HOLOCENE ENVIRONMENTAL CHANGE ON VANCOUVER ISLAND: THE KARST RECORD

There are many limestone caves at differing elevations along the Pacific coast and in the mountainous interior of Vancouver Island (British Columbia, Canada). Previous paleoenvironmental records, notably from Cascade Cave in the interior, have shown that the timing of phases of speleothem growth demarcate glacial advances/retreats due to interruptions of the groundwater flow system. We present new Holocene speleothem records from four caves on the coast. Two samples from a site at sea level have grown from 2.6 ka to present and a third spans 6.8-5.6 ka. Two samples from a mid elevation cave (500 m asl) grew from 14.5-8.6 ka and from 7.0-3.9 ka respectively. In a cave at 750 m asl one sample extends from 8.4 ka to present. There is convergence in the initiation and cessation of the growth phases in these samples, with general cessation at two distinct periods broadly from 8.6 to 7.0 ka and from 3.9 to 2.6 ka. The second period is marked by 1.5^o/oo negative d¹⁸O excursion in the one sample (that at highest elevation) which grew throughout it. The speleothem growth phases and spatial distribution of the samples elucidates the nature of significant Holocene events along the Pacific coast of the island. These include a temperature decline at ~8.7 to 8.2 ka inferred from speleothem fluid inclusions (Zhang et al in progress), and also a freshening event identified at ~4 ka in a sediment core from Effingham Inlet (Chang & Patterson, 2005). The latter (previously interpreted as evidence of increased precipitation) may alternatively be interpreted from the speleothem records as a reorganization of alpine glaciation patterns and melt water paths.