Environmental factors influencing benthic communities in the oxygen minimum zones on the Angolan and Namibian margins

Hanz, Ulrike, Wienberg, Claudia, Hebbeln, Dierk, Duineveld, Gerard, Lavaleye, Marc, Juva, Katriina, Dullo, Wolf-Christian, Freiwald, André, Tamborrino, Leonardo, Reichart, Gert-Jan, Flögel, Sascha and Mienis, Furu (2019) Environmental factors influencing benthic communities in the oxygen minimum zones on the Angolan and Namibian margins Biogeosciences (BG), 16 . pp. 4337-4356. DOI 10.5194/bg-16-4337-2019.

[img]
Preview
Text
bg-16-4337-2019.pdf - Published Version
Available under License Creative Commons: Attribution 4.0.

Download (11Mb) | Preview

Supplementary data:

Abstract

Thriving benthic communities were observed in the oxygen minimum zones along the southwestern African margin. On the Namibian margin, fossil cold-water coral mounds were overgrown by sponges and bryozoans, while the Angolan margin was characterized by cold-water coral mounds covered by a living coral reef. To explore why benthic communities differ in both areas, present-day environmental conditions were assessed, using conductivity–temperature–depth (CTD) transects and bottom landers to investigate spatial and temporal variations of environmental properties. Near-bottom measurements recorded low dissolved oxygen concentrations on the Namibian margin of 0–0.15 mL L−1 (≜0 %–9 % saturation) and on the Angolan margin of 0.5–1.5 mL L−1 (≜7 %–18 % saturation), which were associated with relatively high temperatures (11.8–13.2 ∘C and 6.4–12.6 ∘C, respectively). Semidiurnal barotropic tides were found to interact with the margin topography producing internal waves. These tidal movements deliver water with more suitable characteristics to the benthic communities from below and above the zone of low oxygen. Concurrently, the delivery of a high quantity and quality of organic matter was observed, being an important food source for the benthic fauna. On the Namibian margin, organic matter originated directly from the surface productive zone, whereas on the Angolan margin the geochemical signature of organic matter suggested an additional mechanism of food supply. A nepheloid layer observed above the cold-water corals may constitute a reservoir of organic matter, facilitating a constant supply of food particles by tidal mixing. Our data suggest that the benthic fauna on the Namibian margin, as well as the cold-water coral communities on the Angolan margin, may compensate for unfavorable conditions of low oxygen levels and high temperatures with enhanced availability of food, while anoxic conditions on the Namibian margin are at present a limiting factor for cold-water coral growth. This study provides an example of how benthic ecosystems cope with such extreme environmental conditions since it is expected that oxygen minimum zones will expand in the future due to anthropogenic activities.

Document Type: Article
Keywords: cold-water coral, hypoxic conditions, Namibian and Angolan margin, habitat
Research affiliation: MARUM
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
NIOZ
Refereed: Yes
DOI etc.: 10.5194/bg-16-4337-2019
ISSN: 1726-4170
Projects: FATE, SponGES
Expeditions/Models:
Date Deposited: 05 Mar 2019 08:13
Last Modified: 19 Nov 2019 12:59
URI: http://eprints.uni-kiel.de/id/eprint/45975

Actions (login required)

View Item View Item

Document Downloads

More statistics for this item...