Icebergs still drift through the Atlantic Ocean every year, and in surprisingly large numbers. Hundreds of them travel far enough south each season to cross major shipping lanes near Newfoundland, and giant tabular bergs from Antarctica occasionally wander into the South Atlantic as well. The phenomenon is not a relic of the Titanic era; it is an ongoing feature of Atlantic oceanography, monitored continuously by a dedicated patrol force. In some respects, climate change is making the situation more dynamic rather than less.
Where Atlantic Icebergs Come From
The overwhelming majority of icebergs in the North Atlantic originate from Greenland’s marine-terminating glaciers. These are glaciers whose fronts extend into the sea, and when chunks of ice break away from them, the process is called calving. Together, calving and underwater melting at these glacier fronts account for between a third and half of the mass that the Greenland Ice Sheet dumps into the ocean each year.1PubMed Central. Glacier Calving in Greenland That is an enormous amount of ice entering the water annually, and it ensures a steady supply of new icebergs.
The western coast of Greenland is the most prolific source. Glaciers there calve icebergs into Baffin Bay, the large body of water between Greenland and Canada’s Baffin Island. From there, ocean currents carry many of those bergs southward. Some eastern Greenland glaciers also produce icebergs that eventually make it into Atlantic shipping lanes, but the western route through Baffin Bay is the main pipeline. The South Atlantic gets its icebergs from a completely different source: the Antarctic ice sheet and its surrounding ice shelves, which occasionally release enormous tabular bergs that can drift thousands of kilometers north.
The Route South
Once an iceberg calves from a western Greenland glacier, it enters a well-studied conveyor system. Baffin Bay has a cyclonic (counterclockwise) circulation pattern, and icebergs commonly follow this current loop. Many drift westward across the bay, then turn south along the Canadian coast, carried by the Labrador Current.2Journal of Geophysical Research: Oceans. Sea Ice‐Driven Iceberg Drift in Baffin Bay This cold current acts like a highway, pushing bergs southward along the coasts of Labrador and Newfoundland.
The icebergs that make it far enough south eventually reach the Grand Banks, the shallow continental shelf southeast of Newfoundland. This is where things get dangerous, because the Grand Banks sit at the intersection of multiple busy transatlantic shipping routes. An iceberg that reaches this area is entering some of the most heavily trafficked waters in the world. Sea ice in Baffin Bay also plays a role in the journey: icebergs can become trapped in pack ice during winter and then released as it breaks up in spring, which helps explain the seasonal timing of when they arrive in shipping lanes.
Iceberg Season in the North Atlantic
While icebergs can theoretically appear in the Northwest Atlantic at any time of year, the main season runs from March through July. Data collected over decades shows that this five-month window is when the vast majority of icebergs cross south of 48°N latitude, the benchmark used by monitoring agencies.3Offshore Technology Conference. Prediction ot the Severity of Iceberg Season in Northwest Atlantic Ocean The peak typically falls in April and May, when the spring breakup of sea ice releases bergs that have been locked in place over winter and the Labrador Current is at its most active.
The intensity of each season varies wildly. Some years see fewer than a dozen icebergs crossing 48°N; others see well over a thousand. This variability depends on how much ice Greenland’s glaciers calved in prior years, how winter sea-ice conditions in Baffin Bay affected iceberg transport, and how warm the ocean currents are that season. A warm year can melt bergs before they ever reach shipping lanes, while a cold year with strong southward currents can push an unusually large crop into dangerous waters. Predicting the severity of any given season remains a challenge, though forecasting models have improved considerably.
The International Ice Patrol
The sinking of the Titanic in 1912 prompted one of the earliest international efforts at maritime safety cooperation. In the aftermath, the International Ice Patrol was established to systematically monitor North Atlantic icebergs. The United States Coast Guard has operated the patrol continuously, tracking icebergs and broadcasting their positions to all ships in the area.4Polar Record. The Scientific Work of the International Ice Patrol Board
The patrol uses a combination of aerial reconnaissance, satellite imagery, radar, and oceanographic modeling to locate and track icebergs as they drift south. When a berg enters or approaches shipping lanes, the patrol issues warnings and establishes recommended routes for vessels to avoid. The system has been remarkably effective: since the Ice Patrol began operations, no vessel heeding its warnings has been lost to an iceberg collision. The patrol is funded by the nations whose ships use the transatlantic routes, making it a genuinely international safety effort that has been running for over a century.
