Laminated sediments of Loch Ness, Scotland : indicators of Holocene environmental change
Sediment cores, two approximately 6 metres and one about 1 metre in length, were recovered from the profundal plain of the northern basin of Loch Ness, Scotland. Examination revealed that the sediment is composed of irregular sequences of pale and dark laminations, most sub-millimeter in thickness, some ca 5 mm thick. Enumeration of laminae, and determination of lamination thickness, was carried out using X-radiography and image analysis. A hypothesis was developed that the finer laminations represent varves. This was tested by means of lamination counting, and by radiocarbon dating of material from one 'long' core. Comparison of the two chronologies thus derived suggested that the hypothesis was correct, and that a non-continuous chronology had been obtained, spanning the period ca 9000 to 1500 BP. Lamination thickness data derived from recent sediments was compared with meteorological data, especially rainfall, in order to test the hypothesis that prevailing climate, together with the alignment of the Loch with the predominantly southwesterly airflow, médiates in the production of the volume of allochthonous mineral material eroded from the catchment and its input to the water column. The result of this analysis bas proved inconclusive, and a more complex relationship may be involved. Other proxy climatic data were utilised in order further to investigate this aspect of the study and correlations between the sediment record and several of thèse were shown to be statistically significant. Spectral analysis of the lamination thickness datasets was also employed in order to determine if patterns of sedimentation may be linked to periodic forcing processes. Cyclicities observed in recent sediments include those of ca 210 and ca 90 years, which are also present in many other climatically-related records. Analysis of lamination thickness in the 'long' cores has proved inconclusive, producing evidence of many periodicities, but few of significance. It is believed that this result may be attributed to the non-stationary behaviour of forcing agents through time.