Suess Effect Research Articles

Radiocarbon Concentration Measurements in Tree Leaves near SOCOCIM (Rufisque, Senegal), A Cement Factory

Radiocarbon content in biogenic samples is widely used to study the variation of atmospheric CO2 due to anthropogenic activities. A total of 20 samples of several types of tree leaves, were analyzed for this study. Sampling was carried out at the end of the rainy season in 2017 from the surrounding of the SOCOCIM cement factory in Rufisque town. Rufisque is located on the peninsula of Cape Verde, 25 km east of Dakar, where it is the 《south gate》 of the agglomeration. Reference samples of five different species were collected during the same period (2017) from a clean zone. The 14C method was used for the determination of Δ14C values. The data show that the 14C concentration in the studied sites was significantly lower than the clean area, due to the release of anthropogenic CO2. To estimate the Suess effect, the fossil fuel fraction was determined based on equations of mass balance for CO2 concentration, stable isotopic composition of carbon, and 14C concentration. The results show that selected locations are affected differently according to their distance from the factory and the wind direction.

Spatio-temporal variation in stable isotope and elemental composition of key-species reflect environmental changes in the Baltic Sea

Carbon and nitrogen stable isotope ratios are increasingly used to study long-term change in food web structure and nutrient cycling. We retrospectively analyse elemental composition (C, N and P) and stable isotopes (δ13C, δ15N) in archived monitoring samples of two important taxa from the bottom of the food web; the filamentous ephemeral macroalgae Cladophora spp. and the blue mussel Mytilus edulis trossulus from three contrasting regions in the Baltic Sea (coastal Bothnian Sea and Baltic Proper, open sea central Baltic). The aim is to statistically link the observed spatial and interannual (8–24 years’ time-series) variability in elemental and isotope baselines with their biomass trends and to the oceanographic monitoring data reflecting the ongoing environmental changes (i.e., eutrophication and climate) in this system. We find clear differences in isotope baselines between the two major Baltic Sea basins. However, the temporal variation in Mytilus δ13C was similar among regions and, at the open sea station, mussels and algae δ13C also correlated over time, likely reflecting a global (Suess) effect, whereas δ15N of both taxa varied with local and regional dissolved nitrogen concentrations in water. δ15N in source amino acids allowed detection of diazotrophic N in Mytilus, which was masked in bulk δ15N. Finally, Cladophora N:P reflected regional nutrient levels in the water while P%, which differed for both taxa, was linked to food quality for Mytilus. This study highlights the potential of a multi-taxa and multi-stable isotope approach to understand nutrient dynamics and monitor long-term environmental changes.

Signatures of natural to anthropogenic transition in lake sediments from the Central Himalaya using stable isotopes

Stable isotopic compositions of carbon (C) and nitrogen (N) in lake sediments have the potential to decipher natural and anthropogenic influences in a region, which has undergone significant cultural changes in the recent past. In this study, using carbon (δ13C) and nitrogen (δ15N) isotopic compositions of organic matter along with C isotopic ratio of black carbon (δ13CBC) in sediments collected from a lake in the Lesser Himalaya, an attempt has been made to decipher the biogeochemical changes in the lake under natural and anthropogenic stresses along with fire history of the region. The sediment core, dated using 210Pb and 137Cs, went back to 1949 AD, where isotopic compositions and elemental ratios (TOC/TN) suggested that the lake biogeochemistry was largely controlled by in-lake primary productivity. A noticeable change in isotopic compositions and elemental ratios was observed in the early 1970s, possibly due to increased input of soil organic matter from the catchment, which coincided with the urbanization and other human interventions in the region. At the same time, a consistent increase in differences between the measured and Suess effect corrected δ13C of organic matter from the early 1970s to 2016 AD indicated towards the increased utilization of fossil fuel-induced atmospheric CO2 by the lake biota. Also, a sudden shift in δ13CBC in the early 1970s showed an increase in fossil fuel-induced black C in the region during that time. Overall, a comparison of the current study with other lakes in the region revealed the effect of land use change and population growth on the lake biogeochemistry, which was clearly recorded in elemental contents and stable isotopic composition of different components of lake sediments. However, the response of each lake depended on the location (i.e., distance from the city) and size of the catchment. The larger lakes in the region appeared to have suffered the anthropogenic stress through both atmospheric and terrestrial routes, whereas the smaller and secluded lake, as in the present study, was largely influenced via atmospheric factors.

