Should the cardinal directions be capitalized when used as an adjective? For example,
They sailed throughout the eastern Baltic.
This is really just a style issue so opinions differ.
Here is some guidance that seems reasonable to me, taken from https://www.proofreadnow.com/blog/bid/30440/North-East-South-or-West-Capitalize-or-Not :
Capitalize such words as northern, southern, eastern,and western when they refer to the people in a region or to their political, social, or cultural activities. Do not capitalize these words when they merely indicate general location or refer to the geography or climate of the region.
- Eastern bankers, but the eastern half of Colorado. [...]
NOTE: When terms like western region and southern district are used to name organizational units within a company, capitalize them.
- The Western Region (referring to a part of the national sales staff) reports that sales are 12 percent over budget for the first six months.
When words like northern, southern, eastern, and western precede a place name, they are not ordinarily capitalized, because they merely indicate general location within a region. However, when these words are actually part of the place name, they must be capitalized.
- northern New Jersey, western Massachusetts.
- Northern Ireland, Western Australia.
NOTE: Within certain regions it is not uncommon for many who live there to capitalize the adjective because of the special importance they attach to the regional designation. Thus people who live in southern California may prefer to write Southern California.
Source: The Gregg Reference Manual