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This paper provides a global context for how much environmental variables vary geographically, including with depth in the ocean.

Depth profiles of temperature, oxygen, nutrients, current velocity, and seabed slope, are provided. Geographic patterns for these variables plus salinity are contrasted between the sea surface and seabed.

The variables are used to classify the three-dimensional ‘Ecological Marine Units’ (EMU, Sayre et al. 2017a, b, 2015) into groups, showing how salinity, temperature and depth distinguish these environmental units. The number of EMU decreases with depth because deeper waters tend to be more homogenous and constitute larger units than the more variable and dynamic coastal seas.

The biological significance of EMU remains to be determined. Some species move between depth segregated EMU on a daily basis. Thus, species distribution data are essential to infer ecosystem structure and function for the environmental units.

A stratified sampling approach to ocean sampling is proposed whereby deeper environments, both pelagic and benthic, would be sampled with relatively lower spatial and temporal resolutions. Sampling should combine measurements of physical and chemical parameters with biological species distributions, even though species identification is difficult to automate.  The paper concludes that a globally comprehensive, stratification-based ocean sampling program would be both scientifically justifiable and cost-effective.


Costello MJ, Basher Z, Sayre R. Breyer S, Wright D. 2018. Stratifying ocean sampling globally and with depth to account for environmental variability. (Nature) Scientific Reports 8, 11259. DOI:10.1038/s41598-018-29419-1. Direct download

Sayre, R.G., D.J. Wright, S.P. Breyer, K.A. Butler, K. Van Graafeiland, M.J. Costello, P.T. Harris, K.L. Goodin, J.M. Guinotte, Z. Basher, M.T. Kavanaugh, P.N. Halpin, M.E. Monaco, N. Cressie, P. Aniello, C.E. Frye, and D. Stephens. 2017. A three-dimensional mapping of the ocean based on environmental data. Oceanography 30(1): 90–103.

Sayre, R., J. Dangermond, D. Wright, S. Breyer, K. Butler, K. Van Graafeiland, M.J. Costello, P. Harris, K. Goodin, M. Kavanaugh, N. Cressie, J. Guinotte, Z. Basher, P. Halpin, M. Monaco, P. Aniello, C. Frye, D. Stephens, P. Valentine, J. Smith, R. Smith, D.P. VanSistine, J. Cress, H. Warner, C. Brown, J. Steffenson, D. Cribbs, B. Van Esch, D. Hopkins, G. Noll, S. Kopp, and C. Convis. 2017. A new map of global Ecological Marine Units – an environmental stratification approach. Washington, DC: American Association of Geographers. 36 pages. ISBN 978-0-89291-281-0

Sayre, R., Wright, D., Aniello, P., Breyer, S., Cribbs, D., Frye, C. Vaughan R, Van Esch B, Stephens D, Harris P, Macmillan-Lawler M, Basher Z, Costello, M., Finkbeiner M, Monaco M, Goodin K, Guinotte J, Morgan L, Halpin P. 2015. Mapping EMUs (Ecological Marine Units)–the creation of a global GIS of distinct marine environments to support marine spatial planning, management and conservation. In: GEOHAB 2015, Marine Geological and Biological Habitat Mapping, May 3-8, Salvador Bahia Brazil, Abstract Volume, pp. 21.

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