Controls on the vertical fluxes of the Southern Ocean

with polyacrylamide gel allowing preservation of sinking material in its original shape. Gels were processed on board using stereomicroscopy and digital camera to identify the different particle types (faecal pellet, marine snow aggregates, individual cells, etc.).

The combination of deployments at the base of the mixed layer will provide quantitative and qualitative information on the origin of sinking particles and processes leading to the export of organic matter and biogenic silica from the euphotic zone. At 300 m depth deployments will provide an estimation of the magnitude of flux in the deeper layers (> 300 m) as well as main processes leading to flux attenuation and particle transformation that occur primarily in the upper 200 m of the water column.

Direct measurements of size-specific sinking speed and microbial respiration on different particle types (marine snow aggregates and salp faecel pellets) were performed in the laboratory using a flow chamber and oxygen microsensors.

Water samples from stations PS79/64 and 142 taken at the depth of maximum fluorescence was incubated to form marine snow aggregates using roller tanks.

Sediment traps were deployed at stations PS79/84, 86, 87, 91, 98, 100, 114, 128, 136, 137, 139, 140, and 174.

In addition to short-term surface traps a long-term (1 year) mooring was deployed in the Georgia Basin (Fig. 14.3) in order to study seasonality in the composition and magnitude of fluxes to the deep ocean in an area that is naturally fertilized by iron supply from the shelves around South Georgia.

Preliminary results

Fig. 14.1 shows the collected material for one of the upper (100 m) and the lower (300 m) trap cylinders from four different deployments. The small difference in the amount of material collected at 100 and 300 m indicates that a large part of the particles settled to deeper layers and degradation of settling material was rather low during our study.

Fig. 14.1: Photographs of sediment trap cylinders with collected material from 100 and 300 m depths at four different stations. Station number, duration and depth of trap

cylinder are indicated for each deployment above the photographs.

From material preserved within the gel traps different particle types could be identified. Fecal pellets seemed to dominate fluxes at the peak of the bloom while marine snow became more abundant as the chlorophyll a concentrations in the surface layers decreased. The dominant faecal pellet types differed between stations but consisted mainly either krill or salp pellets. The seemingly high fluxes at 300 m depth could be explained by the dominance of fecal pellets in the settling material, since our onboard measurements showed high sinking speeds of salp pellets reaching 900 m d^-1 for very large pellets (see Fig. 14.2). However, sinking speeds of a few hundreds meter per day may be more realistic for in-situ settling velocity of salp pellets. Observations of salp pellets showed two different types of pellets: - one solid and seemingly fresh pellet type with high sinking speeds - a more loose and possibly partly degraded pellet type with low sinking speeds (see Fig. 14.2). The loose salp pellets resembled marine snow aggregates in appearance and sinking speed which averaged around 100 m d^-1 similar to values measured for marine snow aggregates formed in the roller tank incubations (data not shown).

14. Controls on the vertical fluxes of the Southern Ocean

Data management

Data collected during this cruise will be deposited in PANGAEA.

references

Abelmann A, Gersonde R, Cortese G, Kuhn G, Smetacek V (2006). Extensive phytoplankton blooms in the Atlantic sector of the glacial Southern Ocean. Paleoceanography 21:

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Fowler SW, and Knauer GA (1986). The role of large particles in the transport of elements and organic compounds through the oceanic water column. Prog. Oceanogr. 16: 147-194.

Klaas C, Archer D (2002). Association of sinking organic matter with various types of mineral ballast in the deep sea: Implications for the rain ratio hypothesis. Global Biogeochemical Cycles, 16, doi: 10.1029/2001GB001765.

Sachs O, Sauter EJ, Schluter M, van der Loeff MMR, Jerosch K, Holby O (2009). Benthic organic carbon flux and oxygen penetration reflect different plankton provinces in the Southern Ocean. Deep-Sea Research Part I-Oceanographic Research Papers 56: 1319-1335

Volk, T, Hoffert MI (1985). Ocean carbon pumps: analysis of relative strengths and efficiencies in ocean-driven atmospheric CO₂ changes, p. 99-110. In E. T. Sundquist and W. S. Broecker [eds.], The Carbon Cycle and Atmospheric CO₂: Natural Variations Archean to Present. AGU.

SYSTCO II

The scientific approach of SYSTCO II is based on the first venture and aims to pursue the international and interdisciplinary investigations of the seafloor which had started during ANDEEP-SYSTCO I in 2007/2008 in the Southern Ocean deep sea.

The research area included those stations

that were sampled during the “Eddy Pump” project.

SYSTCO builds on the close cooperation of scientists from different disciplines, such as physical oceanography, planktology, biogeochemistry, sedimentology, and bathymetry with benthologist concentrating on various aspects to shed light on atmospheric-pelagic-benthic coupling processes. This has already been performed with remarkable success on the SYSTCO I cruise.

Our contribution to SYSTCO II focussed on three aspects:

Diversity, distribution and abundance of deep-sea organisms from meiofaunal foraminifera to megafaunal organisms in relation to surface water productivity and sedimentation of organic material to the seafloor.

Ecology of deep-sea fauna with regard to coupling processes utilizing different approaches, like traditional and molecular gut content analyses as well as biochemical investigations (fatty acid profiles and stable isotope C and N ratios).

DNA preservation in the water column and the deep-sea sediments and its possible use to study the eukaryotes diversity in the present and the past.

Data management

Unless stated differently in the respective chapters, all SYSTCO II contributions are subject to the same data management. Metadata of SYSTCO-II can be provided for PANGAEA, however, after final determination and publication of the data, species data will be made available to the public via SCAR-MarBIN (SCAR-Marine Biodiversity Information Network), GBIF or EurOBIS like during previous expeditions, such as SYSTCO or ANDEEP or to the new Antarctic subproject of GBIF (Global Biodiversity Information Facility), ANTABIF (Antarctic Biodiversity Information Facility). Furthermore, all Antarctic species published are reported to Register of Antarctic Marine Species (RAMS). Genetic sequences are standardly submitted to the Genebank.