Suess Effect Research Articles

Regime shift of skeletal δ13C after 1997/1998 El Nino event in Porites coral from Green Island, Taiwan

The 1997/1998 El Niño event caused mass coral bleaching and mortality in many tropical and subtropical regions, including corals on Green Island, Taiwan, in the northwestern Pacific Ocean. This study analyzed coral carbon isotope ratios (δ13C), oxygen isotope ratios (δ18O), and Sr/Ca ratios for 29 years, including the 1997/1998 El Niño period, to examine how high water temperature events are recorded in coral geochemical indicators. Sr/Ca ratios in coral skeletons from Green Island show the lowest peak, means the highest temperature during the 1997/1998 El Niño period. However, we couldn’t observe high-temperature events on δ18O. Furthermore, a negative δ13C shift was observed after El Niño events. The regime shift of δ13C might have been caused by temporal bleaching and/or a decrease in symbiotic algae due to high water temperature stress under the continuous decrease in δ13C in DIC due to the Suess effect.

Revising chronological uncertainties in marine archives using global anthropogenic signals: a case study on the oceanic 13C Suess effect

Abstract. Marine sediments are excellent archives for reconstructing past changes in climate and ocean circulation. Overlapping with instrumental records, they hold the potential to elucidate natural variability and contextualize current changes. Yet, dating uncertainties of traditional approaches (e.g., up to ± 30–50 years for the last 2 centuries) pose major challenges for integrating the shorter instrumental records with these extended marine archives. Hence, robust sediment chronologies are crucial, and most existing age model constraints do not provide sufficient age control, particularly for the 20th century, which is the most critical period for comparing proxy records to historical changes. Here we propose a novel chronostratigraphic approach that uses anthropogenic signals such as the oceanic 13C Suess effect and spheroidal carbonaceous fly-ash particles to reduce age model uncertainties in high-resolution marine archives. As a test, we apply this new approach to a marine sediment core located at the Gardar Drift, in the subpolar North Atlantic, and revise the previously published age model for this site. We further provide a refined estimate of regional reservoir corrections and uncertainties for Gardar Drift.

Revisiting Elevated δ13C Values of Sediment on Modern Carbonate Platforms

AbstractThe measured carbon isotopic compositions of carbonate sediments (δ13Ccarb) on modern platforms are commonly 13C‐enriched compared to predicted values for minerals forming in isotopic equilibrium with the dissolved inorganic carbon (DIC) of modern seawater. This offset undermines the assumption that δ13Ccarb values of analogous facies in the rock record are an accurate archive of information about Earth's global carbon cycle. We present a new data set of the diurnal variation in carbonate chemistry and seawater δ13CDIC values on a modern carbonate platform. These data demonstrate that δ13Ccarb values on modern platforms are broadly representative of seawater, but only after accounting for the recent decrease in the δ13C value of atmospheric CO2 and shallow seawater DIC due to anthropogenic carbon release, a phenomenon commonly referred to as the 13C Suess effect. These findings highlight an important, yet overlooked, aspect of some modern carbonate systems, which must inform their use as ancient analogs.

Carbon cycling through plant and fungal herbarium specimens tracks the Suess effect over more than a century of environmental change

Although the anthropogenic decline in atmospheric carbon stable isotope ratios (δ13C) over the last 150 years (termed the Suess effect) is well-studied, how different terrestrial trophic levels and modes reflect this decline remains unresolved. To evaluate the Suess effect as an opportunistic tracer of terrestrial forest carbon cycling, this study analyzed the δ13C in herbarium specimens collected in Minnesota, USA from 1877 to 2019. Our results suggest that both broadleaf trees and ectomycorrhizal fungi relied on recent photosynthate to produce leaves and sporocarps, while saprotrophic fungi on average used carbon fixed from the atmosphere 32–55 years ago for sporocarp construction. The δ13C values of saprotrophic fungal collections were also sensitive to the age of their plant carbon substrate, with sporocarps of twig specialists tracking changes in atmospheric δ13C more closely than saprotrophs growing on logs. Collectively, this study indicates that natural history collections can quantitatively track carbon cycling among plants and fungi over time.

