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Author Topic:   Questions about marine sediments
Ultima_Squall
Inactive Member


Message 1 of 15 (59227)
10-03-2003 11:46 AM


After last week's geography class, there's a few stuff that's not too clear to me.
1) The teacher mentioned that magnetic reversals are directly linked to ice ages. I assume he's right, but the thing he didn't mention (or i was sleeping ) is how is it linked? Is it because during the reversal, there is no magnetic field protecting us from some of the radioactive solar rays? Here too, i'm not too clear.
2) Another thing I didn't understand is that the prof said something about plankton shells found at the bottom of the ocean reflects the species composition of the organisms living in the water column above. But a while ago, he also said that when those organisms die, they are so small that it can take them years and decades to reach the bottom of the ocean. I mean that means that they would be moved around through large distances horizontally. Thus when they hit the bottom, they might not be anywhere near the (lat/long) location where it lived. At first, i thought that maybe they got eaten or got stuck on bigger organisms which brought them to the bottom faster, but i don't think that's a plausible theory. Any insight about this?
3) Is the red clay, calcareous, siliceous oozes found at the bottowm of the ocean all linked to sea floor spreading and plate tectonics? I didn't really get that part.
Tx in advance for any ideas or comments.
[This message has been edited by Ultima_Squall, 10-03-2003]

Replies to this message:
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 Message 11 by Bill Birkeland, posted 10-03-2003 10:54 PM Ultima_Squall has not replied
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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 2 of 15 (59230)
10-03-2003 12:15 PM
Reply to: Message 1 by Ultima_Squall
10-03-2003 11:46 AM


I'm not a geophysicist, Squall, so I'm going on memory here (and no time for looking things up at the moment) but :
I think you're teacher is wrong about the ice age and reversal linkages. The reversals have been going on for a long time and the ice ages are relativly recent (or this most recent bout of them is ). In addition, I remember reading that there has been no obvious effects found at the reversal times, that is no die offs or anything.
That is good thinking about the oceanic ooze. I'm guessing that the particular organisms being discussed are those that are very wide spread in the ocean before they die. So moving them around after death doesn't make a lot of difference. What is interesting is the vertical (time )distribution of them. As the species change over much longer than decades that is recorded in the bottom sediments.

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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 3 of 15 (59231)
10-03-2003 12:17 PM
Reply to: Message 1 by Ultima_Squall
10-03-2003 11:46 AM


guess who might be wrong again!!
have a look here
http://www.iceagenow.com/Magnetic_Reversal_Chart.htm

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Ultima_Squall
Inactive Member


Message 4 of 15 (59232)
10-03-2003 12:23 PM


lol i was about to send you this link too. Well I do know that they are linked, but in what way? I think it must have something to do with the shift in the amount of solar energy. But wouldn't a reversal disable this magnetic field for a short while which makes the earth receive more solar energy. Shouldn't this warm the earth instead of cooling it? I'm kinda confused as you can see.

Replies to this message:
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Minnemooseus
Member
Posts: 3941
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 10.0


Message 5 of 15 (59236)
10-03-2003 12:31 PM
Reply to: Message 3 by NosyNed
10-03-2003 12:17 PM


I have nothing offhand to back this up, but I'm inclined to suspect that they are paying attention to the reversals that correlate with ice ages, and are ignoring the rest of the reversals.
I may be wrong,
Moose

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Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 6 of 15 (59242)
10-03-2003 12:59 PM


Okay, I'll step out on a limb...
In all the geology and ice age stuff I have read, I have never heard any hint of magnetic reversals being regularly correlated with anything above the earth's crust. Not ice ages, not solar storms, not extinctions, not volcanic activity, not anything. I just don't believe it.
Added by edit: Please realize I'm not saying they're not correlated with anything, only that we have no evidence so far of their correlation with anything. I wouldn't be at all surprised if correlations eventually turn up, but neither would I be surprised if none ever did. Any that do turn up may well be very subtle, since more obvious ones would have been apparent by now. An evolutionary effect might be one expected correlation, since diminished protection from cosmic rays could cause a higher mutation rate.
To address question 3, the sedimentary ooze on the ocean floor relates to sea floor spreading and plate tectonics in at least a couple of ways I can think of. First, the further from mid-oceanic ridges where sea floor forms the deeper the sediment, since older sea floor has had more time to accumulate sediments. Second, tectonic movements can push up mountains, and so you often find deep ocean deposits atop mountains, such as in the Alps and Himalayas.
--Percy
[This message has been edited by Percipient, 10-03-2003]

