AN EXPANDED HOLOCENE DATABASE OF RELATIVE SEA LEVELS FOR NORTH AMERICA AND THE CARIBBEAN: IMPLICATIONS FOR 20TH CENTURY SEA-LEVEL RISE AND GEOPHYSICAL MODELS

We have expanded the previously available quality-controlled database of relative sea-level (RSL) observations for the U.S. Atlantic coast with data from the Pacific coast of the USA and Canada, and the Caribbean. The Holocene sea-level database for the U.S. Atlantic coast consisted of 836 sea-level indicators. The database documented a decreasing rate of relative sea-level (RSL) rise through time with no evidence of sea level being above present in the middle to late Holocene. The highest rates of rise were found in the mid-Atlantic region. We employed the database to constrain an ensemble of glacial isostatic adjustment (GIA) models using two ice models (ICE-5G and ICE-6G) and two models of the radial variation of mantle viscosity (VM5a and VM5b). We identified significant misfits between observations and predictions using ICE-5G with the VM5a viscosity profile. ICE-6G provides some improvement for the northern Atlantic region, but misfits remain elsewhere. Decreasing the upper mantle and transition zone viscosity from 0.5*10²¹ Pa s (VM5a) to 0.25*10²¹ Pa s (VM5b) removed significant discrepancies between observations and predictions along the mid-Atlantic coastline, although misfits remained in the southern Atlantic region. We compared the rates of sea-level rise obtained from geological data during the late Holocene (the last 4000 years) to the rate recorded by the tide gauges during the 20^th century. The mean rate of sea-level rise on the U.S. Atlantic coast was 1.7 mm per year during the 20^th century. We have expanded the database to include further data from regions that were formerly glaciated (Pacific coast of Canada), are undergoing significant forebulge collapse (Pacific coast of the USA) and sites where forebulge collapse is minimal or absent (Caribbean). The addition of new data has enabled us to further investigate the VM5b mantle viscosity profile and to develop a greater understanding of 20^th century sea-level rise.