scholarly journals Circulation and oxygenation of the glacial South China Sea

2016 ◽  
Author(s):  
Shuh-Ji Kao ◽  
Tzu-Ling Chiang ◽  
Da-Wei Li ◽  
Yi-Chia Hsin ◽  
Li-Wei Zheng ◽  
...  
Keyword(s):  
Organic Matter ◽  
South China Sea ◽  
Residence Time ◽  
Primary Productivity ◽  
Circulation Pattern ◽  
Water Residence Time ◽  
Reducing Environment ◽  
The Mean ◽  
Monsoon Wind ◽  
Wind Intensity

Abstract. Degree of oxygenation in intermediate water modulates the downward transferring efficiency of primary productivity (PP) from surface water to deep water for carbon sequestration, consequently, the storage of nutrients versus the delivery and sedimentary burial fluxes of organic matter and associated biomarkers. To better decipher the PP history of the South China Sea (SCS), appreciation about the glacial-interglacial variation of the Luzon Strait (LS) throughflow, which determines the mean residence time and oxygenation of water mass in the SCS interior, is required. Based on a well-established physical model, we conducted a 3-D modeling exercise to quantify the effects of sea level drop and monsoon wind intensity on glacial circulation pattern, thus, to evaluate effects of productivity and circulation-induced oxygenation on the burial of organic matter. Under modern climatology wind conditions, a 135 m sea level drop results in a greater basin closeness and a ~ 23 % of reduction in the LS intermediate westward throughflow, consequently, an increase in the mean water residence time (from 19 to 23 year). However, when the wind intensity was doubled during glacial low, the throughflow restored largely to reach a similar residence time (18.4 years) as today regardless its closeness. Comparing with present day SCS, surface circulation pattern in glacial model exhibits (1) stronger upwellings at the west off Luzon Island and the east off Vietnam, and (2) an intensified southwestward jet current along the western boundary of the SCS basin. Superimposed hypothetically by stronger monsoon wind, the glacial SCS conditions facilitate greater primary productivity. Manganese, a redox sensitive indicator, in IMAGES core MD972142 at southeastern SCS revealed a relatively reducing environment in glacial periods. Considering the similarity in the mean water residence time between modern and glacial cases, the reducing environment of the glacial southeastern SCS was thus ascribed to a productivity-induced rather than ventilation-induced consequence.

scholarly journals A modern snapshot of the isotopic composition of lacustrine biogenic carbonates – Records of seasonal water temperature variability

2021 ◽  
Author(s):  
Inga Labuhn ◽  
Franziska Tell ◽  
Ulrich von Grafenstein ◽  
Dan Hammarlund ◽  
Henning Kuhnert ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Water Temperature ◽  
Residence Time ◽  
Water Depth ◽  
Lake Water ◽  
The Other ◽  
Carbonate Precipitation ◽  
Water Residence Time ◽  
Oxygen Isotope Fractionation ◽  
The Mean

