Deglacial North Eastern Atlantic Oxygen Minimum Zone changes registered by Benthic foraminifera

Abstract

The eastern north Atlantic hosts a volumetrically important oxygen minimum zone (OMZ) influenced by the subtropical ocean circulation in the area and the upwelling off NW Africa. Ocean warming related to the increase in greenhouse gases and coastal eutrophication due to anthropogenic activity, leads to ocean deoxygenation and OMZs expansion. This makes relevant to study of the north Atlantic middle depth variability analogs in past climate change scenarios, to understand the future of the north Atlantic OMZ. During this study, we used benthic foraminifera from site GeoB9512-5 (793 m water depth) off NW Africa to reconstruct the bottom water oxygen concentration changes in the north Atlantic OMZ during the last 27,000 years. This high-resolution record registered an enhanced OMZ during the Bølling–Allerød (B-A) and Holocene that declined during the Heinrich Stadial 1 (HS1) and Younger Dryas (YD). These shifts are related to changes in bottom water ventilation and organic matter concentrations during the last deglaciation. Low benthic foraminifera diversity is synchronous with the oxygen decline of the B-A and Holocene, and benthic foraminifera assemblages show relevant changes consistent with these oxygenation shifts seen in our site. We provide new evidence of potential north Atlantic OMZ expansion in times of reduced bottom water ventilation during the B-A and Holocene times. This changes were driven by the shifts in the subtropical circulation during the last deglaciation registered in previous studies, and are relevant for understanding the future of OMZs in a climate change scenario and its possible consequences for marine biodiversity.