Earth's climate in "Deep Time"

Week

GEOS 3410

Week Schedule

Tuesday

  • Ice core presentations
  • Ancient climate
  • snowball glaciations

Thursday

  • Less ancient climate
  • Paleocene-Eocene Thermal Maximum/Anomaly
  • Cenozoic cooling

Outside of class

  • Week reading (syllabus)
  • Wrap-up/review in-class activities
  • Term paper outline [Nov. 1] — 5pm Friday

No class next Tuesday:

Go vote (down-ballot matters!) and look after yourself & friends.

Term paper outline

  • All arguments, ideas, and information of the final paper
  • Cite every source you plan to cite
  • Alphanumeric formatting:     I, II, III → A, B, C → 1, 2, 3 → a, b, c
  • ≥25% on the physical climate processes underlying your topic
  • ≥25% on solutions (both adaptation & mitigation)
Friday Nov. 1 by 5pm (Canvas/Analog)

Ancient Climate

Faint young sun

The Sun's luminosity (red) was ∼30% dimmer in Earth's early history.

≪10% changes drive glacial periods in the modern
Wikimedia

Anoxic young Earth

Atmospheric oxygen appears after 2 Ga, and abundant after 1 Ga.
Other GHGs available in anoxia:
methane (CH4), ethane (C2H6)
Adapted from: H. Holland (Wikimedia)

Diamictites & dropstones as early as 2.9 Ga

Diamictite
lithified, poorly-sorted sediments.
(tillites = glacial diamictite)
The Geological Society
Melezhik+ 2012

Paleogeography from paleomagnetism

Magnetic minerals record the magnetic field inclinations when they form.

Magnetic field line inclinations vary with latitude.

Paleomagnetic orientations record paleolatitude → paleogeography

The Marinoan Glaciation (650–630 Ma)

☆ = (near) glacial deposits

Glacial deposits spanning the tropics to mid-latitudes

Hoffman+ 2017

Snowball Earth glaciation

(Overall) accepted snowball glaciations

Age Event
650–630 Ma Marinoan glaciation
720–660 MaSturtian glaciation
2.4 GaHuronian glaciation

Banded Iron Formations (BIFs)

Banded Iron Formations (BIFs)

  • Alternating bands of iron-poor red chert (SiO2) and gray iron oxides (Fe3O4, Fe2O3)
  • 💧 Aqueous environment 💧
  • Ferrous iron (Fe2+) is soluble, ferric iron (Fe3+) is insoluble
  • →→→ Intermittent oxygenation of anoxic waters

After oxygenation (∼2 Ga), BIFs return only during Cryogenian Period (720–635 Ma)

Wikimedia

Ice sheets a significant source of iron today

[ghe]
Blood Falls, Taylor Valley, Antarctica

🧊 Entering Snowball Earth 🧊

Entering Snowball Earth

Inorganic carbon (carbonate-silicate) cycle
Krause 2023

Entering Snowball Earth

Hypothesize a scenario that leads to runaway glaciation, given:
  • Continents concentrated at low latitudes
  • Extensive continental shelf environments
  • Silicate weathering outpaces volcanic outgassing
  • Low mid-ocean ridge CO2 flux (Dutkiewicz+ 2024)
  • Paleoproterozoic: Fainter Sun and greater reliance on GHGs (Huronian glaciation)
☆ = (near) glacial deposits
Hoffman+ 2017

Escaping Snowball Earth

Escaping Snowball Earth

Inorganic carbon (carbonate-silicate) cycle
What part of the system is broken, now?
Krause 2023

Escaping Snowball Earth

Overlying cap carbonate: ∼ 10 m thick, deposited in < 1000 years
Basal diamicton with ice-rafted debris
IUGS

Variations on a snowball

  1. Snowball: continents and oceans completely glaciated
  2. Slushball: tropical to mid-latitude ocean/puddles
  3. Jormungand (Waterbelt): narrow thawed ocean belt that shifts seasonally
Image: Bindeman & Lee 2018

Less ancient climate

δ18O as a measure of hot/cold climates

Cenozoic Climate (66 Ma to present)

Gradual cooling trend across Cenozoic (More on this later!)
Data from: Zachos+ 2001

Paleocene-Eocene Transition

Carbonate shelf (calcareous ooze) sediments in Paleocene and Eocene interrupted by a pulse of carbonate dissolution that gradually recovered.

