scholarly journals Iron budgets for three distinct biogeochemical sites around the Kerguelen archipelago (Southern Ocean) during the natural fertilisation experiment KEOPS-2

2014 ◽  
Vol 11 (12) ◽  
pp. 17861-17923 ◽  
Author(s):  
A. R. Bowie ◽  
P. van der Merwe ◽  
F. Quéroué ◽  
T. Trull ◽  
M. Fourquez ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Standing Stock ◽  
Minor Component ◽  
Carbon Export ◽  
Iron Dissolution ◽  
Transport Pathways ◽  
Dissolved Iron ◽  
Iron Supply ◽  
Particulate Iron ◽  
Internal Cycling

Abstract. Iron availability in the Southern Ocean controls phytoplankton growth, community composition and the uptake of atmospheric CO2 by the biological pump. The KEOPS-2 experiment took place around the Kerguelen plateau in the Indian sector of the Southern Ocean, a region naturally fertilised with iron at the scale of hundreds to thousands of square kilometres, producing a mosaic of spring blooms which showed distinct biological and biogeochemical responses to fertilisation. This paper presents biogeochemical iron budgets (incorporating vertical and lateral supply, internal cycling, and sinks) for three contrasting sites: an upstream high-nutrient low-chlorophyll reference, over the plateau, and in the offshore plume east of Kerguelen Island. These budgets show that distinct regional environments driven by complex circulation and transport pathways are responsible for differences in the mode and strength of iron supply, with vertical supply dominant on the plateau and lateral supply dominant in the plume. Iron supply from "new" sources to surface waters of the plume was double that above the plateau and 20 times greater than at the reference site, whilst iron demand (measured by cellular uptake) in the plume was similar to the plateau but 40 times greater than the reference. "Recycled" iron supply by bacterial regeneration and zooplankton grazing was a relative minor component at all sites (<8% of "new" supply), in contrast to earlier findings from other biogeochemical iron budgets in the Southern Ocean. Over the plateau, a particulate iron dissolution term of 2.5% was invoked to balance the budget; this approximately doubled the standing stock of dissolved iron in the mixed layer. The exchange of iron between dissolved, biogenic and lithogenic particulate pools was highly dynamic in time and space, resulting in a decoupling of iron supply and carbon export and, importantly, controlling the efficiency of fertilisation.

scholarly journals Iron budgets for three distinct biogeochemical sites around the Kerguelen Archipelago (Southern Ocean) during the natural fertilisation study, KEOPS-2

2015 ◽  
Vol 12 (14) ◽  
pp. 4421-4445 ◽  
Author(s):  
A. R. Bowie ◽  
P. van der Merwe ◽  
F. Quéroué ◽  
T. Trull ◽  
M. Fourquez ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Reference Site ◽  
Standing Stock ◽  
Minor Component ◽  
Carbon Export ◽  
Transport Pathways ◽  
Dissolved Iron ◽  
Iron Supply ◽  
Particulate Iron ◽  
Lateral Advection

Abstract. Iron availability in the Southern Ocean controls phytoplankton growth, community composition and the uptake of atmospheric CO2 by the biological pump. The KEOPS-2 (KErguelen Ocean and Plateau compared Study 2) "process study", took place around the Kerguelen Plateau in the Indian sector of the Southern Ocean. This is a region naturally fertilised with iron on the scale of hundreds to thousands of square kilometres, producing a mosaic of spring blooms which show distinct biological and biogeochemical responses to fertilisation. This paper presents biogeochemical iron budgets (incorporating vertical and lateral supply, internal cycling, and sinks) for three contrasting sites: an upstream high-nutrient low-chlorophyll reference, over the plateau and in the offshore plume east of the Kerguelen Islands. These budgets show that distinct regional environments driven by complex circulation and transport pathways are responsible for differences in the mode and strength of iron supply, with vertical supply dominant on the plateau and lateral supply dominant in the plume. Iron supply from "new" sources (diffusion, upwelling, entrainment, lateral advection, atmospheric dust) to the surface waters of the plume was double that above the plateau and 20 times greater than at the reference site, whilst iron demand (measured by cellular uptake) in the plume was similar to that above the plateau but 40 times greater than at the reference site. "Recycled" iron supply by bacterial regeneration and zooplankton grazing was a relatively minor component at all sites (< 8 % of new supply), in contrast to earlier findings from other biogeochemical iron budgets in the Southern Ocean. Over the plateau, a particulate iron dissolution term of 2.5 % was invoked to balance the budget; this approximately doubled the standing stock of dissolved iron in the mixed layer. The exchange of iron between dissolved, biogenic particulate and lithogenic particulate pools was highly dynamic in time and space, resulting in a decoupling of the iron supply and carbon export and, importantly, controlling the efficiency of fertilisation.

