Week 7

• The Earth’s fluid environment includes the ocean, its constituents, and its circulation.
• Phil Goodwin is a lecturer on the ocean, its constituents, and its circulation.
• The main chemical constituents of the ocean include nutrients needed for life, which are distributed differently to other ocean chemicals.
• Almost all substances have a solid phase that is more dense than the liquid phase.
• In ice, each water molecule forms a 'hydrogen' bond with 4 other water molecules in a crystal pattern, spreading the water molecules out and making ice less dense than water, so it floats.
• If the ocean froze from the bottom up, the whole ocean could freeze more easily, making life impossible.
• Sea ice forms when the atmosphere above cools the surface ocean.
• Water usually gets more dense as it gets colder, so as the surface ocean cools it should sink to the bottom before it freezes.
• Ice is less dense than water, so it floats on the surface, and water close to freezing is less dense than water just above freezing, allowing sea ice to form and float.
• Many oceanic phenomena can be explained through considering the ocean as 'water on a planet that spins', including how the ocean is an excellent solvent, freezes from the surface, contributes to energy transport, and gives rise to circular motion, gyres, and western boundary currents.
• Pressure gradients and Earth’s spin produce 'Geostrophic Flow'.
• Water helps transfer heat from the equator towards the poles.
• Earth is unique in the solar system in having water exist in all three forms at the planet’s surface: solid (ice), liquid (water), and gas (water vapour).
• The nutrients vital for life (‘extra’ inorganic carbon, Nitrate and Phosphate) occur in a ‘Redfield ratio’ in seawater: ‘extra’ Carbon to Nitrates to Phosphates ratio: C extra :N:P = 106:16:1 (ratio in moles dissolved).
• This ‘Redfield ratio’ is the same ratio found in organisms’ organic material.
• Nitrates and Phosphates can become depleted in surface waters, which limits biological activity.
• The nutrients vital for life (‘extra’ inorganic carbon, Nitrate and Phosphate) occur in a ‘Redfield ratio’ in seawater: ‘extra’ Carbon to Nitrates to Phosphates ratio: C extra :N:P = 106:16:1 (ratio in moles dissolved).
• This ‘Redfield ratio’ is the same ratio found in organisms’ organic material.
• Nitrates and Phosphates can become depleted in surface waters, which limits biological activity.
• Water is made from two of the most abundant elements in the solar system, Oxygen and Hydrogen.
• Water dissolves more substances than any other liquid, making it a great 'solvent'.
• Ekman coastal upwelling brings cold, nutrient rich waters to the surface.
• The Ocean’s deep circulation can be viewed as the movement of large scale ‘water masses’, each with characteristic temperature and salinity values.
• Antarctic Intermediate Water (AAIW) is formed by winds driving water beneath the surface.
• Antarctic Bottom Water (AABW) is formed by brine rejection making water more salty when freezing occurs.
• North Atlantic Deep Water (NADW) is formed by cooling the surface ocean.
• The thermocline/pycnocline is the upper ocean where temperature and density are changing rapidly with depth.
• Atlantic water masses and circulation are characterized by a salinity profile with a maximum at 20°N, 40°S and a minimum at 60°S, 40°S.
• The property that allows water to dissolve many substances is that Oxygen is slightly negatively charged, and the two Hydrogen atoms are slightly positively charged when they share electrons in a covalent bond.
• One mole per kilogram is equivalent to 6.023(10^23) ions or molecules per kilogram of seawater.
• The relative concentrations in column 4 provide the number of ions of each constituent in one kilogram of seawater as compared to the number of chloride ions in one kilogram of seawater.
• Ocean chemistry: Main chemical constituents
• Principal constituents of seawater include chloride, sodium, magnesium, sulfate, calcium, potassium, carbon (inorganic), bromide, boron, strontium, fluoride.
• The relative concentrations in column 4 provide the number of ions of each constituent in one kilogram of seawater as compared to the number of chloride ions in one kilogram of seawater.
• Ocean chemistry: Salinity
• More salty where evaporation removes fresh water, less salty where precipitation adds fresh water.
• Variation in surface ocean salinity is influenced by evaporation, precipitation, and winds.
• Deep ocean filled with water from high latitudes, less deep ocean variation in salinity.
• Most chemical constituents vary in step with each other via salinity.
• Surface salinity variations are confined to the upper ocean.