GE G Climate Science Lab
Leslye Mitty MohonDepartment of Geography, Texas A&M University
“Validating annual growth bands of deep sea black corals and calculatingocean ventilation ages from the Gulf of Mexico and Southeastern United
States”
Outline
• Introduction• Objective• Background• Research Design• Significance/Conclusion
O&M Building at Texas A&M University
Introduction of Deep Sea Corals
• Deep sea corals are only beginning to be used as a paleoclimate archive that can extend our observation of ocean dynamics and climate well beyond instrumental records.
• The main methods for radiometric dating are 210Pb, radiocarbon, and Uranium-Thorium (U/Th)
• Deep sea corals can be found between 30 to 6,000 meters depth• Can be 500 to 40,000 years old • Provide habitat for many marine organisms especially important commercial fish and endangered species.
• Deep sea black corals grow in a tree-like fashion and form annual growth rings that can produce paleoceanographic records.• Deep sea black corals can be used to calculate ventilation ages of deep water masses.
Prouty et al. 2011 and Roark et al. 2006
Study Site
• My two study sites are (marked with red “X”) the Gulf of Mexico and Southeastern United Stated (SEUS).
Druffel et al. 2008
Research Question and Corals
By validating independent age and growth rates estimates of deep sea black corals, what are the
radiocarbon derived ocean ventilation ages in the Gulf of Mexico and SEUS?
Objectives
• Objective 1: Validate the age, life spans, and growth rates of black corals using visual ring counts and scanning electron microscope (SEM) analysis (e.g. Images) and comparing them to radiocarbon ages.
Objectives
• Objective 1: Validate the age, life spans, and growth rates of black corals using visual ring counts and scanning electron microscope (SEM) analysis (e.g. Images) and comparing them to radiocarbon ages.
• Objective 2: Developing ocean ventilation records from the Gulf of Mexico and SEUS using radiocarbon analyses.
Objectives
• Objective 1: Validate the age, life spans, and growth rates of black corals using visual ring counts and scanning electron microscope (SEM) analysis (e.g. Images) and comparing them to radiocarbon ages.
• Objective 2: Developing ocean ventilation records from the Gulf of Mexico and SEUS using radiocarbon analyses.
• Objective 3: Using U/Th dating method as an independent chronology to validate coral and ocean ventilation ages
Background
Knowns
Black corals are the longest living corals.
Corals produce decadally and perhaps annually resolved paleoceanographic records.
210Pb, Radiocarbon, and U/Th has been used to calculate growth rates and ages of corals.
Compared to radiocarbon and 210Pb, U/Th dating method is more accurate and can date corals up 500,000 years old.
Gaps
Are growth band annual in black corals?
Can Iodine be used to identify annual growth bands in black corals?
What are the growth rates and ages of black corals?
What are the ocean ventilation ages in the GOM and SEUS?
Lack of knowledge of black corals from the Gulf of Mexico and SEUS.
Background
GAPCan Iodine be used
to identify annual growth bands in black corals?
Nowak et al. 2009
Research Design
Prouty et al. 2011
Objective 1: Validate the age, life spans, and growth rates of black corals using visual ring counts and scanning electron microscope (SEM) analysis (e.g. Images) and comparing them to radiocarbon ages
Research Design
• By projecting paleo-Δ14C values back in time to their intersection with atmospheric record, the residence time or ventilation age of deep water masses may be calculated. This can get complicated by the mixing of multiple water masses with different convection histories (Hillaire-Marcel and Vernal 2007).
• By developing chronometers, equivalent to radiocarbon as a tracer, it is possible to reconstruct ventilation ages in different oceans as far back as the Last Glacial Maximum (Robinson et al. 2005).
Objective 2: Developing ocean ventilation records from the Gulf of Mexico and SEUS using radiocarbon analyses.
Research Design
• U/Th has an advantage over radiocarbon dating besides accuracy. U/Th dating can be used to date objects up to 500,000 years old, while
14C is good for only a few tens of thousands of years at best. U/Th can be used as independent chronometer, and pairing the result to
radiocarbon measurement, to reconstruct ventilation histories in different oceans (Robinson et al. 2005).
• Measuring U/Th is done by calculating an age from the degree to which equilibrium has been restored between the radioactive isotope thorium-230 and its radioactive parent uranium-234 within a sample.
• The thorium-230 is itself radioactive with a half-life of 75,000 years
Objective 3: Using Uranium-Thorium (U/Th) dating method as an independent chronology to validate coral and ocean ventilation ages
Significance
Value to Society
Help understand ocean and atmospheric processes to possibly make future climatic predictions.
Conservation of corals that provide habitat to commercially important fish and endangered species.
Minimize human impacts (e.g. bottom trawling and jewelry trade).
New Information: Validating Ages and
growth rates of black Corals
Iodine analysis U/Th Dating
• Ocean Ventilation Ages…
How ocean circulations have changed in the past
Learn more about biological processes in the deep ocean.
Past CO2 cycling in the atmosphere and oceans
THE END
QUESTIONS OR SUGGERSTIONS?