A SEA-LEVEL DATABASE FOR THE CENTRAL PACIFIC COAST OF NORTH AMERICA

Regional databases of relative sea-level (RSL) provide a framework for developing our understanding of the primary mechanisms of RSL change since the Last Glacial Maximum and a long-term baseline against which to gauge changes in sea-level during the 20^th century and forecasts for the 21^st.

Here we have constructed a database of published and new RSL data for the past 16 ka to constrain the sea-level histories of the central Pacific coast of North America (southern British Columbia to central California). Our reevaluation of the stratigraphic context and radiocarbon age of samples from geological and archaeological investigations yields 605 sea-level index points and 203 sea-level limiting points. We sub-divided the database into 12 regions based on the availability of data, tectonic setting, and distance from the former Cordilleran ice sheet. Most index (95%) and limiting points (60%) are <7 ka; older data comes mainly from British Columbia and San Francisco Bay. The stratigraphic position of index points was used as a first-order assessment of the contribution of compaction of Holocene strata to RSL change.

Formerly glaciated sites show non-monotonic RSL change due to the complex interplay of rising eustatic sea level and isostatic adjustment. Where data is present, highstands of RSL occur immediately post-deglaciation and in the mid- to late-Holocene. Sites at the periphery and distant to the formerly glaciated region demonstrate a monotonic rise in RSL with a decreasing rate through time due to the collapse of the peripheral forebulge and the reduction in meltwater input during deglaciation. Late Holocene RSL change varies from falling at 0.6 ± 0.4 mm a^-1 in southern British Columbia to rising at 1.6 ± 0.2 mm a^-1 in central California. The variable sea-level histories are an ongoing isostatic response to deglaciation of the Cordilleran and Laurentide Ice Sheets.