Abstract. Carbonate shells and encrustations from lacustrine organisms provide proxy records of past environmental and climatic changes. The carbon isotopic composition (δ13C) of such carbonates depends on the δ13C of dissolved inorganic carbon (DIC). Their oxygen isotopic composition (δ18O) is controlled by the δ18O of the lake water and on water temperature during carbonate precipitation. Lake water δ18O, in turn, reflects the δ18O of precipitation in the catchment, water residence time and mixing, and evaporation. A paleoclimate interpretation of carbonate isotope records requires a site-specific calibration based on an understanding of these local conditions. For this study, samples of different carbonate components and water were collected in the littoral zone of Lake Locknesjön, central Sweden (62.99° N, 14.85° E, 328 m a.s.l.) along a water depth gradient from 1 to 8 m. Samples from living organisms and sub-recent samples in surface sediments were taken from the calcifying alga Chara hispida, mollusks from the genus Pisidium, and adult and juvenile instars of two ostracod species, Candona candida and Candona neglecta. Neither the isotopic composition of carbonates nor the δ18O of water vary significantly with water depth, indicating a well-mixed epilimnion. The mean δ13C of Chara hispida encrustations is 4 ‰ higher than the other carbonates. This is due to fractionation related to photosynthesis, which preferentially incorporates 12C in the organic matter and increases the δ13C of the encrustations. A small effect of photosynthetic 13C enrichment in DIC is seen in contemporaneously formed valves of juvenile ostracods. The largest differences in the mean carbonate δ18O between species are caused by vital offsets, i.e. the species-specific deviations from the δ18O of inorganic carbonate which would have been precipitated in isotopic equilibrium with the water. After subtraction of these offsets, the remaining differences in the mean carbonate δ18O between species can mainly be attributed to seasonal water temperature changes. The lowest δ18O values are observed in Chara hispida encrustations, which form during the summer months when photosynthesis is most intense. Adult ostracods, which calcify their valves during the cold season, display the highest δ18O values. This is because an increase in water temperature leads to a decrease in fractionation between carbonate and water, and therefore to a decrease in carbonate δ18O. At the same time, an increase in air temperature leads to an increase in the δ18O of lake water through its effect on precipitation δ18O and on evaporation from the lake, and consequently to an increase in carbonate δ18O, opposite to the effect of increasing water temperature on oxygen-isotope fractionation. However, the seasonal and inter-annual variability in lake water δ18O is small (~0.5 ‰) due to the long water residence time of the lake. Seasonal changes in the temperature-dependent fractionation are therefore the dominant cause of carbonate δ18O differences between species when vital offsets are corrected. Temperature reconstructions based on paleotemperature equations for equilibrium carbonate precipitation using the mean δ18O of each species and the mean δ18O of lake water are well in agreement with the observed seasonal water temperature range. The high carbonate δ18O variability of samples within a species, on the other hand, leads to a large scatter in the reconstructed temperatures based on individual samples. This implies that care must be taken to obtain a representative sample size for paleotemperature reconstructions.

scholarly journals Water residence time in the Włocławek dam reservoir (the Vistula river, Poland) affects its macrozoobenthos structure

2018 ◽  
Vol 54 ◽  
pp. 24
Author(s):  
Daria Mimier ◽  
Elżbieta Żbikowska ◽  
Janusz Żbikowski
Keyword(s):  
Organic Matter ◽  
Residence Time ◽  
Organic Matter Content ◽  
Matter Content ◽  
Bottom Fauna ◽  
Water Residence Time ◽  
Dam Reservoir ◽  
Vistula River ◽  
Chironomidae Larvae ◽  
Potamothrix Hammoniensis

The aim of our study was to compare the macrozoobenthos structure as well as water and organic matter content of the bottom sediments of two hydrologically different zones of a strongly fluvial the Włocławek Dam Reservoir. Samples were collected from the Włocławek Dam Resevoir at six sites. Three of them were located in the upper, rheolimnic part (URP) of the reservoir and three others in its lower, limnetic part (LLP). Water transparency, sediment water content and organic matter content in the sediments were higher in the LLP. The higher number of taxa and diversity of macrozoobenthos were found in the URP of the reservoir. The density of bottom fauna was slightly higher in the LLP (90,990 ind. m−2) than in the UPR (73,486 ind.  m−2), while the significantly higher biomass of macrozoobenthos was found in the URP of the reservoir (2314 g · m−2) than in the LLP (336 g · m−2). The dominant taxa of Oligochaeta and Chironomidae larvae did not show significant differences in the density between both zones. Some taxa were found only in the URP. In this zone, significantly higher densities of other taxa were observed. The only species with greater abundance in the LLP was Potamothrix hammoniensis (Oligochaeta). Due to the very short water residence time, the differences in the parameters under study between the URP and the LLP of the reservoir were smaller as well as the abundance of the macrozoobenthos was distinctly higher than in other reservoirs.

