Interstadial conditions over the Southern Alps during the early penultimate glacial (MIS 6): a multiproxy record from Rio Martino Cave (Italy)

Identifying the hydrological and environmental response of the European Alpine region to different
combinations of climate boundary conditions is crucial to advance the reliability of predictive climate
models and thus shape climate adaptation policies that will impact millions of people in seven countries.
Here we present a high-resolution multiproxy speleothem record (stable oxygen and carbon isotope
ratios, petrography and magnetic properties) from Rio Martino Cave (Piedmont, Southern Alps, Italy),
which covers the first part of the Penultimate Glacial (early MIS 6, 182e157 ka). During early MIS 6, the
combination of high climatic precession and obliquity amplified the peak in Northern Hemisphere (NH)
summer insolation intensity at ca. 174 ka to almost interglacial levels, leading to northward migration of
the Intertropical Convergence Zone and the enhancement of the boreal monsoon system. At orbital scale,
the hydroclimatic record from Rio Martino closely follows the precession pattern, and shows a wet
interstadial phase between 180 and 170 ka, peaking at the precession minimum, characterized by glacial
retreat and by the likely development of soils and vegetation up to 1900e2000 m a.s.l. in this alpine
sector. This phase can be traced across the Southern Alps, and corresponds to pluvial conditions inferred
from Western Mediterranean records, and to the interval of deposition of the cold Sapropel S6 in the
eastern Mediterranean. We suggest that the interaction between an intensified northwesterly cold flow
(relating to increased ice volume under glacial conditions), and the relatively warm waters of the NW
Mediterranean (due to the peculiar atmospheric configuration occurring at the precession minimum)
strongly enhanced the autumn cyclogenesis in the Northern Tyrrhenian Sea, fuelling intense precipitation
to reach the Southern Alps. The Rio Martino record also shows a prominent sub-orbital variability,
the overall structure of which is coherent with hemispheric changes in climate driven by cyclic perturbations
of North Atlantic conditions related to the operation of the bipolar seesaw.