are you ready for s330

8/11/2019 Are You Ready for S330

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Contents

1 Introduction 1

2 Suggested prior study (OU courses) 1

3 Key concepts assumed and developed in S330 2

4 Mathematical and related skills 13

5 Other skills 17

6 Answers to self-assessment questions 18

1 Introduction

If you are intending to study S330 Oceanography, you will want to make sure

that you have the necessary background knowledge and skills to be able to enjoy

the course fully and give yourself the best possible chance of completing it

successfully.

Please read through this material carefully and work through the self-assessment

questions. It will be of use to you, even if you have already studied other Open

University Science courses and have completed the courses listed as useful for

S330 in Section 2 below. It will remind you of some of the facts, skills and

conceptual knowledge that we assume you will bring with you from those earliercourses.

If, after reading through this material, you are still unsure whether S330 is the

right course for you, you should seek further help and advice from our Student

Registration and Enquiry Service on 0845 300 60 90.

2 Suggested prior study

Everything in the oceans relates to everything else. Our aim in this course is to

help you perceive and understand the links between the different fields of

Oceanography, which covers all of the four scientific disciplines of Physics,

Chemistry,Biology andEarth Science.You will be well prepared if you have successfully completed S104Exploring

Scienceor one of its predecessors (S100/S101/S102/S103), combined with good

passes in at least twolevel 2 science courses, preferably in differentdisciplines.

Such courses could include S204Biology; Uniformity and Diversity, S207 The

Physical World, S260 Geology, S279 Our Dynamic Planet(or its predecessors

S267How the Earth Works: The Earths Interior and S269Earth and Life), S205

The Molecular World. S250 Science in Context, an interdisciplinary course, also

provides a certain amount of useful background knowledge as well as skills

development, as indicated in further reading in Section 3.5. These are by no

means your only options. You will also be able to start S330 if you have taken

fairly recently science-based courses equivalent to HND or second-yearuniversity level and passed with good grades.

Copyright 2008 The Open University WEB 00204 0

3.1

S330 Oceanography

Are you ready for S330

Oceanography?


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If you are coming to S330 without having studied some of the courses

recommended above, then it is essential that you establish whether or not

your background and experience have given you a sound platform from

which to tackle the work.

Oceanography is a level 3 course and requires a correspondingly high standard of

academic work. You should therefore be prepared to undertake tasks such as

synthesising and evaluating sets of oceanographic data, and reading and

interpreting short extracts from recent research papers. An analytical approach toproblem-solving, the ability to look for correlations and to make judgements on

available evidence and decide to what extent it supports a particular scientific

scenario, are all key skills in tackling S330 assignments. The knowledge and

skills that you will develop whilst studying S330 will provide you with a practical

and realistic approach to the subject that can be applied to unfamiliar

oceanographic data presented in assignments.

The self-assessment questions included in Sections 3 and 4 focus on the

interpretation of a variety of data which all contribute to our understanding of the

way the oceans work. Examples are drawn from course material and include

some background information which, combined with knowledge gained from

your previous study, should enable you to answer the questions. The questionsare grouped under subject areas but also test skills relevant to the graphical and

numerical sections. We therefore advise you to read through all the sections of

the document before tackling the questions.You may find you are more

proficient in some areas than others. If you have identified any areas in which

you feel less confident, then you will find it helpful to do some extra work using

the resources recommended at the end of each section. If you find you complete

fewer than half of the total number of questions correctly, then you may

wish to reconsider your course choice. Your Regional Centre can advise you on

the most appropriate courses to help you prepare for S330.

3 Key concepts assumed and developed in S330The list of concepts used in S330, most of which you will probably have met in

level 1 and/or level 2 Science courses specified in Section 2, are given here.

These concepts are further developed and applied in varying situations in S330,

so it will obviously be to your benefit if you already have a sound understanding

of them. The more of these concepts you are familiar with, the easier you will

find the course. Do not worry if a few of the concepts listed are new to you, as

most are revised briefly as they come up in the course.

