Increased density stratification and mixed-layer shallowing, caused by warming, freshening and sea ice decline, can alter light climate and nutrient availability within the surface mixed layer  . As light and nutrient levels drive photosynthesis, changes in these drivers directly affect primary producers, often in different directions . Decreased upward nutrient supply is expected to decrease primary production in the low-latitude ocean  . Alternatively, higher mean underwater light levels resulting from changes in sea ice and/or mixed layer shallowing can increase primary production in high-latitude offshore regions, provided nutrient levels remain sufficiently high  . In some parts of the open Southern Ocean, where iron limitation largely controls primary productivity , changes in wind fields will deepen the summer mixed-layer depth , entrain more nutrients, and raise primary productivity in the future  .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report