The impact of the 4.2kyr event in the Indian Ocean basin: major drying or insignificant event?
Abstract
The 4.2 kyr event is regarded as one of the major climate perturbations of the Holocene with well characterized changes centered on the Mediterranean and Middle East, and significant negative impacts on regional civilizations. Beyond this data-rich heartland, the impacts of the 4.2 kyr event on climate and ancient societies is less clear and the attribution of the 4.2 kyr event to any climatic anomaly between 4.5 and 3.5 kyr BP is common. Of particular interest is the tropical rainfall response in the Indian Ocean where the end of the mature urban phase of the Indus valley Harappan civilization occurred close to 3.9 kyr BP, and where the 4.2 kyr event and formal stratigraphic subdivision of the Holocene is officially defined.
Here, we assess a suite of precisely dated records of tropical hydroclimate from around the Indian Ocean basin. We conduct Principal Component Analysis on a suite of twelve hydroclimate records with sub-20-year resolution, including a brand-new speleothem record from north-western Madagascar. Our new record, covering 5.1-1.9 kyr BP at sub-decadal resolution, provides an important southern hemisphere perspective on tropical hydroclimate during the middle to late Holocene generally, and the 4.2 kyr event specifically. At Madagascar a hiatus indicates dry conditions between 4.3 and 3.8 kyr BP, overlapping the 4.2 kyr event but stretching beyond it. However, our basin-wide analysis indicates the dominant mode of variability between 5 and 3 kyr BP is a gradual basin wide drying between 4.1 and 3.5 kyr BP. A shorter event from 4.2 kyr to 4.0 kyr BP is recognized in the second principal component and matches the timing of the 4.2 kyr event in the Mediterranean and Middle East. However, this shorter event has a mixed wet or dry response depending on location and is not of unusual magnitude or duration compared to other centennial scale variability. Region wide gradual drying in the first principal component is more consistent with the end of the Harrappan civilization than an abrupt event at 4.2 kyr BP.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGC11G1132S
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSES;
- 1616 Climate variability;
- GLOBAL CHANGE;
- 1620 Climate dynamics;
- GLOBAL CHANGE