The Potential of Tufa as a Tool for Paleoenvironmental Research—A Study of Tufa from the Zrmanja River Canyon, Croatia

Tufa is a fresh-water surface calcium carbonate deposit precipitated at or near ambient temperature, and commonly contains the remains of macro- and microphytes. Many Holocene tufas are found along the Zrmanja River, Dalmatian karst, Croatia. In this work we present radiocarbon dating results of older tufa that was found for the first time at the Zrmanja River near the Village of Sanaderi. Tufa outcrops were observed at different levels, between the river bed and up to 26 m above its present level. Radiocarbon dating of the carbonate fraction revealed ages from modern, at the river bed, up to 40 kBP ~20 m above its present level. These ages fit well with the hypothesis that the Zrmanja River had a previous surface connection with the Krka River, and changed its flow direction toward the Novigrad Sea approximately 40 kBP (Marine Isotope Stage 3). Radiocarbon AMS dating of tufa organic residue yielded a maximum conventional age of 17 kBP for the highest outcrop position indicating probable penetration of younger organic material to hollow tufa structures, as confirmed by radiocarbon analyses of humin extracted from the samples. Stable carbon isotope composition (δ13C) of the carbonate fraction of (−10.4 ± 0.6)‰ and (−9.7 ± 0.8)‰ for the Holocene and the older samples, respectively, indicate the autochthonous origin of the carbonate. The δ13C values of (−30.5 ± 0.3)‰ and (−29.6 ± 0.6)‰ for organic residue, having ages <500 BP and >5000 BP, respectively, suggest a unique carbon source for photosynthesis, mainly atmospheric CO2, with an indication of the Suess effect in δ13C during last centuries. The oxygen isotopic composition (δ18O) agrees well with deposition of tufa samples in two stages, the Holocene (−8.02 ± 0.72‰) and “old” (mainly MIS 3 and the beginning of MIS 2) (−6.89 ± 0.34‰), suggesting a ~4 °C lower temperature in MIS 3 compared to the current one.

Incorporating the stable carbon isotope <sup>13</sup>C in the ocean biogeochemical component of the Max Planck Institute Earth System Model

Abstract. The stable carbon isotopic composition (δ13C) is an important variable to study the ocean carbon cycle across different timescales. We include a new representation of the stable carbon isotope 13C into the HAMburg Ocean Carbon Cycle model (HAMOCC), the ocean biogeochemical component of the Max Planck Institute Earth System Model (MPI-ESM). 13C is explicitly resolved for all oceanic carbon pools considered. We account for fractionation during air–sea gas exchange and for biological fractionation ϵp associated with photosynthetic carbon fixation during phytoplankton growth. We examine two ϵp parameterisations of different complexity: ϵpPopp varies with surface dissolved CO2 concentration (Popp et al., 1989), while ϵpLaws additionally depends on local phytoplankton growth rates (Laws et al., 1995). When compared to observations of δ13C of dissolved inorganic carbon (DIC), both parameterisations yield similar performance. However, with regard to δ13C in particulate organic carbon (POC) ϵpPopp shows a considerably improved performance compared to ϵpLaws. This is because ϵpLaws produces too strong a preference for 12C, resulting in δ13CPOC that is too low in our model. The model also well reproduces the global oceanic anthropogenic CO2 sink and the oceanic 13C Suess effect, i.e. the intrusion and distribution of the isotopically light anthropogenic CO2 in the ocean. The satisfactory model performance of the present-day oceanic δ13C distribution using ϵpPopp and of the anthropogenic CO2 uptake allows us to further investigate the potential sources of uncertainty of the Eide et al. (2017a) approach for estimating the oceanic 13C Suess effect. Eide et al. (2017a) derived the first global oceanic 13C Suess effect estimate based on observations. They have noted a potential underestimation, but their approach does not provide any insight about the cause. By applying the Eide et al. (2017a) approach to the model data we are able to investigate in detail potential sources of underestimation of the 13C Suess effect. Based on our model we find underestimations of the 13C Suess effect at 200 m by 0.24 ‰ in the Indian Ocean, 0.21 ‰ in the North Pacific, 0.26 ‰ in the South Pacific, 0.1 ‰ in the North Atlantic and 0.14 ‰ in the South Atlantic. We attribute the major sources of underestimation to two assumptions in the Eide et al. (2017a) approach: the spatially uniform preformed component of δ13CDIC in year 1940 and the neglect of processes that are not directly linked to the oceanic uptake and transport of chlorofluorocarbon-12 (CFC-12) such as the decrease in δ13CPOC over the industrial period. The new 13C module in the ocean biogeochemical component of MPI-ESM shows satisfying performance. It is a useful tool to study the ocean carbon sink under the anthropogenic influences, and it will be applied to investigating variations of ocean carbon cycle in the past.

