Transcript Exploring the Cold Oceans of the North P.B.Rhines

Notes on the Sense of Time
Peter Rhines
School of Oceanography
Dept of Atmospheric Sciences
Honors Program
University of Washington
Deep time
showing the
cooling of the
Earth since the
end of the
Creaceous period
(the dinosaur era).
There was little or no
snow or ice on Earth
then. Abruptly, about 2.5
million years ago,
the curve starts
oscillating wildly:
the beginning of the
ice ages
Haug et al
Nature 2006
time
On my first voyage to Greenland, we approached from Iceland, and saw the coastal mountains covered in cloud. But
then the clouds turned to ice. It was the ice cap, flowing slowly over the mountaintops to descend into the sea.
Glaciers flow at rates of roughly 100m per year, yet they flow like rivers and produce trains of icebergs at sea. The
Jakobshavn glacier at Illulissat in west Greenland has accelerated greatly in the past few years. You can see it flow!
Emerson Hiller, the Captain of the Knorr, was an adventurer.
As a joke I sent a request to him on the bridge
showing the next day’s course…straight through the south
tip of Greenland, known as Cape Farewell. He came back
with the map at the right, having found a fjord we could
possibly sail through. We did, so and saved several days
steaming to our goal, the Labrador Sea. The fjord was
about 100 km of narrow passage between tall cliffs of ancient
mountains, with the ice sheet peering down from their tops,
and small icebergs all round us.
R/V Knorr in Labrador Sea. At the time of this research cruise, the first
deep ice cores were being drilled on the summit of Greenland.
The iceberg likely calved off the Jakobshavn glacier in west
Greenland. The strata, faintly visible, record climates back
120,000 years. Air bubbles in the ice accurately give us a
whiff of ancient climates, showing the high correlation between
Earth’s temperature and the amount of carbon dioxide and methane in the air
Wikipedia: ice ages
Vostok ice core, Antarctica. The ice ages currently
are in a 100,000 year cycle. The Earth is almost always
cooling down, interspersed with sudden warming events:
ice ages end quickly.
Antarctica was covered by ice about 40M years ago, and today we can
observe its mass field with orbiting satellites (the twins known as Grace).
90% of the worlds ice is here. Only in the past 3 or 4 years has it been possible to
measure the mass of the Earth’s ice. Were Greenland to melt
it would raise sea-level by 7m on average, throughout the globe, and Antarctica’s
melting would contribute another 61m. Sea-level currently seems to be rising abou
4 cm per decade, with substantial contributions from both melting ice and global
warming ( leading to thermal expansion of sea water).
Vogelherd horse carved 32,000 years ago from mammoth tusk. This, along with the
cave paintings in France and Spain, represent the earliest discovered art works of
humans. This was the peak of the last ice age, when glacial ice must have been just
north of the site of this art. Development of human intelligence may have occurred
at times of extreme climate and climate change.
Pacemakers
ice ages (40,000 year, now 100,000 year
cycles)
Earth/Sun orbit: precession, ellipticity…
Let’s start with the sun
diameter: 1.38 million km
distance from Earth (mean): 149.6 million km (93 million miles)*
disc of the
sun
tilt of Earth’s rotation axis relative to its orbit round the sun:
23.50
Earth
the orbit is an ellipse, but only about 2% different from a
circle: the orbital eccentriciy**= 0.017
rotation period: 23.9 hours
angle Θ
length of day: 24 hours
On July 4 this year the Earth is farthest from the sun (aphelion);
on Jan 4 it was closest (perihelion); about 7% more sunlight (rate of energy falling
on Earth) in Jan than in July. As Northern Hemisphere goes, so goes
climate!
The eccentricity shifts with 100,000 year period from 0.05 to nearly zero.
perihelion shifts with 21,000 year period
obliquity (tilt of axis) shifts with 41,000 year period …..all these slight changes alter the amount of sunshine
and its distribution at the Earth’s surface, somehow leading to ice ages….cycles of cold and warm climate.
