Tutorial 4: Reconstructing Past Changes in Atmospheric Climate

Week 1, Day 4, Paleoclimate

Content creators: Sloane Garelick

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Tutorial Objectives

Estimated timing of tutorial: 20 minutes

In this tutorial, we’ll analyze δD and atmospheric CO₂ data from the EPICA Dome C ice core. Recall from the video that δD and δ¹⁸O measurements on ice cores record past changes in temperature and that measurements of CO₂ trapped in ice cores can be used for reconstructing past changes in Earth’s atmospheric composition.

By the end of this tutorial you will be able to:

• Plot δD and CO₂ records from the EPICA Dome C ice core

• Assess changes in temperature and atmospheric greenhouse gas concentration over the past 800,000 years

Setup

# installations ( uncomment and run this cell ONLY when using google colab or kaggle )

# !pip install pyleoclim

# imports
import pandas as pd
import matplotlib.pyplot as plt
import pooch
import os
import tempfile
import pyleoclim as pyleo

Install and import feedback gadget

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# @title Install and import feedback gadget

!pip3 install vibecheck datatops --quiet

from vibecheck import DatatopsContentReviewContainer
def content_review(notebook_section: str):
    return DatatopsContentReviewContainer(
        "",  # No text prompt
        notebook_section,
        {
            "url": "https://pmyvdlilci.execute-api.us-east-1.amazonaws.com/klab",
            "name": "comptools_4clim",
            "user_key": "l5jpxuee",
        },
    ).render()


feedback_prefix = "W1D4_T4"

Figure Settings

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# @title Figure Settings
import ipywidgets as widgets  # interactive display

%config InlineBackend.figure_format = 'retina'
plt.style.use(
    "https://raw.githubusercontent.com/neuromatch/climate-course-content/main/cma.mplstyle"
)

Helper functions

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# @title Helper functions

def pooch_load(filelocation=None, filename=None, processor=None):
    shared_location = "/home/jovyan/shared/Data/tutorials/W1D4_Paleoclimate"  # this is different for each day
    user_temp_cache = tempfile.gettempdir()

    if os.path.exists(os.path.join(shared_location, filename)):
        file = os.path.join(shared_location, filename)
    else:
        file = pooch.retrieve(
            filelocation,
            known_hash=None,
            fname=os.path.join(user_temp_cache, filename),
            processor=processor,
        )

    return file

Video 1: Atmospheric Climate Proxies

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content_review(f"{feedback_prefix}_Atmospheric_Climate_Proxies_Video")

If you want to download the slides: https://osf.io/download/szyhp/

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Section 1: Exploring past variations in atmospheric CO₂

As we learned in the video, paleoclimatologists can reconstruct past changes in atmospheric composition by measuring gases trapped in layers of ice from ice cores retrieved from polar regions and high-elevation mountain glaciers. We’ll specifically be focusing on paleoclimate records produced from the EPICA Dome C ice core from Antarctica.

Credit: Conway et al 2015, Nature Communications

Let’s start by downloading the data for the composite CO₂ record for EPICA Dome C in Antarctica:

# download the data using the url
filename_antarctica2015 = "antarctica2015co2composite.txt"
url_antarctica2015 = "https://www.ncei.noaa.gov/pub/data/paleo/icecore/antarctica/antarctica2015co2composite.txt"

data_path = pooch_load(
    filelocation=url_antarctica2015, filename=filename_antarctica2015
)  # open the file

co2df = pd.read_csv(data_path, skiprows=137, sep="\t")

co2df.head()

	age_gas_calBP	co2_ppm	co2_1s_ppm
0	-51.03	368.02	0.06
1	-48.00	361.78	0.37
2	-46.28	359.65	0.10
3	-44.41	357.11	0.16
4	-43.08	353.95	0.04

Next, we can store this data as a Series in Pyleoclim:

ts_co2 = pyleo.Series(
    time=co2df["age_gas_calBP"] / 1000,
    value=co2df["co2_ppm"],
    time_name="Age",
    time_unit="kyr BP",
    value_name=r"$CO_2$",
    value_unit="ppm",
    label="EPICA Dome C CO2",
)

Time axis values sorted in ascending order

/tmp/ipykernel_112451/2608164936.py:1: UserWarning: auto_time_params is not specified. Currently default behavior sets this to True, which might modify your supplied time metadata.  Please set to False if you want a different behavior.
  ts_co2 = pyleo.Series(

We can now plot age vs. CO₂ from EPICA Dome C:

ts_co2.plot(color="C1")

(<Figure size 1000x400 with 1 Axes>,
 <Axes: xlabel='Age [kyr BP]', ylabel='$CO_2$ [ppm]'>)

Notice that the x-axis is plotted with present-day (0 kyr) on the left and the past (800 kyr) on the right. This is a common practice when plotting paleoclimate time series data.

These changes in CO₂ are tracking glacial-interglacial cycles (Ice Ages) over the past 800,000 years. Recall that these Ice Ages occur as a result of changes in the orbital cycles of Earth: eccentricity (100,000 year cycle), obliquity (40,000 year cycle), and precession (21,000 year cycle). Can you observe them in the graph above?

