References

Ocean Science

Ocean Sci.

1812-0792

Copernicus Publications

Göttingen, Germany

10.5194/os-7-113-2011

Phytoplankton distribution and nitrogen dynamics in the southwest indian subtropical gyre and Southern Ocean waters

Thomalla

S. J.

¹ ² Waldron

H. N.

¹ Lucas

M. I.

³ Read

J. F.

⁴ Ansorge

I. J.

¹ Pakhomov

⁵ ⁶

Department of Oceanography, University of Cape Town, Private Bag, Rondebosch, Cape Town 7701, South Africa

Ocean Systems and Climate Group, CSIR, P.O. Box 320 Stellenbosch, 7599, South Africa

Department of Zoology, University of Cape Town, Private Bag, Rondebosch, Cape Town 7701, South Africa

National Oceanographic Centre (NOC), Southampton, SO143ZH, UK

Department of Earth and Ocean Sciences, 6339 Stores Road, Univ. of British Columbia, Vancouver, BC, V6T 1Z4, Canada

Department of Zoology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa

08 02 2011

7 1 113 127

2011

This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/

This article is available from https://os.copernicus.org/articles/7/113/2011/os-7-113-2011.html

The full text article is available as a PDF file from https://os.copernicus.org/articles/7/113/2011/os-7-113-2011.pdf

During the 1999 Marion Island Oceanographic Survey (MIOS 4) in late austral summer, a northbound and reciprocal southbound transect were taken along the Southwest Indian and Madagascar Ridge, between the Prince Edward Islands and 31° S. The sections crossed a number of major fronts and smaller mesoscale features and covered a wide productivity spectrum from subtropical to subantarctic waters. Associated with the physical survey were measurements of size fractionated chlorophyll, nutrients and nitrogen (NO3, NH4 and urea) uptake rates. Subtropical waters were characterised by low chlorophyll concentrations (max = 0.27.3 mg m−3 dominated by pico-phytoplankton cells (> 81%) and very low f-ratios (< 0.1), indicative of productivity based almost entirely on recycled ammonium and urea. Micro-phytoplankton growth was limited by the availability of NO3 (< 0.5 mmol m−3 and Si(OH)4 (< 1.5 mmol m−3 through strong vertical stratification preventing the upward flux of nutrients into the euphotic zone. Biomass accumulation of small cells was likely controlled by micro-zooplankton grazing. In subantarctic waters, total chlorophyll concentrations increased (max = 0.74 mg m−3 relative to the subtropical waters and larger cells became more prevalent, however smaller phytoplankton cells and low f-ratios (< 0.14) still dominated, despite sufficient NO3 availability. The results from this study favour Si(OH)4 limitation, light-limited deep mixing and likely Fe deficiency as the dominant mechanisms controlling significant new production by micro-phytoplankton. The percentage of micro-phytoplankton cells and rates of new production did however increase at oceanic frontal regions (58.6% and 11.22%, respectively), and in the region of the Prince Edward archipelago (61.4% and 14.16%, respectively). Here, water column stabilization and local Fe-enrichment are thought to stimulate phytoplankton growth rates. Open ocean regions such as these provide important areas for local but significant particulate organic carbon export and biological CO2 draw-down in an overall high nutrient low chlorophyll Southern Ocean.

References 1

Allanson, B. R., Hart, R. C., and Lutjerharms, J. R. E.: Observations on the nutrients, chlorophyll and primary production of the Southern Ocean south of Africa, South African Journal of Antarctic Research, 10(11), 3–14, 1981.

Ansorge, I. J., Froneman, P. W., Pakhamov, E. A., Lutjerharms, J. R. E., Perissinotto, R., and van Ballegooyen, R. C.: Physical-biological coupling in the waters surrounding the Prince Edward Islands (Southern Ocean), Polar Biol., 21, 135–145, 1999.

Atkinson, A., Whitehouse, M. J., Priddle, J., Cripps, G. C., Ward, P., and Brandon, M. A.: South Georgia, Antarctica: a productive, cold water, pelagic ecosystem, Mar. Ecol. Prog.-Ser., 216, 279–308, 2001.

Bakker, D. C. E., Nielsdottir, M. C., Morris, P., Venables, H. J., and Watson, A. J.: The island mass effect and biological carbon uptake for the subantarctic Crozet Archipelago, Deep-Sea Res. II, 54, 2174–2190, 2007.

