Midterm 3 Flashcards
(125 cards)
1
Q
How does the surface ocean circulate?
A
Wind stress
2
Q
How does the deep ocean circulate?
A
density (temperature/saltiness)
3
Q
How is the ocean and atmosphere coupled?
A
energy/heat exchange
mass exchange (hydrologic cycle, carbon cycle)
momentum exchange (surface wind stress)
4
Q
the specific heat of the atmosphere is ________ J
A
1,000
5
Q
the specific heat of the ocean is _______j
A
4,000
6
Q
it takes more energy to heat up the _______ (atmosphere/ocean).
A
Ocean. Specific heat is higher
7
Q
Surface gyres
A
large, circular ocean currents driven by wind and the Earth’s rotation
8
Q
Gyres move ________ (clockwise/counterclockwise) in SH
A
counterclockwise
9
Q
Gyres move ________ (clockwise/counterclockwise) in NH
A
clockwise
10
Q
Function of poleward brand
A
brings warm low latitude water toward the colder midlatitudes and polar regions
11
Q
function of equatorward branch
A
brings cold high latitude water toward the warm tropics
12
Q
what ocean is least likely to have a gyre? why
A
Southern Ocean because there are no continental boundaries to contain one
13
Q
gulf stream
A
a narrow stream of warm, tropical waters flowing northward on the western side of the atlantic basin (referred to as western boundary current)
14
Q
what happens when water converges in the centre of a gyre?
A
ekman transport and geostrophic flow
15
Q
Ekman spiral steps
A
- surface water is moved by the wind
- top layer of water moving drags down the layer beneath it - this second layer is further deflected by coriolis
- The deeper below the surface the farther each layer is deflected to the right (NH) + the amount of water transports decreases
16
Q
in the ekman spiral, the direction of the water is deflected about _______ degrees from the wind due to the coriolis effect
A
20-45
17
Q
_________ (divergence/convergence) occurs in the middle of the Ekman Spiral
A
convergence
18
Q
Convergence results in ________ (downwelling/upwelling)
A
downwelling
19
Q
divergence at the equator results in ________ (downwelling/upwelling)
A
upwelling
20
Q
downwelling
A
surface layer thickens due to mass convergence on both sides, transporting warming waters below
21
Q
upwelling
A
surface layer thins due to mass divergence on both sides, bringing colder, nutrient-rich water from deeper ocean layers to the surface
22
Q
divergence occurs at the ______ eastern/western boundary currents and at the ______ poles/equator
A
eastern/equator
23
Q
where does convergence (downwelling) usually occur?
A
polar regions and where surface currents converge, centers of subtropical gyres
24
Q
many ocean currents will change in response to _____ causing subtropical gyres to _______
A
wind stress; intensify
25
the ocean warms from ______ (top/bottom; bottom/top)
top/bottom
26
why may surface winds intensify
The ocean warms from top to bottom
Surface waters are more buoyant, and less mixing occurs with layers beneath The surface layers are narrower, so the winds are pushing the same amount of water through a smaller “pipe” so it has to speed up.
27
The net transport of water in the top 100m of the ocean will be at a ___-degree angle from the surface wind. what does this describe?
90. Ekman transport
28
Easterly trades and midlatitude westerlies lead to circulation cells in surface water known as ______
gyres
29
what do gyres explain?
cold eastern ocean boundaries, upwelling along the equator
30
water piles up in the middle of a ______ (gyre/geostrophic flow)
gyre
31
In ______ regions, the surface water piles up and the sea surface rises, which causes water to sink
convergence (downwelling)
32
in ______ regions, the surface water moves away, and the sea surface thins, which causes water to move up
divergence (upwelling)
33
Ekman transport is to the _____ (right/left) of the wind direction
right
34
do you think that waters right off the US west coast are relatively warm or cool?
cool because the movement of surface water away from the shore leads to upwelling - cold, nutrient water from deeper in the ocean rises to replace the surface water
35
Strong subtropical overturning cells move warm surface water __________ (poleward/equatorward) and colder water ____________(poleward/equatorward)
poleward;equatorward
36
thermohaline circulation
differences in water density (from salinity and temperature) that drive vertical exchange
37
Fresh water is _____ (MORE/LESS) dense
less
38
saltier water is _____ (MORE/LESS) dense
more
39
where is the saltiest water?
the atlantic
40
Atlantic Meridional Overturning Circulation (AMOC)
1. cold, deep waters forms near greenland and sinks
2. these waters spread and flow away from the origins
3. once it reaches the Southern Ocean, water upwells
4. Near-surface currents close the flow - move toward where the deep water is sinking
41
how long does AMOC take?
