the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
A field study on ice melting and breakup in a boreal lake, Pääjärvi, in Finland
- 1State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China
- 2Lammi Biological Station, University of Helsinki, Finland
- 3Department of Civil, Environmental and Mechanical Engineering, University of Trento, Italy
- 4Institute of Atmospheric and Earth Sciences, University of Helsinki, Helsinki, Finland
- 5Water Conservancy and Civil Engineering College, Inner-Mongolia Agricultural University, Hohhot, China
- 6College of Water Conservancy, Shenyang Agricultural University, Shenyang, China
- 1State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China
- 2Lammi Biological Station, University of Helsinki, Finland
- 3Department of Civil, Environmental and Mechanical Engineering, University of Trento, Italy
- 4Institute of Atmospheric and Earth Sciences, University of Helsinki, Helsinki, Finland
- 5Water Conservancy and Civil Engineering College, Inner-Mongolia Agricultural University, Hohhot, China
- 6College of Water Conservancy, Shenyang Agricultural University, Shenyang, China
Abstract. Lake ice melting and breakup form a fast, nonlinear process with important mechanical, chemical, and biological consequences. The process is difficult to study in the field due to safety issues, and therefore relatively little is known about its details. In the present work, ice monitoring was based on foot, hydrocopter, and boat to get a full time-series of the evolution of ice structure and geochemical properties through the melting period. The field observations were made in Lake Pääjärvi during the ice decay periods in 2018 and 2022. In 2022, the maximum thickness of ice was 55 cm with 60 % snow-ice, and based on the data and heat budget analysis, the ice melted by 33 cm from the surface and 22 cm from the bottom while porosity increased to 40–50 % at breakup. In 2018, the snow-ice layer was small and bottom and internal melting dominated during the decay. Due to global warming, the ice breakup date became earlier. The mean melting rates were 1.31 cm d–1 in 2022 and 1.55 cm d–1 in 2018. In 2022 the electrical conductivity (EC) in ice was 11.4±5.79 S cm–1, one order of magnitude lower than in the lake water, and ice pH was 6.44±0.28, lower by 0.4 than in water. pH and EC of ice and lake water decreased along the ice decay except slight increases in ice due to flushing by lake water. Chlorophyll a was less than 0.5 g L–1 in porous ice, approximately one-third of that in the lake water. These results are important for further development of numerical models and understanding the process of ice decay with consequences to lake ecology and to safety of ice cover for human activities.
Yaodan Zhang et al.
Status: final response (author comments only)
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RC1: 'Comment on tc-2022-232', Anonymous Referee #1, 09 Jan 2023
The study presents detailed observations on variations of lake ice properties during two melting periods in a boreal lake. The observations encompass ice structure, porosity, density, biogeochemical characteristics (pH, electrical conductivity, Chlorophyll a) and were performed at daily to weekly intervals covering the latest stages of the ice-covered period. The study design and the approach are relevant to the state-of-the-art of the lake ice studies. The newly collected data have a potential to make a valuable contribution to the current knowledge on the mechanisms of the seasonal ice cover melt.
The presentation of the results is however extremely hard to follow, too lengthy and poorly structured. Description of methods pops up in the middle of results presentation, while new introductory information and collateral results, which are only loosely connected to the subject of the study, unexpectedly start the discussion part. The authors should analyze, synthesize, summarize and---finally---present scientific results in a concise, well-structured way.
Endless recitation of dry unbound numbers throughout long paragraphs, repeating the information presented in tables, without an integrated analysis of the field information is redundant and superficial. Last but not least: the poor language and style make the study hard to read. Overall, the style reminds that of a plain field report rather than a research paper. Many sentences are barely understandable because of poor English use. Reworking of the text with significant shortening, restructuring and language improvement is strongly recommended. The length of the ms should conform to the amount of the reported results, which suggest shortening it by 1/3-1/2. Below are some specific comments aimed to provide guidance on the revision. The comments are aligned with the text flow. The remarks on language and style are not exhaustive and serve just as the most evident examples.
L49 “structure” -> “structures”
L56: “physics of climate sensitivity…” poor wording
L61: “seasonal” -> “seasonally”
L67: “productive” -> “production”
L69: remove “the extent to”
L72: “protects the ice..” from what? Remove “by its presence”
L73: “immediately when” -> “immediately after”
L79: “difficult conditions”: difficult for what?