Barange, M., Pakhomov, E. A., Perissinotto, R., Froneman, P. W., Verheye, H. M., Taunton-Clark, J., and Lucas, M. I.: Pelagic community structure of the subtropical Convergence region south of Africa and in the mid-Atlantic Ocean, Deep-Sea Res., 45, 1663–1687, 1998.

Barrie, A., Davies, J. E., Park, A. J., and Workman, C. T.: Continuous-flows stable isotope analysis for biologists, Spectroscopy, 4, 42–52, 1989.

Bathmann, U., Priddle, J., Treguer, P., Lucas, M. I., Parslow, J., and Hall, J.: Plankton ecology and biogeochemistry in the Southern Ocean: A first review of Southern Ocean JGOFS, in: The Changing Ocean carbon Cycle: a midterm synthesis of the Joint Global Ocean Flux Study, edited by: Hanson, R. B., Ducklow, H. W., and Field, J. G., IGBP Book Series 5, Cambridge University Press, London, 2000.

Belkin, I. M. and Gordon, A.L.: Southern Ocean fronts from the Greenwich meridian to Tasmania, J. Geophys. Res., 101, 3675–3696, 1996.

Blain, S., Treguer, P., Belviso, S., Bucciarelli, E., Denis, M., Desabre, S., Fial, M., Jézéquel, V. M., Le Fèvre, J., Mayzaud, P., Marty, J., and Razouls, S.: A biogeochemical study of the island mass effect in the context of the iron hypothesis: Kerguelen Islands, Southern Ocean, Deep-Sea Res. II, 48(1), 163–187, 2001.

Blain, S., Queguiner, B., Armand, L., Belviso, S., Bombled, B., Bopp, L., Bowie, A., Brunet, C., Brussaard, C., Carlotti, F., Christaki, U., Corbiere, A., Durand, I., Ebersbach, F., Fuda, J., Garcia, N., Gerringa, L., Griffiths, B., Guigue, C., Guillerm, C., Jacquet, S., Jeandel, C., Laan, P., Lefevre,., D., Lo Monaco, C., Malits, A., Mosseri, J., Obernosterer, I., Park, Y., Picheral, M., Pondaven, P., Remenyi, T., Sandroni, V., Sarthou, G., Savoye, N., Scouarnec, L., Souhaut, M., Thuiller, D., Timmermans, K., Trull, T., Uitz, J., van Beek, P., Veldhuis, M., Vincent, D., Viollier, E., Vong, L., and Wagener, T.: Effect of natural iron fertilization on carbon sequestration in the Southern Ocean, Nature, 446, 1070–1074, 2007.

Boyd, P., Watson, A., Law, C., Abraham, E., Trull, T., Murdoch, R., Bakker, D., Bowie, A., Buesseler, K. O., Chang, H., Charette, M., Croot, P., Downing, K., Frew, R., Gall, M., Hadfield, M., Hall, J., Harvey, M., Jameson, G., LaRoche, J., Liddicoat, M., Ling, R., Maldonado, M., McKay, R. M., Nodder, S., Pickmere, S., Pridmore, R., Rintoul, S., Safi, K., Sutton, P., Strzepek, R., Tanneberger, K., Turner, S., Waite, A., and Zeldis, J.: A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization, Nature, 407, 695–702, 2000.

Boyd, P. W., Jickells, T., Law, C. S., Blain, S., Boyle, E. A., Buesseler, K. O., Coale, K. H., Cullen, J. J., de Baar, H. J. W., Follows, M., Harvey, M., Lancelot, C., Levasseur, M., Owens, N. P. J., Pollard, R., Rivkin, R. B., Sarmiento, J., Schoemann, V., Smetacek, V., Takeda, S., Tsuda, A., Turner, S., and Watson, A. J.: Mesoscale Iron enrichment experiments 1993–2005: Synthesis and future directions, Science, 315, 612–617, 2007.

Bury, S. J., Owens, N. J. P., and Preston, T.: 13C and 15N uptake by phytoplankton in the marginal ice zone of the Bellingshausen Sea, Deep-Sea Res. II, 42, 1225–1252, 1995.

