Calcification Depth Research Articles

Calcification and ecological depth preferences of the planktonic foraminifer Trilobatus trilobus in the central Atlantic.

Understanding the controls behind the calcification and distribution of planktonic foraminifera in the modern ocean is important when these organisms are used for palaeoceanographic reconstructions. This study combines previously reported shell mass data with new shell geochemistry, light microscopy and X-ray micro-computed tomography analyses to dissect various parameters of Trilobatus trilobus shells from surface sediments, investigating the factors influencing their biometry. The goal is to understand which aspects of the marine environment are critical for the calcification and vertical distribution of this species. Trilobatus trilobus is found to produce larger, thinner and overall lighter shells in equatorial regions than in subtropical gyre regions, where the shells are up to 4% smaller, more than 60% thicker and approximately 45% heavier. The skeletal mass percentage together with other calcification metrics (shell weight and thickness) are found to depend primarily on ambient seawater salinity rather than carbonate chemistry. In line with their degree of calcification, on the basis of geochemically reconstructed apparent calcification depths, this group of organisms is found shallower in the water column at the Equator and the subtropical gyres, while its habitat deepens in between these regions at the extra-equatorial sites. Furthermore, it is demonstrated that in the (central) Atlantic, it occupies a density layer slightly below the salinity maximum isopycnal at various depths, presumably by adjusting its shell properties.

The vertical calcification mode of planktonic foraminifera in the Western Pacific Warm Pool

A thorough knowledge of the ecology of planktonic foraminifera throughout the water column is necessary for a reliable reconstruction of the paleooceanographic environment of the upper-middle water column. However, little is known about the planktonic foraminifera in the Western Pacific Warm Pool (WPWP), especially for the deep dwelling species. Here we present the stable oxygen isotope (δ18O) data of eight species collected from vertically stratified plankton tows across 0–500 m water depth from 5 sites in the WPWP during autumn, the vertical mode of foraminiferal calcification is explored. Vertical plankton tows provide more detailed information than other materials, it indicates a wider depth range of foraminiferal calcification than the other sample types. All the species exhibit a complex vertical calcification process that the majority of specimens precipitate their tests out of the depth at which they were obtained. It could be connected to the intricate hydrological conditions in the WPWP and/or the foraminiferal ontogenetic trajectory. Calcification depth range of the investigated species is substantially smaller than their living depth, and most of them prefer to calcify inside the abundant layers. Additionally, we found no clear correlation between foraminiferal test size and shell δ18O for any of the species that were studied at any of the locations.

Morphotypical and Geochemical Variations of Planktic Foraminiferal Species in Siberian and Central Arctic Ocean Core Tops

Abstract In this work, we utilize a transect of core top, mid- to late Holocene, sediments from the Eastern Siberian Sea to the central Arctic Ocean, spanning gradients in upper-ocean water column properties, to examine regional planktic foraminiferal species abundances and geochemistry. We present species- and morphotype-specific foraminiferal assemblages at these sites and stable isotope analyses of neogloboquadrinids. We find little variation in planktic species populations, and only small variations in N. pachyderma morphotype distributions, between sites. Spatial averages of N. pachyderma morphotype and N. incompta δ18O values show no significant differences, suggesting a similar calcification depth for all morphotypes of N. pachyderma and N. incompta across our sites, which we estimate to be between ∼ 50–150 m. Values of δ18O of a group of unencrusted specimens delineate a shallower calcification habitat. Neogloboquadrina pachyderma-2 Mg/Ca values yield temperatures outside the range of observations using available calibration equations, pointing toward the need for more Arctic-specific Mg/Ca-temperature calibrations.

