CHM and PHY Analysis of Seawater Test 1

Pelagic Zone

open water

benthic zone

ocean bottom

Describe thermocline. Where does it lie? What type of water is it most commonly found?

temperature changes rapidly with depth, barrier btwn top and bottom layers (keeps from mixing), reduces oxygen tranport to deeper layers, lies between surface layer and deep layer, most commonly found in tropical oceans

Describe halocline layer. Where does it lie? What type of water is it most commonly found?

layer where salinity changes with depth, effects density, forms due to freshwater influx, common in river-ocean interfaces, can lie above or below the thermocline

Describe the pycnocline layer. Where does it lie? What type of water is it most commonly found?

water density increases rapidly with depth, most important in ocean stratification, overlaps with thermocline and halocline, most commonly found in polar regions

relationship between temperature and density

density decreases as temperature increases (above 0 degrees celcius), freezing water will rapidly decrease in density from 0 degrees and increase slightly as temperature drops

What are some effects of stratification?

distribution of heat, nutrients, and dissolved gases; biological productivity, deep ocean ventilation

Describe the distribution of major ions throughout the ocean.

Residence time for major ions in the ocean is larger than the residence time for water in the ocean. Uniform distribution throughout the ocean, maintains same ratio to one another

What pH is seawater?

8

How does pH vary with depth of the ocean? Why?

pH decreases from the surface to around 1000 meter deep and then remains constant with depth. The pH decreases with depth because there i more dissolved CO2 from organic matter decomposing. CO2 reacts with water to form H+, decreasing the pH. Past 1000 meters, the concentration of CO2 remains relatively constant. On the surface, CO2 is exchanged with the atmosphere.

Why is the pacific ocean more acidic?

The pacific ocean has is “older” and therefore has more accumulated CO2.

Advantages and Disadvantages of pH paper

Advantages

• cheap

• fast

Disadvantages

• mostly qualitative

Advantages and Disadvantages of indicators

Advantages

• accurate (0.001 pH units)

• not effected by ionic strength

Disadvantages

• slow

Advantages and Disadvantages of glass eletrode

Advantages

• fast

• accurate (0.01 pH units)

Disadvantages

• effected by ionic strength

How does pH indicator work?

Changes color depending on the pH of the solution it is in. It exists in a protonated and deprotonated form, both of which absorb light differently. If the indicator is placed in an acidic solution, the equilibrium will shift to the indicators protonated form. If the solution is basic, the equilibrium will shift to its deprotonated form.

What is an isobestic point?

A wavelength at which both forms have the same molar absorptivity

How does pH electrode work?

electrode measures the activity of H+ through interaction with silica glass bulb within the probe

What will decrease the activity of H+ in a solution?

The presence of other ions like sodium, sulfate, chloride, calcium, potassium, and nitrate.

What are the two types of electrodes? What is one thing they must have?

1) Saturated Calomel Electrode (SCE)

2) Silver/silver chloride (internal reference)

The reference electrode must have a stable known potential independent of pH.

Give the expanded Nernst equation and what each variable means.

Assuming ideal response and a solution at 25 degrees, give the simplified Nernst equation.

How is the “real” potential of the solution measured?

build up on glass electrode + Silver/silver chloride (internal reference) + reference electrode

what is the isopotential point?

characteristic pH where potential is zero.

In an ideal pH probe, what is the output at a pH of 7?

± 30 mV

Is voltage positive or negative at pH >7?

negative

What is the slope at 25 degrees? 0 degrees? 100 degrees?

-59.16 mV/pH at 25 degrees, -54.2 mV per pH unit at 0 °C, -74.04 mV per pH unit at 100 °C

Relationship between mV and pH

inverse

Acceptable slope range?

between 95 - 102% (100% = 59.2 mV/pH)

Potential sources of error if slope is not 59.2.

• Junction potential drift

• Aging or fouling of the glass membrane

• Reference electrode contamination

How does salinity effect pH in natural waters?

saltwater has higher pH than freshwater

How does depth effect pH in an estuary?

generally saltwater is on bottom because it is denser, therefore the bottom pH is greater than surface pH

What factors can effect pH and how?

