Climate Change During Late Holocene Reflected By Sediment Record In Faiyum Depression, Egypt

Recently, formation and evolution of monsoon and its impact on regional or global climate have become hot research spots. African is one of area affected remarkably by climate-monsoon change. During the early and mid- Holocene, Sahra Desert was totally not like today, where oasis prevailed and ancient civilization flourished. However, monsoon began to weaken from late Holocene and Nile River became drought, which resulted in collapes of ancient Egypt civilization. It is not difficult to understand that climate-monsoon change have a profound impact on the process of human civilization, which is necciserily needed to be studied further.The Faiyum Depression, a flood plain of the Nile downstream, lies in the margin of the Sahara Desert. It is feeded by sediments of the Nile and the Sahara Desert, so it has been an important agricultural area in Egypt history. The Nile runoff is mainly controlled by upstream monsoonal rainfall that depends heavily on ITCZ (Intertropical Convengence Zone) movement and intensity of the Indian Ocean monsoon. In this study, we got a late Holocene core FAYM in the northeast of Faiyum Depression. Through analysis of 14C dating, grain size, magnetism, clay mineral,as well as mineral statistic, the paper is aiming to discuss local response to late Holocene climate-monsoon change in northern Africa.The result showed that Faiyum sediments of late Holocene recorded several changes of climate and monsoon:During 3800-3200cal.yrBP, sediment is mainly composed of silt and clay and grain-size frequency shows biomodal distribution pattern:high peak with fine grain size and low one with with coarse grain size. Subangular quartze grains have a high propotion in the sediments and magnetism parameters of balk sediment are relatively high. All above indicates the Fayium receives more sediments from Nile River than Sahara, which further suggests northward movement of ITCZ and high intensity of Indian Ocean monsoon.From 3200 to 2500cal.yrBP, sediment become coarse and grain-size distribution becomes from biomodal to unimodal pattern gradually which is characteristic of a very coarse high peak. The content of smectite and illite increase and kaolinite decreses. The eolian quartz and gypsum content increase, but the content of carbonate decreses. All these imply that Sahara Desert has been a major provenance of Faiyum and Nile runoff reduces sharply due to southward movement of ITCZ and weak Indian Ocean monsoon.From 2500 to 2000cal.yrBP, sediment suddenly become fine with a biomodal pattern of sediment grain-size distribution. The high modal peak is located in fine grain size and the low peak in the coarse sediment. The magnetism increases in the earlier period (3.30-2.86m at depth) and largely decreases during the late period (2.86-2.60m), maybe indicating deeper water. This is also witnessed by high content of carbonate. Round quartz grains reduces remarkably, implying Nile sediment supply. All these changes indicate relative wet climate and large discharges of Nile River, which is benificial from northward movement of ITCZ and intensified Indian Ocean monsoon.Since 2000cal BP, the magnetism parameter is the highest. In the mean time gypsum content increases and carbonate reduces. More round quartze grains are found. These suggest that climate begins to be dry and the lake becomes shallow. Besides, human activities become strong and frequent during this period which can be seen from water conservancy projects, dams, and irrigation channels. These activities can artifically regulat Nile flood and disturb surficial sediments in Faiyum, which is the possible reason of high magnetism. In short, these changes reveal that climate is dry and Nile runoff reduces, due to southward movement of ITCZ and weakened Indian Ocean monsoon.