During RV SONNE cruise SO239 in March/April 2015 five sites in the area of the Clarion-Clipperton Fracture Zone (CCZ) in the eastern equatorial Pacific were visited as part of the JPI Oceans pilot action Ecological Aspects of Deep-Sea Mining“. Here, we present a comparable study on (1) the redox zonation in the sediments induced by the input flux of organic matter, (2) biogeochemical reactions including the driver of organic matter degradation and (3) diagenetic manganese redistribution and implications for manganese nodule formation

Geibert, Walter

Kasten, Sabine

Koschinsky, Andrea

Martínez Arbizu, Pedro

Mogollón, José M.

Versteegh, Gerard

Volz, Jessica

The abyssal seafloor in the equatorial Pacific Ocean bounded by the Clarion and Clipperton Fracture Zones (CCZ) is covered by polymetallic nodules. The International Seabed Authority (ISA) has granted exploration license areas in the CCZ and declared nine Areas of Particular Environmental Interest (APEIs). The APEIs are excluded from any mining activities and are designated for the protection of biodiversity and ecosystem functioning. However, little is known about the spatial variation in sediment geochemistry across the license areas and the APEIs. We present a comparative study on six sites on (1) the redox zonation in the sediments and (2) the dominating biogeochemical processes. As part of the EU-BMBF funded JPI Oceans Pilot Action „Ecological aspects of deep-sea mining“, we visited five European license areas and the APEI3 located north of the CCZ during RV SONNE cruise SO239 in 2015. The recovered multiple and gravity cores were sampled for comprehensive pore-water and solid-phase analyses. Due to low POC fluxes of  6 m sediment depth. Aerobic respiration is the dominant process and accounts for 90% of the organic carbon degradation whereas denitrification is negligible. Below the oxygen penetration depth (OPD), Mn2+ is released into the suboxic zone and coexists with NO3-. At several sites the Mn2+ pore-water profiles indicate an upward diffusion of O2 from the underlying basaltic basement. The distinctly different geochemical conditions found in the six areas result from differences in (1) surface water productivity and POC flux, (2) sedimentation rates, (3) deep Mn reduction and (4) diffusive upward flux of O2 from the basaltic basement. The conditions at the APEI3 site differ significantly from the geochemical settings in the investigated European license areas

Mogollón, J. M.

Martínez Arbizu, P.

Electronic Publication Information Center

Natural variability of Geochemical Conditions, Biogeochemical Processes and Element Fluxes in Sediments of the Eastern CCZ, Pacific Ocean

