Outline for today

• Volunteer for today’s highlights on Friday __________• Highlights of last Friday’s class – Casey Lawler

ESS 203 - Glaciers and Global Change

• Ice cores and climate history

Wednesday February 12, 2020

Library Homework

• Due at class on Friday• You and your partner are locating 5 items• Make a single report answering the questions in the assignment.• Both partners review all 5 items. • Both partners certify that the items are not “false positives”.

Mid-term #1

Ed Q1 –Water in glaciers 6.8 /10Joel Q2 – Glaciers and climate 8.4 /10 Joel Q3 – Griselda’s mission 8.2 /10

Total 23.4 /30

If you didn’t do as well as hoped, remember that each quiz is worth only 12.5% of the class grade.

If the study session times didn’t work well for you, let me know and I can set up different or additional times for the second test.

Facing death and extinction

in the cryosphere

But this is weather, not climate.

At least not yet …

The political challenge with climate change …

Where are we now?

• We know what is a glacier.• We know how scientists communicate results.• Now we will explore how glaciers and ice sheets

tell us about past climate.• Environmental clues embedded in ice (ice cores)• Historical changes in the size of glaciers

Crew processing an Antarctic ice core at NSF Ice Core Facility (NSF-ICF) in Denver - 2016

T.J. Spruce??? Sean

1751-m core54,000 years

SPICEcore drill operation

http://spicecore.org/photos.shtml

NSF Ice Core Facility - Denver

• a facility for storing, curating, and studying meteoric ice cores recovered from the glaciated regions of the world.

• NSF-ICF holds over 17,000 meters of ice core from various locations in Antarctica, Greenland, and North America.

Ice Cores as Paleo-Weather Stations

What features of today’s weather might you want to know about in a weather report?• Temperature• Precipitation• Wind• Pollution or air quality• Others?

What features of past weather and climate might you want to know about?

We can’t measure the past climate as directly as today’s weather

Temperature of the ice today is not the same as the temperature of the snow when it fell long ago.

• Snow can warm up or cool down as it is buried and converted to ice (can’t just stick a thermometer on an ice core, to measure temperature in the ancient past J).

• The direct memory of past air temperature has been overwritten by more recent air temperatures, i.e. the surface of the world knows only its present (or very recent) temperature.

• How can we learn what the temperature was back then?

Proxies

We have to use proxies. What is a "proxy"?

• A measurable quantity that is used as a substitute for another (perhaps unmeasurable) quantity.

(How does this relate to a Microsoft Inc. shareholders�Annual Meeting?)

A Proxy for Past Temperature

If we want to know what the temperature was in the past: • We need to identify "something" that collected on the

polar ice sheets in the past.

• Some characteristic about the "thing" deposited had to be different when it was deposited at different temperatures (so that we have a "handle" to go back and deduce what the temperature was back then).

• Obviously the characteristic that we are interested in should always have the same value for the sametemperature.

Groups of Curious Scientists seek a "Proxy" Temperature Record

Many years later, we drill through the ice sheet, to discover the temperature history here.• What is the "thing" that we collect as a temperature proxy?• What is the characteristic of the "thing" that we want to convert

to a temperature record?Suppose bead throwers were fickle, and changed their minds day by day, on what temperature constituted a "cold" day. Maybe one day they thought –30oC was cold, but the next day they thought -30oC was "average", and -50oC was cold.• Would you still like this proxy record?

Suppose that in the past, somebody threw a handful of colored beads onto a polar ice sheet every day.

• On warm days, the beads were red.• On cold days, the beads were blue.• On average days the beads were white.

Composition of AtomsRemember that the nucleus of any atom is made up of • protons (which have a �+� charge), and

• neutrons (which have no charge).• The nucleus is surrounded by a cloud of electrons (with �-� charge) in orbits specified by rules from quantum mechanics (which will not be on the next test!).

• The number of electrons is equal to the number of protons in the nucleus, in order to preserve the charge balance.

http://www.pbs.org/wgbh/aso/tryit/atom/elempartp.html

The Periodic TableThe number of electrons in an atom determines which

element it is in the periodic table. Why is that?• An atom uses its electrons to form chemical bonds

with other atoms.• Its neutrons don’t matter (much).

Stable isotopes of Oxygen

OXYGEN atoms in the natural environment come in 2 forms, or "isotopes".

• This is also true for oxygen in water molecules (H2O).• The 2 isotopes, oxygen-18 (18O) and oxygen-16 (16O)

are both stable atoms (i.e. they not radioactive).• The only difference is that 18O has 2 extra neutrons in its

nucleus, making each 18O atom a little bit heavier than an 16O atom.

• Approximately 1 in every 500 oxygen atoms is an 18O atom.

• There are also a few oxygen molecules with 9 neutrons, but oxygen-17 (17O) is very rare.

Stable isotopes of Oxygen – 16O and 18O

Stable Isotopes and Environmental Research

An H2O molecule can contain either 18O or 16O.

In the 1950’s scientists knew that:• When it rains, the water molecules (H2O) containing

an 18O atom tend to fall out preferentially in the rain.

