Appendix: What on Earth Happened in 3200 BC?
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Patience! This takes a minute to load but the information is worth it!For the latest from the GISP2 team (Jan 96 Science) click HERE (takes 30 sec to load). For a lighter, less technical version of this page click HERE.
For indices of all 3200 BC scientific data:
Click for chronological sort
Compilation of recent graphical representations of various paleoclimatic data signals from ice cores and other sources normalized to a common 9000-0 calendar year BP base. Most of the plots are scanned directly from the original sources. Brief technical notes relevant to the 5000 yrs BP period and data sources follow.
a) Sulfate in GISP2 ice core; curve is a low-tension robust spline of sulfate concentrations with average about 30 ppb. The cause of the 150 year peak at 5.2K yrs BP is not known, but the authors suggest the possibility of an anomalous nearby temporary body of open water (polynya) which generated marine biogenic sulfate. Zielinski, GA et al, Nature, 264 948 (1994).
b) Atmospheric methane from GRIP ice core with lowest value 580 ppbv at 5.2K yrs. BP followed by rapid increase of 40 ppbv over 200 years; variously attributed to clathrate or permafrost outgassing, decrease in tropospheric oxidation, or abrupt increase in low-latitude wetlands. Blunier, T, et al, Nature, 374 47 (1995).
c) Dead Sea levels peaking at 300 ft. above present levels at 5.0 and 8.0K gv BP. Frumkin et al, The Holocene, 1 3 191-200 (1991). For further discussions of North African lake behavior and possible relation of century-scale Holocene arid intervals and cooler sea temperatures in the North Atlantic see Lamb, H F et al, Nature, 373 134 (1995).
d) GISP2 100-year smoothed oxygen isotope ratio; Meese, D.A> et al Science, 266, 680, (1994)
e) Greenland Dye 3 oxygen isotope ratio. Minimum value between 2000 and 8000 cal yrs BP occurs just before 5.0K yrs BP. Data from National Snow and Ice Data Center. A large acid peak at 3150 BC is suggestive of a volcanic event. Fisher et al, The Holocene 5, 1, 19, (1995). For additional ice data from the southern hemisphere click here.
f) Data from Belfast 7272 year oak tree ring chronology; (f) is an index of the tree ring narrowness corresponding to cold weather and following growth disturbance in bogs due possibly to flooding with some peaks correlatable to volcanic activity; (g) represents relative availability of oak samples in Northern Ireland. The peak in (g) at about 3150 BC followed by the maximum tree and site sample representation suggest a major climatic event at this time. Baillie, MGL and Munro, MAR, Nature, 332 345 (1988).Similar sudden increase in swamp oak (mooreichen, still used to make furniture in Germany) shows up at 5100 BP on the Danube. Becher and Schirmer, Boreas, d) GISP2 100-year smoothed oxygen isotope ratio; Meese, D.A> et al Science, 266, 680, (1994) 6, 300 (1977).
h) Inferred heavy flooding in American Southwest based on paleoflooding studies. The peak at 5K yrs BP represents 8 sites. Baker, Victor, Science ???, ?? (199?).
i) Arid interval 5010-4860 (+/- 150) at Tigalmamine in montane Morocco. Corresponding decline in oaks (Quercus rotundifolia and canariensis) in favor of Gramineae suggests reduced winter precipitation corresponding to cooler sea temperatures in North Atlantic. Lamb, H. F. et al, Nature, 373 p 134 (1995).
Some tentative conclusions: Millennial-scale warming terminates with a period of climatic disturbance (so-called Piora oscillation")and flooding in the lower latitudes (Nile, Arizona, Morocco, Israel, Mesopotamia), followed by a drought; general, worldwide, climate-driven shock to early societies living in "edenic" geography of plenty with "fertile crescent" survivors organizing into more centrally directed and hierarchical culture based on irrigation. Abrupt cooling at higher latitudes, possibly related to oceanic effects, especially in Northern Europe, corresponding to peak of megalith cultures. Probable oscillation in sea level at 3000 BC followed by 10-15 ft. alluvial deposition in river valleys.
Illustrations show the lower Tigris-Euphrates valley as it changed from 5500 to 5000 BP.