Lab 5 Reading and Lab Slides Review

What does seawater contain?

• dissolved inorganic salts (3.5%) of its weight

• dissolved gases

• traces of dissolved organic molecules

What causes profound effects of the heat budget and climate of the Earth?

Chemical/physical exchanges at the interface between the ocean and atmosphere

What are the various properties of seawater?

Temperature, salinity, oxygen, nutrient content, degree of penetration of sunlight

How do the various properties of seawater affect marine species?

they strongly affect the distribution of marine species

What does the abundance of dissolved nutirents provide?

Fundamental control on biological productivity within the shallow surface layer of the oceans

Why is water unique?

provides necessary conditions for life/ exists in all 3 states of matter

Why is temperature an important physical property of seawater?

Measure of the amount of heat stored in the oceans, has a great affect on seawater density, effects chemical activity of water

Which gases are most soluble in cold water?

Nitrogen, oxygen, and carbon dioxide

What is seawater?

Complex mixture of salts in soultion derived from chemical weathering of crust and volatiles released by volcanic gases

What is the salt content of seawater typically expressed as?

Concentration of ions in seawater or grams of dissolved solids per kg (1000 grams) of seawater

• kg of avg. seawater contains 34.7 grams of dissolved salts

• salinity of 34.7%

When does salinity increase?

When pure water is removed by evaporation/formation of ice

When does salinity decrease?

When water is added by precipitation or ice melting

What does the addition of salt to water do?

Increases its density, lowers its freezing point

What are the sources of dissolved salts?

River waters, gases from volcanic eruptions, fluids from hydrothermal vents at the ridge and rise system

What are the 2 primary sinks (processes that remove salts)?

• Many dissolved elements get incorporated into deep-sea sediments (result of biological or inorganic processes)

• Some dissolves salts get removed from seawater by fluids that circulate into ocean ridges (ridges are a sink for some elements when cold fluids circulate into them and a source for others when hot fluids leave hydrothermal vents)

So, sinks include sedimentation and subduction, and circulation of water through ocean ridge system

What does density do/why is it important?

Density controls deep-ocean circulation

What is density primarily a function of?

Temperature and salinity

What is high density favored by?

High temperature and high salinity

What does carbon dioxide produce when it reacts chemically with water and why?

Highly soluble, reacts chemically with water to produce a weak acid (carbonic acid), which dissociates to form hydrogen and bicarbonate ions

What is the DIC?

Dissolved Inorganic Carbon, the sum of all forms of CO2, carbonic acid, hydrogen ions, bicarbonate and carbinate ions

What is an acid?

Any compound that releases hydrogen ions (H+, also called protons) when dissolved in water, in creasing their concentration in solution

If an acid dissolves in water, what happens?

The hydrogen ion concentration will increase as the acid dissociates

What is an alkaline substance (a base)?

One that dissociates in water releasing hydroxyl ions (OH-) into solution

If a strongly alkaline substance is dissolved in water, what happens?

The concentration of OH- ions in the solution will increase

What is pH defined as?

The logarithm of the concentration of H-: pH=-log10[H-]

• pH is the negative logarithm of the hydrogen ion concentration, ranges from 0-14

• A logarithm is the exponent you need to raise a base number to in order to get another number. In simpler terms, it's a way of asking: “To what power must we raise this base to get that number?

What does the “-” sign mean in the definition of pH?

Extra H+ lowers the pH, so:

• acidic solutions have pH values less than 7

• alkaline solutions have pH values greater than 7

What is the average pH of the oceans?

Ranges from 7.5-8.4, slightly alkaline and remarkably stable within this range

What is the carbonate buffer system?

The primary chemical mechanism that keeps the ocean’s pH at a slightly basic level

• Bicarbonate ions act as a buffer to keep seawater from becoming to acidic or basic

• if you add more of any reactant, the reaction will move away from that reactant, maintaining the pH

What happens if seawater becomes too acidic?

Reaction not favored, bicarbonate tends to combine with hydrogen ions to make carbonic acid, CO2, and water

In general, the higher the total CO2 content of water, the more _____ it is

Acidic

Why is pH stability important?

For proper functioning of biological systems,a ll enzymes have optimal pH ranges for efficient functioning

What is polarity?

Means it (water) has a positive charge on one end, negative on the other

How does water’s polarity make it unique?

Makes it an excellent solvent, forms hydrogen bonds as a result of polarity

• Hydrogen bonds are what gives water high melting/boiling points

How is seawater different from regular water?

• High salinity (dissolved salt content) at around 34.7 PSU or g/kg

• Principle of Constant Proportions: relative proportions of these salts is very consistent worldwide

How to calculate salinity:

• if you know one ionic abundance (e.g., Cl-), you can calculate total salinity:

• Salinity (‰) = 1.805 x Chlorinity (‰)

What is salinity usually expressed in?

Parts per thousand (per mile = ‰) or grams of salt per kg or water

• no unit or PSU

• Can also be in parts per hundred (percent = %)

How do we determine salinity in modern day?

Conductivity meters: the more dissolved ions in a solution, the more electrically conductive it is

• Ions such as Ns+ and Cl- drawn towards opposite charged ends, generates a small current, which is measured by a meter as the distance between electrodes

• once this distance is known, conductivity is calculated in S/cm

What is another way to measure salinity?

The Refractometer, which measures salinity as a beam of light changing its angle when it passes through one medium with a refractive index to another medium with a refractive index

What is the Chemical Residence Time?

Average length of time an element spends in the ocean between its addition and removal

What is the residence time formula?

Res. Time = Amount of element in ocean/

Element's rate of removal (or addition) from the ocean

As H+ increases, pH does what?

Drops, why acids have a pH <7

As H+ decreases, pH does what?

Goes up, why bases have a pH >7

If you add an acid, what is released?

More H+

If you add an alkaline, what is released?

More OH-

The more H+, the more _____ a solution; the more OH-, the more ________ or _______ it is

Acidic, alkaline, basic