Bivalve tissues as a recorder of multidecadal global anthropogenic and climate‐mediated change in coastal areas

AbstractRecent rapid changes in climate and environmental conditions have significantly impacted coastal ecosystem functioning. However, the complex interplay between global and local effects makes it challenging to pinpoint the primary drivers. In a multi‐ecosystem study, we analyzed pluri‐decadal trends of bivalve‐δ13C as recorder of global environmental changes. These trends were correlated with large‐scale natural and anthropogenic climate proxies to identify whether coastal biota responded to global effects. Our findings revealed decreasing bivalve‐δ13C trends in all sea regions, mainly linked with increased temperature and atmospheric‐CO2 concentrations, the later generating a decrease in atmospheric‐CO2 δ13C values (Suess effect) because of fossil‐fuel burning. After removing the Suess effect from bivalve‐δ13C trends, ongoing global climate variability continues to affect most ecosystems, possibly intensified by combined, interacting regional or local effects. These results highlight the need to consider large‐scale effects to fully understand ecosystem and food web responses to the multiple effects of global change.

Source appointment of δ13C in sediments of a maar lake in southern China: Implications of fossil fuel CO2 emissions

Stable carbon isotopes (δ13C) in lake sediments can record changes in CO2 emissions from fossil fuels (FFs) combustion; however, the exact proportion of δ13C changes caused by FFs combustion remains unclear. Here, taking the Huguangyan Maar Lake (HGY) located in low latitude with high intensity of human activities in southern China as an example, we used the MixSIAR Bayesian stable isotope mixing model to trace the source change of δ13C in the HGY sediments over the past 130 years. The δ13C value, ranging from −20.23‰ to −24.29‰, with an average of −22.39 ± 1.5‰, displayed a continuous downward trend from the bottom to top throughout the core, with the fastest decline occurring between 1950AD and 1996AD. Quantitative source appointment indicates that the contribution of FFs sources to δ13C depletion in the HGY sediments has increased nearly three-fold over the past 130 years, from 18.6% to 67.8%, which may be related to the Suess Effect of the 13C-depleted FFs burning. The increase in δ13C in HGY sediments in the past decade was consistent with the increase in δ13C–CO2 emitted by global fossil-fuel consumption, and was also related to the decrease in fossil fuels consumption caused by China's Clean Air Act. This study demonstrates that the isotope traceability model is helpful for source appointment of δ13C in lake sediments and that the δ13C in maar lake sediments can be used to trace CO2 emissions from global FFs combustion. This therefore provides new insights on the carbon cycle during the Anthropocene.

Reconstructed seasonality during the Mid Piacenzian Warm Interval and early Pleistocene cooling as recorded by growth temperatures from Mercenaria shells

The Mid Piacenzian Warm Interval (MPWI) has been identified as an analogue for future global warming because it had warmer temperatures and higher atmospheric CO2 levels than today, while subsequent early Pleistocene cooling is more similar to modern climate. However, reconstructions of these intervals lack seasonal-scale temperature reconstructions. Seasonal sea surface temperature (SST) reconstructions from deep-time archives can potentially provide insight into the nature of the climate system on sub-annual scales during critical climate states. Here we compared seasonal variability in growth temperatures during the MPWI and subsequent early Pleistocene cooling to modern climate reconstructed from oxygen isotope ratios recorded by the bivalve Mercenaria. Modern shells were collected from the University of North Carolina's Marine Sanctuary. Fossil shells from the Mid-Atlantic Coastal Plain (North Carolina) were collected from the Duplin Formation (MPWI) and the Waccamaw Formation (early Pleistocene). Oxygen isotope ratios range from −1 to 2.4 ‰ during the MPWI, −1–2.4 ‰ during the early Pleistocene, and −2.2 to 2.3 ‰ in modern shells. Stable carbon isotope ratios ranged from −0.91 to 1.67 ‰ during the MPWI, 0.19–1.87 ‰ during the early Pleistocene, and −2.46 to 0.60 ‰ in modern shells. Average seasonal growth temperature variations for the MPWI (∼11 ± 3 °C) are reduced compared to modern instrument records (∼16 ± 3 °C), while the early Pleistocene (∼14 ± 2 °C) was more similar to today. Modern Mercenaria record dark increment formation during the summer while fossil Mercenaria record dark increment formation during the winter. We hypothesize that this difference is timing of dark increment formation may be due in part to differences in water depth (∼1m for modern shells and ∼20m for fossil shells) or a shift in the location of the boundary between biogeographic zones. A −1.6 ‰ shift in mean stable carbon isotope ratios between fossil (0.92 ± 0.66 ‰) and modern (−0.65 ± 0.44 ‰) shells has been observed and may be a result of the “Suess Effect” and/or influences of estuarine/freshwater relative to marine settings.

