scholarly journals Atmospheric inputs of volcanic iron around Heard and McDonald Islands, Southern ocean

2021 ◽  
Author(s):  
Morgane M. G. Perron ◽  
Bernadette C. Proemse ◽  
Michal Strzelec ◽  
Melanie Gault-Ringold ◽  
Andrew R. Bowie
Keyword(s):  
Southern Ocean ◽  
Kerguelen Plateau ◽  
Heard Island ◽  
Atmospheric Inputs

Increased atmospheric Fe loading and solubility was attributed to emissions from Heard Island volcano (Kerguelen plateau), emphasizing the need for models to consider volcanoes as a source of aeolian Fe to remote oceanic regions.

scholarly journals Unveiling the Si cycle using isotopes in an iron-fertilized zone of the Southern Ocean: from mixed-layer supply to export

2016 ◽  
Vol 13 (21) ◽  
pp. 6049-6066 ◽  
Author(s):  
Ivia Closset ◽  
Damien Cardinal ◽  
Mathieu Rembauville ◽  
François Thil ◽  
Stéphane Blain
Keyword(s):  
Southern Ocean ◽  
Isotopic Composition ◽  
Mass Balance ◽  
Silicic Acid ◽  
Surface Waters ◽  
Polar Front ◽  
Biogeochemical Cycle ◽  
Reference Station ◽  
Kerguelen Plateau ◽  
Fractionation Factor

Abstract. A massive diatom bloom forms annually in the surface waters of the naturally iron-fertilized Kerguelen Plateau (Southern Ocean). In this study, silicon isotopic signatures (δ30Si) of silicic acid (DSi) and suspended biogenic silica (BSi) were investigated through the whole water column with unprecedented spatial resolution, during the KEOPS-2 experiment (spring 2011). We used δ30Si measurements to track the sources of silicon that fuelled the bloom, and investigated the seasonal evolution of the Si biogeochemical cycle in the iron-fertilized area. We compared the results from stations with various degrees of iron enrichment and bloom conditions to an HNLC reference station. Dissolved and particulate δ30Si signatures were highly variable in the upper 500 m, reflecting the effect of intense silicon utilization in spring, while they were quite homogeneous in deeper waters. The Si isotopic and mass balance identified a unique Winter Water (WW) Si source for the iron-fertilized area that originated from southeast of the Kerguelen Plateau and spread northward. When the WW reached a retroflection of the Polar Front (PF), the δ30Si composition of the silicic acid pool became progressively heavier. This would result from sequential diapycnal and isopycnal mixings between the initial WW and ML water masses, highlighting the strong circulation of surface waters that defined this zone. When comparing the results from the two KEOPS expeditions, the relationship between DSi depletion, BSi production, and their isotopic composition appears decoupled in the iron-fertilized area. This seasonal decoupling could help to explain the low apparent fractionation factor observed in the ML at the end of summer. Taking into account these considerations, we refined the seasonal net BSi production in the ML of the iron-fertilized area to 3.0 ± 0.3 mol Si m−2 yr−1, which was exclusively sustained by surface water phytoplankton populations. These insights confirm that the isotopic composition of dissolved and particulate silicon is a promising tool to improve our understanding of the Si biogeochemical cycle since the isotopic and mass balance allows resolution of processes in the Si cycle (i.e. uptake, dissolution, mixing).

scholarly journals High Lability Fe Particles Sourced From Glacial Erosion Can Meet Previously Unaccounted Biological Demand: Heard Island, Southern Ocean

2019 ◽  
Vol 6 ◽  
Author(s):  
Pier van der Merwe ◽  
Kathrin Wuttig ◽  
Thomas Holmes ◽  
Thomas W. Trull ◽  
Zanna Chase ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Glacial Erosion ◽  
Heard Island ◽  
High Lability

Dissolved rare earth elements tracing lithogenic inputs over the Kerguelen Plateau (Southern Ocean)

