Orientation to Marine Science

Total: 183 marks — Investigation 1: 45 · Investigation 2: 48 · Investigation 3: 37 · Investigation 4: 53.

Investigation 1 — the Secchi disk

• Q1 (8): As allocated. Site B should sit well above Site A throughout, with A dipping sharply on Day 3 and both dipping on Day 5. Accept a line or a bar chart; a line is better because day is continuous.
• Q2 (6): Aim (1): to determine how water clarity differs between an estuary mouth and an open-coast site, and how it responds to weather. Independent (1): site, and day/weather conditions. Dependent (1): Secchi depth. Controlled (3, 1 each): time of day, same observer, same disk, shaded side, same method of averaging. Reject "the weather" as a controlled variable — it is the thing being varied.
• Q3 (3): The two depths differ because the eye detects disappearance and reappearance at slightly different points (2). Averaging reduces that observer bias and gives a more repeatable value (1).
• Q4 (4): More rain gives lower Secchi depth at Site A (2), supported by figures — 0 mm on Days 1, 2 and 6 gives 1.8–2.0 m; 4 mm gives 1.2 m; 18 mm gives 0.7 m (2). Accept "negative relationship". Do not accept "directly proportional".
• Q5 (4): Site A is an estuary mouth, so it receives the river directly, and the river carries suspended silt and soil washed off the catchment (2). Site B is open coast with no river input at that point, so rain falling on the sea does not add sediment — the run-off has nowhere to enter (2).
• Q6 (4): Wind-driven waves and swell stirred up sediment already lying on the seabed — resuspension (2). At Site B this is the dominant mechanism because there is no river to supply silt, and the observer note of a heavy breaking swell and pale green cloudy water supports it (2). This is a different mechanism from Day 3, and full marks require saying so.
• Q7 (5): Any defensible rewrite. Must (a) remove the false general claim (1), (b) restrict the rain effect to sites receiving run-off (2), and (c) recognise that clarity also falls without rain, through wind and wave resuspension (2). Model: "Heavy rain reduces water clarity at sites that receive river run-off, because the river carries suspended sediment into the sea. Clarity can also fall without any rain, when strong wind and swell resuspend sediment from the seabed."
• Q8 (4): Any two, 2 each: suspended sediment or silt; dissolved organic matter staining the water brown, as from a blackwater river; bubbles and foam in surf; stirred-up detritus. Accept sunlight angle or cloud cover as an observer-side effect.
• Q9 (3): Same time of day — sun angle and light level change what the eye can detect (1). Same observer — eyesight and judgement of "just disappeared" differ between people (1). Shade — glare off the surface stops you seeing the disk at all, and would give a falsely shallow reading (1).
• Q10 (4): Neither is wrong (1). A Secchi depth is a judgement made by a human eye, not a reading off a scale, so a spread of a few tens of centimetres is normal and expected (2). It tells you the instrument has limited precision and that readings should be repeated and averaged, and that trends matter more than any single value (1).

Investigation 2 — instruments and the profile

• Q11 (15): 3 each — 1 for the instrument, 2 for the justification. (a) Argo floats — only they give basin-wide coverage of the upper 2 000 m sustained over decades; a ship cannot be everywhere and a satellite cannot see below the surface. (b) Satellite remote sensing — ocean colour gives chlorophyll across a whole region within a day, which is the only way to see the extent of a bloom this week. (c) A mooring — it is fixed, so hourly readings for a year at one depth are exactly what it is built for, and any change must be a change in time. (d) Marine animal CTD — under winter sea ice a ship cannot reach and a float cannot surface to transmit; a tagged seal dives there anyway. (e) CTD with a rosette — the question demands physical bottles of water from a stated depth, which only the rosette can deliver.
• Q12 (7): As allocated. Depth must increase downward — a profile drawn with depth increasing upward loses those 2 marks even if otherwise perfect.
• Q13 (3): The mixed layer is the near-uniform surface layer from 0 to about 30 m, where temperature barely changes (21.4 → 21.0 °C) (2). "Mixed" means wind and waves have stirred it so thoroughly that it is effectively uniform from top to bottom (1).
• Q14 (4): The thermocline is the zone of rapid temperature decrease, steepest between about 30 and 100 m (2). Over 30–100 m the drop is 21.0 → 13.4 °C = 7.6 °C in 70 m, which is about 10.9 °C per 100 m (2). Accept a range of 30–150 m with correct arithmetic for that range.
• Q15 (2): Because the graph is drawn to look like the ocean itself — the surface at the top and increasing depth below it — so the shape of the plot matches the physical structure it describes (2).
• Q16 (4): A salinity minimum with saltier water both above and below indicates a distinct water mass of different origin sliding in at that depth (2). In the South Atlantic this is Antarctic Intermediate Water — relatively fresh, cold water that sank near Antarctica and is spreading northward at intermediate depth (2). Accept any answer identifying a separate water mass of polar origin; do not require the name.
• Q17 (5): Most likely an Argo float (1) — it profiles temperature and salinity from 2 000 m to the surface, which is exactly the range and both variables shown. Two that could not (2 each): an XBT, because it measures temperature only and gives no salinity, and reaches only about 760 m; a satellite, because it sees only the surface skin and cannot return anything below it. Also accept mooring (fixed sensors at set depths, not a continuous profile) with sound reasoning.
• Q18 (4): A Deep Argo float, a ship-lowered CTD, or an ROV/submersible (2). What you give up depends on the choice (2): a ship-lowered CTD costs enormous amounts of ship time and gives you one location on one day; a deep float is far rarer, so basin-wide coverage is much sparser.
• Q19 (4): A CTD detects conductivity, temperature and pressure (2). Salinity is calculated from conductivity together with temperature — necessary because warm water conducts better too, so conductivity alone would be ambiguous — and depth is calculated from pressure (2).