Bomb radiocarbon determines absolute age of adult fin whales, and validates use of earplug growth bands for age determination

Baleen whales are one of the few vertebrate taxa for which there are no confirmed estimates of longevity or methods of age determination. Lamina counts in the waxy earplug are assumed to represent age, but ageing accuracy is completely unknown. In this study, bomb radiocarbon assays of the earplug growth sequence in three adult fin whales (Balaenoptera physalus) were used to prepare the most complete within-individual bomb radiocarbon chronologies yet reported for any vertebrate. The whale radiocarbon chronologies matched those of known-age carbonate reference chronologies very well, indicating that the earplug laminae were both metabolically stable and formed throughout the life of the whale. Earplug lamina counts accurately represented absolute ages of 65-85 yr to within 6% of the correct age. Detection of a significant declining trend in δ13C with year of lamina formation within individual whales was consistent with that of the Suess effect, again underlining the metabolic stability of the earplug laminae. Given our results, recent applications of earplug laminae for reconstructing diet and life history events appear to be firmly based, with the potential for further elemental and isotopic applications analogous to those of the otolith.

Mammal communities of primeval forests as sentinels of global change.

Understanding the drivers and consequences of global environmental change is crucial to inform predictions of effects on ecosystems. We used the mammal community of Białowieża Forest, the last lowland near-primeval forest in temperate Europe, as a sentinel of global change. We analyzed changes in stable carbon (δ13 C) and nitrogen (δ15 N) isotope values of hair in 687 specimens from 50 mammal species across seven decades (1946-2011). We classified mammals into four taxonomic-dietary groups (herbivores, carnivores, insectivores, and bats). We found a significant negative trend in hair δ15 N for the mammal community, particularly strong for herbivores. This trend is consistent with temporal patterns in nitrogen deposition from (15 N depleted) industrial fertilizers and fossil fuel emissions. It is also in line with global-scale declines in δ15 N reported in forests and other unfertilized, non-urban terrestrial ecosystems and with local decreases in N foliar concentrations. The global depletion of 13 C content in atmospheric CO2 due to fossil fuel burning (Suess effect) was detected in all groups. After correcting for this effect, the hair δ13 C trend became non-significant for both community and groups, except for bats, which showed a strong decline in δ13 C. This could be related to an increase in the relative abundance of freshwater insects taken by bats or increased use of methane-derived carbon in food webs used by bats. This work is the first broad-scale and long-term mammal isotope ecology study in a near-primeval forest in temperate Europe. Mammal communities from natural forests represent a unique benchmark in global change research; investigating their isotopic temporal variation can help identify patterns and early detections of ecosystem changes and provide more comprehensive and integrative assessments than single species approaches.

Late glacial–Younger Dryas climate in interior Alaska as inferred from the isotope values of land snail shells

AbstractThe isotope values of fossil snail shells can be important archives of climate. Here, we present the first carbon (δ13C) and oxygen (δ18O) isotope values of snail shells in interior Alaska to explore changes in vegetation and humidity through the late-glacial period. Snail shell δ13C values were relatively consistent through the late glacial. However, late-glacial shell δ13C values are 2.8‰ higher than those of modern shells. This offset is best explained by the Suess effect and changes in the δ13C values of snail diet. Snail shell δ18O values varied through the late glacial, which can be partially explained by changes in relative humidity (RH). RH during the snail growing period was modeled based on a published flux balance model. Results suggest a dry period toward the beginning of the Bølling–Allerød (~14 ka) followed by two distinct stages of the Younger Dryas, a wetter stage in the early Younger Dryas from 12.9 to 12.3 ka, and subsequent drier stage in the late Younger Dryas between 12.3 and 11.7 ka. The results show that land snail isotopes in high-latitude regions may be used as a supplementary paleoclimate proxy to help clarify complex climate histories, such as those of interior Alaska during the Younger Dryas.

