CoAuthors

Gary Mitchum (College of Marine Science, University of South Florida, United States)

Global mean seal level over the past century is reconstructed from global measurements from tide gauges on coastlines and islands. These measurements reflect not only sea level variations but also vertical movement of the land on which tide gauges sit. In addition, the sea level variations measured by tide gauges can differ from these over the open ocean due to the coastal ocean dynamics. These features of tide gauge measurements raise the question whether mean sea level derived from tide gauges is able to represent global mean sea level. Several studies compared mean sea level derived from tide gauges with that obtained from altimetry observation that has nearly global coverage, and showed that the linear trends of mean sea level obtained from the two datasets differ over short period (10 years), but agree well with each other over longer periods (longer than 15 years). On one hand, the vertical land motions (VLMs) of tide gauges in some of these studies are estimated with a Glacial Isostatic Adjustment (GIA) model, which would be invalid when other processes like tectonic activities occur; on the other hand, the altimetry data is less accurate when approaching the land. Global Positioning System (GPS) data analysis provides useful information for estimating VLMs and an algorithm for assigning a GPS-derived vertical land motion rate to a tide gauge has been developed. The linear trends of the corrected coastal sea level from tide gauges are calculated and compared with those derived from altimetry over the adjacent deep ocean. Preliminary results show that coastal sea level trends from tide gauges agree well with offshore sea level trends from altimetry in large-scale pattern, but have large differences in some regions, possibly owing to coastal ocean dynamics. Analysis of these differences will be presented at the meeting.