Regional and seasonal differences in microplankton biomass, productivity, and structure across the Scotia Sea: Implications for the export of biogenic carbon

Korb, Rebecca E.; Whitehouse, Martin J.; Ward, Peter; Gordon, Marina; Venables, Hugh J.; Poulton, Alex J.

doi:10.1016/j.dsr2.2011.06.006

Cited by 59 publications

(50 citation statements)

References 52 publications

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“…continental shelf waves, cross-shelf or vertical mixing; Young et al, 2011). Over the island's shelf region the model produces an average mixed layer depth of about 20 m. This value is very close to the mixed layer depth estimated in austral summer by Ward et al, 2005 over the northwestern shelf of the island; however, it is below values estimated by Korb et al, 2012 andsimulated by Young et al, 2011 who used a model with a 3 km resolution validated with a very extensive data set of in situ temperature and salinity measurements.…”

Section: Atmospheric and Sedimentary Sources Of Ironmentioning

confidence: 69%

Sedimentary and atmospheric sources of iron around South Georgia, Southern Ocean: a modelling perspective

et al. 2014

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Abstract. In high-nutrient low-chlorophyll waters of the western Atlantic sector of the Southern Ocean, an intense phytoplankton bloom is observed annually north of South Georgia. Multiple sources, including shallow sediments and atmospheric dust deposition, are thought to introduce iron to the region. However, the relative importance of each source is still unclear, owing in part to the scarcity of dissolved iron (dFe) measurements in the South Georgia region. In this study, we combine results from a recently published dFe data set around South Georgia with a coupled regional hydrodynamic and biogeochemical model to further investigate iron supply around the island. The biogeochemical component of the model includes an iron cycle, where sediments and dust deposition are the sources of iron to the ocean. The model captures the characteristic flow patterns around South Georgia, hence simulating a large phytoplankton bloom to the north (i.e. downstream) of the island. Modelled dFe concentrations agree well with observations (mean difference and root mean square errors of ∼ 0.02 nM and ∼ 0.81 nM) and form a large plume to the north of the island that extends eastwards for more than 800 km. In agreement with observations, highest dFe concentrations are located along the coast and decrease with distance from the island. Sensitivity tests indicate that most of the iron measured in the main bloom area originates from the coast and very shallow shelf-sediments (depths < 20 m). Dust deposition exerts almost no effect on surface chlorophyll a concentrations. Other sources of iron such as run-off and glacial melt are not represented explicitly in the model, however we discuss their role in the local iron budget.

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Section: Atmospheric and Sedimentary Sources Of Ironmentioning

confidence: 69%

Sedimentary and atmospheric sources of iron around South Georgia, Southern Ocean: a modelling perspective

et al. 2014

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“…However, especially in surface waters with high productivity, large temporal (daily and seasonal) variations in DO 14 C can occur, as observed for the eastern North Pacific Beaupré and Druffel, 2009). The increase of surface DOC concentrations and decrease of the average age of the 200 m samples across the PF towards the north might be related to seasonally enhanced primary production (Geibert et al, 2010;Park et al, 2010;Korb et al, 2012) with subsequent bacterial decomposition (Rosenstock et al, 2005;Dumont et al, 2011;Pearce et al, 2011) of the fresh organic matter. In the Southern Ocean, phytoplankton production is accompanied by enhanced POC export (Carlson et al, 1998(Carlson et al, , 2000 compared to other ocean regimes.…”

Section: Ft-icr Ms Age Model Validationmentioning

confidence: 99%

Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean

Lechtenfeld

Kattner

Flerus

et al. 2014

Geochimica et Cosmochimica Acta

276

259

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More than 90% of the global ocean dissolved organic carbon (DOC) is refractory, has an average age of 4000-6000 years and a lifespan from months to millennia. The fraction of dissolved organic matter (DOM) that is resistant to degradation is a long-term buffer in the global carbon cycle but its chemical composition, structure, and biochemical formation and degradation mechanisms are still unresolved. We have compiled the most comprehensive molecular dataset of 197 Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses from solid-phase extracted marine DOM covering two major oceans, the Atlantic sector of the Southern Ocean and the East Atlantic Ocean (ranging from 50°N to 70°S). Molecular trends and radiocarbon dating of 34 DOM samples (comprising D 14 C values from À229& to À495&) were combined to model an integrated degradation rate for bulk DOC resulting in a predicted age of >24 ka for the most persistent DOM fraction. First order kinetic degradation rates for 1557 mass peaks indicate that numerous DOM molecules cycle on timescales much longer than the turnover of the bulk DOC pool (estimated residence times of up to~100 ka) and the range of validity of radiocarbon dating. Changes in elemental composition were determined by assigning molecular formulae to the detected mass peaks. The combination of residence times with molecular information enabled modelling of the average elemental composition of the slowest degrading fraction of the DOM pool. In our dataset, a group of 361 molecular formulae represented the most stable composition in the oceanic environment ("island of stability"). These most persistent compounds encompass only a narrow range of the molecular elemental ratios H/C (average of 1.17 ± 0.13), and O/C (average of 0.52 ± 0.10) and molecular masses (360 ± 28 and 497 ± 51 Da). In the Weddell Sea DOC concentrations in the surface waters were low (46.3 ± 3.3 lM) while the organic radiocarbon was significantly more depleted than that of the East Atlantic, representing average surface water DOM ages of 4920 ± 180 a. These results are in accordance with a highly degraded DOM in the Weddell Sea surface water as also shown by the molecular degradation index I DEG obtained from FT-ICR MS data. Further, we identified 339 molecular formulae which probably contribute to an increased DOC concentration in the Southern Ocean and potentially reflect an accumulation or enhanced sequestration of refractory DOC in the Weddell Sea. These results will contribute to a better understanding of the persistent nature of marine DOM and its role as an oceanic carbon buffer in a changing climate.

