Climate and water - Homework #4

1. Environmental change can affect the circulation of the oceans. During the Cretaceous (ca. 100 million years ago), the continents were in different places (look at the time period between 65-135 mya, figure 6-26 c-d in the Kump book) and there was no ice at the poles. Write an essay (no more than 2 pages) explaining how you think this would affect ocean circulation (both surface and deep currents). Include at least one sketch.
2. One small component of North Atlantic Deep Water is derived from very saline (38.9 g/L) outflow of the Mediterranean Sea through the lower half of the shallow Straits of Gibraltar. Surface water (35.0 g/L) from the Atlantic flows into the Med through the upper half of the water column in the Straits and eventually loses a fraction of its original volume to evaporation (E). Within the Med, mean E loss is 1.5 meters/year, while precipitation (P) plus river inflow (Q) equals about 0.5 meters/year. The net evaporation loss of 1.0 meters/year of fresh water to the evaporation causes the salinity increase of +3.9 g/L for Atlantic surface water while in the Med. The total water surface area of the Med is 2.5 million km².
• How much net loss of fresh water occurs from the Med to the atmosphere (in m³/year) by excess of E compared to (P + Q)?
• What is this net loss rate of fresh water from Med to the atmosphere expressed in Sverdrups (1 Sv = 1 million m³/sec)?
• What fraction of inflowing Atlantic surface water volume is lost by evaporation during its residence within the Med before leaving to form saline upper NADW? (Hint, use the salinity data for inflow vs outflow.)
• From the above results, calculate the rate (in Sverdrups) of saline outflow from the Mediterranean to form saline upper NADW?
• How does the rate of Mediterranean contribution of saline upper NADW compare with the much colder, less saline main outflow of NADW generated in the various regions near Greenland? NADW forms at a rate of 15 million cubic meters/second.