Modern tracking technology has made the patrol more sophisticated. Satellite-based synthetic aperture radar can detect icebergs even through clouds and fog, and GPS-equipped buoys are sometimes placed directly on large bergs to monitor their drift in real time. Despite all this technology, smaller icebergs and “growlers” (bergs barely protruding above the waterline) remain difficult to spot, especially in rough seas. These smaller pieces are often the most dangerous to ships because they sit low in the water and may not register clearly on radar.
How Icebergs Deteriorate at Sea
An iceberg that calves off Greenland may survive for months or even years before it fully melts, depending on its size and the conditions it encounters. Several processes work together to whittle it down. Wave erosion at the waterline is one of the most important: ocean waves cut a notch into the ice right at the surface, undermining the structure above. This waterline melting accounts for a substantial portion of total mass loss and drives fragmentation, because once the base is undercut, large pieces can break away.5Journal of Geophysical Research: Oceans. Buoyancy Feedbacks on Wave‐Induced Melting of Icebergs Wave erosion of ice cliffs is recognized as one of the main mechanisms for waterline ablation of both icebergs and glacier fronts.6Journal of Fluid Mechanics. Wave erosion of ice cliffs: melt rate due to reflection of non-breaking surface waves
Below the waterline, warmer ocean water melts the submerged portion of the berg, which typically represents about 80 to 90 percent of the total mass. Solar heating of the surface also plays a role, especially as a berg drifts into warmer waters. When enough ice melts unevenly, the iceberg’s center of gravity shifts, and the whole thing can roll or capsize dramatically. This is one reason ships are warned to keep a wide distance even from bergs that appear stable. The combination of wave erosion, underwater melting, and fragmentation means that an iceberg is constantly evolving as it drifts, changing shape and losing mass in unpredictable bursts.
Climate Change and Iceberg Production
A natural question is whether warming temperatures mean fewer or more icebergs. The answer, at least for now, is more complicated than “warming equals less ice in the ocean.” Greenland’s ice losses have been increasing, driven largely by glacier acceleration and retreat in response to increased heat reaching the glaciers from the oceans.1PubMed Central. Glacier Calving in Greenland Warmer ocean water eats away at glacier fronts from below, destabilizing them and causing more calving. In this sense, climate change may be increasing the rate at which new icebergs are produced, at least from certain glaciers and in certain periods.
But there is a counterbalancing effect. Warmer ocean temperatures also mean that icebergs melt faster once they are afloat. A berg that would have survived the journey to the Grand Banks in a cooler climate might now melt before it gets there. So while Greenland may be producing more icebergs overall, the number that actually reach shipping lanes in any given year depends on the tug-of-war between increased calving and increased melting en route. Over very long timescales, if Greenland’s marine-terminating glaciers retreat far enough inland that they no longer reach the sea, calving will decrease dramatically. But that transition is likely decades or centuries away for many of the major outlet glaciers. For the foreseeable future, icebergs in the Atlantic are not going away.
What Giant Icebergs Do to the Ocean Around Them
Icebergs are not just obstacles to navigation. They actively alter the ocean environment they pass through. As they melt, they release cold, fresh water into the surrounding sea, changing both temperature and salinity. When a giant Antarctic iceberg called A68A drifted through the Scotia Sea in the South Atlantic, satellite data showed that its gradual edge-wasting contributed to a freshening of the surface ocean extending hundreds of kilometers ahead of the berg, while a cooling effect was more pronounced in its wake.7Geophysical Research Letters. Impact of Giant Iceberg A68A on the Physical Conditions of the Surface South Atlantic, Derived Using Remote Sensing That single iceberg was large enough to measurably change the physical properties of a vast stretch of ocean.
Icebergs also carry nutrients. As glaciers grind over bedrock, they pick up sediment containing iron, manganese, and other minerals. When the resulting icebergs melt at sea, those nutrients are released into the water. This fertilizing effect can be significant in nutrient-poor regions. In the Southern Ocean especially, where low availability of iron and manganese limits the growth of phytoplankton, icebergs have been described as floating fertilizer dispensers and biological hotspots.8The Cryosphere. The macronutrient and micronutrient (iron and manganese) content of icebergs The sediment trapped inside the ice can contain high concentrations of iron and manganese that get released directly into the ocean with little processing, fueling plankton blooms that draw down carbon dioxide from the atmosphere.9Eos. Icebergs Fertilize Southern Ocean, Sequester Carbon
In the North Atlantic, the nutrient effect of icebergs is less studied but still relevant. The freshwater they release can influence local ocean stratification, affecting how surface water mixes with deeper, nutrient-rich layers. Icebergs also serve as physical platforms for seabirds and seals, which rest on them and in turn deposit nutrients of their own. The ecological footprint of a single large iceberg can extend well beyond the immediate area of the ice itself.
