"Decadal variations" refers to changes or patterns that occur over a period of 10 years. It refers to fluctuations, shifts, or trends that are observed in various aspects such as climate, economy, or population over a decade. Full definition
Chen & Tung claim that changes in salinity in the North Atlantic is the driver of decadal variation in ocean mixing, rather than the IPO. (skepticalscience.com)
Zhang, Y. - C., W.B. Rossow, P.W. Stackhouse, A. Romanou, and B.A. Wielicki, 2007: Decadal variations of global energy and ocean heat budget and meridional energy transports inferred from recent global data sets. (pubs.giss.nasa.gov)
The smooth curve shows decadal variations (see Appendix 3. (ipcc.ch)