I have too many abstract ideas for work I could make, but no concrete imagery to work from

This is where researching other artists' work could help - see how they represent what you are finding unrepresentable. Perhaps if they are attempting to depict the sublime, they refer to vast wildernesses, like Caspar David Friedrich, or outer space, like Katie Paterson. Remember that you do not necessarily have to produce 2D imagery. It could be that a film, performance or sculpture would be a better expression of what you are trying to say.
Sometimes it is easier to create complex meaning for imagery by making the work first and thinking analytically about it later. Produce a series of studies using different techniques, experimenting with materials, and try not to think too hard about the subject matter. This often sparks ideas for visually interesting work that can express nuanced emotions without you consciously thinking about it. Take advantage of what is around you - if it's snowing, take photographs in the snow or use it to make a sculpture. It may melt in an interesting way. Artists are opportunists. Chance or risk in making an artwork often makes it more appealing.