Size-fractionated Primary Production in the South Atlantic and Atlantic Sectors of the Southern Ocean

Froneman, P. William; Laubscher, R. K.; McQuaid, Christopher D.

doi:10.1093/plankt/23.6.611

Cited by 38 publications

(18 citation statements)

References 38 publications

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“…; Froneman et al. ), the PEIs support a diverse (~550 species) and biomass‐rich inter‐island benthic community (Branch et al. ; Pakhomov and Froneman ) due to the enhanced productivity associated with bloom formation at these islands (Perissinotto ; Branch et al.…”

Section: Introductionmentioning

confidence: 98%

Critical indirect effects of climate change on sub‐Antarctic ecosystem functioning

Allan

Froneman

Durgadoo

et al. 2013

Ecology and Evolution

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Sub-Antarctic islands represent critical breeding habitats for land-based top predators that dominate Southern Ocean food webs. Reproduction and molting incur high energetic demands that are sustained at the sub-Antarctic Prince Edward Islands (PEIs) by both inshore (phytoplankton blooms; “island mass effect”; autochthonous) and offshore (allochthonous) productivity. As the relative contributions of these sustenance pathways are, in turn, affected by oceanographic conditions around the PEIs, we address the consequences of climatically driven changes in the physical environment on this island ecosystem. We show that there has been a measurable long-term shift in the carbon isotope signatures of the benthos inhabiting the shallow shelf region of the PEIs, most likely reflecting a long-term decline in enhanced phytoplankton productivity at the islands in response to a climate-driven shift in the position of the sub-Antarctic Front. Our results indicate that regional climate change has affected the balance between allochthonous and autochthonous productivity at the PEIs. Over the last three decades, inshore-feeding top predators at the islands have shown a marked decrease in their population sizes. Conversely, population sizes of offshore-feeding predators that forage over great distances from the islands have remained stable or increased, with one exception. Population decline of predators that rely heavily on organisms inhabiting the inshore region strongly suggest changes in prey availability, which are likely driven by factors such as fisheries impacts on some prey populations and shifts in competitive interactions among predators. In addition to these local factors, our analysis indicates that changes in prey availability may also result indirectly through regional climate change effects on the islands' marine ecosystem. Most importantly, our results indicate that a fundamental shift in the balance between allochthonous and autochthonous trophic pathways within this island ecosystem may be detected throughout the food web, demonstrating that the most powerful effects of climate change on marine systems may be indirect.

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Section: Introductionmentioning

confidence: 98%

Critical indirect effects of climate change on sub‐Antarctic ecosystem functioning

Allan

Froneman

Durgadoo

et al. 2013

Ecology and Evolution

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“…Froneman et al (2001) reported an ADP between 60 and 266 mg C m Ϫ2 d Ϫ1 south of and within the Antarctic Polar Front (Atlantic sector) in January/February 1993. Parallel to the investigations of Jochem et al (1995), Detmer and Bathmann (1997) observed that pico-and nanophytoplankton contributed more than 70-80% to total Chl a when Chl a concentration was Ͻ0.6 mg m Ϫ3 .…”

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confidence: 99%

Changes in primary productivity and chlorophyll a in response to iron fertilization in the Southern Polar Frontal Zone

