REVIEW 2 major objections 2 minor
Internal wave mixing in warming Lake Grevelingen
T0 review · 2 major / 2 minor · reviewed 2026-05-24 · grok-4.3
Pith's one-line read Turbulent mixing from internal waves in Lake Grevelingen warms near-bottom waters over summer but cannot prevent anoxia from biological oxygen consumption.
desk verdict This is a short observational report giving turbulence numbers from a 3-day spring mooring in one Dutch lake; the summer extrapolation is the main uncertainty. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
High-resolution temperature sensors moored with a current meter to compute local eddy diffusivity and turbulence dissipation rate from observed temperature and velocity fluctuations in a stratified coastal basin.
What would settle it
A full-summer mooring record or direct bottom temperature and oxygen observations showing integrated turbulent fluxes inconsistent with the reported mean Kz of 4 x 10^{-5} m2 s^{-1}.
Extended reading notes
Core claim
In Lake Grevelingen, internal wave motions supported by the stratification generate episodic shear-driven turbulence that produces an average vertical turbulent exchange sufficient to warm the near-bottom waters over the course of summer but insufficient to prevent the biology from over-consuming oxygen contents.
Load-bearing premise
The three-day mid-spring mooring record captures the typical turbulent mixing rates that occur throughout the summer when anoxia develops at the site.
Editorial extensions
If this is right
- Near-bottom waters warm gradually due to the integrated turbulent heat flux over summer.
- Oxygen levels drop to anoxic conditions because turbulent oxygen supply cannot match consumption.
- Turbulence is episodic rather than continuous, tied to cooling events, winds, and wave breaking.
- A layer of weak turbulence persists just below the main pycnocline, as seen in freshwater lakes.
Reading between the lines
- In other stratified coastal basins, internal-wave mixing may routinely set heat budgets while leaving oxygen budgets biology-dominated.
- Longer seasonal records would test whether spring-derived diffusivity values hold when anoxia is actively developing.
- Management focused on lowering respiration rates could prove more effective than attempts to increase physical mixing.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports three-day mid-spring mooring observations of temperature and currents in 36 m depth in Lake Grevelingen. It derives a 30-m mean eddy diffusivity <Kz> = 4±2×10^{-5} m² s^{-1} and mean dissipation rate <ε> = 1.1±0.6×10^{-7} m² s^{-3}, attributing episodic turbulence to night-time cooling, wind events, sparse internal-wave breaking at the pycnocline, and near-bottom shear. The authors conclude that these rates suffice to warm near-bottom waters over summer but are insufficient to offset biological oxygen consumption that produces anoxia.
Significance. Direct, in-situ quantification of internal-wave-driven mixing in a tidally refreshed coastal basin is valuable for separating physical and biological controls on seasonal hypoxia. The work supplies concrete numbers for Kz and ε without model fitting or parameter tuning, and the episodic character of the mixing is clearly documented. The short record and spring timing, however, leave the seasonal extrapolation as the primary uncertainty.
major comments (2)
- [Abstract] Abstract: The claim that the observed turbulent exchange 'is sufficient to warm the near-bottom waters over the course of summer, but insufficient to prevent the biology from over-consuming oxygen contents' rests on applying the three-day mid-spring <Kz> and <ε> values throughout the summer. No supporting analysis shows that the time-averaged fluxes remain unchanged once the main pycnocline strengthens and internal-wave critical layers or shear production evolve under fully developed summer stratification.
- [Abstract] Abstract and mooring description: The reported mean values and uncertainties are stated directly, yet the manuscript supplies no information on data processing steps, quality control, sensor calibration, or the precise method used to convert the high-resolution temperature and current records into the quoted Kz and ε estimates. These quantities are load-bearing for both the physical results and the seasonal conclusion.
minor comments (2)
- [Abstract] The abstract states that shear-driven turbulence 'is not commonly found in fresh-water lakes' and that a weak-turbulence layer exists 'just below the main pycnocline around mid-depth, as in fresh-water lakes.' A brief comparison of the observed shear production mechanisms with typical lake literature would clarify the distinction.
- [Abstract] Notation: The abstract uses <[Kz]> and <[epsilon]> with square brackets; consistent use of angle brackets or an explicit definition of the averaging operator would improve readability.
