Reliability of AMS and ARM/KARM to reconstruct the relative vigor and variability of sea-bottom currents during the Last Glacial Period in the North-West Iberian Continental Margin.

We explore the potential and reliability of the anisotropy of magnetic susceptibility (AMS) to reconstruct the relative vigor of the sea-bottom currents by comparison with the widely-used paleo current proxy `sortable silt' mean (SS) grain size. SS and AMS are used as two independent proxies to determine relative changes in bottom-current speed, and their consistency tested against each other. The suitability of the magnetic grainsize proxy ARM/KARM ratio as a proxy for bottom-current variability is also investigated. The results are based on CI12PC3 core from the Galicia Interior Basin (North West Iberian Continental Margin) spanning the last 80 ka. The majority of AMS ellipsoid minimum axes (K3) in core CI12PC3 are close to vertical (INCmean= 80o) and nearly orthogonal to the bedding plane. Maximum axes (K1) are well-grouped marking two main magnetic lineation directions. Their orientations are consistent with present-day bottom-currents flow directions along the continental margin. Down-core variations in the degree of anisotropy (Pj) showed significantly higher values during Heinrich Stadials (cold) than during interstadials (warm). CI12PC3 also shows systematically lower ARM/KARM values during the stadials than during interstadials, indicating provenance induced coarsening of the magnetic fraction during the cold periods. We have noted that Pj down-core changes are independent of magnetic grain size, and interpreted them as the result of differences in the degree of grain alignment. These changes can be attributed to the variability in the strength of the bottom currents, indicating that they are stronger during stadials, which is consistent with the SS results. Magnetic properties and AMS of core CI12PC3 are climatically modulated on a millennial time scale reflecting the evolution in the near bottom-currents of the North West Iberian Continental Margin. Their variability exposes unchartered links with the AMOC and with the North Atlantic climate variability during the LGP.