The Science Beneath the Surface of Icebergs

“SOS Titanic calling. We have struck ice and require immediate assistance.” – April 15th, 1912

Image of the RMS Titanic from 1912
RMS Titanic 1912 – Source: Wikimedia Commons

Everyone knows the tragic history of the sinking of the “unsinkable” Titanic. But how much do people know about the culprit of the catastrophe…icebergs? While the iceberg that took down the Titanic has long since dissipated, icebergs are still a common and actively tracked occurrence today. How are icebergs formed? Why do they float? What do the varying sizes and colors mean? What actually IS an iceberg? 

Icebergs can be seen all across the oceans but are most common in the North Atlantic Ocean near Greenland (formed from tidewater glaciers), and in the Arctic and Southern Oceans (formed from ice shelves). Icebergs are different from sea ice, which is simply frozen seawater. The extent of sea ice ebbs and flows throughout the year, mainly depending on the temperature of the ocean and the season. This cycle of sea ice formation plays a critical role in regional ecosystems, and the earth’s climate as a whole. While scientists are deeply invested in the study of sea ice and climate change, they also study iceberg lifecycles to better understand the impact changing climate is having on ice shelf collapse. 

A large tabular iceberg that was calved from an Antarctic ice shelf
A large tabular iceberg that was calved from an Antarctic ice shelf. Image source: Wikimedia Commons

Each year, roughly 40,000 icebergs break off, or calve, from glaciers and ice shelves across the world. Since icebergs originate from land they are made of freshwater and not saltwater. The differing freezing points of freshwater and saltwater (32 degrees Fahrenheit versus 28.4 degrees Fahrenheit respectively) impact why icebergs float, as do the varying densities. Freshwater has a density of 1.0 g/mL, however when it freezes the water molecules expand, causing the density of ice to be lower at .92 g/mL. This density difference can be seen in a simple glass of water with ice cubes! Saltwater, however, has a slightly higher density than freshwater, at 1.03 g/mL. This allows these “mass”-ive chunks of ice to float effortlessly across the ocean. 

The term “iceberg” actually only refers to chunks of ice that are taller than 5 meters above sea level and over 465 sq. meters in size. Smaller chunks of ice are referred to as “growlers” (less than 1 meter high) and “bergy bits” (less than 5 meters high). Imagine these like a small floating frozen sedan and cottage, respectively. From there, icebergs are classified as small, medium, large, or very large. Again, think small office buildings through Vegas-sized hotel complexes. Additionally, icebergs are classified by their shape. Tabular icebergs have a flat top and very steep sides. Non-tabular icebergs are everything else, formed into irregular shapes like pinnacles, domes, and wedges. Most icebergs appear white or at times a slight blue to green color. This is due to the numerous amounts of tiny air bubbles frozen throughout the ice. These air bubbles prevent sunlight from penetrating very far into the iceberg, scattering the sunlight of all wavelengths… giving off the appearance that they are white!

Icebergs Shapes: (top left) tabular, domed, pinnacled, (bottom left) blocky, drydock, wedge. More information and source

Entering the ocean is the beginning of the end of the life of these mountains of ice. Glaciers are formed by thousands of years of snow building up and compressing into very dense ice. The enormous mass of these glaciers causes them to slowly move seaward, sometimes at a rate of 20 meters a day! The ends of these glaciers then break off into the ocean. Once an iceberg is calved, they have seen nearly 3,000 years pass. Icebergs then begin to move along ocean currents, due to the fact that 90% of their mass is now underwater. Only a small fraction of icebergs ever find their way into shipping lanes or reach shores again, at least in their iceberg form! The ocean currents are able to access a greater surface area of the iceberg, than the wind above, and the iceberg is simply along for the ride. Along this journey, icebergs slowly break apart and can smash into shores or even get caught in shallow waters. Eventually, icebergs hit warmer waters and they are no match for the new climate; most icebergs will fully destruct within 1 – 3 years of their initial calving into the ocean. 

As they melt, water can pool and form wide cracks across the icebergs. Source: Creative Commons

In addition to climate change, icebergs are studied and tracked for a wide variety of reasons. Oceanographers are interested in how the melting freshwater impacts ocean currents and circulation. Biologists study how icebergs impact the ecosystems of the ocean and the surrounding land. Icebergs can also pose a great danger to ships traveling through major shipping lanes. It was actually the sinking of the Titanic that prompted the creation of the International Ice Patrol in 1914, to track icebergs and help protect ships in the North Atlantic. In 1995, the U.S. National Ice Center was formed to monitor icebergs worldwide and help produce forecasts and analyses of future ice conditions.

While icebergs are commonly used as the metaphor for not knowing “what’s hidden beneath the surface,” we really know quite a lot about the science beneath that surface. Maybe the next time you want to chill your beverage, don’t reach for the ice cubes, go for the tiny “growlers” instead!

National Snow and Ice Data Center – Quick Facts on Icebergs

The Ohio State University – All About Icebergs

International Ice Patrol – Icebergs and Sea Ice

International Ice Patrol – Iceberg Formation

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