Just try reading this word correctly the first time you see it. It’s as though someone took three each of i, m, n, and o, shuffled them together, and then stuck an l right in the middle. On the left side, two each of m and o and one each of n and i; on the right, the converse. But it’s such a forest of dodging and dancing, with only the o’s to break up the incessant railway ties of the lines, that your eyes will likely glaze and cross and grasp only at that medial limen, the numinous minimal l that limns the mileu. It is all mixed up.
So you see mono, minion, moon, loom, onion, minim, lion… After grasping at it like the spokes of a whirling wheel, you take the l and pull apart there: monimo limnion. But what could that be? Look to Greek for the roots: μόνιμος monimos ‘stable, steady’; λιμνίον limnion ‘small lake’. Assembled in the 20th century from parts used in other words; used to describe the bottom layer of a meromictic lake.
OK, so that doesn’t get us a whole lot farther, does it? What is a meromictic lake? It is a lake in which the upper and lower layers never mix.
Say what? Upper and lower layers? Yes, lakes tend to have layers. You thought because it’s all fluid it must just swirl about and all be the same? No. Look at the sky: different kinds of clouds scud on different plateaux in the air. Fluids layer, and not just in bar shooters. Most lakes have at least occasional mixing of layers, due to wind or seasonal changes. But a meromictic lake has a lower layer that is somewhat denser and has much less oxygen, and an upper layer that is more changeable and oxygenated, and the twain do not mingle. The upper layer is called the mixolimnion, because it mixes – but not with the monimolimnion.
Meromictic lakes are not common; most lakes are called holomictic and have a mixing of the layers at least once or twice a year. In a meromictic lake the monimolimnion makes up most of the volume and lies down there, deep, anoxic (having little or no oxygen), unmixing, unchanging, unwelcoming, building up layer upon layer of stable sediment. It may build up gases such as carbon dioxide. If there is a disturbance that causes mixing of the monomolimnion with the mixolimnion – an earthquake, for instance – that’s bad news for things that live on the oxygen in the mixolimnion. And it can be bad news for things and people that live near the lake if built-up gas is released: in 1986, such a disturbance of Lake Nyos in Cameroon killed 1800 people.
But don’t think that meromictic bodies of water are all dark and foreboding. They can be quite pretty. And they include in their number the Black Sea. Also, I note, Lower Mystic Lake, in Medford, Massachusetts, near Tufts University, where I went to grad school; it’s surrounded by town and is popular for boating. I doubt most of those who besport themselves on it are aware that it’s layered like some shotglass drink with a rude name favoured by frat boys. Let alone that the lower layer has a name they would never get past their eyes after having a few of said drinks.