The Flower Garden Banks Siderastrea siderea coral as a candidate Global boundary Stratotype Section and Point for the Anthropocene series

The proposed Anthropocene Global Boundary Stratotype Section and Point (GSSP) candidate site of West Flower Garden Bank (27.8762°N, 93.8147°W) is an open ocean location in the Gulf of Mexico with a submerged coral reef and few direct human impacts. Corals contain highly accurate and precise (<±1 year) internal chronologies, similar to tree rings, and their exoskeletons are formed of aragonite and can be preserved in the rock record. Here we present results from a large Siderastrea siderea coral (core 05WFGB3; 1755–2005 CE) sampled with annual and monthly resolutions that show clear markers of global and regional human impacts. Atmospheric nuclear bomb testing by-products (14C, 239+240Pu) have clear increases in this coral starting in 1957 for 14C and the first increase in 1956 for 239+240Pu (potential bases for the Anthropocene GSSP). Coral δ13C declined especially after 1956 consistent with the Suess effect resulting from the burning of fossil fuels. Coral skeletal δ15N starts to increase in 1963 corresponding with the increase in agricultural fertilizers. Coral Hg concentrations (1933–1980) loosely track fluctuations in industrial pollution and coral Ba/Ca increases from 1965–1983 when offshore oil operations expand after 1947. Coral temperature proxies contain the 20th-century global warming trend whereas coral growth declines during this interval.

North Flinders Reef (Coral Sea, Australia) Porites sp. corals as a candidate Global boundary Stratotype Section and Point for the Anthropocene series

Corals are unique in the suite of proposed Anthropocene Global Boundary Stratotype Section and Point (GSSP) archives, as living organisms that produce aragonite exoskeletons preserved in the geological record that contain highly accurate and precise (<±1 year) internal chronologies. The GSSP candidate site North Flinders Reef in the Coral Sea (Australia) is an offshore oceanic reef, and therefore less vulnerable to local human influences than those closer to the coast. Here, we present geochemical records from two Porites sp. corals sampled at an annual to pluri-annual (i.e. 3–5 years) resolution that shows clear global and regional human impacts. Atmospheric nuclear bomb testing by-products (14C,239+240Pu) show a clear increase in the Flinders Reef corals coincident with well-dated nuclear testing operations. By contrast, the radionuclides 241Am and 137Cs are present at low or undetectable levels, as are spheroidal carbonaceous fly-ash particles. Coral δ13C shows centennial variability likely influenced by growth effects in the 18th century and with a progression to lower values starting in 1880 CE and accelerating post-1970 CE. The latter may be related to the Suess effect resulting from 13C-depleted fossil fuel burning. Coral δ15N decreased between 1710 and 1954 CE with a reversal post-1954 CE. Coral temperature proxies indicate prominent centennial variability with equally warm conditions in the 18th and end of 20th century. However, the exact mechanisms responsible for the mid-20th century changes in these parameters need to be scrutinised in further detail. Plain Language summary: This work proposes a candidate natural archive for the official marker of the Anthropocene that geologists will use to mark this important interval in time. Our candidate is a live coral from North Flinders Reef in the Coral Sea (Australia), located 150 km east of the Great Barrier Reef, a location that is remote from direct local human influences. Corals are a unique archive of tropical ocean change because they incorporate the geochemical signature from seawater into their limestone skeleton during their long life-spans. Here we investigated a number of geochemical markers in yearly growth layers of the corals to define several markers for the Anthropocene based on changes in temperature, water chemistry, chemicals from pollution and fertilisers, radioactive products from nuclear bomb testing, and by-products from burning fossil fuels. We have detected clear human influences in several of these markers.

Preliminary Bat Guano Isotope Evidence for Past Vegetation and Climate Change in Southwest Virginia

