Pilskaln, C. Dept. of Oceanography, pilskaln@maine.maine.edu
Brzezinski, M. Marine Science Institute and Department of Ecology Evolution and Marine Biology,
Lipschultz, F. Bermduda Biological Station for Research, fred@bbsr.edu
Gardner, G. B. Environmental, Coastal and Ocean Sciences Prg.,, bernie.gardner@umb.edu

 
NEW ESTIMATES OF UPWARD OCEANIC NITRATE FLUXES BY MIGRATING DIATOM MATS (RHIZOSOLENIA MATS)
 
The open sea contains a flora of very large phytoplankton cells that migrate between deep nutrient pools and the surface. This migration contributes to new production via upward nitrate transport; however, flux calculations have been hampered by difficulties in quantifying these rare cells. We used remote videography to enumerate a previously undersampled class of diatom (Rhizosolenia) mats throughout the upper 150 m of the central North Pacific. These Rhizosolenia mats are abundant but virtually invisible to divers. Their presence increases calculated phytoplankton-mediated nitrate transport into the surface ocean up to 8-fold. Cruise averages indicated Rhizosolenia mats transported 18-97 Ámol N m-2 d-1 ; however, this value reached 171 Ámol N m-2 d-1 at Individual stations, or 86% of the estimated turbulent diffusive flux. This estimate was based on a size scaling argument that assumed a conservative value for the nitrogen content (7%) of small mats compared to the traditionally sampled larger mats; however, this value could be low by factor of 2. While considerable temporal and spatial variability occurs, upward biological transport is an important source of new nitrogen to the surface ocean and may contribute to other regional elemental cycles as well.
 
Day: Thursday, Feb. 4
Time:
Location: Sweeney Center
 
Code: CS55TH0105S