Water Reservoirs: Locations where water is stored, including oceans, ice caps, groundwater, lakes, rivers, and the atmosphere.
Fluxes: Movements of water between reservoirs, represented by arrows in diagrams.
Examples of Fluxes:
Evaporation: The process of water vaporizing into the atmosphere, influenced by solar radiation.
Transpiration: Evaporation of water from plant surfaces.
Runoff: Water moving from land to oceans.
Precipitation: Water falling from the atmosphere to the Earth's surface.
Estimates of Earth's Water:
97% of Earth's water is saltwater in oceans.
Only 3% is freshwater:
Two-thirds of the freshwater is groundwater.
One-third is stored in ice (glaciers and ice caps).
Remaining freshwater is in lakes, rivers, vegetation, and the atmosphere.
Importance of Desalination
Desalination Plants: Facilities convert seawater to freshwater using fine membranes due to the inability to consume saltwater.
Salinity and Ocean Water Composition
Definition of Salinity: Grams of salt per kilogram of seawater.
Average ocean salinity: 35 grams of salt per kilogram, or 35 parts per thousand.
Practical Salinity Units (PSU) is another system used for measuring salinity.
Major Ions of Ocean Salt:
Sodium (30.6%) and Chloride (55%) are the most abundant ions, resulting in the salty taste of ocean water.
Other ions: sulfate, magnesium, calcium, potassium, and trace elements exist in smaller concentrations.
A typical composition example for 1 kg of seawater:
55% Chloride
30.6% Sodium
8% Sulfate
Salinity Stability
Conservative Ions: These ions do not significantly change over time and primarily include sodium and chloride.
Used as tracers in oceanography to identify water masses and their history.
Measuring Salinity
Conductivity Meter: A device used in labs that measures water conductivity to infer salinity, indicating the number of ions present.
Dissolved Gases in Seawater
Dissolved Oxygen: Essential for marine life; its levels vary with depth.
Surface Ocean: High oxygen levels due to atmospheric diffusion and photosynthesis.
Oxygen Minimum Zone (between 500 and 1000 meters): Decreased oxygen levels due to decomposition of organic matter by bacteria that consume oxygen.
Solubility of Gases: Depends on pressure, temperature, and salinity.
Increased solubility with low temperature and high pressure.
Equilibrium dynamics of oxygen and carbon dioxide in ocean waters.
Carbon Dioxide Dynamics
Role of CO₂: Transitions from atmosphere to seawater, forming carbonic acid, bicarbonate, and carbonate, affecting ocean chemistry and buffering systems.
Photosynthesis consumes CO₂ and produces oxygen, while decomposition has the opposite effect.
Ocean holds significantly more CO₂ than the atmosphere (50-60 times more), affecting climate buffering.
Ocean Acidification and pH
pH Scale: Ranges from 0 (acidic) to 14 (basic), with 7 as neutral.
Example: Seawater has an average pH of 8.1.
Acidification impacts the balance of chemical species in seawater, crucial for organisms that require calcium carbonate for shells.
Dissolution of shells: Lower pH makes calcium carbonate shells dissolve more easily.
Shifts in pH: Determining fractions of carbon species in seawater can significantly impact marine life.
Nitrogen Cycle
Nitrogen in Atmosphere: Predominantly as N₂ gas, which most animals cannot utilize directly.
Nitrogen Fixation: Process where nitrogen-fixing bacteria convert atmospheric nitrogen to forms usable by plants (e.g., ammonium).
Key Processes: Includes nitrification, assimilation by primary producers like phytoplankton.
Nutrient Classes:
Conservative Elements: Long residence time and minimal alteration (e.g., sodium, chloride).
Nutrient Elements: Vary in abundance due to consumption by phytoplankton at surface levels.
Scavenged Elements: Minor constituents high near the surface, decreasing with depth.
Stable Gases: Unreactive gases that do not enter into chemical alterations, such as nitrogen gas, argon, and neon.
Implications of Oxygen and Nutrient Cycles
Hypoxia and Anoxia: Terms describing low to zero oxygen conditions in water bodies, affecting marine life and ecological health.
Case Study: Algal blooms leading to hypoxic conditions, examples of severe environmental impacts.
Research Importance: Monitoring dissolved oxygen variation is essential for understanding broader ecological and societal impacts.
Significance of tracking nitrogen and nutrient cycling in coastal waters for ecosystem management and conservation efforts.