Vertical distribution of natural abundance of stable carbon and nitrogen isotopes along the soil profile and the underlying mechanisms

Understanding the changes of natural abundance of stable carbon and nitrogen isotopes (δ13C and δ15N) along soil profile is of great importance in revealing the mechanisms of soil carbon and nitrogen cycling in terrestrial ecosystems. Based on a comprehensive review on the distribution of δ13C and δ15N along soil profile, the mechanisms underlying their vertical distribution were mainly introduced here. There were three mechanisms driving the δ13C vertical distribution in soil profile: 1) historical changes of vegetation δ13C value, 2) changes of C3-C4 species dominance in plant communities, 3) accumulation of 13C-enriched microbial-derived carbon during decomposition. The effects of 13C Suess effect on the vertical distribution of δ13C in soil profile were also discussed. There were four mechanisms underlying the vertical distribution of δ15N in soil profile: 1) 15N-depletion gas loss during denitrification, 2) accumulation of 15N-enriched microbial-derived nitrogen during decomposition, 3) accumulation of 15N-encriched mycorrhizal fungi residues in deep soil as a result of transferring 15N-depleted nitrogen compounds to plants by mycorrhizae, 4) intera-ction between soil organic matter and mineral substance. We proposed important concerning points for the future study on vertical distribution of natural abundance of stable carbon and nitrogen isotopes in soil profile.

SuessR: Regional corrections for the effects of anthropogenic CO2 on δ13C data from marine organisms

Abstract Anthropogenic CO2 emissions associated with fossil fuel combustion have caused declines in baseline oceanic δ13C values. This phenomenon, called the Suess effect, can confound comparisons of marine δ13C data from different years. The Suess effect can be corrected for mathematically; however, a variety of disparate techniques are currently used, often resulting in corrections that differ substantially. SuessR is a free, user‐friendly tool that allows researchers to calculate and apply regional Suess corrections to δ13C data from marine systems using a unified approach. SuessR updates existing methods for calculating region‐specific Suess corrections for samples collected from 1850 to 2020. It also estimates changes in phytoplankton 13C fractionation associated with increasing water temperature and aqueous CO2 concentrations, referred to here as the Laws effect. SuessR version 0.1.3 contains four built‐in regions, including three in the subpolar North Pacific (Bering Sea, Aleutian Islands and Gulf of Alaska) and one North Atlantic region (Subpolar North Atlantic). Users can also supply environmental data for regions not currently built into SuessR to generate their own custom corrections. In 2020, net corrections (Suess + Laws corrections) were as follows—Bering Sea: 1.29‰; Aleutian Islands: 1.30‰, Gulf of Alaska: 1.30‰; and Subpolar North Atlantic: 1.31‰ (compared to a global atmospheric CO2 change of ~2.43‰ across the same period). For samples collected in 2020, the net correction exceeds instrumental error (±0.2‰) when making comparisons across only eight years (i.e. 2013–2020). The magnitude of the Suess effect calculated by SuessR aligns with published estimates, whereas the Laws effect is smaller than previously calculated, resulting from updated estimates of average community cell sizes, growth rates and permeability of phytoplankton plasmalemmas (the plasma membrane which bounds the cell) to CO2. The increasing magnitude of the Suess effect means this phenomenon is no longer only of concern to historical ecologists, but now affects contemporary ecological studies using δ13C data. This highlights the importance of a unified approach for generating Suess corrections. The SuessR package provides a customizable tool that is simple to use and will improve the interpretability and comparability of future stable isotopic studies of marine ecology. ​

Seeing the forest for the trees-and the grasses: revisiting the evidence for grazer-maintained grasslands in Madagascar's Central Highlands.

Seeing the forest for the trees-and the grasses: revisiting the evidence for grazer-maintained grasslands in Madagascar's Central Highlands.

