This graph depicts seawater temperature against depth and latitude (south to north). In this graph you can see that the cooler, high nutrient seawater is at shallower depths as we proceed north (to the right in the graph). It is due to this nutrient rich cooler water approaching the surface that results in the phytoplankton becoming more concentrated in shallower depths as we approach the Winter Front at 32N latitude. The winter front is amazingly far north this year and this is the first time the Subtropical Front was farther north than latitude 33N. What this means or may have been caused by, is too premature for me to speculate here.