Icebergs and the Offshore Industry
For offshore oil and gas operations in iceberg-prone waters, particularly off the coast of Newfoundland and in the Arctic, icebergs represent an operational hazard that has to be actively managed. The standard approach is not to shut down and evacuate every time a berg appears on the horizon. Instead, operators use tugboats to tow icebergs out of the path of drilling rigs and production platforms. This towing practice has minimized ice-related downtime and contributed to safety in harsh environments.10SNAME 7th International Conference and Exhibition on Performance of Ships and Structures in Ice. Statistical Analysis of the Optimum Amount of Bollard Pull Required for Towing an Iceberg
Towing an iceberg is exactly as difficult as it sounds. The amount of force required depends on the berg’s mass, shape, and how much of it sits below the surface. Engineers calculate the necessary “bollard pull,” which is the pulling force a tug can exert, and assign vessels accordingly. Smaller bergs can be redirected with a single tug and a heavy line. Larger ones may require multiple tugs working in coordination, or a technique where a long net or cable is looped around the berg and pulled from both sides. When a berg is simply too large to move, the platform may need to disconnect and drift off its drilling location temporarily, then return once the threat has passed.
Beyond oil operations, there is a small but real commercial market for iceberg ice. Entrepreneurs in Newfoundland and Labrador harvest chunks of icebergs to produce bottled water, vodka, and beer, marketing the ice as tens of thousands of years old and exceptionally pure. The harvesting process involves spotting suitable growlers from boats, hauling pieces aboard with nets or grappling equipment, and melting the ice under controlled conditions. It is a niche industry, but it underscores how routinely icebergs appear close enough to shore to be commercially accessible.
Ancient Evidence on the Seafloor
Today’s icebergs in the Atlantic are part of a pattern that stretches back hundreds of thousands of years. The geological record shows that during past periods of rapid climate change associated with ice-sheet oscillations, pulses of iceberg discharge sent bergs much farther south than they travel today. Evidence for this comes from iceberg scour marks found on continental shelves, including along the southern United States Atlantic margin, far south of where modern icebergs reach.11Geology. Iceberg scours along the southern U.S. Atlantic margin These scours are grooves carved into the seabed by the keels of deep-drafting icebergs as they were dragged along by currents.
Ice-rafted debris, sediment dropped to the ocean floor as melting icebergs released their embedded rocks and dirt, is found across wide swaths of the North Atlantic basin. Layers of this debris in sediment cores correspond to known cold events like Heinrich events, when massive fleets of icebergs surged out of the Arctic and sub-Arctic. The picture these records paint is of an Atlantic Ocean that has periodically been far more crowded with icebergs than it is today. Current conditions, while active enough to keep the Ice Patrol busy every spring, represent a relatively modest iceberg regime by the standards of Earth’s recent geological past.
Icebergs You Cannot See from a Ship
One of the persistent misconceptions about icebergs is that they are all towering white mountains visible from miles away. Some are, particularly freshly calved bergs from major glaciers. But many of the bergs that reach the Grand Banks have already been at sea for a year or more. They have been eroded, rolled, and fragmented. What remains may be a low, flat slab of ice barely rising above the wave tops, called a “bergy bit” if it is roughly the size of a small house, or a “growler” if it is even smaller.
Growlers are a particular hazard because they can be nearly invisible in rough seas, and they are dense enough to punch through a ship’s hull. They also sit too low to reliably appear on marine radar, especially when sea clutter from waves masks the return signal. This is one reason the International Ice Patrol issues broad area warnings rather than attempting to pinpoint every piece of ice: in a region with active icebergs, there will almost certainly be smaller fragments scattered over a wide area that no survey has individually located. Captains transiting these waters during iceberg season are expected to post dedicated lookouts and reduce speed, just as they were advised to do in 1912, because the fundamental challenge of spotting small ice in open ocean has never been fully solved by technology.