Woods Hole Oceanographic Institution
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Measured δSW-S relationship in the eastern equatorial Pacific. The main trend of points within the Panama Bight, and in the eastern Pacific near the ITCZ (EPIC 5.7-11?N) has an apparent freshwater endmember of -7.8 to -8.5 ?. Two distributions that splay off the main trend, in the EPIC survey near the equator (EPIC 1?S-5.6?N) and within the Panama Bight, project freshwater endmembers of -4.7 to -4.8 ?, consistent with the measured average δP in the region (Fig. 2.2). Subsurface waters (41-400 m) define a relatively steep trend with an apparent freshwater endmember of -16.2 ?, which is related to mixing with northern (NPMW) and southern (SPMW) subtropical mode waters. The intersection of subsurface and surface water points, with δ18O of 0.3 ? and S of 34.9 PSU, documents mixing with water that upwells in the eastern equatorial Pacific and in the Costa Rica Dome. This upwelling component (UPW) is characteristic of ?13?C Water? (Toggweiler et al., 1991; Tsuchiya and Talley, 1998), and can be described as a mixture of ~60% South Pacific Tropical Waters (SPTW) and ~20% subtropical mode waters of either South Pacific (SPMW) or North Pacific (NPMW) origin. Deep waters (>400 m) define a trend that is related to mixing between subtropical mode waters and Pacific Deep Water (PDW). Published data points (Schmidt et al., 1999) in light gray are used in combination with water mass definitions based on temperature, salinity, and depth (Toggweiler et al., 1991; Tsuchiya and Talley, 1998) to characterize the following regional water masses in δSW-S space: South Pacific Tropical Water (SPTW), South Pacific Mode Water (SPMW), North Pacific Mode Water (NPMW), Pacific Deep Water (PDW), Antarctic Intermediate Water (AAIW), and North Pacific Intermediate Water (NPIW). Ellipses represent average δSW and S ? one standard deviation. (Benway and Mix (2004))
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