The subtropical nutrient spiral
MetadataShow full item record
We present an extended series of observations and more comprehensive analysis of a tracer-based measure of new production in the Sargasso Sea near Bermuda using the 3He flux gauge technique. The estimated annually averaged nitrate flux of 0.84 ± 0.26 mol m−2 yr−1 constitutes only that nitrate physically transported to the euphotic zone, not nitrogen from biological sources (e.g., nitrogen fixation or zooplankton migration). We show that the flux estimate is quantitatively consistent with other observations, including decade timescale evolution of the 3H + 3He inventory in the main thermocline and export production estimates. However, we argue that the flux cannot be supplied in the long term by local diapycnal or isopycnal processes. These considerations lead us to propose a three-dimensional pathway whereby nutrients remineralized within the main thermocline are returned to the seasonally accessible layers within the subtropical gyre. We describe this mechanism, which we call “the nutrient spiral,” as a sequence of steps where (1) nutrient-rich thermocline waters are entrained into the Gulf Stream, (2) enhanced diapycnal mixing moves nutrients upward onto lighter densities, (3) detrainment and enhanced isopycnal mixing injects these waters into the seasonally accessible layer of the gyre recirculation region, and (4) the nutrients become available to biota via eddy heaving and wintertime convection. The spiral is closed when nutrients are utilized, exported, and then remineralized within the thermocline. We present evidence regarding the characteristics of the spiral and discuss some implications of its operation within the biogeochemical cycle of the subtropical ocean.
Author Posting. © American Geophysical Union, 2003. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 17 (2003): 1110, doi:10.1029/2003GB002085.
Showing items related by title, author, creator and subject.
Macroalgal responses to experimental nutrient enrichment in shallow coastal waters : growth, internal nutrient pools, and isotopic signatures Teichberg, Mirta; Fox, Sophia E.; Aguila, Carolina; Olsen, Ylva S.; Valiela, Ivan (Inter-Research, 2008-09-25)Increased nutrient inputs to temperate coastal waters have led to increased occurrences of macroalgal blooms worldwide. To identify nutrients that are limiting to macroalgae and to determine whether different forms of these ...
Species compositional differences on different-aged glacial landscapes drive contrasting responses of tundra to nutrient addition Hobbie, Sarah E.; Gough, Laura; Shaver, Gaius R. (2005-01-17)In the northern foothills of the Brooks Range, Alaska, moist non-acidic tundra dominates more recently deglaciated upland landscapes, whereas moist acidic tundra dominates older upland landscapes. In previous studies, ...
Deegan, Linda A.; Bowen, Jennifer L.; Drake, Deanne C.; Fleeger, John W.; Friedrichs, Carl T.; Galvan, Kari A.; Hobbie, John E.; Hopkinson, Charles S.; Johnson, J. Michael; Johnson, David S.; LeMay, Lynsey E.; Miller, Erin; Peterson, Bruce J.; Picard, Christian; Sheldon, Sallie; Sutherland, Michael; Vallino, Joseph J.; Warren, R. Scott (2006-03-15)The sustainability of coastal ecosystems in the face of widespread environmental change is an issue of pressing concern throughout the world (Emeis et al. 2001). Coastal ecosystems form a dynamic interface between terrestrial ...