Constraining the age of superimposed glacial advances in the Cantabrian Mountains (SW Europe) through multiple dating methods reveals important glaciation during MIS 3
Résumé
The growing application of different dating methods has brought to light two issues: (i)
the most extensive glacier advance recorded in multiple mountain environments slightly
pre-dates the global Last Glacial Maximum and lies within the Marine Isotope Stage 3 or
MIS 3; and (ii) the numerous cases of timing differences between observed glacial
advances might be caused by limitations related to the dating techniques without having
paleoclimate significance. In this regard, the frequent use of a single technique to date
numerically a given glacial sequence makes it difficult to address to what extent age
differences can be an artifact related to biased numerical age results or a paleoclimate
signature. Here we focus on the study of Pleistocene glacial advances in the central
Cantabrian Mountains of the Iberian Peninsula, where numerous chronologies based on
radiocarbon and Optically Stimulated Luminescence suggest a pre-LGM advance of
glaciers to their maximum front positions (Serrano et al., 2017 and references therein). A
preliminary study developed in the Porma valley (central Cantabrian Mountains) based
on the 10Be surface exposure dating of 75 boulders from moraines, erratics and rock
glaciers pointed to a complex exposure history of glacial advances and retreats spanning
the Last Glacial Cycle, where the age of the local glacial maximum advance was older
than MIS 5d (Stage I: ∼110 ka) (Rodríguez-Rodríguez et al., 2016). Here we present a
new set of 43 numerical ages based on three dating techniques —10Be surface exposure
dating; radiocarbon; and OSL— that complement the chronology of Pleistocene glacial
advances in the Porma valley. Results complement previous chronologies in the area,
supporting an important glacial advance during MIS 3 (Stage IIa: ∼56 ka) that culminated
with the LGM advance (Stage IIb: ∼33–24 ka) of MIS 2 in response to increased rainfall
and solar insolation minima. Glacier fronts reached elevations as low as 1130 m a.s.l.
possibly without overriding evidence related to the previous Pleistocene glacial maximum extent. Glacier recession in the Cantabrian Mountains started at 21–20 ka ago,
after the global LGM. We suggest that the recession was initiated by increased insolation
followed by hyper-cool and dry conditions during Heinrich Stadial 1 in response to
meltwater discharges in the North Atlantic.