Namibia 5000 Year Rock Hyrax Midden Nitrogen Isotope Data ----------------------------------------------------------------------- World Data Center for Paleoclimatology, Boulder and NOAA Paleoclimatology Program ----------------------------------------------------------------------- NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!! NAME OF DATA SET: Namibia 5000 Year Rock Hyrax Midden Nitrogen Isotope Data LAST UPDATE: 7/2010 (Original receipt by WDC Paleo) CONTRIBUTORS: Chase, B.M., M.E. Meadows, A.S. Carr, and P.J. Reimer IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2010-072 WDC PALEO CONTRIBUTION SERIES CITATION: Chase, B.M., et al. 2010. Namibia 5000 Year Rock Hyrax Midden Nitrogen Isotope Data. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # 2010-072. NOAA/NCDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCE: Chase, B.M., M.E. Meadows, A.S. Carr, and P.J. Reimer. 2010. Evidence for progressive Holocene aridification in southern Africa recorded in Namibian hyrax middens: Implications for African Monsoon dynamics and the "African Humid Period". Quaternary Research, Vol. 74, pp. 36-45. doi:10.1016/j.yqres.2010.04.006 ABSTRACT: Presented here are stable nitrogen isotope data from a rock hyrax (Procavia capensis) middens from northwestern Namibia that record a series of rapid aridification events beginning at ca. 3800 cal yr BP, and which mark a progressive decrease in regional humidity across the Holocene. Strong correlations exist between this record and other terrestrial and marine archives from southern Africa, indicating that the observed pattern of climate change is regionally coherent. Combined, these data indicate hemispheric synchrony in tropical African climate change during the Holocene, with similar trends characterising the termination of the 'African Humid Period' (AHP) in both the northern and southern tropics. These findings run counter to the widely accepted model of direct low-latitude insolation forcing, which requires an antiphase relationship to exist between the hemispheres. The combined dataset highlights: 1) the importance of forcing mechanisms influencing the high northern latitudes in effecting low-latitude climate change in Africa, and 2) the potential importance of solar forcing and variations in the Earth's geomagnetic shield in determining both long-term and rapid centennial-scale climate changes, identifying a possible mechanism for the variations marking the AHP termination in both the southern and northern tropics. ADDITIONAL REFERENCES: Ambrose, S.H., and M.J. DeNiro. 1986. The isotopic ecology of East African mammals. Oecologia 69, 395-406. Aranibar, J.N., L. Otter, S.A. Macko, C.J.W. Feral, H.E. Epstein, P.R. Dowty, F. Eckardt, H.H. Shugart, and R.J. Swap. 2004. Nitrogen cycling in the soil-plant system along a precipitation gradient in the Kalahari sands. Global Change Biology 10, 359-373. Chase, B.M., M.E. Meadows, L. Scott, D.S.G. Thomas, E. Marais, J. Sealy, and P.J. Reimer. 2009. A record of rapid Holocene climate change preserved in hyrax middens from southwestern Africa. Geology, Vol. 37, No. 8, pp. 703-706, August 2009. doi: 10.1130/G30053A.1. Codron, D., J. Codron, J. Lee-Thorp, M. Sponheimer, D. de Ruiter, and J. Brink. 2007. Stable isotope characterization of mammalian predator-prey relationships in a South African savanna. European Journal of Wildlife Research, 53, 161-170. Heaton, T.H.E. 1987. The 15N/14N ratios of plants in South Africa and Namibia: relationship to climate and coastal/saline environments. Oecologia 74, 236-246. Heaton, T.H.E., J.C. Vogel, G. von la Chevallerie, and G. Collet. 1986. Climate influence on the isotopic composition of bone nitrogen. Nature 322, 822-823. Murphy, B.P., and D.M.J.S. Bowman. 2006. Kangaroo metabolism does not cause the relationship between bone collagen d15N and water availability. Functional Ecology 20, 1062-1069. Swap, R.J., J.N. Aranibar, P.R. Dowty, W.P. Gilhooly, and S.A. Macko. 