Comment on cp-2021-162

doi:10.5194/cp-2021-162-rc1

Abstract

This study provides a detailed reconstruction of cold-water coral mound build-up within the East Melilla Coral Province (Southeast Alboran Sea) over the last 300 ky. Based on benthic foraminiferal assemblages, macrofaunal quantification, grain size analysis, sediment geochemistry, and foraminiferal stable isotope compositions, a reconstruction of environmental conditions having prevailed in the region is proposed. The variations in planktonic and benthic δ18O values indicate that cold-water coral mound build-up follows and records global climate variability. In contrast to northeast Atlantic counterparts, coral mound build-up in the southeast Alboran Sea occurs during glacial as well as during interglacial periods and at very low aggradation rates (between 1 and 10 cm.ky−1). Environmental conditions during glacial periods, particularly during the Last Glacial Maximum, appear to better suit the ecological requirements of the erect cheilostome bryozoan Buskea dichotoma. We propose that Buskea dichotoma has an important role in the build-up of cold-water coral mounds at the East Melilla Coral Province during glacial periods. Benthic foraminiferal assemblages suggest that important terrestrial input favoured cold-water coral proliferation during interglacial periods. The existence of strong Alboran Gyres during interglacial periods, promoting mixing between surface and intermediate water masses and bottom water turbulence, was possibly beneficial for cold-water coral development. Conversely, benthic foraminiferal assemblages indicate that the seafloor received less organic matter during glacial periods. Overall, the arid continental conditions combined to more stratified water masses resulted in limited coral proliferation during glacial times.

Highlights

Cold-water coral (CWC) reefs are diverse marine ecosystems that are common on Earth (Freiwald et al, 2004; Roberts et al, 2009)
The chronostratigraphy of core MD13-3462G is based on the combination of the coral ages (U-series dating), the planktonic and benthic stable oxygen isotope records, and the foraminiferal radiocarbon ages for the top first meter of the core (Figs 3 and 4)
The U-series coral ages indicate that core MD13-3462G extends approximately from 300 ka BP (Marine Isotope Stage 9) to the Holocene (Figs 3 and 4, Table 2)

Summary

Introduction

Cold-water coral (CWC) reefs are diverse marine ecosystems that are common on Earth (Freiwald et al, 2004; Roberts et al, 2009). The most important reef building CWC species in the Atlantic Ocean and Mediterranean Sea are the scleractinian species Desmophyllum pertusum (formerly known as Lophelia pertusa, see Addamo et al., 2016) and Madrepora oculata (Roberts et al, 2009). These predominantly suspension-feeding organisms depend on enhanced hydrodynamic regimes that provide food to their polyps (White et al, 2005; Mienis et al, 2007; Carlier et al, 2009; Davies et al, 2009; Roberts et al, 2009; Hanz et al, 2019). The sensitivity of CWCs to climate change is useful to monitor variations in environmental conditions (e.g., water mass variability, surface productivity, bottom current velocity; Rüggeberg et al, 2007; Huvenne et al, 2009; Hebbeln et al, 2016; Wienberg et al, 2018; 2020)

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