They asked the questions:• Where does rain water come from?• Can meteorologists track water back to its source

using 18O?

Willi Dansgaard’s MysteryA young Danish physicist was interested in isotopes as a

tracer in rainwater in the 1950’s.

Here is one of his early, very sophisticated experiments on rainwater in Copenhagen in 1952.

W. Dansgaard. 2005. Frozen Annals – Greenland Ice Cap Research. Niels Bohr Institute, Copenhagen.

Although Carlsberg has often funded ice-core science in Denmark, the 18O content, and ultimate fate of initial contents of this high-tech laboratory research vessel have been lost to the history of science …J

On a research trip to Greenland …to study precipitation, Willi Dansgaard took samples of

ice from several icebergs.

• He found large differences in the ratio of 18O to 16O among icebergs.

• Some values were like rain and snow that Dansgaard collected along the coast.

• Others had much less 18O.

• What was going on here?

Willi Dansgaard’s IcebergsThe icebergs came from glaciers that drain the center of

the Greenland Ice Sheet.• The icebergs with lower amounts of 18O came from

deep in the glaciers. • The icebergs with higher amounts of 18O came from

shallower in the glaciers.

ELA

• Which ice had traveled farther?• Which ice was older?• Is this a climate-change story?

Maybe …

d18O - a way to report isotope ratios

Geochemists find it is easier to measure the differencebetween the ratio Rsample of 18O to 16O in a sample and the ratio Rstandard of 18O to 16O in a reference standard, than it is to measure the absolute amount of 18O in a sample.

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æ=

OOR 16

18

1000R

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é -=d

The standard is called �Vienna Standard Mean Ocean Water�, or V-SMOW.

• R is the ratio of 18O atoms to 16O atoms in a sample.

Definition of d18O

TCS (Team Curious Scientists) figures out d18O

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18

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The standard is called �Standard Mean Ocean Water�, or SMOW.

• You can buy it from IAEA (Intl Atomic Energy Agency).

• What is the d-value of the water in your bottle of SMOW (from �Trader SMOW’s” J)?

• Why do you think scientists might define d this way?

• R is the ratio of 18O atoms to 16O atoms in a sample.

It’s a Nutty WorldYou are watching the Super Bowl along with a Bowl of

Super-Duper® Mixed Nuts.• Every 15 minutes, you reach in, stir up the nuts, and then

you take out a handful.• You then also reach back into the bowl and pick out a

few extra cashews, and add them to your handful.• You eat your handful of nuts.• What has just happened to the cashews as a fraction of

the remaining nut mix?• The remaining nut mixture is progressively more

depleted in cashews after every handful.• The decreasing fraction of cashews in the bowl can be

related directly to the number of handfuls that you have extracted, or to the time into the game.

d18O and Cloud TemperatureWater vapor evaporates from a tropical or temperate ocean.• Vapor moves toward the polar regions in storm systems.• Whenever an air mass cools by 1oC, a predictable fraction

of the vapor condenses, and falls out as rain or snow. • The heavy isotope preferentially falls out in the rain or

snow in a predictable way. [like your extra cashews].• The remaining vapor in the cloud is progressively more

depleted in the heavy isotope as the air mass cools. [like the cashews remaining in your nut bowl]

• The isotopic composition d18O of the precipitation can be related directly to the amount of rain or snow that has fallen from the clouds, or to the temperature in the clouds where the droplets condensed from water vapor.

d18O as a Temperature Proxy

Choosing an Ice-Core Site

Near the summit is often best.

• Climate signal relates to the same place for ice of all ages.

Layers get thinner over time due to flow.

• When are layers too thin to resolve annual signal?

Willi Dansgaard’sLegacy

NEEM – drilling finished in 2012• Found ice from entire previous

warm interglacial period.

South Dome core - 1983• Dye 3 (Cold War radar site).• Core went back into last ice age.Summit - GRIP 1992/GISP2 1993• 2 cores, 30 km apart. 110 ka ice.• Fast climate changes are not ice-

flow artifacts.NGRIP - 2003• Recovered ice from end of

previous warm interglacial period (>110 ka BP).

.eGRIP

NGRIP – 2016 -• Currently underway• Studying NEGIS(ice-stream) onset.

NEGIS

Dating an Ice Core

GISP2 ice core, ~20,000 years old

Age-Depth relation for

central Greenland

• How many years of ice can we recover in 1 meter of core at each depth?

• How old is the oldest recoverable ice?

From an ice-flow model.

Going backwards in the Time Machine

Younger Dryas 11.6-12.9 ka• Last gasp of the Ice Age.

Wisconsinan Ice Age, 18-110 ka• Huge and fast transitions in climate in just a few years

(sometimes in less than a decade).• All humans are hunter-gatherers (Why would anyone want to

be a farmer in a world like this?)

20oC

d18O – a proxy for past temperatures in Greenland

Holocene 0-10ka BP• Climate stable and warm.• Human civilizations and

agriculture are possible.