1. Marine Science Institute, The University of Texas at Austin, 750 Channel View Drive, Port Aransas, Texas 78373, USA
2. School of Marine Sciences, 5741 Libby Hall, University of Maine, Orono, Maine 04469, USA
3. Marine Science Institute and Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California 93106, USA
4. Bermuda Biological Station for Research, Inc., 17 Biological Station Lane, Ferry Reach, GE01 Bermuda
5. Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
6. Environmental, Coastal and Ocean Sciences Program, University of Massachusetts, 100 Morrissey Boulevard, Boston, Massachusetts 02125, USA

Correspondence to: Tracy A. Villareal¹ Correspondence and requests for materials should be addressed to T.A.V. (e-mail: Email: tracy@utmsi.utexas.edu).

The oligotrophic gyres of the open sea are home to a flora that includes the largest known phytoplankton. These rare species migrate as solitary cells or aggregations (mats) between deep nutrient pools (below 80–100 m) and the surface. This migration contributes to new production because of the concomitant upward transport of nitrate^{1, 2, 3}. But just how significant this contribution is remains uncertain because of the difficulty of making quantitative measurements of these rare cells⁴. Here we report remote video observations of a previously undersampled class of diatom (Rhizosolenia) mats throughout the upper 150 m of the central North Pacific Ocean. These mats are virtually invisible to divers, and their presence increases the calculated phytoplankton-mediated nitrate transport into the surface ocean by up to a factor of eight. Cruise averages indicate that Rhizosolenia mats transport 18–97 mol N m^-2 d^-1; however, this value reached 171 mol N m^-2 d^-1 at individual stations, a value equivalent to 59% of the export production⁵. Although considerable temporal and spatial variability occurs, this means of upward nutrient transport appears to be an important source of new nitrogen to the surface ocean, and may contribute to other regional elemental cycles as well⁶.