This phenomenal study by Alexandre Pohl and colleagues investigates in a very comprehensive way how estimates of the #oxygen #isotope composition of seawater bias our #climate reconstructions, one of the most important uncertainties in #paleoclimate research.
https://www.sciencedirect.com/science/article/pii/S0012821X25002171
Collin et al investigate the genetics of Late Pleistocene horses in North America and Beringia. One interesting finding is how the initial migration of horses through the "ice free corridor" between the Cordillera and Laurentide ice sheets was delayed after initial deglaciation.
Paleo sea level estimates from before 12,000 years ago are pretty rare. Medri et al make estimates of paleo sea level between 13.8 and 15.9 thousand years ago off the coast of central California, estimating paleo sea level between 86-99 m below present after tectonic correction.
Maxwell et al investigate fossil coral reefs on Luzon Island in the Philippines to determine past relative sea level and tectonic uplift rate. They conclude that it is 1.17 mm/yr, based on analysis of the MIS 5e terrace, currently at 155 m.
14-May-2025
#Alaska: Ancient cave sediments provide new #climate clues
Discovery of 20,000-year-old cave #sediments on Prince of Wales Island offers rare land-based evidence of ancient #meltwater events
https://www.eurekalert.org/news-releases/1083622
#science #paleoClimate #glaciers
Paul Wilcox, a geologist at the University of Innsbruck, has discovered the first land-based evidence of meltwater pulses from the Cordilleran Ice Sheet during the last ice age about 20,000 years ago. The age of the cave sediments was constrained via optical dating techniques, which is crucial to help piece together the sequence of climate events leading to a warming planet. The results were published in the journal Nature Geoscience.
Fatourou et al use biological proxies to investigate the connection of the Gulf of Corinth in Greece with the Mediterranean Sea during the Middle and Late Pleistocene. The connection for the past 400,000 years has been through the western Rion Sill, which is currently at 60 m depth.
During glacial periods, sea level fell sufficiently to isolate the Gulf of Corinth from the Mediterranean Sea. Therefore, this record can be used as a way to estimate global ice volume. The major glacial periods of MIS 18, 14, 8, 6, 4 and 2 show a complete isolation of the Gulf.
The major interglacials of MIS 17, 13, 11 and 9 indicate fully connected conditions. MIS 7 shows fluctuations, indicating that ice volume varied. This is perhaps not surprising, since there is a large interruption in MIS 7 with a sharp rise in δ¹⁸O in the marine records, likely a brief glaciation.
During MIS 5, there is also fluctuations, with evidence of isolation during the MIS 5b stadial. During MIS 3, there is evidence that sea level must have risen enough that there was periodically a connection with the Mediterranean Sea (i.e. sea level > -60 m).
Obviously, pin-pointing a specific sea level from these data is difficult, since the height of the sill likely varied due to tectonics, and the "connection" based on these proxies probably does not depend precisely on sea level being above or below -60 m.
Andersen et al investigate the in-situ cosmogenic isotopes from Gaustatoppen Mountain in southern Norway. The amount of cosmogenic isotopes in the rocks can be used to tell how long the mountain was buried by ice from the Scandinavian Ice Sheet.
They conclude based on ¹⁴C, they conclude the mountain was covered for at least 20-25 thousand years during the LGM. The inheritance signature of cosmogenic ²⁶Al and ¹⁰Be indicates a substantial erosional event during the penultimate glacial cycle.
Regnéll et al provide an absolute dating for the "zero year" of the Swedish varve record. The varves are annual layers of sediment deposited in proglacial lakes. This allows for an absolute chronology for events during the deglaciation of the Scandinavian Ice Sheet.
Coulombe et al report on a buried glacial ice deposit on Bylot Island in northern Canada. This ice, based on paleomagnetism measurements is from the Early Pleistocene. Since it overlies a forest deposit, they hypothesize it is 2.4-2.8 million years old. Remarkably old!
Niels de Winter
Dr. Evan J. Gowan
michael
Steve Paradis