  
Rei
Member (Idle past 7013 days)
Posts: 1546
From: Iowa City, IA
Joined: 09-03-2003


Message 7 of 15 (59254)
10-03-2003 3:06 PM
Reply to: Message 4 by Ultima_Squall
10-03-2003 12:23 PM


Don't confuse cosmic rays with light Cosmic radiation is typically streams of high-energy charged particles (both protons and electrons, and some larger particles occasionally). Light is photons. The former are affected by the magnetic field (due to Lorentz force). The latter is not (although it is affected by Earth's gravity). What limits the ability of certain types of light (such as UV, X-rays, gamma rays, etc) from entering is the absorption spectra at different altitudes.
I do not believe that cosmic radiation plays a significant role in heating bodies that don't have magnetic fields, although I could be wrong.
------------------
"Illuminant light,
illuminate me."

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roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 8 of 15 (59269)
10-03-2003 5:07 PM
Reply to: Message 3 by NosyNed
10-03-2003 12:17 PM


I have never personally heard of magnetic reversals linked to ice ages, but rather to Milankovitch cycles, location of continental plates, the carbon cycle (and other stuff I can't remember ); however, something else I read on that site got me thinking.
They discuss the occurrences of major flood basalt volcanism coinciding with a couple of the largest extinction events in history, the K-T and Permian events. The K-T event appears to temporally coincide with the Deccan Traps in India, while the Permian event temporally conicides with the Siberian Traps.
It is thought that these flood basalts are sourced from deep within the earth, possibly from as far down as the mantle-core boundary. The molten rocks rise to the surface as massive plumes (picture a lava lamp - a perfect example!!) and when they erupt on the surface, contribute major amounts of gases and particulates to the atmosphere. Which often affects the earth's climate, either cooling it via particulate matter or warming it up via greenhouse gases.
Now what is not very well understood is what sets off these eruptions. In other words, what causes these plumes to get started.
What if the same thing that controls the Earth's magnetism - motion/fluidity of the earth's core - also sets off these giant plumes? Is that possible? I don't know enough about planetary magnetism or plume dynamics and latest theories to make a good argument, unfortunately.
I'm not saying that motions in the core always set off plumes or cause reversals, but perhaps they are related in some way. I suppose one way to check this out would be to plot ages of known plumes, magnetic reversals, ice ages, and perhaps other things, such as extinction events and changes in the carbon cycle.
Some of the most significant and lasting ice ages (correct me if I'm wrong) occurred in the Precambrian and in fact one immediately precedes the Cambrian *explosion.* However, I can't remember if any massive flood basalts have been dated to that time period.
(Sorry, hope I didn't migrate too far off the topic.)
P.S. Sorry nosyned, I started with a reply to your post and sort of went off on a tangent instead.
[This message has been edited by roxrkool, 10-03-2003]
[This message has been edited by roxrkool, 10-03-2003]
[This message has been edited by roxrkool, 10-06-2003]

This message is a reply to:
 Message 3 by NosyNed, posted 10-03-2003 12:17 PM NosyNed has replied

Replies to this message:
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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 9 of 15 (59273)
10-03-2003 5:46 PM
Reply to: Message 8 by roxrkool
10-03-2003 5:07 PM


we are all charging off on to explanations for a phenomenon that may not be real.
I agree with Moose, I think I'd like to see a good analysis of the correlation.

