Regions of colour in the coastal sea

For the discussion of the sciences. Physics problems, chemistry equations, biology weirdness, it all goes here.

Moderators: gmalivuk, Moderators General, Prelates

User avatar
SpitValve
Not a mod.
Posts: 5129
Joined: Tue Sep 26, 2006 9:51 am UTC
Location: Lower pork village

Regions of colour in the coastal sea

Postby SpitValve » Mon Sep 03, 2007 3:12 am UTC

So when I was flying from Wellington to Auckland up the west coast of the north island of new zealand, I had a good window seat. I noticed that the water near the coast was browner than the water further out - which makes sense, the water is shallower there so dust stirred up from the sea-floor is more likely to reach the surface.

What puzzled me is that there often seemed to be quite sharp borders between regions of different brown-ness. So you'd have a browny region by the coast, then suddenly it changes into a less brown region, which then suddenly changes into a greeny-blue region. And the interfaces between the regions didn't appear to be following the coastline or anything like that.

so... any ideas?

zealo
Posts: 321
Joined: Sun Dec 17, 2006 11:36 am UTC
Location: perth, australia
Contact:

Postby zealo » Mon Sep 03, 2007 3:29 am UTC

i've noticed this while in boats, driving along and it suddenly changes from dirty to clear (it's algae that makes it that color btw, not dust).

i've always assumed it had something to do with the currents

prysorra
Posts: 45
Joined: Mon Jun 18, 2007 4:37 am UTC

Postby prysorra » Mon Sep 03, 2007 4:58 am UTC

There's a few factors, actually.

- Depth

- Currents

- Biomass (there's a reason it's called RED tide)

- Other crap that doesn't belong.


I guess you can say depths and current are closely related.

Well, in any case, the sharpness makes sense. The continental shelf is a pretty steep cut off.

User avatar
Swordfish
Weathermaaaaaaan!
Posts: 954
Joined: Fri Mar 02, 2007 10:39 pm UTC
Location: Philadelphia
Contact:

Postby Swordfish » Mon Sep 03, 2007 6:08 am UTC

prysorra wrote:Well, in any case, the sharpness makes sense. The continental shelf is a pretty steep cut off.


Steep? In the grand scheme of things, yes it is steep, but I don't think it would cause such sharp changes in water color. The Continental Slope is only a slope of about 4 degrees on average. In any event, I might be able to help if I had paid more attention in my Oceanography classes.
"If I had a nickel for every time I was wrong, I'd be broke." Stephen Colbert

zealo
Posts: 321
Joined: Sun Dec 17, 2006 11:36 am UTC
Location: perth, australia
Contact:

Postby zealo » Mon Sep 03, 2007 2:01 pm UTC

prysorra wrote:There's a few factors, actually.

- Depth

- Currents

- Biomass (there's a reason it's called RED tide)

- Other crap that doesn't belong.


depth generally does not seem to affect 'browness', unless whatever is on the bottom is brown in color, and it is very shallow indeed.

for the other 3, why does it form sharp cutoffs of 'clear' and 'not clear'?

User avatar
Master Gunner
Posts: 546
Joined: Thu Jul 19, 2007 1:40 am UTC
Location: Canada, eh?
Contact:

Postby Master Gunner » Mon Sep 03, 2007 2:47 pm UTC

When I've being out boating I often notice small currents that cause a sharp contrast between different regions of water (different density in the current?), so that's what I'd place my money on.

User avatar
Dibley
Posts: 1346
Joined: Tue Jun 12, 2007 8:00 pm UTC
Location: Napa Valley, California
Contact:

Re: Regions of colour in the coastal sea

Postby Dibley » Sat Apr 12, 2008 7:52 am UTC

God uses cell shading.

User avatar
Bobber
contains Disodium Phosphate
Posts: 1357
Joined: Wed Jan 16, 2008 2:09 pm UTC
Location: Holme, Denmark.
Contact:

Re: Regions of colour in the coastal sea

Postby Bobber » Sat Apr 12, 2008 12:51 pm UTC

Dibley wrote:God uses cell shading.


I saw this thread and thought "Hey, weren't there a thread about this half a year ago?"
And yes, there was a thread like this half a year ago.
This thread.
I don't twist the truth, I just make it complex.
mrbaggins wrote:There are two tools in life, duct tape and WD40. If it moves and shouldn't, use the tape. If it doesn't move and should, use the WD40.

User avatar
SpitValve
Not a mod.
Posts: 5129
Joined: Tue Sep 26, 2006 9:51 am UTC
Location: Lower pork village

Re: Regions of colour in the coastal sea

Postby SpitValve » Sat Apr 12, 2008 4:12 pm UTC

It takes dedication to necro a thread for such a one-liner...

Anyway, this is a little like what I was talking about back in September (plus a special google maps flaw), but the regions seemed to be larger and more dramatic when I was on the plane.

Similarly here there's a sharp cutoff between light blue and dark blue water, that doesn't appear to be a google maps artefact.

User avatar
Interactive Civilian
Posts: 468
Joined: Sun Jan 06, 2008 7:53 am UTC
Location: Bangkok, Krung Thep, Thailand
Contact:

Re: Regions of colour in the coastal sea

Postby Interactive Civilian » Sat Apr 12, 2008 5:14 pm UTC

SpitValve wrote:It takes dedication to necro a thread for such a one-liner...

