The timing, two-pulsed nature, and variable climatic expression of the 4.2 ka event: A review and new high-resolution stalagmite data from Namibia

L. Bruce Railsback, Fuyuan Liang, G. A. Brook, Ny Riavo G. Voarintsoa, Hillary R. Sletten, Eugene Marais, Ben Hardt, Hai Cheng, R. Lawrence Edwards

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

The climatic event between 4.2 and 3.9 ka BP known as the “4.2 ka event” is commonly considered to be a synchronous global drought that happened as one pulse. However, careful comparison of records from around the world shows that synchrony is possible only if the published chronologies of the various records are shifted to the extent allowed by the uncertainties of their age data, that several records suggest a two-pulsed event, and that some records suggest a wet rather than dry event. The radiometric ages constraining those records have uncertainties of several decades if not hundreds of years, and in some records the event is represented by only one or two analyses. This paper reports a new record from Stalagmite DP1 from northeastern Namibia in which high 230Th/232Th activity ratios allow small age uncertainties ranging between only 10–28 years, and the event is documented by more than 35 isotopic analyses and by petrographic observation of a surface of dissolution. The ages from Stalagmite DP1 combine with results from 11 other records from around the world to suggest an event centered at about 4.07 ka BP with bracketing ages of 4.15 to 3.93 ka BP. The isotopic and petrographic results suggest a two-pulsed wet event in northeastern Namibia, which is in the Southern Hemisphere's summer rainfall zone where more rain presumably fell with southward migration of the Inter-Tropical Convergence Zone as the result of cooling in the Northern Hemisphere. Comparison with other records from outside the region of dryness from the Mediterranean to eastern Asia suggests that multiple climatic zones similarly moved southward during the event, in some cases bringing wetter conditions that contradict the notion of global drought.

Original languageEnglish (US)
Pages (from-to)78-90
Number of pages13
JournalQuaternary Science Reviews
Volume186
DOIs
StatePublished - Apr 15 2018

Bibliographical note

Funding Information:
We thank the late Mr. Jurg-Reiner Otto and Dr. Renate Otto for permission to work on their property and thus for access to the cave. Relevant permits to carry out research on stalagmites were granted by the National Heritage Council , the Ministry of Environment and Tourism , and the Commissioner of Mines in Namibia . We thank the National Museum of Namibia and the Geological Survey of Namibia for facilitating the research. Stalagmite DP1 was sectioned with the kind help of Mr. Tom Oglesby and the staff of Keystone Memorials Inc. of Elberton, Georgia. Funding was provided by National Science Foundation Grant 0002193 to Brook and by Dr. Celeste M. Condit. The manuscript was improved by the comments of Dr. Giovanni Zanchetta and an anonymous reviewer. Dr. David Psomiadis kindly shared data from the new Stalagmite MAR_L record to allow generation of Fig. 4 b.

Funding Information:
We thank the late Mr. Jurg-Reiner Otto and Dr. Renate Otto for permission to work on their property and thus for access to the cave. Relevant permits to carry out research on stalagmites were granted by the National Heritage Council, the Ministry of Environment and Tourism, and the Commissioner of Mines in Namibia. We thank the National Museum of Namibia and the Geological Survey of Namibia for facilitating the research. Stalagmite DP1 was sectioned with the kind help of Mr. Tom Oglesby and the staff of Keystone Memorials Inc. of Elberton, Georgia. Funding was provided by National Science Foundation Grant 0002193 to Brook and by Dr. Celeste M. Condit. The manuscript was improved by the comments of Dr. Giovanni Zanchetta and an anonymous reviewer. Dr. David Psomiadis kindly shared data from the new Stalagmite MAR_L record to allow generation of Fig. 4b.

Publisher Copyright:
© 2018 Elsevier Ltd

Keywords

  • 4.2 ka event
  • Africa
  • Holocene
  • Inter-tropical convergence zone
  • Namibia
  • Paleoclimate
  • Paleoclimatology
  • Speleothems
  • Stalagmite

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