Harro A. J. Meijer

The role of solar forcing upon climate change.

Evidence for millennial-scale climate changes during the last 60,000 years has been found in Greenland ice cores and North Atlantic ocean cores. Until now, the cause of these climate changes remained a matter of debate. We argue that variations in solar activity may have played a significant role in forcing these climate changes. We review the coincidence of variations in cosmogenic isotopes (14C and 10Be) with climate changes during the Holocene and the upper part of the last Glacial, and present two possible mechanisms (involving the role of solar UV variations and solar wind/cosmic rays) that may explain how small variations in solar activity are amplified to cause significant climate changes. Accepting the idea of solar forcing of Holocene and Glacial climatic shifts has major implications for our view of present and future climate. It implies that the climate system is far more sensitive to small variations in solar activity than generally believed.

Spatiotemporal patterns of carbon‐13 in the global surface oceans and the oceanic suess effect

A global synthesis of the 13C/12C ratio of dissolved inorganic carbon (DIC) in the surface ocean is attempted by summarizing high-precision data obtained from 1978 to 1997 in all major ocean basins. The data, mainly along transects but including three subtropical time series, are accompanied by simultaneous, precise measurements of DIC concentration and titration alkalinity. The reduced isotopic ratio, δ13C, in the surface ocean water is governed by a balance between biological and thermodynamic processes. These processes have strongly opposing tendencies, which result in a complex spatial pattern in δ13C with relatively little variability. The most distinctive feature in the spatial distribution of δ13C seen in our data is a maximum of δ13C near the subantarctic front with sharply falling values to the south. We attribute this feature to a combination of biological uptake of CO2 depleted in 13C (low δ13C) and air-sea exchange near the front and upwelling further south of waters with low δ13C resulting from the remineralization of organic matter. Additional features are maxima in δ13C downstream of upwelling regions, reflecting biological uptake, and minima in the subtropical gyres caused by strongly temperature dependent thermodynamic isotopic fractionation. At the time series stations, two in the North Atlantic Ocean and one in the North Pacific, distinct seasonal cycles in δ13C are observed, the Pacific data exhibiting only about half the amplitude of the Atlantic. Secular decreases in δ13C caused by the invasion of isotopically light anthropogenic CO2 into the ocean (the 13C Suess effect) have been identified at these time series stations and also in data from repeated transects in the Indian Ocean and the tropical Pacific. A tentative global extrapolation of these secular decreases yields a surface oceanic 13C Suess effect of approximately −0.018‰ yr−1 from 1980 to 1995. This effect is nearly the same as the 13C Suess effect observed globally in the atmosphere over the same period. We attribute this response to a deceleration in the growth rate of anthropogenic CO2 emissions after 1979, which subsequently has reduced the atmospheric 13C Suess effect more than the surface ocean effect.

A three-dimensional synthesis study of δ18O in atmospheric CO2: 1. Surface fluxes

The isotope O-18 in CO2 is of particular interest in studying the global carbon cycle because it is sensitive to the processes by which the global land biosphere absorbs and respires CO2. Carbon dioxide and water exchange isotopically both in leaves and in soils, and the O-18 character of atmospheric CO2 is strongly influenced by the land biota, which should constrain the gross primary productivity and total respiration of land ecosystems, In this study we calculate the global surface fluxes of O-18 for vegetation and soils using the SiB2 biosphere model coupled with the Colorado State University general circulation model. This approach makes it possible to use physiological variables that are consistently weighted by the carbon assimilation rate and integrated through the vegetation canopy, We also calculate the air-sea exchange of O-18 and the isotopic character of fossil emissions and biomass burning. Global mean values of the isotopic exchange with each reservoir are used to close the global budget of O-18 in CO2 results confirm the fact that the land biota exert a dominant control on the delta(18)O of the atmospheric reservoir, At the global scale, exchange with the canopy produces an isotopic enrichment of CO2, whereas exchange with soils has the opposite effect.

The use of electrolysis for accurate delta O-17 and delta O-18 isotope measurements in water

Abstract We present a new system to measure the relative isotopic abundances of both rare isotopes of oxygen in water. Using electrolysis with CuSO4 as electrolyte, water is transformed into oxygen gas. This gas is subsequently analyzed with a standard Isotope Ratio Mass Spectrometer. We investigated the features of the system in detail. The results for δ17O and δ18O are carefully calibrated against δ18O of VSMOW using our “conventional” H2O-CO2 equilibrium system. For the electrolysis system, we obtain an accuracy (including calibration) of 0.10‰ for δ18O, and 0.07‰ for δ17O. Finally, we demonstrate the usefulness and accuracy of the system by analyzing a large set of natural waters (both fresh and salt waters). We establish the 17O and 18O relation to be of the type: 1 + δ17O = (1 + δ18O)λ, and find λ to be 0.5281 ± 0.0015. We conclude that the 17O fractionation in water appears to be completely analogous to that of 18O. Still, measurements concerning the equilibrium and kinetic fractionation of the eva...