~1000 years
42
AMOC brings warm water _______ (northward/southward) while bringing colder water ____ (northward/southward)
northward/southward
43
in a warmer world, the water near the poles will be ______ (warmer/cooler) and ______ (fresher/saltier). why?
warmer; fresher because direct heating of the ocean, the release of melted ice water + increased precipitation
44
What would happen if Greenland melt accelerates, and a lot of fresh water is dumped here?
Would reduce deep water formation and slow down the conveyer belt
Reduces the energy that is transported toward the poles.
45
If the AMOC slows in response to warming global temperatures, what will this do to local temperatures in Western Europe?
Less heat being delivered to the N Atlantic Ocean at the surface, and less warming in Europe too
Less heat and CO2 being delivered to the deep Atlantic – instead they remain at the surface, so global surface temperatures would rise more quickly
46
AMOC projections
slows down the most under scenarios with an 8.5
very likely to decline in the 21st century, but low confidence in the projected timeline/magnitude
47
Ocean influences on global temperature
- The oceans slow global warming, so far reducing global warming by about 1K (compared to how much warming would have occurred had the oceans been very shallow and not able to take up heat)
- Ocean circulation plays a key role in shaping the spatial pattern of global warming
- Other important roles for the ocean (Sea level rise & The oceans take up a lot of the CO2 we emit)
48
What is the role of the cryosphere in the climate system
- energy balance through albedo changes
- ocean interactions through salinity of the ocean (AMOC) and blocking exchanges with the atmosphere
- atmosphere interactions (large scale circulation)S
49
Sea ice
o Thin pancakes when forming or thicker
o Fluctuates and changes throughout the seasons (Thinner)
o Forms directly from seawater
50
Icebergs
o Small or tabular (massive and geometric)
o Floating and forming year round
o Used to be part of ice sheet and broke off and float away
o Fresh water
51
Ice Sheet
o Surface river of melt that carves out canyon on both sides
o Stable throughout the seasons (Thicker)
o Ice sheets are formed by snowfall on land
o Grow to thickness of several Kms
o Fresh water
52
Sea ice growth
once it's formed, it continues to grow throughout the winter at its base, freezing more seawater beneath the existing ice. In spring/summer, it begins to melt at the surface and its base (if seawater temp is above freezing). the melt rate is independent of sea ice thickness. If its thick enough = multi-year ice
53
multi-year ice
thick enough sea ice that same of it will survive through the summer to the winter.
much more common in the arctic than antarctic
54
when is arctic sea ice at its max. extent?
march (end of winter season)
55
Why is the seasonal fluctuation of sea ice different in the Arctic vs. Antarctic?
- The Arctic is a semi-enclosed ocean -> sea ice is less mobile and tends to stay in the cold Arctic waters
- The Antarctic is a land mass surrounded by ocean -> the sea ice that forms can move freely away toward warmer waters
56
Why is the spatial pattern of sea ice different in the Arctic vs. Antarctic?
- Warm Atlantic currents flow into the Artic at the surface (AMOC)
- Strong circumpolar winds drive surface flow away from Antarctica (Ekman Transport)
57
Sea Ice & Energy Balance - January?
Looks like snow-covered land to atmosphere.
Very cold air over ice.
Nearby oceans remain warm (above freezing) due to:
Large heat capacity (slow to cool).
Northward ocean heat transport
58
Sea Ice & Energy Balance - July?
Looks like a surface at melting point (0°C) to atmosphere.
Nearby oceans & land get much warmer.
59
How does sea ice affect sunlight reflection?
Reflects sunlight (albedo ~0.7 vs. ocean ~0.1).
