Age of the Most Extensive Glaciation in the Alps

Previous research suggested that the Alpine glaciers of the Northern Swiss Foreland reached their maximum extensive position during the Middle Pleistocene. Relict tills and glaciofluvial deposits, attributed to the Most Extensive Glaciation (MEG), have been found only beyond the extents of the Last Glacial Maximum (LGM). Traditionally, these sediments have been correlated to the Riss glaciation sensu Penck and Brückner and have been morphostratigraphically classified as the Higher Terrace (HT) deposits. The age of the MEG glaciation was originally proposed to be intermediate to the Brunhes/Matuyama transition (780 ka) and the Marine Isotope Stage 6 (191 ka). In this study, we focused on the glacial deposits in Möhlin (Canton of Aargau, Switzerland), in order to constrain the age of the MEG. The sediments from these deposits were analyzed to determine the provenance and depositional environments. We applied isochron-burial dating, with cosmogenic 10Be and 26Al, to the till layer in the Bünten gravel pit near Möhlin. Our results indicate that a glacier of Alpine origin reached its most extensive position during the Middle Pleistocene (500 ± 100 ka). The age of the MEG thus appears to be synchronous with the most extensive glaciations in the northern hemisphere.

Geomorphological, chronological, and paleoenvironmental context of the Mousterian site at Roca San Miguel (Arén, Huesca, Spain) from the penultimate to the last glacial cycle

The Roca San Miguel (RSM) archaeological site was occupied during Mousterian times. Here we present a geoarchaeological and paleoenvironmental reconstruction of the site. Five stratigraphic units (A to E) formed by different archaeological levels are identified. Three optically stimulated luminescence (OSL) ages show that Unit A dates to between 169.6 ± 9.1 and 151.9 ± 11.1 ka, during the penultimate glacial period (PGP), and contains numerous signs of recurring hearths. Unit B is unexcavated. Unit C dates to between 118.9 ± 11.5 and 103.4 ± 6.9 ka (late Eemian–marine isotope stage (MIS) 5d) and shows an abundance of lithic remains as well as some faunal elements. Unit C is covered by Unit D, which incorporates materials moved downslope, and is dated at 81.2 ± 4.7 ka. These OSL ages concur with U/Th ages (129.3 ± 1.5 and 123.6 ± 0.6 ka) derived from a flowstone covered by both -C and D- post-flowstone units. Finally, Unit E covers the archaeological site, which was partially eroded during MIS2. The robust and well-constrained chronology of the RSM site and surroundings enables the establishment of its evolutionary model from the PGP to the last glacial cycle. The RSM site is the oldest Neanderthal occupation accurately dated in the Pre-Pyrenean region.

Compilation of Last Interglacial (Marine Isotope Stage 5e) sea level indicators in the Bahamas, Turks and Caicos, and the east coast of Florida, USA

This paper provides a summary of published sea level archives representing the past position of sea level during the Last Interglacial sea level highstand in the Bahamas, Turks and Caicos, and the eastern (Atlantic) coast of Florida, USA. These data were assembled as part of a community effort to build the World Atlas of Last Interglacial Shorelines (WALIS) database. Shallow marine deposits from this sea level highstand are widespread across the region and are dominated by carbonate sedimentary features. In addition to depositional (constructional) sedimentary indicators of past sea level position, there is also evidence of erosion, dissolution, and/or subaerial exposure in places that can place an upper limit on the position of sea level. The sea level indicators that have been observed within this region and attributed to Marine Isotope Stage (MIS) 5e include corals, oolites, and other coastal sedimentary features. Here we compile a total of 50 relative sea level indicators including 36 in the Bahamas, three in West Caicos, and a remaining 10 for the eastern seaboard of Florida. We have also compiled U-Th age data for 24 fossil corals and 56 oolite samples. While some of these archives have been dated using U-Th disequilibrium methods, amino acid racemization, or optically stimulated luminescence, other features have more uncertain ages that have been deduced in the context of regional mapping and stratigraphy. Sedimentary archives in this region that constrain the elevation of the past position of sea level are associated with uncertainties that range from a couple decimeters to several meters. Across the Bahamas and on West Caicos, one of the observations that emerges from this compilation is that estimation of sea level position in this region during Marine Isotope Stage 5e is complicated by widespread stratigraphic evidence for at least one sea level oscillation. This evidence is defined by submarine features separated by erosion and subaerial exposure, meaning that there were likely multiple distinct peaks in sea level rather than just one. To this end, the timing of these individual sea level indicators becomes important when compiling and comparing data across the region given that different archives may have formed during different sub-orbital peaks in sea level.

Evolution of mean ocean temperature in Marine Isotope Stage 4

Deglaciations are characterized by relatively fast and near-synchronous changes in ice sheet volume, ocean temperature, and atmospheric greenhouse gas concentrations, but glacial inception occurs more gradually. Understanding the evolution of ice sheet, ocean, and atmosphere conditions from interglacial to glacial maximum provides insight into the interplay of these components of the climate system. Using noble gas measurements in ancient ice samples, we reconstruct mean ocean temperature (MOT) from 74 to 59.7 ka, covering the Marine Isotope Stage (MIS) 5a–4 boundary, MIS 4, and part of the MIS 4–3 transition. Comparing this MOT reconstruction to previously published MOT reconstructions from the last and penultimate deglaciation, we find that the majority of the last interglacial–glacial ocean cooling must have occurred within MIS 5. MOT reached equally cold conditions in MIS 4 as in MIS 2 (−2.7 ± 0.3 ∘C relative to the Holocene, −0.1 ± 0.3 ∘C relative to MIS 2). Using a carbon cycle model to quantify the CO2 solubility pump, we show that ocean cooling can explain most of the CO2 drawdown (32 ± 4 of 40 ppm) across MIS 5. Comparing MOT to contemporaneous records of benthic δ18O, we find that ocean cooling can also explain the majority of the δ18O increase across MIS 5 (0.7 ‰ of 1.3 ‰). The timing of ocean warming and cooling in the record and the comparison to coeval Antarctic isotope data suggest an intimate link between ocean heat content, Southern Hemisphere high-latitude climate, and ocean circulation on orbital and millennial timescales.

Was there a glacial outburst flood in the Torngat Mountains during Marine Isotope Stage 3?

We report previously unpublished evidence for a Marine Isotope Stage 3 (MIS 3; 60–26 ka) glacial outburst flood in the Torngat Mountains (northern Quebec/Labrador, Canada). We present 10Be cosmogenic exposure ages from legacy fieldwork for a glacial lake shoreline with evidence for outburst flooding in the Torngat Mountains, with a minimum age of 36 ± 3 ka (we consider the most likely age, corrected for burial, to be ~56 ± 3 ka). This shoreline position and age can potentially constrain the Laurentide Ice Sheet margin in the Torngat Mountains. This region, considered a site of glacial inception, has no published dated geologic constraints for high-elevation MIS 3 ice margins. We estimate the freshwater flux associated with the inferred glacial outburst flood using high-resolution digital elevation maps corrected for glacial isostatic adjustment. Using assumptions about the ice-dammed locations we find that a freshwater flood volume of 1.14 × 1012 m3 could have entered the Hudson Strait. This glacial outburst flood volume could have contributed to surface ocean freshening to cause a measurable meltwater signal in δ18O records, but would not necessarily have been associated with substantial ice rafted debris. Future work is required to refine estimates of the size and timing of such a glacial outburst flood. Nevertheless, we outline testable hypotheses about the Laurentide Ice Sheet and glacial outburst floods, including possible implications for Heinrich events and glacial inception in North America, that can be assessed with additional fieldwork and cosmogenic measurements.