Surface-to-deep-ocean ecosystem responses to orbital-to-millennial-scale paleoceanographic variability across the mid-Brunhes at the Iberian margin

Abstract

This study provides new insights into how oceanographic changes along the mid-Brunhes interval (MBI) influenced interactions between surface productivity and deep-sea environment in the North Atlantic, southwestern Iberian Margin (SW IbM) region. High-resolution ichnological and sediment colour analyses from International Ocean Discovery Program (IODP) Site U1385 reveal that the transfer of organic matter from the surface ocean to the seafloor was strongly modulated by both orbital- and suborbital-scale climate variability. Variations in the composition of the ichnological assemblages (including ichnotaxa Chondrites, Ophiomorpha, Planolites, Scolicia, Taenidium, Teichichnus, Thalassinoides, and Zoophycos), bioturbation, and sediment colour patters, assessed between Marine Isotope Stages (MIS) 12 to 9 (∼450 to 339 ka), indicate a sensitive response of deep-sea macrobenthic tracemaker communities. The integration of this data with high-resolution reconstructions of surface productivity and surface-to-deep hydrology at the studied site indicates that surface ocean conditions and production patterns were not always recorded in the sediments and benthic communities. This highlights the key role of bottom-water conditions and deep-water ventilation on the preservation of organic matter and the benthic ecosystem dynamics. Reduced oxygenation during Heinrich-type events likely limited tracemaker activity, as reflected in decreasing both ichnodiversity and bioturbation abundance, whereas interglacial periods supported more diverse and active communities. These findings underscore the value of integrating ichnological data with micropaleontological and geochemical proxies as a key route to reconstruct surface-to-deep ocean ecosystem and hydrodynamic linkages. Together with this, findings in this research provide new insights into how the mid-latitude North Atlantic deep-sea ecosystems responded to past climate variability across the key mid-Brunhes transition of the Pleistocene.