Palaeoclimatology Questions and Answers

Answer: A

Correct answer: a measurable quantity that varies with climate

A proxy is something preserved in a natural archive whose value depended on climate at the time it formed - a ring width, an isotope ratio, a pollen assemblage - and which can therefore be calibrated against instrumental records and used to infer climate before those records began. It is an indirect measurement, which is exactly what distinguishes it from a thermometer reading.

Answer: B

Correct answer: A-2, B-4, C-1, D-3

Resolution and span trade against one another across the four archives. Tree rings give annual resolution over centuries to millennia. Ice cores give annual to decadal resolution over hundreds of thousands of years. Ocean sediments accumulate so slowly that they smooth to centennial or millennial resolution but reach back millions of years. Corals band monthly but live only centuries.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the cause. Fine resolution requires rapid accumulation, and a rapidly accumulating archive either fills its basin or outlives its organism within a few thousand years. A slowly accumulating one lasts far longer but averages each sample over centuries, and bioturbation smooths it further. That is why palaeoclimate reconstruction always combines archives rather than relying on one.

Answer: D

Correct answer: the volume of ice and the temperature

The oxygen isotope ratio in foraminiferal carbonate reflects both the temperature at which the shell formed and the isotopic composition of the seawater, which itself depends on how much light isotope is locked up in ice sheets. Separating the two contributions is the central difficulty of the method, and it is usually done by combining the record with an independent temperature proxy.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the mechanism. Water containing oxygen-16 is lighter and evaporates more readily, so the vapour reaching the poles is isotopically light and the ice built from it is lighter still. During a glaciation that light water is removed from the ocean and stored on land, leaving the remaining seawater enriched in oxygen-18. The effect is large enough that the marine record is read primarily as an ice volume signal.

Answer: B

The first two are correct. The third is wrong and the distinction matters: the ice records local temperature while the marine record chiefly reflects global ice volume. Calibration is site specific. The two records answer different questions.

Answer: C

They give a direct measurement of past carbon dioxide and methane concentrations rather than a proxy for them. This is what makes the ice core record so central to the greenhouse argument. Not a proxy but the gas itself.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is exactly why the distinction holds. As snow compacts into ice the pore spaces close off and trap samples of the atmosphere of the time, so measuring carbon dioxide or methane in those bubbles measures the ancient air itself rather than inferring it from something correlated with it. The one caveat is that the air is younger than the ice enclosing it, since the pores stay open for some centuries near the surface.

Answer: A

Correct answer: thermometer records from weather stations

A thermometer measures temperature directly, so it is an instrumental record rather than a proxy - and it is what proxies are calibrated against over their period of overlap. Ring widths, pollen assemblages and ice isotopes are all quantities that varied with climate and must be interpreted through a calibration.

Answer: B

Eccentricity, obliquity and precession together modulate the seasonal distribution of sunlight. They pace the ice ages rather than changing the total energy the Earth receives appreciably. Three separate cycles are involved.