Cools the poles.
Ice-albedo feedback: Amplifies warming in the Arctic under global warming.
60
Sea Ice & Thermohaline Circulation?
Sea ice rejects salt when growing.
This salt rejection helps drive the thermohaline circulation.
If sea ice melts faster: North Atlantic gets fresher -> surface water less dense -> thermohaline circulation slows.
61
Why doesn't sea ice melt contribute to sea level rise?
Sea ice is floating (less dense than water, ~90%).
90% below surface, 10% above.
The ice below the surface already displaces water.
When it melts, it occupies roughly the same volume as the water it displaced.
Conclusion: Sea ice melt does not contribute to sea level rise.
62
What if sea ice was DENSER than water?
It would sink!
Melting would then contribute to sea level rise as the water it displaces would be less than its total volume.
63
What if sea ice was EVEN LESS dense?
More of it would float above the surface.
It would still displace the same mass of water as its own mass when floating, so melting would still not contribute to sea level rise. (Archimedes' Principle still applies).
64
Arctic Sea Ice Health Indicators?
Thickness & Age of ice.
Older ice (multi-year ice) means it survived summer, can get thicker next winter.
65
Arctic Sea Ice Trends (1940s vs. Post-1979)?
Area generally increased from 1979 until about 2016.
Different from the Arctic trend.
66
Antarctic Sea Ice Trends (Post-2016)?
Since 2016: Record lows & high variability observed.
Current area of research to understand rapid drop.
67
Why slower Antarctic Sea Ice loss (initially)?
Wind-driven upwelling of unmodified waters from below.
This slows Southern Ocean warming.
68
Main driver of Arctic summer sea ice loss (IPCC AR6)?
More than half of satellite-observed Arctic summer sea ice loss.
Driven by increased concentrations of atmospheric GHGs.
69
Arctic Sea Ice Projections (Mid-Century)?
loss projected to continue through mid-century
70
Arctic Sea Ice Projections (Post-Mid-Century)?
Differences depend on magnitude of global warming.
Could have ice-free summers in the next few decades.
71
Glacier
A large ice mass, created by transformed snowfall, that moves and deforms under its own weight.
72
Ice sheet
Large masses of glacial ice; a glacier "continental" in scale.
73
How do glaciers/ice sheets form?
1. Snow falls. It’s fluffy! Lots of air space
2. If the snow lasts through the summer more snow falls on top the next year
3. The weight of the overlying snow ->compression -> snow recrystallizes
4. The snow grains grow, and the pockets of air shrink
5. Snow -> firn (a state between snow and ice)
6. More snow falls on top. More compression! Ice crystals grow, air pockets are tiny
7. The layers on the bottom are now ice
74
firn
a state between snow and ice
75
how does ice move (glaciers/ice sheets)
1. Net gain in the accumulation zone due to snowfall (colder up high)
2. Glacier movement due to gravity
3. Net loss in the ablation zone due to melting (warmer temperatures down here)
- Deformation
o Glaciers flow under the force of gravity as snow accumulates on the upper parts of the glacier and moves downslope
76
Glacier Movement: Accumulation Zone?
Net gain due to snowfall (colder up high).
77
Glacier Movement: Primary driver?
Glacier movement due to gravity.
78
Glacier Movement: Ablation Zone?
Net loss due to melting (warmer temperatures down here).
79
Glacier Movement: Deformation?
Glaciers flow under gravity as snow accumulates uphill and moves downslope.
80
Glacier Movement: Sliding?
Occurs if liquid water or slippery mud is at the glacier bed, allowing the whole glacier to slide.
81
Where do glaciers end?
Where ice can no longer be sustained year-round; melt > gain (accumulation + uphill ice).
82
Glacier Mass Balance: How is mass added?
Addition of mass via snow.
83
Glacier Mass Balance: How is mass lost?
Loss of mass through melt or calving.
84
Glacier Mass Balance: Equilibrium?
Total accumulation = total melt.
85
Glacier Mass Balance: When is it negative?
If snowfall decreases OR if surface melt increases.
86
How does Land Ice affect Global Climate (Sunlight)?
