Field observations and modelling of Holocene sea-level changes in the southern Bay of Biscay: implication for understanding current rates of relative sea-level change and vertical land motion along the Atlantic coast of SW Europe

Abstract

The absence of basal peat in the stratigraphic sequences of the southern Bay of Biscay has long precluded the development of Holocene sea-level curves. We have approached this problem by combining the indicative depositional meaning (derived from the micropalaeontological composition and sand content) with radiocarbon ages of 55 borehole samples obtained from three estuarine areas of the southern Bay of Biscay. These new sea-level index points have produced the first complete Holocene sea-level curve from this area. We further reviewed all available sea-level data from SW Europe to provide the regional trend and use these data to calibrate a recently developed isostatic model. Field data and model reconstructions present a good agreement for the region considered. A north-south trend is apparent in the data and this is shown to be dominated by the influence of the deglaciation of Eurasian ice sheets, as suggested by previous studies for this region. However, some data-model discrepancy in the south of the Iberian Peninsula suggests that local factors tend to dominate during the late Holocene. On comparing our results to estimates of recent sea-level rise obtained from tide gauges and high-resolution proxy records, it is clear that this region has experienced a significant acceleration in sea level during the past century or so.