Answer to Question 1
Answer: The water at the equator is warmed at the equator, causing evaporation and an increase in salinity. This water heads away from the equator because it is less dense and therefore is caught in the shallow northward moving current. As the water moves north it radiates its heat into the air, causing the water to cool. This cool water is now highly salty and begins to sink as density increases. It then is caught in the deep water current and brought back to the equator, rising again as it warms and starting the process again.
Answer to Question 2
Answer: Tree rings serve as a proxy through which the conditions present at the time of growth can be observed. A small cylinder of the tree is removed and the rings examined. The size of each ring gives clues about the conditions at that particular year.