Topic 4 Properties of Ocean Water

Topic 4 Properties of Ocean Water

4.1 Physical properties of water

Nature of science:

• Understanding of the structure of water molecules has created a consistent understanding across a range of phenomena.

Understandings:

• Water molecule and its hydrogen bonds leads to many properties of water

• Light, sound and heat are transmitted through oceans

• Temperature, pressure and salinity affect density of seawater

• Density differences influence the vertical structure of oceans

Applications and skills:

• Skill: Determining the effects of temperature and/or salinity on density.

• Examining the changes in intensity and spectra of light at depths in ocean

4.2 Chemical properties of seawater

Nature of science:

• Making accurate quantitative measurements while understanding the limitations and sources of error of each technique is crucial to measurement of salinity, pH, density and temperature of in situ ocean waters.

Understandings:

• The solvent properties of water make it the solvent that can dissolve many salts as well as gases

• Relative proportions of salts within seawater is relatively constant though the concentration of salt to water varies

• Sources of salt; sources of dissolved gases

• Relative concentrations of dissolved nitrogen, oxygen and carbon dioxide gases is different from their relative concentrations in the atmosphere.

• Temperature affects the concentration of dissolved gasses

• There is little variation seawater pH because of the buffering capacity of seawater

• Nitrate, phosphate, silicate, iron, and calcium are nutrients required by photosynthetic organisms

• Nutrient concentrations fluctuate seasonally

Applications and skills:

• Skill: Measuring salinity by two or more methods

• Skill: Measuring dissolved gases by two or more methods

• Skill: Demonstrating the effect of temperature on dissolved gas concentration

• Skill: Measuring the buffering capacity of seawater

• Skill: Evaluating methods of measuring salinity, dissolved gases, pH

• Skill: Designing a practical to explore one property of seawater (practical 3)

4.3 Ocean acidification

Nature of science:

• Scientists look for patterns and correlations to discover how changes in one system affect changes in another system.

• Problem-solving requires risk analysis, precautionary principle and international dialogue to meet the concerns for human-enhanced carbon dioxide levels in the atmosphere and the impact on ocean acidification.

Understandings:

• Carbon dioxide is more soluble in water than in air

• The ocean is a carbon dioxide sink/reservoir

• Dissolved carbon dioxide raises the acidity of oceans

• Increased atmospheric carbon dioxide leads to acidification of ocean waters

• There are dire consequences of acidification on marine ecosystems

Applications and skills:

• Analysing data about ocean acidification and a named ecosystem

• Skill: measuring pH effects of carbon dioxide forced into aqueous solution

• Discussion of what can be done to solve acidification problems

• Skill: drawing a representation of the carbon cycle and annotating marine reservoirs and relative residence times.

4.4 Ocean water profiles

Nature of science:

• Marine scientists collect data from direct and indirect measurements in search for patterns, trends and discrepancies.

Understandings:

• Physical and chemical characteristics of in situ ocean water vary with depth

• Tools for measuring and monitoring surface and deep waters have been developed.

• Wind has an influence on the ocean profiles causing mixing as well as upwelling.

• The deep water conveyor belt moves deep ocean water causing whole ocean mixing at a slow pace.

Applications and skills:

• Skill: describing methods for collecting data to construct profiles of thermoclines, haloclines and pycnoclines

• Skill: describing the distribution of oxygen and carbon dioxide with depth.

• Skill: Construct a temperature-depth profile and identify the thermocline or model the development of a thermocline. (practical 4)

• Skill: developing a density-depth profile and identify the pycnocline

• Skill: developing a salinity-depth profile and with a halocline

• Application: explore formation of Mediterranean Intermediate Water in the Atlantic Ocean