1. GEOTRACES Atlantic Workshop
Importance of mesopelagic fluxes and recycling to trace element biogeochemistry Peter J Statham and Richard Lampitt- NOC Southampton UK
Can regard the mesopelagic later as a valve- if material passes likely to be locked away in deep ocean for decades to centuries, if recycled to dissolved forms may be re-entrained into upper ocean
Existing focus on C (inorganic and organic) Si N & P
However potentially critical for other elements e.g. Fe, Mn Ba- but little known about detailed processes
As identified in IMBER and GEOTRACES science plans, understanding recycling of elements in the mesopelagic crucial to fate of many key bio-reactive elements
GEOTRACES Atlantic Workshop

2. GEOTRACES Atlantic Workshop
Some of the challenges
How to improve collection of particles and estimate vertical fluxes?
How to estimate recycling from water column particles?
Relevance of episodic large events vs background processes (time-scales and measurement locations?)
Bacterial processes appear to dominate recycling- BUT how much do we know about these processes?
Role of aggregate processes in recycling?
GEOTRACES Atlantic Workshop

3. Possible approaches and where in Atlantic
Direct measurements of flux/processes
Improvements to shallow traps - use of neutrally buoyant traps to reduce artefacts
In situ sampling of real settling particles, and incubations
PELAGRA
Examples of indirect measurement of fluxes
Th-234- (T½ 24.1d) potentially time-integrating (See recent review in Mar Chem.) C and other TEI fluxes
Other Th isotopes e.g. Th-228 (T½ ~1.9yr)
ANIMATE mooring network
Where in the Atlantic ??
Contrasting productivity locations
Link to existing long term stations e.g. ANIMATE programme, BATS
GEOTRACES Atlantic Workshop

4. GEOTRACES Atlantic Workshop