Potential influence of Bond events on mid-Holocene climate and vegetation in southern Pyrenees as assessed from Burg lake LOI and pollen records.

Abstract

Superimposed on the long-term climate variability attributed to orbital forcing, there are other modes of variability covering timescales from interannual to millennial throughout the Holocene. Their signatures in climate proxy archives can differ substantially because of their lower magnitude and regional diversity. However, if identified they can yield better understanding of the physical mechanisms regionally linking causes and effects. Here we describe a high-resolution record of organic matter accumulation in the sediments of Burg lake (Pyrenees, NE Iberian Peninsula), as assessed using loss on ignition (LOI), and compare it with the ice rafted debris (IRD) indexes from the North Atlantic. The LOI record indicates two main phases in the water body, a lacustrine phase as a shallow lake and a palustrine phase as a fen. The latter covers the period 2600—7200 cal. yr BP and within it there is a high coherence between LOI and IRD, which indicates submillennial climate fluctuations in the Pyrenees that can be related to the North Atlantic influence. The Burg’s LOI record suggests wetter (and occasionally colder) situations in the Pyrenees during high IRD in the Atlantic (Bond oscillations). These fluctuations would likely affect the snow covered period in the mountains (winter and spring seasons) the most, the period in which Atlantic westerlies currently have higher influence on precipitation over the Pyrenees. These climatic oscillations could have favoured Abies penetration during the mid Holocene, as evidenced by increased pollen percentages of this taxon during low IRD values (drier conditions). The pollen record also suggests potential relationships between climate and human activity as early as at mid Holocene, as human-related cereals increase during all the low IRD periods. The human signature (charcoal, cereals) becomes particularly evident at around 2800 cal. yr BP; in this oscillation Pinus overtake Abies in the conifer response to low IRD.