Coale, K. H., Johnson, K. S., Chavez, F. P., Buesseler, K. O., Barber, R. T., Brzezinski, M. A., Cochlan, W. P., Falkowski, P. G., Bauer, J. E., Wanninkhof, R. H., Kudela, R. M., Altabet, M. A., Hales, B. E., Takahashi, T., Landry, M. R., Bidigare, R. R., Wang, X., Chase, Z., Strutton, P. G., Friederich, G. E., Gorbunov, M. Y., Lance, V. P., Hilting, A. K., Hiscock, M. R., Demarest, M., Hiscock, W. T., Sullivan, K. F., Tanner, S. J., Gordon, R. M., Hunter, C. N., Elrod, V. A., Fitzwater, S. E., Jones, J. L., Tozzi, S., Koblizek, M., Roberts, A. E., Brewster, J., Ladizinsky, N., Smith, G., Cooper, D., Timothy, D., Brown, S. L., Selph, K. E., Sheridan, C. C., Twining, B. S., and Johnson, Z. I.: Southern Ocean iron enrichment experiment: carbon cycling in the high- and low- Si waters, Science, 304, 408–414, 2004.

Cochlan, W. P.: Nitrogen uptake in the Southern Ocean, in: Nitrogen in the Marine Environment, 2nd Edn., edited by: Capone, D. G., Bronk, D. A., Mulholland, M. R., and Carpenter, E. J., Academic Press, Elsevier, 569–596, 2008.

Cullen, J. J.: Hypotheses to explain high-nutrient conditions in the open sea, Limnol. Oceanogr., 36, 1578–1599, 1991.

De Baar, H. J. W., Buma, A. G. J., Nolting, R. F., Cadee, G. C., Jacques, G., and Treguer, P. J.: On iron limitation in the Southern Ocean: Experimental observations in the Weddel and Scotia Seas, Mar. Ecol. Prog.-Ser., 65, 105–122, 1990.

De Baar, H. J. W., Boyd, P. W., Coale, K. H., Landry, M. R., Tsuda, A., Assmy, P., Bakker, D. C. E., Bozec, Y., Barber, R. T., Brzezinski, M. A., Buesseler, K. O., Boye, M., Croot, P. L., Gervais, F., Gorbunov, M. Y., Harrison, P. J., Hiscock, W. T., Laan, P., Lancelot, C., Law, C. S., Levasseur, M., Marchetti, A., Millero, F. J., Nishioka, J., Nojiri, Y., Van Oijen, T., Riebesell, U., Rijkenberg, M. J. A., Saito, H., Takeda, S., Timmermans, K. R., Veldhuis, M. J. W., Waite, A. M., Wong, C. S. M., Bugg, W., Efremenko, Y., Kamyshkov, Y., Kozlov, A., Nakamura, Y., Karwowski, H. J., Markoff, D. M., Nakamura, K., Rohm, R. M., Tornow, W., Wendell, R., Chen, M. J., Wang, Y. F., Piquemal, F., and Wong, C. S. D. M.: Synthesis of iron fertilization experiments: From the Iron Age in the Age of Enlightenment, J. Geophys. Res., 110, C09S16, <a href="http://dx.doi.org/10.1029/2004JC002601">https://doi.org/10.1029/2004JC002601</a>, 2005.

Diaz, F. and Raimbault, P.: Nitrogen regeneration and dissolved organic nitrogen release during spring in a NW Mediterranean coastal zone (Gulf of Lions): implications for the estimation of new production, Mar. Ecol. Prog.-Ser., 197, 51–65, 2000.

Donald, K. M., Joint, I., Rees, A. P., Woodward, E. M. S., and Savidge, G.: Uptake of carbon, nitrogen and phosphorus by phytoplankton along the $20^\circ$ W meridian in the NE Atlantic between $57.5^\circ$ N and $37^\circ$ N, Deep-Sea Res. II, 48, 873–897, 2001.

Dore, J. E. and Karl, D. M.: Nitrification in the euphotic zone as a source for nitrite, nitrate, and nitrous oxide at station ALOHA, Limnol. Oceanogr., 41, 1619–1628, 1996.

Dower, K. M. and Lucas, M. I.: Photosynthesis-irradiance relationships and production associated with a warm-core ring shed from the Subtropical Retroflection south of Africa, Mar. Ecol. Prog.-Ser., 95, 141–154, 1993.

Dugdale, R. C. and Goering, J. J.: Uptake of new and regenerated forms of nitrogen in primary productivity, Limnol. Oceanogr., 12(2), 196–206, 1967.

