Figure 1

(a) Location of sampling sites in the Sansha Yongle Blue Hole and the surrounding regions. (b) Arial view of the Sansha Yongle Blue Hole. (c) Vertical cross-section of the Sansha Yongle Blue Hole.

(a) Location of sampling sites in the Sansha Yongle Blue Hole and the surrounding regions. (b) Arial view of the Sansha Yongle Blue Hole. (c) Vertical cross-section of the Sansha Yongle Blue Hole.