Spatial and seasonal variations of subtidal free-living nematode assemblages in the northern Beibu Gulf, South China Sea

2011 ◽  
Vol 92 (2) ◽  
pp. 255-264 ◽  
Author(s):  
S.J. Fu ◽  
L.Z. Cai ◽  
J. Yang ◽  
X.P. Zhou ◽  
X. Peng ◽  
...  
Keyword(s):  
Organic Matter ◽  
South China Sea ◽  
Water Depth ◽  
Environmental Variables ◽  
Beibu Gulf ◽  
Free Living ◽  
Deposit Feeders ◽  
Free Living Nematode ◽  
Offshore Station ◽  
The Mean

This study determined the spatial and seasonal density, number of genera, genera composition, maturity index and trophic structure of free-living nematode assemblages in the subtidal waters of the northern Beibu Gulf, South China Sea, and explored whether these five biotic characteristics were related to various environmental variables. Based on the data derived from samples collected seasonally at nine stations, the mean densities of nematodes decreased from alongshore to offshore station in the northern Beibu Gulf. However, the number of nematode genera increased from alongshore to offshore station. Non-parametric multidimensional scaling analysis showed no clear seasonal changes for nematode assemblages in most sampling stations. Higher densities of the generaElzaliaandTricomawere found in offshore sampling stations, and a higher density of the genusCheironchuswas found in alongshore sampling stations. The mean percentage of each feeding type compared to the total numbers was highest in epigrowth feeders (2A), second highest in non-selective deposit feeders (1B), third highest in predators (2B), and lowest in selective deposit feeders (1A). There were significant negative correlations between nematode density and water depth and temperature; significant positive correlations between the number of nematode genera and water depth and salinity; and significant negative correlation between the maturity index of the nematode assemblage and organic matter. BIOENV analysis indicated that water depth, salinity, pH, median sediment particle size and organic matter were the most correlated combination of environmental variables affecting the nematode assemblages.

A modern snapshot of the isotopic composition of lacustrine biogenic carbonates: Records of seasonal water temperature variability

2021 ◽  
Author(s):  
Inga Labuhn ◽  
Franziska Tell ◽  
Ulrich von Grafenstein ◽  
Dan Hammarlund ◽  
Henning Kuhnert ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Water Temperature ◽  
Residence Time ◽  
Water Depth ◽  
Lake Water ◽  
Carbonate Precipitation ◽  
Water Residence Time ◽  
Local Conditions ◽  
Temperature Reconstructions ◽  
The Mean

