scholarly journals Glacial-interglacial changes in the surface water characteristics of the Andaman Sea: Evidence from stable isotopic ratios of planktonic foraminifera

2000 ◽  
Vol 109 (1) ◽  
pp. 153-156 ◽  
Author(s):  
S. M. Ahmad ◽  
D. J. Patil ◽  
P. S. Rao ◽  
B. N. Nath ◽  
B. R. Rao ◽  
...  
Keyword(s):  
Surface Water ◽  
Planktonic Foraminifera ◽  
Andaman Sea ◽  
Isotopic Ratios ◽  
Water Characteristics ◽  
Stable Isotopic

Stable isotopes in planktonic and benthic foraminifera from Arctic Ocean surface sediments

1988 ◽  
Vol 25 (5) ◽  
pp. 701-709 ◽  
Author(s):  
A. E. Aksu ◽  
G. Vilks
Keyword(s):  
Surface Water ◽  
Arctic Ocean ◽  
Sea Water ◽  
Ocean Surface ◽  
The Arctic ◽  
Size Fractions ◽  
Isotopic Compositions ◽  
Isotopic Analyses ◽  
Stable Isotopic ◽  
Surface Water Salinity

Oxygen and carbon isotopic analyses have been performed on the tests of Planulina wuellerstorfi and three size fractions of sinistral Neogloboquadrina pachyderma recovered from 33 Arctic Ocean surface-sediment samples. Stable isotopic compositions of N. pachyderma are found to be dependent on the test size: larger specimens show considerable enrichment in both δ18O and δ18C. The difference between the isotopic compositions of the 63–125 and 125–250 μm size fractions in N. pachyderma can be explained by biogenic fractionation effects during foraminiferal test growth. Larger (250–500 μm) N. pachyderma displayed accretions of secondary calcite, i.e., the outermost shell contained significant amounts of inorganically precipitated magnesium calcite. Thus, larger foraminifera may not be suited for down-core stable isotopic studies. There is a difference of ~2‰ between δ18O values of surface samples from the eastern and western Arctic Ocean, reflecting large differences between surface-water salinity in these regions. Therefore, oxygen isotopic data may have limited use as a chronostratigraphic tool in down-core studies in the Arctic Ocean, but we can use them to infer past variations in surface-water salinities. Planulina wuellerstorfi also showed depletions of both δ18O and δ18C in its calcite tests relative to calcite precipitated in isotopic equilibrium with ambient sea water; these depletions ranged from −0.8 to −0.9‰ in δ18Oand −1.2 to −0.9‰ in δ18C. This taxon is found to deposit its shell very close to the δ18C of ΣCO2 of bottom waters.

scholarly journals Calcification intensity in planktonic Foraminifera reflects ambient conditions irrespective of environmental stress

2013 ◽  
Vol 10 (10) ◽  
pp. 6639-6655 ◽  
Author(s):  
M. F. G. Weinkauf ◽  
T. Moller ◽  
M. C. Koch ◽  
M. Kučera
Keyword(s):  
Surface Water ◽  
Environmental Factors ◽  
Physiological Stress ◽  
Planktonic Foraminifera ◽  
Ambient Conditions ◽  
Shell Weight ◽  
Ambient Seawater ◽  
Ecological Stress ◽  
Water Composition ◽  
Oceanic Carbon

Abstract. Planktonic Foraminifera are important marine calcifiers, and the ongoing change in the oceanic carbon system makes it essential to understand the influence of environmental factors on the biomineralization of their shells. The amount of calcite deposited by planktonic Foraminifera during calcification has been hypothesized to reflect a range of environmental factors. However, it has never been assessed whether their calcification only passively responds to the conditions of the ambient seawater or whether it reflects changes in resource allocation due to physiological stress. To disentangle these two end-member scenarios, an experiment is required where the two processes are separated. A natural analogue to such an experiment occurred during the deposition of the Mediterranean sapropels, where large changes in surface water composition and stratification at the onset of the sapropel deposition were decoupled from local extinctions of planktonic Foraminifera species. We took advantage of this natural experiment and investigated the reaction of calcification intensity, expressed as mean area density (MAD), of four species of planktonic Foraminifera to changing conditions during the onset of Sapropel S5 (126–121 ka) in a sediment core from the Levantine Basin. We observed a significant relationship between MAD and surface water properties, as reflected by stable isotopes in the calcite of Foraminifera shells, but we failed to observe any reaction of calcification intensity on ecological stress during times of decreasing abundance culminating in local extinction. The reaction of calcification intensity to surface water perturbation at the onset of the sapropel was observed only in surface-dwelling species, but all species calcified more strongly prior to the sapropel deposition and less strongly within the sapropel than at similar conditions during the present-day. These results indicate that the high-salinity environment of the glacial Mediterranean Sea prior to sapropel deposition induced a~more intense calcification, whereas the freshwater injection to the surface waters associated with sapropel deposition inhibited calcification. The results are robust to changes in carbonate preservation and collectively imply that changes in normalized shell weight in planktonic Foraminifera should reflect mainly abiotic forcing.