This message is a reply to:
 Message 8 by roxrkool, posted 10-03-2003 5:07 PM roxrkool has replied

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roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 10 of 15 (59278)
10-03-2003 7:14 PM
Reply to: Message 9 by NosyNed
10-03-2003 5:46 PM


Sure, that's why I mentioned having a look to see if the available evidence correlates at all. Seeing as there is so much info out there, I would think someone has done this already or at least wouldn't be too difficult to do. TC??? Even just placing an ice age timeline against a magnetic reversal timeline should suffice, no?
I'd do it, but lack the time.
Actually, Ned, I wasn't trying to explain it, it was just something that popped into this big black hole I sometimes call a brain.
[This message has been edited by roxrkool, 10-03-2003]

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Bill Birkeland
Member (Idle past 2531 days)
Posts: 165
From: Louisiana
Joined: 01-30-2003


Message 11 of 15 (59303)
10-03-2003 10:54 PM
Reply to: Message 1 by Ultima_Squall
10-03-2003 11:46 AM


Express Shipping (Downward) by F.P.E.
Ultima Squall asked:
"2) Another thing I didn't understand is
that the prof said something about
plankton shells found at the bottom
of the ocean reflects the species
composition of the organisms living in
the water column above. But a while
ago, he also said that when those
organisms die, they are so small that
it can take them years and decades
to reach the bottom of the ocean."
The answer to this question is summarized in the "G201, 17 April 2001, Lecture 23: Deep Sea Sediment" at:
Center for Geophysical Investigation of the Shallow Subsurface - CGISS
These notes stated:
"Plankton 'package' small particles
into larger particles, which fall much
faster (weeks to months). Sediments on
the seafloor resemble surface
oceanography."
What this brief sentence summarizes is observation that many plankton shells don't fall as individual particles. Rather, they fall in clumps of plankton shells that have far more greater fall velocities than the individual plankton shells. These clumps form by larger marine animals eating the plankton, digesting them, and excreting their undigestable shells clumped together in fecal pellets. The plankton shells clumped together in fecal pellets will take only weeks to months to fall instead of the centuries that individual plankton shells. In fact, many of the individual plankton shells composed of calcium carbonate will never make it to the bottom as they will dissolve in the seawater before they ever reach the bottom. This is summarized in the "Fecal Pellet Express" (F.P.E.) at:
Page not found | Guilford College
On that web page, it is stated:
"In water, bigger heavier particles
sink faster than smaller lighter ones.
Because planktonic organisms are so
small, it seems like they should take
a long time to sink and might get dispersed
by currents, hitting the bottom far
from where they originally lived. However,
species on the ocean floor tend to
represent the species in the surface
water very well, so this kind of dispersal
doesn't happen. Why? Because of the
fecal pellet express. When big organisms
eat plankton, they can't digest the
shells. The shells are excreted in
fecal pellets which sink rapidly to
the ocean floor and then break down."
Also, some shells of plankton get stuck to marine snow and are carried down to the bottom with the marine snow at a faster rate than they would settle as individual shells. Marine snow consists of aggregates of various marine bacteria that eventually grow large enough that they become so heavy that they settle to the bottom like snow.
Other web pages:
Marine Sediments
http://www.ldeo.columbia.edu/~rroberts/Lect-3.pdf
Request Rejected
Yours,
Bill Birkeland
[This message has been edited by Bill Birkeland, 10-03-2003]

This message is a reply to:
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Ultima_Squall
Inactive Member


Message 12 of 15 (59321)
10-04-2003 12:59 AM


Tx a lot Bill, that was very helpful.

  
Bill Birkeland
Member (Idle past 2531 days)
Posts: 165
From: Louisiana
Joined: 01-30-2003


Message 13 of 15 (59326)
10-04-2003 1:46 AM
Reply to: Message 1 by Ultima_Squall
10-03-2003 11:46 AM


