Before the 1860s, how much exploration/contact was there by these East Asian cultures with the Okhotsk Sea region and the Kamchatka Peninsula? I have heard of Chinese and Japanese ventures into Sakhalin island, but what about points north?
Kamchatka itself I'm afraid I don't know too much about.
Ah, Kamchatka is referred to as the 'Ghost Country' (Liuguiguo 流鬼國) in Tang records, and there was trade between China and Kamchatka in this period. I'm afraid I don't know if any specific Chinese people actually ended up going there. Sailors and merchants maybe, but that would just be an inference. It's possible the Tang sent an embassy there, but dynastic records don't typically list these things.
I believe Koreans in the 17th century at least were aware of there being open sea beyond Hokkaido, but not sure if they knew any details beyond that. I wouldn't be surprised at all if Korean sailors went up into that area on occasion. They certainly had the technology and capacity to.
There's actually an interesting account of some sailors that were caught in a storm and ended up in that area, eventually getting home by way of Hokkaido.
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If you do come across anything, I'd be interested to hear it. As you said, I've heard that Korea in the early-modern period was a fairly competent naval state. I just don't know how inclined they were to send their sailors in a northward direction...
I wonder if they left any record of the things they saw. That would be interesting.
The they would have gone up there intentionally for fishing, whaling, or small-scale trading with the locals, but again I don't know of it being mentioned in an official capacity so anything that did happen would be informal exclusively by individuals.
They actually did. A learned man was among them and wrote about the trip. Here's a translation from 1924: http://www.raskb.com/transactions/VOL15/KORS0749D_VOL15.pdf
Interesting, the Tang is earlier than I expected. I wonder if perhaps there are Chinese maps or other forms of records which could give us some indication of how well the Chinese knew the region...