The Ocean Twilight Zone is the largest habitat on Earth. It is a vast ecosystem that does not depend on sunlight directly. This is the place where organisms have evolved seemingly bizarre adaptations such as bioluminescence and reproduction modes such as the Angler Fish with a parasitic male. The clues for chemical origins for how life may have started could be there in thermal vents.
The discovery of diel vertical migration of fish and zooplankton forming the deep sound scattering layer of the twilight zone opens up new questions. Will deep sea harvesting interrupt and reduce the carbon sequestration capacity of this vast habitat? For this reason we must urgently understand carbon budget and turnover in this massive ecosystem so that we can calculate the impact of industrial scale fish harvesting soon to discover this yet untapped resource. It is estimated that up to 95 percent of all fish live in the twilight zone. It is curious that the lantern fish is one of the most abundant species in this layer. Siphonophores have also been a cryptic group of species observed rarely only when they come close to surface waters. Scientists survey this layer by extracting fragments of DNA shed into the water by resident species. This indirect sampling of environmental DNA (eDNA) method proves very useful. High throughput sequencing technologies enable detection of informative lengths of genomic DNA from many species confirming presence and absence of species occupying the habitat. Scientists call this kind of DNA based environmental sampling metagenomics.
In our Human-dominated time, we have been dumping a lot of carbondiokside into the atmosphere leading to a cascade of environmental problems including ocean acidification. Atmospheric CO2 levels are rising fast. In fact, you can check the most up to date atmospheric CO2 reading from Hawaii yourself. If the carbon absorption rates of the twilight zone biota is impeded we may experience even greater levels of run-away greenhouse effect which causes global warming.
Global climate is tightly linked to the behavior of oceans. Worlds oceans are linked to one another not only with surface currents but also through Global Thermohaline Circulation. Major currents such as the North Atlantic Deep Water Current is driven by sinking of cold high-salinity water. Sinking water gets carried away to the South along the North Atlantic Deep Water Current. North Atlantic Deep Water Current is suspected to be the major influencer of abrubt climatic swings observed in glacial ice core data such as the Dansgaard-Oeschger cycles.
The biggest hub in global ocean circulation is the Antarctic Circumpolar Current. This current is the largest on our planet. The region around latitude 60 south is the only part of the Earth where the ocean can flow all the way around the world with no land barriers. The surface and deep waters together flow from west to east around Antarctica. The Antarctic circumpolar current links the world’s oceans and allows the deep water circulation from the Atlantic to move into upwelling zones in the Indian and Pacific Oceans.
Woods Hole Oceanographic Institution (WHOI) oceanographer Andone Lavery and her team of scientists, technicians and engineers have been exploring the twilight zone. Since the Jacques Cousteau’s hugely influential 1964 documentary “World Without Sun” a lot have changed. We have numerous quite sophisticated remotely operated deep diving vehicles such as the legendary DSV Alvin submarine that can capture outstanding observations.
Indeed we know more about the surface of the Moon than that of our own planet. The frantic search for Malaysia Airline Flight 370 revealed no results after three years. Since its disappearence off of the radar screens we still do not know its final resting place. This is quite telling of how little we know about oceans below the surface. As of 2020 only one-fifth of Earth’s ocean floor has been mapped.
Written and Directed by Jennifer L. Berglund
Supervising Director and Writer Nick Stringer
Edited by Danielle S. Myers and Jennifer L. Berglund
Narrated by Jackie Mahon
Music and Sound Design by Travis G. Pullman
Chief Scientist, Andone Lavery
Shot on Location aboard The NOAA Ship Henry B. Bigelow
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