Averaged over the globe, sunlight falling on Earth in July (aphelion) is indeed about 7% less intense than it is in January (perihelion)." That's
the good news. The bad news is it's still hot. "In fact," says Spencer, "the average temperature of Earth at aphelion is about 40 F (2.30 C) higher
than it is at perihelion." Earth is actually warmer when we're farther from the Sun !
www.cwru.edu,
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http://science.nasa.gov/headlines/y2001/ast03jul_1.htm
*(these two numbers together tell us how big the disc of the
sun appears in the
sky….the relationship is
tan ½Θ = ½ diameter/distance (see diagram above)
For small angles tanΘ us approximately Θ, measured in radians.
So, Θ = 1.38/149.6 = 0.00922 radians or .00922 x 360/2Л
degrees. This is 0.53 degrees….roughly ½ degree,almost the same
angular size as the moon, which is why we have such perfect eclipses)
============================================
**the eccentricity of an ellipse is defined as the ratio √(1-b2/a2) where a is the
largest diameter (the major axis) and b is perpendicular to it, the smallest
diameter
This wood and canvas kayak is of northwest Greenland design, with high
bow designed to cut through big waves. Over 6000 years of occupation of
that land, the kayak design was optimized slowly, and is competitive with any
modern plastic kayak. The difference is, “there’s nothing in this boat that
you couldn’t eat”. It has a small ecological footprint.
6 people,6 kayaks,6 days
Hunting seals is a major occupation of the north Greenlander. In winter,
with much frozen ocean, the hunter waits for hours
poised with a spear, for the seal to appear at a small breathing hole in the ice. His
kayak, and the women’s umiak, is covered in seal-skin, with a light, strong frame
made of drift wood. It’s length is twice the span of his arms (twice his height)
and its width is his hips plus his hands.
Here the floating Arctic sea ice, which is very animated in response to winds,
and is flowing in response to ocean circulation, contrasts the pearlescent ice
mountain of Greenland. It is the only high topography of the far North, and
extends one quarter of the way between Pole and Equator (2000 km).
The breathing of the Earth: phytoplankton at sea and green plants on
land…animation of the seasonal waxing and waning of plants cover
American Golden Plover .. seasonal migration: energy and time. The plover comes to
ANWR, the coastal plain of Alaska, to have its young in summer, then it doubles its body
weight for the flight over the ocean to South America, eating no food on the journey. Its
northward migration depends on stopovers at reliable wildlife preserves in the U.S.
In ANWR the numbers of plovers seems to be declining at about 8% per year, though
it is very difficult to count them.
see Richard
Brown’s short
description of
Arctic spring in
Voyage of the Iceberg
Large Cod taken in the Godthåbsfjord W
Greenland in 1951. The food chain in the
Arctic is among the most intensely productive in
spring…it lights up, from single-cell plankton to
fish, whales and birds.
Whaling by the Inupiat natives of Alaska’s north slope (image by
Charles Wohlforth, author of The Whale and the Supercomputer).
These bowhead whales weight about 100,000 lbs and may live in
excess of 200 years. This says something about the stability of their
environment.
Southern hemisphere and northern hemisphere circulations: weather introduces new
time-scales into high latitude life. Left is south polar view, right is north polar view.
There are natural cycles over 10 years and longer, as well as global warming related
change in weather patterns, temperature and rainfall.
(dynamic height at 1000 Hpa (colors: blue = low pressure cyclones, red=high pressure
anticyclones), 300 Hpa, 30 Hpa 1993 (NH), 1996 (SH) winters, 100 days each
Andy Goldsworthy, Rivers and Tides
Roald Amundson finally
navigated the entire NW passage in 19031906. Harald Sverdrup then joined
Amundson on the Maud for their 6 years in
the western Arctic, 1919-1925.
Accelerating polar melting (e.g. Abdalati 2006):
Sea-level rise, formerly dominated by simple
thermal expansion, is feeling increasing melt
contribution.
Of the ~ 3 mm yr-1 rise, fully 0.4 mm yr-1 came from
Antarctic melting and 0.25 mm yr-1 from Greenland
melting, 0.27 mm yr-1 from Alaskan glaciers
(± large error bars) in 2002-2005; alimeters, GRACE
gravity satellites
Ice-sheet models did not have the rapid-response of
bed lubrication to surface melting and so this was
a surprise.