Paleoceanography 1: Hothouse and Icehouse Earth

Palm trees, alligators, and warm weather might conjure thoughts of the tropics, but for a period during Earth’s history, all of these things could be found in polar regions! Today the Arctic and Antarctic are frozen landscapes, but millions of years ago the climate of these regions more closely resembled modern California or Florida!

Divisions of major periods of Earth’s history over geologic time. Image from: https://upload.wikimedia.org/wikipedia/commons/7/77/Geologic_Clock_with_events_and_periods.svg

Earth has undergone several major climatic shifts, oscillating between “hothouse” or “icehouse” states over millions of years. During “hothouse” conditions, Earth has no major ice sheets, atmospheric concentrations of greenhouse gasses like carbon dioxide are high, and temperature gradients between the tropics and polar regions are small. During icehouse periods, Earth’s climate is cooler, with large ice sheets and periods of glacial growth and retreat.

Recreation of global surface temperature anomalies during the Cenozoic Era to present. From: Nikolov, Ned & Zeller, Karl. (2011). Unified Theory of Climate – Expanding the Concept of Atmospheric Greenhouse Effect Using Thermodynamic Principles: Implications for Predicting Future Climate Change.

The Cenozoic Era began 66 million years ago, and continues to the present. In the early Cenozoic Era, Earth was in a hothouse phase; temperatures at the tropics were around 40 C (110 F), and 20 C (70 F) at the poles. During the Cenozoic Era, Earth began to cool, entering a period known as the Pleistocene Icehouse roughly 2.5 million years ago. The Pleistocene is typically what is referred to as an “Ice Age”; glaciers formed and temperature gradients between the poles were larger. Today, Earth is still in an icehouse stage.

Scientists seek to understand what drove the cooling trend during the Cenozoic Era to answer questions about our climate today, such as how warm temperatures were maintained in polar regions despite spending 6 months of the year in darkness, and what initiated the shift from hothouse to icehouse conditions using clues left behind millions of years ago.

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

Early Oceanography 3: The Azoic Hypothesis

This is Jim Fiorendino, your host for On the Ocean. With frigid temperatures, constant darkness, and crushing pressure, the deep ocean is a hostile environment. Despite these conditions, life has found a way to thrive, assuming many strange and fascinating forms. Today, submersibles and advanced technologies allow scientists to study creatures that make their home in the deep ocean. To early oceanographers, deep-sea life was a great mystery; for 25 years, many early oceanographers and biologists were convinced no life at all existed at the greatest ocean depths.

Portrait of Edward Forbes, image from: https://upload.wikimedia.org/wikipedia/commons/2/21/Edward_Forbes.jpg

Edward Forbes was a British naturalist known for the Azoic Hypothesis, which described the abundance of life in the oceans with depth and concluded no life could exist below 1,800 ft. Forbes served on the HMS Beacon, a survey ship used to map the sea floor. In April 1841, the HMS Beacon left Malta for a mapping expedition in the Aegean Sea.
While aboard, Forbes took samples of life at the bottom of the sea by dredging. Forbes observed less diverse communities of generally smaller organisms at greater depths in his samples and extrapolated to estimate the depth below which no life would be found. Many scientists were quick to accept Forbes’ hypothesis, believing the deep ocean to be a thoroughly hostile and barren environment.

Early dredges used to collect organisms living on the seafloor. Forbes used the dredge shown in panel (b). Image from Anderson and Rice (2006).

Today, we know that there is a great abundance and variety of life in the oceans, even at great depths. Oddly enough, starfish, worms, and other organisms had already been collected at depths greater than the limit proposed by Forbes. The Azoic hypothesis was eventually disproven by Michael Sars and Charles Wyville Thomson, who found life while dredging well below depths of 1,800 feet.

A page from Charles Wyville Thomson’s The Depths of the Sea showing illustrations of deep-sea fauna. From: https://archive.org/stream/depthsofseaaccou00tho/#page/464/mode/1up

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: James M. Fiorendino

Featured Image from Pexels

Early Oceanography 2: Depth Sounding

This is Jim Fiorendino, your host for On the Ocean. How deep is the ocean? Today, we know that the average depth of the ocean is about 4000 meters, or 12,000 feet. For early oceanographers, answering this question was of particular importance, especially in coastal waters where ships may run aground.

