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SUMMARY:Water-column nutrient fluxes along the continental margin of the  
 Peruvian oxygen minimum zone - Lee Bryant\, University of Bath
DTSTART:20150408T130000Z
DTEND:20150408T140000Z
UID:TALK54685@talks.cam.ac.uk
CONTACT:Dr Dan Jones
DESCRIPTION:While oxygen minimum zones (OMZ) are frequently referred to as
  ‘dead zones’ from a biological standpoint\, coastal OMZ can actually 
 be highly dynamic in regard to nutrient cycling. Under the low-oxygen cond
 itions (≤ 10 µM O2) that define OMZ\, nutrients are released from the s
 ediment to the water and can contribute to increased primary production in
  surface water. However\, considerable nitrogen (N) loss to the atmosphere
 \, one of the key processes limiting primary productivity\, can also occur
 . Diapycnal mixing due to internal waves\, coastal upwelling and lateral a
 dvective and diffusive transport can significantly enhance these processes
  by accelerating nutrient supply to the near-surface layers.\n\nThere are 
 conflicting opinions on which biochemical processes (e.g.\, denitrificatio
 n\, dissimilatory nitrate reduction to ammonium\, and/or anammox) control 
 N cycling within OMZ. Furthermore\, while it is known that internal waves 
 can significantly affect nutrient fluxes\, hydrodynamics in coastal OMZ ca
 n be highly variable and effects on the nutrient distribution are not curr
 ently understood. We thus performed a process study focusing on the Peruvi
 an OMZ in the Eastern Tropical South Pacific boundary current system\, a r
 egion which is characterized by both (1) an extreme N deficit due to N los
 s and (2) elevated non-linear internal waves. Paired microstructure and CT
 D data were used to assess water-column turbulence and nutrient concentrat
 ions\, respectively\, and benthic chambers were used to evaluate nutrient 
 fluxes from the sediment. Velocity and hydrographic time series from a moo
 ring array allowed for investigation of advective and eddy nutrient transp
 ort. With these data\, a nutrient budget was determined by quantifying wat
 er-column flux divergences of N species at the upper continental slope and
  shelf regions. Together with N fluxes from the sediment\, we established 
 an overall N balance which we then used to evaluate which biochemical proc
 esses were likely contributors to N cycling in this critical region.\n
LOCATION:British Antarctic Survey\, Room 307
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