By Wyss Yim
The University of Hong Kong
Patches of abnormally hot seawater beneath the ocean surface referred to as Blobs are naturally generated by submarine volcanic eruptions. A recent example is the North Pacific Blob1 which caused weird weather conditions accompanied by major ecological changes in the Pacific northeast including two years without winters in 2013 and 20142. This was featured as a ‘heat wave’ in the September 2016 issue of National Geographic and was used to support the anthropogenic global warming alarm. However, based on the study of available information including satellite and ARGO data buoy records, the release of geothermal heat from the Nishinoshima volcanic eruption 940 km south of Tokyo3 from March 2013 to August 2015 was identified the culprit4,5.
This study examines the climatic impacts of another Blob created by the eruption of a new submarine volcano on the floor of southwest Indian Ocean off Mayotte in the Comoros. Subsequent ocean circulation changes led to the development of an exceptionally strong positive phase of the Indian Ocean Dipole (IOD)6. Regional climatic impacts in the southwest Indian Ocean included torrential rainfall and the establishment of a new record of 10 intense tropical cyclones during the 2018-2019 season. In the East Indian Ocean, the corresponding cooling of sea-surface waters gave rise to severe drought conditions in land areas of Indonesia and Australia.
Marc Chaussidon, director of the Institute of Geophysics in Paris was responsible for the discovery of the new as yet unnamed submarine volcano off the southeast coast of Mayotte7. Through looking at seafloor maps and a recently concluded mission, Chaussidon identified a new submarine volcano 800 meters high and 5 kilometers across rising above the ocean floor erupted within 6 months after November 2018 between Africa and Madagascar.
Multibeam sonar mapping of the sea floor indicated as much as 5 cubic kilometers of magma was erupted onto the seafloor. Based on the Volcanic Explosivity Index used for the measurement of terrestrial eruptions, the scale is 5 which is moderately strong. The sonar was able to detect plumes of gas-rich water rising from the flanks and central part of the volcano.
An examination of NOAA satellite sea-surface anomalies map archives has revealed that Blob was already well developed in early December 2018, the beginning of the southern hemisphere summer. This hot seawater assisted by solar heating was responsible for setting the new record of 10 intense tropical cyclones during the 2018-2019 season. Out of 10, the most severe was intense tropical cyclone Idai. The total cost of damage was estimated to exceed US$2 billion and the minimum death toll was 1007 because many bodies have not been recovered. Storm surge flooding was the worst on record with the destruction of 111,163 homes and damage to 112,735 houses in central and western Mozambique8.
Summary table of the 10 intense tropical cyclones during the record breaking 2018-2019 season in southwest Indian Ocean. Source: Wikipedia9
Previous work10 has demonstrated the importance of Indian Ocean variability in southeast Australia’s worst droughts. This is supported by the present study by the coincidence in timing of the Blob in causing positive IOD conditions during the southern hemisphere summer.
In late May, 2019, as a result of an extremely dry summer Sydney Water, Australia announced the enforcement of water restrictions throughout the greater Sydney area. As of May 29, 2019, Greater Sydney water supply levels are 53.4%, which is significantly lower than May 2018, in which supply levels were 73% in major catchments. These restrictions began on June 1, 2019.
In conclusion, severe weather events including tropical cyclones, droughts and floods may be caused by Blobs formed by the natural release of geothermal heat through submarine volcanic eruptions in combination with the sun to warm the surface waters of regional oceans. This warming in the West Indian Ocean was responsible for the development of a strong positive phase in the IOD resulting in oceanic and atmospheric circulation changes regionally which cannot be accounted for by carbon dioxide variations. Currently the natural release of geothermal heat into oceans is underestimated by the scientific community and may also represent a significant proportion of the missing heat in oceans proposed to explain the post-1998 pause in global temperature rise.
- Welch, C. 2016. Heat wave. National Geographic, September 2016, 54-75.
- Yim, W. 2016. Explanation for the northern Pacific Blob. Imperial Engineer Autumn 2016, 15.
- Yim, W. 2017. Geothermal heat: an episodic heat source in oceans. Imperial Engineer Spring 2017, 14-15.
- Ummenhofer, C.C. 2009. What causes southeast Australia’s worst droughts? Geophysical Research Letters 36(4): L04706. Bibcode: 2009GeoRL..36.4706U. doi:10.1029/2008GL036801.