A 4600-YR HIGH-RESOLUTION STALAGMITE PALEOCLIMATE RECORD FOR NORTHEASTERN NAMIBIA

Multiple lines of evidence from a stalagmite from northeastern Namibia combine to provide a record of changing climate over the past 4600 years. Stalagmite DP1 from Dante Cave is a 1.5 m stalagmite composed of both calcite and aragonite layers that vary greatly in width. 23 U-series dates indicate deposition between 4600 BP and 74 BP with significant changes in growth rate. 148 stable isotope samples analyzed to date show considerable changes in δ¹³C, which ranges from -10.4 to -3.1 ‰ vs. VPDB, and in δ¹⁸O, which ranges from -11.5 to -6.6 ‰ vs. VPDB.

U-series dating indicates that three episodes of very slow deposition or hiatuses, designated with S(n), occurred at approximately 3000 BP to 1800 BP (S3), 1120 BP to 800 BP (S2), and 600 BP to 370 BP (S1). Each of these intervals of slower growth is coincident with increased δ¹³C, increased δ¹⁸O, a decrease in stalagmite width, and deposition of aragonite, all of which suggest three episodes of exceptionally drier conditions.

Below S3, Stalagmite DP1 is consistently narrow, has relatively large values of δ¹³C averaging roughly -6 ‰ vs. VPDB, has relatively large values of δ¹⁸O averaging about -8 ‰ vs. VPDB, consists entirely of aragonite, and has a slow growth rate. These characteristics suggest a long period of consistently dry conditions from 4600 BP to at least 3000 BP, when conditions became even drier to give Interval S3 its peak values of δ¹³C and exceptionally slow growth. Above S3, Stalagmite DP1 is wider, has generally lesser values of δ¹³C averaging about -8 ‰, has generally lesser values of δ¹⁸O averaging about -9 ‰, consists alternately of aragonite and calcite, and has a faster average growth rate. These characteristics suggest generally wetter conditions since about 1800 BP, with the exception of two drier episodes noted above as S2 and S1.

Narrower sections of the stalagmite are consistently aragonite during drier phases within or near the hiatuses, whereas wider sections tend to alternate between calcite and aragonite during wetter phases. The consistency in the patterns before, during and after each slow growth interval indicates that climate was the controlling factor in depositional changes, instead of shifts in local drip water source or location. The result is one the first high-resolution paleoclimate records for this region of Namibia.