Variability of Shallow Water Masses of the Northern and Tropical Oceans as Viewed in Nine Ocean Analyses

2 This paper explores the mean state and variability of upper ocean water properties in the northern and tropical oceans during the years 1962-2001 as represented in nine ocean analyses. We begin by examining the winter-spring characteristics of SST and the mixed layer which regulate the sources water masses to the upper ocean. We then compare variability of the depth of constant density surfaces, particularly the 25.5σ surface to that described in previous studies focusing on representative climate phenomena. In the western North Pacific all analyses show a decadal succession of depth anomalies which circulate clockwise around the subtropical gyre consistent with the behavior previously described by Miller and Schneider (2000). On longer timescales the 25.5σ surface undergoes a reduction in its zonal slope between the intervals 1970-1977 and 1990-1999, a reduction that McPhaden and Zhang (2002) associate with a slowing down of the shallow meridional overturning circulation in this basin. Comparisons with time series records at Hawaii and Bermuda show that while the analyses are able to reproduce observed responses to anomalous surface forcing, they differ significantly in the far field representation of those anomalies. In the subpolar North Atlantic five of the analyses are able to reproduce observed the Great Salinity Anomaly fresh events of the 1970s and 1980s. Examination of these five show three that allow a significant role for freshwater transport from the Arctic Ocean, while two suggest a dominant role for local sources of freshwater. 3 1.