Section 2: Exploring the relationship between δD and atmospheric CO₂

To investigate the relationship between glacial cycles, atmospheric CO₂ and temperature, we can compare CO₂ to a record of hydrogen isotopic values (δD) of ice cores, which is a proxy for temperature in this case. Remember, when interpreting isotopic measurements of ice cores, a more depleted δD value indicates cooler temperatures, and a more enriched δD value indicates warmer temperatures. This is the opposite relationship we have looked at previously with δ¹⁸O, not because we are looking at a different isotope, but because we are not looking at the isotopic composition of ice rather than the isotopic composition of the ocean.

Let’s download the EPICA Dome C δD data, store it as a Series, and plot the data:

# download the data using the url
filename_edc3deuttemp2007 = "edc3deuttemp2007.txt"
url_edc3deuttemp2007 = "https://www.ncei.noaa.gov/pub/data/paleo/icecore/antarctica/epica_domec/edc3deuttemp2007.txt"
data_path = pooch_load(
    filelocation=url_edc3deuttemp2007, filename=filename_edc3deuttemp2007
)  # open the file

dDdf = pd.read_csv(data_path, skiprows=91, encoding="unicode_escape", sep="\s+")
# remove nan values
dDdf.dropna(inplace=True)

dDdf.head()

	Bag	ztop	Age	Deuterium	Temperature
12	13	6.60	38.37379	-390.9	0.88
13	14	7.15	46.81203	-385.1	1.84
14	15	7.70	55.05624	-377.8	3.04
15	16	8.25	64.41511	-394.1	0.35
16	17	8.80	73.15077	-398.7	-0.42

dDts = pyleo.Series(
    time=dDdf["Age"] / 1000,
    value=dDdf["Deuterium"],
    time_name="Age",
    time_unit="kyr BP",
    value_name=r"$\delta D$",
    value_unit="\u2030",
    label=r"EPICA Dome C $\delta D$",
)

Time axis values sorted in ascending order

/tmp/ipykernel_112451/432984493.py:1: UserWarning: auto_time_params is not specified. Currently default behavior sets this to True, which might modify your supplied time metadata.  Please set to False if you want a different behavior.
  dDts = pyleo.Series(

dDts.plot()

(<Figure size 1000x400 with 1 Axes>,
 <Axes: xlabel='Age [kyr BP]', ylabel='$\\delta D$ [‰]'>)

When we observe the δD data, we see very similar patterns as in the atmospheric CO₂ data. To more easily compare the two records, we can plot the two series side by side by putting them into a MultipleSeries object. Since the δD and CO₂ values have different units, we can first standardize the series and then plot the data.

# combine series
ms = pyleo.MultipleSeries([dDts, ts_co2])

# standarize series and plot
ms.standardize().plot()

(<Figure size 1000x400 with 1 Axes>, <Axes: xlabel='Age [ka]', ylabel='value'>)

Now we can more easily compare the timing and magnitude of changes in CO₂ and δD at EPICA Dome C over the past 800,000 years. During glacial periods, δD was more depleted (cooler temperatures) and atmospheric CO₂ was lower. During interglacial periods, δD was more enriched (warmer temperatures) and atmospheric CO₂ was higher.

Questions 2: Climate Connection

1. Why do δD, CO₂ and glacial cycles covary so closely?

2. Can you identify glacial and interglacial periods? Today, are we in an interglacial or glacial period?

3. Do the cooling and warming periods of the cycles happen at the same rate?

4. What climate forcings do you think are driving these cycles?

Click for solution

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Summary

In this tutorial, we dove into the captivating world of paleoclimatology, focusing on the analysis of hydrogen isotopes (δD) and atmospheric CO₂ data from the EPICA Dome C ice core. This involved understanding how δD and δ¹⁸O measurements from ice cores can enlighten us about past temperature changes, and how trapped CO₂ in these ice cores can help us reconstruct shifts in Earth’s atmospheric composition.

By the end of the tutorial, you should be comfortable with plotting δD and CO₂ records from the EPICA Dome C ice core and assessing changes in temperature and atmospheric greenhouse gas concentrations over the past 800,000 years. In the next tutorial, we’ll introduce various paleoclimate data analysis tools.

Resources

Code for this tutorial is based on an existing notebook from LinkedEarth that explores EPICA Dome C paleoclimate records.

Data from the following sources are used in this tutorial:

• Jouzel, J., et al. Orbital and Millennial Antarctic Climate Variability over the Past 800,000 Years, Science (2007). https://doi.org/10.1126/science.1141038.

• Lüthi, D., Le Floch, M., Bereiter, B. et al. High-resolution carbon dioxide concentration record 650,000–800,000 years before present. Nature 453, 379–382 (2008). https://doi.org/10.1038/nature06949.

• Bereiter, B. et al., Revision of the EPICA Dome C CO₂ record from 800 to 600 kyr before present, Geoph. Res. Let. (2014). https://doi.org/10.1002/2014GL061957.