Hydrogen sulphide eruptions in the Atlantic Ocean off southern Africa: Implications of a new view based on SeaWiFS satellite imagery

Scarla J. Weeks, Bronwen Currie, Andrew Bakun, Kathleen R. Peard

Research output: Contribution to journalArticle

82 Citations (Scopus)

Abstract

Conventional wisdom has held that eruptions of toxic hydrogen sulphide that occur from time to time in the ocean off southwestern Africa were rather isolated near-coastal features, limited both in extent and in ecosystem-scale consequences. Now, however, it has become possible to identify sulphide outbreaks by satellite remote sensing. This new capability appears to lead to a complete revision of the conventional view, with some eruption episodes being observed to affect areas of ocean surface exceeding 20,000km2. The occurrences are also seen to be more frequent and longer lasting than previously supposed. Example sequences of Sea-viewing Wide Field of View (SeaWiFS) images are presented to indicate general classes of eruption types that are observed and to support discussion of potential eruption mechanisms. Certain methodological problems in interpreting effects on local productivity are outlined. Spatial configurations of eruptions indicate that simple upward advection in the upwelling process may not be a sufficient explanation for the range of eruption characteristics experienced. Eruptions seem often to be coincident with one of two contrasting types of atmospheric weather situation: either (1) increased intensity of wind driven coastal upwelling, or (2) indications of passage of a low pressure weather cell (e.g. interruption of coastal upwelling, sudden warming of the sea surface, rainfall in the hinterland). Such a pattern may imply that related lowering of hydrostatic pressure at depth may tend to trigger incipient eruptions. It also suggests an episodic mechanism driven by the buoyancy introduced by the effervescence of gases trapped by hydrostatic pressure within the sea-floor sediments. Connotations of these phenomena to the local ecology and to that of the entire Benguela Current regional ecosystem would appear to be major. Their relevance to the valuable but extremely variable fishery resource populations of the region, which have undergone drastic declines in recent decades, is likely to be high.

Original languageEnglish
Pages (from-to)153-172
Number of pages20
JournalDeep-Sea Research Part I: Oceanographic Research Papers
Volume51
Issue number2
DOIs
StatePublished - Feb 1 2004

Fingerprint

SeaWiFS
hydrogen sulfide
Southern Africa
Atlantic Ocean
satellite imagery
volcanic eruption
ocean
weather
oceans
ecosystems
fishery resources
sulfides
upwelling
remote sensing
hydrostatic pressure
gases
rain
ecology
sea surface
sediments

Keywords

  • 10°E-17°E
  • 17°S-29°S.
  • Benguela
  • Eruption
  • Hydrogen sulphide
  • Hypoxia
  • Methane
  • Monitoring
  • Namibia
  • Satellite identification
  • SeaWiFS
  • Southern Africa

ASJC Scopus subject areas

  • Aquatic Science
  • Geology
  • Oceanography

Cite this

Hydrogen sulphide eruptions in the Atlantic Ocean off southern Africa : Implications of a new view based on SeaWiFS satellite imagery. / Weeks, Scarla J.; Currie, Bronwen; Bakun, Andrew; Peard, Kathleen R.

In: Deep-Sea Research Part I: Oceanographic Research Papers, Vol. 51, No. 2, 01.02.2004, p. 153-172.

Research output: Contribution to journalArticle

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