Reduction on Frequency and Intensity of Extreme Thermocline Gradient from 1960-2017l

Thermocline is the part of the ocean with strong vertical temperature gradient. It separates the warm, well-mixed upper layer (i.e., isothermal layer) from the colder, deep water below. The thermocline gradient (G_th) affects the heat exchange between the isothermal layer and the deep layer, and influences the heat stored in the isothermal layer. In turn, it affects the heat and moisture fluxes at the ocean surface, impacts the climate change. On the base of double-gradient feature (near-zero gradient in the isothermal layer and evident gradient in the thermocline), a dataset named “Global ocean synoptic thermocline gradient, isothermal layer depth, and other thermal parameters” with 1,202,061 sets worldwide from 1960 to 2017 was established from the NOAA/NCEI World Ocean Database 2018 (WOD18) at https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.nodc:0173210 for public use. We divide the G_th data into two groups: reference period (1960-1985) and warming period (1986-2017). Probability density function (PDF) and cumulative density function (CDF) of G_th are obtained from this dataset for the two periods. We find evident reduction of frequency and intensity of G_th with the event rareness under warming period from the difference between the two sets of (PDF, CDF).