Where two oceans meet, debunked

Cape Reinga, at the very northern tip of New Zealand's North Island, is one of the few places in the world where you can watch two oceans collide. So say the guidebooks, anyway. The truth is a little more complicated. First of all, you can find photos online like this. I took that from a kayak in Svalbard, up in the Arctic, two very different-coloured waters separated by a bit of foam. People online claim that photos like it show one of the few places in the world where two oceans meet but don't mix. But no, that's just where a river is washing fresh water filled with sediment out into the sea. The truth of where two oceans meet is just not that dramatic. Here, at least, you can see the waves from the Tasman Sea coming in from the west and clashing with the Pacific Ocean waves from the east. Right? No. Ocean currents and waves have many causes. The weather, our water temperature, water salinity, how much salt is in there. And they're three-dimensional. Now, with all the complicated geography and wind here at the very tip of the country, of course it's chaotic down there, it's turbulent. Of course you have different sets of waves meeting. But those are local effects. As soon as you get away from land, the water here will become part of the massive system that's defined by global weather and ocean currents. And those ocean currents are measured in Sverdrup. One Sverdrup is a million cubic metres of water moving at a metre per second, and the largest currents measure more than a hundred Sverdrup. Those are amounts that make no sense on any human scale. While there are often currents here that might contribute to that particular weird wave pattern, this is just one very, very small bit of the ocean with waves that look messy on a human scale because of the land nearby. And despite what the guidebooks say, this isn't even where the Tasman Sea ends and the Pacific begins. Not according to the maps. The official limits of oceans and seas are defined by the International Hydrographic Organization. And those standards are arbitrary lines designed to make sure that everyone can agree on what's where, so that weather warnings and marine charts describe the same areas no matter who's producing them. And those lines are nothing to do with the position of any ocean currents. And according to those standards, the Tasman Sea meets the Pacific at North Cape, a closed nature reserve about two kilometres that way. This is just a windy bit of rock with a lighthouse and a road. That doesn't mean you shouldn't come here, though. Cape Ranga is beautiful. It's part of the local mythology, and it's worth the trip. But when they say it's where two oceans collide, that just isn't quite true.