Nutrient streams and their induction into the mixed layer

[1] Nutrients are transferred from the nutricline into the winter mixed layer through a combination of vertical and lateral advection, referred to here as induction, the reverse of the subduction process. This advective supply of nutrients maintains the high productivity at high latitudes over timescales of several years and longer. Climatological diagnostics over the North Atlantic reveal that the induction of nutrients into the winter mixed layer is dominated by lateral advection even in the subpolar gyre where there is significant Ekman upwelling. The induction flux of nutrients is itself sustained by nutrient streams, strong nutrient transport associated with the western boundary currents. In the North Atlantic basin, the integrated induction flux accounts for typically 40% of the nitrate flux in the nutrient stream at 36°N, while the remaining fraction is recirculated in the thermocline of the subtropical gyre. The relationship between the nutrient stream and induction flux is illustrated using a numerical model of the circulation and biogeochemistry of the North Atlantic. The model studies suggest that the nutrient stream preferentially supplies nutrients to isopycnals outcropping in the subpolar gyre. The nutrient sources for the nutrient stream are either mode waters originating from the Southern Ocean or the tropics, where the eastern upwelling circulation and particle fallout focuses nutrients onto the lighter isopycnal surfaces of the nutrient stream.

[1]  S. Gorshkov,et al.  World ocean atlas , 1976 .

[2]  D. M. Glover,et al.  Estimates of wintertime mixed layer nutrient concentrations in the North Atlantic , 1988 .

[3]  L. Talley,et al.  Chapter 5.4 Mode waters , 2001 .

[4]  R. Usbecka,et al.  Particle fluxes in the ocean : comparison of sediment trap data with results from inverse modeling , 2003 .

[5]  M. Follows,et al.  Estimating the convective supply of nitrate and implied variability in export production over the North Atlantic , 2000 .

[6]  S. Levitus.  Climatological Atlas of the World Ocean , 1982 .

[7]  M. Follows,et al.  Role of bottom water transport and diapycnic mixing in determining the radiocarbon distribution in the Pacific , 2004 .

[8]  S. Drijfhout,et al.  The origin of Intermediate and Subpolar Mode Waters crossing the Atlantic equator in OCCAM , 2005 .

[9]  A. Tréguier,et al.  Effects of the Mixed Layer Time Variability on Kinematic Subduction Rate Diagnostics , 2005 .

[10]  J. Marshall,et al.  Inferring the Subduction Rate and Period over the North Atlantic , 1993 .

[11]  Rainer Bleck,et al.  A Wind-Driven Isopycnic Coordinate Model of the North and Equatorial Atlantic Ocean 1 , 1990 .

[12]  B. Qiu,et al.  Ventilation of the North Atlantic and North Pacific: Subduction Versus Obduction , 1995 .

[13]  T. D. Dickey,et al.  Influence of mesoscale eddies on new production in the Sargasso Sea , 1998, Nature.

[14]  Nicolas Gruber,et al.  Global patterns of marine nitrogen fixation and denitrification , 1997 .

[15]  G. Fischer,et al.  Particle fluxes in the ocean: comparison of sediment trap data with results from inverse modeling , 2003 .

[16]  L. Hasse,et al.  The Bunker climate atlas of the North Atlantic Ocean. Volume II: Air-sea interactions , 1985 .

[17]  J. Toggweiler,et al.  Downward transport and fate of organic matter in the ocean: Simulations with a general circulation model , 1992 .

[18]  J. Pelegrí,et al.  The North Atlantic nutrient stream , 1996 .

[19]  M. Lozier,et al.  The effect of advection on the nutrient reservoir in the North Atlantic subtropical gyre , 2005, Nature.

[20]  G. Wolff,et al.  Physical supply of nitrogen to phytoplankton in the Atlantic Ocean , 2004 .

[21]  J. Pelegrí,et al.  Nutrient irrigation of the North Atlantic , 2006 .

[22]  J. Pelegrí,et al.  Diapycnal mixing in western boundary currents , 1994 .

[23]  C. Wunsch,et al.  Mass, heat, oxygen and nutrient fluxes and budgets in the North Atlantic Ocean , 1991 .

[24]  Nelson G. Hogg,et al.  On the transport of the gulf stream between cape hatteras and the grand banks , 1992 .

[25]  W. J. Jenkins,et al.  The subtropical nutrient spiral , 2003 .

[26]  M. Follows,et al.  The Ekman transfer of nutrients and maintenance of new production over the North Atlantic , 1998 .

[27]  M. Follows,et al.  Physical Transport of Nutrients and the Maintenance of Biological Production , 2003 .

[28]  J. Pelegrí,et al.  Nutrient transport and mixing in the Gulf Stream , 1991 .