Atmospheric nutrients in seawater under current and high pCO2 conditions after Saharan dust deposition: Results from three minicosm experiments

J. Louis, F. Gazeau, Cecile Guieu

Research output: Contribution to journalArticle

Abstract

The Mediterranean basin receives among the highest dust fluxes in the world ocean, and also appears to be one of the regions the most strongly impacted by ocean acidification. The aim of this study was to assess, on a short time scale (one-week), the effect of ocean acidification on the dissolution of nutrients (inorganic nitrogen, phosphate and iron) from Saharan dust. Three experiments were performed in three distinct seasons: in May, after the spring bloom with low autotrophic biomass, in September, at the end of the oligotrophic period, and in January, during the winter bloom. On each occasion, a dust flux of 10 g m−2 was simulated at the surface of two minicosms (tanks of ∼0.3 m3) filled with filtered (<0.2 µm) seawater collected in the Bay of Villefranche (NW Mediterranean Sea). One minicosm served as a control and the other was acidified to reach a partial pressure of CO2 (pCO2) close to that projected for the end of this century (∼1250 μatm). Following a high-resolution sampling protocol, results showed that whatever the season and in situ biogeochemical conditions (1) all nitrogen from dust was soluble in seawater, allowing a large and stable increase in the stock of NOx (nitrate + nitrite) under the two pCO2 conditions (ambient and future), (2) transient increases in dissolved iron and phosphate concentrations were driven by scavenging processes, with a low dissolution percentage averaging 0.14 ± 0.08 and 4.7 ± 1.2%, respectively. While the absence of pCO2 effects on the release of atmospheric nitrogen was confirmed in the present study, no clear conclusion could be drawn for phosphate and dissolved iron as a consequence of very low concentrations and rapid (within less than 1 h) dissolved-particulate exchanges. Nevertheless, as the lifetime of these elements in solution is limited to a few hours, whatever the pH conditions, our results suggest that ocean acidification would have only a minor impact on their bioavailability for surface phytoplankton communities in such Low Nutrient Low Chlorophyll areas.

Original languageEnglish (US)
Pages (from-to)40-49
Number of pages10
JournalProgress in Oceanography
Volume163
DOIs
StatePublished - Apr 1 2018

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dust
seawater
nutrient
phosphate
nutrients
phosphates
iron
algal bloom
nitrogen
experiment
dissolution
inorganic nitrogen
partial pressure
Mediterranean Sea
nitrites
bioavailability
nitrite
particulates
chlorophyll
oceans

Keywords

  • Bioavailability
  • Dissolution
  • Mediterranean Sea
  • Nutrients
  • Ocean acidification
  • Scavenging

ASJC Scopus subject areas

  • Aquatic Science
  • Geology

Cite this

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title = "Atmospheric nutrients in seawater under current and high pCO2 conditions after Saharan dust deposition: Results from three minicosm experiments",
abstract = "The Mediterranean basin receives among the highest dust fluxes in the world ocean, and also appears to be one of the regions the most strongly impacted by ocean acidification. The aim of this study was to assess, on a short time scale (one-week), the effect of ocean acidification on the dissolution of nutrients (inorganic nitrogen, phosphate and iron) from Saharan dust. Three experiments were performed in three distinct seasons: in May, after the spring bloom with low autotrophic biomass, in September, at the end of the oligotrophic period, and in January, during the winter bloom. On each occasion, a dust flux of 10 g m−2 was simulated at the surface of two minicosms (tanks of ∼0.3 m3) filled with filtered (<0.2 µm) seawater collected in the Bay of Villefranche (NW Mediterranean Sea). One minicosm served as a control and the other was acidified to reach a partial pressure of CO2 (pCO2) close to that projected for the end of this century (∼1250 μatm). Following a high-resolution sampling protocol, results showed that whatever the season and in situ biogeochemical conditions (1) all nitrogen from dust was soluble in seawater, allowing a large and stable increase in the stock of NOx (nitrate + nitrite) under the two pCO2 conditions (ambient and future), (2) transient increases in dissolved iron and phosphate concentrations were driven by scavenging processes, with a low dissolution percentage averaging 0.14 ± 0.08 and 4.7 ± 1.2{\%}, respectively. While the absence of pCO2 effects on the release of atmospheric nitrogen was confirmed in the present study, no clear conclusion could be drawn for phosphate and dissolved iron as a consequence of very low concentrations and rapid (within less than 1 h) dissolved-particulate exchanges. Nevertheless, as the lifetime of these elements in solution is limited to a few hours, whatever the pH conditions, our results suggest that ocean acidification would have only a minor impact on their bioavailability for surface phytoplankton communities in such Low Nutrient Low Chlorophyll areas.",
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T1 - Atmospheric nutrients in seawater under current and high pCO2 conditions after Saharan dust deposition

T2 - Results from three minicosm experiments

AU - Louis, J.