Simulated Author's Rebuttal
We thank the referee for the constructive assessment and for highlighting the value of the in-situ observations. We respond point-by-point to the major comments below.
read point-by-point responses
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Referee: [Abstract] Abstract: The claim that the observed turbulent exchange 'is sufficient to warm the near-bottom waters over the course of summer, but insufficient to prevent the biology from over-consuming oxygen contents' rests on applying the three-day mid-spring <Kz> and <ε> values throughout the summer. No supporting analysis shows that the time-averaged fluxes remain unchanged once the main pycnocline strengthens and internal-wave critical layers or shear production evolve under fully developed summer stratification.
Authors: We agree that the seasonal extrapolation rests on an assumption that cannot be verified with the available three-day spring record. The manuscript already notes the episodic nature of the mixing and the short duration, but we will revise the abstract and add a paragraph in the discussion to explicitly qualify the conclusion as conditional on the observed spring rates persisting and to highlight the uncertainty arising from potential changes in pycnocline strength and internal-wave dynamics under stronger summer stratification. revision: partial
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Referee: [Abstract] Abstract and mooring description: The reported mean values and uncertainties are stated directly, yet the manuscript supplies no information on data processing steps, quality control, sensor calibration, or the precise method used to convert the high-resolution temperature and current records into the quoted Kz and ε estimates. These quantities are load-bearing for both the physical results and the seasonal conclusion.
Authors: The full manuscript contains a dedicated methods section describing the mooring setup, sensor specifications, and the Thorpe-scale approach used to estimate Kz together with the dissipation-rate calculation from the current-meter shear. However, we acknowledge that these steps are not sufficiently detailed or self-contained in the current version. We will expand the methods section with explicit descriptions of data processing, quality-control criteria, sensor calibration procedures, and the precise conversion algorithms, including uncertainty propagation, to ensure reproducibility. revision: yes
- Absence of summer observations that would allow direct verification of whether time-averaged Kz and ε remain similar once the pycnocline strengthens.
Circularity Check
Observational paper reports direct measurements with no derivation or fitting chain
full rationale
The manuscript computes time-averaged eddy diffusivity <Kz> and dissipation rate <ε> directly from high-resolution temperature and current-meter data collected over three days. These quantities are presented as observed values without any parameter fitting to a data subset, self-referential definitions, or renormalization that reduces the reported numbers to prior inputs. The statements on sufficiency for summer warming and oxygen consumption are straightforward inferences from the measured fluxes, not outputs of a closed derivation loop. No load-bearing self-citations or uniqueness theorems appear in the provided text. The analysis is therefore self-contained against external benchmarks.
Assumptions & free parameters
Cite this review
Pith. "Pith review of Internal wave mixing in warming Lake Grevelingen." pith.science (2026). https://pith.science/paper/2BIA3BHR
@misc{pith2026190711410,
author = {Pith},
title = {Pith review of: Internal wave mixing in warming Lake Grevelingen},
year = {2026},
howpublished = {\url{https://pith.science/paper/2BIA3BHR}},
note = {Machine review of arXiv:1907.11410}
}
read the original abstract
Seasonal hypoxia or even anoxia can occur in some local deep basins of coastal waters. Such low summertime oxygen contents especially affect benthic life. The seasonal coastal hypoxia is commonly related to biological increased respiration and to physical limited vertical turbulent exchange that is associated with increased vertical stable density stratification. However, the same stratification can support internal waves that may break and locally generate turbulence. Here, we investigate the physics of internal wave motions in saltwater Lake Grevelingen (SW-Netherlands) during warming in mid-spring. Grevelingen is refreshed by weak tidal motions through an open sluice in its dam to the North Sea. The outer North Sea has a surface tidal range of about 3 m, but the lake surface tidal range is negligible (<0.1 m). To quantify vertical turbulent exchange, high-resolution temperature sensors were moored in conjunction with a current meter in 36 m water depth for three days. The site is known for anoxic conditions near the bottom in summer. While a 3-day, 30-m mean eddy diffusivity of <[Kz]> = 4+/-2x10-5 m2 s-1 is found, the overall mean turbulence dissipation rate (turbulent flux) is <[epsilon]> = 1.1+/-0.6x10-7 m2 s-3. Turbulent mixing occurs episodically, via near-surface cooling during night and increased winds, via sparse shear-driven breaking of internal waves at the main pycnocline, and via sheared near-bottom currents. Shear-driven turbulence is not commonly found in fresh-water lakes. Just below the main pycnocline around mid-depth a layer of weak turbulence is observed, as in fresh-water lakes. The observed turbulent exchange is sufficient to warm the near-bottom waters over the course of summer, but insufficient to prevent the biology from over-consuming oxygen contents.
Reviewed May 24, 2026 · model on record in the stance chip above.
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