scholarly journals A circumpolar dust conveyor in the glacial Southern Ocean

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Torben Struve ◽  
Katharina Pahnke ◽  
Frank Lamy ◽  
Marc Wengler ◽  
Philipp Böning ◽  
...  
Keyword(s):  
South America ◽  
Southern Ocean ◽  
Net Primary Production ◽  
South Pacific ◽  
Dust Deposition ◽  
Carbon Export ◽  
Transport Pathways ◽  
Dust Transport ◽  
Glacial Periods ◽  
Central South

Abstract The increased flux of soluble iron (Fe) to the Fe-deficient Southern Ocean by atmospheric dust is considered to have stimulated the net primary production and carbon export, thus promoting atmospheric CO2 drawdown during glacial periods. Yet, little is known about the sources and transport pathways of Southern Hemisphere dust during the Last Glacial Maximum (LGM). Here we show that Central South America (~24‒32°S) contributed up to ~80% of the dust deposition in the South Pacific Subantarctic Zone via efficient circum-Antarctic dust transport during the LGM, whereas the Antarctic Zone was dominated by dust from Australia. This pattern is in contrast to the modern/Holocene pattern, when South Pacific dust fluxes are thought to be primarily supported by Australian sources. Our findings reveal that in the glacial Southern Ocean, Fe fertilization critically relies on the dynamic interaction of changes in dust-Fe sources in Central South America with the circumpolar westerly wind system.

scholarly journals An iron budget during the natural iron fertilisation experiment KEOPS (Kerguelen Islands, Southern Ocean)

2009 ◽  
Vol 6 (4) ◽  
pp. 6803-6837 ◽  
Author(s):  
F. Chever ◽  
G. Sarthou ◽  
E. Bucciarelli ◽  
S. Blain ◽  
A. R. Bowie
Keyword(s):  
Southern Ocean ◽  
Dissolved Iron ◽  
Heard Island ◽  
Natural Iron ◽  
Particulate Iron ◽  
The Difference ◽  
The One ◽  
Iron Pool ◽  
Lateral Advection ◽  
Very High

Abstract. Total dissolvable iron (TDFe) was measured in the water column above and in the surrounding of the Kerguelen Plateau (Indian sector of the Southern Ocean) during the KErguelen Ocean Plateau compared Study (KEOPS) cruise. TDFe concentrations ranged from 0.90 to 65.6 nmol L−1 above the plateau and from 0.34 to 2.23 nmol L−1 offshore of the plateau. Station C1 located south of the plateau, near Heard Island, exhibited very high values (329–770 nmol L−1). Apparent particulate iron (Feapp), calculated as the difference between the TDFe and the dissolved iron measured on board (DFe) represented 95±5% of the TDFe above the plateau, suggesting that particles and refractory colloids largely dominated the iron pool. This paper presents a budget of DFe and Feapp above the plateau. Lateral advection of water that had been in contact with the continental shelf of Heard Island seems to be the predominant source of Feapp and DFe above the plateau, with a supply of 9.7±2.3×106 and 8.3±6.7×103 mol d−1, respectively. The residence times of 1.7 and 48 days estimated for Feapp and DFe, respectively, indicate a rapid turnover in the surface water. A comparison between Feapp and total particulate iron (TPFe) suggests that the total dissolved fraction is mainly constituted of small refractory colloids. This fraction does not seem to be a potential source of iron to the phytoplankton in our study. Finally, when taking into account the lateral supply of dissolved iron, the seasonal carbon sequestration efficiency was estimated at 154 000 mol C (mol Fe)−1, which is 4-fold lower than the previously estimated value in this area but still 18-fold higher than the one estimated during the other study of a natural iron fertilisation experiment, CROZEX.

scholarly journals An iron budget during the natural iron fertilisation experiment KEOPS (Kerguelen Islands, Southern Ocean)

2010 ◽  
Vol 7 (2) ◽  
pp. 455-468 ◽  
Author(s):  
F. Chever ◽  
G. Sarthou ◽  
E. Bucciarelli ◽  
S. Blain ◽  
A. R. Bowie
Keyword(s):  
Southern Ocean ◽  
Dissolved Iron ◽  
Heard Island ◽  
Natural Iron ◽  
Particulate Iron ◽  
The Difference ◽  
The One ◽  
Iron Pool ◽  
Lateral Advection ◽  
Very High

