It’s always been mind-boggling to me how some of the largest and heaviest things we build on Earth are ships that float on water. Cruise ships are like floating towns, some able to accommodate over 5,000 people. How can it be that these gigantic, impossibly heavy objects made of steel can float on water? The key is displacement and realising the considerable weight that the water already supports.

In a lake or ocean, each drop of water is supported by the water around it. 1m³ of fresh water weighs 1 metric tonne, which is 1,000 kg. If a ship displaces 1m³ of water, the buoyant force of the surrounding water supports 1 tonne of the ship’s weight. Therefore, a ship weighing 50,000 tonnes will just float if it displaces 50,000m³ of water.

Sea water contains salt, which makes it denser than freshwater. As the denser water supports a greater weight, a ship will float slightly higher in salt water than in fresh. The International Load Line, previously called the Plimsoll line, shows how deep a boat sits in the water.

To realise the immense power of water, you can try submerging a biscuit tin in a bath. It’ll put up quite a fight.

Buoyancy

Point Nemo is the furthest point in the ocean from any land.

Imagine falling overboard and needing to swim to the nearest shore; the longest possible swim would start at Point Nemo. This puzzle, known as the Longest Swim Problem, finds its solution far into the Pacific Ocean at Point Nemo.

The furthest point from land is a point with a maximum equal distance to three points of land. If you moved in any direction from there, you'd be closer to one of the points. The three nearest landmasses to Point Nemo, each about 2,688 km away, are:

Moto Nui, a small islet off the coast of the well-known Rapa Nui (Easter Island)

Maher Island, off the coast of Antarctica

If you’ve ever been somewhere with only the sea in all directions, imagine what it would feel like to begin a 2,688 km swim from there.

The antipode to Point Nemo, the point directly opposite it on Earth's surface, lies somewhere in Kazakhstan.

Croatian survey engineer Hrvoje Lukatela identified and named Point Nemo after Captain Nemo from Jules Verne's classic "Twenty Thousand Leagues Under the Sea." Lukatela faced challenges in determining its exact coordinates, such as choosing the edge of Ducie Atoll's tidal sandbar and Maher Island being beneath ice for most of the year.

Being so remote, space agencies use the area around Point Nemo as a spacecraft cemetery, sending old satellites and space debris to fall there. Likely, the closest people to Point Nemo are often those in the International Space Station passing overhead a mere 400km above.

Point Nemo is also known as the Oceanic Pole of Inaccessibility. In contrast, the continental point of inaccessibility—the point on land furthest from the ocean—is in northwestern China near Kazakhstan, a remarkable 2,645 km from the nearest shore.

Point Nemo has a lovely spread in Simon Kuestenmacher's book Marvellous Maps. Writing about Point Nemo makes me want to rewatch Life of Pi (and listen to the captivating music).

Point Nemo

Mangroves are many species of tree adapted to living in salty water along coastlines and tidal rivers not far from the equator. They are remarkable in many ways and confer a host of benefits to their habitats. Here are some significant ones.

Mangroves and mangrove habitats play a major role in protecting coastal settlements from storm surges and waves. Mangroves significantly reduce the energy of waves, lowering wave height inland, including from tsunamis, and reduce surges from tropical storms. We took a boat through the mangroves in Southern Vietnam once, and it was an eye-opening maze of channels and islands. I could see how they act like a natural breakwater.

Mangroves help stabilise land from erosion. This helps plants and fauna inland make their homes. Mangrove root systems also trap sediment brought downriver or from the sea, building their environment and creating peaty soil when they decay.

Their incredible prop root network creates a wonderful sheltered space for marine wildlife to grow and develop. The nooks and crannies help protect young from predators until they are older and can better fend for themselves. This protective environment increases populations and helps local fishers and communities. The calm and sheltered waters inside mangrove habitats also provide sanctuary for birds and a host of other non-marine wildlife.

Mangroves are an excellent carbon sink. They capture carbon as they grow, and the low-oxygen sediments deposited beneath them help lock carbon away.

I've contributed to plant trees through Eden Projects with a portion of any monthly or one-off support I receive. I wanted to explain Mangroves partly because, as of July 2023, together, we've passed 26,000 trees planted, most in mangrove restoration projects in Madagascar, and provided over 350 work days for locals.

"Madagascar is one of the world's top biodiversity conservation priorities because of its endemic species and severe habitat loss rates. Restoration in Madagascar is important because the destruction of the mangrove estuaries along the coastline has caused mudflats to wash into the ocean, destroying once-productive fisheries and increasing the vulnerability of coastal communities to hurricanes, tsunamis, and floods. In the dry deciduous forests, deforestation threatens one of the world's rarest and most diverse forest systems."

Mangroves make a real difference. To everyone who's helped make this happen, thank you!

Mangroves

The strand line is the often lovely line of interesting seaweed, driftwood and things to find left behind by the waves at the top of high tide. Hopefully, with not too much plastic.

Strand line

There are just two countries that are double-landlocked: Liechtenstein and Uzbekistan. Their unusual claim to fame is that not only are they landlocked with no access to the high seas themselves, but they are also surrounded by countries that are themselves landlocked.

Another way to put it is that you have to cross two national boundaries before you can reach water connected to the oceans.

Growing up on the island of Great Britain I somewhat took for granted that with a few hours in most directions and I’d be looking out onto the sea. But that’s not at all the case if you were born in a landlocked country.

Double-landlocked countries

If you were to dig straight down from where you’re standing and pass straight through the centre of the Earth and keep on digging — you’d now be tunnelling up I guess — where you come out would be your antipode. Though most of them would first have you springing a leak at the bottom of the ocean, so be careful.

Antipodes

Moon pools are protected entrances to water that can even give the remarkable ability to enter from under the water.

First created to support drilling operations on offshore platforms, moon pools can include entrances on the decks or undersides of ships or an entry and exit for divers from permanent underwater research bases.

For underwater entrances, also known as wet porches, the trick is to pressurize the air around the pool to the same pressure as the surrounding water. The raised pressure keeps the water from gushing in and enables a swimming pool-like entrance even though you’re already below the surface.

I've never used one, but I'd absolutely love to. One of my earliest memories of a moon pool and corresponding bafflement and wonder was in James Cameron's 1989 film The Abyss. A moon pool features in the recent trailer for the remastered version of The Abyss

Moon pool

Not the easiest switch to make but given that jellyfish and starfish are not at all fish there is a move to call them sea jelly and sea star. As long as we all work to help protect them clearly it doesn’t matter a whole lot, but I think the move to sea jellies and sea stars makes good sense alongside others like the sea horse, sea cucumber, sea lion, sea lily, sea gooseberry…well, actually the sea horse is a type of fish, but you get the idea.

Sea jelly, sea star

Ghost fishing is when lost or abandoned fishing gear continues to catch fish. And those who are caught attract larger predators who can also get caught.

Also see Bycatch—other stuff you caught while trying to catch something else.

And quite different from ghost cooking—the art of cooking leaving a sparkling, untouched kitchen.

Nurse shark drawn using How to draw a grey nurse shark.

Ghost fishing

The International Load Line, formerly called the Plimsoll Line, is an internationally adopted system for ensuring ships aren’t overloaded. Safe loading levels vary depending on the salinity—how salty it is—and the temperature of the water.

Oceans sketches