Site U1608

Site U1608 (proposed Site MB-06D) was cored at 74°7.6818′N, 60°58.3172′W at 607 meters below sea level (mbsl) on the middle section of the northwest Greenland shelf, west of the Melville Bay Ridge and graben structures formed during Cretaceous rifting (Figure F1; see Figure F4 in the Expedition 400 summary chapter [Knutz et al., 2025b]). The main coring targets are mounded contourite drift deposits of expected Pliocene age associated with Megaunit B (Knutz et al., 2015, 2019; Aubrey et al., 2021) and overlying sediments of Megaunit A, recording the transition into glacigenic deposits of earliest trough mouth fan (TMF) progradation (Figure F2). The expanded interval of Megaunit B, captured at Sites U1606 and U1608, reflects deposition below a major incised escarpment that is at least 500 m tall and extends into disturbed sediment packages interpreted as mass transport deposits (Figure F3). The base of the contourite drift accumulation is defined by Horizon c1 of probable Late Miocene age (Knutz et al., 2015). Site U1608 ends ~100 m above Horizon c1, which at this location is characterized by an erosional unconformity related to the slope instability that is strongly expressed in the seismic record (Figure F3). In the context of the full development of the Melville Bugt TMF, Site U1608 targeted TMF Seismic Unit 1, which records the first advance of the northwestern Greenland ice sheet (GrIS) onto the continental shelf, which is hypothesized to correspond to the Pleistocene/Pliocene boundary (Knutz et al., 2019) (Figures F2, F3). Combined, the cores from middle shelf Sites U1606 and U1608 access archives of ocean and climate conditions presumably much warmer than today that were buried by glacial deposits representing global cooling and expansion of northern hemisphere glaciers. These sites use the dynamic drift morphology to capture different parts of Megaunit B strata to capture high-resolution records of the Pliocene ocean-climate system at high Arctic latitudes.