As a rule, icebergs south of New Zealand rarely get above the latitude of 55° South and the occasional ones that do tend to become celebrities and have sheep shorn on them, writes Matt Vance.

Until you see one, the idea of an iceberg can seem quite academic. Seen for the first time it will look astonishingly white. This whiteness comes from the bubbles of air trapped in the ice and will tend more towards blue if the ice has been compressed in its formation.

These bubbles are fascinating to climate scientists as they are perfect samples of the atmosphere from times past. The Antarctic ice sheet, where these icebergs are formed, is up to 4km thick in places and this can provide examples of atmosphere back a good 200,000 years or so.

That is far enough back to record major climate events and the ill-conceived sins of civilization. Volcanic eruptions, nuclear tests and the rise of the coal-fired steam engine are layered in there, to name a few.

At their heart, icebergs are pieces of freshwater ice formed on land and transported to the ocean. The icebergs of the Southern Ocean come from the glaciers and ice shelves of Antarctica. Over thousands of years the ice has travelled down a valley or slope and continued out over the ocean, where at their extreme edge, they calve off into icebergs.

The Ross Ice Shelf, south of New Zealand, is the size of France and so it has prodigious ability to create bergs of colossal size. For that reason, Southern Ocean bergs are usually large and tabular, flat on top and horizontal in configuration.

They are not to be confused with sea ice or pack ice, as it is known, which is frozen saltwater. Icebergs are harder, bigger and denser than sea ice and can plough through it like it isn’t there.

To qualify as an iceberg, the freshwater ice must be at least 15m long. If it is the size of a 20ft shipping container it is considered a bergy bit and if it is the size of a six-seater dining table it is called a growler. When an around-the-world racing yacht doing 20 knots-plus disappears without a trace deep in the Southern Ocean, it will be a growler that’s the culprit.

Most of the bergs encountered in the Southern Ocean are flyweights under 2km long. Occasionally much larger bergs, the size of a province or an island, calve off the Ross Ice Shelf and require naming. Unlike hurricanes, icebergs are not given human names. Perhaps this is because they bear a certain resemblance to our own life cycle or, that by naming them, we fear becoming attached to them.

Bergs over 20km long are tracked by satellite and given a code. The berg is labelled according to the quadrant of Antarctica it broke off from. Quadrants are labelled A through D and the bergs are also given a number like B-12. If the subsequent berg breaks into smaller pieces over 20km long these are given their own label: B-12A, B-12B. It sounds like a game of Battleships but on an enormous scale.

As you slide further south in the Southern Ocean below the Antarctic convergence zone the icebergs come thick and fast. The bergs this far from the edge of Antarctica are nearing the end of their life and some may even have circumnavigated the continent.

Their age means they have been ravaged by time and the weather into all manner of tortuous shapes and sizes. Like cloud watching, berg watching lends itself to the imagination. For some, this is all esoteric nonsense, but occasionally one of the nonbelievers I sail with will sheepishly confide to me that they have seen the Virgin Mary herself somewhere near 62o South.

Each berg represents a different time in history. The air trapped in one might have been breathed by the baby Jesus; another may have had the thin ash deposit from Vesuvius stripped through it. Watching them is like stargazing in that you are seeing different periods of history all at one time. They make the idea of ‘now’ seem absurd.

Norwegian explorer, Fridtjof Nansen, who attempted to drift across the North Pole, was the first to notice that the icebergs that surrounded his ship, Fram, were drifting consistently 40o to the right of the prevailing wind direction.

It was the first evidence of the Coriolis Effect in action, which in turn, led to the beginnings of the fledgling science of Oceanography. Watching icebergs for any length of time will show up some odd behaviour. This is largely due to their deep keels, which are up to 85% of their mass. It is not uncommon to see one charging upwind like it knows where it is going, as deep, unseen currents grip its keel.

Around 2000 a truly massive iceberg calved off the Ross Ice Shelf. In the fashion of berg identification, it was named B-15 and measured 292km long by 37km wide. With each high tide, it hopped its way along the coast of Ross Island and broke in two with the effort.

This berg was not only large it was long-lived – remnants of it were still being tracked up until 2018. When an icebreaker I was on at the time approached the Ross Sea, B-15A was partly blocking the entry to McMurdo Sound, where it had wedged itself on the bottom.

At roughly 160km long it was enough to contain much of the sea ice which annually broke out of the sound. This was causing havoc with the local penguin rookeries and scientific bases, which both relied on a degree of open water over the summer months to obtain their food and supplies.

Although B-15A was roughly half the size of the original, it still took the ship the best part of 24 hours to steam along its length. While many of the sculpted bergs further north were elderly, B-15A was in the first flush of youth.

It was angular and monotonous in its geometry and full of hard-edge arrogance. It demanded attention like the tapping of a branch against the window in a gale. On each low tide, its southern end ground into the bottom, causing seismic tremors, which registered at listening stations as far north as Tonga.

Being aground and stable meant we could get in for a closer look at B-15A. As we approached the berg by Zodiac, the air temperature dropped noticeably. Bergs are much cooler than the sea and the sea ice and this gives the impression of an aura of cold around them.

The 80m or so of the berg above the waterline contained thin layers of time that glowed hospital-white with hints of antiseptic blue. B-15A, like most icebergs, had its own accompanying symphony. At the top of the scale, there was a slow tinkle of falling ice dust and the slop and gurgle of small waves licking at the waterline.

This all occurred over a background fizz, as air bubbles of ancient atmosphere were released into the dark waters below. Occasionally this gentle sonnet was punctuated by a bowel-tightening groan as something shifted deep within the huge mass.

When looking at an iceberg, it is hard to imagine they ever die; they seem immortal. But die they do. Some show a decrepit slow decline as the effects of wind and sea whittle them down into a geriatric stoop. Others go spectacularly, like a TV celebrity, with much noise and fuss.

Not far on from B-15A we encounter the remains of a berg that has disintegrated. There are bergy bits and growlers with the fresh blue hint of a urinal lozenge, some still working out their centre of gravity and writhing in pain. Among the larger bits lay a scattering of smaller pieces that form a soup around the entire scene. All is silent on board the ship.

A live iceberg is a lonely thing; a dead one is a scene of utter desolation.