Calcification depth of pteropods in the Coral Sea using stable oxygen isotopes

Pteropods are marine holoplanktonic gastropods inhabiting epipelagic and mesopelagic waters with a wide distribution from tropical to polar regions. However, their ontogeny and calcification depth/habitat depth are not well understood. To this end, we analyzed the stable oxygen isotopic composition of five pteropod species (Diacavolinia angulata, Diacavolinia longirostris, Heliconoides inflatus, Limacina bulimoides and Telodiacria quadridentata) from two multicores recovered offshore north-eastern Australia between 15°S and 26°S in the Coral Sea. We applied the Limacina dissolution index (LDX) to evaluate the preservation status of the pteropods, which revealed very good to moderate aragonite preservation at both locations. Comparison of the pteropod shell oxygen isotopic composition with predicted aragonite equilibrium oxygen isotope values implies calcification depths of 50 ± 20 m for D. longirostris and 75 ± 30 m for D. angulata, suggesting that they predominantly calcify in the mixed layer during austral summer. The apparent calcification depths of T. quadridentata and H. inflatus at 90 ± 30 m and 120 ± 30 m at both sites indicate a year-round, lower mixed layer and upper thermocline habitat depth, respectively, while T. quadridentata appear to calcify at temperatures above 22 °C. The calcification depth of L. bulimoides is deeper (100 ± 15 m) at the northern station and shallower (75 ± 30 m) at the southern station that might also hint to a temperature control. The relative narrow calcification depth ranges of the investigated pteropod species in the Coral Sea bolster their potential for reconstructing past ocean conditions at the mixed layer and thermocline.

Benthic Foraminiferal Mn/Ca as Low‐Oxygen Proxy in Fjord Sediments

AbstractFjord systems are typically affected by low‐oxygen conditions, which are increasing in extent and severity, forced by ongoing global changes. Fjord sedimentary records can provide high temporal resolution archives to aid our understanding of the underlying mechanisms and impacts of current deoxygenation. However, such archives can only be interpreted with well‐calibrated proxies. Bottom‐water oxygen conditions determine redox regime and availability of redox‐sensitive trace elements such as manganese, which in turn may be recorded by manganese‐to‐calcium ratios (Mn/Ca) in biogenic calcium carbonates (e.g., benthic foraminifera tests). However, biological influences on Mn incorporation (e.g., species‐specific Mn fractionation, ontogeny, living and calcification depths) are still poorly constrained. We analyzed Mn/Ca of living benthic foraminifera (Bulimina marginata, Nonionellina labradorica), sampled at low‐ to well‐oxygenated conditions over a seasonal gradient in Gullmar Fjord, Swedish West coast (71–217 μmol/L oxygen (O2)), by laser‐ablation ICP‐MS. High pore‐water Mn availability in the fjord supported Mn incorporation by foraminifera. B. marginata recorded contrasting Mn redox regimes sensitively and demonstrated potential as proxy for low‐oxygen conditions. Synchrotron‐based scanning X‐ray fluorescence nanoimaging of Mn distributions across B. marginata tests displayed Mn/Ca shifts by chambers, reflecting bottom‐water oxygenation history and/or ontogeny‐driven life strategy preferences. In contrast, Mn/Ca signals of N. labradorica were extremely high and insensitive to environmental variability. We explore potential biologically controlled mechanisms that could potentially explain this species‐specific response. Our data suggest that with the selection of sensitive candidate species, the Mn/Ca proxy has potential to be further developed for quantitative oxygen reconstructions in the low‐oxygen range.

The pteropod species Heliconoides inflatus as an archive of late Pleistocene to Holocene environmental conditions on the Northwest Shelf of Australia

