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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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Journal ArticleDOI
TL;DR: In this paper, the authors examined the traditional interpretation of Coccolithus pelagicus as a cold water proxy based on its distribution patterns in the water column off the Portuguese coast (using data from eleven cruises) and in Holocene surface sediment samples and Quaternary cores from the same region.

156 citations

Journal ArticleDOI
01 Apr 1991-Nature
TL;DR: In this paper, the authors report measurements of 137Cs and 210Pb in cores from several stations throughout the three basins of Lake Baikal, and show that the effective settling rate of these radionuclides is the same as that in the Great Lakes.
Abstract: RADIONUCLIDES in lake sediments may act as indicators of the sedimentation rate of particles on which they are adsorbed; these rates in turn provide a direct indication of the residence times of particles in the water column. The radionuclide 137Cs is anthropogenic (an atomic-bomb product), so that its concentration in sediments also reveals the input history of this species and thus a record of atmospheric contamination by this nuclide in the lake's watershed. Here we report measurements of 137Cs and the natural radionuclide 210Pb in cores from several stations throughout the three basins of Lake Baikal. The results confirm earlier indirect estimates1 of the mean sedimentation rate, and show that the effective settling rate of these radionuclides is the same as that in the Great Lakes; the longer residence times for Lake Baikal are therefore simply a consequence of its greater depth. As well as allowing estimates of fluxes at the sediment–water interface2–1, our results provide information on the timing of palaeolimnological events5, on the existence of different depositional zones throughout the lake, on the long-term (decadal) diffusion of nuclides in sediments6 and for the development of mass-balance models for sediments and contaminants7–9.

156 citations

Journal ArticleDOI
TL;DR: Benthic incubation chambers and sediment pore water profiles were used to study early diagenesis of organic matter in equatorial Pacific sediments as mentioned in this paper, and the results of both fits indicate that at least 70% of the organic matter degradation occurs within the upper 1-2 cm of sediment.
Abstract: Benthic incubation chambers and sediment pore water profiles were used to study early diagenesis of organic matter in equatorial Pacific sediments. Replicate measurements with a flux chamber covering 720 cm2 indicated that the spatial variability of oxygen, TCO2, alkalinity, nitrate and silica fluxes at a single station did not exceed 10–35%. In contrast, diffusive fluxes of oxygen from replicate cores covering 70 cm2 at a single station often showed greater variation. In January 1992, benthic oxygen consumption was fairly constant along the equator from 103°W to 140°W at 0.6-0.8 mmol m−2 day−1. In November 1992, consumption was roughly symmetrical across the equator along 140°W, with rates of 0.6-0.8 mmol m−2 day−1 between 2°S and 2°N, declining to rates of 0.1-0.2 mmol m−2 day−1 at 12°S and 9°N. Pore water oxygen profiles were fit with a reaction-diffusion model equation to evaluate reaction kinetics. Most profiles were adequately fit with a model that assumed reaction rates declined exponentially with depth, but at low latitudes better fits often were obtained with a model that assumed decomposing organic matter has two labile components and that each decays with first-order kinetics and decreases exponentially with depth. Results of both fits indicate that at least 70% of the organic matter degradation occurs within the upper 1–2 cm of sediment. At the low-latitude stations fit with the two-component model, 70–90% of the flux is attributable to the more labile component which has an average 1/e penetration depth of 0.4 ± 0.1 cm. The more refractory component at these stations has a penetration depth of 4.4 ± 0.4 cm. From estimates of sediment mixing rates, the mean life of all degrading organic matter at the higher latitude stations is 4–55 years, while at the stations fit with the two-component model, the lifetime of the more labile fraction is weeks to months, and the lifetime of the less labile component is 40–300 years. A third carbon fraction exists at all stations that is far more refractory. The O2:CO2 stoichiometry of remineralization is −1.45 ± 0.17, and the C:N ratio is 8 ± 1. Both ratios are in good agreement with those observed from sediment trap and hydrographic studies in the water column, and suggest that degrading organic matter has about 70% of its carbon in -CH2O-groups and 30% in -CH2-groups. The C:P atom ratios for benthic remineralization differ by a factor of 3 for the two cruises, showing substantial temporal variability and de-coupling from carbon, although the mean for the two cruises (170 ± 85) is not significantly different than remineralization ratios observed in the water column. The aerally-integrated benthic respiration rate for the equatorial Pacific upwelling region is at least 25% of the integrated respiration rate for the continental margin (slope + rise) areas of the Pacific, emphasizing the importance of the equatorial Pacific sediments as a major site of benthic carbon recycling. Benthic carbon remineralization rates determined during the past decade near the equator and 140°W have varied by a factor of 2, which is not surprising given the short lifetime of the majority of the carbon degrading. The temporal patterns of carbon remineralization rates resemble those of sea-surface temperature, suggesting that benthic carbon oxidation at this site may reflect water column productivity over relatively short timescales.

