Sinkholes and Blue holes
I’m McKensie Daugherty, your host for on the ocean. We’ve all seen images of sinkholes opening in the middle of busy intersections; a sudden, gaping hole in the Earth swallowing cars in the road. But what causes these holes to form and what can we learn from them? Sinkholes form in regions where the underlying geology is dominated by carbonate rock, such as Florida and the Bahamas. Carbonate rocks are highly susceptible to dissolution by rain, the underlying water table, or by changes in sea level over millennia that carve out underground caves and passageways. Eventually, this erosion may cause the roof of the underground cave to give way, spontaneously engulfing homes, traffic lights, and luxury cars. While we see sinkholes form today, they are not a new phenomenon. Sinkholes have been forming for millions of years. In a marine environment a sink hole, or “blue hole”, will be much deeper than the adjacent seafloor. This drastic change in depth gives marine sinkholes unique characteristics and their color. Sinkholes are often connected to larger subterranean networks through passageways or pores in carbonate rock. Additionally, sinkholes can be protected environments where indicators of climate or landscape use, such as pollen, overwash of sediments and sand from storms, or dead animals, are deposited and archived in sediments. Researchers at Texas A&M exploit the sedimentary archives of both marine and terrestrial sink holes to learn how our climate has changed over Earth’s history, and what additional changes we might expect in an uncertain future. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click “On the Ocean”.
Script Author: Richard Sullivan
I’m McKensie Daugherty, your host for on the ocean. Last week, we learned that precipitation and sea-level change can form sinkholes and blue holes on carbonate landscapes. These holes can record evidence of changes in plants and animals, as well as variations in precipitation patterns within an environment. Over time small pieces of rock and plants are deposited at the bottom of the sinkhole as sediment. Researchers at Texas A&M collect bottom sediments and use various laboratory techniques to analyze the sediments and gather evidence of what the environment and climate may have been like 12,000 years ago. The Caribbean basin remains a good place to reconstruct past environments because there are many sinkholes and blue holes on the islands where sediment cores can be taken. Completed work on sediments from the Northern Bahamas indicate regional precipitation patterns changed in the region during the last 8,000 years. These changes during the last 3,000 years support evidence that precipitation changes are associated with larger-scale global atmospheric shifts. Additionally, shifts in regional plant and animal species have also changed through time. Sediments recorded in these sinkholes and blue holes can provide insight into how changes in climate impact local ecosystems and precipitation patterns. Understanding past environmental changes throughout the Caribbean can be crucial to understanding how climate change will affect our ecosystems in the future. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click “On the Ocean”.
Script Author: Anne Tamalavage
Hurricane activity of Little Bahama Bank over the last 700 years
I’m McKensie Daugherty, your host for on the ocean. Scientists predict the frequency of intense hurricanes will increase as Earth continues to warm. Records of hurricane activity are only available for the last 150 years, so current knowledge of the relationship between climate and hurricane activity is limited. Knowing how hurricanes behaved when the Earth’s climate was different than it is today may help scientists determine how changes in climate will affect the intensity of hurricanes in the future. In the Caribbean, flooded sinkholes, known as blue holes, collect sand that is washed in by strong hurricanes. Blue holes promote excellent sediment accumulation and preservation through time. Normally, the sediment that is deposited in the blue holes is fine-grain mud, so these sand layers serve as long-term indicators of hurricane activity. Texas A&M researchers are developing a hurricane record based on a 30-foot long sediment core from Thatchpoint Bluehole near Abaco Island in the Northern Bahamas. Sedimentation occurs at a rate of ½ an inch per year at the Thatchpoint Bluehole. The sediment record reaches 700 years into the past and has sand layers that correspond to ten of the twelve Category 2 or greater hurricanes that came within 30 miles of this site since 1866. Based on the Thatchpoint Bluehole sediment record, four active intervals of increased hurricane activity occurred near Abaco Island since 1200 AD. Further analysis of this record may provide new insights into the drivers of hurricane activity during the last millennium. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click “On the Ocean”.
Script Author: Tyler Winkler
Sea Surface temperature
I’m McKensie Daugherty, your host for On the Ocean. With human-caused greenhouse gasses on the rise, predicting how the atmosphere and ocean will respond to global climate change has become very important. Scientists at Texas A&M University have used historical data, dating back to 1815, to investigate long-term climate trends such as identifying changes in sea surface temperatures and ocean circulation patterns. Using this historical data, numerical calculations were conducted and showed that global sea surface temperature in the ocean has sea surface temperature cooling and warming trends per decade. The most notable warming trend has occurred since the 1980’s, with average warming of 1.4 degrees Fahrenheit. Since the heat that the ocean is holding is increasing, the ocean circulations are changing in response. An important circulation called the Atlantic Meridional Overturning Circulation, which is known for its uptake of human introduced gasses from the atmosphere, is showing signs of slowing down as global temperatures increase. Researchers at Texas A&M University are continuing to use this information to understand what effects this circulation may have on the atmosphere, the ocean, and our future climate. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.
Script Author: Lauren Replogle
Contributing Professor: Dr. Benjamin Giese
Published Results: from http://onlinelibrary.wiley.com/doi/10.1002/2016JC012079/full
The ensemble mean SST tendency (shaded) in °C Century−1 and wind stress tendency (vectors) in N m−2 Century−1 from 1815 through 2013.
SST from the second EOF averaged from 90°W to 20°E and from 35°N to 80°N in °C plotted as a black line (left axis). Also shown is the maximum of the stream function in the North Atlantic Ocean in Sverdrups is shown as a red line (right axis). Both time series have been smoothed with a 5 year box-car average.