I was on top of Constitution Hill in Aberystwyth one fine Saturday afternoon when I spotted these magnificently clear sediment plumes in the ocean water below the headland.
The sediment is likely eroded sediment from the beach at the foot of the cliffs and is broken up to the right of this image due to areas of rock, which aren't picked up by the water like sand is.
As for why the sediment is carried out to sea, that is because the water pushed ashore by the waves is travelling back out to sea and taking the sediment with it.
As for why the sediment then travels to the left, which is South, is a little more mysterious. My first thought was long shore drift, whereby suspended sediment is gradually pushed in the direction the waves are coming from. Interestingly, while the reported weather for Aberystwyth at the time this photo was taken does have a north westerly wind (which one could expect to move the sediment like this), the waves in the photo are clearly coming from the south west. So my theory is that this is a localised current, perhaps a gentle rip current (a current caused by a pile up of water on the beach due to the waves) taking water away from the enclosed bay and around the headland to the south, just because the environment is shaped in a way which favours it. The suspended sediment concentration appears to decrease to the left of the headland, as the water colour fades to a darker blue, which could indicate that the current is very weak and so much of the sediment is being entrained and remaining in that same bay.
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