What is the concentration of precious metals in sea water, and how (if
at all) does it vary with depth in the ocean or location on the globe?

Hello snesprogrammer and thank you for your question.

When I saw your question I thought the answer would be that sea water
contains only insignificant ammounts of precious metals, but no, there
is rather alot! (Although economocally, it might me expensive
extracting it) The average concentration of gold in the worlds oceans
is about 13 ppt, and spread geographically all over the oceans.  See
below for further information.

Unfortunatley the following website is only available in the Google
cache, nevertheless, all the information is available on the first
page:

"Seawater contains vast quantities of dissolved gold, perhaps as much
as 10 trillion dollars (US) worth, though in dilute concentrations.
Recent evidence suggests that much of the earths continental gold
deposits have biological origins. Certain bacteria are believed to
have been involved in the precipitation of gold out of dilute
hydrothermal solutions. A possible avenue for commercially viable gold
recovery from seawater might involve such a bacterium, or a
specifically engineered microbe."

"When considering only the data gathered since 1980, reported values
for the concentration of gold in seawater have ranged from 5 to 50 ppt
(Lucas 1985), with the average concentration at about 13 ppt. Some of
the highest concentrations recently reported have come from seawater
samples taken from the Bering Sea at 50 ppt"
http://64.233.167.104/search?q=cache:xqwFM2ffB5wJ:www.goldfever.com/gold_sea.htm++%22Gold,+Silver+and+Uranium+from+Seas+and+Oceans%22&hl=en

"Lovley isn't encouraging. Although dissolved gold is found in all
water, even seawater, the use of these microbes to harvest gold does
not make economic sense, he said. "You couldn't use this process to
harvest the gold from the ocean. The cost in pumping the water would
be more than how much gold you could recover," he said. The gold
particles excreted by the microbes are so tiny it would take about a
million microbes to produce a gram of solid gold.

Nonetheless, the gold industry thinks the research is worth watching,
said Paul Bateman, executive director of The Gold Institute in
Washington, D.C"
http://news.nationalgeographic.com/news/2001/08/0830_goldbug.html

"The recent discovery of fabulous deposits of gold, silver, and other
precious metals in volcanic vents off the coast of Japan will
undoubtedly spark similar searches in other areas of the world's
oceans."
http://www.expanding-earth.org/page_12.htm

Not currently available but worth keeping an eye on:
"Gold, Silver, and Uranium from Seas and Oceans: The Emerging Technology"
http://www.amazon.com/exec/obidos/ASIN/1877582174/sharefisgoldnugg/103-0011813-9099049

Thank you for your question, and if you need any clarification of my
answer, do not hesitate to ask.

Now where did I leave my extremophiles?

Very best regards

THX1138

(To read more articles, click on my search strategy below)

Search strategy included:
"Gold, from the Seas OR sea OR Oceans OR ocean"
://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&safe=off&as_qdr=all&q=+%22Gold%2C+from+the+Seas+OR+sea+OR+Oceans+OR+ocean%22&btnG=Search

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Request for Answer Clarification by snesprogrammer-ga on 07 May 2004 15:17 PDT

Wow, the fluctuation in concentration is much larger than I would expect!
Being near Alaska is 10 x's greater than other areas... amazing.

Anyway, I was curious why you only checked on gold.  It's not even the
most expensive of the precious metals.  Can you check on platinum and
silver as well?

And as for the variation due to depth ... there just really isn't any?
A gold atom is pretty heavy compared to a water molecule, so I'd
expect there to be some.  Hmm... but then again I think only the ions
are soluble, and water, being polar, should form "shells" of molecules
around ions ... since this would roughly move together, maybe it is
necessary to consider the weight of the whole average "gold-water
structure".  If many molecules are involved, the difference in density
compared to salt water may be negligible.  So after thinking that out,
I'm not really sure what to expect for variation due to depth.

Thanks.

