Tracking rainfall in the northern Mediterranean borderlands during sapropel deposition

Abstract

International audienceThe role of mid-latitude precipitation in the hydrological forcing leading to the deposition of sapropels in the Mediterranean Sea remains unclear. The new GDEC-4-2 borehole, East Corsica margin (northern Tyrrhenian Sea), provides the first precisely dated evidence for enhanced rainfall in the Western Mediterranean during warm intervals of interglacial periods over the last 547 kyr. Comparison of GDEC-4-2 proxy records with pollen sequences and speleothems from the central and eastern Mediterranean reveals that these pluvial events were regional in character and occurred probably in response to the intensification of the Mediterranean storm track along the northern Mediterranean borderlands in autumn/winter. Our dataset suggests that the timing of maxima of the Mediterranean autumn/winter storm track precipitation coincide with that of the North African summer monsoon and sapropel deposition. Besides highlighting a close coupling between mid- and low-latitude hydrological changes, our findings suggest that during warm intervals of interglacial periods the reduced sea-surface water salinities, together with the high flux of nutrient and organic matter, produced by the monsoonal Nile (and wadi-systems) floods, were maintained throughout the winter by the Mediterranean rainfall. This provides an important additional constraint on the hydrological perturbation causing sapropel formation

Precession‐ and Obliquity‐Induced Changes in Moisture Sources for Enhanced Precipitation Over the Mediterranean Sea

“…These are related to changes in the Azores High with corresponding changes in wind and moisture transport. Importantly, neither local nor external mechanisms seem to be related to changes in North Atlantic storm tracks as suggested in earlier studies (e.g., Kutzbach et al, 2013;Toucanne et al, 2015). Such external sources could be important for sapropel formation, as external sources are most important in late winter when deep water formation occurs (e.g., Rohling et al, 2015).…”

“…The climatic origin of these cycles, including sapropels (or organic-rich layers) and carbonate cycles, is still debated after decades of research (e.g., Bosmans et al, 2015;Rohling et al, 2015). Wetter conditions over the Mediterranean and its borderlands are attributed to increases in winter precipitation (e.g., Milner et al, 2012;Toucanne et al, 2015;Tzedakis, 2009). Simultaneously, the North African monsoon and its runoff into the Mediterranean also intensify during precession minima and obliquity maxima (e.g., Bosmans et al, 2015a;Kutzbach et al, 2013).…”

Precessional Drivers of Late Miocene Mediterranean Sedimentary Sequences: African Summer Monsoon and Atlantic Winter Storm Tracks

“…The combination of the two seasonally‐distinct moisture sources could have led to year‐round wetter conditions during times of precession minima from North Africa to the Mediterranean and the Middle East. This may not only be relevant for the late Miocene, but also during the more recent African humid periods, with potentially important implications for human migrations (Hoffmann et al, ; Kutzbach et al, ; Toucanne et al, ).…”

“…Rohling and Hilgen, ; van der Laan et al, ) and linked to winter rather than summer precipitation (e.g. Meijer and Tuenter, ; Toucanne et al, ). Late Miocene geological sections on the Atlantic margin, not connected to the Mediterranean Sea (e.g., western Morocco and western Spain; see Figure ) and sediment cores from the Iberian Margin, have also been correlated to the Mediterranean sedimentary successions (e.g.…”

Precessional variability of87Sr/86Sr in the late Miocene Sorbas Basin: An interdisciplinary study of drivers of interbasin exchange

“…The GCM results indicate that in the western Mediterranean, maximum precipitation also occurs during precession minima. However, by comparison with the eastern basin, the variation in precipitation and river runoff between precession minima and maxima is less than half (Table S1), resulting from precessional shifts in a separate climate system originating over the Atlantic, known as winter storm tracks [Kutzbach et al, 2014;Toucanne et al, 2015]. This is consistent with relatively constant Al/Ti ratios in the four precessional cycles studied ; in this context, changes in Al/Ti ratios would have indicated changes in river discharge recorded by changes in fluvially derived clays.…”