CG

Chapter 2 Notes: The Ocean in Motion and Properties of Seawater

2.1 The Ocean in Motion

  • Atmospheric Circulation and Ocean Link

    • The ocean and atmosphere are closely linked.
    • Evaporation moves water from the sea into the air.
    • Rain directly or indirectly returns water to the sea.

  • Waves

    • Waves transfer energy from the wind to the water, but do not move the actual water mass.
    • Waves start out as tiny capillary waves.
    • In shallow water, waves behave differently (shoaling, breaking effects).

  • Properties of Waves

    • Key terms: wavelength ($\lambda$), wave height ($H$), crest, trough, period ($T$).
    • Fetch: the distance traveled by wind or waves across open water.

  • Tsunami

    • Caused by large disturbances to the sea, such as earthquakes.
    • Tsunami warning systems can save many lives.

  • Tides

    • Tides are long-period waves caused by the Moon–Earth and Sun–Earth gravitational systems.
    • Spring tides vs. neap tides:
    • Spring tide: The Sun and Moon align with the Earth, producing stronger gravitational effects and higher high tides and lower low tides.
    • Neap tide: Sun–Earth–Moon geometry at right angles reduces the overall tidal range.
    • Tidal patterns around the globe are influenced by land masses (coastal configurations).

  • Tide Patterns (global patterns)

    • Major tidal patterns: semidiurnal, diurnal, and mixed semidiurnal.

  • Organisms and Tides

    • Organisms living in areas exposed during low tide are especially affected during spring tides.
    • Tidal movement drives significant mixing of water, affecting organisms.
    • Many organisms synchronize reproduction, dispersal, and feeding with the tides.

  • Surface Currents

    • Caused by winds transferring momentum to the water.
    • Stable wind patterns produce large, slow-moving currents that transfer huge volumes of water.
    • Coriolis effect deflects surface water from wind direction.
    • Ekman spiral: water movement direction changes with depth.
    • Gyres are circular moving surface currents; can be enormous.
    • Eddies are smaller, rotating current systems that can travel long distances.

  • Major Surface Currents of the Ocean (Gyres)

    • The gyre system includes major features such as the North Equatorial Current/Monsoon Drift, South Equatorial Current, Canary Current, California Current, Peru/It is implied in the diagram; warm and cold currents interact with winds to create gyres.
    • Currents and gyres are driven by global wind patterns and deflected by the Coriolis effect.
    • Distinct warm and cold currents interact with coasts and ecosystems.

  • El Niño–Southern Oscillation (ENSO)

    • El Niño is a departure from normal current patterns at the equator.
    • The thermocline is depressed and surface water temperatures rise.
    • Global weather patterns are impacted as a result.

  • Case Study: The Great Pacific Garbage Patch

    • Garbage is carried thousands of kilometers and trapped in gyres.
    • Plastic does not break down for thousands of years; small fragments accumulate into a plastic soup.

  • Vertical Water Movements: Upwelling

    • Upwelling occurs when winds remove warm surface waters, allowing cool, nutrient-rich deep waters to rise.
    • This process provides surface waters with nutrients, leading to high primary productivity.

  • Vertical Water Movements: Thermohaline Circulation

    • Surface water density varies; denser water sinks and flows horizontally.
    • This transfers oxygen-rich waters to deeper parts of the ocean.
    • Referred to as the “Great Ocean Conveyor” (GOC).

  • 2.2 Properties of Seawater: Pure Water and Seawater Fundamentals

    • Water is a small yet remarkable molecule; hydrogen bonds drive many properties.

  • Viscosity and Surface Tension

    • Viscosity helps marine organisms maintain positions and creates drag for swimming animals.
    • Surface tension allows some organisms to walk on water.

  • Density–Temperature Relationships and Ice

    • Colder water is denser and sinks but holds more oxygen.
    • Ice floats because density of water decreases when it is cooler than 4°C.
    • If ice did not float, oceans would freeze from the seafloor up.

  • Heat Capacity and Stability

    • Water has a high heat capacity, absorbing or releasing heat with only modest temperature change.
    • This provides a stable environment for organisms.

  • Water as the Solvent of Life

    • Water dissolves most naturally occurring substances, including salts.
    • Facilitates many chemical reactions necessary for life.

  • Seawater Composition: 96.5% Pure Water; 3.5% Dissolved Substances

    • Organic compounds occur naturally and provide food for small bacteria.
    • Manmade organic nutrients arise from pollution.

  • Major Ions in Seawater (composition and percentages)

    • Chloride (Cl-): ~19.345 g/kg, 55.03%
    • Sodium (Na+): ~10.752 g/kg, 30.59%
    • Sulfate (SO4^2-): ~2.701 g/kg, 7.68%
    • Magnesium (Mg^2+): ~1.295 g/kg, 3.68%
    • Calcium (Ca^2+): ~0.416 g/kg, 1.18%
    • Potassium (K+): ~0.390 g/kg, 1.11% (approximate)
    • Bicarbonate (HCO3-): ~0.145 g/kg, 0.41%
    • Bromide (Br-): ~0.066 g/kg, 0.19%
    • Borate (H2BO3-): ~0.027 g/kg, 0.08%
    • Strontium (Sr^2+): ~0.013 g/kg, 0.04%
    • Fluoride (F-): ~0.001 g/kg, 0.003%
    • Other dissolved materials: <0.001%
    • Note: These values are representative and presented as % of total salinity by weight.