L80: “melt rate” -> “rate of melt” or “melting rate”
L86: “has reached” -> “reaches”
L171: “unifiltered” -> “unfiltered” (?)
L173: “high accuracy” -> provide the accuracy values.
L176: “long wavelength” -> provide the wavelength range
L192: add the spatial scales and explain the color scale in Fig. 2
L195-196: remove “As we can see from Fig 3a-f”, add “(Fig 3a-f)” at the end of the sentence.
L200: “became more and more” -> “increased”
L207-208: “rachis-shaped” revise wording
L212: Remove “Then”
L213: “temperature rose…” Temperature of what? The same for L217
L226-236: Fig 3 is not comprehensible and should be shortened to present the essential information only.
L244-254: The paragraph mostly repeats information from Table 2 and should be shortened to 1-2 sentences.
L262: Equation 1 is wrong.
L264-265: revise the style of the sentence
L277-279: awkward phrasing. Revise the sentence
L303 and elsewhere: “S cm^-1” Is it “uS cm^-1”? Check the units across the entire text.
L307: remove double “in”
L315: shorten Table 5, remove information repeating Fig. 5
L339, Section 4: The section represents the rare attempt to analyze the observed data beyond their straightforward listing. However, the heat budget model, as presented here, is rather crude and lacks support by background physics of the heat exchange between air and ice surface. The monthly climatic means of solar radiation are too rough for such a model and can be replaced by data from reanalysis or nearby weather monitoring for the actual dates. Assumption of constant albedo is also weakly supported for the melting periods, especially with snowfall and rain events. Several approaches exist for albedo parameterization, with the simplest ones based on air temperature. Still, one could expect even more sophisticated albedo parameterizations, taking into account the detailed information on ice properties and drone images of the surface conditions. There is no clear model described for the long-wave radiation budget in the ice-air system and for the sensible/latent fluxes at the ice surface. By this, the inconsistency of the oversimplified model with the data (L376-378) is not surprising. The approach should be deeply revised based on the current knowledge on the surface heat budget.
L388, Section 5.1: This section appears absolutely unexpected and does not fit in line with the general flow of the study. Section is an odd mix of newly presented data lacking a thorough analysis of their relevance, statistical significance and processing methods (Figs. 6-7) with unnecessary common places (L411-412), and information on ice phenology from other lakes irrelevant to the subject of the study. The whole section reads inorganic and should be either removed or deeply revised with proper redistribution between methods, results and discussion, including adequate analysis of data reliability.
L430, Section 5.2: “comparisons with ice melting” - comparisons of what? The section title is senseless.
L453: “if further generalized…” This generalization _is_ actually what the reader expects from the authors at this point: generalize your results and put them into the context of the present knowledge on the subject. The whole section should be deeply revised. Move Fig. 8 with the accompanying data to Results and write a new, more focused discussion.
L526-527: “...a surge of phytoplankton…” - Do you mean a phytoplankton bloom? If yes, can you demonstrate a correlation between pH variations and Cl_a content? This passage reads too speculative and unsupported. Revise it, demonstrating support by data analysis, or remove completely.
L555-556: Awkward sentence, should be revised or removed.
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RC2: 'Comment on tc-2022-232', Anonymous Referee #2, 09 Jan 2023
The manuscript focused on the melting regime of lake ice, which has been seldomly investigated despite its crucial impacts on ice break-up, air-lake mass and heat exchange, and lake habitats and ecosystems. The manuscript, using varied technologies, investigated the melting rate, the evolutions of lake ice texture, pore, and crystalline structure, and the concurrent pH, EC, and Chl-a profiles with their relationships with the decaying ice. These observational results are quite important to understand the ice breakup regime and its effects on lake habitats and ecology.
However, the manuscript is too long and poorly-structured and is suffered to linguistic issues, so it is not easy to follow what the authors wanted to deliver to readers. E.g., there are a number of repetitions of sentences in the text, which can be removed or shortened. I am not sure of if the section 5.1 should be presented in Results or Discussion. I recommend that the manuscript should reorganized and carefully language-checked when revising.