2004. Natural abundance of 13C and 15N in C3 and C4 vegetation of southern Africa: patterns and implications. Global Change Biology 10, 350-358. GEOGRAPHIC REGION: Southwestern Africa PERIOD OF RECORD: 4,880-1,460 YrBP FUNDING SOURCE: Leverhulme Trust DESCRIPTION: This dataset comprises stable nitrogen isotope data from a rock hyrax (Procavia capensis) middens from northwestern Namibia that record a series of rapid aridification events beginning at c. 3800 cal yr BP, and which mark a progressive decrease in regional humidity across the Holocene. Strong correlations exist between this record and other terrestrial and marine archives from southern Africa, indicating that the observed pattern of climate change is regionally coherent. Combined, these data indicate hemispheric synchrony in tropical African climate change during the Holocene, with similar trends characterising the termination of the 'African Humid Period' (AHP) in both the northern and southern tropics. These findings run counter to the widely accepted model of direct low latitude insolation forcing, which requires an anti-phase relationship to exist between the hemispheres. The combined dataset highlights: 1) the importance of forcing mechanisms influencing the high northern latitudes in effecting low latitude climate change in Africa, and 2) the potential importance of solar forcing and variations in the Earth's geomagnetic shield in determining both long-term and rapid centennial-scale climate changes, identifying a possible mechanism for the variations marking the AHP termination in both the southern and northern tropics. Stable isotope data (d15N) from a rock hyrax midden recovered from northwest-facing Austerlitz cave in northwestern Namibia (20°27.83'S, 14°26.54'E) on the southern margin of the limestone karstveld region, south of the Etendeka and Kamajab plateaus. AMS radiocarbon analyses of the Austerlitz midden indicate that it was deposited between 4538-4825 cal (calibrated) yr BP (UBA 9441) and 1385-1522 cal yr BP (UBA-9436). The distribution of ages as a function of depth shows continuous deposition, with no apparent hiatuses. Accumulation rates average ~30 µm yr-1, with slightly higher rates (~48 µm yr-1) at the base of the section. Each 1 mm isotope sample thus integrates approximately 20 – 35 years of accumulation. The d15N values of the Austerlitz midden vary from 12.5 to -19.4‰. From the beginning of the record, there is a clear, progressive enrichment in d15N values, with sharp increases occurring between c. 3500 – 3400 cal yr BP and c. 3000 – 2800 cal yr BP. These trends show close similarities with the d15N record from the hyrax middens recovered from Spitzkoppe massif, 160 km to the southwest (Chase et al., 2009), and reveal a coherent, regional-scale midden 15N signal at this time. The potential of nitrogen stable isotope compositions as a climatic indicator has long been recognised, but studies of modern ecosystems have produced complex data sets, that have proved difficult to interpret (e.g. Heaton, 1987; Heaton et al., 1986). Among herbivores, 15N abundance in animal tissues is strongly influenced by climate, diet and/or physiology (Ambrose and DeNiro, 1986; Heaton et al., 1986). While early studies focused on the possible effects that animal metabolism would have on the signal (Ambrose and DeNiro, 1986), subsequent studies of d15N values in plants across aridity gradients have indicated that it may not be necessary to look towards herbivore metabolism for the link between d15N values and rainfall, as clear correlations are identified between higher d15N values and decreased rainfall in both C3 and C4 plants (Heaton, 1987; Murphy and Bowman, 2006; Swap et al., 2004) and soils (Aranibar et al., 2004). Murphy and Bowman's (2006) spatially-extensive studies of d15N values in both grass and kangaroo bone from across Australia reveal a remarkably consistent relationship between plant and bone d15N signals, suggesting that water availability, through its influence on the isotopic signature of plants/diet, is the primary control on animal d15N with metabolism having no clear effect. Austerlitz midden: 20°27.83'S, 14°26.54'E DATA: Chase et al. 2010 Austerlitz, Namibia hyrax midden d15N data Column 1: Age, Calendar years before present Column 2: d15N, per mil CalYrBP d15N(‰) 1461 17.57 1522 18.26 1643 19.21 1733 18.91 1794 19.39 1885 18 1945 18.48 2036 17.9 2096 17.58 2187 17.04 2247 16.86 2368 17.38 2459 17.34 2520 17.33 2610 18.42 2701 16.51 2792 15.46 2883 14.66 2977 15.26 3042 17.23 3141 16.78 3206 16.67 3304 14.05 3370 14.99 3468 14.38 3533 13.87 3631 13.56 3697 14.75 3795 15.28 3860 14.56 3958 13.85 4012 12.51 4075 14.22 4139 15.29 4202 13.26 4265 15.15 4307 14.95 4350 15.81 4413 13.73 4476 14.18 4518 14.04 4560 14.26 4603 13.7 4666 13.49 4708 13.58 4771 12.84 4814 13.06 4877 12.68