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AU - Guieu, Cecile

PY - 2018/4/1

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N2 - The Mediterranean basin receives among the highest dust fluxes in the world ocean, and also appears to be one of the regions the most strongly impacted by ocean acidification. The aim of this study was to assess, on a short time scale (one-week), the effect of ocean acidification on the dissolution of nutrients (inorganic nitrogen, phosphate and iron) from Saharan dust. Three experiments were performed in three distinct seasons: in May, after the spring bloom with low autotrophic biomass, in September, at the end of the oligotrophic period, and in January, during the winter bloom. On each occasion, a dust flux of 10 g m−2 was simulated at the surface of two minicosms (tanks of ∼0.3 m3) filled with filtered (<0.2 µm) seawater collected in the Bay of Villefranche (NW Mediterranean Sea). One minicosm served as a control and the other was acidified to reach a partial pressure of CO2 (pCO2) close to that projected for the end of this century (∼1250 μatm). Following a high-resolution sampling protocol, results showed that whatever the season and in situ biogeochemical conditions (1) all nitrogen from dust was soluble in seawater, allowing a large and stable increase in the stock of NOx (nitrate + nitrite) under the two pCO2 conditions (ambient and future), (2) transient increases in dissolved iron and phosphate concentrations were driven by scavenging processes, with a low dissolution percentage averaging 0.14 ± 0.08 and 4.7 ± 1.2%, respectively. While the absence of pCO2 effects on the release of atmospheric nitrogen was confirmed in the present study, no clear conclusion could be drawn for phosphate and dissolved iron as a consequence of very low concentrations and rapid (within less than 1 h) dissolved-particulate exchanges. Nevertheless, as the lifetime of these elements in solution is limited to a few hours, whatever the pH conditions, our results suggest that ocean acidification would have only a minor impact on their bioavailability for surface phytoplankton communities in such Low Nutrient Low Chlorophyll areas.

AB - The Mediterranean basin receives among the highest dust fluxes in the world ocean, and also appears to be one of the regions the most strongly impacted by ocean acidification. The aim of this study was to assess, on a short time scale (one-week), the effect of ocean acidification on the dissolution of nutrients (inorganic nitrogen, phosphate and iron) from Saharan dust. Three experiments were performed in three distinct seasons: in May, after the spring bloom with low autotrophic biomass, in September, at the end of the oligotrophic period, and in January, during the winter bloom. On each occasion, a dust flux of 10 g m−2 was simulated at the surface of two minicosms (tanks of ∼0.3 m3) filled with filtered (<0.2 µm) seawater collected in the Bay of Villefranche (NW Mediterranean Sea). One minicosm served as a control and the other was acidified to reach a partial pressure of CO2 (pCO2) close to that projected for the end of this century (∼1250 μatm). Following a high-resolution sampling protocol, results showed that whatever the season and in situ biogeochemical conditions (1) all nitrogen from dust was soluble in seawater, allowing a large and stable increase in the stock of NOx (nitrate + nitrite) under the two pCO2 conditions (ambient and future), (2) transient increases in dissolved iron and phosphate concentrations were driven by scavenging processes, with a low dissolution percentage averaging 0.14 ± 0.08 and 4.7 ± 1.2%, respectively. While the absence of pCO2 effects on the release of atmospheric nitrogen was confirmed in the present study, no clear conclusion could be drawn for phosphate and dissolved iron as a consequence of very low concentrations and rapid (within less than 1 h) dissolved-particulate exchanges. Nevertheless, as the lifetime of these elements in solution is limited to a few hours, whatever the pH conditions, our results suggest that ocean acidification would have only a minor impact on their bioavailability for surface phytoplankton communities in such Low Nutrient Low Chlorophyll areas.

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