• rainfall: is acidic —> decreases pH

• photosynthesis: decreases CO2 acidifcation —> increases pH

What biochemical processes depend on dissolved oxygen?

aerobic respiration and organic matter decomposition

Global distributions of DO

DO levels are lowest in oceanic water, primarily around the equator

Relationship between temperature and DO. Why?

inverse relationship because temperature increases the movement of the O2 molecule reducing the chance of inducing a dipole

Relationship between salinity and DO. Why?

inverse relationship because the more NaCl molecules, the more likely the water is to dissolve the salt rather than the DO

Relationship between gas pressure and DO

proportional

Relationship between depth and DO

DO decreases with depth up until 1000 meters and then increases again and then levels out

Biological controls of DO

Photosynthesis produces DO, respiration consumes DO

Why is DO highest at the surface?

It is in equilibrium with the atmosphere (Henry’s Law). Additionally, photosynthesis.

Why does the pacific ocean have more less DO than the Atlantic ocean in deeper waters?

The pacific ocean is older so has more time for DO to be used up in the oxidation of organic matter

What is henry’s law?

What is a YSI meter and how is it used to measure DO? What are its advantages and disadvantages?

The YSI meters contains an electrode and a cathode. Electrolyte solution is present around the electrodes in order to transport the electrical charge. The meter is placed in the water by which the O2 is taken up and passes through a membrane that is covering the sensor. A voltage is applied and the O2 undergoes a reaction, consequently changing the concentration of the O2 and allowing it to be known.

Advantages: quick, easy, and portable.

Disadvantages: consumes all of O2

Describe the Winkler Method. What are some advantages and disadvantages?

MnSO4 is added to the sample, the O2 oxidizes the Mn2+. KI is added and the oxidized Mn reacts with the iodide to produce iodide. A know concentration of thiosulfate is added until all of the iodide has reacted, in which the amount of iodide can be determined and consequently (using mole ratios), the O2.

Advantages: precise, accurate

Disadvantages: takes time, cannot do in the field

How does a fluorescent optode work? What are the advantages and disadvantages?

measures dissolved oxygen using an oxygen-sensitive dye that glows when exposed to light. O₂ quenches the glow, so more oxygen means less light and less oxygen means more light.

Advantages: does not consume oxygen

Disadvantages: fluorescent compound can photobleech over time and lose sensitivity

What are some possible reasons why salinity and DO are proportional in the Cape Fear?

Because the main control is utilization of DO in respiration and oxidation

Sources of turbidity

• Runoff from watersheds

• breakdown of Aquatic weeds/algae

• Decay of plants into organic compounds

• Leaves

• Iron

• Air bubbles

What are some positive or neutral effects of turbidity?

• shield organisms from harmful UV rays

• storm-induced sediment resuspension

What are some negative effects of turbidity?

• reduced light penetration - limits photosynthesis

• smothering of seabed life by sediment

• fish and other organisms may struggle to breathe

• absorption of heat into water

• suspended particles can carry pollutants

• poor visibility for humans

Ways to measure DO

clark electrode, winkler titration, and fluorescent optode

How does a Secchi disk work? What are its advantages and disadvantages?

Black and white disk is lowered into the water until it can no longer be seen, the depth is then recorded as a measure of the transparency of the water

Advantages: quick, easy, cheap, integrates turbidity over depth

Disadvantage: cant be used in shallow waters

How does a turbidity tube work? What are its advantages and disadvantages?

Measures turbidity based on a contrast disk at the bottom of a tube.

Advantages: cheap, easy, quick

Disadvantages: less precise (more qualitative), cannot measure very low turbities

How does a turbidity meter work? What are its advantages and disadvantages?

A detector measures the intensity of light light scattered by particles at a 90 degree angle. The amount of scattered light is proportional to particle concentration.

Advantages: very accurate, direct measure of light scattering

Disadvantages: high cost, need power supply

How are turbidity meters calibrated? Why?

Through formazin stock solutions. To ensure accuracy and consistency.

Why is formazin used as a standard for turbidity calibration?

It creates a stable colloidal suspension responsible for turbidity, that can scatter light, mimicking the behavior of suspended solids in water. It is stable and reproducible.

What factors effect turbidity in an estuary?

• rainfall

• stormwater runoff

• earth-disturbing activities

What causes a Estuarine Turbidity Maxima?

Area in an estuary where there is high levels of turbidity due to the resuspension of sediment as a result of tidal forces pushing salinity beneath outflowing river water.

What is irradiance? Units?