Change of coral carbon isotopic response to anthropogenic Suess effect since around 2000s

The stable carbon isotope composition (δ13C) in coral skeletons can be used to reconstruct the evolution of the dissolved inorganic carbon (DIC) in surface seawater, and its long-term declining trend during the past 200 years (~1800–2000) reflects the effect of anthropogenic Suess effect on carbonate chemistry in surface oceans. The global atmospheric CO2 concentration still has been increasing since 2000, and the Suess effect is intensifying. Considering the coral's ability of resilience and acclimatization to external environmental stressors, the response of coral δ13C to Suess effect may change and needs to be re-evaluated. In this study, ten long coral δ13C time series synthesized from different oceans were used to re-evaluate the response of coral carbonate chemistry to Suess effect under the changing environments. These δ13C time series showed a long-term declining trend since 1960s, but the declining rates slowed in eight time series since around 2000s. Considering that the declining rates of the DIC-δ13C in surface seawater from the Hawaii Ocean Time-series Station and Bermuda Atlantic Time-series Station has not changed since 2000 compared with those during 1960–1999, the change in the coral δ13C trends at eight of ten locations may indicate that the response of coral δ13C to the anthropogenic Suess effect has changed since around 2000s. This change may have resulted from coral acclimatization to external environmental stressors. To adapt to acidifying oceans, coral may have the ability to regulate the source of DIC in extracellular calcifying fluid and/or the utilization way of DIC, therefore the response of coral δ13C to anthropogenic Suess effect will change accordingly.

Evolution of the Oceanic 13C Suess Effect in the Southeastern Indian Ocean Between 1994 and 2018

AbstractThe decrease in δ13C of dissolved inorganic carbon (δ13CDIC) owing to uptake of anthropogenic CO2 (the oceanic 13C Suess effect) in the Southeastern Indian Ocean over the last decade was calculated using an extended multiparameter linear regression technique. Samples collected on the CROCCA‐2S (Coring to Reconstruct Ocean Circulation and Carbon Dioxide Across 2 Seas) cruise in November–December 2018 were compared to samples from the CLIVAR (Climate and Ocean: Variability, Predictability, and Change) and OISO (Océan Indien Service d'Observation) programs from 2007 to 2009. Surface ocean δ13CDIC decreased by an average of −0.53 ± 0.04‰ across this period, at an average rate of −0.053 ± 0.004‰ per year. This rate of δ13CDIC change is an increase from −0.021 ± 0.024‰ per year between 1994 and 2008. We find that the interior water mass most impacted by the oceanic 13C Suess effect between 2008 and 2018 was Subantarctic Mode Water (SAMW), within which δ13CDIC decreased by −0.044 ± 0.002‰ per year. Using previously published relationships between the oceanic 13C Suess effect and anthropogenic carbon, we estimate the annual storage of anthropogenic carbon within SAMW in the southeastern Indian Ocean has increased from ∼2.0 ± 0.2 μmol/kg per year between 1994 and 2008 to 5.5 ± 0.6 μmol/kg per year between 2008 and 2018.

Time series of atmospheric Δ14CO2 recorded in tree rings from Northwest China (1957–2015)

Radiocarbon (14C) is a unique and important tool for understanding carbon cycle in the nature, and its use can be significantly enhanced where reliable historical atmospheric Δ14CO2 records can be established. In China, continuous atmospheric Δ14CO2 records since the 1950s are scarce, a period when dramatic variations of Δ14CO2 occurred caused by intensive human activities. In this research, Δ14C of Qinghai spruce tree rings collected from Huangzhong (HZ) (36.27°N, 101.67°E, 2982 m amsl) were measured by Accelerator Mass Spectrometry, and a Δ14CO2 time series from 1957 to 2015 was reconstructed. The results show that HZ Δ14C was generally higher than the contemporaneous average level in the mid-high latitudes of the Northern Hemisphere. The peak value of HZ Δ14C occurred in 1964 (as bomb peak) was higher than that of other tree ring records in East Asia at a similar latitude, likely due to the impact of the atmosphere nuclear tests at Semipalatinsk (Kazakhstan). The record shows no obvious disturbance of Lop Nor nuclear weapons tests (in Northwest China) during 1964–1980, except for 1971. A local Suess effect began to appear since 2001, and the estimated atmospheric fossil fuel-derived CO2 (CO2ff) concentration increased from 3.5 ppm to 8.8 ppm from 2006 to 2015. This is associated with the implementation of the “Western Development” strategy in China. HZ Δ14C records document background Δ14C data, useful for regional carbon cycle research and atmospheric CO2ff quantification in the region. These data also provide baseline values for assessment environmental safety connected with nuclear power plants in China.

