There are two options for you:
- Using Advanced Editing
- Using Buffers and Geometric Differences
ArcGIS in 10.3+ can align features to each other. Specifically in your case the
Align To Shape tool found in the Advanced Editing Toolbar. As I've not got access to 10.3 at the moment I can't test this any further or determine it's suitability for automation.
Using Buffers and Differences
- Buffer each land polygon by a factor of x
X needs to be large enough to cover any gaps between the current land and ocean polygon. I also can't remember off the top of my head whether ArcGIS passes the attributes to the buffered layer or not - if not you may have to add a joining step here.
- Select all bordering polygons of the land polygon by their touching, overlapping and intersecting nature
This should give you all bordering land and sea polygons.
- Run a tool such as
Arc Toolbox -> Analysis tools -> Overlay -> Erase to Erase any part of the land polygon that is overlapped by its surrounding parts
Chances are you would fare well to create a temporary merged layer of the surrounding selected polygons to use for the Erase operation. Erase is also known as Difference in some other GIS'.
Automation for a global dataset
There are multiple ways you could automate this process, though the quickest I could think of in ArcGIS is to use the Model Builder and use the builtin looping function. No need to create a new output for the enhanced land polygons either, unless you want to keep the input data, as the operation effectively changes the shape but leaves everything else as is.