By Michael Stocker, bioacoustician and founder of Ocean Conservation Research – a research and policy development organization focused on the impacts of anthropogenic noise on marine habitat. For more information on industrial noise see www.ocean-noise.com
While the specter of seabed mining is one of the more recent assaults on the ocean, it is a practice that falls under the longer-running and larger rubric of the industrialization of the sea.
The ocean is a difficult – even hostile work environment. The surface is only occasionally calm. Due to the darkness of depth and turbidity visibility is all but obscured. Salt water is corrosive; and as operations submerge ever deeper they are subject to crushing hydro-static pressures. But advances in materials, processes, and communication technologies are opening up vast areas of the sea that have heretofore been out of reach and un-tappable. Increasingly deeper areas of the global Outer Continental Shelf (OCS) and even the deep sea are being exploited by extraction industries seeking oil and gas, minerals, and biological booty – largely unregulated, and certainly un-monitored by any regulatory oversight.
The sea bottom below the waves is not the flat abyssal plain that many imagine; rather it is every bit as detailed as the terrestrial surface beneath the sky. With mountain ridges, deep canyons, sacred grottos, coral and sponge forests, freshwater seeps, and volcanic fumaroles. If we could ever walk across the deep sea and see it with our eyes we would likely be deeply enchanted by the landscape. And while there are “desert plains” across the deepest ocean basins, they are layered with the excreted, off-cast, and dead artifacts from the planktonic and seafaring life in the water column above – from “marine snow” to whale falls, all becoming the staff of life for benthic organisms flourishing on the sea floor
It is in fact this subducted detritus from above over millions of years that has transformed into the oil and gas which has captivated the minions of the hydrocarbon industry, just as the minerals ejected from beneath the earth’s crust has enthralled the seabed miners. The unfortunate correlation here is that the detailed marine environments that bear the most promise for the extractors also provide the varied habitats which attract and support a diverse living ecosystem. So extracting anything from these habitats presupposes a certain amount of marine carnage.
It surprises me that even in my own field of marine conservation few realize that huge industrial factories are located and are being built on the sea floor. “Subsea” oil wells are nothing like the Spindletop gusher with Texas Crude erupting out of the top of an oil derrick. These subsea oil fields are vast and technologically stunning – with complex well-head manifolds, “blow-out preventers,” seafloor separators, multiphase and high-pressure reinjection pumps, with autonomous and remotely controlled vessels tending to the operations.
When hydrocarbon deposits below the seabed are tapped, the well produces oil, but it also produces gas, brine, sand, and other chemicals. All of these substances need to be separated from the oil and piped to where they can be disposed of – which usually means reinjecting the brine and solids back into the earth, and piping the oil and gas to the surface, where the gas is flared and the oil can be stored or transferred to tankers on the way to on-shore refineries. All of these processes involve large and complex equipment, much of which is set up thousands of feet below the surface.
Seabed mining faces a similar dilemma; wanted materials need to be separated from unwanted materials and routed or disposed of efficiently. But with seabed mining the unwanted materials – silt, sand, stone, and biologicals – there is no way to inject it back into the earth so it plumes and settles in the surrounding ocean environs and marine habitat – smothering everything it settles upon.
So the mechanics of these industrial processes – mining and hydrocarbon extraction, disrupts the seabed: equipment, infrastructure, pipes and cables, sediment, spills, and silt. But what may be even more disruptive in the subsea operations is noise.
The subsea oil fields typically operate under extreme well-head pressures from 1000 to 15,000 pounds per square inch, routing and processing solids, gas, and fluids through pipes, pumps, and separation chambers, then pumped up to the surface or compressed and reinjected back into the earth. This is not a formula for quiet (see fig. 1). Seabed mining, while not under the same processing pressures will nonetheless involve large materials-handling equipment with excavators, grinders, pumps, and lift systems – all roaring away at their designated tasks.
But the noises that may be even more insidious are the communications signals that are used to monitor and control this equipment. Due to the extreme pressures and hostile environment none these pieces of equipment are controlled locally by humans in submarines, rather they are all controlled from the surface. And while some of the earlier technologies involved remotely operated vessels on “umbilical cables,” increasingly the equipment is being controlled through acoustical modems. Multi-nodal communications networks keep a constant tab on equipment conditions, locations, and operations – instructing valves to open or close, maneuvering armatures and pipes, locating and orienting surface platforms, monitoring ocean currents and surface “altitude,” and alerting autonomous vessels when something needs adjusting or attending.
Due to the required data rates and the propagation characteristics of sound in water most of these communication signals happen between 10kHz and 100kHz – right in the acoustical “sweet-spot” of odontocetes (the toothed whales including dolphins, porpoises, beaked whales, and sperm whales). These noises also overlap the hearing range of forage fish such as herring and shad. And given that the typical digital control signal needs to have a decisive “on and off” state – they are usually characterized by fast rise-time, raspy sounding signals which are particularly annoying (Remember the the old telephone modems used on early computer internet connections?)
So these industrial operations are generating huge soundfields – from the loud low frequency mechanical noise of equipment and materials handling, to the screaming and roaring of high-pressure fluids and gasses in pipes and pumps, to the ripping high-frequency chatter of acoustical communications networks.
So while marine habitat is being physically compromised by seafloor industrial operations, even larger areas of the ocean are being colonized by the many noises of these enterprises. Marine extractive industries can be extremely profitable to the operators, but at a very high cost to the marine life that lives in the surrounding sea.