There is growing interest in the use of pteropods as potential archives of past changes in ocean chemistry. However, pteropods have rarely been used in studies of millennial-scale sedimentary records, especially in shallow-marine environments. This study obtained core data for the last 16 kyr from the Northwest Shelf of Australia (NWS). Changes in the carbonate saturation state were assessed based on the carbon isotope ratios (δ13C) of shells and the Limacina dissolution index (LDX) measured on the planktonic pteropod species Heliconoides inflatus. In addition, the calcification depth of the pteropods was estimated based on oxygen isotope values (δ18O) of pteropod shells and seawater. Our findings indicate that H. inflatus calcifies at a depth of 95–140 m. This confirms that H. inflatus records a shallow-marine signal on the NWS. The δ13C values of the pteropods record a notable decrease in carbonate ion concentrations after 8.5 ka. This decrease is associated with the post-glacial onset of humid conditions on the NWS. The studied pteropod shells are pristine throughout the 16 kyr section and have low LDX values. Therefore, the LDX proxy appears to lack the sensitivity to be applicable in this highly supersaturated, shallow-marine environment. Until this study, proxies derived from H. inflatus have been exclusively utilized in open-marine settings. Our results indicate that the δ13C values of H. inflatus also represent a useful proxy for carbonate ion concentrations in shallow-marine environments.

Barium enrichment in the non-spinose planktic foraminifer, Globorotalia truncatulinoides

Observations of elevated barium-to-calcium ratios (Ba/Ca) in Globorotalia truncatulinoides have been attributed to contaminant phases, deep calcification depth and diagenetic processes. Here we investigate intra- and inter-test Ba/Ca variability in the non-spinose planktic foraminifer, G. truncatulinoides, from a sediment trap time series in the northern Gulf of Mexico to gain insights into the environmental influences on barium enrichment in this and other non-spinose species. We use laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to differentiate between the elemental composition of the crust and lamellar calcite in non-encrusted (<150 m calcification depth) and encrusted (>150 m calcification depth) specimens of G. truncatulinoides. We find that the Ba/Ca ratio in lamellar calcite is between two and three orders of magnitude higher (10–280 μmol/mol) than that of the crust (0–3 μmol/mol). We include seasonal water column profiles of the Ba/Ca ratio in the northern Gulf of Mexico and determine that the vertical gradient in seawater barium concentration cannot account for the intra-test Ba/Ca variations in G. truncatulinoides. We find the Ba/Ca ratio of the crust to be within the range observed in co-occurring spinose species of foraminifera (pink and white chromotypes of Globigerinoides ruber, and Orbulina universa) while the range of Ba/Ca in lamellar calcite is consistent with co-occurring non-spinose foraminifera (Pulleniatina obliquiloculata, Globorotalia menardii, G. tumida, and Neogloboquadrina dutertrei). Our data are consistent with the hypothesis that G. truncatulinoides calcifies in a marine snow aggregate microenvironment that is enriched in barium relative to ambient seawater. We suggest that G. truncatulinoides crust is formed after the rhizopodia retract and the foraminifer detaches from its marine snow substrate.

Stable oxygen isotopes in planktonic foraminifera from surface sediments in the California Current system

Stable oxygen isotopes of Globigerinoides ruber s.l. and Globigerina bulloides have been widely used to infer the variability of the water column hydrographic structure over various time scales. However, the reliability of this geochemical tool requires a regional analysis since the inferred calcification depth and temperature of planktonic foraminifera depend on local environmental conditions. In the present study, δ18O values of G. ruber s.l and G. bulloides collected from 21 surface sediment samples were used to infer their calcification depth in the southwestern margin of the Baja California peninsula. The δ18O values of G. ruber s.l. represented oceanographic conditions from warm tropical water masses (summer-autumn), while G. bulloides represented upwelling conditions and cold-water masses (winter-spring). Estimated calcification depths ranged from 0 to 30 m for both species. The isotopic difference between them (1.2‰ in this study and 1.1‰ in the Guaymas basin sediment trap) suggests a sea temperature difference of ~5 °C, which is very similar to the difference inferred from the Mg/Ca ratio for both species 3 to 14 ka. This suggests that G. ruber s.l. and G. bulloides have calcified over the same depth interval but under contrasting seasonal oceanographic conditions i.e. upwelling (winter-spring) and stratification of the water column (summer-autumn).