scholarly journals Qualitative and quantitative reconstruction of surface water characteristics and recent hydrographic changes in the Trondheimsfjord, central Norway

2013 ◽  
Vol 9 (4) ◽  
pp. 4553-4598 ◽  
Author(s):  
G. Milzer ◽  
J. Giraudeau ◽  
S. Schmidt ◽  
F. Eynaud ◽  
J. Faust
Keyword(s):  
Surface Water ◽  
Sea Surface ◽  
Surface Mixed Layer ◽  
210Pb And 137Cs ◽  
The North ◽  
Water Characteristics ◽  
Run Off ◽  
Modern Analogue ◽  
The North Atlantic Oscillation ◽  
The Impact

Abstract. In the present study we investigate dinocyst assemblages in the Trondheimsfjord over the last 25 to 50 yr from three well-dated multi-cores (210Pb and 137Cs) retrieved along the fjord axis. The downcore distribution of the cysts is discussed in view of changes of the key surface water parameters sea-surface temperatures (SSTs) and sea-surface salinities (SSSs) monitored in the fjord, as well as river discharges. We examine the impact of the North Atlantic Oscillation pattern and of waste water supply from the local industry and agriculture on the fjord ecological state and hence dinocyst species diversity. Our results show that dinocyst production and diversity in the fjord is not evidently affected by human-induced eutrophication. Instead the assemblages appear to be mainly controlled by the NAO-related changes in physico-chemical characteristics of the surface mixed layer. Still, discharges of major rivers were modulated, since 1985 by the implementation of hydropower plants which certainly influences the freshwater and nutrient supply into the fjord. The impact, however, is variable according to the local geographical setting, and barely differentiated from natural changes in river run off. We ultimately test the use of the modern analogue technique (MAT) for the reconstruction of winter and summer SSTs and SSSs and annual primary productivity (PP) in this particular fjord setting. The reconstructed data are compared with time-series of SSTs and SSSs measured at 10 m water depth, as well as with mean annual PPs along the Norwegian coast and within Scandinavian fjords. The reconstructions are in general good agreement with the instrumental measurements and observations from other fjords. Major deviations can be addressed to peculiarities in the assemblages linked to the particular fjord setting and the related hydrological structure.

scholarly journals Lagoon Biogeochemical Processing is Reflected in Spatial Patterns of Sediment Stable Isotopic Ratios

2020 ◽  
Vol 8 (11) ◽  
pp. 874
Author(s):  
Elizabeth Burke Watson ◽  
Alejandro Hinojosa-Corona ◽  
Johannes R. Krause ◽  
Juan Carlos Herguera ◽  
Julianna McDonnell ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Spatial Patterns ◽  
Nitrogen Isotopes ◽  
Carbon Accumulation ◽  
Isotopic Ratios ◽  
Spatial Gradients ◽  
Seagrass Meadows ◽  
The Pacific ◽  
Stable Isotopic ◽  
Sediment Carbon

The spatial analysis of biota, particulate organic matter, and sediments for stable isotopes of carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) have proved useful for identifying patterns in productivity, nutrient pollution, and relationships between biological and physiochemical variables at the local and global scales. Yet such approaches are rarely applied to studies of lagoon or estuarine metabolism. Focusing on Bahía San Quintín, a heterotrophic seagrass-dominated lagoon on the Pacific coast of Baja California, México, we report on spatial patterns in surficial sediment CNS stable isotopic ratios as tracers of lagoon biogeochemical function. Stable nitrogen isotopes highlighted potential spatial variability in the balance between denitrification and nitrogen-fixation within the lagoon and identified an association between elevated δ15N levels and oyster culture, suggesting that oyster presence may be enhancing N2 production. Spatial patterns in δ34S covaried with sediment particle size, underlining the importance of sediment texture in determining the depth of sub-oxic-anoxic redox zones. Sediment carbon stable isotope ratios highlighted the lack of incorporation of seagrass carbon into seagrass meadow sediments, thus emphasizing the importance of phytoplankton or microphytobenthos for carbon accumulation in seagrass meadows. This report highlights the value of sediment isotopic values in corroborating spatial patterns in estuarine metabolism or macronutrient processing identified from chamber or flux-based studies. Stable isotope mapping can provide a useful addition to assessment of estuarine metabolism, or act as a stand-alone tool for generating hypotheses, identifying the influence of spatial gradients, and/or suggesting prime locations for investigation of microbial abundance or function.

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