Primary production in the oceans results from allochthonous nutrient inputs to the euphotic zone (new production) and from nutrient recycling in the surface waters (regenerated production). Global new production is of the order of 3.4−4.7 × 109 tons of carbon per year and approximates the sinking flux of paniculate organic matter to the deep ocean.

Particulate organic matter flux and planktonic new production in the deep ocean

Role of large particles in the transport of elements and organic compounds through the oceanic water column

The distribution of 234Th, 230Th, and 228Th between dissolved and particulate forms was determined in 17 seawater samples from the Guatemala and Panama basins. Sampling was carried out in situ with battery-powered, submersible pumping systems in which the seawater first passed through a Nuclepore filter (1.0-μm pore size) and then through a cartridge packed with Nitex netting that was impregnated with MnO2 to scavenge the dissolved Th isotopes. Natural 234Th was used as the tracer for monitoring the efficiency of scavenging. For all three isotopes, most of the activity was found in the dissolved form. On the average 4% of the 234Th, 15% of the 228Th, and 17% of the 230Th occurred in the particulate form, though the percentages were found to be strongly dependent on particle concentration. These distributions are not consistent with chemical scavenging models that assume irreversible uptake of Th on particle surfaces. The results can be explained, however, if continuous exchange of Th isotopes between seawater and the particle surfaces is assumed. Vertical profiles of both particulate and dissolved 230Th show increasing concentrations with depth, as required by the assumption of reversible exchange. Some of the dissolved 230Th profiles, however, show a reversal of this trend near the bottom, indicating accelerated scavenging near the water/sediment interface. Kinetics of both adsorption and desorption can be examined if at least two Th isotopes are measured in the same samples. Results show that reaction times are short (a few months) compared to the residence time of suspended matter in the deep ocean (several years), indicating that particles suspended in the deep sea are close to equilibrium with respect to exchange of metals at their surfaces.

Distribution of thorium isotopes between dissolved and particulate forms in 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.

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Man and the last great wilderness: human impact on the deep sea.

The elemental composition of plankton

Zirconium-95--niobium-95 and Ce/sup 144/ were detected by gamma spectrometry in two samples of sea-cucumbers collected off the Oregon coast west of Newport in April 1963. Sea-cucumbers of the genus Paelopatides were found at 2800 m, 65 miles offshore; Stichopus californicus were taken in 200 m of water 25 miles off Newport. The gamma spectra of the two benthic sediment feeders were remarkably similar, except for a lower Zn/sup 65/ peak in the spectrum of Paelopatides sp. It is suggested that biological processes are responsible for the relative abundance of fission products in deep bottom feeders. It was concluded that fallout radionuclides can reach the ocean bottom quite rapidly under certain conditions, and it is proposed that the great numbers of herbivorous zooplankton in the upper layers of the ocean are largely responsible for this phenomenon. (P.C.H.)

Acceleration of Sinking Rates of Radionuclides in the Ocean

Deep-sea sedimentation and sediment-fauna interaction in Cascadia Channel and on Cascadia Abyssal Plain☆

Ecology of North American Arctic continental shelf benthos: a review

The ice fauna in the shallow southwestern Beaufort Sea, Arctic Ocean

Benthic macro-infauna were sampled in the northeast Pacific Ocean at 12 stations on an east-west transect across Cascadia and Eastern Tufts abyssal plains to determine ecological effects of continental influences and depth on those communities. The two plains, separated by the East Pacific Rise, differ in depth and distance from the continental margin. Tufts Plain lies to the west; primary production in the overlying water and the amount of organic carbon in the surface sediments are lower than for the Cascadia Plain region. Five benthic ecological zones were distinguished: (1) Cascadia Plain Slope-Base; (2) Eastern Cascadia Plain; (3) Cascadia Deep-Sea Channel; (4) Western Cascadia Plain; and (5) Eastern Tufts Plain. These differ in faunal biomass, numerical density, gross composition of the fauna by phyla, and composition of sediment. Comparatively, the slope-base environment supports the most abundant fauna. The numerical density of infauna on Eastern Tufts Plain is similar to that on Eastern and Western Cascadia Plain; however, the biomass tends to be lower in the deeper, more distant environment. It is concluded that these differences in the benthic fauna are probably caused by varying levels of input from primary production in overlying waters and differences in the transport of organic-rich particles off the continental shelf. Distance-related environmental characteristics are shown to be critical in the deep sea for controlling benthic community structure. On Cascadia Abyssal Plain, a plateau-like feature, the gross structure of communities changes with increasing distance from the continent but at constant depth. Faunal densities, biomass, and composition by phyla lie within the range of values normally associated with upper abyssal environments.

Andrew G. Carey

Papers

Acceleration of Sinking Rates of Radionuclides in the Ocean

Deep-sea sedimentation and sediment-fauna interaction in Cascadia Channel and on Cascadia Abyssal Plain☆

Ecology of North American Arctic continental shelf benthos: a review

The ice fauna in the shallow southwestern Beaufort Sea, Arctic Ocean

A comparison of benthic infaunal abundance on two abyssal plains in the northeast Pacific Ocean