The Appalachian Mountains, one of the most biologically diverse regions in the temperate world, have been heavily altered by human activity for millennia yet the relative roles of human and other disturbances and climate change in creating modern landscapes are not well understood. Holocene paleoenvironmental records could provide a window into past Appalachian landscapes, but are restricted by a dearth of appropriate sites, such as natural lakes. Recent research suggests that bat guano deposits can serve as valuable archives of past environmental change. Carbon isotope (δ13C) values of guano from insectivorous bats can reflect the relative abundance of forest (C3) versus grassland (C4) vegetation at a regional scale, while guano nitrogen isotope (δ15N) values have been linked to landscape-scale N-cycling and precipitation. To investigate the paleoenvironmental history of an Appalachian site in southwest Virginia, we collected a 170 cm guano core from a limestone cave on Salt Pond Mountain. Bats are no longer active in the cave, but recovered bones indicate the past presence of Myotis species. Preliminary results show clear trends of increasing δ15N values and decreasing δ13C values from deep in the core toward the surface. δ13C and δ15N values are also significantly negatively correlated (R2=0.6, p=5.6e-15). The increase in δ15N values may signal a moistening climate toward the present, a finding consistent with regional Holocene pollen records. Higher δ13C values deep in the core likely indicate a greater prevalence of C4 grassland vegetation on the landscape, which could be linked to drier climate, indigenous burning, or both. Increased variation in δ13C and δ15N values below about 65 cm may indicate more variable climate or increased disturbance during the time represented. Forthcoming radiocarbon dates will anchor these trends in time and inform correction for the Suess effect, while other proxies could help disentangle the drivers of landscape change.

CHARACTERISTICS OF PINE NEEDLES EXPOSED TO MULTI-SOURCE POLLUTION IN SILESIA: RADIOCARBON CONCENTRATION IN PINE NEEDLES AND ELEMENTAL ANALYSIS OF THE NEEDLES’ SURFACE DEPOSITS

ABSTRACTWe present here the analysis of the radiocarbon concentration and the components deposited on 2-year-old Pinus sylvestris L. needles collected in 2021, which were exposed to air contaminants for approximately two years. The needles were collected from seven sampling sites located near roads, households, and industrial factories in Silesia, the most industrialized part of Poland. The radiocarbon concentration was investigated using liquid scintillation spectrometry. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to quantitatively analyze the elements deposited on the surface of pine needles. The depletion of the radiocarbon concentration in pine needles relative to clean air was observed at most of the investigated sites. Although it has been observed that in the research area, the fossil fuel CO2 emission ranging from 0.4 to 3%, we cannot exclude that Suess effect may be underestimated due to biomass burning and mixing of the 14CO2 origin from different sources. A significant amount of silicon, nitrogen, and sulfur was commonly found in samples, Metal elements of Ca, Fe, Al, Mg, and K were also present in most samples. Heavier elements of Fe and Ti were present in higher concentrations only in needles obtained from sites nearer to the heat and power plant in Łaziska Górne.

Stable carbon isotopes of dissolved inorganic carbon in the Western North Pacific Ocean: Proxy for water mixing and dynamics

The uptake of atmospheric CO2 and the cycle of dissolved inorganic carbon (DIC) in the ocean are the major mechanisms and pathways controlling global climate change and carbon cycling. The stable carbon isotope (δ13C) of DIC, therefore, provides an important tracer for processes such as air-sea exchange, photosynthesis, and water dynamics in the ocean. Here, we present new δ13C-DIC data on water samples collected from a north-south transect (13°N–40°N, 150°E) in the western North Pacific (NP) Ocean in November 2019 and compare the results with those previously reported for similar transects (149.3°E) during WOCE and CLIVAR projects over the past three decades. The values of δ13C-DIC, ranging from -0.83‰ to 0.86‰, were higher in the surface waters and decreased with depth. The high δ13C-DIC values in the surface waters were influenced primarily by isotopic fractionation during air-sea exchange and photosynthesis. With depth, the movement of different water masses and mixing, as well as bathypelagic respiration in the dark water of the ocean, all play important roles in influencing the distribution and isotopic signatures of δ13C-DIC in the western NP Ocean. The δ13C-DIC values of the 0–200 m water layer varied from -0.17‰ to 0.86‰, with lower values at high latitudes, affected by the low δ13C-DIC values carried by the Oyashio Current to the Kuroshio Extension (KE) region. A downward trend was present in the δ13C-DIC signature from north to south in the North Pacific Intermediate Water (NPIW) and Pacific Deep Water (PDW) in the western NP, which reflected the remineralization of organic matter with a horizontal transport of NPIW and PDW. We found a strong 13C Suess Effect in the upper 2,000 m in the western NP Ocean, and δ13C-DIC at the surface (<50 m) has decreased by 0.60‰-0.85‰ since 1993. The mean δ13C-DIC change in the surface ocean was estimated at 0.28‰ per decade between 1993 and 2019. The air-sea exchange and water mixing in the study area may have accelerated the absorption of anthropogenic CO2 in recent years, which likely caused a slightly faster rate of decrease in the δ13C-DIC from 2005–2019 than that observed from 1993–2005.

