Subtropical gyre variability observed by ocean-color satellites

McClain, Charles R.; Signorini, Sérgio R.; Christian, James R.

doi:10.1016/j.dsr2.2003.08.002

Cited by 207 publications

(253 citation statements)

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“…Raimbault and Garcia (2008) found the highest N 2 -fixation rates (1.8 nM N day À1 ) in the upper 50 m of the water column in the eastern and central SPG, but these rates declined rapidly below 50 m. In contrast, our measured nitrogenfixation rates were similar throughout the surface mixed layer in the center of the gyre during December 2006/January 2007 (Figure 3, Supplementary Figure S3). The SPG usually reaches its maximum expansion and thus the minimum chl a concentrations in September, although the magnitude of seasonal variation is not as large as that in other subtropical gyres (McClain et al, 2004;Morel et al, 2007). Hence, the fact that N 2 -fixation was found to be important even during our sampling in the austral summer, strongly implies that N 2 -fixation is a significant source of fixed nitrogen to this ultraoligotrophic system throughout the year.…”

Section: Resultsmentioning

confidence: 64%

“…The largest of all gyre systems is the South Pacific Gyre (SPG). Owing to its extreme remoteness from any continents, surface water of the SPG is the most oligotrophic in global oceans, with the lowest sea surface chlorophyll a (chl a) concentrations and the clearest natural water in the world (McClain et al, 2004;Morel et al, 2007). In contrast to the subtropical gyres of the northern hemisphere, investigations of N-cycling in the southern hemisphere are scarce.…”

Section: Introductionmentioning

confidence: 99%

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Heterotrophic organisms dominate nitrogen fixation in the South Pacific Gyre

et al. 2011

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Oceanic subtropical gyres are considered biological deserts because of the extremely low availability of nutrients and thus minimum productivities. The major source of nutrient nitrogen in these ecosystems is N 2 -fixation. The South Pacific Gyre (SPG) is the largest ocean gyre in the world, but measurements of N 2 -fixation therein, or identification of microorganisms involved, are scarce. In the 2006/2007 austral summer, we investigated nitrogen and carbon assimilation at 11 stations throughout the SPG. In the ultra-oligotrophic waters of the SPG, the chlorophyll maxima reached as deep as 200 m. Surface primary production seemed limited by nitrogen, as dissolved inorganic carbon uptake was stimulated upon additions of 15 N-labeled ammonium and leucine in our incubation experiments. N 2 -fixation was detectable throughout the upper 200 m at most stations, with rates ranging from 0.001 to 0.19 nM N h À1 . N 2 -fixation in the SPG may account for the production of 8-20% of global oceanic new nitrogen. Interestingly, comparable 15 N 2 -fixation rates were measured under light and dark conditions. Meanwhile, phylogenetic analyses for the functional gene biomarker nifH and its transcripts could not detect any common photoautotrophic diazotrophs, such as, Trichodesmium, but a prevalence of c-proteobacteria and the unicellular photoheterotrophic Group A cyanobacteria. The dominance of these likely heterotrophic diazotrophs was further verified by quantitative PCR. Hence, our combined results show that the ultra-oligotrophic SPG harbors a hitherto unknown heterotrophic diazotrophic community, clearly distinct from other oceanic gyres previously visited.

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Section: Resultsmentioning

confidence: 64%

Section: Introductionmentioning

confidence: 99%

Heterotrophic organisms dominate nitrogen fixation in the South Pacific Gyre

et al. 2011

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“…In the oceans, satellite-derived changes in the area of the subtropical gyres [e.g., Polovina et al, 2008], changes in chlorophyll a [e.g., McClain et al, 2004;Gregg et al, 2005], changes in primary productivity [e.g., Behrenfeld et al, 2006], and shifts in species ranges from in situ measurement [e.g., Beaugrand et al, 2002;Beaugrand and Reid, 2003] are suggested as signs of an altered marine environment.…”

