GOSML: A Global Ocean Surface Mixed Layer Statistical Monthly Climatology: Means, Percentiles, Skewness, and Kurtosis

Here we discuss a global ocean surface mixed layer statistical monthly climatology (GOSML) of depth, temperature, and salinity that includes means; variances; 5th, 50th, and 95th percentiles; as well as skewness and kurtosis. Ocean surface mixed layer properties are influenced by gravity and a wide variety of factors that operate over a wide variety of time scales. Mixed layer depths can shoal very quickly as a result of surface heating, precipitation, or slumping of horizontal density gradients. However, deepening the mixed layer in the presence of a strong pycnocline requires substantial buoyancy loss or strong wind mixing, which often takes more time. This pattern is clear in the annual cycle monthly mixed layer depth values, with deepening in the fall much slower than shoaling in the spring. The 95th percentile values are chosen as a reasonable indicator of ventilation depth, robust to extreme outliers. Mean mixed layer depths are on average 0.56 of 95th percentile mixed layer depths, with only 1% of values below 0.31% and 1% above 0.81. Over 71% of mixed layer depth distributions are skewed positive, usually when there are more shallow mixed layer depths than not and deep mixed layer tails are strong. Comparing 95th percentile depth conditions to mean values shows in late winter temperatures are generally lower in the subtropics and salinities generally higher in the subpolar regions, consistent with the importance of temperature in the midlatitudes and salinity in the higher latitudes in setting stratification.

Automated summary

This article discusses the statistical climatology of depth, temperature, and salinity in the global ocean surface mixed layer. The properties of the mixed layer are influenced by various factors that operate over different time scales. The depth of the mixed layer can change rapidly due to surface heating, precipitation, or density gradients, but deepening the mixed layer requires substantial buoyancy loss or strong wind mixing, which takes more time. The distribution of mixed layer depth is skewed positive, with temperature and salinity exhibiting different characteristics in different regions.