The influence of seasonal calcification depth change on the planktonic foraminiferal stable oxygen isotope signal

Seasonal changes in temperature and habitat migration both leave large imprints on the stable oxygen isotope composition (δ18O) of planktonic foraminiferal tests, but little is known about how much the depth habitat change affects the calcite δ18O on seasonal timescales, potentially introducing numerous errors to the study of seasonality applied individual foraminifera. In this study, two time series sediment trap moorings deployed in the northern South China Sea (SCS) from July 2012 to April 2013 and southern SCS (upwelling area) from April to October 2014 were used to infer seasonal calcification depth variations for four commonly used planktonic foraminiferal species, Globigerinoides ruber, Trilobatus sacculifer, without a sac-like final chamber, Pulleniatina obliquiloculata and Neogloboquadrina dutertrei by analyzing their test δ18O values. The findings demonstrate that planktonic foraminifera deposit their tests shallower in the winter and during cold water upwelling activity, and deeper in the summer, with a changing seasonal depth habitat for all species that tends to follow the isothermals. More importantly, we devised a new approach for quantifying the effect of seasonal calcification depth changes on the δ18O signature of planktonic foraminiferal tests. After applying this method to our trap site and nine other published global sediment trap sites, the results show that foraminiferal seasonal δ18O signal is strongly distorted (amplified or damped) by seasonal variations in their habitat depth, particularly for the species living in low latitude, attributed to the strong vertical temperature gradient relative to the seasonal temperature change at a given water depth. Surface water species that live in the homogeneous mixed layer may be able to provide the most comprehensive seasonality information.

Constraining calcification habitat using oxygen isotope measurements in tropical planktonic foraminiferal tests from surface sediments

Geochemical signals from planktonic foraminiferal tests provide a wide array of tools to investigate past hydrographic changes, but these techniques are limited by our understanding of the habitat at which these organisms form their shell. Quantitative constraints on the variability of the calcification habitat of these organisms can thus lead to better interpretations of these signals and more quantitative constraints on indirect properties related to these signals. We compiled oxygen isotope data from the Tropics to investigate global trends in the apparent calcification depth (ACD) of commonly used planktonic foraminifera. Using Globigerinoides ruber albus, Trilobatus sacculifer, Globorotalia tumida, Neogloboquadrina dutertrei and Pulleniatina obliquiloculata, we find that our ACD estimates for the global tropics largely match regional ACD estimates from other studies. G. ruber and T. sacculifer seem to calcify in the surface mixed layer with a mean ACD and 95% confidence interval of 17 [0,86] m and 48 [0,128] m, respectively, and G. tumida, N. dutertrei, and P. obliquiloculata seem to calcify below the mixed layer with a mean ACD of 210 [123,385] m, 114 [42,173] m, and 94 [0,169] m, respectively. The global data set enables the determination of calcification depths across locations with a wide range of thermocline depths. We find that G. tumida exhibits a calcification depth that is more spatially invariant, while N. dutertrei and P. obliquiloculata seem to calcify deeper in the water column in regions where the thermocline is deeper, as has been previously suggested.

Paleoceanographic significance of Globigerinoides ruber (white) morphotypes from the Andaman Sea

