Seawater temperature at 500m depth in °C.

=== Original Data Source ===
WORLD OCEAN ATLAS 2018 Volume 1: Temperature

From the World Ocean Atlas: This atlas consists of a description
of data analysis procedures and horizontal maps of climatological
distribution fields of temperature at selected standard depth levels
of the World Ocean on one-degree and quarter-degree
latitude-longitude grids.  The aim of the maps is to illustrate
large-scale characteristics of the distribution of ocean
temperature.  The fields used to generate these climatological maps
were computed by objective analysis of all scientifically
quality-controlled historical temperature data in the World Ocean
Database 2018.  Maps are presented for climatological composite
periods (annual, seasonal, monthly, seasonal and monthly difference
fields from the annual mean field, and the number of observations)
at 102 standard depths.

Citation:
Locarnini, R. A., A. V. Mishonov, O. K. Baranova, T. P.
Boyer, M. M. Zweng, H. E. Garcia, J. R. Reagan, D. Seidov, K. W.
Weathers, C. R. Paver, I.  V. Smolyar, 2019: World Ocean Atlas
2018, Volume 1: Temperature.  A. V.  Mishonov, Technical Ed.,
NOAA Atlas NESDIS 81

Citation URL:
https://data.nodc.noaa.gov/woa/WOA18/DOC/woa18_vol1.pdf