Articles | Volume 12, issue 20
Biogeosciences, 12, 6045–6058, 2015

Special issue: Low oxygen environments in marine, fresh and estuarine...

Biogeosciences, 12, 6045–6058, 2015

Research article 22 Oct 2015

Research article | 22 Oct 2015

Interdecadal changes in intensity of the oxygen minimum zone off Concepción, Chile (~ 36° S), over the last century

B. Srain1, S. Pantoja2,3, J. Sepúlveda4,a, C. B. Lange2,3, P. Muñoz5, R. E. Summons4, J. McKay6, and M. Salamanca2 B. Srain et al.
  • 1Graduate Program in Oceanography, Department of Oceanography, University of Concepción, Concepción, Chile
  • 2Departmento de Oceanografía, Universidad de Concepción, Concepción, Chile
  • 3Centro de Investigación Oceanográfica en el Pacífico sur-Oriental (COPAS Sur-Austral), Universidad de Concepción, Concepción, Chile
  • 4Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
  • 5Facultad de Ciencias del Mar y Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Universidad Católica del Norte, Coquimbo, Chile
  • 6College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA
  • anow at: Department of Geological Sciences and Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, CO, USA

Abstract. We reconstructed oxygenation changes in the upwelling ecosystem off Concepción (36° S), Chile, using inorganic and organic proxies in a sediment core covering the last ca. 110 years of sedimentation in this area. Authigenic enrichments of Mo, U and Cd were observed between ca. 1935 and 1971 CE, implying a prolonged period with predominantly more reduced conditions in bottom waters and surface sediments. Significant positive correlations between redox-sensitive metals, algal sterols, biomarkers of micro-aerophilic and anaerobic microorganisms, and archaeal glycerol dialkyl glycerol tetraethers point to a tight coupling among bottom water O2 depletion and increased primary and export production. The time interval with low O2 of ca. 35 years seems to follow low-frequency interdecadal variation of the Pacific Decadal Oscillation, and it may have resulted in O2 depletion over the entire continental shelf off Concepción. Taking this together with the concurrent increase in sedimentary molecular indicators of micro-aerophilic and anaerobic microbes, we can suggest that changes in oxygenation of the water column are reflected by changes in microbial community. This study can inform our understanding of ecological consequences to projected trends in ocean deoxygenation.

Final-revised paper