Dissolved iron in the Australian sector of the Southern Ocean (CLIVAR SR3 section): Meridional and seasonal trends

Abstract Over the last ten years, satellite and geographically constrained in situ observations largely focused on the northern hemisphere have suggested that annual phytoplankton biomass cycles cannot be fully understood from environmental properties controlling phytoplankton division rates (e.g., nutrients and light), as they omit the role of ecological and environmental loss processes (e.g., grazing, viruses, sinking). Here, we use multi-year observations from a very large array of robotic drifting floats in the Southern Ocean to determine key factors governing phytoplankton biomass dynamics over the annual cycle. Our analysis reveals seasonal phytoplankton accumulation (‘blooming’) events occurring during periods of declining modeled division rates, an observation that highlights the importance of loss processes in dictating the evolution of the seasonal cycle in biomass. In the open Southern Ocean, the spring bloom magnitude is found to be greatest in areas with high dissolved iron concentrations, consistent with iron being a well-established primary limiting nutrient in this region. Under ice observations show that biomass starts increasing in early winter, well before sea ice begins to retreat. The average theoretical sensitivity of the Southern Ocean to potential changes in seasonal nutrient and light availability suggests that a 10% change in phytoplankton division rate may be associated with a 50% reduction in mean bloom magnitude and annual primary productivity, assuming simple changes in the seasonal magnitude of phytoplankton division rates. Overall, our results highlight the importance of quantifying and accounting for both division and loss processes when modeling future changes in phytoplankton biomass cycles.

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

Biogeosciences Discussions ◽

10.5194/bgd-6-6803-2009 ◽

2009 ◽

Vol 6 (4) ◽

pp. 6803-6837 ◽

Cited By ~ 1

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.

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Dissolved iron in the Southern Ocean (Atlantic sector)

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/j.dsr2.2010.10.042 ◽

2011 ◽

Vol 58 (25-26) ◽

pp. 2678-2694 ◽

Cited By ~ 157

Author(s):

M.B. Klunder ◽

P. Laan ◽

R. Middag ◽

H.J.W. De Baar ◽

J.C. van Ooijen

Keyword(s):

Southern Ocean ◽

Atlantic Sector ◽

Dissolved Iron

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

Biogeosciences ◽

10.5194/bg-7-455-2010 ◽

2010 ◽

Vol 7 (2) ◽

pp. 455-468 ◽

Cited By ~ 57

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.

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A synthesis of upper ocean carbon and dissolved iron budgets for Southern Ocean natural iron fertilisation studies

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/j.dsr2.2013.02.001 ◽

2013 ◽

Vol 90 ◽

pp. 147-157 ◽

Cited By ~ 21

Author(s):

Paul J. Morris ◽

Matthew A. Charette

Keyword(s):

Southern Ocean ◽

Upper Ocean ◽

Dissolved Iron ◽

Natural Iron ◽

Ocean Carbon

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Seasonal trends in the pigment and amino acid compositions of sinking particles in biogenic CaCO3 and SiO2 dominated regions of the Pacific sector of the Southern Ocean along 170°W

Deep Sea Research Part I Oceanographic Research Papers ◽

10.1016/j.dsr.2006.01.004 ◽

2006 ◽

Vol 53 (5) ◽

pp. 836-859 ◽

Cited By ~ 42

Author(s):

Anitra E. Ingalls ◽

Zhanfei Liu ◽

Cindy Lee

Keyword(s):

Amino Acid ◽

Southern Ocean ◽

Amino Acid Compositions ◽

Seasonal Trends ◽

Sinking Particles ◽

The Pacific

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Isotopic signature of dissolved iron delivered to the Southern Ocean from hydrothermal vents in the East Scotia Sea

Geology ◽

10.1130/g38432.1 ◽

2017 ◽

Vol 45 (4) ◽

pp. 351-354 ◽

Cited By ~ 11

Author(s):

Jessica K. Klar ◽

Rachael H. James ◽

Dakota Gibbs ◽

Alastair Lough ◽

Ian Parkinson ◽

...

Keyword(s):

Southern Ocean ◽

Hydrothermal Vents ◽

Isotopic Signature ◽

Scotia Sea ◽

Dissolved Iron

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A global compilation of dissolved iron measurements: focus on distributions and processes in the Southern Ocean

Biogeosciences ◽

10.5194/bg-9-2333-2012 ◽

2012 ◽

Vol 9 (6) ◽

pp. 2333-2349 ◽

Cited By ~ 114

Author(s):

A. Tagliabue ◽

T. Mtshali ◽

O. Aumont ◽

A. R. Bowie ◽

M. B. Klunder ◽

...

Keyword(s):

Southern Ocean ◽

Future Research ◽

Ocean Water ◽

Missing Measurements ◽

Antarctic Region ◽

Dissolved Iron ◽

Limiting Nutrient ◽

Modelling Studies ◽

The Antarctic ◽

Subantarctic Region

Abstract. Due to its importance as a limiting nutrient for phytoplankton growth in large regions of the world's oceans, ocean water column observations of concentration of the trace-metal iron (Fe) have increased markedly over recent decades. Here we compile >13 000 global measurements of dissolved Fe (dFe) and make this available to the community. We then conduct a synthesis study focussed on the Southern Ocean, where dFe plays a fundamental role in governing the carbon cycle, using four regions, six basins and five depth intervals as a framework. Our analysis highlights depth-dependent trends in the properties of dFe between different regions and basins. In general, surface dFe is highest in the Atlantic basin and the Antarctic region. While attributing drivers to these patterns is uncertain, inter-basin patterns in surface dFe might be linked to differing degrees of dFe inputs, while variability in biological consumption between regions covaries with the associated surface dFe differences. Opposite to the surface, dFe concentrations at depth are typically higher in the Indian basin and the Subantarctic region. The inter-region trends can be reconciled with similar ligand variability (although only from one cruise), and the inter-basin difference might be explained by differences in hydrothermal inputs suggested by modelling studies (Tagliabue et al., 2010) that await observational confirmation. We find that even in regions where many dFe measurements exist, the processes governing the seasonal evolution of dFe remain enigmatic, suggesting that, aside from broad Subantarctic – Antarctic trends, biological consumption might not be the major driver of dFe variability. This highlights the apparent importance of other processes such as exogenous inputs, physical transport/mixing or dFe recycling processes. Nevertheless, missing measurements during key seasonal transitions make it difficult to better quantify and understand surface water replenishment processes and the seasonal Fe cycle. Finally, we detail the degree of seasonal coverage by region, basin and depth. By synthesising prior measurements, we suggest a role for different processes and highlight key gaps in understanding, which we hope can help structure future research efforts in the Southern Ocean.

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