A high-resolution Holocene sediment record from Húnaflóaáll, N Iceland margin: centuryto millennial-scale varability since the Vedde tephra

Abstract

MD99-2269 is a 25 m long core from Hunaflóadll, a deep trough which runs northward towards the shelf break from the narrow neck of land which joins the Northwest Peninsula of Iceland with the ‘mainland’. The core was recovered from the thickest part of an elongate shelf sediment body, underlain by glacial diamictons with ages 26 ka BP. 3.5 kHz profiles indicate the presence of a reflector, RI, which can be traced over long distances. Twelve AMS radiocarbon dates and the presence of the Saksunarvatn tephra (which is the origin for the RI reflector at 21 m core depth) define a linear depth/age relation with an accumulation rate of 200 cm/ky. The date on the core top is ‘modem’. X-radiographs indicate that the sediments are principally massive. bioturbated muds. The data were measured at resolutions of between 5 and 40 yr/sample. Our primary data represent aspects of (a) multisensor track measurements, (b) colour, (c) grain size, (d) sediment properties and (e) sediment magnetic properties. Principal component analysis (PCA) was used to simplify the analysis of these five data sets, and resulted in nine significant axes compared to over 70 original variables. The explained variance on the first axes varied between 47 and 96%. These time series were reduced to a common 50-yr sample interval which were then also subject to PCA. Using the resulting PC scores we present three primary axes of environmental variability in Hunaflóaall that have century-scale quasi-periodicities, and demonstrate that these are highly correlated with specific ‘raw’ variables. We focus on variables linked to changes in grain size and productivity and show regional coherence (cores B997-321 and 330) in the coercivity/grain size measure ARMJ(20)/ARMJ(0), which have a close similarity to the detrended A14C series. This provides a potential link to the vigour of the thermohaline circulation to the north of the Iceland shelf in the Iceland and Greenland Seas. Our data indicate increased variability in our proxies during the Neoglacial period.