Climate signals in stable carbon and hydrogen isotopes of lignin methoxy groups from southern German beech trees

Abstract. Stable hydrogen and carbon isotope ratios of wood lignin methoxy groups (δ13CLM and δ2HLM values) have been shown to be reliable proxies of past temperature variations. Previous studies showed that δ2HLM values even work in temperate environments where classical tree-ring width and maximum latewood density measurements are less successful for climate reconstructions. Here, we analyse the annually resolved δ13CLM values from 1916–2015 of four beech trees (Fagus sylvatica) from a temperate site near Hohenpeißenberg in southern Germany and compare these data with regional- to continental-scale climate observations. Initial δ13CLM values were corrected for the Suess effect (a decrease of δ13C in atmospheric CO2) and physiological tree responses to increasing atmospheric CO2 concentrations considering a range of published discrimination factors. The calibration of δ13CLM chronologies against instrumental data reveals the highest correlations with regional summer (r=0.68) and mean annual temperatures (r=0.66), as well as previous-year September to current-year August temperatures (r=0.61), all calculated from 1916–2015 and reaching p<0.001. Additional calibration trials using detrended δ13CLM values and climate data (to constrain effects of autocorrelation on significance levels) returned rsummer=0.46 (p<0.001), rannual=0.25 (p<0.05) and rprev.September-August=0.18 (p>0.05). The new δ13CLM chronologies were finally compared with the previously produced δ2HLM values of the same trees in order to evaluate the additional gain of assessing past climate variability using a dual-isotope approach. Compared to δ13CLM, δ2HLM values correlate substantially more strongly with large-scale temperatures averaged over western Europe (rprev.September-August=0.69), whereas only weak and mainly insignificant correlations are obtained between precipitation and both isotope chronologies (δ13CLM and δ2HLM values). Our results indicate the great potential of using δ13CLM values from temperate environments as a proxy for local temperatures and, in combination with δ2HLM values, to assess regional- to sub-continental scale temperature patterns.

Highly resolved δ13C and trace element ratios of precisely dated stalagmite from northwestern China: Hydroclimate reconstruction during the last two millennia

Compared with the widely used stable oxygen isotope (δ18O), the climate response of the stable carbon isotope (δ13C) of speleothems in monsoonal China has received less attention, mainly because of its relatively complex controlling factors. Nevertheless, an increasing number of studies are suggesting that δ13C can represent hydroclimatic changes. Here, we present highly resolved continuous δ13C and trace element ratio records of a speleothem from Wanxiang Cave, northwestern China, spanning the last two millennia. Our results show that δ13C values oscillated around the mean value on centennial scales, indicating that the overlying vegetation types and soil humidity did not change significantly. High consistency was found between detrended δ13C and δ18O (δ13Cd and δ18Od) records, suggesting that soil moisture balance and vegetation density related to the regional hydrological cycle is an important factor controlling δ13C variations on multidecadal-centennial scales. The regional hydrological cycle is mainly controlled by summer precipitation induced by the Asian summer monsoon (ASM) and the stable prior calcite precipitation (PCP), which was inferred from trace element ratio (Mg/Ca, Sr/Ca, Ba/Ca) records. The δ13C and trace element ratio records, consistent with δ18O throughout the considered periods, are not only closely coupled with the intensity of the El Niño-Southern Oscillation and north-south shift of the Intertropical Convergence Zone but also respond to solar activity and temperature variations in the Northern Hemisphere. However, both δ13C and trace element ratios exhibited a persistent significantly decreasing trend in the last 150 years. Furthermore, the variation of δ18O during the Current Warm Period (AD. 1850–2000) suggests that anthropogenic emissions of atmospheric CO2 and aerosols rather than ASM caused an unusual increase of regional precipitation and depletion of atmospheric δ13C, which induced increased infiltration of atmospheric CO2 and available water into soil pores and caves without any obvious PCP effect. The abnormal changes in our speleothem δ13C are analogous to the oceanic 13C Suess effect, suggesting that stalagmite δ13C record is greatly affected by atmospheric CO2 concentration under global warming.

