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17. Distribution of zooplankton in the Indian sector of the Southern Ocean

Author

V. Venkataramana, S. C. Tripathy, Amit Sarkar, R. K. Mishra, Honey U. K. Pillai, Soares Melena Augusta, N. Anilkumar, Kerrie M. Swadling, and P. Sabu

Subjects
0106 biological sciences, Polar front, 010504 meteorology & atmospheric sciences, biology, 010604 marine biology & hydrobiology, Front (oceanography), Geology, Plankton, Oceanography, biology.organism_classification, 01 natural sciences, Zooplankton, Abundance (ecology), Indicator species, Environmental science, Calocalanus, Subtropical front, Ecology, Evolution, Behavior and Systematics, 0105 earth and related environmental sciences
Abstract

The community composition of zooplankton with an emphasis on copepods was assessed in the frontal zones of the Indian sector of the Southern Ocean (SO) during summer 2013. Copepods were the dominant group in both the bongo net and multiple plankton sampler across the entire region. High zooplankton abundance was recorded along each transect in the Polar Front (PF). Community structure in this front was dominated by common taxa, including Ctenocalanus citer, Clausocalanus spp., Calanoides acutus, Calanus propinquus, Calanus australis and Rhincalanus gigas, which together accounted for > 62% of the total abundance. Calocalanus spp., Neocalanus tonsus and C. propinquus were indicator species in the Sub-Tropical Front (STF), Sub-Antarctic Front and PF, respectively. A strong contrast in population structure and biovolume was observed between then PF and the STF. The community structure of smaller copepods was associated with the high-temperature region, whereas communities of larger copepods were associated with the low-temperature region. Thus, it seems probable that physical and biological characteristics of the SO frontal regions are controlling the abundance and distribution of zooplankton community structure by restricting some species to the warmer stratified zones and some species to the well-mixed zone.

Published
2020
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21. Potential Role of Major Phytoplankton Communities on pCO2Modulation in the Indian Sector of Southern Ocean

Author

Sarkar, Amit, Mishra, Rajanikant, Bhaskar, Parli V., Anilkumar, N., Sabu, Prabhakaran, and Soares, Melena

Abstract

Spatial variations in the phytoplankton community compositions, carbon dioxide system and ancillary water column properties, were monitored across various frontal systems in the Indian Sector of Southern Ocean (ISSO) during austral summer 2013. Four major frontal systems, namely, the Agulhas Return Front (ARF), Southern Subtropical Front (SSTF), Subantarctic Front (SAF) and Polar Front (PF) were identified along the study area. Major groups of phytoplankton were distinguished adopting single marker pigment approach. Statistical computations showed the distribution of diatoms were influenced by the availability of inorganic nutrients (primarily silicate and nitrate) and mixed layer depths (MLD). Haptophytes were strongly dependent on phosphate availability, whereas, picoplankton flourished in water where regenerated nutrient ammonium was present. The lowest surface pCO2(267.26–291.5 µatm) along with in situ oxygen production (> 10 µM) was encountered at the two warmer fronts, ARF and SSTF, dominated by haptophytes and picoplankton. The colder Antarctic fronts, SAF and PF were dominated by diatoms where surface pCO2was relatively higher (> 350µatm). Poor statistical correlation among temperature and total chlorophyll with pCO2revealed complex interplay of multiple factors. Contribution of major phytoplankton groups towards pCO2drawdown was computed using a one-dimensional model describing the relative contributions of biological activities. In ISSO, calcifying and photosynthesizing haptophytes were observed to play a crucial role in the “biological pump” of CO2drawdown at ARF, SSTF and SAF, while the silicifying micro phytoplankton diatoms and picoplankton were more effective at PF.

Published
2021
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23. Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX

Author

Martin, Patrick, van der Loeff, Michiel Rutgers, Cassar, Nicolas, Vandromme, Pieter, d'Ovidio, Francesco, Stemmann, Lars, Rengarajan, R., Soares, Melena, González, Humberto E., Ebersbach, Friederike, Lampitt, Richard S., Sanders, Richard, Barnett, Bruce A., Smetacek, Victor, Naqvi, S. Wajih A., Martin, Patrick, van der Loeff, Michiel Rutgers, Cassar, Nicolas, Vandromme, Pieter, d'Ovidio, Francesco, Stemmann, Lars, Rengarajan, R., Soares, Melena, González, Humberto E., Ebersbach, Friederike, Lampitt, Richard S., Sanders, Richard, Barnett, Bruce A., Smetacek, Victor, and Naqvi, S. Wajih A.

Abstract

A closed eddy core in the Subantarctic Atlantic Ocean was fertilized twice with two tons of iron (as FeSO 4), and the 300 km2 fertilized patch was studied for 39 days to test whether fertilization enhances downward particle flux into the deep ocean. Chlorophyll a and primary productivity doubled after fertilization, and photosynthetic quantum yield (FV/FM) increased from 0.33 to ≥ 0.40. Silicic acid (<2 μmol L1) limited diatoms, which contributed <10% of phytoplankton biomass. Copepods exerted high grazing pressure. This is the first study of particle flux out of an artificially fertilized bloom with very low diatom biomass. Net community production (NCP) inside the patch, estimated from O2:Ar ratios, averaged 21 mmol POC m2 d1, probably±20%. 234Th profiles implied constant export of ~6.3 mmol POC m2 d1 in the patch, similar to unfertilized waters. The difference between NCP and 234Th-derived export partly accumulated in the mixed layer and was partly remineralized between the mixed layer and 100 m. Neutrally buoyant sediment traps at 200 and 450 m inside and outside the patch caught mostly <1.1 mmol POC m2 d1, predominantly of fecal origin; flux did not increase upon fertilization. Our data thus indicate intense flux attenuation between 100 and 200 m, and probably between the mixed layer and 100 m. We attribute the lack of fertilization-induced export to silicon limitation of diatoms and reprocessing of sinking particles by detritus feeders. Our data are consistent with the view that nitrate-rich but silicate-deficient waters are not poised for enhanced particle export upon iron addition.

Published
2013

24. Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX

Author

Martin, Patrick, primary, van der Loeff, Michiel Rutgers, additional, Cassar, Nicolas, additional, Vandromme, Pieter, additional, d'Ovidio, Francesco, additional, Stemmann, Lars, additional, Rengarajan, R., additional, Soares, Melena, additional, González, Humberto E., additional, Ebersbach, Friederike, additional, Lampitt, Richard S., additional, Sanders, Richard, additional, Barnett, Bruce A., additional, Smetacek, Victor, additional, and Naqvi, S. Wajih A., additional

Published
2013
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