Fluxes of biogenic components from sediment trap deployment in circumpolar waters of the Drake Passage

Circumpolar surface waters dominate the circulation of the Southern Ocean and sustain one of the ocean's largest standing stocks of biomass thereby producing a significant output of biogenic components, mainly diatoms, to the bottom sediments. Generally transit of biogenic matter from the sea surface to the sea floor affects nutrient regeneration fuels benthic life and transfers signals to the sediment record1–5. Reliable quantification of the relationship between biological production, fractionation of skeletal and tissue components and bottom sediment accumulation depends on direct vertical flux measurements from sediment trap deployments6–9, which have proved to be most scientifically productive10–13. We now present data on vertical mass fluxes from the Southern Ocean and evidence for strong biogeochemical fractionation between organic carbon-, nitrogen- and phosphorus-containing compounds, siliceous and calcareous skeletal remains, and refractory aluminosilicates

Man and the Last Great Wilderness: Human Impact on the Deep Sea

The deep sea, the largest ecosystem on Earth and one of the least studied, harbours high biodiversity and provides a wealth of resources. Although humans have used the oceans for millennia, technological developments now allow exploitation of fisheries resources, hydrocarbons and minerals below 2000 m depth. The remoteness of the deep seafloor has promoted the disposal of residues and litter. Ocean acidification and climate change now bring a new dimension of global effects. Thus the challenges facing the deep sea are large and accelerating, providing a new imperative for the science community, industry and national and international organizations to work together to develop successful exploitation management and conservation of the deep-sea ecosystem. This paper provides scientific expert judgement and a semi-quantitative analysis of past, present and future impacts of human-related activities on global deep-sea habitats within three categories: disposal, exploitation and climate change. The analysis is the result of a Census of Marine Life – SYNDEEP workshop (September 2008). A detailed review of known impacts and their effects is provided. The analysis shows how, in recent decades, the most significant anthropogenic activities that affect the deep sea have evolved from mainly disposal (past) to exploitation (present). We predict that from now and into the future, increases in atmospheric CO2 and facets and consequences of climate change will have the most impact on deep-sea habitats and their fauna. Synergies between different anthropogenic pressures and associated effects are discussed, indicating that most synergies are related to increased atmospheric CO2 and climate change effects. We identify deep-sea ecosystems we believe are at higher risk from human impacts in the near future: benthic communities on sedimentary upper slopes, cold-water corals, canyon benthic communities and seamount pelagic and benthic communities. We finalise this review with a short discussion on protection and management methods

Microbial Ecology of Lake Kivu

peer reviewedWe review available data on archaea, bacteria and small eukaryotes in an attempt to provide a general picture of microbial diversity, abundances and microbe-driven processes in Lake Kivu surface and intermediate waters (ca. 0–100 m). The various water layers present contrasting physical and chemical properties and harbour very different microbial communities supported by the vertical redox structure. For instance, we found a clear vertical segregation of archaeal and bacterial assemblages between the oxic and the anoxic zone of the surface waters. The presence of specific bacterial (e.g. Green Sulfur Bacteria) and archaeal (e.g. ammonia-oxidising archaea) communities and the prevailing physico-chemical conditions point towards the redoxcline as the most active and metabolically diverse water layer. The archaeal assemblage in the surface and intermediate water column layers was mainly composed by the phylum Crenarchaeota , by the recently defined phylum Thaumarchaeota and by the phylum Euryarchaeota . In turn, the bacterial assemblage comprised mainly ubiquitous members of planktonic assemblages of freshwater environments (Actinobacteria, Bacteroidetes and Betaproteobacteria among others) and other less commonly retrieved phyla (e.g. Chlorobi, Clostridium and Deltaproteobacteria). The community of small eukaryotes (<5 µm) mainly comprised Stramenopiles , Alveolata , Cryptophyta , Chytridiomycota , Kinetoplastea and Choanoflagellida, by decreasing order of richness. The total prokaryotic abundance ranged between 0.5 × 10^6 and 2.0 × 10^6 cells mL−1 , with maxima located in the 0–20 m layer, while phycoerythrin-rich Synechococcus-like picocyanobacteria populations were comprised between 0.5 × 10^5 and 2.0 × 10^5 cells mL−1 in the same surface layer. Brown-coloured species of Green Sulfur Bacteria permanently developed at 11m depth in Kabuno Bay and sporadically in the anoxic waters of the lower mixolimnion of the main basin. The mean bacterial production was estimated to 336 mg C m−2 day−1 . First estimates of the re-assimilation by bacterioplankton of dissolved organic matter excreted by phytoplankton showed high values of dissolved primary production (ca. 50% of total production). The bacterial carbon demand can totally be fuelled by phytoplankton production. Overall, recent studies have revealed a high microbial diversity in Lake Kivu, and point towards a central role of microbes in the biogeochemical and ecological functioning of the surface layers, comprising the mixolimnion and the upper chemocline