24 research outputs found
Editorial: Virtual paleobiology—advances in X-ray computed microtomography and 3D visualization of fossils
Calcification, Dissolution and Test Properties of Modern Planktonic Foraminifera From the Central Atlantic Ocean
The mass of well-preserved calcite in planktonic foraminifera shells provides an indication of the calcification potential of the surface ocean. Here we report the shell weight of 8 different abundant planktonic foraminifera species from a set of core-top sediments along the Mid-Atlantic Ridge. The analyses showed that near the equator, foraminifera shells of equivalent size weigh on average 1/3 less than those from the middle latitudes. The carbonate preservation state of the samples was assessed by high resolution X-ray microcomputed tomographic analyses of Globigerinoides ruber and Globorotalia truncatulinoides specimens. The specimen preservation was deemed good and does not overall explain the observed shell mass variations. However, G. ruber shell weights might be to some extent compromised by residual fine debris internal contamination. Deep dwelling species possess heavier tests than their surface-dwelling counterparts, suggesting that the weight of the foraminifera shells changes as a function of the depth habitat. Ambient seawater carbonate chemistry of declining carbonate ion concentration with depth cannot account for this interspecies difference. The results suggest a depth regulating function for plankton calcification, which is not dictated by water column acidity
Influence of surface ocean density on planktonic foraminifera calcification.
This study provides evidence that ambient seawater density influences calcification and may account for the observed planktonic foraminifera shell mass increase during glacial times. Volumes of weighed fossil Globigerina bulloides shells were accurately determined using X-ray Computer Tomography and were combined with water density reconstructions from Mg/Ca and δ18O measurements to estimate the buoyancy force exerted on each shell. After assessment of dissolution effects, the resulting relationship between shell mass and buoyancy suggests that heavier shells would need to be precipitated in glacial climates in order for these organisms to remain at their optimum living depth, and counterbalance the increased buoyant force of a denser, glacial ocean. Furthermore, the reanalysis of bibliographic data allowed the determination of a relationship between G. bulloides shell mass and ocean density, which introduces implications of a negative feedback mechanism for the uptake of atmospheric CO2 by the oceans
Influence of surface ocean density on planktonic foraminifera calcification
This study provides evidence that ambient seawater density influences calcification and may account for the observed planktonic foraminifera shell mass increase during glacial times. Volumes of weighed fossil Globigerina bulloides shells were accurately determined using X-ray Computer Tomography and were combined with water density reconstructions from Mg/Ca and δ18O measurements to estimate the buoyancy force exerted on each shell. After assessment of dissolution effects, the resulting relationship between shell mass and buoyancy suggests that heavier shells would need to be precipitated in glacial climates in order for these organisms to remain at their optimum living depth, and counterbalance the increased buoyant force of a denser, glacial ocean. Furthermore, the reanalysis of bibliographic data allowed the determination of a relationship between G. bulloides shell mass and ocean density, which introduces implications of a negative feedback mechanism for the uptake of atmospheric CO2 by the oceans
Calcification, dissolution and test properties of modern planktonic foraminifera from the central Atlantic Ocean
This research was supported in part by a Royal Society Newton International postdoctoral Fellowship to SZ from the Royal Society of London. JWBR acknowledges funding from the European Research Council under the European Union’s Horizon 2020 research and innovation program (grant agreement 805246). We also acknowledge support from U.K. NERC Grant (PUCCA) NE/V011049/1.The mass of well-preserved calcite in planktonic foraminifera shells provides an indication of the calcification potential of the surface ocean. Here we report the shell weight of 8 different abundant planktonic foraminifera species from a set of core-to sediments along the Mid-Atlantic Ridge. The analyses showed that near the equator, foraminifera shells of equivalent size weigh on average 1/3 less than those from the middle latitudes. The carbonate preservation state of the samples was assessed by high resolution X-ray microcomputed tomographic analyses of Globigerinoides ruber and Globorotalia truncatulinoides specimens. The specimen preservation was deemed good and does not overall explain the observed shell mass variations. However, G. ruber shell weights might be to some extent compromised by residual fine debris internal contamination. Deep dwelling species possess heavier tests than their surface-dwelling counterparts, suggesting that the weight of the foraminifera shells changes as a function of the depth habitat. Ambient seawater carbonate chemistry of declining carbonate ion concentration with depth cannot account for this interspecies difference. The results suggest a depth regulating function for plankton calcification, which is not dictated by water column acidity.Publisher PDFPeer reviewe
