Department of Earth System Science

Nutrient transport and productivity teleconnections with the Southern Ocean are diagnosed in a data-assimilated circulation model coupled to a jointly optimized simple phosphorus cycling model. The North Atlantic has the strongest extratropical teleconnections with the Southern Ocean: phosphate (PO₄) last utilized in the Southern Ocean sustains 29 ± 6% of the subpolar and 14 ± 6% of the subtropical, new production in the North Atlantic. A PO₄ path-density diagnostic shows that these teleconnections are mediated by thermocline paths and reveals that most paths to anywhere north of 40°S lie in the deep Pacific. Forcing nearly complete Southern-Ocean nutrient utilization increases the overall number of paths to anywhere north of 40°S, but reduces the number of paths from the Pacific to the North Atlantic by trapping nutrients in return paths to the Southern Ocean. At the same time, the mean export-to-uptake transit times to anywhere north of 40°S increase, while the mean transit times to the North Atlantic decrease. Correspondingly, the amount of North-Atlantic production sustained by Southern-Ocean export increases in spite of decreased total production in response to Southern-Ocean nutrient trapping. The distributions of export-to-uptake, export-to-surface, and surface-to-surface transit times are computed and summarized in terms of their mean transit times and their mean interior residence times. The combined particle and advective–diffusive transport of nutrients is characterized by broad, skewed transit-time distributions, which result in mean residence times much longer than the mean transit times, in turn much longer than the most probable transit times.