Department of Geology and Planetary Science, University of Pittsburgh, 4107 O'Hara Street, Pittsburgh, PA 15260, USA.
Proc Natl Acad Sci U S A. 2011 May 24;108(21):8583-8. doi: 10.1073/pnas.1003719108. Epub 2011 May 9.
Decadal and centennial mean state changes in South American summer monsoon (SASM) precipitation during the last 2,300 years are detailed using an annually resolved authigenic calcite record of precipitation δ(18)O from a varved lake in the Central Peruvian Andes. This unique sediment record shows that δ(18)O peaked during the Medieval Climate Anomaly (MCA) from A.D. 900 to 1100, providing evidence that the SASM weakened considerably during this period. Minimum δ(18)O values occurred during the Little Ice Age (LIA) between A.D. 1400 and 1820, reflecting a prolonged intensification of the SASM that was regionally synchronous. After the LIA, δ(18)O increased rapidly, particularly during the current warm period (CWP; A.D. 1900 to present), indicating a return to reduced SASM precipitation that was more abrupt and sustained than the onset of the MCA. Diminished SASM precipitation during the MCA and CWP tracks reconstructed Northern Hemisphere and North Atlantic warming and a northward displacement of the Intertropical Convergence Zone (ITCZ) over the Atlantic, and likely the Pacific. Intensified SASM precipitation during the LIA follows reconstructed Northern Hemisphere and North Atlantic cooling, El Niño-like warming in the Pacific, and a southward displacement of the ITCZ over both oceans. These results suggest that SASM mean state changes are sensitive to ITCZ variability as mediated by Western Hemisphere tropical sea surface temperatures, particularly in the Atlantic. Continued Northern Hemisphere and North Atlantic warming may therefore help perpetuate the recent reductions in SASM precipitation that characterize the last 100 years, which would negatively impact Andean water resources.
过去 2300 年中，南美夏季季风（SASM）降水的年代际和百年际均值变化，是使用来自秘鲁中部安第斯山脉一个具有纹层的湖泊中沉淀的碳酸钙δ（18）O 的年分辨率记录来详细说明的。这个独特的沉积记录表明，δ（18）O 在公元 900 年至 1100 年的中世纪气候异常期间达到峰值，这表明在这一时期，SASM 明显减弱。最小的δ（18）O 值出现在公元 1400 年至 1820 年的小冰期期间，反映了 SASM 的长时间增强，且在区域上是同步的。小冰期之后，δ（18）O 迅速增加，特别是在当前的温暖期（公元 1900 年至今），表明 SASM 降水减少的情况有所恢复，与中世纪气候异常的开始相比，这种情况更为突然和持续。MCA 和 CWP 期间 SASM 降水减少的情况与重建的北半球和北大西洋变暖以及热带辐合带（ITCZ）在大西洋上向北的位移有关，可能还与太平洋有关。小冰期期间 SASM 降水增强与重建的北半球和北大西洋冷却、太平洋类似厄尔尼诺的变暖以及两个大洋上 ITCZ 的南移有关。这些结果表明，SASM 均值状态变化对热带西半球海表温度介导的 ITCZ 变率敏感，特别是在大西洋。因此，持续的北半球和北大西洋变暖可能会使最近 100 年来 SASM 降水减少的情况持续下去，这将对安第斯水资源产生负面影响。