Dugdale, R. C. and Wilkerson, F. P.: Silicate regulation of new production in the equatorial Pacific upwelling, Nature, 391, 270–273, 1998.

Eppley, R., Rogers, J., and McCarthy, J.: Half-Saturation Constants for Uptake of Nitrate and Ammonium by Marine Phytoplankton, Limnol. Oceanogr., 14, 912–920, 1969.

Eppley, R. W.: New Production: History, Methods and Problems, in: Productivity of the Ocean: Present and Past, edited by: Berger, W. H., Smetacek, V. S., and Wefer, G., John Wiley and Sons, New York, 85–97, 1989.

Eppley, R. W. and Peterson, B. J.: Particulate organic matter flux and planktonic new production in the deep ocean, Nature, 282, 677–680, 1979.

Falkowski, P. G. and Raven, J. A.: Aquatic photosynthesis, Blackwell Science, Oxford, 1997.

Falkowski, P. G., Scholes, R. J., Boyle, E., Canadell, J., Canfield, D., Elser, J., Gruber, N., Hibbard, K., Hogberg, P., Linder, S., Mackenzie, F. T., Moore III, B., Pedersen, T., Rosenthal, Y., Seitzinger, S., Smetacek, V., and Steffen, W.: The global carbon cycle: A test of our knowledge of earth as a system, Science, 290, 291–296, 2000.

Fernandez, C. and Raimbault, P.: Nitrogen regeneration in the Northeast Atlantic Ocean and its impact on seasonal new, regenerated and export production, Mar. Ecol. Prog.-Ser., 337, 79–92, 2007.

Froneman, P. W. and Perissinotto, R.: Microzooplankton grazing and protozooplankton community structure in the South Atlantic and in the Atlantic sector of the Southern Ocean, Deep-Sea Res. I, 43, 703–721, 1996.

Geider, R. J. and La Roche, J.: Redfield revisited: variability of C:N:P in marine microalgae and its biochemical basis, Eur. J. Phycol., 37, 1–17, 2002.

Gervais, F., Riebesell, U., and Gorbunov, M. Y.: Changes in primary productivity and chlorophyll a in response to iron fertilization in the Southern Polar Frontal Zone, Limnol. Oceanogr., 47, 1324–1335, 2002.

Glibert, P. M., Lipschultz, F., McCarthy, J. J., and Altabet, M. A.: Isotope dilution models of uptake and remineralization of ammonium by marine plankton, Limnol. Oceanogr., 27, 639–650, 1982.

Glibert, P. M., Miller, C. A., Garside, C., Roman, M. R., and McManus, G. B.: NH4+ regeneration and grazing: interdependent processes in size-fractionated 15NH4+ experiments, Mar. Ecol.-Prog. Ser., 82, 65–74, 1992.

Grasshoff, K. M., Ehrhardt, M., and Kremling, K.: Determination of urea (9.5), in: Methods of seawater analysis, 2nd Edn., Verlag Chemie, Wienheim, Germany, 158–162, 1983.

Grundlingh, M. L.: Observation of a large meander in the Agulhas Current, J. Geophys. Res., 84, 3776–3778, 1979.

Harrison, W. G. and Harris, I. R.: Isotope dilution and its effects on measurements of nitrogen and phosphorous uptake by oceanic microplankton, Mar. Ecol.-Prog. Ser., 27, 253–261, 1986.

Hoffmann, L. J., Peeken, I., Lochte, K., Assmy, P., and Veldhuis, M.: Different reactions of Southern Ocean phytoplankton size classes to iron fertilization, Limnol. Oceanogr., 51(3), 1217–1229, 2006.

Honjo, S., Francois, R., Manganini, S., Dymond, J., and Collier, R.: Particle fluxes to the interior of the Southern Ocean in the Western Pacific sector along $170^\circ$ W, Deep-Sea Res. II, 47(15–16), 3521–3548, 2000.

Kirk, J. T. O.: Light and photosynthesis in aquatic ecosystems, 2nd Edn., Cambridge University Press, Cambridge, 1994.

Knauer, G. A., Redalje, D. G., Harrison, W. G., and Karl, D. M.: New production at the VERTEX time-series site, Deep-Sea Res., 37(7), 1121–1134, 1990.

