Day 22: 12 July 2020
We found it! Our wish came true after about two hours of ROV diving in the dark on the legendary Reykjanes Ridge structure: The long desired hydrothermal vent field suddenly appeared in front of the cameras! Spewing out hot water up to 300°C, these little vents enable unique biodiversity in a peculiar looking environment. If I didn’t know we were about 700m under water, I’d probably think we had landed on the moon: standing on bizarrely-formed rocks and watching a chimney 1.5m high that pours hot fluid into the near-freezing cold water column is an extraordinary experience. Huge red fish, a giant halibut and numerous squids joined our dive through this dreamlike world. Unlike our former dive areas, where sediment and coral reefs prevailed, this one looks like as if giants had played cosmic marbles: the seafloor is covered in rocks (pillow lavas) that are almost perfect spheres, each about 0.5 – 1m in diameter. And what seems to be inhospitably rough environment is in fact full of life. A fundamental part is played by the large bacteria mats that spread in a smooth white layer over the rocks. They feed on the hydrothermal fluids and announce themselves by dispersing what look like big snowflakes in the water column. Hence each time we felt like flying through a cold winter night’s landscape, those bacteria mats couldn’t be far! And where they are, hydrothermal activity must be, thus they act as perfect signpost for our vent hunt. Many species rely on these mats, amongst them are a variety of anemones, crustaceans, corals and fish. They also enjoy the warmth of the vents and they vanish once the hydrothermal activity stops – that is why we passed over vast coral graveyards: similar to volcanoes on land, hydrothermal vents have an expiration date and cease to be when their time is up. The surrounding water that used to be lovely 20°C cools down to about 5°C which makes it uninhabitable for these corals. They die and leave behind fields of brittle bony pieces.
