Mercator Ocean International (MOi) oceanographers examine marine heatwaves across the global ocean. They analyse a variety of datasets from observations (satellite sea surface temperature maps) to numerical model analyses (assimilating satellite and in situ observations) and derive forecasts for a 7 day period.[1]
Assessment for April 9th
Zone Europe
Mediterranean Sea
In the Tyrrhenian Sea, the marine heatwave intensity increases with predominantly strong category. In the Ionian Sea, the marine heat wave intensity increases with strong and severe categories. In the eastern Mediterranean, the marine heatwave intensity decreases towards moderate category.
Global Ocean
Atlantic Ocean
North Atlantic Ocean – On the European Atlantic coast, and in the Bay of Biscay, the marine heatwave that has been present for several months no longer exists.. Along the Maroccan coast, the marine heatwave is stable with moderate and strong categories.
North Tropical Atlantic Ocean – In the North Tropical Atlantic and Caribbean Sea the marine heatwave is stable.
South Tropical Atlantic Ocean – In the South Tropical Atlantic and at the equator, the marine heatwave extent is stable. Off the African coast the marine heatwave extent decrease. Along north Brazilian coast there is a category intensification from strong to severe.
Southern Ocean
The marine heatwave in the Antarctic Ocean, off the South Africa (between 30°W and 30°E) is stable.
Pacific Ocean
Tropical Pacific Ocean – In the tropical Pacific Ocean, the marineheat wave be due to El Niño condition decreases in the center of the basin. Near to the Papua New Guinea, the marine heatwave increases in intensity towards strong category.
South Pacific, east of New Zealand – The marine heatwave remains stable overall.
Indian Ocean
In the Indian Ocean, the marine heatwave extent increases in intensity in the North of the Arabian Sea with the presence of moderate and strong categories.
Mediterranean Sea – 1.5°C to 2.5°C
North Atlantic Ocean– No significant temperature anomalies.
North Tropical Atlantic Ocean – 0.5°C to 1.5°C
South Tropical Atlantic Ocean – 1°C to 2°C
Southern Ocean – 1°C to 3°C
Tropical Pacific Ocean – 0.5°C to 1.5°C
South Pacific Ocean – 2 °C to 3°C
Indian Ocean – 0.5°C to 1°C
Zone Europe
Mediterranean Sea
For the 16th of April, the Mercator Ocean International forecast system forecasts a marine heatwave with moderate category in Alboran Sea. Between Corsica and Balearic Islands the marine heatwave extent decreased. In the middle and in the Eastern of the Mediterranean, the marine heatwave increases with strong to severe category and extreme locally.
Global Ocean
Atlantic Ocean
North Atlantic Ocean – The MOi forecast system forecasts a new marine heatwave in the Bay of Biscay with moderate category. Off the Moroccan coast, the marine heatwave surface area will increase with moderate and strong categories.
North Tropical Atlantic Ocean – The marine heatwave in the North Tropical Atlantic Ocean off the Moroccan coast will increase with category strong and severe. In the Caribbean Sea and the equator, the marine heatwave will decrease in intensity with moderate category.
South Tropical Atlantic Ocean – The marine heatwave will remain stable.
Southern Ocean
The marine heatwave in the Antarctic Ocean, off the South Africa (between 30°W and 30°E) will increase with strong category.
Océan Pacifique
Tropical Pacific Ocean – In the Tropical Pacific, marine heatwaves linked to El Niño conditions will remain stable. In the western part of the basin, near Papua New Guinea, the marine heatwave will be decreasing in intensity, with a switch to the moderate category.
South Pacific, east of New Zealand – The marine heatwave will remain stable.
Indian Ocean
The marine heatwave will remain stable.
What are marine heatwaves?
Marine heatwaves (MHW) are extreme rises in ocean temperature for an extended period of time. They can occur at different locations in the ocean, and their magnitude and frequency have increased over the last couple of decades, with harmful impacts on ecosystems, and human activities. According to the latest report released by the Intergovernmental Panel on Climate Change (IPCC AR6 SYR), it is found with high confidence that in the near-term at 1.5°C global warming, the increasing frequency of marine heatwaves will increase risks of biodiversity loss in the oceans, including from mass mortality events.[2]
How are marine heatwaves calculated?
A marine heatwave is a heat episode during which the temperature is significantly higher than a certain threshold for at least 5 consecutive days.
Figure adapted from Hobday et al. (2018)
The seasonally-varying threshold is defined on a daily basis according to a sufficiently long climatic period (in this case 1993-2016). So, for a given place and a given day, knowing all the surface temperatures observed over the last 30 years, a heatwave situation is defined as one where the temperature measured is within 10% of the maximum values observed (i.e. above the 90th quantile, see diagram), for at least 5 consecutive days.
The main characteristics of heatwaves are their duration and intensity. The intensity for a given day corresponds to the value in degrees above the 90th quantile (blue arrow), which can either be calculated as the cumulative intensity throughout the heatwave event, or the maximum intensity.
Heatwaves are categorised on the basis of their deviation from the mean temperature or anomaly (green arrow): a deviation of more than 2 times the difference between the 90th quantile and the mean corresponds to a heatwave in the strong category; a deviation of more than 3 times corresponds to a heatwave in the severe category; and a deviation of more than 4 times corresponds to a heatwave in the extreme category.
[1]Analysis of datasets: SST OSTIA (Copernicus Marine Service), OISST (NOAA), GLO12 (Copernicus Marine Service / Mercator Ocean International), PSY4 (Copernicus Marine Service / Mercator Ocean International), and GLO12 et PSY4 forecasts.
[2]IPCC AR6 SYR chapter 4.3 https://www.ipcc.ch/report/ar6/syr/downloads/report/IPCC_AR6_SYR_LongerReport.pdf