3.1 Physical concepts

You should be familiar with

velocity, acceleration

gravity

Newtons laws including the law of gravitation

orbital motion, centre of mass

centripetal and centrifugal forces

density

pressure

viscosity conduction, convection


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specific heat, latent heat

evaporation, condensation

types of energy and conservation of energy

principles of sinusoidal wave motion as applied to sound, light and surface

waves in the oceans, diffraction, reflection and refraction

electromagnetic spectrum of solar radiation.Now try Questions 14, which make use of some of these concepts and give you

a chance to try out your skills and understanding. In each case, begin by reading

the introductory text.

The discovery of hydrothermal vents (hot springs) at mid-ocean ridges has

revolutionised our understanding of the processes involved at divergent

(constructive) plate margins. Cold seawater circulating through newly formed,

hot, fractured oceanic crust exchanges chemical elements and re-emerges on the

ocean floor as a very hot, chemically altered fluid. The release of these hot vent

waters into very cold deep ocean waters can be detected by sensitive probes

which can record very small temperature differences that remain after extensive

mixing between the cold seawater and the vent fluid. Figure 1 shows evidence ofboth small-scale continuous venting activity the deep plume and a much

larger scale single release of fluids known as a megaplume. The temperature

anomaly contours in degrees Celsius indicate by how much the seawater has

warmed as a consequence of the mixing of warm vent fluids and cold seawater.

(b)

1200

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Figure 1 A megaplume in 1986 on the Cleft Segment of the Juan de Fuca Ridge(see map). Contours are temperature anomaly (C) relative to ambient water at the

same depth. (a) Plan view showing also the 2400 m and 2200 m bathymetric

contours; (b) northsouth cross-section, which reveals the smaller steady-state

plume (deep plume) below the megaplume. For use with Question 1.


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Question 1 This question tests your understanding of the concept of specific

heat, the rearrangement of a formula, the use of scientific notation and scientific

units, contoured maps and sections, latitude and longitude.

Use Figure 1 to help you answer the following questions:

(a) How do the heights to which the two types of plume extend differ?

(b) Examine the shape of the temperature contours and suggest how these showthat bottom currents affect the deep plume.

(c) What is the latitude and longitude of the centre of the megaplume?

(d) What is the magnitude of the temperature anomaly at the centre of the

megaplume at about 1600m depth?

(e) The megaplume was stated to have a volume of some 130 km3and to have an

additional heat supply, E, of about 6.7 1016 J. Given that the specific heat

of water, c, is 4.18 103 J kg1 C1, and assuming that 1 m3 of water has a

mass of 103 kg, estimate by how much the average temperature of the

megaplume exceeded that of the ambient seawater. Give your answer to two

significant figures. (Hint: rearrange Equation 1 so that T is the subject, and

substitute values for m, the mass of water in the megaplume,Eand c.)

E= mc T (Equation 1)

The plumes of hydrothermal vent fluid described above mix and moveupwards

because they are warmer and less dense than the ambient seawater. You will meet

the concept of density in a wide variety of situations in S330. Knowing the

density of seawater allows us to understand and predict (1) the degree of mixing

occurring between different bodies of seawater and (2) circulatory patterns in the

oceans. Three important processes alter the density of seawater:

changes in temperature, which affect the volume of the water

alteration of the mass or average concentration of saltsin seawater (known as

salinity)

changes in hydrostatic pressure.

Question 2 This question tests your ability to make logical deductions based on

your understanding of the concept of density.

The majority of processes affecting the density of seawater occur at the surface so

here pressure changes will be ignored and you should concentrate on changes to

temperature and salinity. For each of the following scenarios, describe firstly how

you think the process listed would affect the density of surface seawater and

secondly whether any density change would make the surface waters moreor lessdense than the underlying waters:

(a) heavy prolonged rainfall near the Equator (where precipitation exceeds

evaporation)

(b) increased evaporation in a cold dry wind

(c) addition of snow and ice melt at high latitudes

(d) addition of river flood waters to coastal waters

(e) prolonged heating of the ocean surface in an arid climate (where evaporation

exceeds precipitation)

(f) formation of sea ice (sea ice is essentially freshwater ice).

You should now check the answer to this question (in Section 6) before reading on.


