The Postglacial Isotopic Record of Intermediate Water Connects Mediterranean Sapropels and Organic‐Rich Layers

Abstract

Carbon-rich layers exist at both sides of the Mediterranean Sea sedimentary record and are called sapropels and organic rich layers (ORLs), respectively, in the eastern and western basins. They have different levels of organic carbon accumulation and seafloor oxygen deprivation. The most recent sapropel and ORL depositions have a different timing, approximately 10.8-6.1 and 14.5-9.0 ka, respectively. Here we investigate oxygen isotopic records of three foraminifera species that occupy different habitats within the Sicily Channel water column since~12.0 ka, thus in the sill between the eastern and western Mediterranean basins. These data are ice volume corrected, to get information on water masses density variability, and are accompanied by benthic foraminifera δ 13 C measurements to establish Sicily Channel seafloor ventilation. Our results, and the comparison with other chronologically well-constrained Mediterranean records, highlight the connection of the two subbasins due to monsoon activity. The end of the maximum Nile River flooding at~9.2 ka, and eastern Mediterranean seafloor reventilation above 1,800-1,500 m depth at~8.2 and 7.2 ka, left a clear signature in the intermediate water isotopic record of the Sicily Channel. Concurrently, the western Mediterranean deep water circulation experienced a significant recovery after a long period of slowdown. We argue that African monsoon weakening was transmitted into the western Mediterranean, through the intermediate layer of circulation, where deep water formation took place and brought oxygen to the seafloor.

Assessing atmospheric and oceanic teleconnections between the eastern and western Mediterranean over the past 8000 years

“…We selected three marine sediment cores: (i) KESC9-14 in the western Mediterranean from the Ligurian Sea (43. 31°N, 7.11°E, Le Houedec et al, 2021), (ii) PS009PC (32°07.7′N, 34°24.4′E, Hennekam et al, 2014;Le Houedec et al, 2020) in the eastern Mediterranean, from the Levantine Sea and (iii) ODP Site 963 (Hole D) (37°02.148′N, 13°10.686′E, Incarbona and Sprovieri, 2020) in the central Mediterranean, close to Sicily Strait (Figure 1). The three cores are located at similar water depths, respectively at 537, 552, and 469 m below sea level, and are positioned on the LIW trajectory.…”

“…These findings support the notion of a well-connected atmosphere-surface ocean system that operates largely in tune on millennial timescales throughout the past 8000 years. Furthermore, we infer that (Incarbona and Sprovieri, 2020). For the cave spelaeothems, Site 'a' marks the position of the Corchia Cave spelaeothem (Bar-Matthews and Ayalon, 2011), and Site 'b' displays the position of the Soreq Cave spelaeothem (Zanchetta et al, 2007).…”

“…In the Mediterranean Sea, a direct consequence of the atmosphere-sea exchanges is the modulation of the flow rate/production of the modern intermediate Mediterranean waters (LIW and WIW). For instance, the production rate of LIW was shown to be affected by the amount of freshwater input to the eastern basin from the Nile River ultimately controlled by the East Africa/Indian monsoonal activity at year to centennial time scales and thus to the seasonal climatic variability (Hennekam et al, 2014; Incarbona and Sprovieri, 2020; Mojtahid et al, 2015; Rohling et al, 2015). On orbital time scales, a similarly persistent monsoonal forcing controls the amount of Mediterranean Outflow Water, which is also governed by LIW production in the eastern basin (Bahr et al, 2015).…”

“…(a) Map of the region with site locations. For marine sediment cores, number 1 corresponds to the western Mediterranean Core KESC9-14, number 2 indicates eastern Mediterranean Core PS009PC and number 3 the central Mediterranean Site ODP 963 (Incarbona and Sprovieri, 2020). For the cave spelaeothems, Site ‘a’ marks the position of the Corchia Cave spelaeothem (Bar-Matthews and Ayalon, 2011), and Site ‘b’ displays the position of the Soreq Cave spelaeothem (Zanchetta et al, 2007).…”

Ichnological evidence for bottom water oxygenation during organic rich layer deposition in the westernmost Mediterranean over the Last Glacial Cycle

“…8). The significance of these restriction events in combination with factors including the LIW characteristics could have led to the differences among the different ORLs, or even stand as the main cause behind these differences, as LIW composition can affect the sinking and composition of the WMDW (Incarbona and Sprovieri, 2020). Notably, during Heinrich events, low saline water coming from the polar iceberg melting entered through the Gibraltar Strait, impacting circulation in the Mediterranean (Cacho et al, 2002;Sierro et al, 2005), notwithstanding, it did not produce substantial deep-water restriction (Sierro et al, 2005), which is coherent with the apparent absence of any relation between the Heinrich events and either the greyscale of the bioturbational features in the studied record.…”