Psalm 46/Notes/Textual.v. 3.950577

Furthermore, in v. 3c, the MT has בְּלֵב יַמִּים ("in the heart of... ", singular), but the LXX has ἐν καρδίαις θαλασσῶν (“in hearts of seas”). This could be a case of harmonization with the plural form of "seas." The plural יַמִּים is taken here as amplified, i.e., representing an extremely deep sea. Note also that v. 4 uses 3ms suffixes in relation to the seas (“its”; i.e., “its waters,” “its swelling”).