Since the beginning of the Neolithic Era, ca. 9500 B.P., some of the first and most outstanding human civilizations rose across the Fertile Crescent, extending between northern Persian Gulf in Iran and the eastern Mediterranean Sea. Evidence is mounting from paleoclimate proxy records around the globe that human societies have been impacted by abrupt climate shifts throughout the Holocene. Very few studies, however, have been conducted in West Asia that document climate variability at interannual to centennial time scales, which are most relevant to the flourishing and diminishing of human societies. This project establishes the first chronologically-robust records of interannual atmospheric dust deposition originating in the African-Asian 'dust belt,' and centennial reconstruction of paleo-moisture based on organic biomarkers, from two rain-fed peat mires in NW Iran. A significant transformative aspect of this project is the combination of organic and inorganic geochemical proxies, which allows documentation of a detailed history of atmospheric exchange between West Asia, the North Atlantic and the African-Asian monsoon system, and their influence on the dominant climate regime in West Asia. Unraveling the role of mid-latitude westerlies, the Siberian Anticyclone and the Indian Ocean summer monsoon (IOSM) in shaping the Holocene climate in this region has major implications for modern societies, as well as ancient civilizations. If, for instance, the insolation-induced intensification of the IOSM coincided with expansion of dry climate over West Asia during the early Holocene, similar conditions can be expected from changes in IOSM intensity from anthropogenically enhanced global warming, with potentially dire socio-economical consequences across the Middle East. High-resolution records from this study also present a rare opportunity to examine possible links between solar activity and changes in mid-latitude atmospheric circulation pattern on interannual to millennial time scales. Broader Impacts: The project is part of a 5-year endeavor by an early-career PI to establish a Holocene Climate Laboratory. Paleoclimate research in this lab will foster international collaborations among researchers from RSMAS Climate Studies, Virginia Institute of Marine Science, Texas A&M University, Institut méditerranéen d'écologie et de paléoécologie (France), the Iranian National Center for Oceanography and the University of Tehran, Iran. The lab encourages enthusiastic undergraduate students to participate in paleoclimate-related research using clean-lab geochemical methods. This project provides opportunities for at least three undergraduate students to receive practical training in this facility. Undergraduate students are involved in sample preparation and analytical measurements performed using a new state-of-the-art Neptune High-resolution Multi-collector Inductively Coupled Plasma Mass Spectrometer. In addition, a new course on the historical and modern impact of Holocene climate change on human societies will be taught. The material and data collected during the course of this NSF-funded project is used in this and other paleoclimate courses. Traditionally, organic and inorganic geochemical proxies have been utilized independently in paleoclimate studies. This is because few investigators have had the opportunity to receive training in these two areas of paleoclimate research. This collaboration between an inorganic paleoclimatologist and an organic geochemist will equip a new generation of students with expertise in the combined use of inorganic and organic paleo proxies to explore new frontiers in the broad field of paleoclimate research.
Since the beginning of the Neolithic Era ca. 9500 years before present (y BP), some of the first and most outstanding human civilizations rose across the Fertile Crescent, an area extending between the northern Persian Gulf and the eastern and southeastern Mediterranean Sea. Evidence is mounting from paleoclimate reconstructions that human societies have been impacted by abrupt climate change on the scale of decades to centuries throughout the Holocene, the current period of interglaciation that began ~11,700 y BP. Few high-resolution studies, however, have been conducted in the interior of West Asia that document climate variability at decadal to centennial timescales, which are most relevant to the flourishing and diminishing of human societies. With extensive involvement and contributions from two undergradate and one graduate students, we developed high-resolution records of changes in atmospheric dust input and paleo-environmental conditions based on inorganic and organic geochemical data from two ombrotrophic (rain fed) peat mires in NW Iran that encompass the last 13000 y BP. In the longest record from the Neor peat mire (37°57'37"N, 48°33'19"E), down-core variations in major and trace elements, organic carbon accumulation, stable carbon isotope values, organic biomarker abundances and compound-specific hydrogen isotope values for leaf wax compounds suggest that dry and dusty conditions prevailed prior to the Holocene followed by a wet and low dust period during the early Holocene (~11000-6000 y BP). In contrast, higher dust and lower moisture availability were dominant during middle to late Holocene (6000 y BP-present). Geochemical fingerprinting of dust particles with radiogenic Sr-Nd-Hf isotopic composition and rare earth element anomalies indicated changes in the sources of dust to the study area prior to and during the Holocene. Time-series analysis of aeolian input revealed periodicities at 540, 1050 and 2940 years that correspond with solar variability and internal climate feedbacks. Transitions in major Mesopotamian and Persian civilizations, including the collapse of the Akkadian empire at 4,200 y BP, Ur III empire at 3,955 yr BP, the Elam empire at 2,500 y BP and the Achaemenids around 2,280 y BP overlap with major dust events (dryer periods) from this study. As the Mediterranean climate of northwest Iran is influenced by mid-latitude Westerlies and the winter expansion of the Siberian Anticyclone, preservation of organic matter within the crater peat of Almalou (37°39′55″N, 46°37′55″E) recorded changes in atmospheric deposition and paleo-environmental conditions during the last 2400 years. We studied a high-resolution multi-proxy record of climate variability from a 3-m peat core recovered from the crater peat. Down-core X-ray fluorescence measurements of selected lithogenic and redox-sensitive elements revealed several periods of elevated abundances that we interpret to correspond with enhanced atmospheric dust deposition. These intervals of high atmospheric dust coincide with historical records of drought and famine in Iran since 2000 BP. Wavelet analysis conducted on selected lithogenic elements for the first 1500 years revealed a major periodicity around 261 y., which may be related to the De Vries (~210 y) and 520-year solar cycles through internal climate feedbacks. When compared with a pollen record of anthropogenic herbs from the same crater peat, stable carbon isotopes and lithogenic elements from our study indicate that contributions from anthropogenic plant species, which provide a measure of ancient agricultural activities in the region, increased during times of low atmospheric dust (wetter periods) and were coincident with shifts in the values of bulk stable carbon isotopes. We performed climate modeling experiments to examine the role of solar forcing on the position of the Northern Hemisphere Westerly Jet over West Asia as a possible mechanism for shifts in dust sources. The results indicate a clear poleward (equatorward) shift in the main axis of the northern Hemisphere Westerly Jet when boreal summer insolation was high (low). These findings corroborate that shifts in dust source provenance during the Holocene were likely caused by changes in atmospheric circulation over the region. This highlights the importance of orbital forcing on the circulation dynamics of the Northern Hemisphere mid-latitudes. Previous studies in the Arabian Sea, an area strongly influenced by the Indian Ocean Summer Monsoon and meridional migration of the Westerlies have shown a strong atmospheric teleconnection between the North Atlantic climate and the Indian Ocean on millennial timescales during the last glacial period. Agreement between terrestrial multi-proxy records from this study and other regional records, including the strength of the Siberian Anticyclone, confirm the prevalence of this teleconnection between North Atlantic climate and West Asia during the last glacial termination and the Holocene. Along with existing materials, findings from this study have been utilized in the development of a new undergraduate course on Climate Change that is now part of the curriculum for a minor undergraduate degree at the Marine Science Program of the Rosenstiel School of Marine and Atmospheric Science of the University of Miami.