Globigerinoides ruber (white), a tropical to sub-tropical planktonic foraminiferal species which dwells in the mixed layer, has garnered significant attention of paleoceanographic investigations. Recent studies on G. ruber (w) morphotypes (G. ruber sensu stricto (s.s.) and G. ruber sensu lato (s.l.)) have inferred differences in seasonal calcification depths and offsets in isotopic and elemental data. To decipher if the morphotype abundances vary in response to changes in Indian Summer Monsoon (ISM), two well-dated sediment cores from the Andaman Sea, a core monsoon area in the northeastern Indian Ocean, are investigated. The abundance variations of G. ruber s.s. are very similar to total G. ruber (w), whereas G. ruber s.l. is very sensitive to the hydrologic changes linked to the ISM variability. Increased abundances of G. ruber s.l. were observed during periods of weak stratification and the resultant increase in productivity. The last glacial maximum (LGM), deglacial, Younger Dryas (YD) and late Holocene periods with weak ISM are characterized by a high abundance of G. ruber s.l. Conversely, this morphotype abundance decreased from 30 to 23 ka, Bølling/Allerød (B/A), early and mid-Holocene when the ISM was enhanced. The large variation of G. ruber morphotypes in the Andaman Sea is attributed to the selective preference of nutrient-rich water which varied with water column changes (salinity-controlled stratification) associated with ISM evolution. The elevated abundances of G. ruber s.l. during the glacial period closely match with the available records from other regions, possibly making them potential climatic markers.

Using the Stable Isotopic Composition of Heliconoides inflatus Pteropod Shells to Determine Calcification Depth in the Cariaco Basin

Pteropods have been hailed as the “canary in the coal mine” for ocean acidification, however, questions remain about their life history, habitat, and the environmental parameters that the isotopic composition of their shells reflect. In order to use pteropods as recorders of ocean chemistry, it is first necessary to understand where they calcify and how this may change through the year, whether this signal is affected by dissolution, and if shells are retained in the subfossil, and eventually fossil, record. Here we create the first annual record of the stable isotopic composition of shells of the pteropodHeliconoides inflatusin the Cariaco Basin, Venezuela utilizing samples and data from the CARIACO time series. Sixty-fourH. inflatusspecimens from 17 sediment trap samples between November 1996 and April 1998, and 22 specimens from the late Holocene-aged CAR2000-MC-2 core were analyzed for shell condition (an assessment of the amount of dissolution that a shell has experienced), size, and carbon and oxygen isotopic composition. Carbon isotopic measurements of juveniles (&amp;lt; 1mm) were more variable than those in adults (&amp;gt;1 mm), suggesting juvenile pteropods likely have a higher growth rate, and therefore different metabolic vital effects, and a more varied diet than adult pteropods.H. inflatuswas found to have an apparent calcification depth of 51.2 ± 34.0 m, suggesting they calcify at the shallowest part of their diurnal migration in the mixed layer (10–35 m in the Cariaco Basin).H. inflatusshell calcification will therefore only be impacted by changes in water chemistry at mixed layer depths. The shell condition did not impact the stable isotopic composition of the shells in either the sediment trap or core sample, suggesting the potential for using the isotopic composition of pteropod shells as oceanographic proxies when they are preserved. Comparisons between sediment trap and core sample show a 0.5°C warming that is marginally significant and a significant 0.45‰ decrease in δ13C between the late Holocene and the late 1990's. These measurements reflect changes in oceanic conditions linked to anthropogenic fossil fuel emissions known as the Suess effect, and lay the groundwork for establishing pteropods as paleoceanographic proxies in the future.

Stable Oxygen Isotope Composition Is Biased by Shell Calcification Intensity in Planktonic Foraminifera

AbstractPlanktonic Foraminifera are widely used for environmental reconstructions through measurements of their shell's geochemical characteristics, including its stable oxygen and carbon isotope composition. Using these parameters as unbiased proxies requires a firm knowledge of all potential confounding factors influencing foraminiferal shell geochemistry. One such parameter is the shell calcification intensity (shell weight normalized for shell size) that may influence the shell δ18O value either bioenergetically (by reducing energy available and required for equilibrium isotope fractionation during faster calcification) or kinetically (by influencing calcification depth through the shell's density contrast with seawater). Specimens from the Globigerinoides ruber/elongatus complex from a sediment trap in the North Atlantic have been used to quantify the influence of shell calcification intensity on shell δ18O values. Shell calcification intensity was found to have a significant effect on the shell stable oxygen isotope composition in all species. Through model fitting, it is suggested that the effect size may be in a range of 1‰ to 2‰ (depending on species, depth migration, and local oceanographic conditions). We show that the confounding effect of shell calcification intensity on stable oxygen isotope composition can be of importance, depending on the anticipated precision of the derived reconstructions. A framework is provided to quantify this effect in future studies.

