Expedition 401 is part of the larger Investigating Miocene Mediterranean-Atlantic Exchange (IMMAGE) Project—a collaboration between the International Ocean Discovery Program (IODP) and the International Continental Scientific Drilling Program (ICDP). This expedition aims to identify when the Atlantic first began to receive water flowing out of the Mediterranean with distinctly different physical and chemical properties, understand the cause of the Mediterranean salt giant and its climatic consequences, and test hypotheses around how water with extremely contrasting densities mix in the ocean and improving the numerical representation of this process in ocean circulation models.