Oozes and Clay
Ultima Squall asked:
>3) Is the red clay, calcareous, siliceous
>oozes found at the bottowm of the ocean all
>linked to sea floor spreading and plate
>tectonics? I didn't really get that part.
They are not directly linked to plate tectonics. Essentially, the depth of the ocean and the productivity of (abundance of plankton within) the upper part of the ocean controls the types of sediments.
1, The depth of the ocean controls the type sediment because the water towards the bottom is undersaturated in either calcium carbonate and silica, while the water towards the surface is saturated in both. Thus, the deeper the depth of the ocean bottom, the more the plankton shells settling down to the bottom will be dissolved until below a certain depth all of the plankton shells falling through the water column will be dissolved. Thus, the rate at which the plankton shells accumulate on the bottom, all else being the same will decrease with depth until it at some depth reaches zero. Above that depth the sediments will consist of ooze with increasing proportions of plankton shells. Below that depth, called the "carbonate compensation depth", the sediments will consist only of insoluble material such as eolian dust, volcanic ash, and extraterrestrial debris falling into the ocean. Thus, water depth controls the type of sediments found on the ocean bottom.
2. The productivity of the surface waters also effects the type of bottom sediments. In areas of high productivity, i.e. the oceans along the equator and along the edge of continents, the abundance of plankton within the surface waters produces an enormous amount of siliceous and calcareous shells of plankton. As they fall through the lower part of water column and some are dissolved. There is so much material that they reduce the corrosive nature before they can all be dissolved and some of the shells reach and accumulate on the bottom. Thus, in areas with and abundance of plankton that has a high productivity of plankton shells, oozes not red clays will found on the ocean bottom even if it very deep. Thus, the high productivity of shells in the water column can override the effect of water depth to a significant extent.
Plate tectonic can control indirectly the type of sediment by moving a spot on the ocean floor by increasing the water depth. In this case, the crust becomes denser and sinks as it cools while moving away from a spreading ridge. When created, newly formed crust lies at a depth at which plankton shells can accumulate on the ocean bottom as ooze. As the oceanic crust moves away from a spreading ridge, it sinks and the water depth greatly increases. Eventually, the the depth of the ocean bottom will drop below the the depth at which all of the plankton shells are dissolved as they sink. At that time, the accumulation of ooze will stop and red clay will start accumulating.
Also, plate tectonics can control the types of sediment accumulating on the ocean floor by moving it through a zone of high productivity. For example if a piece of ocean crust is moved under the equator, and adjacent low latitudes, a zone of high productivity, the accumulation of red clays will stop and oozes will accumulate. While that piece of ocean floor lies beneath the equator and adjacent latitudes, oozes will continue to accumulate. Once that piece of ocean floor moves past the high productivity region of the equator and adjacent low latitudes, the accumulation of oozes will stop and the accumulation of red clay will resume as the plankton shells will again be dissolved before reaching the bottom.
Some really nice color figures that shows how plate tectonics influences the types of sediments accumulating within the Pacific and Atlantic Ocean can be found on pages 32 and 33 of "Marine Sediments" that can be downloaded from:
http://www.ldeo.columbia.edu/~rroberts/Lect-3.pdf
How plate tectonics infleunced the types of sediments accumulating within the oceans is also discussed and illustrated in "13. Overview: Marine Sedimentation" at:
http://bell.mma.edu/.../UWMarineGeology/McDuffSediments.html
This web page contains some interesting figures, which show how plate tectonics influences the accumulation of different sediments. The figure that illustrates this process can found at:
http://bell.mma.edu/~jbouch/UWMarineGeology/fs30-4.gif
This is figure 13-5 from:
W.S. Broecker and T.-H. Peng (1982) Tracers
in the Sea, Eldigo Press, 690 pp.
As far as plate tectonics influencing the distribution of various oozes and in relation to the above figures, this web page stated:
"Near to the ridge at which the
basement rock is created, metalliferous
sediment (of hydrothermal origin)
dominates the supply of material.
Once away from this source of sediment,
carbonate material raining from above
accumulates. As the plate subsides,
the dissolution of carbonate increases
such that this material is no longer
preserved and only residual clay material
accumulates (at a much lower sedimentation
rate). As the site passes beneath the
equator, the rate of supply of biogenic
silica exceeds the rate of dissolution
and it accumulates. Further north beyond
the equatorial band of productivity, red
clay dominates again."
Yours,
Bill Birkeland
[This message has been edited by Bill Birkeland, 10-04-2003]

This message is a reply to:
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Coragyps
Member (Idle past 734 days)
Posts: 5553
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 14 of 15 (59364)
10-04-2003 2:00 PM
Reply to: Message 11 by Bill Birkeland
10-03-2003 10:54 PM


Re: Express Shipping (Downward) by F.P.E.
"Fecal Pellet Express"
A better name for a grunge band than for an intercity bus line.....
Bill, once again, thanks for the highly educational posts.

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roxrkool
Member (Idle past 989 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 15 of 15 (59728)
10-06-2003 11:56 AM
Reply to: Message 13 by Bill Birkeland
10-04-2003 1:46 AM


Re: Oozes and Clay
Great posts, Mr. Birkeland! Thanks for all those links, as well.
[This message has been edited by roxrkool, 10-06-2003]

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