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Knowing both the temperature and salinity of seawater allows oceanographers to

calculate the density. Figure 2 shows how the density of seawater varies with

depth at different latitudes. Such a plot, showing the change of a variable with

depth at a particular location, is known as a profile.

1000

2000

3000

4000

1023.0

density (kg m3)

tropics

depth(m)

Equator

high latitudes

1024.0 1025.0 1026.0 1027.0 1028.0

Figure 2 Profiles of density versus depth for different latitudes. In the oceans,

depth zones over which density changes sharply are known as pycnoclines. For

use with Question 3.

Question 3 This question tests your ability to make deductions from profiles

showing density changes with depth.

(a) Examine each of the profiles in Figure 2 in turn and then suggest what featureis common to all three locations.

(b) For the equatorial location, give the depth range over which:

(i) density increases rapidly with increasing depth

(ii) density changes very little with increasing depth.

(c) From your answer to Question 2, suggest a likely explanation for the very

low surface density at the equatorial location.

In the very deep ocean, the density of seawater is affected by hydrostatic

pressure. The hydrostatic equation describes the way in which pressure,P

(N m2), is related to depth,z(m), in a column of fluid such that

P = gz (Equation 2)

wheregis the acceleration due to gravity (9.81m s2) and (the Greek symbol

rho, pronounced row) is the density (kg m3).

The huge changes in pressure with depth in the oceans cover several orders of

magnitude, i.e. several powers of ten. To show the range of pressures

encountered, it is necessary to use a graph with logarithmic scales on both axes.

When plotted on such a graph, the relationship between pressure and depth is

essentially linear. Figure 3 shows such a graph of pressure against depth in the

oceans.


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pressure, P (Nm2)

10

100

1000

depth

,

z

(m)

108

1

10000106 107105

Figure 3 Graph of depth (z) against pressure (P) in the oceans. Both scales are

logarithmic simply to accommodate the range of numbers. The relationship

between pressure and depth is effectively linear when plotted on this scale.

(Pressure is measured in newtons per square metre; 105N m2= 1 bar ~ 1 atm.)

For use with Question 4.

Question 4 This question tests your ability to interpret data plotted on a

logarithmic scale as shown in Figure 3.

(a) By what multiplication factor does pressure increase over the depth range

100 to 1000 m?

(b) Much of the deep ocean floor lies at depths of 45 km. What pressures would

you encounter at these depths?

3.2 Chemical conceptsYou should be familiar with:

chemical symbols, chemical formulae and equations

valency, ions

isotopes of chemical elements

pH/acidity

oxidationreduction reactions

solubility

concentrations expressed as mass per unit volume and molar concentration(and you should be able to convert from one to the other).

You should also be able to:

understand and use simple chemical equations (you are not required to

formulate equations but be able to read them and appreciate that they need

to be balanced)

appreciate the significance of equilibrium (Le Chateliers principle)

carry out simple calculations involving molar ratios.

The average concentration of dissolved salts in the oceans is about 3.5% by

weight. Eleven ions make up 99.9% of the dissolved constituents of seawater;these are known as the major ions. Concentrations are usually given as parts per


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thousand by weight (either grams per kilogram, g kg1or grams per litre, gl1,

assuming 1 litre of water has a mass of 1000 grams). Table 1 gives the average

concentrations of the major ions in seawater inparts per thousand() by

weight.

Table 1 Average concentrations of the major ions in seawater, in by weight

(gkg1 or g 11).

Ion by weight

chloride, Cl 18.980

sulphate, SO42 2.649

hydrogen carbonate, HCO3 * 0.140 Negative ions (anions)

total = 21.861

bromide, Br 0.065

borate, H2BO3 0.026

fluoride, F

0.001sodium, Na+ 10.556

magnesium, Mg2+ 1.272

calcium, Ca2+ 0.400 Positive ions (cations)

total = 12.621

potassium, K+ 0.380

strontium, Sr2+ 0.013

Overall total salinity 34.482

* Includes carbonate, CO3

2.

Question 5 This question tests your ability to convert from mass per unit

volume to molar concentration, ratios and the use of significant figures.

