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Float no.6901512

    Temperature and salinity profiles   Time series plots
  Download the data   Using the float data with ocean analysis maps    

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This PROVOR_III float was launched by French scientists In the Gulf of Lyons south of France at 42°N, 4.7°E on 9 April 2013. It has recorded a total of 147 profiles, and made its last report on 5 May 2014 from 41.4°N,  3.5°E.

float in the water

Float deployment

testing the float

Testing the float

This Bio-Argo float is one of several floats with optical and biogeochemical sensors.
It measures concentrations of chlorophyll-a and nitrate, a plant nutrient.
It also measures light levels. Like all plants, phytoplankton need light and nutrients to grow.

At the time of deployment (April 10) the water column was well mixed in the top 200 m. As a result the the chlorophyll concentration was weak.

The scientists were lucky to deploy at this time. Only a few days later the spring bloom was starting and chlorophyll-a reached its highest concentration on April 15 (figure 1).

chlorophyll profile

Figure 1. Chlorophyll 15-Apr-2013

Question 1.

a) At what depth do you find the highest chlorophyll-a on 15 April?

b) What is the peak chlorophyll-a concentration there?

c) Why does the chlorophyll concentration drop to almost 0 below 25 m?

Click on the image of figure 1 for a high resolution version to help you answer. Afterwards you can click on the float (right) to check your answers.

Argo float
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A1.

annotated chlorophyll profile

Figure 1. Chlorophyll profile for 15-Apr-2013

a) The highest chlorophyll concentration is found at about 12-13 m depth.

b) The concentration there is over 12 milligrams per cubic metre of water (12 mg m-3).

However, chlorophyll concentrations are high in quite a wide band around this depth. It increases rapidly from a depth of 2-3 m to reach its maximum at 12-13 m. Below this it stays relatively high to a depth of about 22 m, then decreases rapidly to almost nothing by 25 m depth.

c) The reason for the low chlorophyll concentration at 25 m and below is lack of light for photosynthesis.

Sea water absorbs light, so light cannot penetrate more than 50-100 m in the clearest tropical water. During a plankton bloom the plankton cells also absorb light, so the light is lost much faster. Between about 10 and 16 m depth there is a band where chlorophyll concentrations reach 10 mg m-3 or more - really quite a dense bloom for the ocean. This acts a bit like the canopy of trees in a forest on land, and shade the water underneath. Plankton below this layer may get some light, but less and less the deeper you go, until there is not enough light for photosynthesis. At this depth the plankton can no longer grow and divide fast enough. This depth is know as the "euphotic depth", and sunlit area above is know as the "euphotic zone".   CLOSE

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This bloom occurs every year in spring, and is essential for marine animal life. Many animals time their spawning so that their larvae can hatch in time to feed on the phytoplankton in the bloom.

The bloom is 'fuelled' by nitrate that has been mixed up from deep water during winter. When the nitrate becomes exhausted at the surface, the bloom declines, and the oligotrophic season (or 'poor season') starts. In this season the phytoplankton are found deeper and deeper; they move down in the water to find the remaining nitrate. A deep chlorophyll maximum (DCM) develops where most of the plankton is found.
 

chlorophyll profile

Figure 2. Chlorophyll time series

   

Q2.
 
 

a) At what depth is the deep chlorophyll maximum (DCM) in figure 2?

b) What happens to the DCM in November?

c) Can you think of a reason for this?

Argo float
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A2.

annotated chlorophyll time series

Chlorophyll time series

a) The chlorophyll maximum descends after the bloom to about 50 m depth, and stays there throughout the summer. Concentrations vary, but the depth is remarkably constant.

b) In early November the DCM has broken down. The chlorohyll concentrations are lower, but about the same (0.7 - 0.9 mg m-3) from the surface to almost 100 m depth.

c) The most likely explanation for this is that mixing of the surface layer by wind and waves has spread the phytoplankton over depth interval of about 100 m from the surface and down. Oceanographers refer to this well mixed surface layer the "wind mixed layer".

c) The reason for the low chlorophyll concentration at 25 m and below is lack of light for photosynthesis.

Sea water absorbs light, so light cannot penetrate more than 50-100 m in the clearest tropical water. During a plankton bloom the plankton cells also absorb light, so the light is lost much faster. Between about 10 and 16 m depth there is a band where chlorophyll concentrations reach 10 mg m-3 or more - really quite a dense bloom for the ocean.

The bloom acts a little like the canopy of trees in a forest on land, and shade the water underneath. Plankton below this layer may get some light for photosynthesis, but less and less the deeper you go. At a certain depth there is no longer enough light for the plankton cells to grow and divide. This depth is know as the "euphotic depth", and the sunlit area above is called the "euphotic zone".   CLOSE

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How to obtain data from this float

You can download the most recent plots of data from this float from
http://www.oao.obs-vlfr.fr/bioargo/PHP/lovbio017b/lovbio017b.jpeg.
Besides chlorophyll the plots include time series of temperature, salinity, CDOM, particle backscattering, dissolved oxygen, nitrate concentration, and particle downwelling irradiance at three different wavelengths (380 nm, 412 nm and 490 nm), as well as phostosynthetically available radiation (PAR).

A guide to interpreting these plots can be found from the Bio-Argo web page .

Temperature and salinity profiles

Temperature profiles Salinity profiles

Profiles of temperature (left) and salinity (right) from Argo float 6901512. The profiles show how temperature (T) and salinity (S) change with depth from the surface to 2000m. Early profiles are dark blue, the latest profiles are deep red or brown. Click on the images for larger plots.     Source of plots: IFREMER/Coriolis.

Time series of temperature and salinity

Temperature section Salinity section

Time series of temperature (left) and salinity (right) from Argo float 6901512. The sections show all the temperature (T) and salinity (S) profiles measured by the float during its life-time side by side. Each profile is represented by a very thin column where deep red is the highest values and deep blue the lowest. The colour bars on the right relate the colours to actual data values. Profile numbers are given along the top of the plot, with corresponding measurement dates along the bottom. Click on the images for larger plots.     Source of plots: IFREMER/Coriolis.

Using the float trajectories with ocean analysis maps

Look at the float trajectory in Google Earth to see where the float has been. (If in doubt about how to reveal the float tracks, see our Google Earth screenshot for help.) Compare this to the maps of temperature and salinity for different depths available for example from Mercator ocean analyses.

Downloading the float data

The Argo Information Centre has more information about this float. You can also download the data from one of the Data Centres - just select Data > Data Downloads.

There are many different formats available. ASCII data can be viewed in spreadsheets such as Excel. The other data types may require more specialist software.

 

Link to the main Euro-Argo project website.