After a week of ROV dives on the spectacular cold-water coral reef at Lóndsjúp (63°N 14°W), east of Iceland, the scientific team on board RV Sonne will now turn their hand to some detective work. The second phase of the IceAGE3 expedition will focus on trying to solve a geological mystery: Iceland sits atop a mid-ocean ridge and is highly volcanically active… but where are all the hydrothermal vents?
The Reykjanes Ridge, immediately to the south of Iceland at about 60ºN, is the northernmost extension of the Mid-Atlantic Ridge (MAR) – the geological structure that runs up the middle of the Atlantic like a giant zipper (see map, below). This is where new ocean crust is formed as the tectonic plates move apart – the North American plate to the west, and the Eurasian plate to the east – and basaltic magma wells up into the gap and in some places forms submarine volcanoes.
The heat driving this process generates hydrothermal activity on the flanks of the mid-ocean ridge: cold seawater is drawn down into the new, hot ocean crust, where it is heated up, becomes enriched in minerals and metals, and is eventually spewed back out onto the seafloor at hydrothermal vents. These vents can develop large chimney-like structures and can become home to very specialised ecosystems inhabited by animals that thrive on the hot temperature and chemical energy provided by these mineral-rich fluids. The picture to the right shows an example of a hydrothermal vent community located further south on the MAR.
Volcanism at the Reykjanes Ridge is very active, generating a huge thickness of ocean crust in this area. This big pile of cooling magma releases a huge amount of heat, so geologists would expect to see lots of hydrothermal activity here as a result. In fact, they would normally expect to see vent sites at least every 100 km along the ridge, if not more frequently. However, to date only one vent site has ever been detected on the MAR between here and the Charlie Gibbs Fracture Zone further south, which is a distance of over 500 km. This is highly unusual, and is a mystery that the IceAGE3 team will strive to shed some light on this weekend!
A previous expedition in 2018 undertook a seafloor mapping exercise that showed lots of underwater volcanoes on the Reykjanes Ridge that might be sites of hydrothermal activity. Special sensors mounted on an Autonomous Underwater Vehicle (AUV) also detected chemical anomalies in the seawater – the hydrothermal fluids have a distinctive chemical signature, so an AUV can be used like a sniffer dog to detect them. However, despite careful searching, the exact site of the hydrothermal vent remained elusive.
Based on the seafloor maps and chemical information from the previous expedition, on Sunday the team will revisit this site on the Reykjanes Ridge and try to locate the hydrothermal vent. The geologists want to know how this huge pile of ocean crust is being cooled and the biologists want to know how the hydrothermal vent ecosystems interact with the fauna on the surrounding deep seafloor. First they will undertake a quick ‘sniff’ of the water using a chemical sensor, and then they will send ROV Kiel 6000 down 800m to the seafloor to have a good look around… who knows what they will find?
Join us for live action from the seafloor, through the eyes of ROV Kiel 6000. The vent-hunting dive starts at 08:00 CET on Sunday 12 July – you can watch and join the live chat on YouTube. You can also follow the expedition blog here.