Sediment cores recovered by the Olduvai Gorge Coring Project (OGCP) in 2014 afford the opportunity to examine the coupling of biogeochemical evidence for climatic and environmental change within the context of hominin evolution at this renowned East African locality. Investigations of elemental (total organic carbon – TOC or Corg wt%, carbon to nitrogen ratio - C/N), molecular (source-specific biomarkers), and isotopic (δ13Corg, δ2HnC31) compositions of organic matter provide evidence for temporal changes in sedimentary materials derived from terrestrial plants (C3, C4) and aquatic producers (algae, sponges, cyanobacteria), and in precipitation. The 13 kyr record of Upper Bed I immediately preceding Tuff IB extends high-resolution stratigraphic profiles of precession-scale alternations of wetter and drier conditions to encompass the entire interval from the Bed I Basalt to Tuff IB. The second wetter interval, designated W2, records local influences on climate and water supply consistent with evidence for discrete sediment sources based its physical properties (e.g., gamma radiation, magnetic susceptibility) compared with the overall sequence. The δ13CTOC values for wetter interval W2 reveal two millennial-scale (~2.5 kyr) drier episodes followed by a shift in the dominance of C3 over C4 plants accompanying the transition to a drier climate (D3). Moreover, biogeochemical data for Upper Bed I show that changes from drier to wetter conditions occur more rapidly (~900 yr) than wetter to drier transitions (>2.6 kyr), based on interpolated ages. In addition, biomarker profiles indicate that aquatic plants, primarily algae and macrophytes, may have been subject to more profound and faster fluctuations than variations in terrestrial vegetation expressed in terms of the relative proportions of woodland and grassland settings. Thus, environmental and climatic changes not only influenced the availability of resources of food and shelter for hominins within the Olduvai region but also led to their variation on centennial to millennial to precessional timescales.
Bibliographical noteFunding Information:
We would like to acknowledge and thank the Stone Age Institute for organizing and funding the Olduvai Gorge Coring Project (OGCP) with grants from the Kamen Foundation , the Gordon and Ann Getty Foundation , the John Templeton Foundation , the Fred Maytag Foundation , Kay and Frank Woods , and NSF ( BCS1623873 ). Additionally, we are grateful to the Tanzanian Commission for Science and Technology, Tanzanian Department of Antiquities, Ministry of Natural Resources & Tourism, and the Ngorongoro Conservation Area Authority (NCAA) for enabling the collection of samples and continuing support of OGCP research. Support for biomarker preparation included funds provided by the Department of Earth and Atmospheric Sciences ( Indiana University ). NSF grant CHE1726633 enabled purchase of the GC-QTOF-MS (Mass Spectrometry Facilities at Indiana University) utilized in this study for all biomarker analyses. We would like to thank Dr. Al Deino (UC Berkeley) and coauthors for sharing new chronological data for OGCP Core 2A prior to publication and Dr. Arndt Schimmelmann (Indiana University) for providing both an n -alkane standard mix, and the squalane standard. In addition, we would like to thank LacCore for their assistance with core handling and sample collection, as well as providing the core scan data. The manuscript also benefited from the comments of anonymous reviewers that prompted extensive revisions.
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