The counterintuitive effect of summer-to-fall mixed layer deepening on eukaryotic new production in the Sargasso Sea

2014 ◽  
Vol 28 (2) ◽  
pp. 86-102 ◽  
Author(s):  
Sarah E. Fawcett ◽  
Michael W. Lomas ◽  
Bess B. Ward ◽  
Daniel M. Sigman
Keyword(s):  
Mixed Layer ◽  
Sargasso Sea ◽  
New Production

Prochlorococcuscontributes to new production in the Sargasso Sea deep chlorophyll maximum

2007 ◽  
Vol 34 (10) ◽  
Author(s):  
John R. Casey ◽  
Michael W. Lomas ◽  
Joanna Mandecki ◽  
Donald E. Walker
Keyword(s):  
Sargasso Sea ◽  
Deep Chlorophyll Maximum ◽  
New Production ◽  
Chlorophyll Maximum

Mesoscale eddies, satellite altimetry, and new production in the Sargasso Sea

1999 ◽  
Vol 104 (C6) ◽  
pp. 13359-13379 ◽  
Author(s):  
David A. Siegel ◽  
Dennis J. McGillicuddy ◽  
Erik A. Fields
Keyword(s):  
Satellite Altimetry ◽  
Mesoscale Eddies ◽  
Sargasso Sea ◽  
New Production

Biogeochemical responses to late-winter storms in the Sargasso Sea, I—Pulses of primary and new production

2009 ◽  
Vol 56 (6) ◽  
pp. 843-860 ◽  
Author(s):  
M.W. Lomas ◽  
F. Lipschultz ◽  
D.M. Nelson ◽  
J.W. Krause ◽  
N.R. Bates
Keyword(s):  
Late Winter ◽  
Sargasso Sea ◽  
New Production ◽  
Winter Storms

Influence of mesoscale eddies on new production in the Sargasso Sea

Nature ◽  
10.1038/28367 ◽  
1998 ◽  
Vol 394 (6690) ◽  
pp. 263-266 ◽  
Author(s):  
D. J. McGillicuddy ◽  
A. R. Robinson ◽  
D. A. Siegel ◽  
H. W. Jannasch ◽  
R. Johnson ◽  
...  
Keyword(s):  
Mesoscale Eddies ◽  
Sargasso Sea ◽  
New Production

scholarly journals Production regime and associated N cycling in the vicinity of Kerguelen Island, Southern Ocean

2015 ◽  
Vol 12 (21) ◽  
pp. 6515-6528 ◽  
Author(s):  
A. J. Cavagna ◽  
F. Fripiat ◽  
M. Elskens ◽  
P. Mangion ◽  
L. Chirurgien ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Primary Production ◽  
Mixed Layer ◽  
Nitrate Uptake ◽  
Net Primary Production ◽  
N Uptake ◽  
Euphotic Zone ◽  
Global Ocean ◽  
Kerguelen Plateau ◽  
New Production

Abstract. Although the Southern Ocean is considered a high-nutrient, low-chlorophyll (HNLC) area, massive and recurrent blooms are observed over and downstream of the Kerguelen Plateau. This mosaic of blooms is triggered by a higher iron supply resulting from the interaction between the Antarctic Circumpolar Current and the local bathymetry. Net primary production, N uptake (NO3− and NH4+), and nitrification rates were measured at eight stations in austral spring 2011 (October–November) during the KEOPS 2 cruise in the Kerguelen Plateau area. Natural iron fertilization stimulated primary production, with mixed layer integrated net primary production and growth rates much higher in the fertilized areas (up to 315 mmol C m−2 d−1 and up to 0.31 d−1 respectively) compared to the HNLC reference site (12 mmol C m−2 d−1 and 0.06 d−1 respectively). Primary production was mainly sustained by nitrate uptake, with f ratios (corresponding to NO3−-uptake / (NO3−-uptake + NH4+-uptake)) lying at the upper end of the observations for the Southern Ocean (up to 0.9). We report high rates of nitrification (up to ~ 3 μmol N L−1 d−1, with ~ 90 % of them < 1 μmol N L−1 d−1) typically occurring below the euphotic zone, as classically observed in the global ocean. The specificity of the studied area is that at most of the stations, the euphotic layer was shallower than the mixed layer, implying that nitrifiers can efficiently compete with phytoplankton for the ammonium produced by remineralization at low-light intensities. Nitrate produced by nitrification in the mixed layer below the euphotic zone is easily supplied to the euphotic zone waters above, and nitrification sustained 70 ± 30 % of the nitrate uptake in the productive area above the Kerguelen Plateau. This complicates estimations of new production as potentially exportable production. We conclude that high productivity in deep mixing system stimulates the N cycle by increasing both assimilation and regeneration.

scholarly journals Submesoscale Water-Mass Spectra in the Sargasso Sea

2015 ◽  
Vol 45 (5) ◽  
pp. 1325-1338 ◽  
Author(s):  
E. Kunze ◽  
J. M. Klymak ◽  
R.-C. Lien ◽  
R. Ferrari ◽  
C. M. Lee ◽  
...  
Keyword(s):  
Internal Waves ◽  
Mixed Layer ◽  
Water Mass ◽  
Layer Structure ◽  
Salinity Gradient ◽  
Sargasso Sea ◽  
Passive Tracer ◽  
Shear Dispersion ◽  
Winter Mixed Layer ◽  
Horizontal Strain

AbstractSubmesoscale stirring contributes to the cascade of tracer variance from large to small scales. Multiple nested surveys in the summer Sargasso Sea with tow-yo and autonomous platforms captured submesoscale water-mass variability in the seasonal pycnocline at 20–60-m depths. To filter out internal waves that dominate dynamic signals on these scales, spectra for salinity anomalies on isopycnals were formed. Salinity-gradient spectra are approximately flat with slopes of −0.2 ± 0.2 over horizontal wavelengths of 0.03–10 km. While the two to three realizations presented here might be biased, more representative measurements in the literature are consistent with a nearly flat submesoscale passive tracer gradient spectrum for horizontal wavelengths in excess of 1 km. A review of mechanisms that could be responsible for a flat passive tracer gradient spectrum rules out (i) quasigeostrophic eddy stirring, (ii) atmospheric forcing through a relict submesoscale winter mixed layer structure or nocturnal mixed layer deepening, (iii) a downscale vortical-mode cascade, and (iv) horizontal diffusion because of shear dispersion of diapycnal mixing. Internal-wave horizontal strain appears to be able to explain horizontal wavenumbers of 0.1–7 cycles per kilometer (cpkm) but not the highest resolved wavenumbers (7–30 cpkm). Submesoscale subduction cannot be ruled out at these depths, though previous observations observe a flat spectrum well below subduction depths, so this seems unlikely. Primitive equation numerical modeling suggests that nonquasigeostrophic subinertial horizontal stirring can produce a flat spectrum. The last need not be limited to mode-one interior or surface Rossby wavenumbers of quasigeostrophic theory but may have a broaderband spectrum extending to smaller horizontal scales associated with frontogenesis and frontal instabilities as well as internal waves.

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