Nitrogen uptake by phytoplankton in surface waters of the Indian sector of Southern Ocean during austral summer
This study reports the nitrogen uptake rate (using 15N tracer) of phytoplankton in surface waters of different frontal zones in the Indian sector of the Southern Ocean (SO) during austral summer of 2013. The investigated area encompasses four major frontal systems, i.e., the subtropical front (STF), subantarctic front (SAF), polar front-1 (PF1) and polar front-2 (PF2). Southward decrease of surface water temperature was observed, whereas surface salinity did not show any significant trend. Nutrient (NO3– and SiO44–) concentrations increased southward from STF to PF; while ammonium (NH4+), nitrite (NO2–) and phosphate (PO43–) remained comparatively stable. Analysis of nutrient ratios indicated potential N-limited conditions at the STF and SAF but no such scenario was observed for PF. In terms of phytoplankton biomass, PF1 was found to be the most productive followed by SAF, whereas PF2 was the least productive region. Nitrate uptake rate increased with increasing latitude, as no systematic spatial variation was discerned for NH4+ and urea (CO(NH2)2). Linear relationship between nitrate and total N-uptake reveals that the studied area is capable of exporting up to 60% of the total production to the deep ocean if the environmental settings are favorable. Like N-uptake rates the f-ratio also increased towards PF region indicating comparatively higher new production in the PF than in the subtropics. The moderately high average f-ratio (0.53) indicates potentially near equal contributions by new production and regenerated production to the total productivity in the study area. Elevation in N-uptake rates with declining temperature suggests that the SO with its vast quantity of cool water could play an important role in drawing down the atmospheric CO2 through the “solubility pump”.
Keywordsnitrogen uptake f-ratio new productivity frontal zones Southern Ocean
Unable to display preview. Download preview PDF.
The authors express gratitude to the Ministry of Earth Sciences, Govt. of India for financial aid to conduct this study, and Director, NCAOR for his constant encouragement and support. We thank, Head of the VMC, NIOT for providing us the vessel and essential logistic supports. Sincerely acknowledge the help from the Captain, crew and scientific members of the SOE-7. The first author earnestly thanks Dr. M. Tiwari and Mr. S. Nagoji of MASTIL, NCAOR for facilitating 15N sample analysis. Support from administration, procurement and finance divisions’ staff of NCAOR is highly acknowledged. This is NCAOR contribution No. 07/2017.
- Anderson F R (2003). What regulates the efficiency of the biological pump in the Southern Ocean. US JGOFS News, 12(2): 1–4Google Scholar
- Blain S, Queguiner B, Armand L, Belviso S, Bombled B, Bopp L, Bowie A, Brunet C, Brussaard C, Carlotti F, Christaki U, Corbière A, Durand I, Ebersbach F, Fuda J L, Garcia N, Gerringa L, Griffiths B, Guigue C, Guillerm C, Jacquet S, Jeandel C, Laan P, Lefèvre D, Lo Monaco C, Malits A, Mosseri J, Obernosterer I, Park Y H, 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, Wagener T (2007). Effect of natural iron fertilization on carbon sequestration in the Southern Ocean. Nature, 446(7139): 1070–1074CrossRefGoogle Scholar
- 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, Watson A J (2007). Mesoscale iron enrichment experiments 1993–2005: synthesis and future directions. Science, 315(5812): 612–617CrossRefGoogle Scholar
- Collos Y, Slawyk G (1986). 13C and 15N uptake by marine phytoplankton-IV. Uptake ratios and the contribution of nitrate to the production of Antarctic waters (Indian Ocean sector). Deep-Sea Res, 33(8): 1039–1051Google Scholar
- de Baar J W H, Boyd P W, Coale K H, Landry M R, Tsuda A, Assmy P, Bakker D C E, Bozec Y, Barber RT, Brzezinski MA, Buesseler K O, Boyé M, Croot P L, Gervais F, GorbunovMY, 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 (2005). Synthesis of iron fertilization experiments: from the Iron Age in the age of enlightment. J Geophys Res, 110(C9): C09S16Google Scholar
- Falkowski P G, Scholes R J, Boyle E, Canadell J, Canfield D, Elser J, Gruber N, Hibbard K, Högberg P, Linder S, Mackenzie F T, Moore III B, Pedersen T, Rosenthal Y, Seitzinger S, Smetacek V, Steffen W (2000). The global carbon cycle: a test of our knowledge of earth as a system. Science, 290(5490): 291–296CrossRefGoogle Scholar
- Jacques G, Fukuchi M (1994). Phytoplankton in the Indian Antarctic Ocean. In: El-Sayed S E, ed. Southern Ocean Ecology: the BIOMASS perspective. Cambridge: Cambridge University Press, 63–78Google Scholar
- Jasmine P, Muraleedharan K R, Madhu N V, Asha Devi C R, Alagarsamy R, Achuthankutty C T, Jayan Z, Sanjeevan V N, Sahayak S (2009). Hydrographic and production characteristics along 45E longitude in the southwestern Indian Ocean and Southern Ocean during austral summer 2004. Mar Ecol Prog Ser, 389: 97–116CrossRefGoogle Scholar
- Pavithran S, Anilkumar N, Krishnan K P, Noronha S B, George J V, Nanajkar M, Chacko R, Dessai D R G, Achuthankutty C T (2012). Contrasting pattern in chlorophyll a distribution within the Polar Front of the Indian sector of Southern Ocean during austral summer 2010. Curr Sci, 102(6): 899–903Google Scholar
- Prakash S, Ramesh R, Sheshshayee M S, Mohan R, Sudhakar M (2015). Nitrogen uptake rates and f-ratios in the Equatorial and Southern Indian Ocean. Curr Sci, 108(2): 239–245Google Scholar
- Sanders R, Morris P J, Stinchcombe M, Seeyave S, Venables H, Lucas M (2007). New production and the f-ratio around the Crozet Plateau in austral summer 2004–2005 diagnosed from seasonal changes in inorganic nutrient levels. Deep Sea Res Part II Top Stud Oceanogr, 54 (18-20): 2191–2207CrossRefGoogle Scholar
- Savoye N, Dehairs F, Elskens M, Cardinal D, Kopczynska E E, Trull T W, Wright S, Baeyens W, Griffiths F B (2004) Regional variation of spring N-uptake and new production in the Southern Ocean. Geophysical Research Letters, doi: 10.1029/2003GL018946Google Scholar
- Strickland J D H, Parsons T R (1972). A practical hand book of seawater analysis. Journal of Fisheries Research Board of Canada, OttawaGoogle Scholar
- Thompson P A, Guo M, Harrison P J (1992). Effects of variation in temperature, I. On the biochemical composition of eight species of marine phytoplankton. J Phycol, 28(4): 481–488Google Scholar
- Tripathy S C, Pavithran S, Sabu P, Pillai H U K, Dessai D R G, Anilkumar N (2015). Deep chlorophyll maximum and primary productivity in the Indian Ocean sector of the Southern Ocean: case study in the Subtropical and Polar Front during austral summer 2011. Deep Sea Res Part II Top Stud Oceanogr, 118: 240–249CrossRefGoogle Scholar
- Tripathy S C, Pavithran S, Sabu S, Naik R K, Noronha S B, Bhaskar P V, Anilkumar N (2014). Is phytoplankton productivity in the Indian Ocean sector of Southern Ocean affected by pigment packaging effect? Curr Sci, 107(6): 1019–1026Google Scholar
- UNESCO (1994). Protocols for the Joint Global Ocean Flux Study (JGOFS) core measurements. Manual and Guides, 170. Scientific Committee on Oceanic Research, 29: 120Google Scholar