Reflects sunlight (ice-albedo feedback works on longer timescales).
87
How does Land Ice affect Global Climate (Ocean Saltiness)?
Release of freshwater to ocean if ice melts -> affects ocean circulation (mostly driven by big ice sheets).
88
How does Land Ice affect Global Climate (Sea Level)?
Contributes to global sea level rise (big ice sheets & mountain glaciers are important).
89
How does Land Ice affect Local Ecosystem (Flooding)?
Loss of glacier ice could lead to outburst flooding events.
90
How does Land Ice affect Local Ecosystem (Rivers)?
Changes runoff to glacially fed rivers.
91
How does Land Ice affect Local Ecosystem (Species)?
Affects plant/animal species with alpine habitats.
92
Greenland Ice Sheet: Key Facts?
Very thick (top ~ Mt. Baker height).
If fully melted: >7 meters global sea level rise.
Loses mass from: Surface melting (~35%) & glacier flow/calving (~65%).
93
Greenland: What is 'calving'?
Surrounded by fjords with ice streams (fast-flowing ice).
Many icebergs break off (calve) at the ends (terminus) of these streams.
94
Greenland Mass Loss: Where observed by GRACE?
Most mass loss on the edges of Greenland.
Contributes ~0.8 mm/year to sea level.
Overall trend: Clearly negative.
95
Why does Greenland's GRACE mass loss graph 'wiggle' annually?
Seasonal oscillation of snowfall in winter / melt in summer.
96
What causes Greenland calving to speed up?
1. Warmer ocean waters undercut ice bottom.
2. Surface melt flows to bottom (through cracks), rises, drawing in warm salty water, causing more melt.
3. Leads to more calving.
97
Greenland Mass Balance: Losses vs. Gains?
Overall: Losses exceed gains (negative mass balance).
Recent losses from: Increased calving rates & increased surface melts.
Melt and calving are normal, but if they exceed accumulation, mass balance becomes negative.
98
Antarctic Ice Sheets: Key Facts?
East (90% mass) & West (10% mass) sheets.
~500k year old ice.
Max thickness: 300m taller than Mt. Rainier.
Has two giant (Ronne Filchner & Ross) and many smaller ice shelves
99
What is the role of Antarctic Ice Shelves?
They float but are connected to the main ice sheet.
Reduce the rate of calving by holding back ground-based ice.
100
Antarctica Mass Loss: Where observed by GRACE?
Observed ice mass loss on the far-right edges of the land (mostly West Antarctica).
Contributes ~0.4 mm/year to sea level.
101
Antarctica: Little warming, but West Antarctica losing mass?
Antarctica (overall) has experienced little surface warming (strong winds keep warm air out; nearby ocean absorbs heat).
Surface melt isn't main cause of loss.
West Antarctica loss: Much bedrock below sea-level, making ice vulnerable to warm ocean water.
102
Antarctica: Potential for accelerated loss?
West Antarctica's bedrock below sea-level -> vulnerable to ocean heat.
Warming ocean affects ice shelf stability.
Ice shelf thinning/collapse -> accelerated calving -> more ice loss
103
Antarctic Ice Sheets: Future Projections?
East Antarctica (the big part) is thought to be (relatively) stable.
West Antarctica is potentially dangerous: 5m sea level rise if it collapsed.
Much of West Antarctica Ice Sheet is under sea level, so warmer ocean water could melt more once melting starts.
104
Land Ice: Future sea level contribution?
Antarctica, Greenland, and mountain glaciers are all expected to continue contributing to sea level rise (Antarctic ice sheets most uncertain).
105
What else influences sea level rise besides ice?
Thermal expansion of seawater (thermosteric component).
Changes in land water storage.
106
Why does warm water take up more space (thermal expansion)?
Cool water: molecules move slowly, less energy.
Warm water: kinetic energy increases, molecules vibrate more, move apart.
Same number of molecules take up more space.
Note: ~90% of global warming is occurring in the ocean.
107
What does 'Land Water Storage' include for sea level rise?
Surface water, soil moisture, groundwater storage, snow. (Excludes glaciers and ice sheets).
108
Why isn't sea level rise uniform globally?
