Hi, Andrzej,

Interesting work!

If you want to stress the correlation between methane and depth you might want to include isobathic lines (not too many!) in your graph. 

I´d also change the text of the legend, perhaps

a) area surveyed

b) area with high probability of methane occurrence

and please use a less bight colour to mark the land - the green attracts too much attention

best wishes

Irene

I suggest you contact the Arctic Emergency Group http://ameg.me/

or Prof Peter Wadhams of Cambridge University http://www.damtp.cam.ac.uk/user/pw11/

It makes sense since methane will only occur in anoxic zones, so, deeper waters increase the chance to have an stratified water column that will lead to the formation of bottom anoxic zones.

I assume you want comments on the map itself. So... There are a few minor things that could be changed to help with the overall layout.

I agree, the legend could be changed. Instead of having two legends on the top map, try to keep it to one. Instead of A = white, B = pink and then A) Area Surveyed, B) Area with...

Just keep it to White = Area Surveyed, Pink = Area with...

That way you don't even need the A and B.

Also, there is room between the two maps in the middle of the page. If you get rid of that space, you can take the text in the upper left corner of your map and put it above the two maps. Or another place would be to move the bottom map up and put it below both maps.

Also, I didn't see the map with green, but there should be some difference between the colors used for land and the colors used for depth. Right now you have gray for land and gray for bathymetry.  To an uniformed reader that would be confusing, I imagine. 

I'm not sure what program you're using, so these comments might not be useful since many programs aren't very easy to manipulate, but at least they can give you an idea. 

If the methane is being produced by melting methane hydrates from buried permafrost, then it could be that the shalower sea bed has already released its methane and the deeper areas are only now warm enough to release their methane.

The Baltic Sea is well known to emit a high quantity of methane during winter and less during summer. My first question is : when did you survey this zone ? The second one is : what about the biomass location compared to this mapping ? The third question is : have you crossed environment data (winds, seasonal upwellings, sea level, etc.) and my last question will be: have you any echograms  showing the vertical profile of the water column to study the layers: surface, mixted or bottom layers ?

We need more clues to comment your result...

 What you see is probably the situation of deep layer waters in the Baltic.

Just a very brief overview over the location. Surely not complete or 100% precise; but enough to understand the specific situation around the Bornholm Basin:

Due to the semi-enclosed structure, the Baltic is the largest brackish sea area in the world. We have salinities of ~8 in the upper layers. Summer parts this low saline volume into an upper warmer part. separated from the deeper low saline winter waters of lower temperatures, by a thermocline. During winter we find this winter water body from the surface down to the halocline.

This halocline is found in the area of the Bornholm Basin (as shown in your map) in a depth of ~60m. This is the hight of the Slupsk Sill. Waters of such higher salinity (around 11... >16, lingering below the lower saline water body due to their higher density) being elevated flow gradually out over the sill into the Gdanks Deep (via Slupsk channel).

The deep and saline waters are captured in the troughs of the deeper Basins from Arkona Basin->Bornholm Basin->Slupsk Channel->Gdanks Deep->.... The volume of the Bornholm Basin below 60m depth is assumed to be something around 220km3 (I hope I remenber this correctly). The captured waters often face a long period of stagnation, where no water exchange takes place. In these stagnation periods we find a layer from the bottom towards the halocline getting more and more anoxic (and also higher in methane concentrations).

Water exchange in these troughs is maily due to Major Baltic Inflow events. These are triggered by climatic events -> see Baltic Sea Index, a more local index, better suitable for the Baltic than the NAO.

So, now some questions arise: when was this situation recorded? I would expect that such a situation is not directly found after an inflow.

Can you give concentrations for the concentrations for your plot?

Some of these topics may be found in this RG paper and the references therein:

Spatial and temporal habitat partitioning by zooplankton in the Bornholm Basin (central Baltic Sea)

Bye, Jan

Article Spatial and temporal habitat partitioning by zooplankton in ...

thanks Jan Schulz. The area is  indicating the  horizontal range  of  methane ebulitions, based on  acoustic  observations and  measurements of the  sebed  properties. The area can  be  correlated with  the  small dynamics  of the  currents and correlated very  soft  sediments. Generally  it  is indicating  the  deposits of the decomposition of  materials produced  due  to  increase  of the  eurtophisation.