2008 ◽  
Vol 55 (5-7) ◽  
pp. 638-652 ◽  
Author(s):  
Y. Zhang ◽  
F. Lacan ◽  
C. Jeandel
Keyword(s):  
Rare Earth ◽  
Southern Ocean ◽  
Rare Earth Elements ◽  
Kerguelen Plateau

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 Time-Mean Flow as the Prevailing Contribution to the Poleward Heat Flux across the Southern Flank of the Antarctic Circumpolar Current: A Case Study in the Fawn Trough, Kerguelen Plateau

2013 ◽  
Vol 43 (3) ◽  
pp. 583-601 ◽  
Author(s):  
H. Sekma ◽  
Y.-H. Park ◽  
F. Vivier
Keyword(s):  
Heat Flux ◽  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Mean Flow ◽  
Kerguelen Plateau ◽  
The Mean ◽  
The Cross ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Southern Flank

Abstract The major mechanisms of the oceanic poleward heat flux in the Southern Ocean are still in debate. The long-standing belief stipulates that the poleward heat flux across the Antarctic Circumpolar Current (ACC) is mainly due to mesoscale transient eddies and the cross-stream heat flux by time-mean flow is insignificant. This belief has recently been challenged by several numerical modeling studies, which stress the importance of mean flow for the meridional heat flux in the Southern Ocean. Here, this study analyzes moored current meter data obtained recently in the Fawn Trough, Kerguelen Plateau, to estimate the cross-stream heat flux caused by the time-mean flow and transient eddies. It is shown that the poleward eddy heat flux in this southern part of the ACC is negligible, while that from the mean flow is overwhelming by two orders of magnitude. This is due to the unusual anticlockwise turning of currents with decreasing depth, which is associated with significant bottom upwelling engendered by strong bottom currents flowing over the sloping topography of the trough. The circumpolar implications of these local observations are discussed in terms of the depth-integrated linear vorticity budget, which suggests that the six topographic features along the southern flank of the ACC equivalent to the Fawn Trough case would yield sufficient poleward heat flux to balance the oceanic heat loss in the subpolar region. As eddy activity on the southern flank of the ACC is too weak to transport sufficient heat poleward, the nonequivalent barotropic structure of the mean flow in several topographically constricted passages should accomplish the required task.

Winter advection of iron can explain the summer phytoplankton bloom that extends 1000 km downstream of the Kerguelen Plateau in the Southern Ocean

2009 ◽  
Vol 67 (2) ◽  
pp. 225-237 ◽  
Author(s):  
M. M. Mongin ◽  
E. R. Abraham ◽  
T. W. Trull
Keyword(s):  
Southern Ocean ◽  
Phytoplankton Bloom ◽  
Kerguelen Plateau

Late Miocene vegetation and palaeoenvironments of the Drygalski Formation, Heard Island, Indian Ocean: evidence from palynology

2005 ◽  
Vol 17 (3) ◽  
pp. 427-442 ◽  
Author(s):  
ELIZABETH M. TRUSWELL ◽  
PATRICK G. QUILTY ◽  
A. MCMINN ◽  
M.K. MACPHAIL ◽  
G.E. WHELLER
Keyword(s):  
Indian Ocean ◽  
Southern Ocean ◽  
Late Miocene ◽  
Tree Species ◽  
Frontal Zone ◽  
Tierra Del Fuego ◽  
Tree Pollen ◽  
Marine Diatoms ◽  
Heard Island ◽  
The Antarctic

Well sorted, fine lithic sandstone within the Drygalski Formation at Cape Lockyer on the southern tip of Heard Island, preserves a diverse terrestrial palynoflora as well as marine diatoms and a few foraminifera. A combination of these elements suggests a Late Miocene age (10–5 Ma). The palaeovegetation was markedly different from that presently on the island, and appears to comprise at least two ecologically distinct communities: open heath or herbfield dominated by grasses and Asteraceae, and a more mesophytic community dominated by ferns but also including lycopods and angiosperms such as Gunnera. This may have represented a coastal flora similar to the ‘fern-bush’ community that exists now on Southern Ocean islands north of the Antarctic Polar Frontal Zone, and in Tierra del Fuego; however, there is no evidence of tree species in the local flora and trace amounts of tree pollen present may have blown in from other landmasses in the region.