Disruption of the Atlantic Meridional Circulation during Deglacial Climates Inferred from Planktonic Foraminiferal Shell Weights
Changes in the density structure of the upper oceanic water masses are an important forcing of changes in the Atlantic Meridional Overturning Circulation (AMOC), which is believed to widely affect Earth’s climate. However, very little is known about past changes in the density structure of the Atlantic Ocean, despite being extensively studied. The physical controls on planktonic foraminifera calcification are explored here, to obtain a first-order approximation of the horizontal density gradient in the eastern Atlantic during the last 200,000 years. Published records of Globigerina bulloides shells from the North and Tropical eastern Atlantic were complemented by the analysis of a South Atlantic core. The masses of the same species shells from three different dissolution assessed sediment cores along the eastern Atlantic Ocean were converted to seawater density values using a calibration equation. Foraminifera, as planktonic organisms, are subject to the physical properties of the seawater and thus their shells are sensitive to buoyancy forcing through surface temperature and salinity perturbations. By using planktonic foraminifera shell weight as an upper ocean density proxy, two intervals of convergence of the shell masses are identified during cold intervals of the last two deglaciations that may be interpreted as weak ocean density gradients, indicating nearly or completely eliminated meridional circulation, while interhemispheric Atlantic density differences appear to alleviate with the onset of the last interglacial. The results confirm the significance of variations in the density of Atlantic surface waters for meridional circulation changes
Evidence of Stable Foraminifera Biomineralization during the Last Two Climate Cycles in the Tropical Atlantic Ocean
Planktonic foraminiferal biomineralization intensity, reflected by the weight of their shell calcite mass, affects global carbonate deposition and is known to follow climatic cycles by being increased during glacial stages and decreased during interglacial stages. Here, we measure the dissolution state and the mass of the shells of the planktonic foraminifera species Globigerina bulloides from a Tropical Eastern North Atlantic site over the last two glacial–interglacial climatic transitions, and we report no major changes in plankton calcite production with the atmospheric pCO2 variations. We attribute this consistency in foraminifera calcification to the climatic and hydrological stability of the tropical regions. However, we recorded increased shell masses midway through the penultimate deglaciation (Termination II). In order to elucidate the cause of the increased shell weights, we performed δ18O, Mg/Ca, and μCT measurements on the same shells from a number of samples surrounding this event. Compared with the lighter ones, we find that the foraminifera of increased weight are internally contaminated by sediment infilling and that their shell masses respond to local surface seawater density changes
Natural Processes and Anthropogenic Activity in the Indus River Sedimentary Environment in Pakistan: A Critical Review
The Indus River is Asia’s longest river, having its origin in the Tibet Mountain northwest of Pakistan. Routed from northern Gilgit and flowing to the plains, the river passes through several provinces and is connected by numerous small and large tributaries. The river was formed tectonically due to the collusion of the Indian and Eurasian plates, which is referred to as the Indus suture Plains zone (ISPZ). The geological setting of the study area is mainly composed of igneous and metamorphic rocks. The river passed through a variety of climatic zones and areas, although the predominant climate is subtropic arid and sub arid to subequatorial. Locally and globally, anthropogenic activities such as building, dams, and water canals for irrigation purposes, mining exploration, and industries and factories all affected the physical and chemical behaviors of the sediments in various rivers. The main effect of human activities is the reworking of weathered soil smectite, a chemical weathering indicator that rises in the offshore record about 5000 years ago. This material indicates increased transport of stronger chemically weathered material, which may result from agriculture-induced erosion of older soil. However, we also see evidence for the incision of large rivers into the floodplain, which is also driving the reworking of this type of material, so the signal may be a combination of the two. Sediments undergo significant changes in form and size due to clashing with one another in the high-charge river
Latitudinal Variation of Planktonic Foraminifera Shell Masses During Termination I
The oceans’ surface layer holds large amounts of dissolved inorganic
carbon that is exchanged rapidly with the atmosphere. Carbon enters the
ocean mainly through the dissolution of atmospheric carbon dioxide
(CO2), and a part of it is converted into carbonate by marine organisms.
