Info on Sea Floor - Black Sea

[Pillar]

I'm looking for a resource on actual sea floor data for different parts of the world, but specifically the Black Sea. Does anyone know of any on the web?

[Pillar]

Nobody?

How about more generally - at what floor depths would I expect to find mud, sand or rock?

[Hitman]

Hello Pillar,

see if this helps you: http://blacksea.orlyonok.ru/e2.shtml

Cheers

[Pillar]

Perfect! Hitman you are my hero!

This is the relevant portion of the site:

Bottom relief of the Black Sea

Black Sea is deep; central area of its bottom is an abyssal plain at 2000m depth, covered by silt sediments, it is an accumulation area of the basin. Maximal depth of the Black Sea is 2210m.



Black Sea shelf is a low gradient underwater slope to 100-150m depth; the shelf narrow (1-2.5km) at the mountainous coasts of the Black Sea (Caucasus, Crimea, Anatolia). The shelf is terminated by the abrupt (up to 20-30о) basin slope to the basin apron area with depths over 1000m. An exclusion is the shallow Nor-Western part of Black Sea all belonging to the shelf zone; actually it is not a part of the Black Sea hollow.



Bottom Sediments of the Black Sea

Nearshore shallow bottom is an underwater continuation of the beach: various types of sand or big rocks. Starting at 30-50 meters depth slow shelf slope is covered by sand, different size gravel, and molluscan shells. As the depth is growing, mussel Mytilus galloprovincialis shells are changed to Modiolus phaseolinus shell fragments; even deeper broken molluscan shells form fine silt covering the rest of Black Sea shelf.



Thickness of sediment layer of Black Sea abyssal plain varies from from 8 to 16 km, thicker in the Western part of the Sea, bordered by the central Black Sea meridional rise. Thickness of the recent sediments layer, accumulated during the last 3000 years of the modern Black Sea history is 20 to 80cm depending on the bottom region.



Sediment layer rests on the 5-10km thick basalt plate that covers the mantle. Intermediate granite layer between sediment and basalt layers is absent in the Black Sea (some fragments of granite layer were found in the Eastern part of the abyssal plain). Thus the Black Sea bottom exhibits features typical for the Ocean bottom.

Am I reading this correctly - that a "rocky" bottom in DW terms would typically represent *Basalt* and not Granite?

Also, most of the ocean floor is a layer of sediment (silt say) covering basalt?

If the answers are affirmative, this makes me wonder where one would find a *rocky* bottom... I've been playing DW (self made scenarios often) with rocky bottoms way too much.

Thanks mate...

[Pillar]

Some general info for anyone interested...

Most of the ocean floor is Basalt (volcanic rock), but you'll get granite off a continental shelf (a steep cliff near the continents underwater). Anywhere near land there is a layer of silt ("sand" bottom type) with a thickness varying according to how far from land you go. Closer to land, particles are bigger and there are lots of them, and smaller stuff gets transported farther out. I'm not sure yet what the distances are, but they are large enough. I mean, we're not talking beaches and shorelines, but miles and miles. More on that as I find info.

Where does the floor turn into pure basalt? For one thing, anywhere you get a *ridge* of the plates you're going to have mostly basalt, i.e. "rock" bottom. The silt stays in the basin and the plates force their way up, for a double-whammy as far as creating pure rock bottom's go.

As for DW, how much of this matters? Generally any time the bottom is within a reasonable distance of the layer, it's going to be silt, as far as I can gather. I'm not 100% sure on that, but indications so far are that this is the case. (Except for ridges.) The deeper regions will have basalt bottoms, mostly because they are farther away from the continents, but then the sound channel there is so deep I'm not sure it effects anything in DW. Essentially the floor becomces "bottomless" at these depths, as sound is concerned.

Just some thoughts, correct me where I'm wrong.

[Dr.Sid]

In DW bottom type seems to be simple multiplication of how far sound travels. Rock is best, mud is worst, sand is something in the middle. You can translate it into 'Sound propagation distance: long, medium, short' .. AFAIK it has no other effect.

[Deamon]

Ahhh, this is good stuff. Brings back memories about the times I was so immersed into it and so obsessed with this subject

[Kapitan]

Time to get my submarine back from overhaul and re load and re crew her for a few more missions as she has been neglected for a long time now, have you ever tried to get through between alaska and russia into the pacfic ie the bearing straights thats a challenge and a half !

it would make a black sea cruise look simple.

[bottomcrawler]

Originally Posted by Pillar

Some general info for anyone interested...

Most of the ocean floor is Basalt (volcanic rock), but you'll get granite off a continental shelf (a steep cliff near the continents underwater). Anywhere near land there is a layer of silt ("sand" bottom type) with a thickness varying according to how far from land you go. Closer to land, particles are bigger and there are lots of them, and smaller stuff gets transported farther out. I'm not sure yet what the distances are, but they are large enough. I mean, we're not talking beaches and shorelines, but miles and miles. More on that as I find info.

Where does the floor turn into pure basalt? For one thing, anywhere you get a *ridge* of the plates you're going to have mostly basalt, i.e. "rock" bottom. The silt stays in the basin and the plates force their way up, for a double-whammy as far as creating pure rock bottom's go.

As for DW, how much of this matters? Generally any time the bottom is within a reasonable distance of the layer, it's going to be silt, as far as I can gather. I'm not 100% sure on that, but indications so far are that this is the case. (Except for ridges.) The deeper regions will have basalt bottoms, mostly because they are farther away from the continents, but then the sound channel there is so deep I'm not sure it effects anything in DW. Essentially the floor becomces "bottomless" at these depths, as sound is concerned.

Just some thoughts, correct me where I'm wrong.

While the ocean floors are made up of basalt, you almost never have any bare rock down there. Only very close to the spreading mid-ocean ridges will sediments not have had time to cover the sea-floor appreciably.

Different parts of the oceans have different kinds of bottoms. In areas with lots of biological productivity at and near the surface, dead organisms will slowly fall to the sea floor and accumulate. Below the CCD (Carbonate Compensation Depth), no calcium carbonates (essentially calcite and aragonite - i.e. mollusc shells) will accumulate as they are completely dissolved on their way down.
Where the CCD surface is lower than the ocean floor, carbonates can accumulate and will then form a carbonaceous ooze together with the fine clay that always sediments all over the world's oceans (the fine particle size that defines clay enables it to stay suspended in both air and water for very long times, months to years).

In some areas, mostly areas of large-scale upwelling such as parts of the Pacific coast of South America, siliceous ooze forms instead because of the silica surplus in deep water reaching the productive surface layer.

Where productivity is low or where the CCD is above the ocean floor, only clay particles settle, forming "red clay".

The thickness of the sediments (i.e. the depth from the ocean bottom to the basalt) varies depending on the age of the ocean floor at any given location. Newly formed crust near the mid-ocean ridges will only have a few thousand or million years of sediments, and given the extremely slow rate of sedimentation (~1-10 mm/1000 years) in the open oceans, the thickness will be a few meters or so.
However, the oldest parts of the oceanic crust are around 300 million years old, and these are also closer to coasts, where sedimentation rates are higher, so thicknesses of several kilometers is to be expected.
Where the sediments are thicker than several tens of meters, different processes gradually turn the unconsolidated sediments into solid rock.

The above is true for ocean bottoms, but the shelf areas are a different matter. There, coarser sediment is washed out from land, forming sandy, silty, clayey or muddy layers, depending on the environment. Where the sea surface temperature is sufficiently high and the supply of terrigenous sediment is low, carbonate deposits form (forming limestone eventually).

In shallow areas, where the storm wave base reaches the bottom or where strong bottom-hugging currents flow, erosion can occur, or at least a diminished rate of deposition, so that the bare rock is exposed, but that really only happens at depths up to 20-30 m. Bare rock could be almost anything, but generally similar to the surface rock found at the nearest coast, unless it's sedimentary shelf material, in which case it's likely sandstone, mudstone or limestone.

Probably my longest first post in a forum ever...

[Deamon]

Thanks bottomcrawler, good stuff!

[LoBlo]

Originally Posted by Deamon

Thanks bottomcrawler, good stuff!

Ditto. That was some good stuff.

[Pillar]

Really excellent stuff, very helpful. Thanks BC.

[bottomcrawler]

Thanks!

But I realise that I didn't really answer the original question. The Black Sea is neither ocean nor shelf...

What I do know, though, is that The Black Sea is strongly stratified, with a "normal" upper water layer, and a bottom layer that is severely anoxic and practically devoid of life. The bottom is likely made of black organic-rich mud, typical of anoxic conditions. It's probably also very soft and practically grades from a dense cloud of suspended/semi-suspended particulate matter to a solid, homogenous and very wet mud. But that's just a guess, based on what I've seen myself from cores taken in fjords with anoxic bottom layers.

I would expect such a bottom to absorb sound extremely well and weaken reflections substantially. But that's another guess.