Late Quaternary (Marine Isotope Stage 3 to Recent) sedimentary evolution of the Basque shelf (southern Bay of Biscay)

Abstract

Late Quaternary (MIS 3 to Recent) oceanographic evolution of the Basque shelf has been analysed for the first time based on the sedimentological analysis of three cores obtained from the middle and outer shelves. The cores are located in two interfluves separated by the San Sebastian canyon. The variability of the percentage of the planktonic foraminifera species Neogloboquadrina pachyderma sin. and of δ 18 Obull allowed us to identify the influence of colder and warmer waters in the Basque shelf during the late Quaternary. From ∼56 cal. ka BP to the end of the Last Glacial Maximum (19 cal. ka BP) the sedimentary record shows a decreasing trend in the mean grain size that correlates with the eustatic sea-level fall. The last Deglaciation (19-11.5 cal. ka BP) is characterized by a sea-level rise that produced an important hiatus in the western outer shelf. During the Holocene, the middle and outer shelves present different behaviours. From 11.5 to 6.7 cal. ka BP, in the outer shelf the sea-level rise that started during the Deglaciation produced a hiatus, whereas in the middle shelf the sedimentary succession records the presence of warm to temperate waters. Between 6.7-4.9 cal. ka BP, the entrance of cold surface water-masses that only affected the middle shelf has been identified, and temperate to warm waters occurred in the outer shelf. The cold surface water-masses retreated during 4.9-4.3 cal. ka BP in the middle shelf. Finally, from 4.3 cal. ka BP to Recent, the middle shelf registers a hiatus due to sea-level stabilization after a generalized transgression, synchronous to a decrease in the energy of the water-masses in the outer shelf. In conclusion, the environmental changes detected in the Basque shelf are attributed to both regional and eustatic sea-level changes.

Combining Small-Vertebrate, Marine and Stable-Isotope Data to Reconstruct Past Environments

“…However, the scarcity of “Northern guest” ostracod species shows the absence of inputs of subpolar bottom waters 4 . The HE 3 (~31.3 ka cal BP) is a remarkable period: the marine record reflects the arrival of both surface and bottom cold subpolar waters into the Basque shelf 4 28 .…”

“…At 23.9 ka cal BP, Heinrich Event (HE) 2 is detected by an increase in the percentage of N. pachyderma sin synchronic to a peak of δ 18 O bull , reflecting the arrival of cold polar surface waters 4 28 . This event is followed by a decrease in the isotopic signal (~23.2 ka cal BP) that corresponds to the warm event GI-2.…”

“…4 ). From ~18.6 to ~15 ka cal BP, the HE 1 is characterized by the variations in relative abundance of N. pachyderma sin, “Northern guests” and δ 18 O bull and δ 18 O lob signals, reflecting the input of both cold surface and bottom water masses into the Basque shelf, coming from the circumpolar area of the North Atlantic Ocean 4 28 . These trend can be correlated with the age previously proposed for HE 1 in the Bay of Biscay, i.e., ~18 ka cal BP 51 52 53 .…”

“…3 ), not so far from Antoliñako Koba site (see Fig. 1 and Methods), has been extensively used for palaeoenvironmental reconstructions in the Quaternary period 4 25 26 27 28 . The planktonic foraminifer Neogloquadrina pachyderma sinistral (sin), in particular, is a polar species that appears in percentages of >90% to the north of the North Atlantic Polar Front 29 , being its abundance a useful proxy to identify the meridional migration of the Polar Front during the Quaternary.…”

Cave monitoring and the potential for palaeoclimate reconstruction from Cueva de Asiul, Cantabria (N. Spain)

“…This region is therefore ideally placed to record variations in competing air masses and is of critical significance for understanding the role of the North Atlantic in controlling Europe's climate (Baldini et al, 2015). Current palaeoclimate records from this International Journal of Speleology 45 (1) 1-9 Tampa, FL (USA) January 2016 region are principally derived from lake (GonzalezSamperiz et al, 2008;Morellón et al, 2009;Roberts et al, 2012) or ocean sediments (Martínez-García et al, 2014, 2015Mojtahid et al, 2013), cave speleothems (Dominguez-Villar et al, 2009;Moreno et al, 2010;Stoll et al, 2013;Martinez-Pillado et al, 2014;Baldini et al, 2015) and from archaeological evidence (LopezMerino et al, 2010). However, few of these records replicate at high resolution over long periods of time.…”