The land may be rising or subsiding (Glacial Isostatic Adjustment, groundwater/fossil fuel extraction).
Gravity effects from ice sheets.
109
Glacial Isostatic Adjustment (GIA): How it causes non-uniform SLR?
Loading (Ice Age): Heavy ice subsides land below, forms bulges at edges.
Deglaciation (Now): Ice melts, land beneath rebounds, peripheral bulges subside.
Takes a long time for surface to flatten.
Rising land helps offset rising seas, sinking land makes it worse.
110
How does groundwater/fossil fuel extraction affect local sea level?
Leads to land subsidence (sinking).
111
How do ice sheets affect local sea level due to gravity?
Melting ice sheets reduce their gravitational pull on nearby water.
Water moves away from the melting ice sheet.
Result: Local lowering of sea level near the melting ice, enhanced sea level rise further away. (e.g., Greenland melt causes local lowering, W. Antarctica melt causes local lowering).
112
Sea Level Projections: Largest source of uncertainty?
How ice sheets will respond (this shows worst-case scenario).
113
Sea Level Projections: End of 21st century (SSP scenarios)?
SSP 8.5 (high emissions): ~0.8 m.
SSP 2.6 (low emissions): ~0.6 m.
114
Long-Term Carbon Cycle: Chemical Weathering process
1. Rainwater takes up CO 2 (making it slightly acidic, pH 5-6).
2. Acidic rainwater reacts with rock minerals, releasing Ca2+and HCO3− ions into water that eventually travels to the ocean.
3. In the ocean, ions are used by marine organisms to make shells (calcium carbonate).
4. Organisms die, shells sink, become sediment, then limestone rock. Removes carbon from atmosphere (very slow process, hundreds of thousands of years).
115
How does buried carbon return to atmosphere via Plate Tectonics?
At plate boundaries, high temp/pressure release CO
2 at depth.
Magma forms, erupts in volcanoes at surface.
Exchange: Chemical weathering removes CO2, volcanoes return it.
116
Carbon Cycle: Natural Perturbations?
Normally, cycles maintain steady state.
Natural variations occur on million-year timescales (e.g., continental movement exposing rock in tropics).
Increased chemical weathering → decreased atmospheric CO2
117
Human Impact: Rate of Carbon Addition?
Adding ~10 GtC/yr to atmosphere.
This is ~100x faster than natural input (volcanoes, physical weathering) and natural removal processes.
118
What happens to a pulse of CO2 added to the atmosphere (short-term)?
Quickly exchanged with surface ocean (years) and land biosphere (decades).
Carbon increases in these reservoirs.
119
What happens to a pulse of CO2 added to the atmosphere (long-term)?
~20% taken up by surface ocean (several years).
~30% taken up by deep ocean (centuries).
~25% remains in atmosphere after 1000 years.
Eventually removed by leaky biological pump & chemical weathering (millions of years!).
Atmospheric lifetime of emitted CO2 is several centuries, plus ~25% forever on human timescales.
120
Current Atmospheric CO2 Levels & Emissions?
Current: ~425 ppm, increasing ~2.5 ppm/year.
Annual emissions: ~11 GtC/yr (~5 ppm/year).
121
What is the contribution of deforestation/land use change to emissions?
Accounts for 10% of anthropogenic emissions to the atmosphere.
122
Evidence #1 for Human-Caused CO2 Increase: Oxygen?
Oxygen concentrations are decreasing.
Oxygen is used when fossil fuels/forests are burned.
If oceans were the sole culprit for Co2 increase, oxygen levels would stay constant.
123
Evidence #2 for Human-Caused CO2 Increase: Chemical Fingerprinting (Isotopes)?
Carbon-12 (98.9%), Carbon-13 (1.1%), Carbon-14 (<0.1%).
Plants preferentially absorb C-12. Fossil fuels are made of ancient plant matter.
124
Evidence: How does δ13C show human impact?
δ13C is a measure of C-13:C-12 ratio.
Trending DOWNWARD.
Burning fossil fuels (ancient plant matter rich in C-12) adds C-12 enriched carbon to the atmosphere lowering the δ13C ratio.
125
