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Spatial and Vertical Benthic Foraminifera Diversity in the Oxygen Minimum Zone of Mejillones Bay, Northern Chile

Authors :
Laura Tavera Martínez
Margarita Marchant
Praxedes Muñoz
Roberto T. Abdala Díaz
Source :
Frontiers in Marine Science, Vol 9 (2022)
Publication Year :
2022
Publisher :
Frontiers Media S.A., 2022.

Abstract

Mejillones Bay is located in northern Chile (23°S) and is influenced by an Oxygen Minimum Zone (OMZ), with oxygen levels below 0.5 ml l–1. This area presents particular ecological characteristics, such as circulation of currents, hotspot, high productivity and industrial activity. This extreme ecosystem generates the need to understand their dynamics and changes across time and space, as well as to identify the main differences with other OMZs. For this reason, we studied the benthic foraminifera to use them as environmental and oxygenation proxies. For this purpose, two sediment cores (ZA and Z1A) were collected, obtaining 14 samples of the first 8 cm (vertical distribution), and 18 samples with a mini boxcore (spatial distribution). When analyzing the foraminifera community, some similarities were found in environmental characteristics of other OMZs, such as the predominance of Bolivina seminuda, Bolivina costata, Epistominella exigua, Fursenkoina sp., and Nonioella stella (species typical of hypoxic conditions). In addition, a high abundance of angular-asymmetric morphologies was observed, indicating eutrophied silty substrates and low current circulation. However, the Mejillones Bay recorded a particular spatial and vertical dynamics respect to others OMZs, due to presence of other species of Bolivinids not reported for this area before, and a high abundance of Buliminella elegantissima, which is not recorded in most of OMZs. Foraminifera with rounded-symmetric morphologies were present and dominant in deeper layers, reflecting a turbulent and high-energy environment. On the basis of depth and conditions of microxia or dysoxia, no significative pattern of spatial and vertical distribution was observed. The latter can be explained by local factors such as cyclonic and anticyclonic whirlpools, wastewater from industrial activity and natural disaster such a Tsunami occurred in 1877. These factors contributed to the mixture of the benthic foraminifera and prevented the formation of spatial and vertical patterns. Finally, an intensification of hypoxia was identified, indicating microxia (0,01 ml l–1) in the superficial layers (0–3 cm from years 1996 to 2012), while the deeper layers (4–8 cm from years 1985 to 1877) presented foraminiferal species that indicated dysoxia conditions (0,07 ml l–1). The latter differs from other OMZs, which show greater oxygenation in the most superficial layers and microxia in deeper layers. This study represents the first ecological reconstruction using benthic foraminifera proxies for the Mejillones Bay, which results indicate an OMZ with ecological and environmental features that differ from other OMZs.

Details

Language :
English
ISSN :
22967745
Volume :
9
Database :
Directory of Open Access Journals
Journal :
Frontiers in Marine Science
Publication Type :
Academic Journal
Accession number :
edsdoj.f34f385d46f14b249d169c3cddd35742
Document Type :
article
Full Text :
https://doi.org/10.3389/fmars.2022.821564