Ocean circulation
Why stronger stratification is changing ocean tides
Open access · cc by · source: Europe PMC
Model and satellite M2 trends since 1993 point to stronger ocean stratification increasing tidal conversion, not just sea-level rise.
How this study connects
Role on claims
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Yearly internal-tide-permitting MITgcm runs relaxed to reanalysis stratification (1993–2020) produce coastal M2 trends of about 0.1 mm/yr that match roughly half of ten tide-gauge cases. Open-ocean M2 is mostly declining; the 3-D runs capture about 60% of satellite regional trends, while relative sea-level rise explains ≲20% at most open-coast sites. German Bight decline is not explained; Northwest European Shelf results are sensitive to steric corrections; altimetry still has uncorrected systematic errors.
Evidence for the claim as stated.
Altimetry, tide gauges and a 3-D tide model do not tell the same M2 story everywhere. Stratification-driven runs capture about 60% of satellite regional trends and about half of ten gauges, but they miss the German Bight decline, and the authors flag uncorrected altimeter systematic errors. A 2-D sea-level-rise tide model explains ≲20% of open-coast change, so blaming M2 trends on mean sea-level rise conflicts with both the 3-D runs and the satellite residual.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
Altimetry, tide gauges and a 3-D tide model do not tell the same M2 story everywhere. Stratification-driven runs capture about 60% of satellite regional trends and about half of ten gauges, but they miss the German Bight decline, and the authors flag uncorrected altimeter systematic errors. A 2-D sea-level-rise tide model explains ≲20% of open-coast change, so blaming M2 trends on mean sea-level rise conflicts with both the 3-D runs and the satellite residual.
Study at a glance
- Design
- Computational / modelling — Yearly internal-tide-permitting MITgcm runs relaxed to reanalysis stratification, compared with altimetry and tide gauges
- N
- 1993–2020 simulations; coastal M2 trends matched about half of 10 tide-gauge cases
- Population
- Global ocean M2 tide, 1993–2020
- Outcome
- Strengthening stratification, not sea-level rise, accounts for much of the observed long-term M2 change
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Inspect source passages
Why stronger stratification is changing ocean tides
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Simulations typically capture 60% of the satellite M2 trend estimate.
Our simulations typically capture 60% of the satellite estimate, pointing to a residual that may arise from model limitations, subtle errors in the altimetry solution, or both (Methods).
Over what period are stratification-forced tide trends diagnosed?
Emphasis is on trends from 1993 to 2020, a period where we have suitable three-dimensional (3D) density data.
Key findings
Stratification-driven coastal M2 trends are about 0.1 mm/yr and match roughly half of ten tide-gauge cases. Open-ocean M2 is mostly declining; the 3-D runs capture about 60% of satellite regional trends, while relative sea-level rise explains ≲20% at most open-coast sites.
Methodology
Authors ran yearly internal-tide-permitting MITgcm simulations relaxed to reanalysis stratification for 1993–2020 and compared M2 trends with altimetry, tide gauges, and a 2-D sea-level-rise tide model.
Limitations
German Bight decline is not explained by these runs; Northwest European Shelf results are sensitive to steric corrections, and altimetry still has uncorrected systematic errors.
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