Paleoceanography 5: Chasing a Ghost

Is it possible to catch a ghost? Major ocean features like western boundary currents are fairly stable today, but millions of years ago they may have been quite different. Unfortunately, unlike living things which may leave fossils or biomarkers for scientists to find, currents have no physical remains. Scientists at Texas A&M University are working to capture a long-dead specter as they attempt to uncover the location of the Kuroshio Current millions of years ago.

Surface waters flow in a circular pattern in major ocean basins, clockwise in the Northern Hemisphere and counter clockwise in the Southern Hemisphere. Western Boundary Currents like the Kuroshio Current occur at the western edge of ocean basins. They are fast and narrow, transporting massive amounts of warm water from the equator to the poles. As the Kuroshio current flows north, it turns to the right, extending into the middle of the Pacific Ocean basin. The greatest temperature gradient with latitude in the western Pacific Ocean occurs between 38- and 40-degrees north. This gradient is associated with the Kuroshio Extension, where the current turns into the open ocean.

This diagram shows the general circulation patterns of the North and South Pacific Ocean. Boundary currents are circled; western boundary currents are found on the western edge of ocean basins, in this case off the coast of New Zealand and Japan. Image from: https://oceanservice.noaa.gov/education/tutorial_currents/04currents3.html

The Kuroshio Extension shifts north or south seasonally and over long time periods. Identifying where both the Kuorshio Current and Extension were millions of years ago is important for reconstructing past heat transport and carbon cycles in the ocean. As the Kuroshio Current flows northward and releases heat, the water cools and the solubility of CO2 increases. Therefore, regions of large temperature gradients associated with western boundary currents are where the greatest amount of CO2 enters the oceans.

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.

Featured image from: Mikkel Juul Jensen/SPL/Cosmos (left) and Aphelleon/Shutterstock (right)

Script Author: James M. Fiorendino

Contributing Professor: Dr. Yige Zhang

Paleoceanography 4: Methane Hydrates, a Molecular Clue

This is Jim Fiorendino, your host for On the Ocean. Scientists follow a trail of biomarkers left by ancient organisms to reconstruct a record of Earth’s climate history. At Texas A&M University, oceanographers are currently hunting for molecular clues in the Tasman Sea using sediment samples collected by the International Ocean Discovery Program.

The Tasman Sea is the body of water located between the east coast of Australia and New Zealand.

Methane hydrates are ice-like substances in which methane gas is trapped; methane is a greenhouse gas, and is composed of three hydrogen atoms bonded to one carbon atom. Some scientists believe there is more methane hydrate in marine sediments than all other forms of fossil fuel combined. Methane is produced by thermogenic processes deep in the earth or through biological activity. Biologically produced methane hydrates can be distinguished from thermogenically produced methane hydrates by studying their carbon isotopes; biologically-produced methane hydrates are depleted in the heavier carbon 13 isotope.

Right: A ball and stick model showing the structure of methane hydrate. A methane molecule is trapped within a cage of water molecules (United States Department of Energy). Left: Burning methane hydrate (United States Geological Survey). https://geology.com/articles/methane-hydrates/

Release of methane hydrates into the world’s oceans and atmosphere could dramatically acidify the oceans and raise global temperatures. Scientists are trying to understand the history of methane hydrate destabilizations, and whether this could have contributed to the major climate shift that occurred during the Cenozoic Era. Release of methane from gas hydrates would mean an all-you-can-eat buffet for microorganisms that eat methane. These methanotrophs produce lipid biomarkers that are preserved in sediments for millions of years, waiting for scientists to discover them and read their ancient record of methane disturbances. To ensure accuracy, records of past methane hydrate release events are compared with a suite of lipid biomarkers, as well as their compound-specific carbon isotopes.

Location of inferred and recovered methane hydrates in the oceans. Image from Council of Canadian Acadamies, based on data from Kvenvolden and Rogers (2005). http://www.globalcarbonproject.org/news/MethaneHydrates.html

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.

Featured image from: Mikkel Juul Jensen/SPL/Cosmos (left) and Aphelleon/Shutterstock (right)

Script Author: James M. Fiorendino

Contributing Professor: Dr. Yige Zhang

Dr. Yige Zhang

Paleoceanography 3: Climate Proxies

This is Jim Fiorendino, your host for On the Ocean. How can we study changes in Earth’s climate that occurred millions of years ago? Fortunately, there are clues left behind by ancient life.

