the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Aug 2024
Current structure, circulation and transport in the Central Baltic Sea observed by array of moorings and gliders
Abstract. An array of moored current meters and gliders were deployed across the Central Baltic Sea. Weak and low persistent currents driven by the wind-driven Ekman transport were observed in the upper layer in the offshore area. Stronger currents with higher persistency were observed near the coast, presumably driven by the local sea level gradient. The kinetic energy was largely observed to be in the low-frequency band (timescales >36 h), but higher kinetic energy on shorter timescales was observed in the areas, where the halocline was close to the seafloor. A strong and highly persistent gravity current was observed in the near bottom layer of the Fårö sill. Circulation pattern, current structure, and meridional transport varied on synoptic and seasonal timescale due to changes in local forcing and caused changes in the water column habitats. A low persistent, cyclonic gyre in the upper layer and meridional transport to the north in the deep layer prevailed in the seasonal (3–4 months) timescale. Circulation patterns with higher persistency formed under stable forcing. A cyclonic circulation in the upper layer was supported by southerly winds and reversed by northerly winds. Northward transport in the deep layer was intensified by northerly winds and reversed by southerlies. Due to the seasonality in the meridional wind component, the pattern associated with northerly (southerly) wind is more common in spring and summer (autumn and winter).
The deep-water transport is approximately 400 km3 y-1 towards the Northern Baltic Proper, which is almost 1/3 of the total deep-water volume in the Northern Baltic Proper, Gulf of Finland, and Western Gotland Basin. This transport mostly occurs during spring and summer and brings denser, oxygen-depleted water to the deep layer of these areas.
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Status: open (until 02 Dec 2024)
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RC1: 'Comment on egusphere-2024-2272', Anonymous Referee #1, 17 Nov 2024
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The manuscript "Current structure, circulation and transport in the Central Baltic Sea observed by array of moorings and gliders" is a description of one year of mooring and glider observations in the Central Baltic across roughly 58.4N. The paper is descriptive of the physical oceanography of the region. This domain displays estuarine dynamics since it is a shallow (~250 m or less), semi-enclosed, saltwater body.
Abstract:
-combine to make one paragraph
- "changes in water column habitats" is mentioned in the abstract but not discussed in the text. please remove from the abstractIntroduction:
- The study "addresses the knowledge gap regarding the current structure and circulation in the Central Baltic Sea." The authors need to provide a better scientific background and reason for completing the study. In the last paragraph of the introduction, the authors describe 4 specific scientific goals of the study. Please describe why you are studying these four items into the first paragraph of the introduction.
- Please remove the sentence "On the one hand, the pycnoclines determine the current shear maxima, but on the other hand, the current structure shapes the pycnoclines" - this statement is vague and not necessary in the introduction.
- The introduction would benefit from a schematic showing what is known about the Central Baltic from modeling studies (and some observations). It would be relevant to the paper to synthesize what is known for the specific study region of the paper.
- Similarly, the paper does not label the Faro Sill on the maps in a way that is clear to me. Please show me the location and bathymetry of Faro Sill. (Could be a part of the schematic)
- On figure 1, what is FD, ND, GD?Methods:
- Please merge the paragraphs that are only one sentence.Results:
- As part of figure 2, include a plot of wind direction
- Line 216 - since you describe there being 3 water masses, you should plot the three water masses on a T-S diagram
- In figure 2, what glider observations were used to make the temperature, salinity, and N^2 plots? All the data? How are they averaged? (in space? in time?)
- Line 226 - A three layer pattern due to the plots of Fig 3 and 4 is not clear. 1) the plots do not show full water column ADCP velocity for most of the mooring sites 2) There is variable bottom depth of the different mooring locations compared to the glider locations to which you are comparing. 3) M5 shows no high shear squared region. I suggest removing this analysis because I do not think that it is strong.
- Line 228 - You state that the current is weaker offshore, but this is not true at M2 and M3 where the current is stronger compared to M4 and M5.
- Line 249 - change peed to "speed"
- Line 250 - Since you compare the speeds of the mean profiles, also plot the standard deviation of the mean speed profiles in figure 5.
- figure 9 - Clearly label the figure's color bar limits that describe the value of correlation. Alternately, make the colorbar go from zero to one.
- Figure 12 - is there a weighted mean employed to achieve the plots from the glider observations? Describe in the methods if too much detail to put in the figure caption.Conclusions:
- Move the first sentence "The first results of the CABLE study were presented" to the last paragraph in the conclusion.Citation: https://doi.org/10.5194/egusphere-2024-2272-RC1
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