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Monday, August 20, 2012
1.5 Million Years of Climate History Revealed
I suspect resolution is
lousy and this work is still a long way from been helpful. However
we do establish an epoch change around 900,000 years ago.
My interpretation of this
epoch change is that is when the Panama isthmus arose and severed the
Atlantic from the Pacific. This then led to a huge expansion of the
northern Ice Sheet with a subsequent drop in sea lave hugely
expanding the barrier itself. Geological data is already supporting
this time frame.
The next question is just
how solid is the 100,000 yr cycle and the 41,000 yr cycle? Orbital
solutions do not work this way. Heat mass solution could possibly
work this way. The fact that it changed at all throws the whole
orbital theory into question even if folks have been relying on it
for a few years.
I think we will have to
wait for more data review.
years of climate history revealed after scientists solve mystery of
1.5 million years
of climatehistory revealed
after scientists solve mystery of the deep Study successfully
reconstructed temperature from the deep sea to reveal how global ice
volume has varied over the glacial-interglacial cycles of the past
1.5 million years
Tabular iceberg. The
production of tabular icebergs is a major mechanism of mass loss from
the Antarctic Ice Sheet. Icebergs are calved during both rapid
ice-shelf collapse and as part of the normal transfer of mass through
the ice sheet to the surrounding ocean.
announced a major breakthrough in understanding the Earth's climate
machine by reconstructing highly accurate records of changes in ice
volume and deep-ocean temperatures over
the last 1.5 million years.
The study, which is
reported in the journal Science, offers new insights into a
decades-long debate about how the shifts in the Earth's orbit
relative to the sun have taken the Earth into and out of an ice-age
Being able to
reconstruct ancient climate change is a critical part of
understanding why the climate behaves the way it does. It also helps
us to predict how the planet might respond to man-made changes, such
as the injection of large quantities of carbon dioxide into the
atmosphere, in the future.
scientists trying to construct an accurate picture of how such
changes caused past climatic shifts have been thwarted by the fact
that the most readily available marine geological record of ice-ages
- changes in the ratio of oxygen isotopes (Oxygen
18 to Oxygen 16) preserved in tiny calcareous deep sea fossils called
foraminifera - is compromised.
This is because the
isotope record shows the combined effects of both deep sea
temperature changes, and changes in the amount of ice volume.
Separating these has in the past proven difficult or impossible, so
researchers have been unable to tell whether changes in the Earth's
orbit were affecting the temperature of the ocean more than the
amount of ice at the Poles, or vice-versa.
The new study, which
was carried out by researchers in the University of Cambridge
Department of Earth Sciences, appears to have resolved this problem
by introducing a new set of temperature-sensitive data. This allowed
them to identify changes in ocean temperatures alone, subtract that
from the original isotopic data set, and then build what they
describe as an unprecedented picture of climatic change over the last
1.5 million years - a record of changes in both oceanic temperature
and global ice volume.
Included in this is a
much fuller representation of what happened during the
"Mid-Pleistocene Transition" (MPT) - a major change in the
Earth's climate system which took place sometime between 1.25 million
and 600 thousand years ago. Before the MPT, the alternation
between glacial periods of extreme cold, and warmer interglacials,
happened at intervals of approximately 41,000 years. After the MPT,
the major cycles became much longer, regularly taking 100,000 years.
The second pattern of climate cycles is the one we are in now.
Interestingly, this change occurred with little or no
didn't really know what happened during this transition, or on either
side of it," Professor Harry Elderfield, who led the research
team, said. "Before you separate the ice volume and temperature
signals, you don't know whether you're seeing a climate record in
which ice volume changed dramatically, the oceans warmed or cooled
substantially, or both."
"Now, for the
first time, we have been able to separate these two components, which
means that we stand a much better chance of understanding the
mechanisms involved. One of the reasons why that is important, is
because we are making changes to the factors that influence the
climate now. The only way we can work out what the likely effects of
that will be in detail is by finding analogues in the geological
past, but that depends on having an accurate picture of the past
behaviour of the climate system."
developed more than 30 different models for how these features of the
climate might have changed in the past, in the course of a debate
which has endured for more than 60 years since pioneering work by
Nobel Laureate Harold Urey in 1946. The new study helps resolve these
problems by introducing a new dataset to the picture - the ratio of
magnesium (Mg) to calcium (Ca) in foraminifera. Because it is easier
for magnesium to be incorporated at higher temperatures, larger
quantities of magnesium in the tiny marine fossils imply that the
deep sea temperature was higher at that point in geological time.
The Mg/Ca dataset was
taken from the fossil record contained in cores drilled on the
Chatham Rise, an area of ocean east of New Zealand. It allowed the
Cambridge team to map ocean temperature change over time. Once this
had been done, they were able to subtract that information from the
oxygen isotopic record. "The calculation tells us the difference
between what water temperature was doing and what the ice sheets were
doing across a 1.5 million year period," Professor Elderfield
picture shows that ice volume has changed much more dramatically than
ocean temperatures in response to changes in orbital geometry.
Glacial periods during the 100,000-year cycles have been
characterised by a very slow build-up of ice which took thousands of
years, the result of ice volume responding to orbital change far more
slowly than the ocean temperatures reacted. Ocean temperature
change, however, reached a lower limit, probably because the freezing
point of sea water put a restriction on how cold the deep ocean could
In addition, the
record shows that the transition from 41,000-year cycles to
100,000-year cycles, the characteristic changeover of the MPT, was
not as gradual as previously thought. In fact, the build-up of
larger ice sheets, associated with longer glacials, appears to have
begun quite suddenly, around 900,000 years ago. The pattern of
the Earth's response to orbital forcing changed dramatically during
this "900,000 year event", as the paper puts it.
The research team now
plan to apply their method to the study of deep-sea temperatures
elsewhere to investigate how orbital changes affected the climate in
different parts of the world.
about the Earth's climate system fuels the sense that we don't really
know how the climate is behaving, either in response to natural
effects or those which are man-made," Professor Elderfield
added. "If we can understand how earlier changes were
initiated and what the impacts were, we stand a much better chance of
being able to predict and prepare for changes in the future."