NOAA/WDS Paleoclimatology - Lago El Gancho, Nicaragua 1600 Year Geochemical Data

Discerning the influences of the El Nino Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) on drought variability in the tropics during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) will help to improve our understanding of climate system responses to internal and external forcing. Sediments from Lago El Gancho, Nicaragua, provide an ~1400 yr record of water balance (precipitation and evaporation) changes from a region that is sensitive to teleconnected Pacific and Atlantic ocean-atmosphere dynamics. Oxygen isotope values of ostracod carapaces (d18Oostracod) are consistently low in El Gancho sediments between ca. A.D. 950 and 1250, indicating that wetter conditions prevailed during the MCA, a period of La Nina-like mean state conditions in the tropical Pacific, and a positive mean state of the NAO. The ~150 yr period between the MCA and LIA was marked by an abrupt shift to persistently drier conditions at a time of highly variable Pacific sea-surface temperatures, and a transition toward a more negative NAO phase. In sediment from ca. A.D. 1450 to the present, d18Oostracod values increase, suggesting that drier conditions persisted through most of the LIA, a time of a relatively negative NAO phase and El Nino-like mean state conditions in the tropical Pacific. The long-term precipitation trends inferred from the El Gancho data are not entirely consistent with modern associations between precipitation in the circum-Caribbean region and the NAO, suggesting that present-day hydroclimatic shifts resulting from variability in synoptic climate patterns are dissimilar to changes resulting from teleconnected ocean-atmosphere dynamics that operated during the MCA and LIA.

厘清厄尔尼诺南方涛动（El Nino Southern Oscillation, ENSO）与北大西洋涛动（North Atlantic Oscillation, NAO）对中世纪暖期（Medieval Climate Anomaly, MCA）及小冰期（Little Ice Age, LIA）热带地区干旱变率的影响，有助于深化我们对气候系统响应内外强迫机制的认知。取自尼加拉瓜埃尔甘乔湖（Lago El Gancho）的沉积物，为这片对太平洋与大西洋遥相关海气动力学敏感的区域，提供了一段约1400年的水量平衡（降水与蒸发）变化记录。公元950年至1250年前后，埃尔甘乔湖沉积物中的介形虫壳体氧同位素（δ¹⁸O_ostracod）值持续偏低，表明中世纪暖期彼时热带太平洋处于类拉尼娜平均状态、北大西洋涛动呈正位相阶段，当地气候更为湿润。中世纪暖期与小冰期之间约150年的时段，以发生突变并转为持续偏干的气候状态为特征，彼时太平洋海表温度波动剧烈，北大西洋涛动向负位相过渡。公元1450年至今的沉积物中，介形虫壳体氧同位素值持续升高，表明小冰期大部分时段气候持续偏干，该时期热带太平洋呈类厄尔尼诺平均状态，北大西洋涛动以负位相为主。基于埃尔甘乔湖沉积物记录推断的长期降水趋势，与现代环加勒比海地区降水与北大西洋涛动的关联并不完全一致，这表明当前由天气气候系统格局变化引发的水文气候偏移，与中世纪暖期及小冰期期间由遥相关海气动力学驱动的气候变化存在显著差异。