Accumulation of Fishing Debris, Plastic Litter, and Other Artefacts, on Heard and Macquarie Islands in the Southern Ocean

1991 ◽  
Vol 18 (3) ◽  
pp. 249-254 ◽  
Author(s):  
David J. Slip ◽  
Harry R. Burton
Keyword(s):  
Southern Ocean ◽  
Catchment Area ◽  
Marine Debris ◽  
Minimum Rate ◽  
Macquarie Island ◽  
Fur Seals ◽  
Heard Island

Sections of coastline of Heard and Macquarie Islands were surveyed for marine debris in the summer of 1987–88 and 1989, respectively. These surveys were carried out at the same sites as previous surveys in 1986–87 at Heard Island, and in 1988 at Macquarie Island. The minimum rate of artefact accumulation was 13 objects per km of shoreline per year for Heard Island, and 90 objects per km of shoreline per year for Macquarie Island. Drift-cards, released from known locations and collected on the two islands, show a similar artefact catchment area.Plastic litter was a major component of the debris at both islands. Fisheries-related debris accounted for 40% of all artefacts on Heard Island, compared with 29% on Macquarie Island. Entanglement of Fur Seals appears to be more common at Heard Island, while plastic ingestion by seabirds appears to be more common at Macquarie Island.

scholarly journals Chemometric perspectives on plankton community responses to natural iron fertilization over and downstream of the Kerguelen Plateau in the Southern Ocean

2014 ◽  
Vol 11 (9) ◽  
pp. 13841-13903 ◽  
Author(s):  
T. W. Trull ◽  
D. M. Davies ◽  
F. Dehairs ◽  
A.-J. Cavagna ◽  
M. Lasbleiz ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Growth Rates ◽  
High Growth ◽  
Large Cell ◽  
Polar Front ◽  
Community Responses ◽  
Kerguelen Plateau ◽  
Austral Spring ◽  
Particulate Nitrogen ◽  
Natural Iron

Abstract. We examined phytoplankton community responses to natural iron fertilisation at 32 sites over and downstream from the Kerguelen Plateau in the Southern Ocean during the austral spring bloom in October–November 2011. Community structure was estimated from chemical and isotopic measurements (particulate organic carbon POC, 13C-POC, particulate nitrogen PN, 15N-PN, and biogenic silica BSi) on size-fractionated samples from surface waters (300, 210, 50, 20, 5, and 1 μm fractions). Higher values of 13C-POC (vs. co-located 13C-DIC source values) were taken as indicative of faster growth rates, and higher values of 15N-PN (vs. co-located 15N-NO3 source values) as indicative of greater nitrate use. Community responses varied in relation to both regional circulation and the advance of the bloom. Iron fertilised waters over the plateau developed dominance by very large diatoms (50–210 μm) with high BSi / POC ratios, high growth rates, and significant ammonium recycling as biomass built up. In contrast, downstream Polar Frontal waters with similar or higher iron supply were dominated by smaller diatoms (20–50 μm) and exhibited greater ammonium recycling. Stations in a deep water bathymetrically trapped recirculation south of the Polar Front with lower iron levels showed the large cell dominance observed on the plateau, but much less biomass. Comparison of these communities to surface water nitrate (and silicate) depletions as a proxy for export shows that the low biomass recirculation feature exported similar amounts of nitrogen to the high biomass blooms over the plateau and north of the Polar Front. This suggests that trophodynamic and export responses differed between regions with persistent low levels vs. punctual high levels of iron fertilisation.

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