Intuitively, the manuscript is more like a report presenting the techniques and straight results than a scientific paper. It should be more focused and tightly compact on what you found and why. In short, the authors observed the melting rate, internal texture with estimated porosity, and basic ice+water geochemistry. It would better if the manuscript directly present the methods and results and discuss what controls the surface, bottom and interior melting, how these melting are related to the evolution of pH\EC\chl-a, and how it expands/deepens our knowledge on lake ice decay and accompanying changes in lake environment, so the interannual variations of ice breakup date and bearing capacity discussion seem redundant and not closely related to the topics.
Below, I have some specific comments and suggestions, which can be considered by the authors during revision.
- L31: by/through altering the heat, mass…
- L36: the under-ice living conditions or the living conditions under the ice
- L43: please specify what the two major practical problems are.
- L53-54: I guess “by about one week over 100 years” is actually true for e.g. boreal lakes? Should be specific here.
- L67: the primary production
- L69: limits the proper assessment of the impacts of…
- L71-90: I suggest this paragraph can be divided to several short paragraphs according to their key points. At its current status, it is not easy to clearly understand what the authors want to tell to the readers.
- L91-98: I guess in this paragraph the authors should introduce briefly the scientific issues to be targeted, what work and analysis has been done, and what problems could be resolved. The snow and ice conditions may be better to be presented in the “2.1 study site”.
- L125: delete “lateral”?
- L164: delete “Measurements of ice density can be found in several studies (Timco and Frederking, 1996).”
- L169-176: please add the measuring accuracy for each variable.
- Table 1: what did x and z denote?
- Figure 2: please add a scale to these maps.
- L221: due to
- (1): there must be mistakes in this equation since it was not consistent with the description bellow it and I cannot see Lf and Δt in the formula.
- L295-296: delete “In practice it is difficult to determine the freeboard/draft ratio as it requires an order of one-millimetre accuracy for the freeboard.”
- Table 5: It would be better if these data can be presented in a plot/plots (i.e., vertical profiles), which can show clearly the vertical structures and temporal variations of EC, pH, and Chl-a.
- L322: how did the data of EC on April 14 confirm the deposition of acidic substances from the atmosphere? And why did EC of ice increase after a snowfall?
- L333-334:“Algae can grow in a slush layer within snow-ice, but not in consolidated ice because of lack of liquid water for living organisms.” However, Fig. 5b shows clearly the Chl-a content in congelation ice increases gradually as melting proceeds. The increase in Chl-a content within the ice is likely to result from the increasing solar radiation and/or the decreasing surface albedo rather than the thinning ice cover.
- (3): it would be better if you present briefly the physical meaning of each formula.
- L359: 4 W m-2 can not be a half of the incoming solar radiation in May.
- L363: does the bottom melting depend on the solar radiation?
- L367: what do you mean by “γ represents the fraction of light in solar radiation”? I guess it is the fraction that penetrates through the ice surface.
- L368: by Qs0=150W m-2, is it the daily-averaged value? It looks like a daytime-averaged value in April. If this is true, Qs0≈75 W m-2, the melt rate can be 0.16 cm d-1, close the observed rate of 0.18 cm d-1.
- (6): Could please give a brief physical background of this equation? What do the terms mean at the right-hand side?
- L389: the second “freezing” should be “melting”
- L397: what do you mean by “the ice freezing days”? freezing duration, or ice-covered duration?
- L433: after the net radiation becomes positive? The net radiation is always positive, I guess. And whether or not the surface, interior, and bottom melting take place depends on different conditions of heat balance.
- L467: “Yang et al. (2012) modelled…too late”, what do you mean?
- L482: “Therefore, … on the structures.”, what do you mean?
- L527: a surge of phytoplankton under ice may indicate a positive net production, which uses CO2 to produce oxygen and biomass, so why it results in an increase of CO2? Could you explain on it a bit more? Maybe the inflow dominates the chemistry regime of the surface layer as is shown in Fig.9?
- Conclusions: Usually, in the conclusion section, notable technologies, results and findings should be presented as well as brief implications if any rather than research background and motivation. Key points that were found in present work were missed here. So I recommend to reorganize this section.
- L555: The present paper/investigation has filled…
Yaodan Zhang et al.
Yaodan Zhang et al.
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