To understand climate change, it is necessary to be able to look back in time and determine what Earth's past circulation patterns were like. Once this has been established, those patterns can be compared to today's, increasing knowledge about this complex system. This, in turn, gives climatologists the information they need to develop computer models to predict future ocean circulation. One of the biggest questions scientists have asked is whether there is some sort of a "switch" that can be turned on or off and can speed up, slow down, or stop the North Atlantic conveyor belt current. The conveyor belt represents a huge force in the ocean. In fact, according to Jerry McManus and Delia Oppo at the Woods Hole Oceanographic Institution, this conveyor belt
This thermal image illustrates how scientists are able to study and track the ocean's surface temperatures. This image, obtained from the AVHRR satellite, records the warmest temperatures in red, orange, and yellow and the coolest temperatures in blues and green. The warm area in this image depicts the location of the Gulf Stream. (Johns Hopkins University Applied Physics Laboratory and Ocean Remote Sensing Group)
responsible for overturning the ocean is equal to roughly 20 times the combined flow of all the world's rivers.
Because of the tremendous amount of heat and energy this current carries, it is critical to understand how and why it behaves as it does. In this attempt, several computer models have been developed. In order to make the models as reliable and realistic as possible, scientists turn to paleoceanography to understand past currents and energy flow and their impacts on climate.
Scientists are able to look back in time by studying proxy data found in sediment cores and dating the fossilized shells of foraminifera.
The analysis of foraminifera can designate when specific water masses formed. In addition, the radioactive decay of naturally-occurring uranium in seawater to its daughter isotopes (protactinium and thorium) found in deep-sea mud is also used to determine how strong and fast the water currents moved.
Of the two daughter isotopes, protactinium stays in the seawater for centuries. This is important because it lasts long enough to be transported to the Southern Ocean by the giant circulation cell. When the conveyor belt slows, the proportion of protactinium buried in the North Atlantic sediments increases. Based on this fact, scientists can use the ratio of protactinium-to-thorium levels in the sediments to see how fast the overturn circulation was moving, thereby providing important clues to the past climate.
For the future, if global warming is not checked and slowed, it could cause the addition of freshwater to the ocean, disrupting the system. An increase in temperature could increase evaporation at lower latitudes and transport freshwater toward the poles where it will return to Earth as snow or into the ocean. Based on all of these studies, it is apparent that there is still a lot of work that needs to be done in order to understand better the synergy of the biosphere, atmosphere, and hydrosphere.
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