Life at the edge - oscillating lower boundary of the Peruvian oxygen minimum zone.

Sommer, Stefan, McGinnis, Daniel F., Linke, Peter , Camilli, R., Mosch, T. and Pfannkuche, Olaf (2010) Life at the edge - oscillating lower boundary of the Peruvian oxygen minimum zone. [Talk] In: Ocean Sciences Meeting 2010 "Oxygen Minimum Zones and Climate Change: Observations and Prediction IV". , 22.02.-26.02.2010, Portland, Oregon, USA . EOS Transactions : Ocean Sciences Meeting Supplement. ; BO24C-08 .

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Presently, oxygen minimum zones (OMZ) are incurring drastic changes from the combined impact of both rapidly declining O2 concentrations and increasing CO2 levels. The lower edge of OMZs, typically characterized by abundant benthic invertebrate communities and fish existing in already precarious conditions, are particularly susceptible to even the slightest O2 changes. Currently, there are very limited benthic O2 data from the upper- and lower-boundaries of OMZs. Using benthic landers and a sediment-water O2 micro-profiler, we resolved time series of O2 and temperature directly above the seafloor at the lower-boundary (depth range of 397 - 1015 m) of the Peruvian OMZ at a transect along 11°S. We observed an oscillating and persistent vertical movement of bottom water (BW) with displacement amplitudes exceeding 100 m. These vertical displacements have a ~ 12 hour period, and appear to be partially driven by tidal forcing. This regular BW vertical motion leads to distinct cyclic fluctuations of local O2 concentration and temperature. At ~ 1000 m water depth, O2 variability ranged from 23 to 44 µM. Cyclical benthic O2 fluctuations were observed with decreasing water depths until O2 concentrations < 3 µM were reached at ~ 400 m. The benthic environment immediately responds to the varying BW O2 levels. At ~ 1000 m, the diffusive oxygen uptake across the sediment water interface fluctuated between 0.5 to 1.4 mmol m-2 d-1, which is seemingly associated to variable O2 BW concentrations. Intermittent local benthic O2 levels affect the colonization and composition of both aerobic and anaerobic life at the lower boundary of the OMZ. The dominant communities have enormous consequences for the distribution and magnitude of benthic redox-sensitive biogeochemical processes. Similarly to investigations in other oxygen deficient environments, we found extremely high densities of epibenthic invertebrates that were sharply centered at ~ 650 m depth close to the oxic-anoxic interface. These organisms benefit substantially from the oscillating benthic oxygen levels. They may therefore inhabit regions deeper within the lower edge of the OMZ, thus exploiting increased availability of e.g. labile organic carbon, and perhaps taking a deep “breath” during high O2 conditions. These oxygen oscillations in association with intricate BW motions imply strong solute exchange between the benthos and the higher water column, which can have unforeseen consequences for the coupling of benthic and pelagic ecosystems in an increasingly oxygen deficient environment.

Document Type: Conference or Workshop Item (Talk)
Keywords: Marine Biology; Biogeosciences; biogeochemical cycles, processes, modeling; food webs and trophodynamics; biological oceanography
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
Open Access Journal?: Yes
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Date Deposited: 23 Dec 2010 14:31
Last Modified: 23 Feb 2012 05:34

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