Talk:Sea level

Isostatic sea level changes

The definition of the meaning of "isostatic" in connection with sea level change seems off to me. It seems to me that this refers to things like isostatic rebound due to glacier melting, but that's not how it seems to be used here. Regardless, there's no sourcing for this definition. --Kent G. Budge (talk) 01:26, 5 January 2021 (UTC)

Responding

Isostasy: "Theory holds that the mantle is able to convect because of its plasticity, and this property also allows for another very important Earth process known as isostasy. The literal meaning of the word isostasy is “equal standstill,” but the importance behind it is the principle that Earth’s crust is floating on the mantle, like a raft floating in the water, rather than resting on the mantle like a raft sitting on the ground." From https://opentextbc.ca/geology/chapter/9-4-isostasy/ and similar definitions abound. The point is that settling seamounts or lowlands such as Bangkok, Manila and the Ganges Delta experience sea level rise - at least in part - rising sea-level (in current time) because their ground surface is actually dropping towards the centre of the Earth by erosion with very little to do with the physics of the mantle. Other places, like eastern Canada, as you say have, experience on-going falling sea levels (over recent geological times) because the surface rocks are still being elevated by as the mantle beneath regains isostatic balance after the melting to teratonnes of ice. — Preceding unsigned comment added by Mickwilson20 (talk • contribs) 07:24, 25 December 2021 (UTC)

The erosion has a lot more to do with the physics of the mantle, as shown by this PMC article.[1] It states: "The strength of any feedbacks between glacial isostasy and ice dynamics depends on the rate at which the solid Earth responds to ice-sheet change, which, in turn, depends on the rheological properties of the mantle." and: "...highlights that the influence of Earth structure on ice sheet evolution depends on both the strength of the climate forcing and the physics adopted in the ice-sheet model.". From what I've seen, the earth does not just float on the mantle like a raft on water, but is more still and flattened. RowanJ LP2 (talk) 19:21, 30 September 2022 (UTC)

Ambiguously defined

The intro section provides a vague definition of "mean sea level" aka "sea level" giving the impression that a reference value for sea level can depend on the system used to define and measure it.

Elaboration and explanation of the system (atmospheric pressure) used to determine sea level would improve the context for the image from the dead sea valley as an example of the use and determination of sea level as an inland vertical datum. Also, an example of the deviation of apsl relative to the sea level depicted in that image would solidify the meaning of apsl.

The final paragraph in the introductory section, regarding the radius of the earth at sea level at the equator, could be moved to a different or new section as an example of using sea level in a calculation, or removed entirely. This paragraph is inappropriate as an introductory paragraph explaining the concept of sea level. The situation of this paragraph in the introductory section seems to imply a direct measurement of the distance to the center of the Earth, which is most likely not yet achieved, or if so needs a citation to a published direct measurement. 67.161.153.127 (talk) 22:40, 16 February 2022 (UTC)