The sight of an iceberg, a colossal mass of ice adrift in the ocean, often sparks curiosity about their sheer number. These remnants of glaciers and ice shelves are captivating features of the polar seas, yet their transient nature makes providing a precise global count a complex endeavor. Icebergs are constantly formed, move across oceans, and eventually melt away, making their observation challenging.
What Qualifies as an Iceberg
An iceberg is a piece of freshwater ice that has broken off from a glacier or an ice shelf and floats freely in open water. To be classified as an iceberg, the ice mass must be more than 15 meters (16 yards) long, or its height must exceed 16 feet above sea level, with a thickness of 98-164 feet and an area of at least 5,382 square feet. Smaller pieces of floating glacier ice are known as “bergy bits” or “growlers.” Bergy bits are 3 to 16 feet above sea level and 1,076-3,229 square feet in area, while growlers are smaller than 3 feet above the surface and about 215 square feet.
Icebergs vary in shape and are broadly categorized as tabular or non-tabular. Tabular icebergs have steep sides and a flat top, resembling a plateau, with their length-to-height ratio exceeding 5:1. These are common in Antarctica, forming from vast ice shelves. Non-tabular icebergs include various other forms:
Dome-shaped (rounded top)
Pinnacled (one or more spires)
Wedge-shaped (steep edge on one side, slope on the other)
Dry-dock (a channel or slot eroded through it)
Blocky (steep, vertical sides and a flat top but proportionally taller than tabular ones)
The Intricacy of Counting Icebergs
Obtaining an exact count of icebergs presents significant challenges. Polar regions, where most icebergs originate and drift, are vast, remote, and often inaccessible, making comprehensive observation difficult. Icebergs are dynamic; they continually form through calving from glaciers or ice shelves. Once calved, they are subject to constant melting, breaking apart into smaller fragments, and moving due to ocean currents and winds.
The variation in size further complicates counting methods, ranging from massive ice islands hundreds of kilometers long to small growlers. About 90% of an iceberg’s mass remains submerged, making visual assessment of their full size and potential hazards challenging. Harsh weather conditions, such as frequent fog, storms, and extended darkness, also hinder observation efforts. These factors mean any “count” is always an estimate.
Strategies for Tracking Icebergs
Despite the challenges, scientists and organizations employ various methods to track and estimate iceberg populations. Satellite imagery plays a primary role, with instruments like Synthetic Aperture Radar (SAR) being particularly effective. SAR can detect icebergs day and night, regardless of cloud cover, by transmitting microwave signals and measuring their reflections. Optical and infrared sensors on satellites also contribute, though optical methods are limited by cloud cover and light conditions. Radar altimeters and scatterometers provide additional data, with altimeters measuring changes in sea level that indicate an iceberg’s presence and scatterometers detecting surface differences.
Aerial surveys provide more detailed, localized observations. These surveys offer higher resolution data than satellites for specific areas but are limited by range and susceptible to weather conditions. Unmanned Aerial Vehicles (UAVs) are increasingly used for detailed surveys and for deploying GPS tracking tags directly onto icebergs, providing precise positional data. Ship-based observations also contribute valuable data, with vessels recording iceberg sightings and providing detailed in-situ information, although their coverage is sporadic and limited to shipping routes.
Global Estimates and Influencing Dynamics
Providing a single, precise number for the world’s icebergs is not feasible due to their dynamic nature and observation challenges. However, estimates suggest hundreds of thousands to millions of icebergs and ice fragments exist in the polar oceans at any given time, with the vast majority being smaller bergy bits or growlers. For instance, approximately 40,000 medium to large icebergs calve from Greenland glaciers annually, though only a fraction reach shipping lanes further south. In the Southern Ocean, an average of around 132,269 icebergs were estimated to be present between 1997 and 2014 based on ship observations.
The number and distribution of icebergs are in constant flux, influenced by several dynamic factors. Glacial calving rates are a primary driver of iceberg production. These rates can be affected by changes in ocean temperature and interactions with the ocean, which may lead to increased calving events. Ocean currents play a significant role in transporting icebergs, sometimes over thousands of miles, while seasonal melting cycles and wave action cause them to deteriorate and break into smaller pieces. While large calving events are episodic, more frequent, smaller calving events contribute substantially to overall ice loss.