ALBERT

Description: Sediment depth age-models, stable carbon isotope data, and radiocarbon data are reported for a suite of sediment cores from Iberian- and Brazil Margins, in the Atlantic basin. The sediment sequences span the last deglaciation (~30,000 years to the present). Stable carbon isotopes were measured on the benthic foraminifer species Cibicidoides wuellerstorfi, in the Godwin Laboratory, University of Cambridge. Each measurement was run on 1-4 individuals with a combined mass of 50-180μg. Samples were reacted with orthophosphoric acid (100%) and analysed, in comparison with a reference gas, using a dual inlet Thermo MAT 253 mass spectrometer connected to a Kiel device. Radiocarbon dates were obtained on monospecific samples of planktonic foraminifera, Globigerinoides ruber (Brazil Margin) or Globigerina bulloides (Iberian Margin), and samples of mixed benthic foraminifera (excluding agglutinated species) picked from the 〉150μm size-fraction. Samples were graphitized in the Godwin Radiocarbon Laboratory at the University of Cambridge, using a standard hydrogen/iron catalyst reduction method. AMS-14C dates were subsequently measured at the 14Chrono Centre, Queens University Belfast. All dates are reported as 'conventional radiocarbon ages', without additional 'corrections' applied. Reservoir ages and radiocarbon ventilation ages are derived based on the sediment core chronologies, and reported as offsets between contemporary marine- and atmospheric radiocarbon ages (based on the 'Intcal13' atmospheric radiocarbon calibration curve).

Description: Mediterranean Outflow Water (MOW) adds salt and density to open ocean intermediate waters and is therefore an important motor of Atlantic meridional overturning circulation (AMOC) and climate variability. However, the variability in strength and depth of MOW on geological timescales is poorly documented. Here we present new detailed records, with excellent age control, of MOW variability from 416 ka to present from rapidly accumulated marine sediments recovered from the West Iberian Margin during Integrated Ocean Drilling Program (IODP) Expedition 339. Our records of x-ray fluorescence (XRF), physical grain size and palaeocurrent information from the anisotropy of magnetic susceptibility (AMS) indicate (i) a close relationship between the orientation of principle AMS axes and glacial-interglacial cycles and (ii) two distinct regimes of MOW behaviour over the last ~416 kyrs in grain size and AMS variability at orbital (mainly precessional) and suborbital timescales. Between marine isotope stages (MIS) 10 and MIS 4, MOW was focused at a generally shallow depth on the West Iberian Margin, and changes in MOW strength were strongly paced by precession. A transition interval occurred during MIS 5 and 4, when MOW deepened and millennial-scale variability in strength flow strength was superimposed on orbitally paced change. During MIS 11 and from MIS 3 to present, MOW was deeply focused and millennial-scale variability dominated. We infer that late Pleistocene variability in MOW strength and depth were strongly climate- influenced and that changes in circum-Mediterranean rainfall climate were likely a primary control.