Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean.

The melting Laurentide Ice Sheet discharged thousands of cubic kilometres of fresh water each year into surrounding oceans, at times suppressing the Atlantic meridional overturning circulation and triggering abrupt climate change. Understanding the physical mechanisms leading to events such as the Younger Dryas cold interval requires identification of the paths and timing of the freshwater discharges. Although Broecker et al. hypothesized in 1989 that an outburst from glacial Lake Agassiz triggered the Younger Dryas, specific evidence has so far proved elusive, leading Broecker to conclude in 2006 that "our inability to identify the path taken by the flood is disconcerting". Here we identify the missing flood path-evident from gravels and a regional erosion surface-running through the Mackenzie River system in the Canadian Arctic Coastal Plain. Our modelling of the isostatically adjusted surface in the upstream Fort McMurray region, and a slight revision of the ice margin at this time, allows Lake Agassiz to spill into the Mackenzie drainage basin. From optically stimulated luminescence dating we have determined the approximate age of this Mackenzie River flood into the Arctic Ocean to be shortly after 13,000 years ago, near the start of the Younger Dryas. We attribute to this flood a boulder terrace near Fort McMurray with calibrated radiocarbon dates of over 11,500 years ago. A large flood into the Arctic Ocean at the start of the Younger Dryas leads us to reject the widespread view that Agassiz overflow at this time was solely eastward into the North Atlantic Ocean.

Longstanding behavioural stability in West Africa extends to the Middle Pleistocene at Bargny, coastal Senegal.

Middle Stone Age (MSA) technologies first appear in the archaeological records of northern, eastern and southern Africa during the Middle Pleistocene epoch. The absence of MSA sites from West Africa limits evaluation of shared behaviours across the continent during the late Middle Pleistocene and the diversity of subsequent regionalized trajectories. Here we present evidence for the late Middle Pleistocene MSA occupation of the West African littoral at Bargny, Senegal, dating to 150 thousand years ago. Palaeoecological evidence suggests that Bargny was a hydrological refugium during the MSA occupation, supporting estuarine conditions during Middle Pleistocene arid phases. The stone tool technology at Bargny presents characteristics widely shared across Africa in the late Middle Pleistocene but which remain uniquely stable in West Africa to the onset of the Holocene. We explore how the persistent habitability of West African environments, including mangroves, contributes to distinctly West African trajectories of behavioural stability.

Timing and dynamics of Late Wolstonian Substage 'Moreton Stadial' (MIS 6) glaciation in the English West Midlands, UK.

Glaciation during the late Middle Pleistocene is widely recognized across continental northwest Europe, but its extent and palaeoenvironmental significance in the British Isles are disputed. Although glaciogenic sediments at Wolston, Warwickshire, in the English West Midlands, have been used to define the stratotype of the Wolstonian Stage, their age has been variably assigned between marine isotope stages (MIS) 12 and 6. Here we present sedimentological and stratigraphical observations from five sites across the English West Midlands whose chronology is constrained by new luminescence ages from glaciofluvial sediments, supplemented by cosmogenic 36Cl exposure dating of erratic boulders. The ages suggest that between 199 ± 5 and 147 ± 2.5 ka the British Ice Sheet advanced into the English West Midlands as far south as Moreton-in-Marsh, Gloucestershire. This advance is assigned to the Moreton Stadial of the Late Wolstonian Substage. Dating of the glaciation to this substage allows correlation of the Moreton Stadial glacial deposits in the English West Midlands with those of the Drenthe Stadial during the Late Saalian Substage across continental northwest Europe.

Continuity of the Middle Stone Age into the Holocene.

The African Middle Stone Age (MSA, typically considered to span ca. 300-30 thousand years ago [ka]), represents our species' first and longest lasting cultural phase. Although the MSA to Later Stone Age (LSA) transition is known to have had a degree of spatial and temporal variability, recent studies have implied that in some regions, the MSA persisted well beyond 30 ka. Here we report two new sites in Senegal that date the end of the MSA to around 11 ka, the youngest yet documented MSA in Africa. This shows that this cultural phase persisted into the Holocene. These results highlight significant spatial and temporal cultural variability in the African Late Pleistocene, consistent with genomic and palaeoanthropological hypotheses that significant, long-standing inter-group cultural differences shaped the later stages of human evolution in Africa.

Long-term sediment decline causes ongoing shrinkage of the Mekong megadelta, Vietnam.

Since the 1990s the Mekong River delta has suffered a large decline in sediment supply causing coastal erosion, following catchment disturbance through hydropower dam construction and sand extraction. However, our new geological reconstruction of 2500-years of delta shoreline changes show that serious coastal erosion actually started much earlier. Data shows the sandy coast bounding river mouths accreted consistently at a rate of +2 to +4 km2/year. In contrast, we identified a variable accretion rate of the muddy deltaic protrusion at Camau; it was < +1 km2/year before 1400 years ago but increased drastically around 600 years ago, forming the entire Camau Peninsula. This high level of mud supply had sharply declined by the early 20th century after a vast canal network was built on the delta. Since then the Peninsula has been eroding, promoted by the conjunction of mud sequestration in the delta plain driven by expansion of rice cultivation, and hysteresis of long-term muddy sedimentation that left the protrusion exposed to wave erosion. Natural mitigation would require substantial increases in sediment supply well above the pre-1990s levels.

Mid-Devensian climate and landscape in England: new data from Finningley, South Yorkshire.

While there is extensive evidence for the Late Devensian, less is known about Early and Middle Devensian (approx. 110-30 ka) climates and environments in the UK. The Greenland ice-core record suggests the UK should have endured multiple changes, but the terrestrial palaeo-record lacks sufficient detail for confirmation from sites in the British Isles. Data from deposits at Finningley, South Yorkshire, can help redress this. A channel with organic silts, dated 40 314-39 552 cal a BP, contained plant macrofossil and insect remains showing tundra with dwarf-shrub heath and bare ground. Soil moisture conditions varied from free draining to riparian, with ponds and wetter vegetated areas. The climate was probably low arctic with snow cover during the winter. Mutual climatic range (MCR), based on Coleoptera, shows the mean monthly winter temperatures of -22 to -2°C and summer ones of 8-14°C. Periglacial structures within the basal gravel deposits and beyond the glacial limits indicate cold-climate conditions, including permafrost. A compilation of MCR reconstructions for other Middle Devensian English sites shows that marine isotope stage 3-between 59 and 28 ka-experienced substantial variation in climate consistent with the Greenland ice-core record. The exact correlation is hampered by temporal resolution, but the Finningley site stadial at approximately 40 ka may correlate with the one of the Greenland stadials 7-11.