Calcifying marine organisms include planktonic foraminifers that
contribute to the marine carbon turnover by generating inorganic carbon
production (CaCO3 shells). Anthropogenic CO2 acidifies the surface
ocean, changes the carbonate chemistry and decreases the saturation
state of carbonate minerals in sea water, thus affecting the biological
precipitation of carbonate shells. Relative changes in average
foraminiferal shell mass can be interpreted as variations in test
thickness and the extent of calcification that subsequently impacts the
global carbonate budgets. The response of calcifying marine organisms to
elevated atmospheric pCO(2) is diverse and complex with studies
reporting from reduced rates of net calcification to neutral receptivity
or even increased calcification intensities. This diverse behavior
implies that the concentration of dissolved inorganic carbon may not be
the dominant factor controlling the amount of carbonate shell masses.
Here we provide further evidence that glacial/interglacial variations of
planktonic foraminifera shell masses are invariant to atmospheric
pCO(2). We identify that differences in shell weights of several
planktonic foraminiferal species from narrow size intervals, over the
most recent deglaciation (Termination I) vary systematically as a
function of latitude. Past intervals of abruptly changing pCO(2) and
temperatures, such as the terminations, can offer a glimpse into the
response of marine calcifying plankton to changes in surface oceans. We
have compiled all the available bibliographic data of planktonic
foraminifera shell weights from restricted sieve fractions of different
species from the Atlantic, Pacific and Indian Oceans and we find that
for the same pCO(2) conditions planktonic foraminifera from equatorial
regions may alter their shell mass only as little as 8.2%, while
towards higher latitudes changes in shell mass reach up to 54% during
the transition from the last glacial to interglacial conditions. We
attribute this low variability in the shell mass of planktonic
foraminifera from the equator to the stability of the physical
oceanographic conditions that characterize the equatorial zone
Latitudinal Differentiation among Modern Planktonic Foraminiferal Populations of Central Mediterranean: Species-Specific Distribution Patterns and Size Variability
Studies of the spatial distribution and size of modern planktonic
foraminifera are still lacking in the Mediterranean Sea. In this study,
17 core-top sediments collected from a north-south transect along the
central Mediterranean have been analyzed for planktonic foraminiferal
content, in terms of their distributional pattern and intraspecific size
variability. Among the analyzed planktonic foraminiferal species,
Globigerina bulloides and Globigerinoides ruber (w) were the most
abundant, presenting an antagonistic behavior and an overall decreasing
trend in their average size values from Adriatic to Ionian sub-basins.
Intraspecific differences have been also documented for G. ruber (w),
with the dominant sensu stricto morphotype to present generally higher
frequencies and more constant shell sizes than sensu lato. The greater
size variability of the latter is possibly related to its adaptation in
particular hydrographic conditions based on its depth habitat preference
and ecological characteristics to reach the (sub)optimum growth
conditions. The rest of the species occur in minor percentages and show
on average 11% increase with decreasing latitude characterized by
distinct species-specific size variations along the transect. Our
results show that the relationship between planktonic foraminifera shell
size and abundance or sea surface temperature are either absent or
weaker than previously reported for other regions and that in central
Mediterranean assemblages’ size may be mainly related to nutrient
availability. Besides the environmental parameters (sea surface
temperature, primary productivity, water depth, stratification), the
possible hidden cryptic diversity, still lingers to be consistently
determined, could give a better understanding of the geographic and
morphological differentiation within the Mediterranean planktonic
populations