  • Seawater Salinity and Its Variability

    • Salinity refers to dissolved salts in seawater.
    • Measured in parts per thousand (‰) or practical salinity units (psu); averages around 35‰.
    • Main causes of salinity fluctuations:
    • Evaporation increases salinity.
    • Precipitation lowers salinity.
    • Freshwater runoff lowers salinity.
    • Melting/freezing of sea ice affects salinity locally.

  • Salt and Water Balance in Organisms

    • Maintaining solute/water balance is crucial for homeostasis.
    • Osmoconformers: internal solute concentrations vary with ambient salinity; tolerate a narrow salinity range; example groups include many marine invertebrates.
    • Osmoregulators: control internal concentrations; tolerate wider salinity ranges; may secrete urine or use glands to regulate salts.

  • Osmoregulation Mechanisms (illustrated concepts)

    • Osmoconformers: less regulatory control; internal concentrations track seawater.
    • Osmoregulators: actively regulate internal ions and water; strategies include minimal urine, selective salt excretion via specialized glands.

  • Gills, Skin, and Salt Balance (illustrative diagrams)

    • Marine fish (a): Water tends to move out by osmosis; they drink seawater; salts absorbed by gut; salts excreted by gills; small volume of relatively salty urine.
    • Freshwater fish (b): Water tends to move in by osmosis; they do not drink seawater; salts pass through the gut; salts absorbed by gills; large volume of dilute urine.

  • Light and Temperature Below the Surface

    • Sun heats surface waters; light penetrates to specific depths depending on water clarity and location.
    • Light in the sea is absorbed spectrally; different wavelengths attenuate at different depths.

  • Spectrum and Depth penetration (visible light region)

    • Visible spectrum and depth distribution include blue/green penetrating deeper than red.
    • Wavelength range for visible light: approximately $0.38\,\mu m$ to $0.78\,\mu m$.
    • UV and infrared constitute a smaller fraction of surface irradiance; infrared is largely absorbed near the surface.
    • The diagram indicates depth-related shifts in light intensity and the general order of wavelengths.

  • Temperature in the Ocean

    • Marine organisms face relatively cool environmental temperatures.
    • Poikilotherms/Ectotherms do not regulate body temperature.
    • Homeotherms/Endotherms maintain body temperature within a narrow range.
    • Fish are largely ectothermic, but some can retain metabolic heat produced by muscles.

  • Pressure with Depth

    • The weight of water produces pressure that increases with depth.
    • Every 10 m of depth adds about 1 atmosphere (ATM) of pressure.
    • At depth h (in meters):
    • $P_{atm} = 1 + \frac{h}{10}$ (in atmospheres)
    • $P_{psi} = 14.7\bigl(1 + \frac{h}{10}\bigr)$ (psi)
    • Example references from the table:
    • 60 m depth: about $7.1$ atm, roughly $\approx 102$–$103$ psi.

  • Ocean pH and Acid–Base Balance

    • Acid–base balance is important for marine organisms.
    • Small changes in pH can negatively affect marine life.
    • Ocean acidification involves a slight decrease in pH, resulting in more acidic ocean waters.

  • pH Scale (conceptual reference)

    • A range of solutions from basic to acidic is shown; seawater typically has alkaline pH values; small changes can impact physiology.

  • Dissolved Nutrients in Seawater

    • Dissolved nutrients like nitrate and phosphate fertilize the sea.
    • Algae and submerged aquatic vegetation use these nutrients for photosynthesis.
    • Nutrients vary with depth, being more abundant in zones of upwelling and at certain depths where biological activity concentrates nutrients.

  • Summary of Key Connections

    • Winds drive surface currents and tides; the Coriolis effect and Ekman spiral shape vertical and horizontal water movement.
    • Gyres, eddies, and upwelling shape nutrient distribution, primary productivity, and ecosystem dynamics.
    • Thermohaline circulation ties surface conditions to deep ocean oxygenation and nutrient transport, linking climate and ocean chemistry.
    • Tides, ENSO, and ocean acidification influence weather, biology, and global biogeochemical cycles.

  • Notable Real-World Implications

    • Upwelling zones support high biological productivity and fisheries.
    • The Great Pacific Garbage Patch highlights the long-term fate of plastic waste in ocean gyres and the need for mitigation.
    • Ocean acidification poses risks to calcifying organisms and reef systems.

  • Foundational Principles Connected to These Topics

    • Energy transfer: wind power and momentum transfer to the ocean.
    • Mass balance and solute transport: osmosis, diffusion, and osmoregulation.
    • Gas exchange and dissolved oxygen: ocean–atmosphere interface and depth-related oxygen availability.
    • Thermodynamics of seawater: heat capacity, phase changes (ice formation), and density-driven circulation.