Stable isotopes (δ13C and δ15N) in black coral as new proxies for environmental record

Stable isotopes (δ13C and δ15N) in marine ecosystem are useful proxies for environmental record. In this study, a time-series analysis of δ13C and δ15N in two black coral samples collected from off-shore and near-shore environment was performed to investigate variations in climate and environment changes over the last 110 years. The results showed a decreasing trend of δ13C in both samples, implying an increase of fossil fuel consumption in modern age - the Suess effect. Meanwhile, a difference in δ15N between the offshore and nearshore black coral samples can be attributed to atmospheric transport of natural terrigenous source input and local anthropogenic activities. This study demonstrates that black coral has advantages as an environmental proxy compared with other traditional ones, and suggests that δ13C and δ15N in black coral can be used as new proxy indicators for climate changes related to anthropogenic activities.

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 (< 1mm) were more variable than those in adults (>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.

Theoretical Establishment of the Mass Balance Equation and Determination of the Proportion (<i>S</i>)<i><sub>ff</sub></i> of Fossil Fuels as an Indicator of the Suess Effect

Mass balance equations can be used to quantify the level of fossil carbon dioxide (CO2)ff at a given site by using samples of tree leaves or tree rings. These sites are often densely populated and highly industrialized areas. In this case, in addition to the natural carbon dioxide level of the site, there are several other components that are added to it. The approaches we propose in this paper are based on the isotopic fractionation of carbon and the laws of matter conservation. Mathematical equations are derived from this and we propose approaches to establish them. Our method has allowed us to come to the conclusion of the relationship that is already found in literature. But we term this relationship in another way by introducing the fraction of carbon modern F and the proportion of CO2 derived from fossil fuels, which will be noted (S)ff for the following. As an indicator of the Suess Effect, we have calculated these values in our different sites. Wooded areas sites which are located in urban areas have higher value of proportion of fossil fuel (S)ff .

Evidence of multi-decadal behavior and ecosystem-level changes revealed by reconstructed lifetime stable isotope profiles of baleen whale earplugs

Biological time series datasets provide an unparalleled opportunity to investigate regional and global changes in the marine environment. Baleen whales are long-lived sentinel species and an integral part of the marine ecosystem. Increasing anthropogenic terrestrial and marine activities alter ocean systems, and such alterations could change foraging and feeding behavior of baleen whales. In this study, we analyzed δ13C and δ15N of baleen whale earplugs from three different species (N = 6 earplugs, n = 337 laminae) to reconstruct the first continuous stable isotope profiles with a six-month resolution. Results of our study provide an unprecedented opportunity to assess behavioral as well as ecological changes. Abrupt shifts and temporal variability observed in δ13C and δ15N profiles could be indicative of behavior change such as shift in foraging location and/or trophic level in response to natural or anthropogenic disturbances. Additionally, five out of six individuals demonstrated long-term declining trends in δ13C profiles, which could suggest influence of emission of depleted 13CO2 from fossil fuel combustion referred to as the Suess effect. After adjusting the δ13C values of earplugs for the estimated Suess effect and re-evaluating δ13C profiles, significant decline in δ13C values as well as different rate of depletion suggest contribution of other sources that could impact δ13C values at the base of the food web.

A multi-decadal record of oceanographic changes of the past ~165 years (1850-2015 AD) from Northwest of Iceland.

