In the northern North Sea, the water column stratifies in summer as the surface layer warms. At the base of this surface layer, intense algal blooms can develop. Since these cannot be seen from space, these layers have been much less well studied than blooms in surface layers. However, preliminary data suggests these regions may be very important in sustaining overall plankton growth in the North Sea, particularly in summer and this plankton production may also be important in sustaining fish growth. This proposal seeks support to study these layers and use the information gained to assess their significance for overall productivity. Climate change is likely to increase stratification in the North Sea and we will also assess the impacts of such changes on phytoplankton productivity and fisheries.