A review of South American monsoon variability over the past 2 millennia based on stable isotopic proxies and model simulations
Abstract
The growing number of high-resolution stable isotopic proxies (speleothems, ice cores, lake sediments) from the South American summer monsoon (SASM) belt, when combined with isotope-enabled General Circulation Models (GCMs), offers new prospects for better understanding the spatiotemporal dynamics of the South American monsoon system and for diagnosing its sensitivities to external forcings and internal modes of ocean-atmosphere variability over the past 2 millennia. In this presentation we will discuss the rationale for interpreting isotopic excursions recorded in various proxies from the SASM region as indicative of changes in monsoon intensity. Over the past 2 millennia isotopic proxies from the SASM belt display a fairly coherent behavior, regardless of the type of archive considered. All proxies exhibit significant decadal to multidecadal variability, superimposed on large excursions during three key periods, the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA) and the Current Warm Period (CWP). We interpret these three periods as times when the SASM mean state was significantly weakened (MCA and CWP) and strengthened (LIA), respectively. During the LIA each of the proxy archives considered contains the most negative δ18O values recorded during the entire record length. On the other hand the monsoon strength is currently rather weak in a 2000- year historical perspective, rivaled only by the low intensity during the MCA. One interpretation of these centennial-scale climate anomalies suggests that they were at least partially driven by temperature changes in the northern hemisphere and in particular over the North Atlantic, leading to a latitudinal displacement of the ITCZ and a change in monsoon intensity and degree of rainout upstream of the proxy locations, over the tropical continent. This interpretation is supported by several independent proxy archives and modeling studies.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2013
- Bibcode:
- 2013AGUSM.U23A..02V
- Keywords:
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- 3344 ATMOSPHERIC PROCESSES / Paleoclimatology;
- 3305 ATMOSPHERIC PROCESSES / Climate change and variability;
- 1041 GEOCHEMISTRY / Stable isotope geochemistry;
- 1620 GLOBAL CHANGE / Climate dynamics