Re: Scientists discover why is the North Pole frozen

From: Daryl Krupa (icycalmca_at_yahoo.com)
Date: 02/25/05 

Date: 24 Feb 2005 20:10:08 -0800

george of the jungle wrote:
> On 24 Feb 2005 09:34:16 -0800, "Daryl Krupa" <icycalmca@yahoo.com>
> wrote:

> ><snip>
> >
> > Heh? I always thought that the principal driver in
> >that system was the formation of North Atlantic
> >Deep Water, that is obliquely referred to above, but
> >its formation is there ascribed to evaporative cooling,
> >rather than the usual explanation of sinking of hyper-
> >saline cold water after the surface layer freezes.
> > But Haug, etc. want to blame it all on wind, and
> >differential salinity in the Pacific and Atlantic.
> >
>
> There is a French web site - Mercator Ocean that has high
> resolution maps of the North Atlantic. The formation of
> deep water looks more complicated than most models would
> have it. The hypersaline freezing model has the problem
> of fresh water layering in the Arctic. The Arctic water
> is typically much fresher than the North Atlantic water
> because the input of rivers in the Arctic so ice formation
> mostly does not make Arctic surface water sink to the
> bottom. Cooling of salty Atlantic water by cold Arctic air
> creates dense water that sinks.

Tree-hugger:
  Okay fine, but does that explain the Labrador Current, or
the Greenland Current?
  Also, I thought that the hypersaline water is what is left
behind after some near-surface seawater water freezes onto
the underside of the pack ice. Some of the water molecules
are frozen out, and most of the salt remains in the seawater.

> There are other problems with the various models of the THC but
> there's not enough time to go further.

  Got a relevant URL handy, or better yet, a hard-copy ref.?

<snip>
> > I have serious problems with their global current diagram,
> >which would make the Califormia Current the product of
> >upwelling, and ignores the formation of Deep Water
> >in the Antarctic.
> >
> Hmmm...I thought the upwelling was a product of the current.

  Upwelling off the California coast, you mean?
  This study, ref'd by Haug's most recent _Nature_ article,
describes it as being "offshore windstress-curl-driven".
It also sought to describe changes in productivity and
seasonality related to a change in upwelling, but it posits a
_reduction_ in productivity and a
_decrease_ in seasonality related to an
_increase_ in upwelling,
off of California, but later (1.7 Myr ago).
  Note that Haug, etc. would have it that a
_decrease_ in upwelling would also cause a
_reduction_ in productivity.

"1.7 Myr ago, a further increase in wind-driven upwelling
or shoaling of the thermocline, accompanied by decreased
stratification at least seasonally, as occurs today,
would have caused total CaCO3 production to drop and
seasonality to increase."

Nature 429, 263 - 267 (20 May 2004); doi:10.1038/nature02567

Regional climate shifts caused by gradual global cooling in
the Pliocene epoch

ANA CHRISTINA RAVELO, DYKE H. ANDREASEN, MITCHELL LYLE,
ANNETTE OLIVAREZ LYLE & MICHAEL W. WARA

> ><snip>
> It's really hard to get a halocline where the water is
> upwelling, which I thought they wrote the NPac was doing.

  Yes, it _was_, until the global conveyor was "short-
circuited", allowing the halocline to develop in the NPac.
  This was supposedly the result of the Gulf Stream bringing
warm water to the North Atlantic.
  That meant more evaporation in the belt of the Westerlies,
and so more precipitation in Russia, and so more fresh water
entering the Arctic Ocean from Siberian rivers.
  The fresher Arctic water was easier to freeze, so the
Arctic Ocean acquired a cover of sea ice.
  This is where it gets chancy: the higher alberdo of the
sea ice cover reduced solar heat input, cooling northern
climate, but at the same time it insulated the Arctic Ocean
from heat loss to the atmosphere. That insulative effect
supposedly reduced the formation of North Atlantic Deep Water
(NADW) and its associated downwelling, and so the global
conveyor was "short-circuited", and no more NADW made its way
around Africa and Australia to eventually upwell in the North
Pacific. (Of course, the NADW would have had to acquire buoyancy
along the way, either by dilution with less-salty water, or by
warming.)

