Water Properties and Circulation in the Deep Southeast Pacific Ocean

We quantify the origins and distribution of deep water masses in the Bauer Basin of the southeast Pacific Ocean using Conductivity-Temperature-Depth (CTD) instrument data collected during nominally meridional oceanographic transects with high-quality, full-depth, closely spaced stations through the basin that were occupied in 1994, 2007, and 2016. We analyze spiciness on isopyncals to quantify the relative fractions of cold and fresh water entering the basin from the North Pacific (NP) to the northwest through fracture zones in the East Pacific Rise vs. warmer and saltier (spicier) water entering the basin from the Yupanqui Basin (YB) to the south through gaps in the Galapagos Rise. While water exceeding the maximum density observed in the Bauer Basin is found in both adjacent basins, our analysis reveals a wedge of primarily cold and fresh NP origin water (75-95%), thickest in the north and overlain by warmer and saltier water that is most prominent in the South. This wedge is invariant with time, with the exception of fine-structure interleaving of NP and YB water that varies among occupations. We apply rotating hydraulic control theory to the fracture zone using density-pressure profiles on either side of the deepest sill in the East Pacific Rise connecting the North Pacific to the Bauer Basin and the deepest gap in the Galapagos Rise connection the Yupanqui Basin to the Bauer Basin. The estimated deep inflows are under 1 Sv, smaller from the south than from the north, consistent with the observed water properties being mostly of North Pacific origin.