Abstract. Total dissolvable iron (TDFe) was measured in the water column above and in the surrounding of the Kerguelen Plateau (Indian sector of the Southern Ocean) during the KErguelen Ocean Plateau compared Study (KEOPS) cruise. TDFe concentrations ranged from 0.90 to 65.6 nmol L−1 above the plateau and from 0.34 to 2.23 nmol L−1 offshore of the plateau. Station C1 located south of the plateau, near Heard Island, exhibited very high values (329–770 nmol L−1). Apparent particulate iron (Feapp), calculated as the difference between the TDFe and the dissolved iron measured on board (DFe) represented 95±5% of the TDFe above the plateau, suggesting that particles and refractory colloids largely dominated the iron pool. This paper presents a budget of DFe and Feapp above the plateau. Lateral advection of water that had been in contact with the continental shelf of Heard Island seems to be the predominant source of Feapp and DFe above the plateau, with a supply of 9.7±3.6×106 and 8.3±11.6×103 mol d−1, respectively. The residence times of 1.7 and 48 days estimated for Feapp and DFe respectively, indicate a rapid turnover in the surface water. A comparison between Feapp and total particulate iron (TPFe) suggests that the total dissolved fraction is mainly constituted of small refractory colloids. This fraction does not seem to be a potential source of iron to the phytoplankton in our study. Finally, when taking into account the lateral supply of dissolved iron, the seasonal carbon sequestration efficiency was estimated at 154 000 mol C (mol Fe)−1, which is 4-fold lower than the previously estimated value in this area but still 18-fold higher than the one estimated during the other study of a natural iron fertilisation experiment, CROZEX.

scholarly journals The interplay between regeneration and scavenging fluxes drives ocean iron cycling

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Alessandro Tagliabue ◽  
Andrew R. Bowie ◽  
Timothy DeVries ◽  
Michael J. Ellwood ◽  
William M. Landing ◽  
...  
Keyword(s):  
Meta Analysis ◽  
Data Sets ◽  
Intermediate Water ◽  
Biogeochemical Processes ◽  
Iron Cycling ◽  
Dissolved Iron ◽  
Particulate Iron ◽  
Rate Controlled ◽  
Data Coverage ◽  
Internal Cycling

Abstract Despite recent advances in observational data coverage, quantitative constraints on how different physical and biogeochemical processes shape dissolved iron distributions remain elusive, lowering confidence in future projections for iron-limited regions. Here we show that dissolved iron is cycled rapidly in Pacific mode and intermediate water and accumulates at a rate controlled by the strongly opposing fluxes of regeneration and scavenging. Combining new data sets within a watermass framework shows that the multidecadal dissolved iron accumulation is much lower than expected from a meta-analysis of iron regeneration fluxes. This mismatch can only be reconciled by invoking significant rates of iron removal  to balance iron regeneration, which imply generation of authigenic particulate iron pools. Consequently, rapid internal cycling of iron, rather than its physical transport, is the main control on observed iron stocks within intermediate waters globally and upper ocean iron limitation will be strongly sensitive to subtle changes to the internal cycling balance.

Carbon export associated with free-drifting icebergs in the Southern Ocean

2011 ◽  
Vol 58 (11-12) ◽  
pp. 1485-1496 ◽  
Author(s):  
K.L. Smith ◽  
A.D. Sherman ◽  
T.J. Shaw ◽  
A.E. Murray ◽  
M. Vernet ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Carbon Export

scholarly journals Imprint of a dissolved cobalt basaltic source on the Kerguelen Plateau

2012 ◽  
Vol 9 (12) ◽  
pp. 5279-5290 ◽  
Author(s):  
J. Bown ◽  
M. Boye ◽  
P. Laan ◽  
A. R. Bowie ◽  
Y.-H. Park ◽  
...  
Keyword(s):  
Surface Waters ◽  
External Input ◽  
Eastern Slope ◽  
Kerguelen Plateau ◽  
Dissolved Iron ◽  
Deep Waters ◽  
Iron Supply ◽  
Natural Iron ◽  
Shelf Sediments ◽  
Lateral Advection

Abstract. Processes of cobalt (Co) entrainment from shelf sediments over the Kerguelen Plateau were studied during the KEOPS (Kerguelen Ocean Plateau compared Study) in order to explain the exceptionally high dissolved cobalt concentrations that have been measured in the surface waters above the Kerguelen Plateau, and in intermediate and deep waters above its eastern slope. Lateral advection and dissolution of Co contained in basalt sediments around Heard Island, a main source of lithogenic Co in the study area, were shown to imprint the process of surface enrichment over the plateau. Dissolved Co enrichment was strongest at the intercept of the eastern slope with intermediate and deep waters, probably due to more efficient mobilisation of the sediments in the slope current, in addition to advection of Co-enriched and low-oxygenated ocean water masses. In surface waters, the strong sedimentary Co inputs were estimated to be much higher than biological Co uptake in phytoplankton blooms, underlining the potential use of dissolved cobalt as tracer of the natural iron fertilization above the Kerguelen Plateau. Based on a simple steady-state balance equation of the external input of dissolved iron over the plateau, the fertilization of iron inferred by using dissolved Co as a tracer of basalt sources is estimated to be 28 × 102 ± 21 × 102 t yr−1 in surface waters of the Kerguelen Plateau. This estimate is consistent with preceding ones (Zhang et al., 2008; Chever et al., 2010), and the calculated iron supply matches with the phytoplankton demand (Sarthou et al., 2008).

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