A thermocline nutrient pump

Lead Research Organisation: National Oceanography Centre
Department Name: Science and Technology


The seasonal thermocline in temperate shelf seas acts as a critical interface in the shelf sea system. It is a physical barrier to vertical exchange, controlling biological growth through the summer and enabling the sequestration of atmospheric CO2. Once the spring bloom is over the seasonal thermocline separates the sun drenched but nutrient deplete surface waters from the dark nutrient rich deep water. The vertical mixing of nutrients across the seasonal thermocline acts to couple this well-lit surface zone with the deep water nutrient supply, leading to the formation of a layer of phytoplankton within the thermocline (the subsurface chlorophyll maxima). This phenomenon is estimated to account for about half of the annual carbon fixation in seasonally stratified shelf seas, and yet the controlling physics is only just being unravelled. The identification and parameterisation of the physical processes which are responsible for the vertical mixing of nutrients across the thermocline is a vital prerequisite to our understanding of shelf sea ecosystems. Our proposal is to investigate the role of wind driven inertial oscillations in driving vertical mixing across the seasonal thermocline, identifying the mechanisms and processes responsible for their generation and dissipation on both special and temporal scales. The proposal will be achieved through an observational campaign closely integrated with numerical model predictions using both 1D and 3D numerical models.


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Description Our most recent result was a demonstration that the mixing of nutrients upwards in the sea towards the plankton is remarkably sensitive to wind. Storms cause nutrients to be mixed upward, but in very strong bursts that last 20 - 30 minutes, not evenly through the whole storm. This is important, because observing these mixing pulses, and modelling them on computers, has in the past completely missed these short nutrient supply events, and so can often fail to correctly account for the amount of biological growth in the sea.
Exploitation Route The findings have implications for the resolution of meteorological data used by operational modelling of shelf sea biological production.
Sectors Environment

URL http://pcwww.liv.ac.uk/~jons/index.htm
Description Our work gets used as a part of regular submissions to the Climate Change Impacts Partnership report cards.
First Year Of Impact 2010
Sector Environment
Impact Types Policy & public services