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Clarification of Answer by thx1138-ga on 08 May 2004 15:14 PDT

Hello again snesprogrammer,

Just a note to say I`ve seen your request for clarification and I will
get right back to you as soon as I can (Almost certainly on Monday)

Very best regards

THX1138

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Clarification of Answer by thx1138-ga on 10 May 2004 07:40 PDT

Hello again snesprogrammer,
The reason I focused on gold is because it seems that this is the
metal that has atracted most attention in terms of potential
extraction, but, before we get on to the subject of other metals (ie.
other than gold) I found this interesting statistic:

"ocean's gold content, estimated at $10,000,000 to $25,-000,000 per cubic mile."
http://www.worthingtonmemory.org/TextFiles/whs0796_001.txt




Now some links to other sites discussing metals in seawater:

"Figure 10.2: Depth Profiles of Background Concentrations of Various
Metals in the Atlantic Ocean"
http://www.mayococo.ie/MCC3/GasTerminal/RSK/Corrib%20Final%20EIS%20PDF/Microsoft%20Word%20-%20Section%2010%20Effluent%20161203.pdf

"Detailed composition of seawater at 3.5 salinity"
http://www.seafriends.org.nz/oceano/seawater.htm

"Of the world's supply of magnesium, 60% comes from the sea, and so
does 70% of the bromine. There are vast amounts of dissolved minerals
in the world's seawater, including 10 million tons of gold and 4
billion tons of uranium, but the concentration is very low (one part
per billion or less). In the case of gold, no method has been devised
in which the cost of extraction does not exceed the value of the
recovered element. Japan, West Germany, and the United States have
expressed an interest in the extraction of uranium. Japan set up a
land-based test plant in 1986 to produce 10 kg (26 lb) of uranium from
seawater per year, but the operation has proved to be expensive, and
the Japanese are looking at methods to use wave energy to run the
system. (Some possible ways to harness wave energy are discussed in
chapter 9.)"
http://www.saddleback.edu/faculty/jvalencic/ocean/textbook/chap5/chap5.html

I hope that additional information was useful to you.

Very best regards

THX1138

"Figure 10.2: Depth Profiles of Background Concentrations of Various
Metals in the Atlantic Ocean" confused me because whether the
concentration increased or not with depth seemed to have nothing to do
with the weight of the element.  Thank you for providing information
explaining those curves ... it makes so much more sense now.

Wow, that "Periodic Table of Elements in the Ocean" is great.  It has
everything.  And the "Detailed composition of seawater at 3.5
salinity" is a nice summary.  I'm amazed that Uranium is at a higher
concentration than Lead, Mercury and even all the precious metals
combined.  That was quite unexpected.

I'm sorry if what I wanted somehow wasn't clear.
But I am now extremely happy with the amount of info you guys found.  Thanks.

A reference you may find useful is the "Periodic Table of Elements in
the Ocean", published by the Monterey Bay Aquarium Research Institute
(http://www.mbari.org/chemsensor/pteo.htm).  It summarizes and
provides fairly up-to-date references for the concentration and
spatial variablity in concentration (both vertical and horizontal) for
all the elements.  It's based on an earlier publication by Yoshiyuki
Nozaki that did a nice job of showing the vertical variation in
elemental concentrations of the elements dissolved in seawater (see
http://www.agu.org/eos_elec/97025e.html).

The vertical variation in the concentration of gold with depth in
seawater is not well known not due to its rather low concentrations. 
Many elements do, however, show dramatic variations in dissolved
concentration as a function of depth.  Elements that are essential
nutrients or are used to form "hard parts" of organisms (e.g., P, Fe,
N, Si) are usually have very low dissolved concentrations in surface
seawater.  These elements are sequestered in particulate matter (fecal
pellets, dead organisms, etc.) in the surface ocean.  These particles
are large and dense enough to settle, and as they settle, they
decompose and re-release the sequestered elements back to seawater. 
The resulting vertical concentation profile shows an increase in the
concentration of these nutrients with increasing depth.

Many trace elements in seawater have concentration profiles that are
similar to nutrients, even though they do not play a (known) role in
biological metabolism.  These elements end up being incorporated in
the organic matter created in surface waters and are then released
along with the nutrients as the particles decompose at depth.

Other elements (e.g., Al) show enhanced dissolved concentrations at
the surface.  These are usually elements for which the major input to
the oceans is in the form of wind-blown particles.  THese elements
usually show a decreasing dissolved concentration with depth because
they end up being scavenged by settling particles that ultimately end
up in sediments.

Hello again snesprogrammer,

Just a note to say thank you for the five star rating and generous
tip.  That was an interesting question and I enjoyed doing the
research, and I too was surprised by the results.  One thing I noticed
was that thermal vents at the bottom of the oceans throw out
relatively high ammounts of metals.
Thank you too to hfshaw-ga, that was some very useful information you provided.

Very best regards to both of you.

THX1138