Water worlds

  • Written by  Benjamin Hennig
  • Published in Mapping
Global ocean chlorophyll concentration Global ocean chlorophyll concentration Benjamin Hennig
07 Feb
Chlorophyll concentrations in the world’s oceans are important indicators for the presence of algae and other plant-like organisms that carry out photosynthesis

As such, phytoplankton (which contains the chlorophyll) is an essential element of the food chain in the seas as it provides the food for numerous animals. Variations and changes in the chlorophyll levels are also relevant for the study of the ecology of the sea. Changing chlorophyll levels can also indicate changing sea temperatures and other conditions in the oceans that cover about 72 per cent ofthe planet’s surface.

In this visualisation, the data used was derived from NASA’s MODIS (MODerate resolution Imaging Spectroradiometer), which shows long-term chlorophyll concentration estimates in mg per cubic metres. The absolute concentration was then calculated for each of the equally-sized grid cells that cover the sea areas. These were resized according to the chlorophyll levels.

The visualisation therefore shows areas that have the highest density of algae and other photosynthetic organisms largest, while those regions with low concentrations disappear into the dark black areas where the grid cells merge.

The map also highlights the increasing levels towards many of the land areas, which appear as bizarrely distorted white islands in the sea. Investigating the changing grid patterns in more detail, higher levels can be seen along the west coasts of the Americas, as well as Africa, where rising cold water streams lift nutrients supporting phytoplankton growth from the ocean floor. Coastal upwellings also influence the high chlorophyll concentrations of the surface waters in the Baltic Sea and other zones along land areas where larger grid cells emerge. Meanwhile, the band along the Equator eastwards from the coast of South America is influenced by the easterly trade winds that also help the upwelling of deeper water layers.

Benjamin Hennig is a senior research fellow in the School of Geography and the Environment at the University of Oxford. He is involved in the Worldmapper project and maintains the visualisation blog www.viewsoftheworld.net.

This story was published in the February 2015  edition of Geographical Magazine

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