In my previous post, you may have noticed I referred to something called El Niño as a driver for coral bleaching events. But what is El Niño?
El Niño is a phase in the El Niño Southern Oscillation (ENSO) cycle, the other phase being La Niña. The ENSO describes the fluctuations in temperature between the ocean and atmosphere in the East-Central Equatorial Pacific, as measured by sea surface temperatures (SST) with La Niña being the cold phase and El Niño the warm phase. The frequency of these events can be quite irregular but they occur, on average, every 2-7 years with El Niño typically occurring more frequently than La Niña.
The last largest El Niño event was in 1997-98 which killed 20,000 people and cost billions in damage as a result of changed weather patterns causing cyclones, floods, droughts, fires and mudslides. It also caused the largest global coral bleaching event to date with 16% of the world's coral lost, with some areas, for example, The Maldives, experiencing catastrophic reef coverage losses of up to 90%.
In October this year, NOAA announced the 3rd ever global coral bleaching event as many forecast the current El Niño event to be the strongest yet. The El Niño of 1997-98 saw sea surface temperatures in the Pacific rise to 2.8 degrees Celsius above average; on 18th November 2015, this figure was 3.1 degrees Celsius, with NOAA expecting El Niño conditions to peak in early winter 2015-16.
Thank you for posting this as I always get confused about what El Nino actually is haha. I have a question though - am I correct in thinking that El Nino causes coral bleaching as the sea temperatures are too high for the algae that lives in symbiosis with the coral polyps?
ReplyDeleteThanks for your question, Ben. You are correct- El Nino episodes cause above average sea temperatures to which corals are extremely sensitive. The prolonged higher temperatures caused by El Nino, cause the corals to expel their algae, without which they ultimately can't survive. My next posts will be about past responses of corals to changing ocean conditions and also how we might be able to address the problem through breeding more resilient corals- watch this space!
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