Details of Award
NERC Reference : NE/L000156/1
In-situ nutrient recharge mechanisms in shelf seas: benthic-pelagic coupling
Training Grant Award
- Lead Supervisor:
- Dr MT Johnson, University of East Anglia, Environmental Sciences
- Grant held at:
- University of East Anglia, Environmental Sciences
- Science Area:
- Atmospheric
- Marine
- Terrestrial
- Overall Classification:
- Marine
- ENRIs:
- Global Change
- Natural Resource Management
- Pollution and Waste
- Science Topics:
- None
- Abstract:
- The seasonal cycle of nitrate in the surface ocean in temperate regions is characterised by high values in winter. Rapid uptake by fast-growing phyotplankton during the spring bloom leads to nitrate concentration decreasing to low levels over the summer. In stratified waters, autumn and winter mixing bring nitrate-rich deep water to the surface, however, in the well mixed southern north sea, isolated from open ocean inputs (and in areas away from significant riverine input), rapid nitrate increases are still observed, suggesting a key role for benthic processes. In order to understand the controls on how much nitrate is available for the spring bloom in waters which have overwintered on the shelf (whether seasonally stratified or not), it is necessary to identify the controls on processes which decouple nitrification (of NH4 to NO3) from dentrification (of nitrate to N2 - and thus loss of N from the water column). Nitrification is ubiquitous in the presence of dissolved oxygen and thus occurs in both sediment and water column, whereas denitrification requires low oxygen concentrations so tends occur predominantly in sediments. The amount of nitrified N which is subsequently denitrified must be a function of the physical nature of sediment, the oxygen regime therein and the degree of benthic disturbance and oragnic matter loading. These factors will be investigated in fieldwork and data synthesis based around three Cefas SmartBuoy sites in the Southern North Sea (where there is extensive biogeochemical data context). Although in permanently well mixed waters, the rate and process data will be equally applicable to the seasonally stratified regions of the shelf. Fieldwork will involve two winter cruises and one summer /autumn cruise on the Cefas Endeavour in which box coring at the sites will be conducted and on-deck sediment resuspension experiments conducted to determine the degree of decoupled nitrification (leading to 'recharge' of nitrate). The student will also conduct a 3d hydrodynamic modelling experiment, using existing model set-ups at Cefas, but implementing a novel linearly-decaying tracer to determine the average age of water on the shelf (i.e. on average, how long the water at any point has spent on the shelf). This will give novel output of a 3d 'age field' for the NW European shelf, contributing valuable insight to NERC-SSB and Cefas core activities. The student will use this as a biogeochemical parameter to relate to winter nitrate concentrations from Cefas data archive and other sources to determine an estimate for net dentrification of ammonium across the shelf. Phosphate and salinity data will be used to correct for the counterbalancing effect of riverine N fluxes. The student will then investigate through biogeochemical box modelling, or 1-d ERSEM (depending on their interest and scientific motivation), the effect of the changing oxygen, nutrient and organic matter loading and benthic disturbance balance for shelf sea carbon fixation - for example, in a warmer, more strongly stratified north sea, denitrification may increase, leading to low nitrate available for carbon fixation and direct export. However, increased terrestrial N nutrient loading may counterbalance the increasing denitrification, leading to net enahncement of the shelf carbon pump by enhanced alkalinity production from anoxic hetertrophic processes. The exact details of these biogoechemical modelling investigations will be determined by the student with guidance from the supervisory team. The student will receive training in various measurement and experimental techniques, including stable isotope mass spectrometry, nutrient analysis and oxygen microelectrode operation. They will learn to conduct ship-based benthic sampling and experiments and to link measurements and modelling through data synthesis and analysis. The project is CASE with Cefas and will inform core Cefas work on SmartBuoys and nutrient cycling.
- NERC Reference:
- NE/L000156/1
- Grant Stage:
- Completed
- Scheme:
- DTG - directed
- Grant Status:
- Closed
- Programme:
- SSB Studentship
This training grant award has a total value of £80,838
FDAB - Financial Details (Award breakdown by headings)
| Total - Fees | Total - Student Stipend | Total - RTSG |
|---|---|---|
| £16,210 | £56,632 | £7,997 |
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