Calcification depths and temperatures of planktonic foraminifera off southwest Hainan Island and their paleoceanographic implications

Abstract The East Asian monsoon system influences the local oceanographic and climatic conditions of South China Sea (SCS), making the habitat depths of planktonic foraminifera (PF) specific for this region.The previous paleo-ocean reconstructions of SCS have been based on calcification habitat depths derived from other oceans, which may have affected the accuracy of interpretations. In this study, the calcification depths of Globigerinoides ruber, Globigerinoides sacculifer, and Neogloboquadrina dutertrei from sediment traps deployed at 1000 m depth off southwest Hainan Island from July 2012 to April 2013 were analyzed with regard to the stable isotopes of oxygen (δ18O) and carbon (δ13C) to calculate their regional apparent calcification depths (ACDs) with the overall aim to improve the reconstruction of the upper ocean thermal structure. ACDs and temperature estimated from foraminifera δ18O ranged from 0 to 42 m and 25°C for G. ruber, 30-65 m and 23.3°C for G. sacculifer, and 75-100 m and 20.3°C for N. dutertrei, respectively. The difference between the thermocline-species (N. dutertrei) and mixed-layer species (G. ruber and G. sacculifer) δ18O (∆δ18OTh–ML) and the temperature (∆T) shows water column stratification. The periods of lower and higher ∆T and ∆δ18O were in phase with the changes in regional overlying wind speed. Additionally, this study reveals that N. dutertrei lives and calcifies its shells within the base of the mixed-layer depth (MLD) and upper thermocline depth in SCS. Overall, the results from this study provide a new insight to understand the mixed-layer and thermocline depth in the northern SCS.

Is the upward release of intermediate ocean heat content a possible engine for low-latitude processes?

Abstract Ocean heat content (OHC) plays an important role in controlling changes in Earth’s climate. However, relatively little research has been conducted into changes in OHC over a millennial scale, or into the mechanisms that control OHC migration in the ocean’s interior. This paucity of research is largely due to the lack of subsurface proxy records. Here, we analyzed planktonic Mg/Ca and δ18O records from species with different calcification depths to reconstruct the thermal structure of the water column and upper OHC changes since 21 kyr B.P. in the South China Sea. The results revealed that temperatures at intermediate and lower thermocline depths were warm during the last the deglaciation and became cool during the Holocene. The water cooling at ∼700 m began at 14.3 kyr B.P., but was delayed until 12.9 kyr B.P. at ∼325 m, and until 9.2 kyr B.P. at ∼250 m. In addition, upper thermocline temperatures at ∼100 m also started to decline at ca. 7.3 kyr B.P. Simultaneously, intermediate and thermocline OHC values were high during the last deglaciation, but surface OHC was low. We infer, therefore, that more heat was stored at intermediate depths during the last deglaciation, and that the upward release of the intermediate OHC resulted in the sequential delays in the cooling of intermediate to upper thermocline water. By combining these results with tropical Pacific records, we also hypothesize that the release of deeper OHC was perhaps the heat source for low-latitude processes during the Holocene.

