HOLOCENE GRASSLAND DYNAMICS IN NORTHERN ARABIA: POLLEN, CARBON ISOTOPE AND PHYTOLITH ANALYSES

The Arabian Peninsula is a key area for understanding late Quaternary climate behaviour and ecosystem responses in the low latitude regions and is central to our understanding of rapid, high-amplitude shifts in climate driven by variations in the forcing of SW monsoonal rainfall. However, no high-resolution terrestrial records exist from the entire Arabian sub-continent, unlike for North Africa and Asia.

The northeastern end of the Rub' al Khali sand sea contains a number of interdune dry lake basins of Holocene age. At Awafi, Ras al-Khaimah, United Arab Emirates, multi-proxy analyses provide a detailed terrestrial record from the Arabian sub-continent which couples pollen and phytolith analyses with physical and chemical methods. This has permitted the study of ecosystem responses to rapid and gradual climatic changes forced by the fluctuations in the SW monsoon from the north-eastern Rub' al Khali over the late Quaternary period.

Phytoliths in particular are well preserved in dryland regions and unlike pollen studies permit the reconstruction of grassland dynamics by distinguishing the dominant grass sub-family. Phytolith indexes are used to distinguish between C3 Pooidae (cool temperate), C3-C4 Panicoideae (warm humid) and short C4 Chloridoideae (warm dry) grass types. In addition phytolith studies can permit tree cover density to be estimated.

The early Holocene record shows the development of savannah grassland with some woodland elements comprising Acacia and Prosopis. The grassland is characterised by unusually high levels of C3-Pooidae (cool temperate) types. This becomes replaced by C4 - Panicoidae grasses adapted to warm humid conditions along with scattered woody elements. An abrupt arid phase in the later Holocene sees the development of scattered short grassland elements of warm dry C4- Chloridoidae types. Comparisons between modern pollen and phtolith samples and those from the Holocene are also made. These data outline the ecosystem dynamics and carbon cycling in response to palaeomonsoon variability during the Holocene.