Consider the question. Examples of proxies include ice cores, tree rings, sub-fossil pollen, boreholes, corals, lake and ocean sediments, and carbonate speleothems. The character of deposition or rate of growth of the proxies' material has been influenced by the climatic conditions of the time in which they were laid down or grew. Chemical traces produced by climatic changes, such as quantities of particular isotopes, can be recovered from proxies. Some proxies, such as gas bubbles trapped in ice, enable traces of the ancient atmosphere to be recovered and measured directly to provide a history of fluctuations in the composition of the Earth's atmosphere. To produce the most precise results, systematic cross-verification between proxy indicators is necessary for accuracy in readings and record-keeping.

What is an example of a natural climate record/proxy?
 If the answer is 'ice cores'; explain the reasoning:
The relevant sentence in the passage is: Examples of proxies include ice cores, tree rings, sub-fossil pollen, boreholes, corals, lake and ocean sediments, and carbonate speleothems.