Extending oceanographic data beyond the instrumental period is highly needed to better characterize and understand multi-decadal to centennial natural ocean variability. Here, a stable isotope record at unprecedented temporal resolution (1 to 2 years) from a new marine core retrieved off western North Iceland is presented. We aim to better constrain the variability of subsurface, Atlantic-derived Subpolar Mode Water (SPMW), using near surface-dwelling planktic foraminifera and Arctic Intermediate Water (AIW) mass changes using benthic foraminifera over the last ~165 years. The reconstruction overlaps in time with instrumental observations and a direct comparison reveals that the δ18O record of Neogloboquadrina pachyderma is reliably representing temperature fluctuations in the SPMWs. Trends in the N. pachyderma δ13C record match the measured phosphate concentration in the upper 200 m on the North Icelandic Shelf well. Near surface-dwelling foraminifera trace anthropogenic CO2 in the Iceland Sea by ~ 1950 ± 8, however, a reduced amplitude shift in the Marine Suess effect is identified. We argue that this is caused by a contemporary ongoing increase in marine primary productivity in the upper ocean due to enhanced Greenland’s freshwater discharge that has contributed to a nutrient-driven fertilization since the 1940s/50s (Perner et al., 2019). Multi-decadal variability is detected. We find that the 16-year periodicity evident in SPMW and AIWs based on the δ18O of N. pachyderma and M. barleeanum is a signal of SST anomalies propagated into the Nordic Seas via the Atlantic inflow branches around Iceland. Spectral analyses of the planktic foraminiferal δ13C signal indicate intermittent 30-year cycles that are likely reflecting the ocean response to atmospheric variability, presumably the East Atlantic Pattern. A long-term trend in benthic δ18O suggests that Atlantic-derived waters are expanding their core within the water column from the subsurface into deeper intermediate depths towards the present day. This is a result of increased transport by the North Icelandic Irminger Current to the North Iceland Shelf over the historical era.

Long-term changes in habitat and trophic level of Southern Ocean squid in relation to environmental conditions

Long-term studies of pelagic nekton in the Southern Ocean and their responses to ongoing environmental change are rare. Using stable isotope ratios measured in squid beaks recovered from diet samples of wandering albatrosses Diomedea exulans, we assessed decadal variation (from 1976 to 2016) in the habitat (δ13C) and trophic level (δ15N) of five important Southern Ocean squid species in relation to indices of environmental conditions—Southern Oscillation Index (SOI) and Southern Annular Mode (SAM). Based on δ13C values, corrected for the Suess effect, habitat had changed over the last 50 years for Taonius sp. B (Voss), Gonatus antarcticus, Galiteuthis glacialis and Histioteuthis atlantica but not Moroteuthopsis longimana. By comparison, mean δ15N values were similar across decades for all five species, suggesting minimal changes in trophic levels. Both SAM and SOI have increased in strength and frequency over the study period but, of the five species, only in Taonius sp. B (Voss) did these indices correlate with, δ13C and δ15N values, indicating direct relationships between environmental conditions, habitat and trophic level. The five cephalopod species therefore changed their habitats with changing environmental conditions over the last 50 years but maintained similar trophic levels. Hence, cephalopods are likely to remain important prey for top predators in Southern Ocean food webs, despite ongoing climate change.

Great Blue Hole (Lighthouse Reef, Belize): A continuous, annually-resolved record of Common Era sea surface temperature, Atlantic Multidecadal Oscillation and cyclone-controlled run-off

The Holocene (<11.7 kyr BP) is characterized by several periods of distinct climate changes. Some of these climate variations had extensive effects on mankind and coincided with demises of extinct high civilizations. Annually-resolved climate reconstructions will certainly play an increasingly important role in public perception, when applying these past patterns to the recent climate debate. The future consequences of the ongoing climate crisis are still challenging to predict, due to the lack of comprehensive, annually-resolved and continuous sea-surface temperature (SST) data. Our 8.55 m long sediment core from the bottom of the Great Blue Hole (Lighthouse Reef, Belize) provides an annually-resolved, continuous and unique south-western Caribbean climate record for the last 1885 years. The varved, “lake-like” sinkhole successions of marine carbonates encompass approximately the entire Common Era (0 CE-modern), a time window, which is key for studying climatic variations and their effects on human society. Our SST record is based on stable isotopes (δ18O) and molecular proxy applications (TEX86). Throughout the Common Era, oxygen isotopes (δ18O) and TEX86 data imply a general SST rise of 0.5 °C and 1.3 °C, respectively, within the south-western Caribbean. The modulation of SST within the Common Era time series likely operated on two different time levels: (1) Solar (e.g., “Gleissberg Cycles”) and volcanic activity triggered climate changes, which in turn induced responses of the Atlantic Multidecadal Oscillation (AMO), the North Atlantic Oscillation (NAO) and the El-Niño-Southern Oscillation (ENSO). Their changing mode of action has been identified as a likely origin of the primary, i.e., centennially scaled SST variability. We suspect long-term positive AMO and NAO modes as the primary key control mechanisms of the Dark Ages Cold and Medieval Warm Period SST patterns. ENSO mode modulation likely exerted primary control on regional SST variability during the Little Ice Age and the Modern Global Warming. (2) Our δ18O data further indicate a striking secondary control on multi-decadal time scales: δ18O variations occur with 32–64 years periodicity. This signal is clearly evidence of SST modulation controlled by AMO phase changes (50–70 years) over almost the entire Common Era. Our carbon isotope record (δ13C) exhibits two remarkable negative anomalies and a long-term up-core decreasing trend. The first excursion (drop of 0.5‰) occurred with the onset of the Medieval Warm Period, which is reconstructed to be a peak time in south-western Caribbean tropical cyclone (TC) activity. This overlap is stressing a potential context between TC activity, enhanced coastal run-off and increased soil-erosion reflected by 13C-depleted carbon isotopes. A second anomaly (>1900 CE) is more likely the result of the “Suess Effect” (anthropogenic impact of the Industrial Revolution on carbon isotopes composition) than another reflection of a TC peak activity interval.

