EAE 03 Oceans (7) Flashcards
How much CO₂ does the ocean absorb?
Every year the ocean absorbs approx ⅓ of human CO₂ emissions.
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Why is temperature important?
- Temperature is important because it reflects the amount of heat held and transported by the ocean.
- It plays important role in circulation via density
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Definition
Adiabatically
Occurring without gain or loss of heat.
I.e. no heat is transferred to or from the fluid.
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How are pressure differences created?
Horizontal differences in height of the water
Density differences between water columns
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What impact does ‘La Nina’ have?
Tropical cyclones more likely to form near Australia
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What is the ‘age’ of water?
The “age” of water is commonly defined as the time since it was last at the surface.
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What are the key ingredients for Tropical cyclone formation?
- Warm water, SST > 26.5
- A latitude at least 5° away from the equator
- Various other criteria not directly ocean conditions that can vary in all locations.
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What influences surface salinity?
Surface salinity is set by
- Rainfall
- Evaporation
- Rivers
- Ice
etc.
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How is pressure created underwater?
Pressure = the weight of water sitting above you
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What influences interior salinity?
Interior salinity is set by currents that take water from the surface to interior regions
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What is the Potential Temperature (θ)?
The temperature a water parcel would have at the surface, if it were raised to the surface adiabatically.
- From gas laws, T is proportional to P
- Thus, as pressure increases, (volume decreases) and temp increases.
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What are the characteristics of water sinking in the Southern Ocean?
- Polynya’s (Holes in the sea ice) expose the relatively warm ocean (2°C) to the very cold atmosphere (-20°C), which leads to intense cooling
- Sea ice formation in these Polynya’s also leads to “brine rejection”, whereby the salt is expelled from the water freezing, which makes the remaining water saltier and denser.
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What is SST?
Sea Surface Temperature
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What impact does the ocean have on temperature?
Ocean effective stabilizes the earth’s temperature.
The ocean can absorb large amounts of heat without a large increase in temperature.
>90% of earths energy imbalance is stored in the ocean.
Thus, the ocean can effectively store large amounts of energy, while releasing this additional energy over long periods of time allows the ocean to play a central role in stabilizing Earth’s climate system.
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What is ‘psu’?
Practical Salinity Units
Equivalent to parts per thousand (ppt)
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How much of the earth’s surface is covered by water?
Water covers approx 71% of world surface
- Pacific Ocean 46%
- Atlantic Ocean 23%
- Indian Ocean 20%
- Others 11%
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What cuases sinking in the North Atlantic?
- Water flowing northward becomes modified through evaporation and mixing with other water masses, leading to increased salinity.
- Upon reaching the North Atlantic, this water cools, and due to its cool temperatures and high salinity it becomes a very dense water mass.
- It is denser than the underlying water, which leads to sinking (oceanic convection).
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How deep are ocean trenches?
Depths can reack 11km.
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What is the average width of continental shelf?
Average width is approximately 65km.
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What is Thermohaline circulation?
The movement of seawater in a pattern of flow dependent on variations in temperature, which give rise to changes in salt content and hence in density.
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What does the sinking water in the North Atlantic become?
North Atlantic Deep Water (NADW)
The sinking water in the North Atlantic can reach depths of 2000m, becomes North Atlantic Deep Water (NADW).
NADW has:
* Temperature of 2-4°C * Salinity of 34.9-35.0 psu * Typically resides at depths of 1.5 to 4 km.
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What are the flows in the Deep Ocean?
- Flow in the deep ocean is very slow, on the order of cm/s
- Models estimates that this can be more than 1000 years, like those of the North Pacific, which houses the oldest waters in the world.
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What is the temperature range of the ocean?
The temperature range in the ocean varies from -2°C at the poles to >28°C at the equator.
The temperature of the ocean is primarily influenced by the heating at the air-sea interface.
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What is the range of density?
- Density depends on salinity, temperature and pressure.
- Seawater density ranges from 1020~1030 kg/m³
- The average density is 1025 kg/m³
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What increases the density of sea-water?
Density of water increases if it is
* Colder * Saltier
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Where are Polynyas found?
- Coastal Polynyas are fairly common around Antarctica, due to the persistent katabatic winds that blow the ice away from the coastline.
- Those in the middle of the open ocean are rare, and need specific conditions. (e.g. the last Weddell Polynya occurred in 1976).
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What is ocean salinity?
Total dissolved solids (mainly sodium chloride or “table salt”)
About 3.5% by weight (i.e. 35 kg of salt in 1,000 kg of pure water on average or 35 psu)
Plays an important part in ocean circulation through its influence on density.
Varies geographically according to
* Evaporation
* Precipitation
* River outflow
* Ice formation
* Ice melt.
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What is the average depth of the ocean?
The average depth 3,800m of the ocean?
This compares with the earth’s radius of 6400km
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What impact does sea surface temperature have on cyclones?
Tropical cyclone intensity can increase with increasing SST.
Hurricane wind speeds doubled as temperatures increased significantly.
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What is the water around the Antartica called?
Antarctic Bottom Water (AABW).
These are the densest water in the world, hence the reference to “Bottom”
They have:
* Temperatures ranging from -0.8oC to 2oC. * Salinities that range from 34.6 to 34.7 psu.
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What impact does ‘La Nino’ have?
Tropical cyclones are less likely to form near Australia
The formation shifts in to central Pacific.
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