Irradiance is the amount of electromagnetic radiation reaching a surface. Measured by power (watts) per area (m²)

What does attenuation consist of?

absorption and scattering

What is UVC, UVB, UVA, and PAR? What wavelengths does each correspond to?

• UVA : ultraviolet aging - 315-400nm

• UVB : ultrabiolet burning - 280-315nm

• UVC : ultraviolet completely blocked - 100-280nm

• PAR : Photosynthetically Active Radiation - 400-700nm

Define DOM, DOC, POM, POC, CDOM, TDN, DIN, DON

• DOM: dissolved organic matter

• DOC: dissolved organic carbon

• POM: particulate organic matter

• POC:particulate organic carbon

• CDOM: chromophoric dissolved organic matter

• TCN: total dissolved nitrogen

• DIN: dissolved inorganic nitrogen

• DON: dissolved organic nitrogen

Types of optical properties of water and what are they

• inherent optical properties: measured using laboratory methods (scattering, absorption, etc.)

• apparent optical properties: measured using available light (diffuse attenuation coefficients)

Major sources of CDOM

• terrestial environment - rivers carry organic matter

• secondary production by by-products - marine organisms breakdown organic matter

Define refractory

Organic matter that breaks down very slowly and can remain in the environment for a long time due to resistance of decomposition by heat or chemical attack

Define Recalcitrant

Organic matter that is very difficult for organisms to break down because of its chemical structure. It is resistant to decomposition

Autochthonous

Organic matter that is produced within the ecosystem itself

Define allochthonous

Organic matter that comes from outside the ecosystem

attenuation consists of…

absorption and scattering

% O2 saturation is equal to..

O2 measured by YSI/theoretical O2 from Henry’s law

What are some examples of constituents that absorb light

• pigments

• detritus

• CDM

What are some examples of constituents that scatter light

suspended sediments

Describe downwelling irradiance measurements.

The light coming down from the surface is measured

Describe upwelling irradiance measurements.

The light coming up (from scattered light) to the surface is measured

Describe scalar irradiance measurements.

Light is measured from all directions.

Describe cosine corrected irradiance measurements.

A correction is made for light that hits the sensor at an angle

What does a typical absorption spectrum for water look like?

What does a typical absorption spectrum for CDOM look like?

What does a typical absorption spectrum for chlorophyll look like?

What does a typical absorption spectrum for detritus look like?

Relationship between irradiance and depth and what that plot looks like

deeper = less irradiance

How is Kd measured and calculated?

You measure the irradiance at the surface and at a certain depth and plug that into this equation.

What are aerosols?

Suspensions of solid or liquid particles in a gas

How is the aerosol population described?

by size, number, composition, morphology, phase, mixing state, and time history

Number vs mass distributions of aerosol metrics

• number: emphasize small particles important for cloud formation

• mass: emphasize larger sea-salt particles important for deposition and chemistry

What are the paramaters of Lognormal size distributions for aerosols particles?

• particle diameter

• particle number concentration

• geometric mean diameter

What are the different aerosol modes in the marine boundary layer? How are they different?

• nucleation: freshly formed, 1-20 nm

• aitken: can grow into CCN, 20-100 nm

• accumulation: cloud processing, organics, aged sea salt, 0.1-1 um

• fresh sea spray: > 1um

How can aerosol particle change and move?

• condensation/evaporation : particles grow/shrink

• Coagulation : particle combine

• deposition: removes particles from atmosphere

• cloud processing : particles gain organic material

What is bubble bursting?

It is a process that creates sea-spray aerosol particles in the atmosphere. Breaking waves trap air in seawater, creating bubbles that rise to the ocean surface. The bubble burst and droplets of seawater are thrown into the air.

jet drops vs film drops

Film drops create many small particles from the bubble’s surface, while jet drops create fewer but larger particles coming from the cavity of the bubble after it burst.

primary vs secondary marine aerosols

Primary marine aerosols come directly from the ocean including sea salt + organics + microbes and ranging in size. Secondary marine aerosols form in the atmosphere from gases/chemicals released by the ocean such as organics and oxidized DMS.

What occurs in the micro layer of the sea surface?

Organic matter is collected on the surface. When bubble rise to the surface, the pick up organics before they burst. The smaller particles can be organically rich, effecting cloud formation when they enter the atmosphere.