Carbon and hydrogen isotopes of taraxerol in mangrove leaves and sediment cores: Implications for paleo-reconstructions

Reconstructing past climate change in mangrove swamps contextualizes ongoing and future developments in these globally important ecosystems. Taraxerol, a well-recognized lipid biomarker for mangroves, is a promising target compound for calibration since it is relatively refractory and well preserved in sediments and since mangrove lipid δ2H and δ13C values have been shown to respond to salinity changes. Here we investigate the δ2H and δ13C values of taraxerol in leaves of two mangrove species (Rhizophora mangle and Laguncularia racemosa) and three dated mangrove cores along a spatial transect from the Shark River Estuary of South Florida, USA, to constrain its applicability for hydroclimate reconstructions. The net 2H discrimination between surface water and taraxerol increased by 1.0‰ ppt−1 over a salinity range of 0.7–32 ppt for both R. mangle and L. racemosa. Although the δ13C values of taraxerol showed a significant positive correlation with salinity in L. racemosa, the inverse trend was observed in R. mangle. The isotopic signature and spatial trends of taraxerol observed in mangrove leaves were well imprinted in mangrove surface sediments.In addition, we further tested if the isotopic signal of taraxerol from mangrove leaves could be preserved in sediment cores on a time scale of ca. 300 yrs. No strong evidence of significant diagenetic alteration was observed for δ2H values of taraxerol. In contrast, an increase up to ∼1.1‰ was observed for δ13C, excluding the Suess effect. Considering the consistent salinity-dependent discrimination of 2H to salinity, and no significant diagenetic alteration of taraxerol δ2H values on centennial time scales, taraxerol H isotopes are a promising proxy for hydroclimate reconstruction in mangrove and mangrove-adjacent systems. However, the interpretation of δ13C values of taraxerol should be treated with caution since its correlation with salinity may be species-specific and a slight diagenetic enrichment in 13C may occur.

ESTIMATION OF THE FOSSIL FUEL FRACTION COMPONENTS DUE TO THE SUESS EFFECT IN URBAN AREA

Long used in the domain of archaeology, the C14 isotope has become an essential tracer in the evaluation of environmental fossil pollution. Since modern times, the combustion of fossil fuels such as coal, oil, natural gas, etc. in urban and/or industrialized areas releases a significant amount of fossil CO2 into the environment. Thisincrease the concentration of CO2, but also causes changes in the isotopic composition of carbon resulting in a deceased of the C14 concentration in the atmosphere and in other carbon reservoirs (terrestrial and marine biosphere).This phenomenon is the SUESS effect. The most favorable types of samples for such a study are leaves of trees or cernes. These reflect better the changes of the radiocarbon concentration in the atmosphere due to the biological assimilation of carbon from the air through photosynthesis. The evaluation of the Suess effect in polluted areas (Dakar region:UCAD Botanic Garden, Mbao Forest, SAR Factory, Beach)can be done using mass balance equations. From this model, we determined the fraction of fossil fuels .The values we found vary between 0.25% in UCAD Botanic Garden and 4.19% in Mbao Forest, and they are all positive, which effectively proves the existence of the Suess effect in our sites.

Sedimentary Anthropogenic Carbon Signals From the Western Pacific Margin for the Last Century

The declining trend of the δ13C of tropical corals over the last century was about −0.01‰ year−1, according to global coral records. The decrease was attributable to the significant input of anthropogenic CO2 (13C Suess effect) to the atmosphere. Previous studies of δ13C in corals suggested that the signal of the anthropogenic carbon in the Pacific and Indian Oceans were weaker than that in the Atlantic Ocean. However, biases relating to environments in which corals grew caused concerns. To investigate the anthropogenic carbon signal in the Western Pacific, foraminiferal records in a suite of 13 box cores with good age control were obtained from the continental slope off southwestern Taiwan between 2004 and 2006. δ18O values of planktonic foraminifera (Globigerinoides sacculifer or so-called Trilobatus sacculifer) in collected cores were relatively stable at −2.5‰ to −2‰ in the last century, but foraminiferal δ13C had a gradual secular decline after the 1900s. The decline trend of δ13C began to intensify after the 1960s, and its rate was similar to that observed in the Atlantic. Similar decline trends of δ13C were also found in coral records at regions where the human activity is high (Liuqiu) and low (Dongsha). Our findings indicate that the anthropogenic carbon signal in the Western Pacific was not weaker than that recorded in the Atlantic, and the nearshore sediment can supplement the lack of δ13C records in corals, which are deficient when the environment is not suitable to grow.