How well is the deep Tore seamount basin ventilated?

<p>The Last Glacial Maximum (LGM) was characterized by increased carbon storage in the deep ocean, as well as extremely poorly ventilated southern-sourced deep water (AABW) compared to northern-sourced deep water (NADW).</p><p>Here we analyse benthic (Cibicidoides wellerstorfi) d<sup>13</sup>C, and compare 3 sites sitting on the deep floor at 5 km water depth: MD13-3473 in the Tore inside basin; MD03-2698 in the Iberian margin; and TN057-21 in the South Atlantic. The Tore Seamount is a geological structure 300 km off the West Iberian margin at 40°N latitude. It has a crater-like morphology with a 5500 m deep basin in its middle, where calypso core MD13-3473 was collected, confined from the open ocean by a summit rim at 2200 m water depth (wd). The only connection between the deepest Tore Seamount basin and the Atlantic circulation is a NE gateway down to 4300 mwd.</p><p>The results for the LGM show similar values around -1.0 ‰ for the South Atlantic and the Iberian margin, in other words these sites were both bathed by AABW. However, the Tore basin record exhibits values around 0 ‰, similarly to open sites in the Iberian margin at 3.5 km depth. This seems to indicate a remarkable isolation of the Tore inside basin from the Atlantic deep bottom waters influence.</p><p>Among other things, we plan to examine the residence time of the Tore basin bottom water by measuring the radiocarbon age difference between benthic and planktonic foraminifera. </p><p>Our results confer to this enclosed environment the status of an in-situ deep ocean laboratory where to test hypotheses of past ocean circulation changes like the role of deep waters in sequestering glacial CO<sub>2</sub>. Core MD13-3473 covers 430 thousands of years, therefore 5 deglacial cycles (Spanish project “TORE5deglaciations”, CTM2017-84113-R, 2018-2020).</p>