This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Although the Near East, including Iran, is described as having a Mediterranean climate, the region actually straddles three climatic zones: Mediterranean, mixed-continental, and monsoonal. Each zone is defined by differences in the seasonality of precipitation. NW Iran is currently a mixture of continental and Mediterranean climate, such that peak precipitation occurs in March to May. Today, SW Iran is dominated by the Mediterranean climate and experiences peak precipitation between December and March. In the past this area may have been influenced by the Indian Ocean monsoon (summer rains), which today does not extend north of Oman. Seasonal timing of precipitation is not inconsequential as it impacts vegetation as well as the timing of river and groundwater recharge, necessitating careful resource management. This study is part of a larger international effort focused on understanding the climatic evolution of western Iran and its impacts on vegetation. This proposal aims to reconstruct effective moisture in western Iran from geochemical and lithologic proxies archived in lake sediments. These data will be shared with collaborators from France, Iran, and Germany to explore phase relationships among climate, vegetation, and lake levels across two interglacials. This project will fill a much-needed gap in the spatial distribution of long climate records necessary to verify climate models. It also presents a unique opportunity to examine variations in the eastern extent of the Mediterranean climate and northern extent of the monsoon climate. Two lakes, Urmia and Maharlou, were chosen for this study based on location and length of records (~200,000 yrs). L. Urmia in NW Iran is located on the boundary between Mediterranean (winter-wet) and continental (spring-wet) climate, and should be sensitive to small and/or abrupt shifts in this boundary. L. Maharlou is located in SW Iran and may record extreme northward excursions of the Indian Ocean monsoon (IOM). Centennial-resolution changes in effective moisture at each lake are based on del-18O and del-13C records of aragonitic fecal pellets. Lake-level reconstructions is a joint effort, with this project contributing carbon/nitrogen and grain-size data. Chronologies are established by a combination of 14C dates on charcoal and Th-U disequilibrium dates on fecal pellets. A test of the latter method has yielded a successful date. The records of effective moisture are combined with pollen (France) and lithologic (Iran, Germany) data to test whether Atlantic sea-surface temperatures are the main factor controlling the position of the westerlies and thus millennial-scale fluctuations in moisture; whether the IOM increased moisture availability in SW Iran during the early part of the Last Interglacial; whether the hydroclimatic evolution of the Last Interglacial will mirror that of the Holocene; and whether during both the penultimate and last glacial periods, interstadials have greater effective moisture marked by decreases in the del-18O values.