  It's explained thusly:
"The added fresh water would have facilitated the formation
of sea ice, which would reflect sunlight and heat back into
space.
It would also act as a barrier blocking heat stored
in the ocean from escaping to the atmosphere above the Arctic.
Both these phenomena would further cool the high latitudes.
In addition, Arctic waters flowing back into the North Atlantic
would have become less cold and salty-short-circuiting the
efficiency of the Ocean Conveyor belt as a global heat pump to
North Atlantic regions."

  Graphically shown here (push the numbered buttons):

http://oceanusmag.whoi.edu/v42n2/haug-en4.html

  This idea of warming-causing-cooling-causing-less-cooling
is supposed to be a resolution of an "apparent" contradiction,
in that the warm Gulf Stream waters are not supposed to cool
down the Northern Hemisphere.
  I don't see it as a clear resolution.

> > What? Now the freshening of the North Pacific
> >is an effect, not a cause, of Northern Hemisphere
> >Glaciation?
> > This conflicts directly with Haug's article in _Nature_.
> > I don't get it.
>
> I'm not sure any of them get it. None of these folks seem to
> get the basic thermodynamics of the THC. I need to take a
> better look at the articles because what I have seen here
> doesn't make much sense.

  The text of the relevant "news and views" commentary in
_Nature_ is copied at the bottom of this post, for your
edification and enjoyment.

> ><snip>

> >Still confused,
> >Daryl Krupa
>
> I'm still confused too. I think that the confusion
> reflects the inadequacies of the models & explanations
> provided by the authors.

  Indeed (re: the explanations).
  In Haug, etc.'s latest article, they repeat this
interpretation that appeared in the conference abstract:

"However, the onset of Northern Hemisphere glaciation
has proved to be inconsistent with ideas regarding the
water vapour requirement 3, 4. It has been suggested that
glaciation began in response to increased North Atlantic
Deep Water formation and the flow of warm Gulf Stream
waters into the high-latitude North Atlantic, associated
with the closure of the Panama seaway 5, 6. However, recent
studies show that this closure and associated changes in
North Atlantic circulation occurred 4.6 Myr ago, well before
the onset of intense Northern Hemisphere glaciation 4, 5."

  Their ref. 5 is a 4-page article in _Nature_ magazine from
1998 (see ref. below).
  Their ref. 4 is Ravelo, et. al (2004), as above.
  Ravelo, et al. does not say that the Panama seaway closed
at 4.6 Myr ago; it says that the "associated changes"
occurred later than that:

"Between 4.5 and 4.0 Myr ago, a marked shift in surface-water
hydrographic gradients between the Pacific and Caribbean
and between the Caribbean and the western tropical Atlantic,
shoaling of the thermocline in the east Pacific, and
circulation changes in the Atlantic, were possibly forced by
tectonic event(s) (for example, restriction of the Panamanian
or Indonesian seaways)."
  Re: restriction of the Panamanian seaway, they refer to a
4-page article from 2001, in _Geology_ magazine, by Haug.
  In citing Ravelo, et al., Haug is being self-referential,
by a circumlocutical path, which I suppose might be thought
appropriate, given the ocean-conveyor subject matter ...

  Lastly, Haug, et al. 2005 does not describe a relationship
between a "short-circuiting" of the ocean conveyor and the
beginning of the stratification of the NPac. They don't give
any generating factor for NPac stratification. They just say
this about the onset of NPac stratification, which implies
that NPAc stratification is _both_ cause and effect of NHG:

"The close association of subarctic Pacific halocline formation
with major Northern Hemisphere glaciation as well as the abrupt
and dramatic nature of both changes suggest a positive feedback
between the two.
We have previously focused on how climate cooling increased the
vertical stability of the North Pacific 13, 14.
This work raised atmospheric CO2 as the possible mechanism by
which polar stratification could, in turn, cause global cooling
and thus participate in a positive feedback.
The sediment core data and climate model output reported here
provide a more direct mechanism by which the development of the
subarctic Pacific halocline set the scene for ice-*** growth
in the Northern Hemisphere."
  Ref. 13 is Haug, et al. (1999), and ref. 14 is Sigman, et al.
(2004)
(see below).
  There is only one mention of the Gulf Stream in Haug, et al.
(2005), and every mention of the Atlantic is accompanied by a
description of the inadequacy of explanations related to North
Atlantic conditions in explaining the onset of NHG.

