Study of the phytoplankton plume dynamics off the Crozet Islands (Southern Ocean): A geochemical-physical coupled approach

Sanial, Virginie; Beek, Pieter van; Lansard, Bruno; d’Ovidio, Francesco; Kestenare, Élodie; Souhaut, Marc; Zhou, Meng; Blain, S.

doi:10.1002/2013jc009305

Cited by 28 publications

(26 citation statements)

References 44 publications

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“…The radium activities reported in this study are shown in Table 1 and fall in the range of previous radium data reported for surface waters near islands of the Southern Ocean (Annett et al, 2013;Charette et al, 2007;Dulaiova et al, 2009;Hanfland, 2002;Kaufman et al, 1973;Sanial et al, 2014;van Beek et al, 2008). The highest 223 Ra, 224 Ra and 228 Ra activities are found in seawater samples collected at shallow stations near the Kerguelen Islands (bathymetry < 200 m; Fig.…”

Section: Radium Distribution In Surface Waterssupporting

confidence: 84%

“…The KEOPS-2 cruise was conducted during austral spring 2011 to the east of the Kerguelen Islands. Natural radio-tracers such as radium isotopes ( 223 Ra, T 1/2 = 11.4 d; 224 Ra, T 1/2 = 3.66 d; 228 Ra, T 1/2 = 5.75 yr) have already been proved to be powerful tools to track the origin and fate of chemical elements -including iron and other micronutrients -which are released by the sediments deposited on the shelves (Annett et al, 2013;van Beek et al, 2008;Charette et al, 2007;Dulaiova et al, 2009;Sanial et al, 2014). In this work, we refer to these latter inputs as "sediment-derived inputs".…”

Section: Sanial Et Al: Use Of Ra Isotopes To Deduce Rapid Transfementioning

confidence: 99%

“…The trajectories were constructed by backward-in-time integration of the altimetric velocity field and were stopped when a hit over the Kerguelen shelf break was detected (indicating a trajectory coming from the shelf) or when a maximum integration time -set to 120 days -was reached (indicating no interaction with the shelf on the past 120 days). This model was applied successfully by Sanial et al (2014) to highlight the key role played by surface horizontal transport in defining the extension of the springtime chlorophyll plume in the Crozet area.…”

Section: Lagrangian Modelmentioning

confidence: 99%

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Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen

et al. 2015

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Abstract. The Southern Ocean is known to be the largest high-nutrient, low-chlorophyll (HNLC) region of the global ocean due to iron limitation. However, a large phytoplankton bloom develops annually downstream of the Kerguelen Islands, a bloom which is sustained partly by iron released from the sediments deposited onto the shelves. In the framework of the KEOPS-2 project, we used radium isotopes ( 224 Ra, T 1/2 = 3.66 d; 223 Ra, T 1/2 = 11.4 d; 228 Ra, T 1/2 = 5.75 yr) to provide information on the origin of iron fertilization and on the timescales of the transfer of sedimentderived inputs (including iron and other micronutrients) towards offshore waters. Significant 224 Ra and 223 Ra activities were found in the near vicinity of the Kerguelen Islands, in agreement with the short half-lives of these isotopes. Significant 224 Ra and 223 Ra activities were also detected up to 200 km downstream of the islands and more unexpectedly in offshore waters south of the polar front. These observations thus clearly indicate (i) that the sediment-derived inputs are rapidly transferred towards offshore waters (on timescales on the order of several days up to several weeks) and (ii) that the polar front is not a physical barrier for the chemical elements released from the sediments of the Kerguelen Plateau. The Ra data set suggests that iron and other micronutrients released by the shelves of the Kerguelen Islands may contribute to fueling the phytoplankton bloom downstream of the islands, despite the presence of the polar front. However, the heterogeneous distribution of the 224 Ra and 223 Ra activities in surface waters suggests that this supply across the front is not a continuous process but rather a process that is highly variable in space and time.

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Section: Radium Distribution In Surface Waterssupporting

confidence: 84%

Section: Sanial Et Al: Use Of Ra Isotopes To Deduce Rapid Transfementioning

confidence: 99%

Section: Lagrangian Modelmentioning

confidence: 99%

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Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen

et al. 2015

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“…In order to estimate iron delivery due to horizontal stirring, we use an advection scheme based on altimetry, extending to the Southern Ocean a Lagrangian model used for predicting the development of the Kerguelen phytoplanktonic plume . The model has been extensively calibrated and validated in the Crozet and Kerguelen regions by integrating satellite data (altimetry and ocean color), lithogenic isotopes, iron measurements, and drifters Sanial et al, 2014Sanial et al, , 2015. model seeds each open ocean location with a particle and finds the particle's most recent contact with a shallow bathymetry by a back trajectory issued from altimetry data.…”

Section: Lagrangian Modeling Of Horizontal Iron Fluxesmentioning

confidence: 99%

Delineating environmental control of phytoplankton biomass and phenology in the Southern Ocean

