Ex situ sulphate reduction rates of sediment at the rim of a vesicomyd clam colony in the Japan Deep Sea Trench (dive 955)

Sediment samples were collected from the rim of a large vesicomyid clam colony in the Japan Deep Sea Trench. Immediately after sample recovery onboard, the sediment core was sub-sampled for ex situ rate measurements. Sulfate reduction were measured ex situ by the whole core injection method with three replicates. We incubated the samples at in situ temperature (1.5°C) for 48 hours with carrier-free 35SO4 (dissolved in water, 50 kBq). Sediment was fixed 20 ml ZnAc solution (20%, w/v) for AOM or SR. Turnover rates were measured as previously described (Kallmeyer et al., 2004).

Ex situ sulphate reduction rates of sediment at the rim of a vesicomyd clam colony in the Japan Deep Sea Trench (dive 957)

Sediment samples were collected from the rim of a large vesicomyid clam colony in the Japan Deep Sea Trench. Immediately after sample recovery onboard, the sediment core was sub-sampled for ex situ rate measurements. Sulfate reduction were measured ex situ by the whole core injection method with three replicates. We incubated the samples at in situ temperature (1.5°C) for 48 hours with carrier-free 35SO4 (dissolved in water, 50 kBq). Sediment was fixed 20 ml ZnAc solution (20%, w/v) for AOM or SR. Turnover rates were measured as previously described (Kallmeyer et al., 2004).

Miocene to Pliocene planktonic foraminifers in ODP Hole 134-832B

One hundred and sixty core samples were analyzed from Hole 832B to evaluate planktonic foraminiferal datum levels, and to zone and correlate the borehole succession. A total of 32 biostratigraphic events were recognized in the interval from Core 134-832B-59R through 134-832B-73R (702.49 through 846.4 meters below seafloor [mbsf]). These include 17 first appearance datum levels (FAD), 10 last appearance datum levels (LAD), and 5 coiling-change events in trochospiral species. The studied succession has been subdivided into nine planktonic foraminiferal zones (viz. downsequence N.22, N.21, N.20, N.19, N.18, N.17B, N.17A-N.16, N.15, N.8). The zonal index species occur in the expected stratigraphic order for zonal correlation, but some of the zonal boundaries may be diachronous compared to other localities in the western Pacific region. The FAD of Globorotalia (Truncorotalia) truncatulinoides (d' Orbigny) at 714.10 mbsf defines the boundary between the Zone N.22 and N.21; the boundary between Zones N.21 and N.20 at 741.73 mbsf is marked by the FAD of Globorotalia (Truncorotalia) tosaensis Takayanagi and Saito. The lower boundary of Zone N.20 is placed at 747.65 mbsf, based on the FAD of Globorotalia (Truncorotalia) crassaformis s.s. (Galloway and Wissler); the FAD of Sphaeroidinella dehiscens (Parker and Jones) at 756.61 mbsf defines the boundary between Zones N.18 and N.19. The FAD of Globorotalia (Globorotalia) tumida tumida (Brady) at 811.15 mbsf marks the boundary between Zones N.18 and N.17B. The boundary between Zones N.17B and N.17Ais placed at 843.52 mbsf, based on the FAD of Pulleniatina primalis Banner and Blow. A change in depositional conditions occurs at 846.4 mbsf just below the Zone N.17B lower boundary and is marked by the first appearance of abundant planktonic foraminifers in the region. The interval between 849.13 and 856.1 mbsf is placed in undifferentiated Zones N.17A and N.16, based on the rare occurrence of Neogloboquadrina acostaensis (Blow). The sparsely fossiliferous volcanic sandstone unit between 934.19 and 955.67 mbsf is positioned within Zone N.15 based on the presence of Globigerina (Zeaglobigerina) nepenthes Todd and Globigerinoides (Zeaglobigerina) druryi Arkers, and absence of N. acostaensis and Globorotalia (Jenkinsella) siakensis LeRoy. An unconformity between 955.67 and 971.80 mbsf may explain the absence of Zones N.14 through N.9. Basal Zone N.8 is recognized at 971.80 to 1008.60 mbsf by the presence of Globigerinoides sicanus De Stefani and the absence of Praeorbulina and Orbulina spp. The age of the succession between 702.49 and 1008.6 mbsf extends from the latest Pliocene or earliest Pleistocene (Zone N.22) to the earliest middle Miocene (Zone N.8). Among the datum levels evaluated here, the following events are considered to be the most reliable for time correlation in the studied region: the FADs of G. (T.) truncatulinoides, G. (T.) tosaensis, G. (T.) crassaformis, S. dehiscens, G. conglobatus (Brady), G. (G.) tumida tumida, and P. primalis; and the LADs of Globorotalia (Menardella) multicamerata Cushman and Jarvis, and Dentoglobigerina altispira altispira (Cushman and Jarvis). Application of a chronometric scale to part of the succession, suggests that the interval of calcareous sediment between 702.49 and 846.4 mbsf accumulated at about 30 m/m.y.