Using the data in Table 1:

(a) What is the molar concentration of sodium ions in mol l1in this sample of

seawater, given that the mass of 1 mole of sodium ions is 23.0g? Give your

answer in scientific notation to two significant figures.

(b) The molar concentration of sodium in water from the Dead Sea (a hypersaline

enclosed body of water) is 1.52mol l1. What is the ratio of the molar

concentration of sodium in Dead Sea water to that of the average seawater inTable 1? Express your answer asx : 1.

(c) In bodies of seawater with differingsalinities, the major ions always occur in

the same proportions, i.e. the ratios of their individual concentrations (C) to

total dissolved salts (S) of that sample are constantwhatever the salinity.

Using this information, together with the sodium concentration and total

salinity from Table 1, estimate the salinity (S) of a seawater sample whose

sodium concentration is 9.500g l1.

Reductionis said to occur when an atom gains electrons (or when the proportion

of oxygen in a compound decreases) during a chemical reaction. Oxidation

involves an atom losing electrons (or the proportion of oxygen in a compound

increasing). Any chemical reaction leading to oxidation of one substance must be

accompanied by the reduction of another substance and vice versa. It has already


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been noted that the chemical composition of hydrothermal vent fluids is markedly

different from that of the seawater from which it originates. The vent fluids are

hot and highly acidic (about pH 4), which affects the solubility of both iron and

manganese. In the acidic conditions of the vent fluids, iron is found in high

concentrations in its soluble reduced form, known as ferrous iron, Fe2+. In typical

oxygen-rich seawater (pH 7.8), the iron readily combines with oxygen, forming

insoluble precipitates where the iron is present as ferric iron, Fe3+.

Question 6 This question tests your understanding of valency, oxidation and

reduction.

(a) What is the valency of iron (i) in its ferrous state and (ii) in its ferric state?

(b) Explain why the change of a ferrous ion to a ferric ion is an oxidation.

Carbon dioxide gas is the most soluble gas in seawater. However, very little

carbon dioxide is present as dissolved gas, as carbon dioxide dissolves veryquickly in surface seawater (CO2(aq)) and forms hydrogen carbonate ions

(HCO3) and carbonate ions (CO32), with the release of hydrogen ions (H+).

Average seawater typically has a pH of around 7.8. The solubility of carbon

dioxide increases with increasing pressure (and therefore depth) in the oceans,forcing more CO2 into solution. Respiration also adds CO2, further increasing the

total dissolved CO2at depth. The bottom waters of the oceans therefore tend to

have a lower pH (a greater concentration of hydrogen ions) than surface waters,allowing dissolution of calcareous shells made of calcium carbonate (CaCO3). In

near-surface waters, both plants and animals make use of calcium ions (Ca2+) and

hydrogen carbonate ions (HCO3) to build their skeletons or shells. CO2is

removed by photosynthesising plants in surface waters and replaced by the

respiration of both animals and plants.

Question 7 This question tests your ability to understand simple chemical

equations.

(a) Using the information above, match the forward reactions of chemical

equations 14 to processes (i)(iv):

(i) dissolution of calcareous skeletons

(ii) photosynthesis

(iii)dissolution of CO2gas in seawater

(iv) precipitation of calcium carbonate to form a calcareous skeleton.

(Note: s, l, g and aq in brackets denote solid, liquid, gas and aqueous states

respectively.)

1 H2O(l) + CO2(g) =H2O(l) + CO2(aq) =HCO3(aq) + H+(aq) =CO32 (aq) + 2H+(aq)

2 6CO2+ 6H2O =C6H12O6+ 6O2

3 Ca2+(aq) + 2HCO3(aq) =H2O(l) + CO2(g) + CaCO3(s)

4 CaCO3(s) + H+(aq) =Ca2+(aq) + HCO3 (aq)

(b) The chemical equation for respiration is:

C6H12O6+ 6O2 = 6CO2+ 6H2O + energy

Write this equation as a sentence.

Le Chateliers principle refers to the effect of external constraints (such as change

of pressure or temperature, or an increase in the concentration of one of the ionsinvolved in the reaction) on the equilibrium position of a reaction. Le Chateliers


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principle states that when a system in dynamic equilibrium is subject to a

constraint the system responds in such as way as to minimise that constraint.