δ18O and Mg/Ca Thermometry in Planktonic Foraminifera: A Multiproxy Approach Toward Tracing Coastal Upwelling Dynamics

AbstractPlanktonic foraminifera δ18O and Mg/Ca ratios are widely considered as a powerful proxy to reconstruct past seawater‐column temperature. Due to the complex interpretation of planktonic foraminifera δ18O data in regard to past seawater temperatures, temperature determination based on the foraminifera shell Mg/Ca ratio is believed to be more accurate. Scarce Mg/Ca calibration data exists for coastal upwelling regions, resulting in incoherent results of past seawater reconstructions. The current study along the NW Iberia coastal upwelling system intends to define the best Mg/Ca temperature equation for the most representative species of this region (Neogloboquadrina incompta, Globigerina bulloides, and Globorotalia inflata). Seawater temperature from δ18O and Mg/Ca of these three planktonic foraminifera species was compared with the surface sediments alkenone derived SST and with the in situ temperatures measured at the depths where these foraminifera species currently live and calcify. The equations that better reflect each species calcification depth were selected as our regional equations for δ18O and Mg/Ca temperature reconstructions. The δ18O‐estimated temperatures for surface sediment specimens were comparable with in situ seawater‐column temperature measurements, whereas the Mg/Ca derived temperatures seem to underestimate in situ values, in special for G. bulloides from samples affected by stronger coastal upwelling. The G. bulloides δ18O and Mg/Ca estimated temperatures from samples located offshore, further from coastal upwelling influence, are comparable to surface sediment alkenone derived temperatures. Our study shows that in upwelling areas, regional calibration of planktonic foraminifera Mg/Ca temperature equations is necessary for reliable interpretations of high‐resolution past temperature variability in these important environments.

Coronary calcification segmentation in intravascular OCT images using deep learning: application to calcification scoring.

.Major calcifications are of great concern when performing percutaneous coronary interventions because they inhibit proper stent deployment. We created a comprehensive software to segment calcifications in intravascular optical coherence tomography (IVOCT) images and to calculate their impact using the stent-deployment calcification score, as reported by Fujino et al. We segmented the vascular lumen and calcifications using the pretrained SegNet, convolutional neural network, which was refined for our task. We cleaned segmentation results using conditional random field processing. We evaluated the method on manually annotated IVOCT volumes of interest (VOIs) without lesions and with calcifications, lipidous, or mixed lesions. The dataset included 48 VOIs taken from 34 clinical pullbacks, giving a total of 2640 in vivo images. Annotations were determined from consensus between two expert analysts. Keeping VOIs intact, we performed 10-fold cross-validation over all data. Following segmentation noise cleaning, we obtained sensitivities of , , and for calcified, lumen, and other tissue classes, respectively. From segmented regions, we automatically determined calcification depth, angle, and thickness attributes. Bland–Altman analysis suggested strong correlation between manually and automatically obtained lumen and calcification attributes. Agreement between manually and automatically obtained stent-deployment calcification scores was good (four of five lesions gave exact agreement). Results are encouraging and suggest our classification approach could be applied clinically for assessment and treatment planning of coronary calcification lesions.

Controls on planktonic foraminifera apparent calcification depths for the northern equatorial Indian Ocean.

Within the world’s oceans, regionally distinct ecological niches develop due to differences in water temperature, nutrients, food availability, predation and light intensity. This results in differences in the vertical dispersion of planktonic foraminifera on the global scale. Understanding the controls on these modern-day distributions is important when using these organisms for paleoceanographic reconstructions. As such, this study constrains modern depth habitats for the northern equatorial Indian Ocean, for 14 planktonic foraminiferal species (G. ruber, G. elongatus, G. pyramidalis, G. rubescens, T. sacculifer, G. siphonifera, G. glutinata, N. dutertrei, G. bulloides, G. ungulata, P. obliquiloculata, G. menardii, G. hexagonus, G. scitula) using stable isotopic signatures (δ18O and δ13C) and Mg/Ca ratios. We evaluate two aspects of inferred depth habitats: (1) the significance of the apparent calcification depth (ACD) calculation method/equations and (2) regional species-specific ACD controls. Through a comparison with five global, (sub)tropical studies we found the choice of applied equation and δ18Osw significant and an important consideration when comparing with the published literature. The ACDs of the surface mixed layer and thermocline species show a tight clustering between 73–109 m water depth coinciding with the deep chlorophyll maximum (DCM). Furthermore, the ACDs for the sub-thermocline species are positioned relative to secondary peaks in the local primary production. We surmise that food source plays a key role in the relative living depths for the majority of the investigated planktonic foraminifera within this oligotrophic environment of the Maldives and elsewhere in the tropical oceans.