→ Time →

Paleocene

Eocene

Paleocene-Eocene boundary (55.8 Ma)
ECORD

Paleocene-Eocene Thermal Maximum (PETM)

Data from: Zachos+ 2001, dates corrected after Li+ 2022

Paleocene-Eocene Thermal Maximum (PETM)

  • 200 kyr event
  • Global temp. ↑ 6°C
  • Dramatic change in marine carbonates (lithology & δ13C)
  • Major environmental changes (Week 13)
Data from: Zachos+ 2001, dates corrected after Li+ 2022

Stable carbon isotopes

Stable carbon isotopes

98.9%
1.1%

Stable carbon isotopes

dell-C thirteen, dell-thirteen-C, delta-C, delta-carbon, … carbon
\[\begin{aligned} \delta^{13}C = 1000\times \left(\frac{^{13}C/^{12}C_{sample}}{^{13}C/^{12}C_{standard}}-1\right) \end{aligned}\]
🦑 Vienna Pee Dee Belemnite (VPDB) 🦑
$\frac{^{13}\text{C}}{^{12}\text{C}} = 0.011100 \pm 0.000026 ~~(2\sigma) $
Hoffman+Rasmussen 2022

Carbon fractionation … by life.

Biological reactions preferentially incorporate lighter C (12C)

🌱 & 🦠

❤️

And heterotrophs eat the low-δ13C producers!

C fractionation by photosynthesis

Wikimedia
In C4 plants, an extra step allows CO2 to convert to HCO3- in the plant. This favors incorporation of...

All the carbon fractionation

Wagner+ 2018

The carbon fractionation you should know

Sourceδ13CVPDB (‰)
Marine carbontes∼0
Volcanism/air −12 to −2
Photosynthesis (most biomass) −30 to −15
Methane (biotic/aboitic) −60 to −30

Reconstructing the PETM

Where does the isotopically light C come from?
Data from: Zachos+ 2001, dates corrected after Li+ 2022

The Carbon Isotope Excursion (CIE)

Varies from site to site
On average, Δδ13C= −4‰
Livsey+ 2019
Δδ13CCIE= −4‰

Volcanism?

🌋 δ13Cvolc= −8‰ 🌋
USGS
Δδ13CCIE= −4‰

(Marine) organic carbon?

🦠 δ13Corg-C= −24‰ 🦠
Oxidation (org-C → CO2) of a dried sea/marine basin
NOAA
Δδ13CCIE= −4‰

Methane

🧊 δ13CCH4= −60‰ 🧊
Clathrate
(CH4 within H2O ice)
Permafrost

Isotope Mass Balance

For δ13C values $\delta$ and reservoir masses $M$ for reservoirs $A,B,\dots$ $$\delta_A~M_A + \delta_B ~ M_B + \dots = \delta_{total} ~ M_{total}$$ $$ where~M_{total} = M_A + M_B + \dots$$
ReservoirMass (GtC)δ13C (‰)
Biomass600−24
Atmosphere800−6
Marine carbonate40,000+1
What is the combined δ13C of the surficial C reservoirs? δt = …

Isotope Mass Balance

How much C ($M_*$) would each source need to release to reproduce the CIE?
$$\delta_*~M_* + \delta_t ~ M_t = (\delta_t-4‰) ~ (M_t + M_*) $$
Source ($*$)δ13C (‰)
🌋 volcanoes 🌋− 8
🦠 marine organic C 🦠−24
🧊 methane (clathrates/permafrost) 🧊−60

Temperature response to C release

3000 GtC → +700 ppm CO2
δ18O excursion → 6°C warming
A very rough estimate
IPCC, AR6, Fig. 4.3

Duration of greenhouse forcing:
CO2 vs. CH4

What about the sudden disappearance of marine shelf carbonate at the PETM?

