ALBERT

Description: We provide stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope measurements in individual calcitic valves of extant ostracode species, Sclerocypris clavularis, from modern sediments in 17 sites across Lake Turkana, eastern Africa. These sediments were collected using a modified Ekman dredge during May-November, 1979. Pooled statistics of these individual ostracode valve analyses (IOVA) of δ¹³C and δ¹⁸O measurements (n = 329) at each site show strong correlations with lake hydrological parameters. Within-site variance in IOVA-δ¹³C is larger (~60%) than that of IOVA-δ¹⁸O. Yet, pooled averages exhibit a systematic pattern with higher δ values towards the southern part of the lake, away from Omo River inflow, which is the largest riverine input into Lake Turkana (comprising ~90% of overall inflows). We suggest that the latitudinal δ¹³C gradient may arise from low riverine δ¹³C and low organic matter δ¹³C as a productivity response to nutrient-rich Omo River inflow towards the north. The δ¹⁸O pattern may be explained by the diminishing influence of Omo River inflows and more evaporation driving higher IOVA-δ¹⁸O values towards the windier, southern basin. We conclude that pooled IOVA statistics in Omo-Turkana sediments can aid interpretations of past regional paleohydrology and its variability in this basin.

Description: This dataset contains measurements of individual ostracode valve analyses (IOVA), including stable oxygen (δ¹⁸O) and carbon (δ¹³C) isotopes, and length/width, and mass measurements, at 17 sites across Lake Turkana, eastern Africa. These sediments were collected using a modified Ekman dredge during May–November 1979. The stable isotopic measurements were conducted at the [Paleo² Laboratory at the University of Arizona|https://thirumalai.geo.arizona.edu/] on a Thermo Kiel IV Carbonate Device coupled to a 253 Plus IRMS; the length/width measurements were performed on a MeijiTechno HDZ7000TS Digital Zoom Microscope System, and mass of each valve was measured using a Sartorius Cubis II Ultra-Micro Balance. Details can be found in https://doi.org/10.1029/2022GC010790

Description: This dataset contains pooled statistics of stable isotope and shell measurements of individual ostracode valve analyses (IOVA) alongside available in-situ measurements of pH, surface and bottom water temperature (BWT), total number of valves analyzed per site, IOVA-δ¹⁸O, IOVA-δ¹³C, shell mass, shell length/width, along with their average and standard deviations at 17 sites across Lake Turkana, eastern Africa. These modern sediments were collected using a modified Ekman dredge during May to November 1979. The stable isotopic measurements were conducted at the [Paleo² Laboratory at the University of Arizona|https://thirumalai.geo.arizona.edu/] on a Thermo Kiel IV Carbonate Device coupled to a 253 Plus IRMS; the length/width measurements were performed on a MeijiTechno HDZ7000TS Digital Zoom Microscope System, and mass of each valve was measured using a Sartorius Cubis II Ultra-Micro Balance. Details about the materials can be found in https://doi.org/10.1029/2022GC010790

Description: It is shown that the existence of neutral interstellar clouds constrains the interaction of any particulate dark-matter candidate with atomic hydrogen to be quite small. Even for a halo particle of mass 1 PeV (10 to the 6 GeV), it is shown that the cross section with hydrogen must be smaller than the typical atomic cross section that is expected for a positively charged particle bound to an electron. The argument presented is that if the clouds are in equilibrium, then the rate at which energy is deposited by collisions with dark-matter particles must be smaller than the rate at which the cloud can cool. This argument is used to constrain the interaction cross section of dark matter with hydrogen. Remarks are made on the general viability of charged dark matter. Comments are also made on a bound which derives from the dynamical stability of the halo.

Description: Despite eastern Africa being a key location in the emergence of Homo sapiens and their subsequent dispersal out of Africa, there is a paucity of long, well-dated climate records in the region to contextualize this history. To address this issue, we dated a ∼293 m long composite sediment core from Chew Bahir, south Ethiopia, using three independent chronometers (radiocarbon, 40Ar/39Ar, and optically stimulated luminescence) combined with geochemical correlation to a known-age tephra. The site is located in a climatically sensitive region, and is close to Omo Kibish, the earliest documented Homo sapiens fossil site in eastern Africa, and to the proposed dispersal routes for H. sapiens out of Africa. The 30 ages generated by the various techniques are internally consistent, stratigraphically coherent, and span the full range of the core depth. A Bayesian age-depth model developed using these ages results in a chronology that forms one of the longest independently dated, high-resolution lacustrine sediment records from eastern Africa. The chronology illustrates that any record of environmental change preserved in the composite sediment core from Chew Bahir would span the entire timescale of modern human evolution and dispersal, encompassing the time period of the transition from Acheulean to Middle Stone Age (MSA), and subsequently to Later Stone Age (LSA) technology, making the core well-placed to address questions regarding environmental change and hominin evolutionary adaptation. The benefits to such studies of direct dating and the use of multiple independent chronometers are discussed. Highlights • Four independent dating methods applied to ∼293 m lake core from southern Ethiopia. • Reveals 620 ka high-resolution sedimentary record near key fossil hominin sites. • Mean accumulation rate of 0.47 mm/a comparable to other African lacustrine sediments. • Accumulation rate fell to 0.1 mm/a during MIS 2, likely due to reduced sediment supply. • Use of multiple independent chronometers is a powerful approach in lake settings.