Laubscher, R. K., Perissinotto, R., and McQuaid, C. D.: Phytoplankton production and biomass at frontal zones in the Atlantic sector of the Southern Ocean, Polar Biol., 13, 471–481,1993.

Longhurst, A. R.: Role of the marine biosphere in the global carbon cycle, Limnol. Oceanogr., 36, 1507–1526, 1991.

Lucas, M. I., Seeyave, S., Sanders, R., Moore, M., and Williamson, R.: New and regenerated production during the Crozex study, Deep-Sea Res. II, 54, 2138–2173, 2007.

Lutjeharms, J. R. E.: Location of frontal systems between Africa and Antarctica; some preliminary results, Deep-Sea Res., 32, 1499–1509, 1985.

Lutjeharms, J. R. E. and Ansorge, I. J.: The Agulhas Return Current, J. Marine Syst., 30(1–2), 115–138, 2001.

Lutjeharms, J. R. E. and Valentine, H. R.: Southern Ocean thermal fronts south of Africa, Deep-Sea Res., 31, 1461–1475, 1984.

Lutjeharms, J. R. E., Fromme, G. A. W., and Valentine, H. R.: Oceanic frontal systems between Africa and Antarctica, EOS, Eos. T. Am. Geophys. Un., 62, p. 942, 1981.

Lutjeharms, J. R. E., Walters, N. M., and Allanson, B. R.: Oceanic frontal systems and biological enhancement, in: Antarctic nutrient cycles and food webs, edited by: Siegfried, W. R., Condy, P. R., and Laws, R. M., Springer-Verlag, Berlin, 11–21, 1985.

Martin, J. H. and Fitzwater, S.: Iron deficiency limits phytoplankton growth in the north-east Pacific subarctic, Nature, 331, 341–343, 1988.

Martin, J. H., Gordan, R., Fitzwater, S., and Brokenkow, W.: VERTEX: phytoplankton/iron studies in the Gulf of Alaska, Deep-Sea Res., 36, 649–680, 1989.

Martin, J. H., Gordon, R. M., and Fitzwater, S. E.: The case for iron, Limnol. Oceanogr., 36, 1793–1802, 1991.

Metzl, N., Tilbrook, B., and Poison, A.: The annual fCO2 cycle and the air-sea CO2 flux in the sub-Antarctic Ocean, Tellus, 51B, 849–861, 1999.

Moore, C. M., Mills, M. M., Milne, A., Langlois, R., Achterberg, E. P., Lochte, K., Geider, R. J., and La Roche, J.: Iron limits primary productivity during spring bloom development in the central North Atlantic, Glob. Change Biol., 12, 626–634, 2006.

Moore, M. C., Seeyave, S., Hickman, A. E., Allen, J. T., Lucas, M. I., Planquette, H., Pollard, R., and Poulton, A. J.: Iron-light interactions during the CROZet natural iron bloom and EXport experiment (CROZEX) I: phytoplankton growth and photophysiology, Deep-Sea Res. II, 54, 2045–2065, 2007a.

Moore, M. C., Hickman, A. E., Poulton, A. J., Seeyave, S., and Lucas, M. I.: Iron-light interactions during the CROZet natural iron bloom and Export experiment (CROZEX) II: taxonomic responses and elemental stoichiometry, Deep-Sea Res. II, 54, 2066–2084, 2007b.

Morel, A.: Light and marine photosynthesis: A spectral model with geochemical and climatological implications, Prog. Oceanogr., 26, 263–306, 1991.

Nelson, D. M. and Smith, W. O.: Sverdrup re-visited: critical depths, maximum chlorophyll levels, and the control of Southern Ocean productivity by the irradiance-mixing regime, Limnol. Oceanogr., 36, 1650–1661, 1991.

Orsi, A. H., Whitworth, T., and Nowlin, W. D.: On the meridional extent and fronts of the Antarctic Circumpolar Current, Deep-Sea Res., 42, 641–673, 1995.

Owens, N. J. P. and Rees, A. P.: Determination of nitrogen-15 at submicrogram levels of nitrogen using automated continuous-flow isotope ratio mass spectrometry, Analyst, 114, 1655–1657, 1989.

Pakhomov, E. A., Froneman, P. W., and Ansorge, I. J.: Prince Edward Islands' offshore oceanographic study: report of research cruise April–May 1997, S. Afr. J. Sci., 94, 153–156, 1998.

