We finally explored the robustness of the median trends with a variety of additional tests. First, we found a negative median trend for the paired residual ZNO3 -ZPO4, which also suggests a faster deepening of the phosphacline relative to the nitracline (Fig. ). Second, there was no indication 15 of a bias due to changing measurement methods during the observation period. After subtracting mean climatological concentrations, we saw no negative trend at depths well below the nutricline where concentrations presumably should be stable (Fig. ). Third, the water density at the depth of the nitracline and phosphacline show decreasing and increasing trends respectively (median TNO3 = -5 x 10 -3 kg m -3 yr -1 , CI95% = [-7 x 10 -3 , -4 x 10 -3 ]; median TPO4 = 3 x 10 -3 kg m -3 yr -1 , CI95% 20 = [8 x 10 -4 , 5 x 10 -3 ]; Fig. ). This indicates that the nutricline depths are shifting independently of density layers, suggesting that biological processes may control the nutricline depth trends.