Gervais

Riebesell

Gorbunov

2002

Limnology & Oceanography

227

165

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EisenEx-the second in situ iron enrichment experiment in the Southern Ocean-was performed in the Atlantic sector over 3 weeks in November 2000 with the overarching goal to test the hypothesis that primary productivity in the Southern Ocean is limited by iron availability in the austral spring. Underwater irradiance, chlorophyll a (Chl a), photochemical efficiency, and primary productivity were measured inside and outside of an iron-enriched patch in order to quantify the response of phytoplankton to iron fertilization. Chl a concentration and photosynthetic rate ( 14 C uptake in simulated in situ incubations) were measured in pico-, nano-, and microphytoplankton. Photochemical efficiency was studied with fast repetition rate fluorometry and xenon-pulse amplitude modulated fluorometry. The high-nutrient low-chlorophyll waters outside the Fe-enriched patch were characterized by deep euphotic zones (63-72 m), low Chl a (48-56 mg m , respectively. As a consequence, the euphotic depth decreased to ϳ41 m. Picophytoplankton biomass hardly changed. Nano-and microphytoplankton biomass increased. In the first 2 weeks of the experiment, when the depth of the upper mixed layer was mostly Ͻ40 m, primary productivity was highly correlated with Chl a. In the third week, productivity was much lower than predicted from Chl a, probably because of a reduction in photosynthetic capacity as a consequence of increased physical variability in the upper water column. These results provide unequivocal evidence that iron supply is the central factor controlling phytoplankton primary productivity in the Southern Ocean, even if the mixing depth is Ͼ80 m.

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“…Apart from the dilution effects of oceanic water and runoffs due to the typhoon [ Delesalle et al , 1993], grazing pressure and reduced temperature might have also contributed to the reduced phytoplankton biomass [ Alpine and Cloern , 1992]. On the other hand, coastal waters usually have abundant microphytoplankton, and offshore waters are usually rich in picophytoplankton [ Chang et al , 1996; Froneman et al , 2001]. Mixing of the coastal and offshore water caused by the strong winds could lead to the increased proportion of pico‐cells (Figure 4a); whereas the consecutive cloudy days after the typhoon (Figure 3a) could have sustained their dominant status for almost one week, as smaller cells with a large surface per unit volume could photosynthesize more efficiently in terms of light use under low‐light conditions [ Raven , 1998; Raven and Kübler , 2002].…”

Section: Discussionmentioning

confidence: 99%

Effects of Typhoon Kaemi on coastal phytoplankton assemblages in the South China Sea, with special reference to the effects of solar UV radiation

Gao

2009

J. Geophys. Res.

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[1] In order to see how physical and chemical changes in coastal environment caused by tropical cyclones would affect primary productivity of phytoplankton, we investigated the photosynthetic carbon fixation, the chlorophyll a concentration, and the species composition of phytoplankton assemblages in the surface coastal waters of the South China Sea, during 18 July to 7 August 2006, before and after Typhoon Kaemi's landing (on 25 July, 122 km away from the experimental site). Chlorophyll a concentration started to decrease from 12.3 mg L À1 30 h before to 1.5 mg L À1 40 h after its landing, reducing the capacity of photosynthetic carbon fixation in the seawater to one eighth. Prior to the typhoon's arrival, microplankton (>20 mm) accounted for 50% of the total chl a, being mainly dominated by the diatom Thalassiosira sp.; during the period 30 h before and 6 days after the typhoon, however, pico-nanoplankton (<20 mm) comprised 98% of the total chl a. By 2 weeks after the typhoon, microcells (>20 mm) dominated the species again, and occupied 60% of the total chl a, with the diatom Nitzschia sp. being the dominant group. Since the typhoon induced changes in taxonomic structure and environmental factors, the apparent photosynthetic efficiency (a) of phytoplankton assemblages was markedly enhanced after the typhoon, while both the light-saturating point (E k ) and noontime photosynthetic rates were significantly reduced. Solar ultraviolet radiation (UVR, >55 W m À2) significantly inhibited the photosynthetic carbon fixation by 17% and 28% before and after the typhoon, respectively, reflecting a higher UVR sensitivity of the posttyphoon phytoplankton assemblages.

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Size-fractionated Primary Production in the South Atlantic and Atlantic Sectors of the Southern Ocean

Cited by 38 publications

References 38 publications

Critical indirect effects of climate change on sub‐Antarctic ecosystem functioning

Critical indirect effects of climate change on sub‐Antarctic ecosystem functioning

Changes in primary productivity and chlorophyll a in response to iron fertilization in the Southern Polar Frontal Zone

Effects of Typhoon Kaemi on coastal phytoplankton assemblages in the South China Sea, with special reference to the effects of solar UV radiation

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