|Fig. 1 Thermometer tracks|
That is, after adding or removing heat, the resulting trajectory will either move the resulting temperature of the water closer to the 4 deg. C maximum density temperature, or away from it.
The consequence of moving in a direction toward 4 deg. C (e.g. from 2 deg C to 3 deg C) is contraction (shrinking).
|Fig. 2 Depends on salinity|
The consequence of moving in a direction away from 4 deg. C (e.g. from 3 deg C to 2 deg C) is expansion.
Thus, when water is at 4 deg C, either the addition of heat, or the removal of heat will cause expansion, because either result is a trajectory away from the 4 deg C maximum density temperature.
That is because at that temperature either warming or cooling causes a temperature movement in a direction away from the maximum density temperature of 4 deg C (e.g. 4 deg C to 5 deg C causes expansion, just as a 4 deg C to 3 deg C temperature change also causes expansion).
The hourglass shaped graphic at Fig. 2 illustrates the point further (see Fig. 1 too).
Where the thermometer says the water temperature is below 4 deg C and warming is applied (represented by the pink arrow pointing toward the maximum density point of 4 deg C), contraction (shrinking) will take place (Fig. 2).
The opposite is the case when the thermometer says that the water temperature is above 4 deg C (etc.).
Those in The Warming Commentariat should explain why they say that thermal expansion is the MAJOR cause of sea level rise (Proof of Concept - 3).
Their inaccurate TEM (The Warming Science Commentariat - 6) gave rise to the conversation about ghost water (The Ghost-Water Constant, 2, 3, 4, 5, 6, 7), which should have clued them in.
The principles I have explained using 4 deg C apply mainly to pure water, a different maximum density temperature applies to deep ocean water and any other water that is not pure (The Warming Science Commentariat - 2).
NOAA focused on aspects of a related event, ocean "freshening", a few years ago:
While previous studies have shown that the bottom water has been warming and freshening over the past few decades, these new results suggest that significantly less of this bottom water has been formed during that time than in previous decades.(NOAA). Since the contraction / expansion principle is the same in all water, and those deepest coldest waters are warming, some sea level fall and some sea level rise is likely to result from it.
“Because of its high density, Antarctic Bottom Water fills most of the deep ocean basins around the world, but we found that the amount of this water has been decreasing at a surprisingly fast rate over the last few decades,” said lead author Sarah Purkey, graduate student at the School of Oceanography at the University of Washington in Seattle, Wash. “In every oceanographic survey repeated around the Southern Ocean since about the 1980s, Antarctic Bottom Water has been shrinking at a similar mean rate, giving us confidence that this surprisingly large contraction is robust.”
Changes in the temperature, salinity, dissolved oxygen, and dissolved carbon dioxide of this prominent water mass have important ramifications for Earth’s climate, including contributions to sea level rise [and fall] and the rate of Earth’s heat uptake.
But not much, percentage wise, compared to ice sheet melt-water contributions from Greenland, Antarctica, and non-ice sheet glaciers.
This full reality needs to be addressed by The Warming Commentariat, because their TEM model that says "MOST sea level rise is caused by solar warming of the ocean surface" is not robust.
At this point, thermal contraction is, by definition, holding back sea level rise, rather than causing, as the TEM says, MOST of it.
The temperature involved is one thing, salinity is another.
So, the fact that "freshening" (decrease in salinity) has been taking place indicates that seawater's maximum density temperature levels are moving upward closer to the 4 deg C maximum density of pure water (Fig 1, Fig 2).
That freshening and warming which has been and still is taking place is surprisingly robust:
In addition, glacier melt has freshened shelf water near the deep-water formation regions in the Weddell Sea (Hellmer et al. 2011). In the Ross Sea, shelf water and bottom water have freshened over the past 50 years (Jacobs and Comiso 1997; Jacobs and Giulivi 2010). Finally, bottom waters off the Adelie Coast have cooled and freshened on isopycnals between the mid-1990s and mid-2000s (Aoki et al. 2005; Rintoul 2007; Johnson et al. 2008a; Jacobs and Giulivi 2010).(Global Contraction of Antarctic Bottom Water, p. 5831-32, 5841). Most money is in the banks, so the robbers rob banks; most ocean water is below the surface, so, the deep water there is where the research needs to be focused.
A slowdown of the AABW production rate is consistent with the freshening of shelf waters in AABW formation regions in the Ross and Weddell Seas in recent decades (Aoki et al. 2005; Jacobs and Giulivi 2010; Hellmer et al. 2011). The surface freshening increases the stability of the water column, making it more difficult for surface waters to sink, possibly causing a slowing of the bottom limb of the MOC (Stouffer et al. 2007). In the Ross Sea, the shelf water and RSBW have freshened by ;0.03 and ;0.01 decade21, respectively, between 1958 and 2008 (Jacobs and Giulivi 2010), most likely caused by recent glacial melt along the Amundsen and Bellingshausen Seas freshening the westward flowing coastal current (Rignot et al. 2008; Jacobs and Giulivi 2010). Along the coast at 1408E and within the central Australian–Antarctic Basin, AABW has also warmed and freshened (Aoki et al. 2005; Johnson et al. 2008a), again pointing toward a freshening of the shelf water end member of either, or both, RSBW and ALBW. In the Weddell Sea, the northwestern shelf water has freshened by 0.09 between 1989 and 2006, owing to increasing glacial meltwater input, changes in sea ice extent, and higher precipitation (Hellmer et al. 2011).
At any rate, thermal expansion / contraction is a minor factor in sea level change (~5.1%).
The major factors of sea level change are ice sheet and glacial melt-water, ice sheet and glacial calving of ice into the oceans, and of course ghost water: The Ghost-Water Constant, 2, 3, 4, 5, 6, 7.