Autonomous profiling float observations of the high-biomass plume downstream of the Kerguelen Plateau in the Southern Ocean

Grenier, Mélanie; Penna, Alice Della; Trull, Thomas W.

doi:10.5194/bg-12-2707-2015

Cited by 28 publications

(30 citation statements)

References 90 publications

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“…This means that mesoscale variability makes satellite-versus-shipboard comparisons difficult, and this problem is exacerbated by frequent cloud cover. Both techniques characterize the very upper water column, with ship samples from ∼ 4 m depth and the satellite ocean colour observations reflecting the efolding penetration depth of ∼ 10-15 m (Grenier et al, 2015;Morel and Maritorena, 2001). Table 1 for voyage leg details and Fig.…”

Section: Representativeness Of Oceanographic Samplingmentioning

confidence: 99%

Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment

et al. 2018

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Abstract. The Southern Ocean provides a vital service by absorbing about one-sixth of humankind's annual emissions of CO 2 . This comes with a cost -an increase in ocean acidity that is expected to have negative impacts on ocean ecosystems. The reduced ability of phytoplankton and zooplankton to precipitate carbonate shells is a clearly identified risk. The impact depends on the significance of these organisms in Southern Ocean ecosystems, but there is very little information on their abundance or distribution. To quantify their presence, we used coulometric measurement of particulate inorganic carbonate (PIC) on particles filtered from surface seawater into two size fractions: 50-1000 µm to capture foraminifera (the most important biogenic carbonate-forming zooplankton) and 1-50 µm to capture coccolithophores (the most important biogenic carbonate-forming phytoplankton). Ancillary measurements of biogenic silica (BSi) and particulate organic carbon (POC) provided context, as estimates of the biomass of diatoms (the highest biomass phytoplankton in polar waters) and total microbial biomass, respectively. Results for nine transects from Australia to Antarctica in 2008-2015 showed low levels of PIC compared to Northern Hemisphere polar waters. Coccolithophores slightly exceeded the biomass of diatoms in subantarctic waters, but their abundance decreased more than 30-fold poleward, while diatom abundances increased, so that on a molar basis PIC was only 1 % of BSi in Antarctic waters. This limited importance of coccolithophores in the Southern Ocean is further emphasized in terms of their associated POC, representing less than 1 % of total POC in Antarctic waters and less than 10 % in subantarctic waters. NASA satellite ocean-colour-based PIC estimates were in reasonable agreement with the shipboard results in subantarctic waters but greatly overestimated PIC in Antarctic waters. Contrastingly, the NASA Ocean Biogeochemical Model (NOBM) shows coccolithophores as overly restricted to subtropical and northern subantarctic waters. The cause of the strong southward decrease in PIC abundance in the Southern Ocean is not yet clear. The poleward decrease in pH is small, and while calcite saturation decreases strongly southward, it remains well above saturation (> 2). Nitrate and phosphate variations would predict a poleward increase. Temperature and competition with diatoms for limiting iron appear likely to be important. While the future trajectory of coccolithophore distributions remains uncertain, their current low abundances suggest small impacts on overall Southern Ocean pelagic ecology.

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Section: Representativeness Of Oceanographic Samplingmentioning

confidence: 99%

Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment

et al. 2018

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“…Previous studies have attributed the iron enrichment to sedimentary sources from the plateau (Blain et al, ; d'Ovidio et al, ; Quéroué et al, ; Trull et al, ; Van Der Merwe et al, ; Zhang et al, 2008). As in other cases of blooms developing in the wake of sub‐Antarctic islands, the shape and extension of the Kerguelen bloom is known to be strongly related to the circulation (Borrione et al, ; d'Ovidio et al, ; Graham et al, ; Grenier et al, ; Mongin et al, ; Robinson et al, ; Trull et al, ). The local circulation is dominated by the Antarctic Circumpolar Current fronts and by the intense mesoscale activity originating from frontal instabilities and their interaction with the shallow bathymetry of the plateau (d'Ovidio et al, ; Park et al, ).…”

Section: Overview Of the Study Regionmentioning

confidence: 98%

Mesoscale Variability of Conditions Favoring an Iron‐Induced Diatom Bloom Downstream of the Kerguelen Plateau

et al. 2018

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Heterogeneity in phytoplankton distribution is related to spatial and temporal variations in biogeochemical and ecological processes. In the open ocean, the interaction of these processes with meso‐ and submeso‐scale dynamics (1‐100 km, few days to months) gives rise to complex spatio‐temporal patterns, whose characterization is difficult without extensive sampling efforts. In this study, we integrate pigment sampling and multisatellite data to assess the link between iron enrichment and diatom dominance in the open ocean region east of the Kerguelen Islands (Indian Sector of the Southern Ocean). In this region, the High Nutrient Low Chlorophyll conditions typical of the Southern Ocean are alleviated by the transport of iron off the Kerguelen Plateau, resulting in a plume of chlorophyll that extends 1,000 km downstream. We show that in situ concentrations of the diatom‐associated pigment fucoxanthin and ocean‐color‐derived estimates of diatom dominance correlate with the “water age”, i.e., the time since the respective water parcel departed the Kerguelen Plateau. We propose a “threshold model” linking diatom ecological success and iron availability of downstream‐advected water parcels. The pattern of diatom dominance generated by this model predicts the extent and spatial structure of satellite‐based estimates at the regional scale (∼100s of km) and describes the mesoscale distribution of diatom dominance in the proximity of the plateau. However, the complexity of diatom dominance patterns further away from the plateau indicates that other physical and ecological mechanisms may drive phytoplankton dominance downstream.

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“…Using a matchup length scale of 25 km (i.e. the ship and satellite observations must be within 25 km of each other on the same day), which is somewhat larger than the correlation length scale for chlorophyll in the Southern Ocean of 10-15 km (Haëntjens et al, 2017), allowed us to retain 116 matchups. These results, shown in Fig.…”

Section: Comparison To Satellite Pic (Spic) Estimatesmentioning

confidence: 99%

Supplementary material to "Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment"

Trull¹,

Passmore²,

Davies³

et al. 2017

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Autonomous profiling float observations of the high-biomass plume downstream of the Kerguelen Plateau in the Southern Ocean

Abstract: International audienc

Cited by 28 publications

References 90 publications

Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment

Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment

Mesoscale Variability of Conditions Favoring an Iron‐Induced Diatom Bloom Downstream of the Kerguelen Plateau

Supplementary material to "Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment"

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Autonomous profiling float observations of the high-biomass plume downstream of the Kerguelen Plateau in the Southern Ocean

Abstract: International audienc

Cited by 28 publications

References 90 publications

Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment

Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment

Mesoscale Variability of Conditions Favoring an Iron‐Induced Diatom Bloom Downstream of the Kerguelen Plateau

Supplementary material to &quot;Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment&quot;

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Supplementary material to "Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment"