Why is the sea not salty round here?

I’m sitting near the sea, west of St. Petersburg. Like many locals, I still think of it as Leningrad. Down below my window, I can see the sea, the Gulf of Finland. I have not been to this part of Russia before and something puzzles me.

All the indications are that the sea water is not salty, although it is an extension of the Baltic Sea. I can’t get down to the water to test it. Anyway, I don’t want to taste it as I suspect it’s not very clean where I am.

There is no seaweed at the water’s edge. There are reeds growing in the water. Trees are growing within a meter of the water and their roots must be below water level. Mallard ducks are floating on it. All the evidence is that it is fresh water, but I know it is open sea. I can see the ships and hydrofoils travelling into Sankt-Peterburg.

Is it possible that the Neva River is producing enough fresh water to make the water fresh in this area? It’s certainly a big river, but can it produce that volume?

Gulf of Finland wiki

It looks like you’re right, but I wanted to point out that none of the diagnostic factors you mention are necessarily indicators of fresh or brackish water.

Nevea Bay isn’t really open sea, it’s an estuary. There’s a lot of fresh water flowing into it from the Nevea river, and very little salt water going the other way. The bay itself is very shallow (wiki says 6m) so there’s only a relatively small volume of water.

The salt has to come from the open ocean, but that’s far away in the Atlantic, so it’s got to flow past Denmark, across the Baltic, into the Gulf of Finland and finally into Nevea Bay. The driving force for this is tidal, and all the bodies of water mentioned above restrict the tidal flow. The only thing that makes sea water salty is evaporation - and that is in short supply in Scandinavia.

I have swum off the coast of southern Finland and it is true that it is noticeably less salty than the Irish Sea. This is a subjective impression based on taste, stinginess and buoyancy.

However you shouldn’t assume that “evaporation is in short supply”, if by that you mean that it is very cold there. In winter, yes, but Helsinki has warm and sunny summers despite being at 60 degrees north. Since the sea is shallow, the rate of evaporation per unit volume is probably quite high.

In addition, the Baltic Sea does get periodic infusements of water from the North Sea, although I don’t know if they make it all the way to the Gulf of Finland or not, so they can get their salinity from more than evaporation – they can get it from other oceanic bodies.

Still quite low compared to, say, the Persian Gulf.

In general, the salinity of any nearly enclosed arm of the sea is going to depend on the balance of freshwater influx versus evaporation. The Baltic Sea has a comparatively high salinity because it has a high influx of freshwater from rivers and relatively low evaporation. Conversely, the Red Sea has a high salinity because it has very little influx from rivers and a high evaporation.

Baltic Sea–Low salinity, you mean, right?

If I recall correctly, one of the reasons Grey whales calf in the bays of Baja California is that enclosed bays + negligable freshwater runoff + lots of evaporation make the water very salty and more bouyant for the newborns. They also offer some protection from Orcas IIRC.

Thank for your comments/discussion.

I notice a freight ship is travelling towards Sankt-Peterburg, and it seems to be lying quite low in the water. At first I thought it was a barge, designed to travel under the Neva bridges. However, its stern is quite high, like a normal ship, and if it was going up river it would have to wait for the bridges to lift at night.

I wonder if that is linked to low salinity, as the buoyancy would be affected. Of course, it may be just heavily loaded.

Low salinity *would *mean the ship sat lower in the water - the displaced water has less weight. Hence this.

Yes, ships float differently in different salinity water. See http://en.wikipedia.org/wiki/Plimsoll_Mark for more on the various classifications of water used.

What you’ll learn is that while there is an effect, it isn’t huge. A big ship may sit a foot or three differently as between fresh & high-salinity water. Meanwhile the same ship can be lightly or heavily loaded across a range of 20 or even 30 feet of draft.

So salinity does matter for safety, but if you see a ship sitting real low in the water, expect it to be heavily loaded, not in a puddle of unusually fresh water.

Ш пгуыы ьн :smack:

Oops quick Control + Shift, excuse me, using Russian key board.

I guess my query’s answered. I suspect this area has particularly low salinity, judging by the factors I pointed to - especially a healthy lime tree growing at the water’s edge, as if it was by a fresh water lake.

I still won’t taste the water, but maybe my wife will be less squeamish. She is more accustomed to the local bugs in northern Russia, and I will invite her to risk herself for the needs of science, like Franklin with his kite. The response may be rude.

two things possible: the surface output of the neva is sufficient to create brackish water out to several miles (the amazon produces brackish out to as much as 50 miles) or, underground solution channels dump more fresh water out to sea more than the river does.