Pakhomov, E. A., Ansorge, I. J., McQuaid, C. D., Kohrs, S., Waldron, H., Hunt, B., Gurney, L., Kaehler, S., Lawrie, S., Held, C., and Machu, E.: The fourth cruise of the Marion Island Oceanographic Survey (MIOS-IV), April to May 1999, S. Afr. J. Sci., 95, 1–3, 1999.

Park, Y. H., Gamberoru, L., and Charriaud, E.: Frontal structure, water masses and circulation in the google scholarCrozet Basin, J. Geophys. Res., 98, 2361–12385, 1993.

Parsons, T. R., Maita, Y., and Lalli, C. M.: A manual of chemical and biological methods for seawater analysis, Pergamon Press, Oxford, 173 pp., 1984.

Plancke, J.: Phytoplankton biomass and productivity in the Subtropical Convergence area and the shelves of the western Indian subantarctic islands, in: Adaptions within Antarctic ecosystems, edited by: Liano, G. A., Smithsonian Institution, Washington, D.C., 51–73, 1977.

Planquette, H., Statham, P. J., Fones, G. R., Charette, M. A., Moore, M., Salter, I., Nédélec, H., Taylor, S. L., French, M., Baker, A. R., Mahowald, N., and Jickells, T. D.: Dissolved iron in the vicinity of the Crozet Islands, Southern Ocean, Deep-Sea Res. II, 54, 1999–2019, 2007.

Pollard, R. T. and Read, J. F.: Circulation pathways and transports of the Southern Ocean in the vicinity of the Southwest Indian Ridge, J. Geophys. Res., 106, 2881–2898, 2001.

Pollard, R. T. and Regier, L. A.: Vorticity and vertical circulation at an ocean front, J. Phys. Oceanogr., 22, 609–625, 1992.

Pollard, R. T., Lucas, M. I., and Read, J. F.: Physical controls on biogeochemical zonation in the Southern Ocean, Deep-Sea Res. II, 49, 16, 3289–3305, 2002.

Pollard, R., Sanders, R., Lucas, M., and Statham, P.: The Crozet natural iron bloom and export experiment (CROZEX), Deep-Sea Res. II, 54, 1905–1914, 2007.

Pollard, R. T., Salter, I., Sanders, R. J., Lucas, M. I., Moore, C. M., Mills, R. A., Statham, P. J., Allen, J. T., Baker, A. R., Bakker, D. C. E., Charette, M. A., Fielding, S., Fones, G. R., French, M., Hickman, A. E., Holland, R. J., Hughes, J. A., Jickells, T. D., Lampitt, R. S., Morris, P. J., Nedelec, F. H., Nielsdottir, M., Planquette, H., Popova, E. E., Poulton, A. J., Read, J. F., Seeyave, S., Smith, T., Stinchcombe, M., Taylor, S., Thomalla, S. J., Venables, H. J., Williamson, R., and Zubkov, M. V.: Southern Ocean deep-water carbon export enhanced by natural iron fertilization, Nature, 457, 577–580, 2009.

Probyn, T. A., Waldron, H. N., Searson, S., and Owens, N. J. P.: Diel variability in nitrogenous nutrient uptake at photic and subphotic depths, J. Plankton. Res., 18, 2063–2079, 1996.

Raimbault, P., Slawyk, G., Boudjellal, B., Coatanoan, C., Conan, P., Coste, B., Garcia, N., Moutin, T., and Pujo-Pay, M.: Carbon and nitrogen uptake and export in the Equatorial Pacific at $150^\circ$ W: Evidence of an efficient regenerated production cycle, J. Geophys. Res., 104, 3341–3356, 1999.

Raven, J. A.: Physiological consequences of extremely small size for autotrophic organisms in the sea, Can. Bull. Fish. Aquat. Sci., 214, 1–70, 1986.

Read, J. F. and Pollard, R. T.: Structure and transport of the Antarctic Circumpolar Current and Agulhas Return Current at $40^\circ$ E, J. Geophys. Res., 98, 12281–12295, 1993.

Read, J. F., Lucas, M. I., Pollard, R. T., and Holley, S. E.: Phytoplankton, nutrients and hydrography in the frontal zone between the Southwest Indian Subtropical gyre and the Southern Ocean, Deep-Sea Res. I, 47, 2341–2368, 2000.