Investigation 3 — the tertiary institutions

• Q20 (10): 2 per institution, correctly and completely filled, including the date checked. A row with no date loses 1 of its 2 marks.
• Q21 (4): Nelson Mandela University and Rhodes University (2). Practical reasons, any two (2): you could live at home or travel cheaply; you could visit the campus before applying; NMU's Ocean Sciences Campus and the Algoa Bay research it supports are on your doorstep; Rhodes sits beside SAIAB.
• Q22 (4): Ichthyology is the study of fishes (2). The institute next door is SAIAB, the South African Institute for Aquatic Biodiversity (2).
• Q23 (4): A BSc requires Maths, Physics and Chemistry in first year, and those courses assume matric Mathematics and Physical Sciences as their starting point (2). Mathematical Literacy is not accepted as a substitute for Mathematics for science degrees, so choosing it in Grade 10 removes the BSc route entirely — and unlike a university specialisation, it cannot be reversed later (2).
• Q24 (4): Advantage (2): more applied and technical training, generally lower entry requirements, and a route into the industry without a Bachelor's pass. Limitation (2): a diploma does not lead directly into research or postgraduate study the way a BSc does, so some careers stay closed without further study.
• Q25 (5): Two reasons (2 each): entry requirements and APS cut-offs are revised annually, so a 2019 figure may simply be wrong now; programmes are renamed, merged or discontinued, so the qualification itself may not exist. Also credit: a third-party site may have copied it incorrectly in the first place. What to do (1): go to the university's own current prospectus or admissions page, and record the date you checked.
• Q26 (6): Marked on reasoning, not on which institution is chosen. Must reference the learner's own stated interest (2), at least one concrete feature of that institution (2), and one honest practical consideration such as cost, distance or entry requirements (2).

Investigation 4 — the visit and the poster

• Q27 (6): 2 each. Temperature logger — water temperature, recorded hourly and stored internally. ADCP — current speed and direction at many depths at once, by timing sound echoes off drifting particles. Acoustic receiver — logs the ID and time of any tagged fish or shark that swims past.
• Q28 (5): The problem is biofouling — organisms growing on the instrument (1). Two consequences (2 each): it can block or coat the sensor so readings drift or fail; it changes the shape and drag of the instrument, and on an acoustic device it muffles the transducer so detections are missed; it also means data quality degrades progressively between service visits, so late data is less trustworthy than early data.
• Q29 (5): The problem is that a change of instrument creates a step or discontinuity in the record, so a shift in the data cannot be told apart from a real change in the ocean (3). Running both together for a year gives an overlap period in which the two can be compared directly, so any offset between them is measured and can be corrected for (2). This is the single most important idea in Investigation 4.
• Q30 (4): A single survey gives one snapshot and cannot distinguish a normal fluctuation from a trend (2). A long record establishes what normal variation looks like, so a genuine change can be recognised against it — and slow changes such as warming are only visible over decades (2).
• Q31 (20): As allocated. Mark the conventions strictly — a poster that cannot be read from two metres has failed at its own job, however good the content. Accept any career.
• Q32 (4): Institution and qualification consistent with the chosen career (2); school subjects including Mathematics and Physical Sciences (1); the disqualifying choice is Mathematical Literacy instead of Mathematics (1).
• Q33 (5): Two strands correctly named from Oceanography, Marine Biology, Marine Ecology, Humans & the Ocean (2), with a genuine explanation of the dependence for each (3). Reject a list with no reasoning.
• Q34 (4): Either verdict can earn full marks. Consumptive — the career removes a resource that does not come back (fisheries, mining). Non-consumptive — it earns from the ocean while leaving it in place (eco-tourism, filming, education, most research). Between — e.g. an aquaculturist grows stock but consumes feed and water quality; a fisheries scientist enables extraction without extracting. 2 for the verdict, 2 for a justification that uses the definition rather than restating it.

Marking note. Q6, Q7 and Q29 are the three that decide whether this sheet worked, and they are the same idea in three costumes. Q6 asks the learner to find a second mechanism behind an effect they have just explained with the first. Q7 makes them rewrite a conclusion that is true in one case and false in another. Q29 asks why a scientist would refuse a better instrument. All three are about the same discipline: before you accept an explanation, ask what else could produce the same observation. A learner who can do that on the first practical of the course will be able to do it on the last.