How deep is the sea. A submersible dive on the "cold seeps".
Maria Cristina Gambi is a marine ecologist at the Anton Dohrn Zoological Station of Naples.
It is not common to have the opportunity of a dive with a submersible in the deep sea. If this involves the icon of the deep sea exploration, the submersible Alvin, the experience is that of a lifetime! In 2010, as marine biologist, I had the privilege to perform a dive at 600 m depth offshore of Oregon, in the United States. This experience allowed me to contribute to the knowledge of the widest cold seeps system known in the world’s oceans, and also produced in me strong emotions that will always remain impressed in my heart.
In July 2010, I attended an expedition on the cold seeps of the Hydrate Ridge, a system of cold gas emission 80 miles offshore of Oregon, in the United States, as specialist of polychaetes, a group of marine worms having a long, cylindrical and segmented body. My experience started onboard the oceanographic vessel Atlantis and ended with a breath-taking dive at 600 m depth with the submersible Alvin.
The aim of the cruise was to study microorganisms and invertebrates living on the bottom of that area, where biogenic rocks originated from the stratification of remains of living organisms can be found. In this environment, polychaetes are one of the dominant groups of organisms and the huge amount of food available result into a true life oasis, characterized by very high levels of biodiversity as compared to normal muddy oceanic deep bottoms.
The cold gas emission, called cold seeps, associated with particular semi-solid compounds where methane molecules are enclosed in a sort of “lattice” – hydrates – originate areas of huge input of nutrients for the development of complex eco-systems.
Our deep dive with Alvin was planned following a strict protocol so that the pilot and the two scientific observers could optimize time and take as many samples as possible to the surface. The total duration of the mission was approximately 8-9 hours, during which we remained seated in a very limited space, not larger for three persons than the anterior part of a car, with an ambient temperature of about 8 °C to observe the oceans through the small round windows.
The sampling of rocks and sediments and the release of the experimental settings for the study of substrates colonization were done with the mechanical arms of Alvin maneuvered by the highly-skilled pilot, while the habitat and the organisms that we observed were really unique. The most conspicuous and fascinating organisms were the big red soft corals Anthomastus, the bivalve mollusks of the genus Calyptogena, the gastropods Neptunea and Provanna, the sea urchins Allocentrotus, and everywhere a thick mat of very bright and colorful methane and sulfur bacteria: like e.g. the Beggiatoa.
The intense scientific activity and our emotion made time fly and soon we had to go back to the surface. The submersible started to go back and once onboard the curiosity of our colleagues welcomed us and was very involving, thus prolonging our intense emotions for various days.
The cruise I participated to was one of the last of Alvin’s missions: in November 2010 it was dismissed and a new submersible is almost ready to operate up to 6000 m depth. I feel I was privileged to have had this opportunity and to have contributed to the knowledge of the widest cold methane seep system known in the world’s oceans, and the wonderful images of the sea bottom and the intense emotions will always remain impressed in my eyes… and in my heart.