156 citations

Journal ArticleDOI
TL;DR: Monitoring in the Arctic Kongsfjord on Spitsbergen from 1996 to 1998 found that organisms in the eulittoral and upper sublittoral zones are affected by UV radiation throughout the polar day, since organisms in deeper water are protected against harmful UV-B radiation.
Abstract: Solar radiation as a primary abiotic factor affecting productivity of seaweeds was monitored in the Arctic Kongsfjord on Spitsbergen from 1996 to 1998. The radiation was measured in air and underwater, with special emphasis on the UV-B (ultraviolet B, 280–320 nm) radiation, which may increase under conditions of stratospheric ozone depletion. The recorded irradiances were related to ozone concentrations measured concurrently in the atmosphere above the Kongsfjord with a balloon-carried ozone probe and by TOMS satellite. For comparison, an ozone index (a spectroradiometrically determined irradiance of a wavelength dependent on ozone concentration, standardized to a non-affected wavelength) was used to indicate the total ozone concentration present in the atmosphere. Weather conditions and, hence, solar irradiance measured at ground level were seldom stable throughout the study. UV-B irradiation was clearly dependent on the actual ozone concentration in the atmosphere with a maximal fluence rate of downward irradiance of 0.27 W m−2 on the ground and a maximal daily fluence (radiation exposure) of 23.3 kJ m−2. To characterize the water body, the light transmittance, temperature and salinity were monitored at two different locations: (1) at a sheltered shallow-water bay and (2) at a wave-exposed, deep-water location within the Kongsfjord. During the clearest water conditions in spring, the vertical attenuation coefficient (Kd) for photosynthetically active radiation (PAR) was 0.12 m−1 and for UV-B 0.34 m−1. In spring, coinciding with low temperatures and clear water conditions, the harmful UV radiation penetrated deeply into the water column and the threshold irradiance negatively affecting primary plant productivity was still found at about 5–6 m depth. The water body in spring was characterized as a Jerlov coastal water type 1. With increasing temperature in summer, snow layers and glacier ice melted, resulting in a high discharge of turbid fresh water into the fjord. This caused a stratification in the optical features, the salinity and temperature of the water body. During melt-water input, a turbid freshwater layer was formed above the more dense sea water. Under these conditions, light attenuation was stronger than defined for a Jerlov coastal water type 9. Solar radiation was strongly attenuated in the first few metres of the water column. Consequently, organisms in deeper water are protected against harmful UV-B radiation. In the surface water, turbidity decreased when rising tide caused an advection of clearer oceanic water. In the course of the summer season, salinity continuously decreased and water temperature increased particularly in shallow water regions. The impact of global climate change on the radiation conditions under water and its effects on primary production of seaweeds are discussed, since organisms in the eulittoral and upper sublittoral zones are affected by UV radiation throughout the polar day. In clearer water conditions during spring, this may also apply to organisms inhabiting greater depths.

156 citations

Journal ArticleDOI
Xiuling Bai1, Shiming Ding1, Chengxin Fan1, Tao Liu1, Dan Shi1, Lu Zhang1 
TL;DR: The proportion of extracted organic P tototal P in sediments was negatively correlated with total P in the water column, as were the proportions for orthophosphate monoesters and DNA, which implies that the majority of organic P in surface sediments is likely stabilized in some way, and does not directly contribute to the internal loading of P from sediments.

156 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023458
2022969
2021497
2020502
2019502
2018466