Calcification depth of deep-dwelling planktonic foraminifera from the eastern North Atlantic constrained by stable oxygen isotope ratios of shells from stratified plankton tows

Abstract. Stable oxygen isotopes (δ18O) of planktonic foraminifera are one of the most used tools to reconstruct environmental conditions of the water column. Since different species live and calcify at different depths in the water column, the δ18O of sedimentary foraminifera reflects to a large degree the vertical habitat and interspecies δ18O differences and can thus potentially provide information on the vertical structure of the water column. However, to fully unlock the potential of foraminifera as recorders of past surface water properties, it is necessary to understand how and under what conditions the environmental signal is incorporated into the calcite shells of individual species. Deep-dwelling species play a particularly important role in this context since their calcification depth reaches below the surface mixed layer. Here we report δ18O measurements made on four deep-dwelling Globorotalia species collected with stratified plankton tows in the eastern North Atlantic. Size and crust effects on the δ18O signal were evaluated showing that a larger size increases the δ18O of G. inflata and G. hirsuta, and a crust effect is reflected in a higher δ18O signal in G. truncatulinoides. The great majority of the δ18O values can be explained without invoking disequilibrium calcification. When interpreted in this way the data imply depth-integrated calcification with progressive addition of calcite with depth to about 300 m for G. inflata and to about 500 m for G. hirsuta. In G. scitula, despite a strong subsurface maximum in abundance, the vertical δ18O profile is flat and appears dominated by a surface layer signal. In G. truncatulinoides, the δ18O profile follows equilibrium for each depth, implying a constant habitat during growth at each depth layer. The δ18O values are more consistent with the predictions of the Shackleton (1974) palaeotemperature equation, except in G. scitula which shows values more consistent with the Kim and O'Neil (1997) prediction. In all cases, we observe a difference between the level where most of the specimens were present and the depth where most of their shell appears to calcify.

The B/Ca and Cd/Ca of a subsurface-dwelling foraminifera Pulleniatina obliquiloculata in the tropical Indo-Pacific Ocean: implications for the subsurface carbonate chemistry estimation

Pulleniatina obliquiloculata shells from 16 core-top samples from the tropical Indo-Pacific Oceans are analyzed for the ratios of boron and cadmium to calcium (B/Ca and Cd/Ca). The B/Ca ratios show a very weak positive relationship with [B(OH)4-] and the dissolved carbonate species at the apparent calcification depth of P. obliquiloculata. The boron partition coefficients (KD) between P. obliquiloculata B/Ca and seawater [B(OH)4-]/[HCO3-] distribute around 1.1×10-3–1.3×10-3 with a mean value of (1.19±0.12)×10-3, and are significantly related to the nutrient concentration, especially phosphate. The lack of any clear correlation between the P. obliquiloculata B/Ca and seawater carbonate chemical parameters suggests that the physiochemical controls on boron incorporation are masked by the complexity of natural seawater condition. But the significant dependence of KD on nutrient may likely be explained by a nutrient related growth-rate effect. Cd/Ca of P. obliquiloculata shows significant correlation with seawater phosphate concentration, and its partition coefficients (DCd) are significantly related to temperature. A first-principle methodology of P. obliquiloculata B/Ca is applied, with the aid of Cd/Ca as a phosphate proxy and a constraint on KD, to estimating sea water carbonate chemistry (e.g., pH). The results are fairly promising and allow us to propose the possibility to apply the combination of B/Ca and Cd/Ca proxies (and also Mg/Ca and δ18O for estimating temperature and salinity) for the paleoreconstruction of seawater carbonate chemistry.