<p>Carbonate shells and encrustations from lacustrine organisms provide proxy records of past environmental and climatic changes. The oxygen isotopic composition (δ<sup>18</sup>O) of such carbonates depends on water temperature during carbonate precipitation, and on the δ<sup>18</sup>O of the lake water. Lake water δ<sup>18</sup>O, in turn, is controlled by the δ<sup>18</sup>O of precipitation in the catchment, water residence time and mixing, and by evaporation. A paleoclimate interpretation of carbonate δ<sup>18</sup>O records requires a site-specific calibration based on an understanding of the local conditions.</p><p>For this study, carbonates and water were sampled in the littoral zone of lake Locknesjön, central Sweden (62.99°N, 14.85°E, 328 m a.s.l.) along a water depth gradient from 1 to 8 m. We took samples from living organisms and sub-recent samples in surface sediments of the calcifying algae <em>Chara hispida</em>, the mollusk <em>Pisidium</em>, and adult and juvenile instars of two ostracod species, <em>Candona candida</em> and <em>Candona neglecta</em>.</p><p>We show that neither the δ<sup>18</sup>O of carbonates nor the δ<sup>18</sup>O of water vary significantly with water depth, indicating a well-mixed epilimnion. The largest differences in the mean carbonate δ<sup>18</sup>O between species are caused by vital offsets, i.e. the species-specific deviation from the δ<sup>18</sup>O of inorganic carbonate which would have been precipitated in isotopic equilibrium with the water. After subtraction of these constant vital offsets, remaining differences in the mean carbonate δ<sup>18</sup>O between species can mainly be attributed to seasonal water temperature changes. The lowest δ<sup>18</sup>O values are observed in <em>C</em><em>h</em><em>ara</em> encrustations, which form during the summer months when photosynthesis is most intense. Adult ostracods, which calcify their valves during the cold season, display the highest δ<sup>18</sup>O values. This is because an increase in temperature leads to a decrease in fractionation between carbonate and water, and therefore to a decrease in carbonate δ<sup>18</sup>O. An increase in temperature also leads to an increase in the δ<sup>18</sup>O of lake water through its effect on precipitation δ<sup>18</sup>O and on evaporation, and consequently to an increase in carbonate δ<sup>18</sup>O, opposite to the temperature effect on fractionation. However, the seasonal and inter-annual variability in lake water δ<sup>18</sup>O is small (0.5‰) due to the long water residence time. Seasonal changes in the temperature-dependent fractionation are therefore the dominant cause of carbonate δ<sup>18</sup>O differences between species.</p><p>Temperature reconstructions based on “paleo-temperature” equations for equilibrium carbonate precipitation using the mean δ<sup>18</sup>O of each species and the mean δ<sup>18</sup>O of lake water are well in agreement with the observed seasonal water temperature range. The high carbonate δ<sup>18</sup>O variability of samples within a species, on the other hand, leads to a large scatter in the reconstructed temperatures based on individual samples. This implies that care must be taken to obtain a representative sample size for paleo-temperature reconstructions.</p>

Evidence for dissolved organic matter as the primary source and sink of photochemically produced hydroxyl radical in arctic surface waters

2014 ◽  
Vol 16 (4) ◽  
pp. 807-822 ◽  
Author(s):  
Sarah E. Page ◽  
J. Robert Logan ◽  
Rose M. Cory ◽  
Kristopher McNeill
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Hydroxyl Radical ◽  
Residence Time ◽  
Surface Waters ◽  
Primary Source ◽  
The Arctic ◽  
Water Residence Time ◽  
Arctic Surface ◽  
Source And Sink

Photochemical hydroxyl radical formation decreases with increasing water residence time in a system of lakes connected by streams in the Arctic.

TURNOVER OF FLUVIAL PARTICULATE ORGANIC MATTER: THE ROLES OF SEDIMENT RESIDENCE TIME AND MICROBIOTA

2019 ◽  
Author(s):  
Marisa Repasch ◽  
◽  
Joel Scheingross ◽  
Joel Scheingross ◽  
Carolin Zakrzewski ◽  
...  
Keyword(s):  
Organic Matter ◽  
Residence Time ◽  
Particulate Organic Matter

Precipitation and filtration of zinc, magnesium, copper and aluminium hydroxides

1982 ◽  
Vol 47 (12) ◽  
pp. 3362-3370
Author(s):  
Otakar Söhnel ◽  
Eva Matějčková
Keyword(s):  
Residence Time ◽  
Mean Residence Time ◽  
Filtration Resistance ◽  
Filtration Pressure ◽  
Bed Porosity ◽  
The Mean ◽  
Filtration Properties

Filtration properties of batchwise precipitated suspensions of Zn(OH)2, Mg(OH)2 and Cu(OH)2 and continuously precipitated Al(OH)3 were studied. For batchwise precipitated suspensions was verified the theoretically predicted dependence of specific filtration resistance on initial supersaturation and for the continuously precipitated Al(OH)3 the relation between the specific filtration resistance and the mean residence time of suspension in the reactor. Dependences were also recorded between the bed porosity and concentration of precipitated solutions, specific filtration resistance and used filtration pressure and the effect of aging of the batchwise precipitated suspension of Mg(OH)2on its filtration properties. The used CST method for determination of filtration characteristics of Zn(OH)2 suspension was also studied.

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