Anyway, this is a little like what I was talking about back in September (plus a special google maps flaw), but the regions seemed to be larger and more dramatic when I was on the plane.

Similarly here there's a sharp cutoff between light blue and dark blue water, that doesn't appear to be a google maps artefact.

The first one looks like turbulence due to uneven depth as the waves approach the breaker zone. Or just uneven depth in shallow water (how much does the depth very in underwater "dunes" or whatever as you approach the breaker zone?) This is a guess.

The second on looks quite different. A wild guess could be... thermocline? Halocline?
I (x2+y2-1)3-x2y3=0 science.

User avatar
Dibley
Posts: 1346
Joined: Tue Jun 12, 2007 8:00 pm UTC
Location: Napa Valley, California
Contact:

Re: Regions of colour in the coastal sea

Postby Dibley » Sat Apr 12, 2008 6:50 pm UTC

I didn't look at the dates on the posts, and I think I got here through a link in someone's post...

Anyways i'd always assumed that those were just the borders of the currents. They are a bit unnerving, though.

User avatar
Swordfish
Weathermaaaaaaan!
Posts: 954
Joined: Fri Mar 02, 2007 10:39 pm UTC
Location: Philadelphia
Contact:

Re: Regions of colour in the coastal sea

Postby Swordfish » Sat Apr 12, 2008 8:57 pm UTC

The second on looks quite different. A wild guess could be... thermocline? Halocline?


I don't think it could be that, the color change is so close to the shore that the water depth is probably so shallow that it doesn't reach the bottom of the mixed layer yet. And, for the second one, it couldn't be a Halocline, because the picture is of a lake.

This is a bit of a challenge, because if it was the depth, I don't think it would just cut off like that, it would probably fade. My guess is that this is probably due to sediments suspended in the water due to wave activity, but again, that leaves problems for the second picture, since I imagine the wave don't get very large due to it being a lake.
"If I had a nickel for every time I was wrong, I'd be broke." Stephen Colbert

User avatar
SpitValve
Not a mod.
Posts: 5129
Joined: Tue Sep 26, 2006 9:51 am UTC
Location: Lower pork village

Re: Regions of colour in the coastal sea

Postby SpitValve » Sun Apr 13, 2008 1:55 am UTC

I think Lake Taupo gets pretty deep pretty fast, because it's the crater from a volcanic explosion, if that makes any difference.

sdedeo
Posts: 36
Joined: Tue Apr 08, 2008 10:52 pm UTC
Contact:

Re: Regions of colour in the coastal sea

Postby sdedeo » Sun Apr 13, 2008 2:14 am UTC

I wonder if some of this sharpness has to do with a bifurcation of the attractors with subtle changes in the relevant parameter space. You get sharp cutoffs, for example, in the formation of vorticies depending on river speed: below a critical speed, none, above, lots. I've seen the phenomenon before myself, of course. In some cases, it's due to an obviously sharp cut off in the physical structure (e.g., on a beach, where you get a sudden drop), but in other cases, you could get sharp transitions in behavior even if the parameters are changing smoothly.

PS: I was just on the South Island (cycle tour) and it rocked. I miss it already.

User avatar
evilbeanfiend
Posts: 2650
Joined: Tue Mar 13, 2007 7:05 am UTC
Location: the old world

Re: Regions of colour in the coastal sea

Postby evilbeanfiend » Mon Apr 14, 2008 12:26 pm UTC

iir c you can get very steep depth changes at the edge of reefs, of course you also get a very steep change in biomass as well there
in ur beanz makin u eveel

User avatar
Velifer
Posts: 1132
Joined: Wed Dec 26, 2007 4:05 pm UTC
Location: 40ºN, 83ºW

Re: Regions of colour in the coastal sea

Postby Velifer » Thu Apr 17, 2008 2:04 pm UTC

Gotta dust off my copy of "Limnology" by Wetzel. Density gradients formed by salinity, temperature, or suspended solids can have very striking effects in large systems. Spin the planet a bit, add some light and heat from a distant source, and all kinds of fun things happen!

In the pictures, I'd guess we're seeing a combination of increased suspended solids in the near-shore breaker zone, decreased depth (not only a transparency issue but also directly related to where the waves begin to break), and some other interesting near-shore effects. The first picture has some great images of suspended material being pulled in the undertow, move a bit to the north and see what looks like a series of small rip currents moving sediment plumes away from shore.

The neat lines and striking beauty here between the darker blue deep water and the lighter water near-shore are from suspended sediments being transported along the shoreline by near-shore currents. I think these are called Keppler waves, but as I said, I need to crack open my old textbooks. This type of water movement (by whatever name) is also responsible for The Onion's "Crypty The Cryptosporidium" mascot, from when these currents effectively transported effluent from a sewage treatment plant right along the shore to the municipal water intake without much mixing at all.

Lake Erie is a great place to study currents: big enough for profound sieche effects, long fetch, shallow on one end, deep on the other, and lots of plankton and sediment to color things.
Time flies like an arrow, fruit flies have nothing to lose but their chains -Marx


Return to “Science”

Who is online

Users browsing this forum: No registered users and 8 guests