Sommer, Stefan, Dengler, Marcus and Treude, Tina (2014) Benthic element cycling, fluxes and transport of solutes across the benthic boundary layer in the Peruvian oxygen minimum zone, (SFB 754) - Cruise No. M92, January 05 - February 03, 2013, Callao (Peru) - Callao (Peru). . METEOR-Berichte, M92 . DFG-Senatskommission für Ozeanographie, Bremen, 55 pp. DOI 10.2312/cr_m92.

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Abstract

Summary

During this cruise a detailed multi-disciplinary research program was conducted at the Peruvian
oxygen minimum zone (OMZ) within the framework of the Kiel SFB 754. Investigations were
primarily conducted along a depth transect at 12° S. Major aim was to advance understanding of
how OMZ´s are maintained and to determine feedbacks of benthic nutrient release on the
currently expanding Peruvian OMZ with a major focus on i. variability of benthic nutrient
release in response to hydrodynamic forcing and regional differences in bottom water levels of
oxygen (O2), nitrate (NO3-), nitrite (NO2-), and sedimentary carbon content, ii. diapycnal and
advective fluxes of excess dinitrogen (N2), ammonium (NH4+), phosphorous (P), iron (Fe),
silicate (Si), and radium isotopes between the benthic boundary layer, and the stratified interior
ocean as well as their entrainment into the surface mixed layer and iii. processes involved in the
respective benthic N, Fe, and P cycles. To achieve this goal, physical and biogeochemical
measurements were conducted in the water column as well as at the sea floor. For investigations
in the water column a total of 84 CTD casts, 41 micro-structure CTD, 20 in situ pump and 12
GoFlo deployments were performed. Sediment samples were obtained during 50 multiple corer
casts, 12 gravity corers and 10 benthic chamber lander deployments. Furthermore a profiler
lander was used to determine in situ microprofiles of O2, NO3- and nitrous oxide (N2O) in situ.
Microprofiles were obtained using glass-microsensors that were pushed into the sediment in 300
μm increments. In order to obtain time series data on the oxygen distribution and the current
regime oceanographic moorings were distributed along the 12°S transect in addition to four
benthic satellite-landers each equipped with upward looking ADCPs. Lastly, a glider swarm was
established at 12°S. These instruments were deployed for the duration of cruise M92 as well as
for the subsequent M93 cruise. Deviating from the cruise proposal, more time was spent for
station works at the depth transect at 12° S. Major aim of this cruise was to obtain a coherent
data set of all involved groups, which however took slightly more time than originally planned,
yet bears a high scientific potential. Additionally, it was discovered that at 12° S in shallow
waters sulphide was released from the seabed into the bottom water. Furthermore, in water
depths from about 120 to 200 m nitrite in addition to nitrate was available in high concentrations
which affects the benthic nitrogen cycle to a hitherto unknown extent. Hence these stations were
more intensely investigated than originally planned. Weather conditions were fine and all
deployments of the scientific gear went very well. It is expected that after analyses and synthesis
of the different data sets from the different disciplines the scientific questions above can be
addressed to broad extent.

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