1 2Jessica Volz , José Mogollón , Walter Geibert , Gerard Versteegh , Andrea Koschinsky , Sabine Kasten11 4 13Pedro Martínez Arbizu , 1Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven2Utrecht University, Department of Earth Sciences - Geochemistry, Utrecht3Forschungsinstitut Senckenberg, DZMB, Wilhelmshaven4Jacobs University Bremen, Department of Physics and Earth Sciences, BremenNatural variability of geochemical conditions, biogeochemical processes and element fluxes in sediments of the CCZIntroductionBREMERHAVENAm Handelshafen 1227570 BremerhavenTel. +49471 4831-0www.awi.deDuring RV SONNE cruise SO239 in March/April 2015 five sites in the area of the Clarion-Clipperton Fracture Zone (CCZ) in the eastern equatorial Pacific were visited as part of the JPI Oceans pilot action Ecological Aspects of Deep-Sea Mining“. Here, we present a comparable study on (1) the redox zonation in the sediments induced by the input flux of organic matter, (2) biogeochemical reactions including the driver of organic matter degradation and (3) diagenetic manganese redistribution and implications for manganese nodule formation.“MethodsFour European exploration license areas including the German BGR area, the InterOceanMetal (IOM) area, the Belgian GSR area and the French IFREMER area were visited as well as one of the Areas of Particular Environmental Interest (APEI) and referred to as APEI3 (Fig. 1). Sediment cores were taken using a multiple corer (MUC) for the retrieval of undisturbed surface sediments and a 10 m long gravity corer (GC) which were subsequently sampled and analysed:Figure 1: Maps of the study area during RV SONNE cruise SO239 showing the bathymetry of the Pacific Ocean (left), the five investigated areas (right) with sampling locations (white circles) and estimated upper limit -2 -1in POC flux [mg C  m  d ] to the seafloor by Lutz et al. (2007) (modified after Vanreusel et al., 2016).orgResults and DiscussionFigure 2: Pore-water profiles and solid-phase contents for the five investigated sites including high-resolution pictures of the GC sediments.ŸThe redox zonation varies from throughout oxygenated sediments ( , ) and oxygen penetration depth (OPD) of 3 m, 3.8 m and 4.5 m (IOM, ) to an oxic zone limited to the 1 m ( ). Below the OPD, the suboxic zone extends from a horizon of 3 m with low conc. () to at least 8 m with high conc. (25 µM, ). Below the suboxic zone,  might re-increase at 3 stations (). ŸŸAPEI3APEI3 APEI3GSRGSRIFREMER without nodules  IFREMER with nodulesIFREMER with nodulesIFREMER with nodulesIFREMER,5 µM, , IOM, ; Mewes et al., 2016 Variations in the POC flux to the seafloor (Fig. 1) correlate with surface sediment TOC and TS contents: 0.4-0.6 wt% in , IOM, 0.3-0.4 wt% in , , ~0.2 wt% in (Fig. 2).The main biogeochemical process during OC degradation is aerobic respiration with diffusive  fluxes within 0.172 and 0.057 m( , ). Bioturbation is limited to the upper 7 cm of sediment and 13 cm at the IOM site. Close correlation of TOC, TS and Ba indicate biogenic barite deposition that could be used as paleoproductivity proxy.The diagenetic redistribution of Mn in the suboxic zone is caused by the abiotic reduction of Mn oxides (Fig. 2) with no recent suboxic diagenetic formation of nodules.BGRBGRBGRBGRBGRO2O mol 2-2 -1 m  dConclusionsAcknowledgementsThanks to the crew and the scientific party of RV SONNE cruise SO239 for the technical and scientific support. Thanks to Jennifer Ciomber, Benjamin Löffler and Vincent Ozegowski for the analytical support onboard. For the analytical support in the home laboratory and during data evaluation we want to give special thanks to Ingrid Stimac, Olaf Kreft, Ingrid Dohrmann and Gerhard Kuhn.This project is BMBF-funded (  and part of the JPI-O EcoMining-DEU - Ecological Aspects of Deep-Sea Mining.03F0707G)ReferencesRevsbech. Limnol.Oceanogr. 34 (2), 474-478 (1989); doi:10.4319/lo.1989.34.2.0474Boudreau. Springer Verlag. 505 (1997)Nöthen and Kasten. Mar. Geol. 287, 1-4  (2011); doi:10.1016/j.margeo.2011.06.008Anderson et al. Limnol. Oceanogr. Methods, 10 (2012); doi:10.4319/lom.2012.10.179Mewes et al. Deep-Sea Res. Pt I 119, 125-141 (2014); doi:10.1016/j.dsr.2014.06.001Mewes et al. Earth Planet. Sci. Lett., 433, 215-225 (2016); doi:10.1016/j.epsl.2015.10.028 Lutz et al. J. Geophys. Res. 112, 1-26 (2007); doi:10.1029/2006JC003706Vanreusel et al. Sci. Rep. 6, 26808 (2016); doi:10.1038/srep26808ŸŸŸThe distinct differerences in geochemical zonations (and TOC degradation) within the studied license areas in the CCZ are a result of (1) surface water productivity and POC fluxes to the seafloor, (2) sedimentaton rates, (3) abiotic Mn reduction and (4) diffusive upward flux of  from basal sedimentsProductivity ultimately determines the intensity of OC degradation and in turn the consumption of  close to the sediment surfaceŸRecently, there is no suboxic diagenetic formation of nodules at any siteThe APEI3 site is not representing the natural geochemical setting of the investigated European license areasO2O2Table 1: Sedimentation rates, POC fluxes for the model input and modelled POC oxidation rates. Nodule sampling area is 0.25 m². The length of scale corresponds to 10 cm. Sedimentation rates for the BGR area were published by Mewes et al. (2014). odule coverage was derived from nearby box corer stations with a nFor the determination of organic carbon (OC) oxidation rates, a one-dimensional reaction transport model was used (Boudreau, 1997).

Natural variability of geochemical conditions, biogeochemical processes and element fluxes in sediments of the CCZ

The abyssal seafloor in the equatorial Pacific Ocean bounded by the Clarion and Clipperton Fracture Zones (CCZ) is covered by polymetallic nodules. The International Seabed Authority (ISA) has granted exploration license areas in the CCZ and declared nine Areas of Particular Environmental Interest (APEIs). The APEIs are excluded from any mining activities and are designated for the protection of biodiversity and ecosystem functioning. However, little is known about the spatial variation in sediment geochemistry across the license areas and the APEIs. We present a comparative study on six sites on (1) the redox zonation in the sediments and (2) the dominating biogeochemical processes.

As part of the EU-BMBF funded JPI Oceans Pilot Action „Ecological aspects of deep-sea mining“, we visited five European license areas and the APEI3 located north of the CCZ during RV SONNE cruise SO239 in 2015. The recovered multiple and gravity cores were sampled for comprehensive pore-water and solid-phase analyses.

Due to low POC fluxes of  6 m sediment depth. Aerobic respiration is the dominant process and accounts for 90% of the organic carbon degradation whereas denitrification is negligible. Below the oxygen penetration depth (OPD), Mn2+ is released into the suboxic zone and coexists with NO3-. At several sites the Mn2+ pore-water profiles indicate an upward diffusion of O2 from the underlying basaltic basement.

The distinctly different geochemical conditions found in the six areas result from differences in (1) surface water productivity and POC flux, (2) sedimentation rates, (3) deep Mn reduction and (4) diffusive upward flux of O2 from the basaltic basement. The conditions at the APEI3 site differ significantly from the geochemical settings in the investigated European license areas

During RV SONNE cruise SO239 in March/April 2015 five sites in the area of the Clarion-Clipperton Fracture Zone (CCZ) in the eastern equatorial Pacific were visited as part of the JPI Oceans pilot action “Ecological Aspects of Deep-Sea Mining“. Here, we present a comparable study on (1) the redox zonation in the sediments induced by the input flux of organic matter, (2) biogeochemical reactions including the driver of organic matter degradation and (3) diagenetic manganese redistribution and implications for manganese nodule formation

Natural variability of geochemical conditions, biogeochemical processes and element fluxes in sediments of the CCZ

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