Description: It has long been known that extreme changes in North African hydroclimate occurred during the late Pleistocene yet many discrepancies exist between sites regarding the timing, duration and abruptness of events such as Heinrich Stadial (HS) 1 and the African Humid Period (AHP). The hydroclimate history of the Nile River is of particular interest due to its lengthy human occupation history yet there are presently few continuous archives from the Nile River corridor, and pre-Holocene studies are rare. Here we present new organic and inorganic geochemical records of Nile Basin hydroclimate from an eastern Mediterranean (EM) Sea sediment core spanning the past 28 ka BP. Our multi-proxy records reflect the fluctuating inputs of Blue Nile versus White Nile material to the EM Sea in response to gradual changes in local insolation and also capture abrupt hydroclimate events driven by remote climate forcings, such as HS1. We find strong evidence for extreme aridity within the Nile Basin evolving in two distinct phases during HS1, from 17.5 to 16 ka BP and from 16 to 14.5 ka BP, whereas peak wet conditions during the AHP are observed from 9 to 7 ka BP. We find that zonal movements of the Congo Air Boundary (CAB), and associated shifts in the dominant moisture source (Atlantic versus Indian Ocean moisture) to the Nile Basin, likely contributed to abrupt hydroclimate variability in northern East Africa during HS1 and the AHP as well as to non-linear behavior of hydroclimate proxies. We note that different proxies show variable gradual and abrupt responses to individual hydroclimate events, and thus might have different inherent sensitivities, which may be a factor contributing to the controversy surrounding the abruptness of past events such as the AHP. During the Late Pleistocene the Nile Basin experienced extreme hydroclimate fluctuations, which presumably impacted Paleolithic cultures residing along the Nile corridor.

Description: Biomass burning on the African continent is widespread and interactions with climate, vegetation dynamics and biogeochemical cycling are complex. To obtain a better understanding of these complex relationships, African fire history has been widely studied, although mostly on relatively short time-scales (i.e. yrs to kyrs) and less commonly on long-term scales. Here, we present a 192-kyr, continuous biomass-burning record from sub-Saharan Northwest Africa based on the fire biomarker levoglucosan in a marine sediment core offshore Guinea. Notable features of our record include an increase in levoglucosan accumulation at 80 ka and two peaks at 50-60 ka. The event at 80 ka is likely related to an overall increase in sedimentation rates rather than an increase in biomass burning in the Northwest African savanna region. Our record indicates that glacial/interglacial changes in regional climate and vegetation composition (C3 vs. C4 plants) were not a major influence on biomass burning over the last 192 kyrs. However, we suggest that the burning events at 50-60 ka might be caused by increased occurrence of C3 vegetation and human settlement in this region. At this time, the savanna region became wetter and fuel loads likely increased. Therefore, the region was more hospitable for humans, who likely used fire for hunting activities. Collectively, we hypothesize that on longer (glacial/interglacial) timescales, biomass burning, regional climate and African vegetation are not necessarily coupled, while around 50-60 ka, higher fuel loads and human fire-use may have influenced fire occurrence in sub-Saharan Northwest Africa.

Description: The study of past sedimentary records from coastal margins allows us to reconstruct variations in terrestrial input into the marine realm and to gain insight into continental climatic variability. There are numerous organic proxies for tracing terrestrial input into marine environments but none that strictly reflect the input of river-produced organic matter. Here, we test the fractional abundance of the C32 alkane 1,15-diol relative to all 1,13- and 1,15-long-chain diols (FC32 1, 15) as a tracer of input of river-produced organic matter in the marine realm in surface and Quaternary (0-45 ka) sediments on the shelf off the Zambezi and nearby smaller rivers in the Mozambique Channel (western Indian Ocean). A Quaternary (0-22 ka) sediment record off the Nile River mouth in the eastern Mediterranean was also studied for long-chain diols. For the Mozambique Channel, surface sediments of sites most proximal to Mozambique rivers showed the highest F1, 15 - C32 (up to 10 k%). The sedimentary record shows high (15-35 k%) pre-Holocene F1, 15 - C32 and low (〈 10 k%) Holocene F1, 15 - C32 values, with a major decrease between 18 and 12 ka. F1, 15 - C32 is significantly correlated (r2 = 0.83, p 〈 0.001) with the branched and isoprenoid tetraether (BIT) index, a proxy for the input of soil and river-produced organic matter in the marine environment, which declines from 0.25 to 0.60 for the pre-Holocene to 〈 0.10 for the Holocene. This decrease in both FC32 1, 15 and the BIT is interpreted to be mainly due to rising sea level, which caused the Zambezi River mouth to become more distal to our study site, thereby decreasing riverine input at the core location. Some small discrepancies are observed between the records of the BIT index and FC32 1, 15 for Heinrich Event 1 (H1) and the Younger Dryas (YD), which may be explained by a change in soil sources in the catchment area rather than a change in river influx. Like for the Mozambique Channel, a significant correlation between FC32 1, 15 and the BIT index (r2 = 0.38, p 〈 0.001) is observed for the eastern Mediterranean Nile record. Here also, the BIT index and FC32 1, 15 are lower in the Holocene than in the pre-Holocene, which is likely due to the sea level rise. In general, the differences between the BIT index and FC32 1, 15 eastern Mediterranean Nile records can be explained by the fact that the BIT index is not only affected by riverine runoff but also by vegetation cover with increasing cover leading to lower soil erosion. Our results confirm that FC32 1, 15 is a complementary proxy for tracing riverine input of organic matter into marine shelf settings, and, in comparison with other proxies, it seems not to be affected by soil and vegetation changes in the catchment area.

Description: This dataset includes branched glycerol dialkyl glycerol tetraether (brGDGT) fractional abundances from sediment core, surface sediments, settling particulate matter, and soils of Lake 578 (61.08° N, 45.61° W), southern Greenland. BrGDGTs are lipids thought to be biosynthesized by anaerobic bacteria. These compounds are abundant in lake sediments and potentially can be used as proxies for evaluating past environmental conditions. To improve the application of the brGDGT paleothermometer in high latitudes, we examine brGDGTs distribution from Lake 578, located in southern Greenland. In July 2016, a 70 cm percussion core was collected from Lake 578, and the sediment trap system was deployed. Sediment traps were assembled using a 25.5 cm diameter funnel with a 100 mL centrifuge tube attached at the bottom and allowed to accumulate material for 1 year. Three sediment traps were placed at 5 m, 10 m, and 14 m depths. Each summer (2017, 2018, and 2019) the sediment traps were recovered, the centrifuge tubes exchanged with new ones, and the traps re-deployed at the same location. 5 surface sediment samples were collected with an Ekman grab sampler in July 2018. 13 catchment soil samples were collected from the Lake 578 watershed area. Sediment trap samples, surface sediment samples, and soil samples were frozen until analysis. The sediment core was stored at 4 °C until analysis. All brGDGT samples were analyzed on an Agilent 1260 UHPLC coupled to an Agilent 6120 MSD with the newer methods of Hopmans et al. (2016) to separate the compounds.