  I really don't see how
changes in North Atlantic circulation
could be connected to
the initiation of NHG by NPac stratification
as described in Haug, et al. (2005).
  AFAICS, the Pliocene ocean conveyor system and
the swings-both-ways effect of increased Gulf Stream warming
in the figures at the next two URLs are truly speculative, and
neither support nor follow from the arguments, modelling, and
evidence in Haug, et al. (2005). Too many cooks in that article?

http://oceanusmag.whoi.edu/v42n2/haug-en2.html

http://oceanusmag.whoi.edu/v42n2/haug-en4.html

  So, while we might now know where the moisture for ice
accumulation in North America came from (not that there was
any serious doubt), we still do not know why that moisture
suddenly became available at about 2.7 Ma, so
we still do not know why the North Pole is frozen, and so
Rosell's claim,
"Scientists discover why is the North Pole frozen",
is still bogus.

  But Thanks very much, George (the first) for setting me
on the track of finding the answer to the question,
"Eh! Paisan! w*********withyou! Eh!"

Less puzzled, now, I think (maybe),
Daryl Krupa

-----------------------------------------------------
[slightly modified to remove ref's to Figures, etc.]

news and views

Nature 433, 809 - 810 (24 February 2005);
doi:10.1038/433809a

Climate change: Snow maker for the ice ages

KATHARINA BILLUPS

In the Northern Hemisphere, large-scale glaciation was
initiated comparatively recently. Paradoxically, it
seems that the trigger was a seasonal warming of the
sea surface in an upwind oceanic region.

Over the past 50 million years, the Earth's climate
has been cooling. Although Antarctica has been
glaciated for at least the past 35 million years,
large ice sheets did not appear in the Northern
Hemisphere until about 2.7 million years ago.
Earth scientists largely agree that overall climate
cooling is associated with decreasing levels of carbon
dioxide in the atmosphere, and that ice sheets can
only grow if sufficient moisture is available and
winter snow survives the summer heat. But what
triggered the onset of the ice ages 2.7 million years
ago? Explanations have focused on continental
temperatures, with identification of potential
moisture sources from the Atlantic, but there
remain many open questions.

Haug et al. (page 821 of this issue) contribute an
important piece to the ice-age puzzle.
Geochemical evidence suggests that, 2.7 million years
ago, the seasonal temperature contrast of the subarctic
Pacific Ocean sea surface became larger as summers
warmed and winters cooled.
Warmer summer sea-surface temperatures result in a
warmer atmosphere that can hold more moisture.
Like a snow gun blasting away at ski slopes, westerly
winds blow the moisture onto the cold North American
continent where it falls as snow and accumulates as ice.

Haug et al. have combined geochemical expertise with
numerical modelling to present an integrated approach to
the origin of the ice ages.
Evidence comes from the floor of the subarctic Pacific
Ocean, on which the remains of certain species of marine
plankton (diatoms, coccolithophores and foraminifera)
have accumulated over time.
The primary evidence for summertime warming 2.7 million
years ago stems from the biochemistry of coccolithophores,
which varies according to temperature.
Augmenting this well-established index are the 18O/16O
ratios in the siliceous tests of diatoms, a comparatively
more complex measure of palaeotemperatures.

At first glance, the results from these two recorders
contrast with other climate indicators in this region.
Foraminiferal 18O/16O ratios - a classical indicator -
from the same deep-sea sediments suggest sea-surface
cooling 2.7 million years ago.
This particular evidence is corroborated by perhaps the
most intuitive indicator of climatic cooling, an increase
in the amount of debris of continental origin delivered
to the site by icebergs.

How can these apparently contradictory observations be
reconciled? Haug et al. point to seasonal changes in
the biological communities of the subarctic Pacific
Ocean where, in modern times, different plankton
communities populate the various seasons.
Coccolithophores and those species of diatoms used for
the geochemical analyses prefer the warm ocean surface
of late summer and autumn. The particular foraminiferan
species used for analysis, on the other hand, are more
prolific during late winter and spring when the sea
surface is fertile due to mixing with deeper, colder,
nutrient-rich water.

