Results of <i>χ</i>² and reduced chi-square (χ˜2) goodness-of-fit test for the site investigated in correspondence of the four sampling periods.

<p>The number of samples, used for the test and distanced of 1 m, is n = 200 corresponding to consider from the surface the first 200 m of depth.</p><p>Results of <i>χ</i>² and reduced chi-square (</p><p></p><p></p><p></p><p></p><p><mi>χ</mi><mo>˜</mo></p><mn>2</mn><p></p><p></p><p></p><p></p>) goodness-of-fit test for the site investigated in correspondence of the four sampling periods.<p></p

Spatio-temporal behaviour of <i>chl a</i> and <i>Dvchl a</i> concentrations.

<p>Contour maps show the content of chlorophyll for (a) Synechococcus, (b) Haptophytes, (c) Prochlorococcus HL, (d) Pelagophytes, (e) Prochlorococcus LL and (f) all phytoplankton groups in the sampling site (39° 30′.00 N, 13°30′.00 E). The values of the parameters used in the model are those shown in Tables <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.t001" target="_blank">1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.t002" target="_blank">2</a>.</p

Magnitude, depth, and width of the DCM, as a function of time.

<p>Red lines indicate theoretical results obtained for a yearly cycle with a time resolution of one month. Green points indicate experimental data acquired in the site analyzed (39° 30′.00 N, 13°30′.00 E) in correspondence of the four sampling periods (VECTOR-TM1, 24 November 2006; VECTOR-TM2, 3 February 2007; VECTOR-TM3, 22 April 2007; VECTOR-TM4, 9 June 2007).</p

How diffusivity, thermocline and incident light intensity modulate the dynamics of deep chlorophyll maximum in Tyrrhenian Sea

<p>During the last few years theoretical works have shed new light and proposed new hypotheses on the mechanisms which regulate the spatiotemporal<br>behaviour of phytoplankton communities in marine pelagic ecosystems.<br>Despite this, relevant physical and biological issues, such as effects of the timedependent mixing in the upper layer, competition between species, and dynamics of non-stationary deep chlorophyll maxima, are still open questions. In this work, we<br>analyze the spatio-temporal behaviour of five phytoplankton species in a real marine<br>ecosystem by using a one-dimensional reaction-diffusion-taxis model. The study is performed, taking into account the seasonal variations of environmental variables, such as light intensity, thickness of upper mixed layer and profiles of vertical turbulent diffusivity, obtained starting from experimental findings. Theoretical distributions of phytoplankton cell concentration was converted in chlorophyll concentration, and compared with the experimental profiles measured in a site of the Tyrrhenian Sea at four different times (seasons) of the year, during four different oceanographic cruises. As a result we find a good agreement between theoretical and<br>experimental distributions of chlorophyll concentration. In particular, theoretical results<br>reveal that the seasonal changes of environmental variables play a key role in the phytoplankton distribution and determine the properties of the deep chlorophyll maximum. This study could be extended to other marine ecosystems to predict future changes in the phytoplankton biomass due to global warming, in view of devising strategies to prevent the decline of the primary production and the  consequent decrease of fish species.</p> <p> </p

Profiles of <i>chl a</i> concentration acquired in the sampling site (39° 30′.00 N, 13° 30′.00 E).

<p>Data were collected during four oceanographic cruises: VECTOR-TM1, 24 November 2006 (panel a); VECTOR-TM2, 3 February 2007 (panel b); VECTOR-TM3, 22 April 2007 (panel c); VECTOR-TM4, 9 June 2007 (panel d). The black lines have been obtained by connecting the experimental points corresponding to samples distanced of 1 meter along the water column. The total number of samples measured in the site is <i>n</i> = 196 for VECTOR-TM1, <i>n</i> = 198 for VECTOR-TM2, <i>n</i> = 199 for VECTOR-TM3, and <i>n</i> = 196 for VECTOR-TM4.</p

Theoretical distributions (red line) and experimental profiles (green line) of the total <i>chl a</i> and <i>Dvchl a</i> concentration.

<p>The numerical results, obtained by the five-population model and given as a function of the depth, are compared with the experimental data collected in the sampling site (39° 30′.00N, 13°30′.00E), during the oceanographic surveys: VECTOR-TM1, 24 November 2006 (panel a); VECTOR-TM2, 3 February 2007 (panel b); VECTOR-TM3, 22 April 2007 (panel c); VECTOR-TM4, 9 June 2007 (panel d).</p

Spatio-temporal behaviour of vertical turbulent diffusivity (left panel) and light intensity (right panel) simulated for the sampling site (39° 30′.00 N, 13°30′.00 E).

<p>The values of the parameters are those of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.t002" target="_blank">Table 2</a>.</p

Spatio-temporal behaviour of the five picophytoplankton groups and phosphorus concentrations simulated by the model.

<p>The contour maps show the cell concentrations of (a) Synechococcus, (b) Haptophytes, (c) Prochlorococcus HL, (d) Pelagophytes, (e) Prochlorococcus LL and (f) nutrient. The values of the parameters used in the model are those shown in Tables <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.t001" target="_blank">1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.t002" target="_blank">2</a>.</p

Parameters used in the model.

<p>The values of the biological and environmental parameters are those typical of five picophytoplankton populations that coexist in the Tyrrhenian Sea during the whole year (Refs. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref016" target="_blank">16</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref018" target="_blank">18</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref069" target="_blank">69</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref070" target="_blank">70</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref074" target="_blank">74</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref078" target="_blank">78</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref084" target="_blank">84</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref085" target="_blank">85</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref085" target="_blank">85</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref088" target="_blank">88</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref092" target="_blank">92</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref093" target="_blank">93</a>]).</p><p>Parameters used in the model.</p

Scheme of the mechanism responsible for the phytoplankton distribution (modified from original figure by Alexey Ryabov).

<p>Inset: (a) Prochlorococcus PCC 9511 (courtesy of Rippka et al., 2000 (Ref. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115468#pone.0115468.ref095" target="_blank">95</a>])), (b) Micromonas NOUM17 (courtesy of Augustin Engman, Rory Welsh, and Alexandra Worden).</p