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Water column
About: Water column is a research topic. Over the lifetime, 13706 publications have been published within this topic receiving 496626 citations.
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TL;DR: An oceanographic transet, extending from Yugoslavia across the Northern Adriatic Sea to the Po delta in Italy, was occupied during 1972 and 1973 to establish the effect of Po river discharge on the phytoplankton communities of the region, suggesting borderline nutrient conditions.
Abstract: An oceanographic transet,, extending from Yugoslavia across the Northern Adriatic Sea to the Po delta in Italy, was occupied during 1972 and 1973 to establish the effect of Po river discharge on the phytoplankton communities of the region. Density distribution showed distinct seasonal features: a winter-spring period of low stability throughout the water column, and a summer period of stratification. The total water-column plant nutrients (nitrate, nitrite, phosphate, silicate) showed a 1.3 to 4.5-fold decrease eastward, with semi-eutrophic conditions restricted to an area off the Po delta. Nannoplankton usually dominated the phytoplankton community, in terms of cell density, surface chlorophyll a concentrations, and surface primary production rates. However, all significant maxima in these characteristics resulted from increases in the microplankton component. Changes in the frequency of major microplankton groups characterized three periods of the annual cycle: September–December, neritic, temperate diatom flora with some littoral elements (e.g. Nitzschia seriata); January–May, neritic, temperate diatom flora of different composition (e.g. Lauderia borealis, Skeletonema costatum); May–August, dinoflagellates (e.g. Prorocentrum micans) at western stations and dinoflagellates plus neritic, warm-water diatoms at eastern stations. The seasonal cycle was characterized by spring and fall maxima tending to coincide with maximum Po river discharge and/or periods of low water-column stability and vertical mixing. The higher nutrient input at western stations was correlated with the co-dominance of only a few species of microplankton during bloom periods, suggesting that these species (S. costatum, N. seriata, and 5 others) can serve as indicators of eutrophic conditions in this region. Assimilation ratios of both the micro- and nannoplankton suggested borderline nutrient conditions. Phosphate was implicated as the limiting nutrient.
120 citations
TL;DR: In this article, a simple box model was used to estimate the water-mass balance and nutrient budgets for the Yellow Sea, which showed that net sink of NO3−, NH4+ and SiO32− can be mainly from water column into bottom sediments and/or transform to other forms of nitrogen.
120 citations
TL;DR: In this paper, a synthesis of recent oceanic observations and paleo-data is shown that certain species of giant diatoms including Rhizosolenia spp. and Ethmodiscus rex may become concentrated at oceanic frontal zones and subsequently form episodes of mass flux to the sediment.
Abstract: From a synthesis of recent oceanic observations and paleo-data it is evident that certain species of giant diatoms including Rhizosolenia spp. Thalassiothrix spp. and Ethmodiscus rex may become concentrated at oceanic frontal zones and subsequently form episodes of mass flux to the sediment. Within the nutrient bearing waters advecting towards frontal boundaries, these species are generally not dominant, but they appear selectively segregated at fronts, and thus may dominate the export flux. Ancient Thalassiothrix diatom mat deposits in the eastern equatorial Pacific and beneath the Polar Front in the Southern Ocean record the highest open ocean sedimentation rates ever documented and represent vast sinks of silica and carbon. Several of the species involved are adapted to a stratified water column and may thrive in Deep Chlorophyll Maxima. Thus in oceanic regions and/or at times prone to enhanced surface water stratification (e.g., during meltwater pulses) they provide a mechanism for generating substantial biomass at depth and its subsequent export with concomitant implications for Si export and C drawdown. This ecology has important implications for ocean biogeochemical models suggesting that more than one diatom “functional type” should be used. In spite of the importance of these giant diatoms for biogeochemical cycling, their large size coupled with the constraints of conventional oceanographic survey schemes and techniques means that they are undersampled. An improved insight into these key species will be an important prerequisite for enhancing our understanding of marine biogeochemical cycling and for assessing the impacts of climate change on ocean export production.
120 citations
TL;DR: An international sampling cruise, the IAEA’97 NW Pacific Expedition, was carried out in 1997 with the primary objective of contributing to better understanding of the present distributions of radionuclides in the open ocean and of the processes affecting their distributions in the water column as mentioned in this paper.
Abstract: An international sampling cruise, the IAEA’97 NW Pacific Expedition, was carried out in 1997 with the primary objective of contributing to better understanding of the present distributions of radionuclides in the open ocean and of the processes affecting their distributions in the water column, to study the sources which have introduced radionuclides to the Pacific Ocean, and to compare present results with historical data sets obtained from the previous expeditions (e.g., the Geochemical Ocean Sections Programme, GEOSECS). The observed temperature, salinity, dissolved oxygen, and silicate levels in water samples collected showed differences in the upper 1000 m layer in all studied profiles. Transuranics water profiles showed typical sub-surface maxima, with concentrations less by about a factor of 4 than the GEOSECS results, at depths greater by about a factor of 2 and a decrease in the water column inventory by about 20% over 24 years, which were less a function of particle-driven vertical processes and more in response to water mass circulation in the region. Increases in concentrations were observed in deep water near the sea floor. Transuranics inventories in the water column substantially exceeded those expected from global fallout. 90Sr and 137Cs data confirm that the observed changes in concentration profiles have resulted from physical circulation of the regional water masses and transport of radionuclides to deep waters. The IAEA’97 results present the most comprehensive recent study on the distribution of 239,240Pu, 90Sr and 137Cs in the NW Pacific Ocean with a description of the behaviour of these radionuclides in the water column and the effects of the physical forcing of water mass circulation over the last 24 years.
119 citations
TL;DR: In this paper, the authors used an improved adsorptive cathodic stripping square-wave voltametry method to determine vertical profiles of three operationally defined fractions of iron in the western North Atlantic Ocean.
Abstract: We used an improved adsorptive cathodic stripping square-wave voltametry method to determine vertical profiles of three operationally defined fractions of iron in the western North Atlantic Ocean. “Dissolved Fe” ( 0.4-pm fraction) increased from 0.1 nM in the surface water to 1.3 nM at depths below 1,000 m. Our results suggest the need to consider the temporal variation of iron and its size fractions in seawater if we are to understand the influence of iron on phytoplankton production in the ocean.
119 citations