Ocean terminus?
Out of sight, out of mind: The oceans have long served as a favorite dumping ground for humans. After all, you can no longer see the dirt there. Now the greenhouse gas carbon dioxide is to be sunk into it.
From radioactive waste water to diluted acid to World War I ammunition: the North Sea and B altic Sea hid everything that manufacturers or authorities on land no longer wanted or could reuse. Today, most of these disposal trips, which were once euphemistically called dumping, are largely prohibited. But parts of humanity - such as energy producers and politicians close to them - still rely on the seemingly endless capacities of the Atlantic, Pacific and their ilk as willing and initially unforgiving garbage chutes. The oceans should absorb large amounts of the greenhouse gas CO2 and thus at least mitigate the upcoming climate change.
In a completely natural way, they are already extracting from the atmosphere at fifty billion tons an estimated third of the additional carbon dioxide released when burning fossil fuels, which algae process during photosynthesis or simply dissolve physically. How much CO2 the plankton actually binds has only been roughly estimated to date, since these processes have been tracked either from space by satellite or at most from ships using small samples. Michael Behrenfeld from Oregon State University in Corvallis and his colleagues are now contributing a much more detailed data set, for which they have cruised almost 60,000 kilometers through the Pacific Ocean over the past twelve years [1].
On these trips, the researchers determined the phytoplankton density of the ocean using fluorescence measurements, which not only provided information about the quantity of algae, but also about their state of he alth. Because if the small floating photosynthetic units suffer from a lack of nutrients or iron, they build additionally produced, fluorescent chlorophyll into their cells, which, however, is not initially used for the production of nutrients. Rather, they store it and fall back on it as soon as iron fertilization occurs from outside – for example, due to a dust storm from the desert that has blown over the sea. In this way, they can quickly ramp up their sales at good times without delay.
This dormant green pigment only lights up under certain gauges and is not distinguished by satellites from its productive twin, ultimately falsifying their phytoplankton counts: the distinct green recorded by space scouts was by no means a signal of increased productivity, it simply indicated a stressful situation for the marine flora. The biologists conclude that the calculation based on the recordings for the carbon dioxide removed is also incorrect. If one calculates the additional pigment effect out of the pictures, the CO2 turnover falls by at least one to two billion tons less - at least two to four percent of the total volume intended for the oceans.
The waters around the Antarctic, the Pacific south of Alaska and a huge area on both sides of the equator, where hardly any iron from the air or from rising deep water promotes algae growth, are particularly affected by the lack of nutrients. Behrenfeld and other researchers have therefore had the idea of fertilizing these regions several times in the past. The goal: More phytoplankton should extract more carbon dioxide from the air and store it temporarily in the deep sea for a very long time after it dies. Theoretically, this could possibly delay or even reduce global warming.
In the experiment on small areas, these gifts also proved to be very effective, and the algae flourished - for a short time. Further iron supply led to only minor growth rates, until finally the zooplankton had followed suit and attacked their plant habitat partners. The marine food chain would have emerged stronger from this, but the world would probably not be able to cope with the industrially intensified greenhouse effect.
Since plowing the seas seems time-consuming and expensive with uncertain success, business and parts of science came up with the idea of sinking the CO2 directly into the deep sea. High pressure and the cool four degrees Celsius water temperature down there convert the gas into a liquid that covers the sea floor like a carpet and does not rise easily. Whether and what consequences this has for the mobile and less mobile creatures in the Abyssal could not be checked for a long time due to a lack of observations or experiments. Are the animals suffocating? Will carbonic acid burn them?
The team led by Fumio Inagaki from the Japanese Authority for Marine Research and Technology in Yokosuka and now guest researchers at the Max Planck Institute for Marine Microbiology in Bremen has now discovered a natural carbon dioxide lake off the coast of Taiwan in around 1400 meters deep, covered by a few centimeters thick layer of sediment and formed as a side effect of volcanic activity in the area [2]. And the gas waters should confirm the worst fears of conservationists: in and around the lake no higher organism moves, while life rages just fifty meters away. There, crabs, among other things, settle close together at so-called black smokers - hydrothermal sources - and feed on thick microbial lawns.
In the area of liquid carbon dioxide, on the other hand, there is a gray wasteland in which at most a few tough archaea and bacterial species endure. In the upper area of the twenty-centimetre-thick layer of sediment, the scientists still counted ten billion microbial cells per cubic centimeter of soil, compared to just ten million directly at the border to the CO2. Only the toughest species survive in this area at all, because liquid carbon dioxide simply dissolves many organic substances - and is therefore used in cleaning as a stain remover. In addition, the low pH value attacks the lime structure or skeleton of the living beings, so that they avoid the lake for this reason.
Simply pumping mankind's carbon dioxide waste into the deep sea would once again have fatal consequences for marine communities; especially since the gas remains mobile and yet could one day come to the surface again. Burying it even deeper in the sediment down there or in pumped out oil and gas fields would be an alternative, saving energy maybe a cheaper one.
