Holocene relative sea-level changes and glacial isostatic adjustment of the US Atlantic coast

The first quality-controlled Holocene sea-level database for the U. S. Atlantic coast has been constructed from 686 sea-level indicators. The database documents 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 RSL rise are found in the mid-Atlantic region. We employ the database to constrain an ensemble of glacial isostatic adjustment models using two ice (ICE-5G, ICE-6G [global ice sheet reconstructions]) and two mantle viscosity (models VM5a, VM5b [VM-radial variation of viscosity in the sublithospheric mantle]) variations to assess whether the spherically symmetric viscoelastic models are able to survive intercomparison with a more refined database of postglacial RSL history. We identify 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 by a factor of 2 to 0.25 x 10(21) Pa s (VM5b) removes significant discrepancies between observations and predictions along the mid-Atlantic coastline, although misfits remain in the southern Atlantic region. These may be an indication of the importance of laterally heterogeneous viscosity in the upper mantle.