Colour logging as a tool in high-resolution palaeoceanography

Colour and diffuse reflectance records can be used to develop astronomically tuned age models for long sediment cores. Here, we present high-resolution (1 mm) colour records from a sediment core from the western Gulf of Cadiz of SW Spain (D13892), spanning the last deglaciation, in parallel with stable isotope (δ18O) and sea surface temperature (SST) proxy data. The age model is based on δ18O stratigraphy complemented by five atomic mass spectroscopy (AMS) radiocarbon datings. We find good comparison between the colour record of D13892 and the GISP2 oxygen isotope series (R2 = 0.81), which strongly suggests that the sediment colour reflects the state of the climate. As sediment colour variability has previously been found to be diagnostic of changes in mineralogical/chemical composition, we relate the causes of the colour variability in D13892 to changes in the local particle flux, and support these observations with data from core-logging X-ray fluorescence (XRF) analyses. The colour and XRF logger records for D13892 suggest that the last glaciation and Younger Dryas were characterized by an enhanced supply of terrigenous detritus into the western Gulf of Cadiz. Cyclicities with wavelengths of 607 and 1375 years are recognized in the colour records for the Holocene. This cyclicity also relates to variability in detrital supply, with an important eolian component implied by enrichment in hematite during cycle maxima.