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

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

doi:10.1002/gbc.20077

Cited by 102 publications

(104 citation statements)

References 87 publications

(114 reference statements)

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“…In contrast, our estimates are higher than the F Th of r1000 dpm m À 2 d À 1 reported during the onset of a bloom by Planchon et al (2015), and during the artificial iron fertilisation experiments SOIREE (Charette and Buesseler, 2000), EisenEx (Rutgers van der Loeff and Vöge, 2001) and LOHAFEX (Martin et al, 2013). However, the SOFeX-South experiment revealed an increase of particle fluxes after fertilisation, which resulted in F Th of $ 1800 dpm m À 2 d À 1 at the MLD .…”

Section: Results and Comparison With Other Studiescontrasting

confidence: 74%

“…In contrast, the F C are higher than those reported in KEOPS II (average: 7 72 mmol C m À 2 d À 1 , Planchon et al, 2015) for a bloom during its growing stage. On the other hand, the F C determined during SOIREE (Charette and Buesseler, 2000), SOFeX-South and LOHA-FEX (Martin et al, 2013) were clearly lower (average r8 mmol C m À 2 d À 1 ) than in this study. In the case of LOHAFEX, it was explained by silica limitation that prevented diatom growth.…”

Section: Poc/ 234contrasting

confidence: 87%

“…The C/N ratios averaged 8 71 and 7 71 for ST and ISP samples, respectively, and were within the range of values previously reported during bloom events (Martin et al, 2013;Morris et al, 2007;Savoye et al, 2008), with a diverse composition of the dominant particle type (diatoms: Salter et al, 2007;faecal material: Ebersbach and Trull, 2008;Ebersbach et al, 2014). , 1997), and the CROZEX project (average: 14 74 mmol C m À 2 d À 1 , Morris et al, 2007).…”

Section: Poc/ 234supporting

confidence: 85%

“…This was attributed to changes in the nature of the sinking particles (less labile or more rapidly sinking) and/or less efficient biological and physical processes responsible for particle break-up and consumption below the bloom. Th and PON/ 234 Th ratios in particles C/Th and N/Th ratios were 410 μmol C dpm À 1 (average: 15 75 μmol C dpm À 1 ) and 41 μmol N dpm À 1 (average: 2 71 μmol N dpm À 1 ), respectively, in all samples collected either with ST or ISP ( 453 μm) at 100 m. Overall, these values were higher than those reported by most studies conducted in the Southern Ocean (Buesseler et al, , 2001aCoppola et al, 2005;Jacquet et al, 2011;Martin et al, 2013;Morris et al, 2007;Planchon et al, 2013;Rutgers van der Loeff et al, 2011Savoye et al, 2008), but similar to others (Cochran et al, 2000;Puigcorbé et al, 2017;Rutgers van der Loeff et al, 2002;Smetacek et al, 2012). Multiple factors may have played a role in shaping the C/Th and N/Th ratios, such as particle source, sinking velocity, Th speciation and remineralisation of C, N and 234 Th associated with sinking particles .…”

Section: Results and Comparison With Other Studiesmentioning

confidence: 61%

“…Diatoms are key exporters of carbon from the ocean surface to deep waters and sediments, and hence play an essential role in reducing the CO 2 content in the atmosphere (Smetacek, 1999). Previous studies have shown that very low macronutrient concentrations, specifically of silicic acid, prevent the development of diatom blooms in benefit of flagellates, resulting in low particulate organic carbon (POC) export fluxes from the ocean surface (Jacquet et al, 2011;Martin et al, 2013). Further, diatoms in the Southern Ocean contribute differently to POC export according to their life cycle strategy in which the degree of silicification is relevant (Assmy et al, 2013;Quéguiner, 2013).…”

Section: Introductionmentioning

confidence: 99%

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High particulate organic carbon export during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean

