OMZ’s: God-For-Saken Pits of Despair

It’s a hard knock life for deep-sea animals.  It’s really cold in the winter.  It’s really cold in the summer. It’s dark and wet…like Boston and Guinness.  Your only source of food, what little you get, is far from fresh and may have passed through the rectum of more than one animal.  If you are a deep-sea organism, you’ve probably asked yourself on more than on occasion how you wound up in this god-for-saken pit of despair.

Lucky deep-sea organisms get the paradise described above.  Ones not so lucky live their lives in the oxygen minimum zone.  This is exactly what it sounds like, an area of no to little oxygen. It even comes with a clever acronym that makes it sound like a combat zone, OMZ.  OMZ’s typically occur at depths of 200-1000 meters forming a band of low oxygen hell in the eastern Pacific, southeast Atlantic, Arabian Sea and the Bay of Bengal.  In OMZ’s larger organisms fair the worse with their numbers typically suppressed.  In contrast, in really small organisms, e.g. bacteria, copepods, nematodes, ostracods, forams and the like, the numbers are the same in and out of the OMZ.  What is also clear is that to survive the OMZ, an organism needs to be packing the right physiological and anatomical toolset.  Accordingly, OMZ species are different than their non-OMZ counterparts.

A new suite of excellent studies on the Pakistan OMZ in the NE Arabian Sea was unleashed in the recent issue of Deep-Sea Research II.  The set of multidisplinary studies exhaustively examines the biological and geochemical processes in this particularly thick (150-1300m) and extreme (near 0 ml/L oxygen concentrations) OMZ.  That’s what she said.  This OMZ is the grandpappy of all OMZ’s.  Some of the findings of the group are that indeed the Pakistan OMZ is hell-hole that becomes more or less so as a result of monsoonal variation, that microbial processes and bioturbation are predictably affected by the suckiness of OMZ life, and even the organic material is more degraded than predicted.  In the core of the Pakistan OMZ (250-750m), where oxygen hits a record low, larger organisms are extremely rare, even more so than other OMZ’s like the nearby Oman OMZ.  All the large organisms move to the OMZ suburbs leaving behind the forams to do as the like and do it absence of predators like ispods and scaphopods. Of course, until an “urban planning commission” “revitalizes” the neighborhood and everyone comes back to the city. Sorry I got caught up in the analogy. Finally, given the harsh conditions of an OMZ and the requirements needed to live in one, a rapid turnover in species makeup is observable as you progress through and out of the OMZ.

Gooday, A., Levin, L., Aranda da Silva, A., Bett, B., Cowie, G., Dissard, D., Gage, J., Hughes, D., Jeffreys, R., & Lamont, P. (2009). Faunal responses to oxygen gradients on the Pakistan margin: A comparison of foraminiferans, macrofauna and megafauna Deep Sea Research Part II: Topical Studies in Oceanography, 56 (6-7), 488-502 DOI: 10.1016/j.dsr2.2008.10.003
Cowie, G., & Levin, L. (2009). Benthic biological and biogeochemical patterns and processes across an oxygen minimum zone (Pakistan margin, NE Arabian Sea) Deep Sea Research Part II: Topical Studies in Oceanography, 56 (6-7), 261-270 DOI: 10.1016/j.dsr2.2008.10.001

Dr. M (1730 Posts)

Craig McClain is the Assistant Director of Science for the National Evolutionary Synthesis Center, a National Science Foundation supported initiative. He has conducted deep-sea research for 20 years and published over 50 papers in the area. He has participated in and led dozens of oceanographic expeditions taken him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses on how energy drives the biology of marine invertebrates from individuals to ecosystems, specifically, seeking to uncover how organisms are adapted to different levels of carbon availability, i.e. food, and how this determines the kinds and number of species in different parts of the oceans. Craig’s research has been featured on National Public Radio, Discovery Channel, Fox News, National Geographic and ABC News. In addition to his scientific research, Craig also advocates the need for scientists to connect with the public and is the founder and chief editor of the acclaimed Deep-Sea News (, a popular ocean-themed blog that has won numerous awards. His writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web. His forthcoming book, Science of the South (, connects cultural icons of South such as pecan pie with the science behind them.

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2 comments on “OMZ’s: God-For-Saken Pits of Despair
  1. Wow . . . did not know these existed. You make them sound only slightly more appealing than life in Guantanamo Bay, a Soviet Gulag, Detroit, or similar. *ducks*

  2. Now I know what a that’s what she said jokes is but you took it to the next level. I guess you can make a twss joke out of anything

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