Abstract
Cold-water coral (CWC) ecosystems occur worldwide and play a major role in the ocean's carbonate budget and atmospheric CO2 balance since the Danian (~65 m.y. ago). However their temporal and spatial evolution against climatic and oceanographic variability is still unclear. For the first time, we combine the main macrofaunal components of a sediment core from a CWC mound of the Melilla Mounds Field in the Eastern Alboran Sea with the associated microfauna and we highlight the importance of foraminifera and ostracods as indicators of CWC mound evolution in the paleorecord. Abundances of macrofauna along the core reveal alternating periods dominated by distinct CWC taxa (mostly Lophelia pertusa, Madrepora oculata) that correspond to major shifts in foraminiferal and ostracod assemblages. The period dominated by M. oculata coincides with a period characterized by increased export of refractory organic matter to the seafloor and rather unstable oceanographic conditions at the benthic boundary layer with periodically decreased water energy and oxygenation, variable bottom water temperature/density and increased sediment flow. The microfaunal and geochemical data strongly suggest that M. oculata and in particular Dendrophylliidae show a higher tolerance to environmental changes than L. pertusa. Finally, we show evidence for sustained CWC growth during the Alleröd-Younger-Dryas in the Eastern Alboran Sea and that this period corresponds to stable benthic conditions with cold/dense and well oxygenated bottom waters, high fluxes of labile organic matter and relatively strong bottom currents
Highlights
Cold-water corals (CWCs) are known since centuries, they became a major research "hot" topic only in the last two decades
The chronology of the cores is constraint by 7 accelerator mass spectrometry (AMS) 14C dating on CWC fragments and 4 on benthic foraminifera coupled to the distribution of planktonic foraminifera (Fig 2, Table 1)
The detailed and integrated study of micro- and macrofossils, coupled together with geochemical proxies, allows the following conclusions regarding the evolution of a cold-water coral mound in the eastern Alboran Sea in relation to oceanographic and climatic variability during the last 13.1 ka: 1. The late Alleröd-early Holocene is characterized by enhanced fluxes of labile organic matter whereas the mid-late Holocene is characterized by more refractory and variable Corg fluxes to the seafloor
Summary
Cold-water corals (CWCs) are known since centuries, they became a major research "hot" topic only in the last two decades. Aquarium cultures of living CWC species collected from the North Atlantic and the Mediterranean Sea and their δ13C and δ15N values from coral tissues have revealed that CWCs are able to feed on a wide range of food sources including fresh macrozooplankton, fecal pellets, degraded phytodetritus, dissolved organic matter and bacteria (e.g., [11,12,13,14]). Comprehensive studies (e.g., [1,15,16]) have demonstrated that the distribution of CWCs is largely driven by the chemo-physical properties of the surrounding water mass where, temperatures, salinities and dissolved oxygen contents usually range within 4–14°C, 31.7–38.8 and 2.6–7.2 ml l-1, respectively. Large-scale water masses characterizations in active CWC settings from the Celtic and Norwegian shelves and distributed over a wide bathymetric range (140– 850 m water depth) have shown that living corals thrive within a water density gradient of sigma-theta (σθ) = 27.35 to 27.65 kg m-3 [17].
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