Stable isotopes of amino acids from reef fishes uncover Suess and nitrogen enrichment effects on local ecosystems

In 1979, the Suess effect was described as decreasing δ13C in the oceans linked to anthropogenic CO2 emissions. After years of over-fertilization of farming soils and runoff, we hypothesized that δ15N in coastal environments would also decline, whereby synthetic fertilizers lead to depletion of the heavy isotope 15N. We used museum-preserved and modern samples of 3 fishes from Otago, New Zealand, to reconstruct the isotopic baselines of C and N and assess specific trophic positions through time (1955-present) based on bulk and amino acid stable isotope values. Our sample set included Odax pullus, a strictly herbivorous species, and 2 commercially important species: Nemadactylus macropterus and Parapercis colias. Muscle tissue of the fishes recorded the change in δ13CBulk through time, which matched estimated Suess effect values for New Zealand. We also resolved the effects on the C isotopic baseline from natural changes in the food web using analysis of the δ13C of essential amino acids and found that while P. colias maintained a steady diet, the food web position of N. macropterus likely changed. Analysis of δ15N of phenylalanine in O. pullus indicated a decrease of 0.023‰ yr-1 since 1955, which corroborates our coastal N-enrichment hypothesis. Furthermore, we found that isotopic changes for N. macropterus were consistent with overfishing and habitat degradation in the region. These data provide vital information for our resolution and understanding of how past environments have changed in terms of both anthropogenic influences on coastal food web structure and biogeochemical cycles of C and N in marine ecosystems.

Simulating stable carbon isotopes in the ocean component of the FAMOUS general circulation model with MOSES1 (XOAVI)

Abstract. Ocean circulation and the marine carbon cycle can be indirectly inferred from stable and radiogenic carbon isotope ratios (δ13C and Δ14C, respectively), measured directly in the water column, or recorded in geological archives such as sedimentary microfossils and corals. However, interpreting these records is non-trivial because they reflect a complex interplay between physical and biogeochemical processes. By directly simulating multiple isotopic tracer fields within numerical models, we can improve our understanding of the processes that control large-scale isotope distributions and interpolate the spatiotemporal gaps in both modern and palaeo datasets. We have added the stable isotope 13C to the ocean component of the FAMOUS coupled atmosphere–ocean general circulation model, which is a valuable tool for simulating complex feedbacks between different Earth system processes on decadal to multi-millennial timescales. We tested three different biological fractionation parameterisations to account for the uncertainty associated with equilibrium fractionation during photosynthesis and used sensitivity experiments to quantify the effects of fractionation during air–sea gas exchange and primary productivity on the simulated δ13CDIC distributions. Following a 10 000-year pre-industrial spin-up, we simulated the Suess effect (the isotopic imprint of anthropogenic fossil fuel burning) to assess the performance of the model in replicating modern observations. Our implementation captures the large-scale structure and range of δ13CDIC observations in the surface ocean, but the simulated values are too high at all depths, which we infer is due to biases in the biological pump. In the first instance, the new 13C tracer will therefore be useful for recalibrating both the physical and biogeochemical components of FAMOUS.