENSO sensitivity to climate changes, paleoclimate proxies of ENSO are commonly used. However, multiple processes affect the amount and intensity of precipitation in the location of paleoclimate archives, and correct interpretation necessitates taking into account not only large-scale ENSO impacts but also regional phenomena. To inform the interpretation of paleo-records from the equatorial Andes, this study uses Weather and Research Forecast, a high-resolution regional model, to simulate precipitation during different types of ENSO events. The results show that different types of ENSO events may distinctly impact the region: The eastern Pacific and coastal El Nino types trigger intense rainfall that affects the western Andean and may cause sediment fluxes into the lake. The warm Central Pacific El Nino and cold La Nina share similar response features where rainfall originating in the Amazon basin causes lighter rainfall rates on the eastern slopes and in the vicinity of the lake. This work shows that distinguishing between these different ENSO types is important for better deciphering records of past ENSO activity and for understanding past and future ENSO changes.