Local fluctuation of plant plankton in oceans

26-10-2011   “There is no dramatic global decline of plant plankton in the oceans’; this is one of the most important conclusions drawn by Marcel Wernand, a NIOZ scientist, in his PhD thesis, which he will defend at Utrecht University on 8 November 2011. This result contrasts sharply with earlier findings.

In his thesis, Marcel Wernand discusses documents, observations and analyses of the colour of the oceans from the period 1600-2000. He also examines a possible link between these colours and climate change, as it is to be expected that the colour of the oceans has seen some long-term changes. Oceans are constantly changing, especially now that they are affected by global warming.

Data based on so-called Forel-Ule scale, which have been collected from aboard ships since 1889, proved to be realistic, and linking them to modern satellite observations of ocean colours, Wernand shows that in the twentieth century colour changes vary from ocean to ocean. Oceans and seas first turned bluer (which points to less plant plankton), and subsequently greener (more plant plankton), but these changes took place in different areas at different times. The relation between plankton and climatological or oceanographical changes is clearly more likely to be regional rather than global.

Wernand’s results contrast sharply with the results published recently by Canadian scientists in the renowned journal Nature. Their article received lots of press coverage across the globe. The Canadians found a dramatic 40% global decline in plant plankton over the past 100 years. Wernand’s results do not confirm this.

At the Plankton2011 symposium, held in Plymouth last September, Wernand’s results were corroborated by other scientists, including scientists working at the Sir Alister Hardy Foundation for Ocean Science (SAHFOS), which has been monitoring plankton in the Atlantic Ocean for the past sixty years. They found a gradual increase in plankton, which corresponds to the increase (by a factor of 3 since 1889, so increasingly green) Wernand found in the data set he used for his dissertation. He also found a decline in plankton in both the Pacific Ocean (by a factor of 2 since 1960) and in the Indian Ocean (by a factor of 3, so increasingly blue).  

Title of the thesis
Wernand, M.R., Poseidon’s Paintbox: Historical Archives of Ocean Colour in Global-Change Perspective, 240 pp.