International Ocean Discovery Program
Expedition 395 Scientific Prospectus Addendum

Reykjanes Mantle Convection and Climate: Mantle Dynamics, Paleoceanography and Climate Evolution in the North Atlantic Ocean¹

¹Parnell-Turner, R., Briais, A., and LeVay, L., 2023. Expedition 395 Scientific Prospectus Addendum: Reykjanes Mantle Convection and Climate. International Ocean Discovery Program. https://doi.org/10.14379/iodp.sp.395add.2023

Abstract

The intersection between the Mid-Atlantic Ridge and Iceland hotspot provides a natural laboratory where the composition and dynamics of Earth’s upper mantle can be observed. Plume-ridge interaction drives variations in the melting regime, which result in a range of crustal types, including a series of V-shaped ridges and V-shaped troughs south of Iceland. Expedition 395 has three objectives: (1) to test contrasting hypotheses for the formation of V-shaped ridges, (2) to understand temporal changes in ocean circulation and explore connections with plume activity, and (3) to reconstruct the evolving chemistry of hydrothermal fluids with increasing crustal age and varying sediment thickness and crustal architecture. After being postponed from summer 2020 due to the COVID-19 pandemic, the drilling objectives of Expedition 395 were partially completed without a science party on board during Expedition 395C in summer 2021, when basalt cores were collected at four sites (U1554, U1555, U1562, and U1563). Sediment cores were collected from these sites, as well as from Site U1564, and casing was installed to 602 meters below seafloor at Site U1554. Expedition 395 is scheduled with sufficient time to complete the planned operations remaining at Sites U1564 and U1554, leaving approximately 22 operating days available for other sites, including a new proposed site, REYK-14B, which is located west of Reykjanes Ridge on the Eirik drift. This addendum provides the operations plan for rescheduled Expedition 395, including details of the additional site.

Plain language summary

In the North Atlantic Ocean, hot rocks are thought to rise up beneath Iceland from deep within Earth’s interior, called the mantle, forming a giant mantle plume. This plume likely plays a key role in shaping the ocean crust around Iceland, including a pattern of distinctive crustal V-shaped ridges (highs) and V-shaped troughs (lows) that stretch over hundreds of kilometers on the seabed south of Iceland. Some think that these V-shaped ridges are generated by increases and decreases in plume activity, but their precise origin is hotly debated. Plume activity variations may also have contributed to changes in the height of oceanic gateways—passages that link Greenland, Iceland, and Scotland, thus controlling the amount of cold, deep water that has been flowing from the Norwegian Sea to the Atlantic Ocean over the past few million years. Expedition 395 will use the age, composition, and history of sediments and basaltic rocks south of Iceland to test several scientific ideas. First scheduled for summer 2020, the objectives of Expedition 395 were partially completed in summer 2021 during Expedition 395C without a science party on board. The remaining objectives are to be completed in summer 2023 during the rescheduled Expedition 395. This addendum details the updated operations plan for Expedition 395, which includes an additional site, REYK-14B, that targets sediments on the eastern margin of Greenland.