Paleocene

Eocene

ECORD, Wikimedia

Aqueous (e.g. ocean) carbonate system

\[\begin{aligned} \text{H}_2\text{O} + \text{CO}~_{2~(aq)} ~&\longleftrightarrow~ \text{H}_2\text{CO}_3 \\\\ \text{H}_2\text{CO}_3 ~&\longleftrightarrow~ \text{H}^{+} + \text{H}\text{CO}_3^- \\\\ \text{H}^{+} + \text{H}\text{CO}_3^- ~&\longleftrightarrow~ 2~\text{H}^{+} + \text{CO}_3^{2-} \\\\ (\text{H}_2\text{O} ~ &\longleftrightarrow ~ \text{H}^+ + \text{OH}^-) \end{aligned}\]
$$\text{Ca}^{2+} + \text{CO}_3^{2-} \longrightarrow \text{CaCO}_3$$

Aqueous (e.g. ocean) carbonate system

$$ \text{H}_2\text{O} ~\longleftrightarrow ~ \text{H}^+ + \text{OH}^- $$
Excess of H+ acidic pH < 7
Excess of OH− basic pH > 7
$$ \text{H}_2\text{O} + \text{CO}~_{2~(aq)} \leftrightarrow \text{H}_2\text{CO}_3 \leftrightarrow \text{H}^{+} + \text{H}\text{CO}_3^- \leftrightarrow 2~\text{H}^{+} + \text{CO}_3^{2-} $$

Aqueous (e.g. ocean) carbonate system

Aqueous (e.g. ocean) carbonate system

  • ↑ pH (↓ H+)… eqn. moves →
  • ↓ pH (↑ H+)… eqn. moves ←
  • ↑CO2 → ↑ H+ → ↓ pH
$$ \text{H}_2\text{O} + \text{CO}~_{2~(aq)} \leftrightarrow \text{H}_2\text{CO}_3 \leftrightarrow \text{H}^{+} + \text{H}\text{CO}_3^- \leftrightarrow 2~\text{H}^{+} + \text{CO}_3^{2-} $$

Calcite solubility

Calcite tends to dissolve (rather than precipitate) as …
↓ pH ↓
↓ Temperature ↓
↑ Pressure ↑
↑ Salinity ↑

So, where in the ocean is calcite least stable?

Calcite compensation depth (CCD)

CaCO3 ⇆ Ca2+ + CO32-
  • Calcite precipitates near the surface and gradually sinks
  • Above CCD, seawater is saturated with respect to calcite
  • Below CCD, calcite (net) dissolves
  • Lysocline: calcite dissolution ↑↑
What does an abrupt halt in global calcite deposition tell us?

The CCD shoaled (shallowed/rose up) due to ocean acidification from ↑↑ atm-CO2

ECORD

Foraminiferal "disaster taxa" precedes (found below) the CIE and dissolution pulse

What does this mean???
Livsey+ 2019

Entering the modern ice house climate

Cenozoic cooling

Data from: Zachos+ 2001

Cenozoic cooling

Data from: Zachos+ 2001
Date, MaEvent
34Antarctica glaciates (Eocene-Oligocene)
26–14Early Miocene warmth
14 →Antarctic ice sheet returns!
<5N Hemisphere ice sheets (Pliocene)

Atmospheric carbon over the Cenozoic

Falling CO2 → cooling… What drives falling CO2?
CENCO2PIP 2023

Mountain ranges → intense weathering

Tibetan plateau uplift began in Cenozoic…

Uplift → silicate weathering → CO2 drawdown
Wikimedia

The last 5 million years

Lowest CO2, coldest T, most ice, climatologicaly noisy.
Data from: Zachos+ 2001

The last 5 million years

Pleistocene epoch (2.6 Ma – present) ← Pliocene (5 – 2.6 Ma)
Why is it noisier?
Data: Lisiecki+Raymo 2004

Next Week ()

  • Week reading (syllabus)
  • Tuesday: No class.
    • Go vote — down-ballot matters!
    • Take good care of yourself
    • Look after your friends
  • Thursday: Cenozoic to Quaternary climate history (😍)
  • Term paper outline [Nov. 1] — 5pm Tomorrow

Next Week ()

  • Week reading (syllabus)
  • Tuesday: Climate Zine / Quaternary Period (🥶)
  • Thursday: The last glacial and its demise
  • Term paper [Nov. 22]