revision questions

• Carbonate ion concentrations decrease with distance along the thermohaline conveyor. Hence concentrations are highest in the N. Atlantic, then decrease as deep waters flow into the S. Atlantic thenthe S. Indian then the S. Pacific, and are lowest in the oldest deep waters in the N. Pacific
• rates on the abyssal plain are low because abyssal plains are deep and a long distance from land.
• Mid-ocean ridges tend to accumulate carbonate sediments
• Upwelling areas tend to be highly productive, so sedimentation rates are high compared to the rest of the open ocean
• Scavenged elements are taken up onto particles descending from the sea surface. The older the deep water, the more time there is for scavenging. Hence old, deep waters will have lowest concentrations ofdissolved Sn.
• Continental shelves only extend to a few hundred meters depth so they are unaffected by deep water moving along the thermohaline conveyor belt.
• Although sulphate shows conservation behaviour in normal (oxygenated) seawater, in anoxic seawater it is reduced to sulphide,so the ratio of sulphate to salinity will be lower than it is in oxygenated seawater.