Roca‐Martí

Puigcorbé

Iversen

et al. 2017

Deep Sea Research Part II: Topical Studies in Oceanography

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a b s t r a c tCarbon fixation by phytoplankton plays a key role in the uptake of atmospheric CO 2 in the Southern Ocean. Yet, it still remains unclear how efficiently the particulate organic carbon (POC) is exported and transferred from ocean surface waters to depth during phytoplankton blooms. In addition, little is known about the processes that control the flux attenuation within the upper twilight zone. Here, we present results of downward POC and particulate organic nitrogen fluxes during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean in summer 2012. We used thorium-234 ( 234 Th) as a particle tracer in combination with drifting sediment traps (ST). Their simultaneous use evidenced a sustained high export rate of 234 Th at 100 m depth in the weeks prior to and during the sampling period. The entire study area, of approximately 8000 km 2 , showed similar vertical export fluxes in spite of the heterogeneity in phytoplankton standing stocks and productivity, indicating a decoupling between production and export. The POC fluxes at 100 m were high, averaging 26 715 mmol C m À 2 d À 1 , although the strength of the biological pump was generally low. Only o 20% of the daily primary production reached 100 m, presumably due to an active recycling of carbon and nutrients. Pigment analyses indicated that direct sinking of diatoms likely caused the high POC transfer efficiencies ( $ 60%) observed between 100 and 300 m, although faecal pellets and transport of POC linked to zooplankton vertical migration might have also contributed to downward fluxes.

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Section: Results and Comparison With Other Studiescontrasting

confidence: 74%

Section: Poc/ 234contrasting

confidence: 87%

Section: Poc/ 234supporting

confidence: 85%

Section: Results and Comparison With Other Studiesmentioning

confidence: 61%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

High particulate organic carbon export during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean

Roca‐Martí

Puigcorbé

Iversen

et al. 2017

Deep Sea Research Part II: Topical Studies in Oceanography

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Late summer net community production in the central Arctic Ocean using multiple approaches

Ulfsbo

Cassar

Korhonen

et al. 2014

Global Biogeochemical Cycles

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Large-scale patterns of net community production (NCP) were estimated during the late summer cruise ARK-XXVI/3 (TransArc, August/September 2011) to the central Arctic Ocean. Several approaches were used based on the following: (i) continuous measurements of surface water oxygen to argon ratios (O 2 /Ar), (ii) underway measurements of surface partial pressure of carbon dioxide (pCO 2 ), (iii) discrete samples of dissolved inorganic carbon, and (iv) dissolved inorganic nitrogen and phosphate. The NCP estimates agreed well within the uncertainties associated with each approach. The highest late summer NCP (up to 6 mol C m À2 ) was observed in the marginal sea ice zone region. Low values (<1 mol C m À2 ) were found in the sea ice-covered deep basins with a strong spatial variability. Lowest values were found in the Amundsen Basin and moderate values in the Nansen and Makarov Basins with slightly higher estimates over the Mendeleev Ridge. Our findings support a coupling of NCP to sea ice coverage and nutrient supply and thus stress a potential change in spatial and temporal distribution of NCP in a future Arctic Ocean.To follow the evolution of NCP in space and time, it is suggested to apply one or several of these approaches in shipboard investigations with a time interval of 3 to 5 years.

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Decoupling of net community and export production on submesoscales in the Sargasso Sea

Estapa

Siegel

Buesseler

et al. 2015

Global Biogeochemical Cycles

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Determinations of the net community production (NCP) in the upper ocean and the particle export production (EP) should balance over long time and large spatial scales. However, recent modeling studies suggest that a horizontal decoupling of flux-regulating processes on submesoscales (≤10 km) could lead to imbalances between individual determinations of NCP and EP. Here we sampled mixed-layer biogeochemical parameters and proxies for NCP and EP during 10, high-spatial resolution (~2 km) surface transects across strong physical gradients in the Sargasso Sea. We observed strong biogeochemical and carbon flux variability in nearly all transects. Spatial coherence among measured biogeochemical parameters within transects was common but rarely did the same parameters covary consistently across transects. Spatial variability was greater in parameters associated with higher trophic levels, such as chlorophyll in >5.0 μm particles, and variability in EP exceeded that of NCP in nearly all cases. Within sampling transects, coincident EP and NCP determinations were uncorrelated. However, when averaged over each transect (30 to 40 km in length), we found NCP and EP to be significantly and positively correlated (R = 0.72, p = 0.04). Transect-averaged EP determinations were slightly smaller than similar NCP values (Type-II regression slope of 0.93, standard deviation = 0.32) but not significantly different from a 1:1 relationship. The results show the importance of appropriate sampling scales when deriving carbon flux budgets from upper ocean observations.

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

Cited by 102 publications

References 87 publications

High particulate organic carbon export during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean

High particulate organic carbon export during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean

Late summer net community production in the central Arctic Ocean using multiple approaches

Decoupling of net community and export production on submesoscales in the Sargasso Sea

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