Extended Data Fig. 7: CS-δ15N changes in comparison with bifurcation latitude of the SEC, the mean equatorial thermocline depth and the ocean heat content in the tropical/subtropical Pacific.
From: Increased tropical South Pacific western boundary current transport over the past century
a, The decadal and long-term decreasing trend in the CS-δ15N are accompanied by changes in the bifurcation latitude of the SEC41. Southward migration of the SEC bifurcation latitude results in more equatorward transport into the Solomon Sea18,74, contributing to decrease in the CS-δ15N. The detrended changes in CS-δ15N are also significantly correlated with changes in the bifurcation latitude (r = 0.38, p = 0.09; 3-year running average). b, The declining trend in CS-δ15N is accompanied by long-term shoaling of the mean thermocline depth in the equatorial Pacific. The thermocline depth in the equatorial Pacific is defined as the depth of the 20 °C isotherm (Z20;75), and is calculated from the global ocean based on the Simple Ocean Data Assimilation (SODA, version 2.1.6) package76 for the equatorial Pacific basin mean (5°S-5°N, 130°E-80°W)77. The detrended changes in CS-δ15N are also significantly correlated with Z20 (r = 0.67, p = 0.01; 3-year running average). c, Decrease in the CS-δ15N, thus increase in the western boundary current transport, appears to coincide with decrease in the ocean heat content in the upper 700 m in the tropical/subtropical Pacific78. This supports the importance of the STCs in contributing to the heat recharge-discharge dynamics on interannual/decadal time scales13. All data are smoothed by 3-yr running mean.
