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Abstract. We mapped, sampled, and quantified gas emissions at the continental margin west of Svalbard during R/V Heincke cruise He-387 in late summer 2012. Hydroacoustic mapping revealed that gas emissions were not limited to a zone just above 396 m water depth. Flares from this depth have gained significant attention in the scientific community in recent years because they may be caused by bottom-water warming-induced hydrate dissolution in the course of global warming and/or by recurring seasonal hydrate formation and decay. We found that gas emissions occurred widespread between about 80 and 415 m water depth, which indicates that hydrate dissolution might only be one of several triggers for active hydrocarbon seepage in that area. Gas emissions were remarkably intensive at the main ridge of the Forlandet moraine complex in 80 to 90 m water depths, and may be related to thawing permafrost.Focused seafloor investigations were performed with the remotely operated vehicle (ROV) "Cherokee". Geochemical analyses of gas bubbles sampled at about 240 m water depth as well as at the 396 m gas emission sites revealed that the vent gas is primarily composed of methane (> 99.70 %) of microbial origin (average δ 13 C = −55.7 ‰ V-PDB).Estimates of the regional gas bubble flux from the seafloor to the water column in the area of possible hydrate decomposition were achieved by combining flare mapping using multibeam and single-beam echosounder data, bubble stream mapping using a ROV-mounted horizontally looking sonar, and quantification of individual bubble streams using ROV imagery and bubble counting. We estimated that about 53 × 10 6 mol methane were annually emitted at the two areas and allow for a large range of uncertainty due to our method (9 to 118 × 10 6 mol yr −1 ). First, these amounts show that gas emissions at the continental margin west of Svalbard were on the same order of magnitude as bubble emissions at other geological settings; second, they may be used to calibrate models predicting hydrate dissolution at present and in the future; and third, they may serve as a baseline (year 2012) estimate of the bubble flux that will potentially increase in the future due to ever-increasing global-warming-induced bottom water warming and hydrate dissociation.

Abstract. 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 largescale 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.

[1] The region off Cape Blanc along the northwest African coast is dominated by persistent upwelling and strong activity of small-scale eddies, filaments, and jets. Vertical particle camera profiles obtained during recent cruises in this region show that there exist two well-marked maxima of particle abundance in the water column, one at the surface and the other in subsurface layers between 200 m and 400 m depths. Using a highresolution (2.7 km) terrain-following coordinate ocean model with built-in ecosystem and sediment transport modules, we show that the surface particle maximum can be explained by local productivity, while the deeper, subsurface particle cloud most likely originates from particulate material eroded from the shallow shelf and transported offshore by vigorous filament activity and dynamic features of the flow. In the numerical experiments, particles are produced either by primary production in the surface layer or from prescribed sediment sources to mimic suspension and erosion along the shelf areas. Good agreement of modeled particle distributions with the data is achieved with a typical settling velocity of 5 m day À1. Time-averaged effective transport patterns of particles reveal distinct maxima between 20.5°N and 23.5°N off Cape Blanc. In the south of Cape Bojador and off Cape Timiris, on the other hand, the effective transport distance patterns suggest energetic offshore activity.Citation: Karakaş, G., N. Nowald, M. Blaas, P. Marchesiello, S. Frickenhaus, and R. Schlitzer (2006), High-resolution modeling of sediment erosion and particle transport across the northwest African shelf,

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