Long-Term Trends in Dynamic Height and Sea Surface Temperature

摘要

Secular changes in the density structure of the upper ocean are investigated to see if they can explain the apparent rise in sea level observed along the continental margins of the world's oceans. The time rate of change of dynamic height is estimated to be -0.8 dyn cm/cent, a value that is indistinguishable statistically from 0. Further, the distribution of individual values entering the grand average are distributed normally to a high degree of approximation. Assuming the change in relative sea level is real, then it could be due to either melting of the polar caps or warming of the upper ocean. Warming, since the turn of the century, of the magnitude suggested in much of the literature would have been detectable in the density structure of the upper ocean. This signal was not seen in the current analysis. A more modest warming, allowing for instrumental biases over the last 50 years and/or melting of the polar caps by just enough to give the observed change in relative sea level would have signatures in the upper ocean density field that would barely be detectable in the current study. A combination of warming and melting together should have had a signal that was marginally detectable. This latter signal was not observed. Comparison of historical sea surface temperature (SST) trends from ship-of-opportunity reports and hydrographic data suggest instrumental bias can account for roughly one-half of the apparent increase in ocean temperature since 1899. Differing measurement methods (buckets vs injection temperature) may also be partially responsible for an apparent discontinuity in the SST series in the early 1940's. (ERA citation 08:044727)