Notes on the Sense of Time

1
Notes on the Sense of Time

• Peter Rhines
• School of Oceanography
• Dept of Atmospheric Sciences
• Honors Program
• University of Washington

2

3
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
time
Haug et al Nature 2006
4
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 days
coursestraight 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.
5

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 Earths temperature and the amount of
carbon dioxide and methane in the air

6
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.
Wikipedia ice ages
7
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 Earths ice. Were
Greenland to meltit would raise sea-level by 7m
on average, throughout the globe, and
Antarcticasmelting would contribute another
61m. Sea-level currently seems to be rising
abou4 cm per decade, with substantial
contributions from both melting ice and global
warming ( leading to thermal expansion of sea
water).
8
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
occurredat times of extreme climate and climate
change.
9
Pacemakers

• ice ages (40,000 year, now 100,000 year cycles)
• Earth/Sun orbit precession, ellipticity

10

• Lets start with the sun
• diameter 1.38 million km
• distance from Earth (mean) 149.6 million km (93
  million miles)
• tilt of Earths rotation axis relative to
  its orbit round the sun
• 23.50
• the orbit is an ellipse, but only about 2
  different from a
• circle the orbital eccentriciy 0.017
• rotation period 23.9 hours
• 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 Earths surface,
  somehow leading to ice ages.cycles of cold and
  warm climate.

www.cwru.edu, http//science.nasa.gov/headlines/y
2001/ast03jul_1.htm
(these two numbers together tell us how big the
disc of the sun appears in the sky.the
relationship is tan ½T ½
diameter/distance (see diagram above) For small
angles tanT us approximately T, measured in
radians. So, T 1.38/149.6 0.00922 radians
or .00922 x 360/2? 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 v(1-b2/a2) where
a is the largest diameter (the major axis) and b
is perpendicular to it, the smallest diameter
11
This wood and canvas kayak is of northwest
Greenland design, with highbow designed to cut
through big waves. Over 6000 years of occupation
of that land, the kayak design was optimized
slowly, and is competitive with anymodern
plastic kayak. The difference is, theres
nothing in this boat thatyou couldnt eat. It
has a small ecological footprint.
6 people,6 kayaks,6 days
12

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 womens umiak, is
covered in seal-skin, with a light, strong
frame made of drift wood. Its length is twice
the span of his arms (twice his height) and its
width is his hips plus his hands.
13
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 icemountain 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).
14
(No Transcript)
15
The breathing of the Earth phytoplankton at sea
and green plants on landanimation of the
seasonal waxing and waning of plants cover
16
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 bodyweight 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, thoughit is very difficult to count them.
17
see Richard Browns short description of Arctic
spring in Voyage of the Iceberg
18
(No Transcript)
19
Whaling by the Inupiat natives of Alaskas 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.
20
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 relatedchange in weather
patterns, temperature and rainfall.(dynamic
height at 1000 Hpa (colors blue low pressure
cyclones, redhigh pressure anticyclones), 300
Hpa, 30 Hpa 1993 (NH), 1996 (SH) winters, 100
days each
21

Andy Goldsworthy, Rivers and Tides
22
(No Transcript)
23
Roald Amundson finally navigated the entire
NW passage in 1903-1906. Harald Sverdrup then
joined Amundson on the Maud for their 6 years in
the western Arctic, 1919-1925.
24
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.