I have heard that ocean tides in spring (vernal equinox) in the northern hemisphere are the some of the largest of the year. Is this true and, if so, is there an explanation?
You might be misunderstanding the rather confusing term "spring tide", which I'll explain in the next 2 paragraphs. If not, bear with me and I'll give an alternate explanation in a moment.
Tides are caused by the gravitational pull of the Moon and Sun on the earth and its oceans. The change in the strength of this pull with distance from the moon (or sun) tends to raise sea level on the side of the Earth facing the moon (or sun); a similar bulge is created on the side opposite the moon (or sun). A previous Madsci response explains why the bulge on the backside is formed. Read the moderator's note at the end!
The sun and moon each raise tidal bulges on the Earth's oceans. When the sun and moon are on the same side of the Earth (new moon) or the opposite side (full moon), their bulges add together to make larger tides than usual: this is called a "spring tide". When the sun and moon are 90 degrees apart (first quarter or last quarter moon), the bulges interfere and cancel each other: this creates the unusually small "neap tide". The word "spring tide" is confusing: I don't think it has anything to do with the season we call spring. It refers to the large tides created when the sun, moon, and Earth come into alignment (about twice each month).
It's possible your question didn't arise from this confusing terminology, and that tides in the spring season really are larger. This could occur because the sun and moon are able to align more precisely during the equinox: I seem to recall the axis of the moon's orbit has the same tilt direction as the Earth's rotational axis, so perfect alignment is more common during equinoxes. However, autumn tides should be exactly the same as springtime tides. This is only a hypothesis: I might be able to give a better explanation if I knew the source of your information.