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The question is quite simple, does there exist a meridian on Earth that only passes over water, with the exception of continental Antarctica of course.

From eyeballing a world map it seems somewhere around 168 °W (192 °E) is the most likely candidate but it might pass through Umnak island.

Is there a sea-only meridian?

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Is there a meridian that only passes through water (excl. continental Antarctica)?

No.

Note: All longitude spans in this answer are from easternmost point to westernmost point.

The mainland of Africa+Eurasia blocks everything from 169°39'07" W (Cape Deznhev in Russia) to 17°32'08" W (Dakar, Senegal). The mainland of the Americas blocks everything from 34°47'35" W (Santa Rita, Paraíba, Brazil) to 168°07'12" W (Cape Prince of Wales, Alaska, U.S.). All that is left are two gaps, one in the Atlantic Ocean between 17°32'08" W and 34°47'35" W, and another in the Bering Strait between 168°07'12" W and 169°39'07" W.

This does not yet account for islands. Three islands suffice to close those gaps. Greenland, which spans from 11°21'36" W to 73°47'35" W, closes the gap in the Atlantic, while Umnak (which spans from 167°47'00" W to 169°07'08" W) and St. Lawrence Island (which spans from 168°41'17" W to 171°51'00" W) together cover in the gap in the Pacific. Note that the westernmost point of Unmak is to the west of the easternmost point of St. Lawrence Island, so there is no gap between these two islands.

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The answer is no.

In the Atlantic Ocean any meridian that would avoid South America and Africa would pass over Greenland.

In the Pacific Ocean, St Lawrence Island, just to the south of the Bering Strait is a major obstacle. This forces any likely meridian to be to the east of the island - as you state around 168° W (192° E). The easternmost point of St Lawrence Island is at 168° 41' 17" W.

To the north of St Lawrence Island is a tiny spec of an island called King Island. It's westernmost point is 168° 05' 53" W. That's a difference of 35' 24" in longitude. Which isn't much room.

As you indicate, that zone lies in in the central region of the Aleutian island of Umnak Island, which extends from 169° 06' 48" W to 167° 47' 07" W.

Johnson Atoll, at around 169° W is close to that that Meridian zone, as is Niue. South of Umnak Island, within that meridian zone there is no land above sea level, but there are geological features such a sea mounts, particularly the line of mounts between Hawaii and Midway Atoll.

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    $\begingroup$ Re This forces any likely meridian to be to the west of the island -- I believe you meant that this forces any likely meridian to be to the east of the island. $\endgroup$ Jan 30 at 10:13
  • $\begingroup$ @DavidHammen: Thank you for the correction. $\endgroup$
    – Fred
    Jan 30 at 11:39

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