T118 Recent Sea-Level Change in a Late Holocene Context

Monday, 5 November 2012
1:30 PM - 3:30 PM
201AB

FIELD OBSERVATIONS AND MODELING OF HOLOCENE SEA-LEVEL CHANGES IN THE SW EUROPE: ASSESSING ANTHROPOGENIC SEA-LEVEL RISE

Paper number: T118-5
Program: Technical Sessions
Time: 2:30 PM – 2:45 PM

Authors

Abstract

Fifty five new sea level index points (SLIPs) obtained from three estuarine areas of the southern Bay of Biscay together with reviewed published data from SW Europe provide the most complete set of Holocene sea-level curves compiled for this region and have been used to calibrate a regional isostatic model. The new SLIPs are calculated combining the indicative depositional meaning with radiocarbon ages of borehole samples. Field data and model reconstructions show good agreement and vertical land movement estimates derived from the isostatic model compare well with observed GPS vertical velocities. At the regional scale, our results support a north-south sea-level trend for SW Europe, where isostatic rebound is minimal in the south of the Iberian Peninsula and local factors tend to dominate during the late Holocene. These newly produced sea-level curves been used to calculate pre-anthropogenic sea-level rise rates against which modern rates can be compared.

The overall sea-level trend in the Bay of Biscay shows two main phases: (1) rapid relative sea-level rise from ca. 27 m below mean sea level (bmsl) at ca 10,000 cal yr BP to ca. 5 m bmsl at ca 7000 cal yr BP; and (2) a relatively slow sea-level rise from ca 7000 cal yr BP until present. The estimation of relative sea-level change rates derived from all the SLIPs younger than 7000 cal yr BP provide a figure between 0.7 and 0.3 mm/yr of pre-anthropogenic sea-level rise. The best fit model has been used to correct tide gauge results and high-resolution geological data for land motion so as to isolate the signal due to ocean surface motion. Removing the modeled vertical land motion trend gives 20th century sea-surface rates of 0.63 mm/yr at Brest (France), 1.42 mm/yr at the southern Bay of Biscay (Spain) and 0.69 mm/yr at Cascais (Portugal). These values indicate a significant difference between the southern Bay of Biscay and the other two sites.