The shell, or test, of Syracosphaera azureaplaneta. This phytoplankter is a coccolithophore, which means it forms intricate tests made of calcite plates. These plates remain in sediments after phytoplankton die. Image from: https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/2018/newoceanplan.jpg

Phytoplankton are microscopic marine organisms capable of photosynthesis, meaning they create food for themselves using CO2 in their environment and light energy. Some compounds phytoplankton produce, like lipids, are resilient and difficult to break down. Lipids are a biomarker, meaning they are produced by living things and their presence or characteristics are indicative of processes within an organism or its environment. When phytoplankton die and degrade, lipid biomarkers remain for scientists to find and study. Lipid biomarkers are also known as “molecular fossils” which complement “hard” fossils like shells, bones, and teeth.

The structure of various unsaturated alkenones. Unsaturated alkenones have double bonds. A diunsaturated alkenone has two double bounds, a triunsaturated alkenone has three double bonds, and a tetraunsaturated alkenone has four double bonds. The number of double bonds in alkenones changes with temperature. Figure from Conte et al. (1998).

The structure and composition of lipid biomarkers are clues to what Earth’s climate was like when those molecules were produced. Alkenones are a type of lipid produced by a few species of phytoplankton. Their defining feature is a very long chain of carbon atoms. The number of double bonds in alkenones is one clue scientists use to study Earth’s climate history. Double bonds in alkenones decrease at higher temperatures to maintain the fluidity of cell membranes; the degree of unsaturation (or number of double bonds) in alkenones is therefore an indicator of ocean temperature. Additionally, the ratio of carbon isotopes in alkenones is indicative of Earth’s atmospheric CO2 levels. Isotopes are atoms of the same element with different atomic mass. Phytoplankton can be picky eaters, preferring to utilize lighter forms of carbon if possible. A high ratio of light carbon to heavy carbon in alkenones means the ocean and atmosphere had more CO2. Using these tools, scientists produce records of Earth’s climate history, including both ocean temperatures and atmospheric CO2 concentrations.

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.

Featured image from: Mikkel Juul Jensen/SPL/Cosmos (left) and Aphelleon/Shutterstock (right)

Script Author: James M. Fiorendino

Contributing Professor: Dr. Yige Zhang

 

 

 

 

 

 

 

 

 

Paleoceanography 2: Climate Forcing

Climate change is a major issue facing our planet today, but it is not the first time Earth has undergone dramatic shifts in climate. Studying how and why Earth’s climate has oscillated in the past is an active area of research.

A plot of the average global temperature anomaly from Earth’s average climate during the last 800,000 years. Temperature anomaly refers to the difference in Earth’s temperature above or below a long-term average. Figure from NOAA and created by Fiona Martin using ice core data collected by the Paleoclimatology Program at NOAA’s National Centers for Environmental Information.

Climate refers to average weather conditions over long periods of time. Climate forcing describes processes that alter the balance of Earth’s energy budget. Earth’s energy budget and climate are determined by incoming radiation from the sun, the planet’s reflectivity or “albedo”, and the atmospheric greenhouse effect which traps heat. On very long time scales radiation reaching Earth from the sun has changed and may have altered Earth’s climate. The faint young sun conundrum is a puzzle to scientists, referring to the fact that early Earth was very warm but less radiation was reaching Earth from the Sun than today.

The above diagram describes Earth’s energy budget and the different paths energy from the sun may take upon reaching Earth. Image from NASA.

Earth underwent a shift in climate from a hothouse state to an icehouse state during the Cenozoic Era beginning 66 million years ago. During that time solar irradiance did not change, so the two most likely factors responsible for this climatic shift are the greenhouse effect and changes in Earth’s albedo. Unfortunately, there is no record of Earth’s long-term albedo, but through chemical proxies scientists can estimate how much CO2, a major greenhouse gas, was present in the atmosphere millions of years ago. During hothouse conditions, CO2 concentrations were over 1000 ppm, and decreased to 180 – 280 ppm during the Pleistocene Icehouse Earth, which began 2.6 million years ago. Today, atmospheric CO2 concentrations are around 400 ppm. Scientists study sources and sinks of CO2 in Earth’s atmosphere to understand how environmental processes alter atmospheric CO2 concentrations, such as volcanic degassing, respiration of organic material, and chemical weathering.

A recreation of Earth’s atmospheric carbon dioxide concentrations for the past 40 million years. From Zhang et al. (2013).

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.