Sio 25 week2

midterm 1

What are temperature anomalies?

A temperature anomaly is the difference between the observed temperature and a reference average

What do temperature anomalies suggest?

- Positive anomaly: Warmer than average.
- Negative anomaly: Cooler than average

How is the cryosphere changing?

What is sea level rise?

Sea level rise is the increase in the average height of the oceans surface relative to the land

Why is sea level rise happening?

- melting glaciers and ice sheets adding to the total volume
- Thermal expansion: as the ocean absorbs heat, water expands and takes up more space
- Oceans have absorbed >90% of excess heat since 1970s

What is the effect of climate change on weather?

-Increases frequency and intensity of extreme events
- More heat waves, intense rain, stronger hurricanes, erratic monsoons, and droughts

How does the effect of the sun (solar irradiance) compare to anthropogenic (human) activities?

- Solar irradiance ≈ constant (~1360 W/m²).
- Sunspot cycles cause only small (~0.2%) short-term fluctuations.
- Anthropogenic CO₂ → large radiative forcing and long-term warming.
- Human activity dominates modern climate change, not the Sun.

What are paleoclimate proxies?

Proxies = indirect indicators of past climate.

Know the different examples of proxy and what each proxy tells us.

1. Foraminifera (marine shells):
measures ocean temp & ice volume
timespan: millions of yrs

2. Ice cores
measures gas bubbles
timespan: 800,000 yrs

3. Tree rings
measures past climate conditions like temperature and precipitation by reflecting the growth patters of a tree over time. (width = temp & rainfall)
timespan: ~10,000 yrs

4. Corals
measures past environmental conditions like sea surfaces temperature and salinity, and ocean chemistry (growth bands = sea temp & chemistry)
timespan: 1,000s of yrs

How do CO2 levels affect Earth's climate?

- CO₂ is the main greenhouse gas controlling global temperature.
- More CO₂ → stronger greenhouse effect → warming.
- Less CO₂ → cooling and glaciation.
- Long-term cooling (last 55 Ma) linked to CO₂ decline from Himalayan uplift/weathering.

Know the main extinction events covered in class

End-Permian

Cretaceous-Paleogene

Paleocene-Eocene

When did the End-Permian occur?

252 MA

When did the Cretaceous-Paleogene occur?

65 MA

When did the Paleocene-Eocene Thermal Maximum occur?

55.8 MA

what is the cause of End-Permian?

massive volcanic eruption in the Siberian Traps -> large scale release of CO₂ (heated atmosphere to lethal lvls, causing global temp increase)

Increased CO₂ was absorbed by oceans, making them more acidic (organisms like coral cant build shells and skeletons)

what is the cause of Cretaceous-Paleogene?

asteroid impact: killed off dinosaurs, ejected massive amounts of dust, rock, and sulfur into atmosphere, which blocked sunlight and causes a sever drop in global temp

what is the cause of Paleocene-Eocene?

Rapid and massive release of carbon into earths atmosphere and oceans
Impact: 5-8 °C global average temperature rise
Ocean acidification & ecosystem disruption

Which one of these events is considered the closest historical analog to current anthropogenic climate change due to fossil fuel burning?

Paleocene-Eocene Thermal Maximum is closest analogy

What are the impacts of volcanic eruptions?

- Short-term: Cooling (sulfate aerosols reflect sunlight).
- Long-term: Warming/extinction if massive CO₂ is released (e.g., Siberian Traps)

How is CO2 related to extinction events?

High CO₂ → global warming, ocean acidification, and deoxygenation → mass die-offs.
Low CO₂ → ice ages and habitat loss.

what is the cooling trend of the last 55 million years?

15°C cooling seen in δ¹⁸O records.

What was the cooling trend of the last 55 million years caused by?

- Uplift of Tibetan Plateau → increased silicate weathering → - CO₂ removal.
Reduced volcanism → less CO₂ input.
- Formation of Antarctic ice sheets

What are Milankovitch Cycles

Orbital variations controlling solar insolation:
Eccentricity (~100k yr): Orbit shape.
Obliquity (~41k yr): Axial tilt changes (21.5-24.5°).
Precession (~23k yr): Wobble of Earth's axis

What happened during the Pleistocene Ice Ages?

Repeated glacial-interglacial cycles (100 kyr period after ~1 Ma).
Driven by Milankovitch cycles + CO₂ feedback.
Ice sheets advanced/retreated across N. America & Europe.

When did Pleistocene Ice Ages happen?

Began ~2.6 Ma; ended ~11.7 ka

What are meltwater pulses?

Rapid releases of meltwater from retreating ice sheets

How does meltwater affect sea level?

