Microfossils Reveal Climatic History of the Gulf of Mexico
Proxy data such as tree rings, ice cores, and microorganisms are collected and analyzed by scientists to unlock past climate records stretching back thousands to millions of years ago. This video podcast examines how scientists can decipher past climate from such records by focusing on a proxy calibration study in the Gulf of Mexico. Microfossils recovered from the northern Gulf of Mexico are used to assess the control of temperature and salinity on the composition of microfossil assemblages and the chemical composition of their shells. The new data will be used to develop better estimates of past conditions from analyses of microfossils in sediment cores.
Episode Number: 154
Location Taken: St. Petersburg, FL, US
Microfossils Reveal Climatic History of the Gulf of Mexico
Hello and welcome to the U.S. Geological Survey Coastal and Marine Geology Podcast. IÕm Matthew Cimitile. Today, we are discussing how scientists are studying the shells of microscopic marine organisms to uncover past ocean temperatures.
Knowledge of EarthÕs climate history is essential to understanding modern climate change and to projecting likely future impacts. Answering questions pertaining to the rate and magnitude of climate variability over the past 1,000 years and beyond is critical to distinguish between natural and human-induced climate change today.
Reliable instrumental records of climate change are available only for the last 150 years. To get at paleoclimate information, or past climate records stretching back thousands of years, scientists use EarthÕs geologic record.
Trees, ice cores, corals, and shelled microorganisms are natural archives that store climate information. For example, ice cores trap gas bubbles at specific layers. The gas can be analyzed for past atmospheric carbon-dioxide concentrations. Trees grow in width by adding concentric rings to their trunks. The rings vary in size depending on environmental conditions like rainfall. However, for these archives or proxy records to be of use in studying climate change, they must be calibrated to modern environmental conditions. Jessica Spear is a geologist at the USGS in St. Petersburg, Florida, and is part of a project team working to develop such calibrations.
ÒCalibrations mathematically align proxy data like the widths of a tree ring, to something known like instrumental data such as the amount of rainfall. For example, the width of a tree ring doesnÕt itself tell you how much it rained in a particular year. But, we can calibrate the ring width to rainfall measurements in a specific location over the same interval of time and use that relation to convert widths of fossil tree rings to past rainfall.Ó
The USGS is conducting a proxy calibration study in the Gulf of Mexico to develop a relation between the chemical composition of planktic forams and modern low-latitude environmental conditions.
ÒPlanktic foraminifera, or forams for short, are these microscopic, unicellular organisms that live within the water column and they build a calcium-carbonate shell that chemically records the conditions of their ocean habitat. When ocean temperature increases, the foram will actually substitute magnesium for calcium into its shell, thereby recording the change in temperature. So in effect, the higher the ocean temperature, the greater is the ratio between magnesium to calcium in its shell, and the lower the temperature, the smaller is the ratio.Ó
To collect the forams, USGS scientists set up a sediment-trap mooring on the seabed of the northern Gulf of Mexico in 2008. The trap consists of a large funnel about a meter and a half wide that captures sinking foram shells into 21 sample cups. Cups are attached to a gear plate that is set to rotate at specific intervals. Cups are currently scheduled to collect material from 7 to 14 days over a 6-month period.
Upon retrieval of the cups, USGS scientists conduct a series of analyses on the forams that provides information on what species are present each season and the magnesium-to-calcium ratios in the shells of those species. Obtaining proxy data from sediment cores and environmental information, such as ocean temperature, over the same time interval provides the necessary information to calibrate the proxy data to instrumental records.
ÒTo compliment the calibration study, we are also collecting and analyzing fossil foram shells from deep-sea sediments of the northern Gulf of Mexico. The relation we developed from the calibration study will allow us to take the chemical ratios that we measure on fossil shells and convert them to temperature. This provides us with a record of how ocean temperature has fluctuated during the past 2,000 years.Ó
USGS scientists plan to continue collecting forams and measuring their magnesium-to-calcium ratios. This will help refine the relation between chemical makeup variability of foram shells and environmental conditions from year to year and seasonally. Sources of proxy data like the Gulf of Mexico planktic forams, are key to reading the archive of ocean temperature and past climate variability to differentiate whether current climate changes are natural or anthropogenically induced.You can learn more about paleoclimate research and USGS science at usgs.gov. The Coastal and Marine Geology podcast is produced in St. Petersburg, Florida, and is a product of the U.S Geological Survey, Department of the Interior.
Title: Microfossils Reveal Climatic History of the Gulf of Mexico
Description: Proxy data such as tree rings, ice cores, and microorganisms are collected and analyzed by scientists to unlock past climate records stretching back thousands to millions of years ago. This video podcast examines how scientists can decipher past climate from such records by focusing on a proxy calibration study in the Gulf of Mexico. Microfossils recovered from the northern Gulf of Mexico are used to assess the control of temperature and salinity on the composition of microfossil assemblages and the chemical composition of their shells. The new data will be used to develop better estimates of past conditions from analyses of microfossils in sediment cores.
Location: St. Petersburg, Fl, U.S.A.
Videographer: Matthew Cimitile, email@example.com, U.S. Geological Survey
Keywords: Paleoclimate, proxy data, microfossils, climate change
Additional Video Credits: Betsy Boynton (editing, graphics), Jessica Spear (Writing, Narration) Greg Arment (Music)