Ocean Atlas of Biological Response to Changing El Niño

Guest article on behalf of Space4Climate by Dr Marie-Fanny Racault, Plymouth Marine Laboratory

The atlas provides key climate impact information to improve prediction of possible risks and opportunities for fisheries-dependent societies. In addition, from a carbon budget perspective, such insights on changing El Niño impacts on ocean’s biology and physics are needed to improve our understanding of the buffering capacity of the oceanic carbon cycle under climate change.

The importance of phytoplankton

Ocean primary producers are part of the very active, natural carbon cycle, fixing CO2 in the surface layer of the ocean into organic matter, some of which subsequently sinks to the deep oceans where it is isolated from the atmosphere for decades. Through this process, ocean primary producers, so-called phytoplankton, help to modulate the increase in atmospheric CO2 that results from the burning of fossil fuels.

Phytoplankton are at the base of the food chain and transfer energy to higher trophic levels. This transfer of energy has a knock-on effect on fisheries and dependent human societies especially in highly productive and coastal upwelling regions. Thus, phytoplankton are key players in the planetary carbon cycle, and they have a societal relevance.

Phytoplankton respond rapidly to climate-driven perturbations, including the dominant mode of variability in the Earth-climate system generated by the El Niño phenomenon. Recently, marked variations have been observed in the in the Equatorial Pacific under El Niño

How the atlas makes use of climate data from space

Through use of space imagery and reanalysis datasets, researchers at the Plymouth Marine Laboratory ihave been able to differentiate the regional environmental conditions, and compile an atlas of associated impacts on oceanic primary producers caused by two extreme types of El Niño. The climate data product used for this atlas is derived from satellite observations of ocean colour.  The product can be accessed from the Ocean Colour Climate Change Initiative dataset, which is produced by the European Space Agency.

 

El Niño types covered by the atlas

There are two types of El Niño that the atlas is based on (see Figure 1); the conventional form (characterised by higher-than-normal warming of sea surface temperature along the western coast of South America) and the Modoki type (or ‘pseudo’ El Niño, characterised by higher-than-normal warming of sea surface temperature in the central tropical Pacific).   The atlas provides robust evidence that during conventional and Modoki types of El Niño, impacts on primary producers can be felt everywhere, but tend to be greatest in the tropics and mid-latitudes, encompassing up to 67% of the total affected areas, with the remaining 33% being areas located in high-latitudes.

Figure 1. Bioloigcal response to changing El Nino climate

Atlas functions

By providing this type of climate information, the atlas of impact of both types of El Niño on oceanic phytoplankton can help inform fisheries management on possible risks and opportunities associated with different El Niño events. In so doing, it helps to improve the effectiveness of mitigation and adaptation plans for local fisheries-dependent societies.

The atlas can also help provide insights on El Niño variability impact, which are needed to improve our understanding of the buffering capacity of the oceanic carbon cycle under climate change. For instance, our analysis highlights considerable and sometimes opposing regional effects on the oceanic carbon cycle.  During conventional El Niño, we estimate that fixation of carbon by phytoplankton into organic material reduces by 56 million tons per year in the tropical eastern Pacific Ocean, and by 82 million tons in the western Indian Ocean, but that it increases by 13 million tons in eastern Indian Ocean. On the other hand, during El Niño Modoki,  carbon fixation decreases by 68 million tons per year in the tropical western Pacific Ocean and by 10 million tons in the central Atlantic Ocean. These regional changes in phytoplankton carbon fixation will in turn influence the ocean’s capacity to take up CO2 from the carbon emissions.

The atlas information can also provide an observational basis for scientists to test model predictions of the impact of climate change on the marine ecosystem.

Find out more here:

Racault, M.-F., Sathyendranath, S., Brewin, R. J. W., Raitsos, D. E., Jackson, T. and Platt, T. (2017) Impact of El Niño Variability on Oceanic Phytoplankton. Frontiers in Marine Science, 4(133).

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Article author:

Dr Marie-Fanny Racault, Plymouth Marine Laboratory

Dr Marie-Fanny Racault is an Earth Observation Scientist at the Plymouth Marine Laboratory, with research expertise in applications of earth observations, particularly in studying the influence of global and regional climate phenomena on the year-to-year variability of primary producers, and assessing future changes under global warming.

Funding acknowledgements

ESA Living Planet Fellowship Program Contract 4000112798/15/I/SBo

ESA Ocean-Colour Climate Change Initiative

NERC The National Centre for Earth Observation (NCEO)

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