GEOL 106 – Winter 2025
ASSIGNMENT 1 – Climate Proxies and Climate Change
Due Date: January 31* (11:59 PM, Kingston time)
Mark: /23
A few things before starting.
• I provide an answer sheet (in Word format) where you can write your answers. Please use this sheet, it makes it easier for the TAs to be consistent in their marking. You need to save as a PDF to submit.
• note that you will be only able to upload the answer sheet as a PDF in OnQ
• information I give you to read through prior to the questions can be useful.
*this is the due date without the 3-day grace period
PART 1 – Climate Proxies
Climate change is not a new phenomenon; it has been occurring throughout Earth history. Part 1 of the assignment examines palaeoclimate data from Earth history and the present. Through use of archives and proxies, Earth scientists can travel back in time and discover what the climate was like in the Earth’s past. By understanding climate change in the past, scientists gain insight into how current conditions fit or diverge from previous behaviour, and how the future climate might look. We discussed climate archives and proxies in class and how they can be used to learn about past climate. This assignment focuses on proxy data (from ice and salt cores) which can be used to reconstruct palaeoclimates.
Ice Core Data
By looking at past concentrations of greenhouse gases (such as CO2 and methane) in air bubbles found in ice cores, scientists can calculate how modern amounts of these gases compare to those of the past and can compare past concentrations of greenhouse gasses to temperature at that time. Ice cores have been collected since the 1950s from locations throughout the world, but the majority come from the ice sheets of Greenland and Antarctica. The ice core data you will be using was collected from Lake Vostok (see above right image). Conditions of glacial ice formation here provide excellent time resolution, and air bubbles in the ice core preserve actual samples of the Earth’s palaeo-atmosphere.
Similar to tree rings, ice cores preserve annual layers which are the result in seasonal differences in snow properties. These annual layers, as well as dust trapped in the ice allow scientists can determine how old a layer of ice is.
19 cm long section of ice core from Antarctica. This section contains 11 annual layers with summer layers (arrowed) sandwiched between darker winter layers. (from the US National Oceanic and Atmospheric Administration)
Through analysis of ice cores, scientists learn about glacial-interglacial cycles, changing atmospheric CO2levels, and climate stability over the last tens of thousands of years. The ice contains air bubbles, and scientists use the isotopic composition oxygen to determine the global average temperature at the time the snow fell. In addition, bubbles of air became trapped in each layer of ice as the snow turned into glacial ice. With temperature and CO2 concentration data, scientists can analyze whether variations in CO2 concentrations in the atmosphere correlates with changes in average global temperatures.
Examining Ice Core Data
You will use ice core data from the East Antarctic Ice Sheet. The ice core is from a drilling operation that drilled to a depth of 3.2 km at the Vostok research station. At this depth in the ice sheet, the drill has reached layers of ice about 420,000 years old. Use the information given as well as the graphs to answer the following questions.
Examine the following graph.
1. This is a smaller version of a graph available in the Graphs file. Let’s look at the X-axis first. Which point is younger? Point A or Point B? (1 mark)
2. What variable does the Y-axis show? (1 mark)? Does 0°C correspond to the freezing point of water? (1 mark)
3. What are the temperatures compared to the modern average at Point A and Point B? (2 marks) (include units)
4. Now, look at graph (the blue line). Briefly describe trends as you move from ~ 250,000 to 150,000 years ago (1 mark).
In the past, did the Earth warm up faster than it cooled down? (1 mark).
The graph below (and in the Graphs file) shows atmospheric CO2 concentrations over the last 420,000 years, extracted from the Vostok ice core. The CO2 concentrations are given in parts per million (ppm). Think of a CO2 value of 230 ppm on the graph as a baseline. The amount of CO2 in the atmosphere was low when its concentration was less than 230 ppm, and becoming higher when its concentration was above 230 ppm.
Data from Petit, J.R. et al. (1999), Nature, 399, 429-436
5. What was the ~ atmospheric CO2 concentration 350,000 years ago? (1 mark) I will accept a limited range of values.
6. Do times of low atmospheric CO2 on the carbon dioxide graph correspond to the times of cooler temperatures seen on the age vs temperature graph? (1 mark)
Salt Core Data
In arid climates, layers of halite (salt) in sedimentary rocks form when salty water evaporates and the salt collects at the bottom of the lake or seabed. Halite (NaCl), which is known as table salt, is a common evaporite mineral. During the formation of halite crystals, microscopic bubbles of fluid are trapped within the crystal. These bubbles are known as fluid inclusions and can be seen in the images below. At times, an air bubble may also be present. Analyzing both the liquid and vapour portions of the fluid inclusions gives information on palaeo-temperatures and atmospheric composition. An interesting note – these fluid inclusions have also been found to contain micro-organisms.
Example of a ‘salt core’. The pinkish/reddish/brownish material are evaporites. This core is 830 million years old.
Examples of fluid inclusions (L) containing air bubbles (V). The air bubbles contain ‘snapshots’ of atmospheric composition at the time of formation.
The graph (right) depicts palaeoclimate data for the past 150,000 years from 4 locations (including Vostok). Answer the following questions about the data from the 4 cores.
7. From 90,000 years ago to the present, is there similarity among the temperature curves from the different locations? (1 mark)
8. If so, which cores generally matchup? (1 mark)
9. Which one(s) seem to reflect a different palaeoclimate history than the others? (1 mark)
10. Based upon these observations, which cores might reflect global climate trends more than local climate trends? (1 mark)
Recently, a Canadian scientist was in the news due to their involvement in an ice drilling project at Little Dome C / Concordia Station in Antarctica. Drilling at this location is part of the Beyond EPICA project .
Read the articles (available in OnQ) and answer the following questions.
11. How long was the ice core? (1 mark)
12. How far back in geological time does the ice core reach? (1 mark)
13. What episode in Earth history do the scientists involved in the project want to study and why? (2 marks)
PART 2 - Present-Day Climate Change
We are living in the Holocene epoch, which began close to 11,700 years ago. The average amount of CO2 in the atmosphere during the Holocene epoch was 280 ppm up until about 1780 AD. The more recent concentrations of CO2 in the atmosphere are not depicted in the Vostok ice core data, which stops around 250 years before present (BP).
14. Using the Keeling Curve (linkin OnQ), report the current atmospheric CO2 concentration and the date. (1 mark)
15. What is your CO2 birth number? Using the interactive plot at NOAA’s Global Monitoring Laboratory (linkin OnQ), determine the following.
a. What is your CO2 birth number (just use month and year)? (1 mark)
b. If your instructor was born (not saying I was) in October 1980, what is their CO2 birth number? (1 mark)
c. How much have CO2 concentrations changed (in ppm) from October 1980 to October 1990? (1 mark)
d. How much have CO2 concentrations changed (in ppm) from your birthday (month and year) to 10 years later? For example, if you were born in January 2004 compare this value to January 2014. (1 mark)
e. Do the answers in c andd indicate an increasing rate at which CO2 is accumulating in the atmosphere? (1 mark)