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“…Productivity over much of the Southern Ocean is limited by the lack of iron, an essential micronutrient for photosynthesis, resulting in there being an excess of macronutrients but low levels of chlorophyll (Martin et al, 1994). However, hotspots of productivity arise where iron becomes available; the region downstream of South Georgia is a notable case of this, with an extensive bloom supported until late summer by macronutrients and iron resupplied from the shelf edge, shelf-sediment interactions and vertical mixing of deep waters (Korb et al, 2008). Mesozooplankton biomass in this region can exceed the Southern Ocean average by a factor of 6 (Ward et al, 1995;Atkinson et al, 1996;Pakhomov et al, 1997), and there are large concentrations of Antarctic krill as well as high densities of marine-and land-based predators (Atkinson et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

“…Small pellets generated by microzooplankton and small copepods have slow sinking rates and are likely to be remineralized by degradation and recycling processes during sinking (Dagg et al, 2003). By contrast, large zooplanktons produce larger FPs that sink more rapidly and are less likely to be remineralized (Lampitt et al, 1990;Wassmann, 1998). They therefore provide a major conduit for the transfer of organic matter to the deep ocean (Komar et al, 1981;Bruland and Silver, 1981).…”

Section: Introductionmentioning

confidence: 99%

The contribution of zooplankton faecal pellets to deep-carbon transport in the Scotia Sea (Southern Ocean)

et al. 2015

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Abstract. The northern Scotia Sea contains the largest seasonal uptake of atmospheric carbon dioxide yet measured in the Southern Ocean. This study examines one of the main routes by which this carbon fluxes to the deep ocean: through the production of faecal pellets (FPs) by the zooplankton community. Deep sediment traps were deployed at two sites with contrasting ocean productivity regimes (P3, naturally iron-fertilized, and P2, iron-limited) within the same water mass. The magnitude and seasonal pattern of particulate organic carbon (POC) and FPs in the traps was markedly different between the two sites. Maximum fluxes at P3 (22.91 mg C m −2 d −1 ; 2534 FP m −2 d −1 ) were 1 order of magnitude higher than at P2 (4.01 mg C m −2 d −1 ; 915 FP m −2 d −1 ), with flux at P3 exhibiting a double seasonal peak, compared to a single flatter peak at P2. The maximum contribution of FP carbon to the total amount of POC was twice as high at P3 (91 %) compared to P2 (40 %). The dominant FP category at P3 varied between round, ovoidal, cylindrical and tabular over the course of the year, while, at P2, ovoidal FPs were consistently dominant, always making up more than 60 % of the FP assemblage. There was also a difference in the FP state between the two sites, with FPs being relatively intact at P3, while FPs were often fragmented with broken peritrophic membranes at P2. The exception was ovoidal FPs, which were relatively intact at both sites. Our observations suggest that there was a community shift from a herbivorous to an omnivorous diet from spring through to autumn at P3, while detritivores had a higher relative importance over the year at P2. Furthermore, the flux was mainly a product of the vertically migrating zooplankton community at P3, while the FP flux was more likely to be generated by deeper-dwelling zooplankton feeding on recycled material at P2. The results demonstrate that the feeding behaviour and vertical distribution of the zooplankton community plays a critical role in controlling the magnitude of carbon export to the deep ocean in this region.

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Regional and seasonal differences in microplankton biomass, productivity, and structure across the Scotia Sea: Implications for the export of biogenic carbon

Cited by 59 publications

References 52 publications

Sedimentary and atmospheric sources of iron around South Georgia, Southern Ocean: a modelling perspective

Sedimentary and atmospheric sources of iron around South Georgia, Southern Ocean: a modelling perspective

Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean

The contribution of zooplankton faecal pellets to deep-carbon transport in the Scotia Sea (Southern Ocean)

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