As a result, the effects of global warming or global cooling on ocean densities are complex, and still poorly understood. (globalwarmingsolved.com)
Johnston and Lambeck (1999) concluded that a solution consistent with geological evidence, including constraints on sea level for the past 6,000 years (Section 11.3.1), is for a non-steric sea level rise (i.e., not resulting from ocean density changes) of 1.0 ± 0.5 mm / yr for the past 100 years, with 5 to 30 % originating from Greenland melting. (ipcc.ch)
Thermohaline circulation, also known as the ocean's conveyor belt, refers to the deep ocean density - driven ocean basin currents. (sciencedaily.com)