Raised sea level by 10-25 m in <1000 years

What is the younger dryas period?

Younger dryas, a period of abrupt, intense cooling

When did the younger dryas period happen?

occurred between ~12,900-11,700 years ago. (Abrupt return to cold conditions during deglaciation)

What was younger dryas period caused by

Freshwater from melting ice diverted into N. Atlantic → weakened AMOC → cooling.

What is AMOC?

Deep ocean "conveyor belt" transferring heat northward and cools water South to regulate global climate

How does AMOC relate to the
Younger Dryas?

Freshwater disrupted sinking in North Atlantic → circulation collapsed → cold period

How does AMOC relate to today's climate?

Greenland meltwater could weaken AMOC again → cooling in Europe, disrupted weather globally

How is the ocean Stratified

-Controls ocean circulation (thermohaline system / AMOC).
- Affects nutrient cycling — strong stratification limits nutrient upwelling to surface ecosystems.
- Influences climate — the ocean stores and redistributes heat globally.
- Climate change can increase stratification (surface warms faster than deep water), reducing vertical mixing.

What are the different layers and how does temperature change between them?

At the surface (mixed layer): Warm due to direct solar heating.
Thermocline: Sharp temperature gradient — strongest in the tropics, weaker at high latitudes.
Deep ocean: Uniformly cold (~2°C) because sunlight doesn't reach there.

How does the thermocline vary with Tropics (0-30°?

- Strong, permanent thermocline
- Warm surface year-round → big temperature contrast between warm surface & cold deep water.

How does the thermocline vary with Mid-latitudes (30-60°)?

- Seasonal thermocline
- Forms in summer when surface warms; weakens or disappears in winter as surface cools and mixes

How does the thermocline vary with High latitudes (60-90°)?

- Weak or absent thermocline
- Surface and deep waters are both cold → little temperature difference

How do salinity and temperature affect density?

Temperature ↓ (colder = denser)
Salinity ↑ (saltier = denser)
- So cold, salty water sinks → drives deep ocean circulation

What latitudes have fresher water?

Equator (0°)

Warm, heavy rainfall
Fresher (lower salinity)
Rain > evaporation dilutes surface water.

High Latitudes (60°+)

Cold, melting ice, low evaporation
Fresher
Ice melt + rainfall lower salinity.
- Low salinity at equator & poles
High salinity in subtropical "evaporation belts"

what latitudes have saltier water?

Subtropics (20-30°)
Hot, dry, low rainfall
Saltiest
High evaporation > precipitation.

how all of this relates to thermohaline circulation.

- Driven by density differences from temperature (thermo) and salinity (haline).
- Cold, salty water sinks in the North Atlantic (around Greenland/Norway) → forms North Atlantic Deep Water (NADW).
- Deep water flows south, mixes with Antarctic water, eventually upwells in the Indian and Pacific Oceans.
- Warm surface currents (like the Gulf Stream) return water poleward → completing the loop.

How does wind affect ocean circulation?

-Surface currents are mainly driven by wind.
- Coriolis effect deflects motion:
Right in Northern Hemisphere
Left in Southern Hemisphere
- Winds + Coriolis + continents → form large rotating systems called gyres.

What are gyres?

-large circular surface current systems in each ocean basin.

Gyres redistribute heat: warm water poleward on the west side, cold water equatorward on the east.

What type of currents are associated with gyres?

ocean: North Atlantic / North Pacific
Subtropical gyres
rotation direction: Clockwise

- ocean: South Atlantic / South Pacific / Indian
Subtropical gyres
rotation direction: Counterclockwise

- Western boundary currents: warm, narrow, fast (e.g., Gulf Stream).
- Eastern boundary currents: cold, broad, slow (e.g., California Current).

How does global warming affect the ocean?

1. Ocean Warming:
~90% of Earth's excess heat is absorbed by the ocean.
Warming strongest in upper 700 m (surface layers).
Leads to thermal expansion → sea level rise.
2. Stratification Increases:
Surface warms faster than deep water → reduced mixing.
Nutrient upwelling weakens → affects marine ecosystems.
3. Deoxygenation:
Warmer water holds less O₂.
Slower circulation → less oxygen transport → "dead zones."
4. Acidification:
Oceans absorb CO₂ → forms carbonic acid → lowers pH → harms corals and shell-forming organisms

How does global warming affect the hydrological cycle?

- A warmer atmosphere holds more water vapor → intensifies the water cycle:
- More evaporation → more precipitation (esp. heavy storms).
- Wet regions get wetter, dry regions get drier.
- Changes rainfall patterns → droughts, floods, and shifting monsoons.
- More water vapor → stronger greenhouse effect (since H₂O is a GHG).