(Table 2) Comparison of annual mass fluxes measured with shallower and deeper sediment traps off Cape Blanc (CB)

The ocean off NW Africa is the second most important coastal upwelling system with a total annual primary production of 0.33 Gt of carbon per year (Carr in Deep Sea Res II 49:59-80, 2002). Deep ocean organic carbon fluxes measured by sediment traps are also fairly high despite low biogenic opal fluxes. Due to a low supply of dissolved silicate from subsurface waters, the ocean off NW Africa is characterized by predominantly carbonate-secreting primary producers, i.e. coccolithophorids. These algae which are key primary producers since millions of years are found in organic- and chlorophyll-rich zooplankton fecal pellets, which sink rapidly through the water column within a few days. Particle flux studies in the Mauretanian upwelling area (Cape Blanc) confirm the hypothesis of Armstrong et al. (Deep Sea Res II 49:219-236, 2002) who proposed that ballast availability, e.g. of carbonate particles, is essential to predict deep ocean organic carbon fluxes. The role of dust as ballast mineral for organic carbon, however, must be also taken into consideration in the coastal settings off NW Africa. There, high settling rates of larger particles approach 400 m day**-1, which may be due to a particular composition of mineral ballast. An assessment of particle settling rates from opal-production systems in the Southern Ocean of the Atlantic Sector, in contrast, provides lower values, consistent with the assumptions of Francois et al. (Global Biogeochem Cycles 16(4):1087, 2002). Satellite chlorophyll distributions, particle distributions and fluxes in the water column off NW Africa as well as modelling studies suggest a significant lateral flux component and export of particles from coastal shelf waters into the open ocean. These transport processes have implications for paleo-reconstructions from sediment cores retrieved at continental margin settings.

Raw grain-size distributions of the sediment trap time series CB 14 upper, CB 15 lower, CB 16 lower, CBi 1 upper, CBi 2 upper and CBi 3 upper

in preparation

(Table 2) Seasonal flux data and percentages of major bulk components of total flux at the mesotrophic sediment trap site CB from 1988 - 2012

A more than two-decadal sediment trap record from the Eastern Boundary Upwelling Ecosystem (EBUE) off Cape Blanc, Mauritania, is analysed with respect to deep ocean mass fluxes, flux components and their variability on seasonal to decadal timescales. The total mass flux revealed interannual fluctuations which were superimposed by fluctuations on decadal timescales. High winter fluxes of biogenic silica (BSi), used as a measure of marine production (mostly by diatoms) largely correspond to a positive North Atlantic Oscillation (NAO) index (December-March). However, this relationship is weak. The highest positive BSi anomaly was in winter 2004-2005 when the NAO was in a neutral state. More episodic BSi sedimentation events occurred in several summer seasons between 2001 and 2005, when the previous winter NAO was neutral or even negative. We suggest that distinct dust outbreaks and deposition in the surface ocean in winter and occasionally in summer/autumn enhanced particle sedimentation and carbon export on short timescales via the ballasting effect. Episodic perturbations of the marine carbon cycle by dust outbreaks (e.g. in 2005) might have weakened the relationships between fluxes and large-scale climatic oscillations. As phytoplankton biomass is high throughout the year, any dry (in winter) or wet (in summer) deposition of fine-grained dust particles is assumed to enhance the efficiency of the biological pump by incorporating dust into dense and fast settling organic-rich aggregates. A good correspondence between BSi and dust fluxes was observed for the dusty year 2005, following a period of rather dry conditions in the Sahara/Sahel region. Large changes of all bulk fluxes occurred during the strongest El Niño-Southern Oscillation (ENSO) in 1997-1999 where low fluxes were obtained for almost 1 year during the warm El Niño and high fluxes in the following cold La Niña phase. For decadal timescales, Bakun (1990) suggested an intensification of coastal upwelling due to increased winds (''Bakun upwelling intensification hypothesis''; Cropper et al., 2014) and global climate change. We did not observe an increase of any flux component off Cape Blanc during the past 2 and a half decades which might support this. Furthermore, fluxes of mineral dust did not show any positive or negative trends over time which might suggest enhanced desertification or ''Saharan greening'' during the last few decades.

Physical oceanography from the TRACTOR project

Primary Objectives - Describe and quantify the present strength and variability of the circulation and oceanic processes of the Nordic Seas regions using primarily observations of the long term spread of a tracer purposefully released into the Greenland Sea Gyre in 1996. - Improve our understanding of ocean processes critical to the thermaholine circulation in the Nordic Seas regions so as to be able to predict how this region may respond to climate change. - Assess the role of mixing and ageing of water masses on the carbon transport and the role of the thermohaline circulation in carbon storage using water transports and mixing coefficients derived from the tracer distribution. Specific Objectives Perform annual hydrographic, chemical and SF6 tracer surveys into the Nordic regions in order to: - Measure lateral and diapycnal mixing rates in the Greenland Sea Gyre and in the surrounding regions. - Document the depth and rates of convective mixing in the Greenland Sea using the SF6 and the water masses characteristics. - Measure the transit time and transport of water from the Greenland Sea to surrounding seas and outflows. Document processes of water mass transformation and entrainment occurring to water emanating from the central Greenland Sea. - Measure diapycnal mixing rates in the bottom and margins of the Greenland Sea basin using the SF6 signal observed there. Quantify the potential role of bottom boundary-layer mixing in the ventilation of the Greenland Sea Deep Water in absence of deep convection. Monitor the variability of the entrainment of water from the Greenland Sea using time series auto-sampler moorings at strategic positions i.e., sill of the Denmark Strait, Labrador Sea, Jan Mayen fracture zone and Fram Strait. Relate the observed variability of the tracer signal in the outflows to convection events in the Greenland Sea and local wind stress events. Obtain a better description of deepwater overflow and entrainment processes in the Denmark Strait and Faeroe Bank Channel overflows and use these to improve modelling of deepwater overflows. Monitor the tracer invasion into the North Atlantic using opportunistic SF6 measurements from other cruises: we anticipate that a number of oceanographic cruises will take place in the north-east Atlantic and the Labrador Sea. It should be possible to get samples from some cruises for SF6 measurements. Use process models to describe the spread of the tracer to achieve better parameterisation for three-dimensional models. One reason that these are so resistant to prediction is that our best ocean models are as yet some distance from being good enough, to predict climate and climate change.