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Sciencenews
They wanted records of past hurricances to make predictions and historical records go back only a few hundred years. Category 4 and 5 hurricanes are rare, so there were only a few in historical times. So, to get more statistics on powerful hurricanes, they used a geological method called paleotempestology to look further back in time.
Hurricanes push ocean and beach sand into coastal lakes and marshes and if we take core samples from those areas, we'd see those layers of sand. This could be used to test if global warming increases the number of hurricanes. The organic material buried in the sand can be dated with radiocarbon dating. This shows that there were more big hurricanes hitting the Gulf coast 3500 to 1000 years ago than the past 1000 years. So there are millennial cycles of hurricane activity on top of the decadal cycle. More recent sand layers had been matched to historical hurricanes.
There is a hypothesis on where the millennial cycle comes from. There is a high pressure area over the ocean called the Bermuda high. It was already figured that maybe the changing position of the Bermuda high causes a cycle over 10000 years where the central and eastern parts of America alternate between getting plenty of rain. It is hypothesized that this cycle in the Bermuda high's position also causes an alternation between lots of hurricanes hitting the Gulf coast and lots of hurricanes going up along the East coast. When the high pressure area is close to the Caribbean and the land, it steers hurricanes towards the Gulf coast. When it is further away, it lets the hurricanes go up the East coast. Now they are collecting data from the East coast to see if hurricane activity alternates between the Gulf and East coasts. So far, the hypothesis has been supported, but they want to continue collecting data to make sure.
There are some other methods of measuring ancient hurricane activity. One is looking at the thickness of tree rings. Trees that lost leaves in hurricanes would have thinner rings for that year. The hurricanes would also affect what pollen is in the sands by messing around with what kinds of plants live in impacted areas. Those methods have some problems because other things like fire can change how plants grow, so results from those methods should be compared with results from other methods. Another method is measuring the ratios of isotopes of oxygen. For some reason, rain from hurricanes have less oxygen 18. A record of this characteristic isotope ratio is preserved in layers in stalagmites and stalactites in caves when the hurricane water washes into the ground down to the caves. This record could also preserved in the carbonate in sea shells.
This will help test models of climate that make predictions of how global temperature changes affect hurricane activity. It will also give insurance companies data to base their policies on. They also think that maybe the cycle is shifting now and there will be more intense storms hitting the Southeast.
Sciencenews
They wanted records of past hurricances to make predictions and historical records go back only a few hundred years. Category 4 and 5 hurricanes are rare, so there were only a few in historical times. So, to get more statistics on powerful hurricanes, they used a geological method called paleotempestology to look further back in time.
Hurricanes push ocean and beach sand into coastal lakes and marshes and if we take core samples from those areas, we'd see those layers of sand. This could be used to test if global warming increases the number of hurricanes. The organic material buried in the sand can be dated with radiocarbon dating. This shows that there were more big hurricanes hitting the Gulf coast 3500 to 1000 years ago than the past 1000 years. So there are millennial cycles of hurricane activity on top of the decadal cycle. More recent sand layers had been matched to historical hurricanes.
There is a hypothesis on where the millennial cycle comes from. There is a high pressure area over the ocean called the Bermuda high. It was already figured that maybe the changing position of the Bermuda high causes a cycle over 10000 years where the central and eastern parts of America alternate between getting plenty of rain. It is hypothesized that this cycle in the Bermuda high's position also causes an alternation between lots of hurricanes hitting the Gulf coast and lots of hurricanes going up along the East coast. When the high pressure area is close to the Caribbean and the land, it steers hurricanes towards the Gulf coast. When it is further away, it lets the hurricanes go up the East coast. Now they are collecting data from the East coast to see if hurricane activity alternates between the Gulf and East coasts. So far, the hypothesis has been supported, but they want to continue collecting data to make sure.
There are some other methods of measuring ancient hurricane activity. One is looking at the thickness of tree rings. Trees that lost leaves in hurricanes would have thinner rings for that year. The hurricanes would also affect what pollen is in the sands by messing around with what kinds of plants live in impacted areas. Those methods have some problems because other things like fire can change how plants grow, so results from those methods should be compared with results from other methods. Another method is measuring the ratios of isotopes of oxygen. For some reason, rain from hurricanes have less oxygen 18. A record of this characteristic isotope ratio is preserved in layers in stalagmites and stalactites in caves when the hurricane water washes into the ground down to the caves. This record could also preserved in the carbonate in sea shells.
This will help test models of climate that make predictions of how global temperature changes affect hurricane activity. It will also give insurance companies data to base their policies on. They also think that maybe the cycle is shifting now and there will be more intense storms hitting the Southeast.
