Well "DC" was the term used under the assumption that it is an amplitude y-axis (DC = Direct Courant). It may not be the correct term to use if the y-axis is in ms but as you say let's just call that "dc".
Yes you can remove the "dc" by subtracting the mean value but by doing this you "define" your dc to be the mean value. What I meant with the other component was, that if you look at your time signal, it looks like a DC of approx. 1000 overlayed with a 50% to 75% of a single period of a signal of amplitude approx. 10 and then something that more or less looks like noise. So I was wondering what signal you were actually chasing? What is the end goal of your measurement? How does an "ideal" signal or result look like? What information do you expect to extract from the power spectrum? etc...