Ardyna

Claustre

Sallée

et al. 2017

Geophysical Research Letters

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124

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The Southern Ocean (SO), an area highly sensitive to climate change, is currently experiencing rapid warming and freshening. Such drastic physical changes might significantly alter the SO's biological pump. For more accurate predictions of the possible evolution of this pump, a better understanding of the environmental factors controlling SO phytoplankton dynamics is needed. Here we present a satellite‐based study deciphering the complex environmental control of phytoplankton biomass (PB) and phenology (PH; timing and magnitude of phytoplankton blooms) in the SO. We reveal that PH and PB are mostly organized in the SO at two scales: a large latitudinal scale and a regional scale. Latitudinally, a clear gradient in the timing of bloom occurrence appears tightly linked to the seasonal cycle in irradiance, with some exceptions in specific light‐limited regimes (i.e., well‐mixed areas). Superimposed on this latitudinal scale, zonal asymmetries, up to 3 orders of magnitude, in regional‐scale PB are mainly driven by local advective and iron supply processes. These findings provide a global understanding of PB and PH in the SO, which is of fundamental interest for identifying and explaining ongoing changes as well as predicting future changes in the SO biological pump.

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“…In support of this hypothesis, in-situ iron measurements from the Atlantic, North Pacific and Tasman Sea reveal high concentrations of iron on the pole-ward edge of the western boundary current extensions, corresponding to the Brazil Current, North Atlantic Current, Kuroshio Current and the East Australia Current (Lam et al, 2006;Nishioka et al, 2007Nishioka et al, , 2011Bowie et al, 2009;Rijkenberg et al, 2014;Schlosser et al, in preparation). Similarly, large fluxes of iron downstream of the Kerguelen and Crozet Islands have been attributed to the lateral advection of shelf sediment iron by ocean fronts (Blain et al, 2007(Blain et al, , 2008Planquette et al, 2007;Chever et al, 2010;Sanial et al, 2014;Van der Merwe et al, 2015). The source of this iron is thought to be from sediment re-suspension as fronts traverse continental and island shelves, as well as continentally weathered material entering coastal regions through surface runoff .…”

Section: The Role Of Ocean Fronts In Iron Supply To the Southern Oceanmentioning

confidence: 99%

Inferring source regions and supply mechanisms of iron in the Southern Ocean from satellite chlorophyll data

Graham

Boer

Sebille

et al. 2015

Deep Sea Research Part I: Oceanographic Research Papers

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Keywords: chlorophyll shelf sediments upwelling ocean fronts sea surface height dust glacial-interglacial cycles a b s t r a c t Primary productivity is limited by the availability of iron over large areas of the global ocean. Changes in the supply of iron to these regions could have major impacts on primary productivity and the carbon cycle. However, source regions and supply mechanisms of iron to the global oceans remain poorly constrained. Shelf sediments are considered one of the largest sources of dissolved iron to the global ocean, and a large shelf sediment iron flux is prescribed in many biogeochemical models over all areas of bathymetry shallower than 1000 m. Here, we infer the likely location of shelf sediment iron sources in the Southern Ocean, by identifying where satellite chlorophyll concentrations are enhanced over shallow bathymetry ( o1000 m). We further compare chlorophyll concentrations with the position of ocean fronts, to assess the relative role of horizontal advection and upwelling for supplying iron to the ocean surface. We show that mean annual chlorophyll concentrations are not visibly enhanced over areas of shallow bathymetry that are located more than 500 km from a coastline. Mean annual chlorophyll concentrations 4 2 mg m À 3 are only found within 50 km of a continental or island coastline. These results suggest that sedimentary iron sources only exist on continental and island shelves. Large sedimentary iron fluxes do not seem present on seamounts and submerged plateaus. Large chlorophyll blooms develop where the western boundary currents detach from the continental shelves, and turn eastward into the Sub-Antarctic Zone. Chlorophyll concentrations are enhanced along contours of sea surface height extending off the continental shelves, as shown by the trajectories of virtual water parcels in satellite altimetry data. These analyses support the hypothesis that bioavailable iron from continental shelves is entrained into western boundary currents, and advected into the Sub-Antarctic Zone along the Dynamical Subtropical Front. Our results indicate that upwelling at fronts in the open ocean is unlikely to deliver iron to the ocean surface from deep sources. Finally, we hypothesise how a reduction in sea level may have altered the distribution of shelf sediment iron sources in the Southern Ocean and increased export production over the Sub-Antarctic Zone during glacial intervals.

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Study of the phytoplankton plume dynamics off the Crozet Islands (Southern Ocean): A geochemical-physical coupled approach

Cited by 28 publications

References 44 publications

Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen

Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen

Delineating environmental control of phytoplankton biomass and phenology in the Southern Ocean

Inferring source regions and supply mechanisms of iron in the Southern Ocean from satellite chlorophyll data

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