Question 8 This question tests your understanding of Le Chateliers principle.

Look at Question 7, equation 4. Using Le Chateliers principle, suggest what

would happen to the amount of solid calcium carbonate if the hydrogen ion

concentration were increased.

During chemical reactions, atoms are neither created nor destroyed, so the

number of atoms shown on the reactant side of a chemical equation must equal

those on the product side. This also applies to the charge where ions are involved.

The equation must be balanced. Breakdown of organic matter by bacterial

respiration in the oceans is generally carried out in oxidising conditions because

seawater is usually well oxygenated. In anoxic (oxygen-depleted) or oxygen-

deficient conditions in the ocean, such as those found in the Black Sea, bacteria

must utilise other oxidising agents. The sulphate ion (SO42) is a major dissolved

constituent in seawater and is utilised when oxygen is not available. Hydrogensulphide (H2S) is formed as a result.

Question 9 This question tests your ability to balance equations and yourunderstanding of molar concentrations.

(a) The partially balanced equation for bacterial respiration in anoxic conditions

is:

C6H12O6+ 3SO42 =3H2S +xHCO3 (wherexis an integer)

Balance this equation to obtain the correct value forx. (You should check

your answer before moving on.)

(b) From your answer to (a), how many moles of sulphate ion are required toproduce 1 mole of hydrogen sulphide (H2S)?

(c) Given that all the sulphate ions in a water sample are converted to hydrogensulphide by bacterial respiration and that the initial molar concentration of

sulphate is 3.50 104moll1, from your answer to part (b) what is the final

molar concentration of hydrogen sulphide in the sample?

3.3 Biological concepts

You should be familiar with:

respiration

photosynthesis

habitats, populations and communities

differences between plants, animals and bacteria

simple classification of organisms (families, genera, species)

trophic levels, energy flow, food chains and webs.

Energy flows through ecosystems, having been initially trapped by autotrophic

primary producers, and passes from one trophic level to the next, e.g. herbivores

feed on plants and carnivores feed on herbivores, other carnivores and

detritivores. Detritivores consume dead material. Relationships in ecosystems are

not always straightforwardly linear forming afood chain, and there may be a web

of interdependent organisms.


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Question 10 This question tests your understanding of food webs and feeding

relationships.

Below is a list of some feeding relationships observed on a rocky shore in the

British Isles. Decide which of the organisms are (1) herbivores, (2) first

carnivores (feeding on herbivores), (3) higher carnivores (feeding on carnivores)

and (4) detritivores; then decide on the best way to describe these relationships,

either a food chain or a food web. Construct an appropriate diagram to showthese relationships.

(Note: diatoms are simple photosynthetic algae, whilst zooplankton are

microscopic animals that graze on algae in near-surface waters; all of the other

organisms mentioned are animals.)

Feeding relationships:

limpets grazing on diatoms attached to rocks

dog whelks eating barnacles and mussels

crabs consuming detritus and dead mussels in crannies in rocks

barnacles feeding on zooplankton

mussels feeding on diatoms

flat periwinkles feeding on diatoms

gulls feeding on dead crabs

turnstones (birds) feeding on dogwhelks, limpets and flat periwinkles.

Phytoplankton (microscopic floating algae) are the principal primary producers in

the oceans, photosynthesising in the upper sunlit (photic) layer. As well as light

levels, an important limiting factor determining total primary production is the

availability of dissolved nutrients in the form of nitrate (NO3), phosphate

(PO43) and silica (SiO2). Primary production is severely curtailed when these

nutrients are depleted and ceases when they are used up entirely. As a result of

decomposition and bacterial respiration, these nutrients are recycled in the upper

layers of the ocean when phytoplankton die, and are then available to sustain the

next generation of phytoplankton. A proportion of the livephytoplankton

population, however, is consumed (grazed) by zooplankton (planktonic animals

that are second-level herbivores).

Figure 4 shows data collected in the North Sea on nutrient content of the

seawater, phytoplankton (algae) concentration and estimated reproductive rate of

phytoplankton.


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1.0

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(b)

are you ready for s330

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