The wind holds a power beyond imaginable – it can shape the surface of the Earth through what is called sandblasting, a process in which potent winds transport soil grains horizontally, producing microscopic particles. A portion of these get carried away in the atmosphere and finally deposit in long-distanced parts of the world, changing the ecosystems.
From the Sahara desert, Saharan dust is transported for about 400 km towards the Canary archipelago by the southeastern warm wind called Calima by the Canary locals. In February 2020, the Calima completely covered the islands with its orange-coloured powder, so fine that it got trapped into all the crevices, including people’s respiratory organs. Although we are here to talk about the effects it has on the marine ecosystems, it is worth mentioning that the Calima alternates our health, too, causing asthma and chronic bronchitis in some individuals.
The dust influences the ecosystems because it brings nutrients and minerals scarcely found in the islands’ sediments. For instance, phosphorus is an important element as it is involved in the structure of nucleic acids, functional proteins such as phosphatases, lipids, sugars like glucose 6-phosphate and especially ATP (energy coin used in metabolic processes). When this element comes in contact with alkaline (high pH) soils, it forms complexes with oxidized metals, becoming unavailable. The contrary occurs during rainfall, when phosphorus is washed from these complexes in a process called earth weathering. During the aforementioned, it becomes again available for assimilation into plant tissues.
On the islands, the amorphous volcanic clay fixates phosphorus in a way that it becomes unavailable for plants. This is where the Calima dust plays a crucial role, since it brings approximately 28 mg/kg of plant-available phosphorus, slightly facilitating plant-growth.
In the ocean, whatsoever, the concentration of phosphorus is higher than the concentration of nitrogen, making nitrogen the limiting factor for algal growth. The reason stands within the fact that fixation of nitrogen occurs with difficulty. Specifically, oligotrophic seas (environments poor in nutrients) such as the Canary waters lack nutrients like iron.
Now wait a minute… Why am I mentioning a third element? Compared to the macronutrients phosphorus and nitrogen, iron is a key micronutrient involved in many enzymatic systems especially important for photosynthesis, respiration and nitrogen fixation. The latter process requires a lot of energy under the form of ATP and the presence of nitrogenase, an enzyme constituted by dinitrogenase reductase and dinitrogenase, both containing iron. In the sea, iron is poorly soluble due to the fact that it gets oxidized above a pH of 4 (the average ocean pH is 8,1). Hence, its demand is high but nevertheless hardly reached. The most common sources of it are fluvial inputs to the sea and from suspended particulate matter.
Unfortunately, in both cases, the majority of iron is trapped in coastal areas and it cannot reach the open sea. Luckily however, the Calima dust again enters in the picture by bringing particulate matter rich in iron, which once deposited in the sea, gets assimilated into the phytoplanktonic communities, now ready to fixated nitrogen and flourish. These communities are the primary producers of the world and take up carbon dioxide to convert it to oxygen through the process of photosynthesis. Carbon is stored under the form of biomass, which represents an important source for the other trophic levels of the marine ecosystem – herbivorous consumers, 1st, 2nd and 3rd carnivorous consumers and lastly top carnivores.
No wonder that when the Calima reaches the Canary archipelago, Nature replenishes itself.
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von Suchodoletz, H., Glaser, B., Thrippleton, T., Broder, T., Zang, U., Eigenmann, R., Kopp, B., Reichert, M. and Ludwig, Z., 2013. The influence of Saharan dust deposits on La Palma soil properties (Canary Islands, Spain). Catena, 103, pp.44-52.
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