The mystery of the meeting of the seas

Today, let’s talk about the subtropics! Or more precisely, one particular point of the subtropics where I was lucky enough to be recently: Cape Reinga.

Cape Reinga, yellow arrow in the very north of New Zealand (after Ezilon.com)

Cape Reinga, yellow arrow in the very north of New Zealand (after Ezilon.com)

When you are in Cape Reinga, you are at the very north of New Zealand’s North Island, at approximately 34.4°S. Actually, there is one point to the east that is slightly more in the north, but Cape Reinga is more beautiful and more symbolic. According to the Maori, you are standing on the edge of the underworld; the spirits of the dead travel all the way north to jump off this cape into the ocean.
“The” ocean? Not exactly.

I was particularly excited to go to this place, for there you can see the meeting of the seas: the Tasman Sea on the left, the Pacific Ocean on the right, and plenty of eddies in the middle.

IMG_5848

And as an oceanographer, I am puzzled by these eddies. I emailed the only New Zealand oceanographer I know, who actually works on Antarctic sea ice and had no idea what I was talking about. So I checked the scientific literature, but found hardly anything, and nothing satisfactory. So dear reader, I need your help. Here are the hypotheses:
– strong tidal currents. In that case, why aren’t both water bodies moving in the same direction? Is the sea floor / geometry of the coast line very different on each side of the cape?
– different water masses. Salinity and temperature look the same to me on both sides of the cape (on the WOCE Atlas).- upwelling (wind-induced). We would see a divergence of the water, right? But to me it looked like it was converging at this particular spot.

Anyway, if you know about it, or know someone who could answer all these vital questions, feel free to contact me!

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