Phytoplankton decline hints trouble for north Atlantic food webs - Oceanographic
https://oceanographicmagazine.com/news/phytoplankton-decline-hints-trouble-for-north-atlantic-food-webs/It has linked the declines primarily to rising sea surface temperatures and changes in mixed layer depth – physical properties that control how nutrients and light are distributed in the upper ocean. As surface waters warm, the ocean stratifies into more distinct layers that are less likely to mix vertically, cutting off the supply of nutrients from depth that phytoplankton depend on to grow.
“While the ocean may appear to be one giant body of water, it is often divided into layers based on temperature,” said Dr Tilstone. “As the ocean warms, these layers become stronger and less likely to vertically mix – a process known as thermal stratification. This matters because the mixing of ocean waters helps transport nutrients from the depths to the surface, where phytoplankton can use them to grow. When that supply is reduced, microalgae productivity can decline.”