Iberian Margin Paleoclimate1
1 Hodell, D.A., Abrantes, F., and Alvarez Zarikian, C.A., 2022. Expedition 397 Scientific Prospectus: Iberian Margin Paleoclimate. International Ocean Discovery Program. https://doi.org/
The Iberian margin is a well-known source of rapidly accumulating sediment that contains a high-fidelity record of millennial climate variability (MCV) for the late Pleistocene. The late Sir Nicholas (Nick) Shackleton demonstrated that piston cores from the region can be correlated precisely to polar ice cores in both hemispheres. Moreover, the narrow continental shelf off Portugal results in the rapid delivery of terrestrial material to the deep-sea environment, thereby permitting correlation of marine and ice core records to European terrestrial sequences. Few places exist in the world where such detailed marine-ice-terrestrial linkages are possible. The continuity, high sedimentation rates, and fidelity of climate signals preserved in Iberian margin sediments make this region a prime target for ocean drilling.
During Integrated Ocean Drilling Program Expedition 339 (Mediterranean Outflow), one of the sites proposed here was drilled to a total depth of 155.9 meters below seafloor in multiple holes. At Site U1385 (the “Shackleton site”) a complete record of hemipelagic sedimentation was recovered for the last 1.45 My corresponding to Marine Isotope Stage 47 with sedimentation rates of 10–20 cm/ky. Preliminary results from Site U1385 demonstrate the great promise of the Iberian margin to yield long records of millennial-scale climate change and land–sea comparisons.
International Ocean Discovery Program (IODP) Expedition 397 will extend this remarkable sediment archive through the Pliocene and expand the depth range of available sites by drilling additional sequences in water depths from 1304 to 4686 meters below sea level (mbsl). This depth transect is designed to complement those sites drilled during Expedition 339 (560–1073 mbsl) where sediment was recovered at intermediate water depth under the influence of Mediterranean Outflow Water (MOW). Together, the sites recovered during Expeditions 339 and 397 will constitute a complete depth transect with which to study past variability of all the major subsurface water masses of the eastern North Atlantic. Because most of the mass, thermal inertia, and carbon in the ocean-atmosphere system is contained in the deep ocean, well-placed depth transects in each of the major ocean basins are needed to understand the underlying mechanisms of glacial–interglacial cycles and MCV. We have identified four primary sites (SHACK-4C, SHACK-10B, SHACK-11B, and SHACK-14A) at which multiple holes will be drilled to ensure complete recovery of the stratigraphic sections at each site, ranging in age from the latest Miocene to Holocene. Building on the success of Site U1385 and given the seminal importance of the Iberian margin for paleoclimatology and marine-ice-terrestrial correlations, the cores recovered during Expedition 397 will provide present and future generations of paleoceanographers with the raw material needed to reconstruct the North Atlantic climate at high temporal resolution for the entire Quaternary and Pliocene.
International Ocean Discovery Program (IODP) Expedition 397 will take place off the Iberia Peninsula where rapidly accumulating sediments contain a high-fidelity record of past climate change. Most sediment in the deep sea accumulates at rates of 1–2 cm every thousand years, whereas sediments in the targeted area accumulate ten times faster (10–20 cm every thousand years), making it possible for climate events to be resolved on timescales of hundreds (centennial) to thousands (millennial) of years.
Previous studies of marine sediment sequences from this area have demonstrated that the sedimentary profiles can be correlated precisely to the polar ice cores in Greenland and Antarctica. Moreover, the narrow continental shelf (ocean bottom at a water depth of 0–200 m) permits a rapid delivery of material from the nearby continent to the deep-sea environment, thereby providing a record of European terrestrial climate at the same location. During Integrated Ocean Drilling Program Expedition 339, Site U1385 was drilled in the same location to 155.9 m below the seafloor. The study of Site U1385 has confirmed the continuity of high sedimentation rates (10–20 cm per thousand years) for the last 1.45 million years and the uniqueness of the detailed marine-ice-terrestrial linkages possible at this location.
Expedition 397 will extend this remarkable sediment archive back to 3–5 million years ago through the geologic periods known as the Quaternary and Pliocene. Furthermore, we will drill additional sequences in water depths of 1304–4686 m below sea level. This depth transect is designed to study the past variability of all the water masses that fill the eastern North Atlantic Basin. Of particular interest are the behavior of the deeper water masses and their role in carbon storage and its effect on atmospheric carbon dioxide. The sediment cores recovered during Expedition 397 will be important for studying the role that millennial climate variability has played in the waxing and waning of the great Northern Hemisphere ice sheets during the last 3 million years.
The fidelity of the climate signals preserved in the sediments to be drilled during Expedition 397 will provide the greatest possible potential to reconstruct the natural variability of the North Atlantic climate (before human impact) at unprecedented temporal resolution back through the Pliocene (last 5 million years).