A surprisingly short early Holocene humid spell inferred from remnant shorelines and palaeolake deposits in northern Arabia

Early Holocene greening of the Sahara has been inferred from many sedimentary archives (e.g. Hoelzmann et al., 2001). Likewise, over the last two decades similar reconstructions of lakes and a more humid climate have been established for the southern Arabian Peninsula (e.g. Fleitmann et al., 2007; Engel et al., 2017) and the Levant (Bar-Matthews et al., 2003). Such evidence also exists for northern Arabia (Schulz and Whitney, 1986; Crassard et al., 2013; Zielhofer et al., 2018), but is limited in sufficiently robust proxy data and chronological resolution, hampering our understanding of the scarce archaeological record of that time (Hilbert et al., 2014). In this paper, we present latest results of the ongoing DFG-funded project CLEAR, which explores the highly resolved palaeolake record of the sabkha basin in the oasis of Tayma, northern Arabia. Today only flooded episodically after rainfall events, the endorheic basin is encircled by a ring of isolated shoreline deposits in an altitudinal corridor of only a few metres, consisting almost entirely of Melanoides tuberculatus and Hydrobia sp. shells, Amphibalanus amphitrite carapaces, foraminifers, and ostracods, with minor amounts of siliciclastic sand (Engel et al., 2012; Pint et al., 2017). These deposits have recently been mapped and dated by 14C and OSL, and indicate the presence of an early Holocene lake with a depth of up to 17 m and an area of up to 22 km². They correlate with partly varved lake sediments of the central basin according to the 14C-(pollen concentrates), varve- and cryptotephra-based chronology (Dinies et al., 2015; Neugebauer et al., 2017). In the framework of CLEAR, the palaeolake sequence was subjected to detailed sedimentological, geochemical and micropalaeontological analyses (grain-size distribution, XRD, µXRF, thin- section studies, foraminifera, ostracods, diatoms, pollen, stable isotopes, C/N, lipid biomarkers). Current results indicate increasing moisture at Tayma from c. 9300 cal. yrs. BP with pronounced humid conditions only over the second half of the 9th millennium BP, represented by an annually varved sequence of aragonite-, diatom-, and clastic silt- dominated laminae. After 7950 cal. yrs. BP, aridification set in, leading to sabkha development at c. 4200 cal. yrs. BP and the accumulation of aeolian sand. The rather short period of increased moisture availability contrasts with adjacent records from southern Arabia and the Levantine region (Bar-Matthews et al., 2003; Fleitmann et al., 2007), which reflect more humid conditions over several millennia during the early to mid-Holocene. This is a contribution to the research project “CLEAR – Holocene Climatic Events of Northern Arabia” (DFG PL 535/2-1; FR 1489/5-1; EN 977/2-1); see also contribution Pint et al. (this conference) and project website https://clear2018.wordpress.com. References: Bar-Matthews, M, et al., Geochim. Cosmochim. Acta 67, 3181–3199 (2003); Crassard, R., et al., PLOS ONE 8, e68061 (2013); Dinies, M., et al., Quat. Int. 382, 293–302 (2015); Engel, M., et al., 2012, Quat. Int. 266, 131–141 (2012); Engel, M., et al., Global Planet. Change 148, 258–267 (2017); Fleitmann, D., et al., Quat. Sci. Rev. 26, 170–188 (2007); Hilbert, Y.H., et al., J. Archaeol. Sci. 50, 460–474 (2014); Hoelzmann, P., et al., Palaeogeogr. Palaeocl. 169, 193–217 (2001); Neugebauer, I., et al., Quat. Sci. Rev. 170 269–275 (2017); Pint, A., et al., J. Foram. Res. 42, 175–187 (2017); Schulz, E., Whitney, Hydrobiologia 143, 175–190 (1986); Zielhofer, C., et al., Quat. Int. 473, 120–140 (2018).

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