Thus the two seemingly opposing temperature trends
2.7 million years ago simply reflect an increase in
seasonality in the subarctic Pacific Ocean, which is
consistent with other reconstructions of events in the
North Pacific Ocean.
This then provides the configuration on which to build
an ice age: late winter cooling reflects climate cooling,
allowing snow to accumulate; late summer warming
increases the atmosphere's potential to hold moisture and
to load the snow gun.

What, then, caused the sudden increase in late summer
temperatures? To answer this question, Haug et al.
refer to the physical properties of sea water itself.
Water has a high heat capacity, which means that the
surface ocean remains warm long after overlying air
and adjacent land masses have cooled.
If there is mixing of the surface ocean with deeper
and cooler water, however, surface waters cannot warm up.
This was the situation before 2.7 million years ago,
evidence for which comes from the high accumulation
rates of diatom skeletal remains at the study site,
implying vigorous diatom productivity in the overlying
sea surface and therefore a continuous supply of nutrients
from deeper waters.

At 2.7 million years ago, the abundance of diatom remains
plummets, suggesting a decrease in the nutrient
availability, like that brought about by the sea surface
being cut off from the deeper ocean, at least on a
seasonal basis.
At the same time, the reduction in vertical mixing allows
the sea surface to warm.
Thus the development of a seasonally layered, or stratified,
surface ocean 2.7 million years ago, which was probably a
regional response to the large-scale climatic changes at
this time, allowed late summer/autumn warming of the sea
surface and provided a moisture source for ice growth.

Haug et al. test the interpretations of the
geochemical records with a suite of numerical
computer-model experiments. The simulated ocean is
'stratified' and 'destratified' to determine whether
this mechanism can account for the geochemically
derived changes in temperature. And it can. The
stratified model state produces more extreme seasons
and a larger North American ice *** than does the
destratified model.

This is an exemplary study. The individual climate
indicators may not have withstood the uncertainties
and assumptions that limit each of them, but put
together by Haug et al. they tell a cogent story of
the origin of the ice ages.

------------------------------------------------------

Ref's:

ANA CHRISTINA RAVELO, DYKE H. ANDREASEN, MITCHELL LYLE,
ANNETTE OLIVAREZ LYLE & MICHAEL W. WARA
2004
Regional climate shifts caused by gradual global cooling in
the Pliocene epoch
Nature 429, 263 - 267 (20 May 2004); doi:10.1038/nature02567

Haug, G. H. & Tiedemann, R.
1998
Effect of the formation of the Isthmus of Panama on
Atlantic Ocean thermohaline circulation.
Nature 393, 673-676

Haug, G. H. et al.
2001
Role of Panama uplift on oceanic freshwater balance.
Geology 29, 207-210

Haug, G. H., Sigman, D. M., Tiedemann, R., Pedersen, T. F. &
Sarnthein, M.
1999
Onset of permanent stratification in the subarctic Pacific Ocean.
Nature 40, 779-782

Sigman, D. M., Jaccard, S. & Haug, G. H.
2004
Polar ocean stratification in a cold climate.
Nature 428, 59-63

GERALD H. HAUG, ANDREY GANOPOLSKI, DANIEL M. SIGMAN,
ANTONI ROSELL-MELE, GEORGE E. A. SWANN, RALF TIEDEMANN,
SAMUEL L. JACCARD, JÖRG BOLLMANN, MARK A. MASLIN,
MELANIE J. LENG & GEOFFREY EGLINTON
2005
North Pacific seasonality and the glaciation of North America
2.7 million years ago
Nature 433, 821 - 825 (24 February 2005); doi:10.1038/nature03332
GERALD H. HAUG1, ANDREY GANOPOLSKI2, DANIEL M. SIGMAN3, ANTONI
ROSELL-MELE4, GEORGE E. A. SWANN5, RALF TIEDEMANN6, SAMUEL L. JACCARD7,
JÖRG BOLLMANN7, MARK A. MASLIN5, MELANIE J. LENG8 & GEOFFREY EGLINTON

http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v433/n7028/full/nature03332_fs.html

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