Correlation circle from the principal component analysis (PCA) applied on the composition of the sediment with respect to carbon and nitrogen (C_tot and N_tot), to organic carbon (C_org), to the isotopic composition of C_tot and C_org (δ¹³C_tot and δ¹³C_org) and organic nitrogen (δ¹⁵N_org) as well as to the pigments concentrations (chlorophyll <i>a</i>, <i>b</i> and <i>c</i>).

<p>Seawater targeted <i>p</i>CO₂ ( μatm) and the depth of sampling (cm) in the sediment have been added as supplementary variables. Axis 1 and axis 2 explained, respectively, 45 and 27% of the overall variance in the data.</p

Sediment-water fluxes of total alkalinity (Δ<i>A</i>_T), dissolved inorganic carbon (Δ<i>C</i>_T), ammonium (ΔNH₄⁺), nitrate (ΔNO₃⁻), nitrite (ΔNO₂⁻), dissolved inorganic phosphorus (ΔDIP) and silicate (ΔSi) observed during the 24 h incubations (n = 5).

<p>Positive rates represent fluxes from the sediment to the overlying water.</p

Experimental conditions (average between initial and final sampling) at which the sediment cores were exposed during the 24 h incubations (n = 5).

<p>:pH_T: pH on the total scale, <i>A</i>_T: total alkalinity, Ω_aragonite and Ω_calcite: saturation state of the overlying seawater with respect to, respectively, aragonite and calcite. Error bars represent the standard deviation.</p

Experimental set-up used in this study. See text for details.

<p>Experimental set-up used in this study. See text for details.</p

Correlation circle from the principal component analysis (PCA) applied on sediment-water fluxes of total alkalinity (<i>A</i>_T), dissolved inorganic carbon (<i>C</i>_T), ammonium (NH₄⁺), nitrate (NO₃⁻), nitrite (NO₂⁻), dissolved inorganic phosphorus (DIP) and silicate (Si).

<p>Seawater temperature (°C) and <i>p</i>CO₂ (μatm) at which sediment cores were exposed during the incubations (average between initial and final sampling) as well as the time elapsed since the start of the experiment (in days) have been added as supplementary variables. Axis 1 and axis 2 explained, respectively, 32 and 21% of the overall variance in the data.</p

Sediment size distribution (%) in the different depth layers, expressed as an average (SD) value between the different cores used in the experiment.

<p>Cores 13 and 14 (1120 μatm treatment) as well as the layer deeper than 4 cm of core 20 (3000 μatm treatment) have not been considered in this analysis and in the subsequent ones as they have been showed to greatly differ from the other samples (See text for details).</p

Sediment-water fluxes of total alkalinity (Δ<i>A</i>_T), dissolved inorganic carbon (Δ<i>C</i>_T), ammonium (ΔNH₄⁺), nitrate (ΔNO₃⁻), nitrite (ΔNO₂⁻), dissolved inorganic phosphorus (ΔDIP) and silicate (ΔSi) observed during the 24 h incubations (n = 5).

<p>Positive rates represent fluxes from the sediment to the overlying water.</p

Seawater temperature and carbonate chemistry controlled in the header tanks during the course of the experiment (∼14 days; n = 7).

<p>Salinity was constant throughout the experiment at 34.5. Measured pH in the total scale (pH_T), dissolved inorganic carbon (<i>C</i>_T) as well as calculated <i>p</i>CO₂ and saturation states with respect to aragonite (Ω_aragonite) and calcite (Ω_calcite), are presented as mean, standard deviation (SD), minimal (Min) and maximal (Max) values.</p

Calcification by <i>L. pertusa.</i>

<p>a) Total calcification, b) calcification separated by food substrate (algae, <i>Artemia</i>). <i>L. pertusa</i> was kept with and without <i>E. norvegica</i>; statistical significance between treatments is indicated as followed: ** p<0.009, * p<0.05, · 0.05</p

Tracer C-partitioning between metabolic components of <i>L. pertusa</i> and <i>E. norvegica</i> separate and together. (n = 3).

*<p>[µg C (day*g C biomass)^−1.</p