Section: Final Commentsmentioning

confidence: 99%

Winners and losers: Ecological and biogeochemical changes in a warming ocean

Dutkiewicz

Scott

Follows

2013

Global Biogeochemical Cycles

145

173

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[1] We employ a marine ecosystem model, with diverse and flexible phytoplankton communities, coupled to an Earth system model of intermediate complexity to explore mechanisms that will alter the biogeography and productivity of phytoplankton populations in a warming world. Simple theoretical frameworks and sensitivity experiments reveal that ecological and biogeochemical changes are driven by a balance between two impacts of a warming climate: higher metabolic rates (the "direct" effect), and changes in the supply of limiting nutrients and altered light environments (the "indirect" effect). On globally integrated productivity, the two effects compensate to a large degree. Regionally, the competition between effects is more complicated; patterns of productivity changes are different between high and low latitudes and are also regulated by how the supply of the limiting nutrient changes. These complex regional patterns are also found in the changes to broad phytoplankton functional groups. On the finer ecological scale of diversity within functional groups, we find that ranges of some phytoplankton types are reduced, while those of others (potentially minor players in the present ocean) expand. Combined change in areal extent of range and in regionally available nutrients leads to global "winners and losers." The model suggests that the strongest and most robust signal of the warming ocean is likely to be the large turnover in local phytoplankton community composition.

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“…This has been remediated to some extent by the availability of decade long, high-quality remotely sensed monitoring of chlorophyll a concentration (hereafter, chl a) (McClain et al, 2004a;McClain, 2009). Analyses incorporating satellite data have revealed a tight link between climate variability and recent decreases in phytoplankton biomass and primary productivity at the global scale (Gregg & Conkright, 2002;Antoine et al, 2005;Gregg et al, 2005;Behrenfeld et al, 2006;Martinez et al, 2009;Vantrepotte & M elin, 2009), the expansion of low chl a concentration areas in the subtropics (McClain et al, 2004b;Polovina et al, 2008;Irwin & Oliver, 2009) and a decline in mean phytoplankton cell size (Polovina & Woodworth, 2012). Studies on marine phenology have focused on the main peak of phytoplankton growth in temperate and polar regions, i.e.…”

Section: Introductionmentioning

confidence: 99%

Seasonality of North Atlantic phytoplankton from space: impact of environmental forcing on a changing phenology (1998–2012)

Taboada

Anadón

2014

Global Change Biology

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Seasonal pulses of phytoplankton drive seasonal cycles of carbon fixation and particle sedimentation, and might condition recruitment success in many exploited species. Taking advantage of long-term series of remotely sensed chlorophyll a (1998-2012), we analysed changes in phytoplankton seasonality in the North Atlantic Ocean. Phytoplankton phenology was analysed based on a probabilistic characterization of bloom incidence. This approach allowed us to detect changes in the prevalence of different seasonal cycles and, at the same time, to estimate bloom timing and magnitude taking into account uncertainty in bloom detection. Deviations between different sensors stressed the importance of a prolonged overlap between successive missions to ensure a correct assessment of phenological changes, as well as the advantage of semi-analytical chlorophyll algorithms over empirical ones to reduce biases. Earlier and more intense blooms were detected in the subpolar Atlantic, while advanced blooms of less magnitude were common in the Subtropical gyre. In the temperate North Atlantic, spring blooms advanced their timing and decreased in magnitude, whereas fall blooms delayed and increased their intensity. At the same time, the prevalence of locations with a single autumn/winter bloom or with a bimodal seasonal cycle increased, in consonance with a poleward expansion of subtropical conditions. Changes in bloom timing and magnitude presented a clear signature of environmental factors, especially wind forcing, although changes on incident photosynthetically active radiation and sea surface temperature were also important depending on latitude. Trends in bloom magnitude matched changes in mean chlorophyll a during the study period, suggesting that seasonal peaks drive long-term trends in chlorophyll a concentration. Our results link changes in North Atlantic climate with recent trends in the phenology of phytoplankton, suggesting an intensification of these impacts in the near future.

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Subtropical gyre variability observed by ocean-color satellites

Cited by 207 publications

References 50 publications

Heterotrophic organisms dominate nitrogen fixation in the South Pacific Gyre

Heterotrophic organisms dominate nitrogen fixation in the South Pacific Gyre

Winners and losers: Ecological and biogeochemical changes in a warming ocean

Seasonality of North Atlantic phytoplankton from space: impact of environmental forcing on a changing phenology (1998–2012)

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