Ocean colour as detected from satellites connects us directly with the heart of the oceans ecosystem. We can use the colour to quantify lots of things about phytoplankton (or algae as they are also referred to) – the microscopic, plant-like organisms, that form the base of the marine food web and provide the oxygen in every other breath you take.

Scientists develop algorithms (calculations applied to satellite data) to measure how much of the pigment chlorophyll is present in the water, an indicator of the amount of phytoplankton. Other algorithms can estimate how much carbon phytoplankton are sequestering, or how much production from their photosynthesis is available higher up in the oceans food webs.

As it is connected to phytoplankton production and the ocean carbon cycle, chlorophyll a has been developed as an essential variable for climate studies. Phytoplankton production is driven by many factors including the availability of light and nutrients (often influenced by ocean currents), competition from other species, and predation. We can see the complex interplay of these factors in the archive of ocean colour data.

TASK

Watch the video of the OC-CCI time series below and see what features you can see in the chlorophyll a concentrations.

What do you think causes the patterns you see? Share some screenshots/comments and see if you are right!

• To have a closer look at this data, visit the OC-CCI portal.

• Select to ‘Start building a map’. Then under ‘Available indicators’ select ‘Chlorophyll indicators’ and then ‘Chlorophyll a concentration.

• Under interval, select ‘Monthly’, and under version, select ‘Version 3.0’.

• Once the data has loaded you can use the bottom tool bar to look at the data through time. Using this portal you can also extract data at a particular location through time. Clicking on the ‘graph symbol’ in the upper left corner will allow you to select a box, or draw a polygon around an area.

• Click and drag to select your area. You can export this data in netCDF format by clicking the ‘Download netCDF’ button. You can also click ‘make a new graph’. This will open another dialogue box. From here you can select the details of the graph you want to produce. A time series will average over the box and show you the general trends in time as below. You may need to use the options in the top right of the graph window to see the full range of the data.

You can also look at a hovmoller plot, which will show you the latitudinal/longitudinal averages with time.

TIP: Selecting a shorter data range using the sliders will mean your graphs general quicker!

Compare some different regions of the ocean, what differences do you see in the annual/seasonal patterns? Do you know why these differences occur?

You can also save the graph (by clicking the disk icon in the upper right corner of the graph window), and export the selected data for later use (by clicking ‘Download’ underneath the graph).