A lead sounding weight attached to a rope. The weight is lowered into the ocean until it hits the bottom, and the depth recorded by marks on the sounding line. from: https://keyassets.timeincuk.net/inspirewp/live/wp-content/uploads/sites/20/2014/11/DSC_9788_SF.jpg

Early oceanographers used a method called sounding to measure the depth of the ocean. Though today we can map the seafloor acoustically, early sounding has nothing to do with “sound”. Instead, sounding involved tying a weight to the end of a long rope and lowering it into the water until it reached the bottom. Ropes were typically marked off at constant length intervals, and the wet part of the rope would indicate how deep the water was at a specific location. Using sounding data, maps of ocean depth could be created with contour lines, illustrating sea floor topography.

Illustration of sounding using a winch, as would have been used by Sir John Ross. From: https://woodshole.er.usgs.gov/operations/sfmapping/images/theb0914.jpg, originally from NOAA.

The first sounding of the deep ocean was conducted by Sir John Ross of the British Navy in 1840. Prior to Ross’s measurement, there was much speculation about how deep the oceans were, with some scientists estimating the deepest parts of the ocean to be about 12 miles. Today, we know the deepest part of the ocean, the Challenger Deep in the Marianas Trench, to be just under 7 miles deep. Ross made his measurement in the Southern Ocean with a sounding line 3,600 fathoms, or just over 4 miles, long with a 76-pound weight. The weight and line were lowered over the side of a small boat from a free-spooling reel. While the weight and line sank, oarsmen worked to keep their small boat stable against wind and currents. At such great depths, it was impossible to feel the weight hit the bottom. Instead, Ross noted when the unraveling of the reel slowed to determine when the weight had reached the bottom.

Bathymetric map of Nova Scotia waters by Nathaniel Blakemore, from Robinson, A.H. 1976.
Bathymetric map of Nova Scotia waters created using depth sounding data by Nathaniel Blakemore, from Robinson, A.H. 1976.

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: James M. Fiorendino

Featured Image from: Pexels

Early Oceanography: Edmond Halley and Magnetic Declination

 

This is Jim Fiorendino, your host for On the Ocean. “If I have seen further, it is by standing on the shoulders of giants.” This famous quote by Isaac Newton describes the process of investigation and discovery; any major scientific breakthrough has been the result of work by many individuals. Though oceanography is a relatively young field, the study of marine environments requires knowledge of several disciplines. Many early oceanographers were experts in other fields, applying their knowledge to investigations of the oceans. Their contributions laid the foundation for modern oceanography.

Oil painting of Edmond Halley (http://collections.rmg.co.uk/mediaLib/393/media-393720/large.jpg)

Much of the early scientific work that may be considered oceanography focused on solving problems of navigation on ships. Edmond Halley, best known for his discovery of the eponymous Halley’s Comet, conducted the first expedition in which the primary goal was furthering scientific knowledge. Halley was commissioned by the British government to study variations in Earth’s magnetic field. He was given command of the Paramore in 1698, and sailed the Atlantic Ocean between 52 degrees north and 52 degrees south.

Halley’s ship, the Paramore, from Thrower’s The Three Voyages of Edmund Halley (https://halleyslog.files.wordpress.com/2013/03/img_6898.jpg?w=425&h=352)

The Paramore expedition lasted two years. Unfortunately, insubordination forced Halley to cut his first voyage short, returning to England before setting sail again in September, 1699. Halley took daily measurements of the angle of his compass needle in relation to a true north and south line. The angle of the compass in relation to this line is known as the magnetic declination. Halley created a contour chart of the magnetic declination he observed in the Atlantic Ocean, in which continuous lines represent equal values of magnetic declination. Originally called Halleyan lines, they were later given the name isogonic lines.

Edmond Halleys' map of magnetic declination, recreated by Murray and Bellhouse (2016). Curved lines represent contours of constant magnetic declination.
Edmond Halleys’ map of magnetic declination, recreated by Murray and Bellhouse (2016). Curved lines represent contours of constant magnetic declination.

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: James M. Fiorendino

Featured image from: Pexels