Definition of "aphotic"

As experiment has shown that light waves capable of effecting chemical changes do not penetrate the water deeper than 400 meters and as the other conditions of assimilation are met above this line, it is proposed to distinguish a diaphanic region including the land and the water to a depth of 400 m. and inhabited by assimilating organisms and an aphotic region including the ocean and lakes below the assimilation-line and the dark caves of the crust, where plant life is impossible.

1894 November–December, E. C. Quereau, “Einleitung in die Geologie als historische Wissenschaft. By Johannes Walther. Jena, 1893–4. [book review]”, in The Journal of Geology, volume II, number 8, Chicago, Ill.: University of Chicago Press, pages 857–858

We have bacteria classified as aërobic and anaërobic, according as they thrive with or without access of air. We need to classify bacteria as photic and aphotic.

1894 July 2, Julius Nelson, The Use of Koch’s Lymph in the Diagnosis of Tuberculosis of Cattle (New Jersey Agricultural College Experiment Station Bulletin; 101), [North Brunswick, N.J.: New Jersey Agricultural Experiment Station], § 2 (What is Known about Tuberculosis), page 12

Photographically the light of the sun is detectable in exceptionally clear-water tropical seas to a depth of about 2,000 feet, but Johnstone places the average depth for all waters at 650 feet, beyond which there is more or less of total darkness, the aphotic realm.

1910 June, Charles Schuchert, “Biologic Principles of Paleogeography”, in J[ames] McKeen Cattell, editor, The Popular Science Monthly, volume LXXVI, New York, N.Y.: The Science Press, page 596

Respiration and organic matter decomposition occur through the water column, and depending on the amount of organic matter present and the extent of wind-mixing, can deplete the dissolved oxygen supply in aphotic (unlighted) layers.

1981, Bruce L. Kimmell, “The Ecological Role(s) of Aquatic Micro-organisms in Lakes and Reservoirs”, in Phillip E. Greeson, editor, Microbiology of the Aquatic Environment (Briefing Papers on Water Quality; Geological Survey Circular; 848-E), [Reston, Va.]: United States Geological Survey, United States Department of the Interior, page E5, column 2

Large systems can always be subdivided. A large lake, for example, will have a surface photic environment, an aphotic system on the lakebed and a coastal system at the land–water interface.

2000, Adrian McDonald, “Ecosystems and Their Management”, in Ashley Kent, editor, Reflective Practice in Geography Teaching, London, Thousand Oaks, Calif.: Paul Chapman Publishing, SAGE Publications, part 1 (Progress in Geography: Changing Viewpoints), page 11

Although algae are frequently found below the photic zone, because of circulation or settling, they are not photosynthesizing under such conditions. In the aphotic, profundal zone food resources are provided exclusively through secondary productivity, consumption of settling detritus (or the organisms that feed on such detritus), and microbial food resources.

2003, Andrew S. Cohen, “The Biological Environment of Lakes”, in Paleolimnology: The History and Evolution of Lake Systems, Oxford, Oxfordshire, New York, N.Y.: Oxford University Press, page 96, column 2

The deep aphotic zone accounts for the largest portion (90%) of the marine benthic environment. Owing to the lack of solar energy, vegetation and photosynthetic primary production are largely nonexistent and food webs are mainly driven by heterotrophy. [...] A special mode of nutrition in the aphotic benthic zone is chemoautotrophy. Here chemoautotrophic bacteria and archaea replace photosynthetic primary production by using geothermally produced inorganic energy as a food source near deep sea vents and cold seeps.

2018, Birte Matthiessen, Franziska Julie Werner, Matthias Paulsen, “Ecological Organization of the Sea”, in Markus Salomon, Till Markus, editors, Handbook on Marine Environment Protection: Science, Impacts and Sustainable Management, volume 1, Cham, Switzerland: Springer Nature, part I (Nature Science Basics), section 2.3.2 (Aphotic (Dark) Oceanic Benthic Zone), page 53