Mapping the Seafloor

Hi everyone, it is Adeline writing today! I’ve been active in Exploring our Oceans MOOC since November 2014 (when I did the course while I was applying for a PhD here at Southampton!). Today, I would like to give you an update on seafloor mapping.

GEBCO World Ocean Map
GEBCO World Ocean Map

In his video, from the first week, Dr Tim Le Bas discussed the proportion of the ocean that has been mapped. I quote: “15% of the seafloor is surveyed by the multibeam technology (size of Africa), but when we get to high-resolution, it is a tiny amount, like the size of Tasmania (0.05%)”.

Furthermore, the entire ocean floor has now been mapped to a maximum resolution of around 5 km, says Jon Copley in Just how little do we know about the ocean floor?. This map is realised from satellites observation (to know more, read this article: Gravity map uncovers sea-floor surprises). If we want to go at a higher resolution and study the seafloor in greater details, we have to use sonars and new technologies built on ships.

In 2016, I participated in a cruise (R/V Meteor 127) in the Atlantic Ocean where we achieved mapping at a different resolution. Every night, the ship was flying over the Mid-Atlantic Ridge to map the seafloor with a multibeam echosounder (at 30 metres resolution). In the daytime, the AUV Abyss (an autonomous underwater vehicle, from the German GEOMAR Research Centre) dived and mapped the study area at a resolution of less than 2 metres. This was outstanding, we saw so many details!

The advantage of an AUV is its autonomy. In few words, we launch it into the water and we bring back on deck 12 hours later. During this time, our research team works on other aspects of the mission (for example, sediment, rock or seawater sampling).

The same AUV has also realised two maps at a very high-resolution (50 cm!) at two different zones of hydrothermal activity. We could even see former vent chimneys! However, this mapping is time-consuming. In order to obtain high-quality data in a location where the bathymetry is highly variable (such as a mid-oceanic ridge), the AUV has to fly over the study area several times at different altitude. Afterwards, our team of excellent geophysicists will compile the data of the different dives to produce a finale high-resolution map.

If you would like to hear more about these missions, read these blog posts:

Now 4 years after Tim and Jon’s videos, surely we have increased the proportion of mapped seafloor. GEBCO is the General Bathymetric Chart of the Ocean. They have several maps free to explore online, and these maps show the names of the main oceanic features GEBCO World Map. Personally, I love it! Today, GEBCO, together with the Nippon Foundation, have a collaborative initiative called “Seabed 2030” with the aim of facilitating the complete mapping of the ocean floor by the year 2030. I am looking forward to taking part in the initiative in my next cruises.

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