Rees, A. P., Malcolm, E., Woodward, S., Robinson, C., Cummings, D. G., Tarran, G. A., and Joint, I.: Size-fractionated nitrogen uptake and carbon fixation during a developing coccolithophore bloom in the North Sea during June 1999, Deep-Sea Res. Part II, 49(15), 2905–2927, 2002.

Salter, I., Lampitt, R. S., Sanders, R. Poulton, A. J., Boorman, B., and Saw, K.: Estimating Export Production From CROZEX using PELAGRA: a Novel Drifting sediment trap, Deep-Sea Res. II, 54, 2233–2259, 2007.

Sanders, R., Morris, P. J., Poulton, A. J., Stinchcombe, M. C., Charalampopoulou, A., Lucas, M. I., and Thomalla,S. J.: Does a ballast effect occur in the surface ocean?, Geophys. Res. Lett., 37, L08602, <a href="http://dx.doi.org/10.1029/2010GL042574">https://doi.org/10.1029/2010GL042574</a>, 2010.

Schlitzer, R.: Electronic Atlas of WOCE Hydrographic and Tracer Data Now Available, Eos Trans. AGU, 81(5), p. 45, 2000.

Schlitzer, R.: Ocean Data View, <a href="http://www.awi-bremerhaven.de/GEO/ODV">http://www.awi-bremerhaven.de/GEO/ODV</a> (last access: 13 May 2010), 2002.

Smetacek, V.: Diatoms and the Silicate factor, Nature, 391, 224–225, 1998.

Thomalla, S. J., Poulton, A. J., Sanders, R., Turnewitsch, Holligan, P. M., and Lucas, M. I.: Variable export fluxes and efficiencies for calcite, opal and organic carbon in the Atlantic Ocean: A ballast effect in action?, Global Biogechem. Cy., 22, GB1010, <a href="http://dx.doi.org/10.1029/2007GB002982">https://doi.org/10.1029/2007GB002982</a>, 2008.

Timmermans, K. R., van der Wagt, B., and de Baar, H. J. W.: Growth rates, half-saturation constants, and silicate, nitrate, and phosphate depletion in relation to iron availability of four large, open-ocean diatoms from the Southern Ocean, Limnol. Oceanogr., 49(6), 2141–2151, 2004.

Tremblay, J. E., Klein, B., and Legendre, L.: Estimation of f-ratios in oceans based on phytoplankton size structure, Limnol. Oceanogr., 42, 595–601, 1997.

Tremblay, J. E., Legendre, L., Klein, B., and Therriault, J. C.: Size-differential uptake of nitrogen and carbon in a marginal sea (Gulf of St. Lawrence, Canada): significance of diel periodicity and urea uptake, Deep-Sea Res. II, 47, 489–518, 2000.

Varela, M. M., Bode, A., Fernández, E., Gónzalez, N., Kitidis, V., Varela, M., and Woodward, E. M. S., Nitrogen uptake and dissolved organic nitrogen release in planktonic communities characterised by phytoplankton size-structure in the Central Atlantic Ocean, Deep Sea Res. I, 52(9), 1637–1661, 2005.

Volk, T. and Hoffert, M. I.: Ocean carbon pumps: analysis of relative strengths and efficiencies in ocean-driven atmospheric CO2 changes, in: The carbon cycle and atmospheric CO2: natural variations Archean to Present, edited by: Sundguist, E. T. and Broeker, W. S., American Geophysical Union, Washington DC, 627 pp., 1985.

Waldron, H. N., Attwood, C. G., Probyn, T. A., and Lucas, M. I.: Nitrogen dynamics in the Bellingghausen Sea during the austral spring of 1992, Deep-Sea Res. II, 42, 1253–1276, 1995.

Weeks, S. J. and Shillington, F. A.: Interannual scales of variation of chlorophyll concentrations from CZCS data in the Benguela Upwelling System and the Subtropical Convergence south of Africa, J. Geophys. Res., 99, 7385–7399, 1994.

Whitworth, T. and Nowlin, W. D.: Water masses and currents of the Southern Ocean at the Greenwich Meridian, J. Geophys. Res., 92, 6462–6476, 1987.

Yool, A., Martin, A. P., Fernandez, C., and Clark, R. J.: Not so new: the significance of nitrification for oceanic "new" production, Nature 447, 999–1002, 2007.