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Ady42 t1_is2ok2a wrote

Research ships deploy instruments called [CTDs](https://en.m.wikipedia.org/wiki/CTD_(instrument)) that collect seawater. There are sensors on the CTD that measure the salinity of the seawater (along with other things of interest). The collected seawater is also measure to calibrate the sensors on the CTD.

There are also [ARGO floats](https://en.m.wikipedia.org/wiki/Argo_(oceanography)) that move around the ocean taking regular measurements of the seawater for things such as the salinity.

At a glance the seawater around Hawaii looks a bit saltier than in some other places, but not the saltiest there is.

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regular_modern_girl t1_is42e64 wrote

They might have meant “saltiest seawater in the world”, but yeah, there are endorrheic lakes or pools that are magnitudes more saline than any part of the ocean.

The average salinity of the ocean is about 3.5% iirc, the southern portion of the Great Salt Lake is about 5%, while the northern portion is as much as 20% (they’ve been separated by a railroad causeway since the 1950s, hence the drastic difference in water chemistry), the Dead Sea is about 30%, Lake Assal in Djibouti is 35%, and Don Juan Pond in Antarctica (the most saline known body of water on Earth, unless you count the concentrated brine pools that sometimes form deep in the ocean) has been measured at over 40% iirc.

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