Interannual variability in the oxygen isotopes of atmospheric CO2 driven by El Nino

The stable isotope ratios of atmospheric CO2 (18O/16O and 13C/12C) have been monitored since 1977 to improve our understanding of the global carbon cycle, because biosphere–atmosphere exchange fluxes affect the different atomic masses in a measurable way. Interpreting the 18O/16O variability has proved difficult, however, because oxygen isotopes in CO2 are influenced by both the carbon cycle and the water cycle. Previous attention focused on the decreasing 18O/16O ratio in the 1990s, observed by the global Cooperative Air Sampling Network of the US National Oceanic and Atmospheric Administration Earth System Research Laboratory. This decrease was attributed variously to a number of processes including an increase in Northern Hemisphere soil respiration; a global increase in C4 crops at the expense of C3 forests; and environmental conditions, such as atmospheric turbulence and solar radiation, that affect CO2 exchange between leaves and the atmosphere. Here we present 30 years’ worth of data on 18O/16O in CO2 from the Scripps Institution of Oceanography global flask network and show that the interannual variability is strongly related to the El Niño/Southern Oscillation. We suggest that the redistribution of moisture and rainfall in the tropics during an El Niño increases the 18O/16O ratio of precipitation and plant water, and that this signal is then passed on to atmospheric CO2 by biosphere–atmosphere gas exchange. We show how the decay time of the El Niño anomaly in this data set can be useful in constraining global gross primary production. Our analysis shows a rapid recovery from El Niño events, implying a shorter cycling time of CO2 with respect to the terrestrial biosphere and oceans than previously estimated. Our analysis suggests that current estimates of global gross primary production, of 120 petagrams of carbon per year, may be too low, and that a best guess of 150–175 petagrams of carbon per year better reflects the observed rapid cycling of CO2. Although still tentative, such a revision would present a new benchmark by which to evaluate global biospheric carbon cycling models.

Comprehensive inter-laboratory calibration of reference materials for delta O-18 versus VSMOW using various on-line high-temperature conversion techniques

Internationally distributed organic and inorganic oxygen isotopic reference materials have been calibrated by six laboratories carrying out more than 5300 measurements using a variety of high-temperature conversion techniques (HTC)a in an evaluation sponsored by the International Union of Pure and Applied Chemistry (IUPAC). To aid in the calibration of these reference materials, which span more than 125 per thousand, an artificially enriched reference water (delta(18)O of +78.91 per thousand) and two barium sulfates (one depleted and one enriched in (18)O) were prepared and calibrated relative to VSMOW2b and SLAP reference waters. These materials were used to calibrate the other isotopic reference materials in this study, which yielded: Reference material delta(18)O and estimated combined uncertainty IAEA-602 benzoic acid+71.28 +/- 0.36 per thousand USGS 35 sodium nitrate+56.81 +/- 0.31 per thousand IAEA-NO-3 potassium nitrate+25.32 +/- 0.29 per thousand IAEA-601 benzoic acid+23.14 +/- 0.19 per thousand IAEA-SO-5 barium sulfate+12.13 +/- 0.33 per thousand NBS 127 barium sulfate+8.59 +/- 0.26 per thousand VSMOW2 water 0 per thousand IAEA-600 caffeine-3.48 +/- 0.53 per thousand IAEA-SO-6 barium sulfate-11.35 +/- 0.31 per thousand USGS 34 potassium nitrate-27.78 +/- 0.37 per thousand SLAP water-55.5 per thousand The seemingly large estimated combined uncertainties arise from differences in instrumentation and methodology and difficulty in accounting for all measurement bias. They are composed of the 3-fold standard errors directly calculated from the measurements and provision for systematic errors discussed in this paper. A primary conclusion of this study is that nitrate samples analyzed for delta(18)O should be analyzed with internationally distributed isotopic nitrates, and likewise for sulfates and organics. Authors reporting relative differences of oxygen-isotope ratios (delta(18)O) of nitrates, sulfates, or organic material should explicitly state in their reports the delta(18)O values of two or more internationally distributed nitrates (USGS 34, IAEA-NO-3, and USGS 35), sulfates (IAEA-SO-5, IAEA-SO-6, and NBS 127), or organic material (IAEA-601 benzoic acid, IAEA-602 benzoic acid, and IAEA-600 caffeine), as appropriate to the material being analyzed, had these reference materials been analyzed with unknowns. This procedure ensures that readers will be able to normalize the delta(18)O values at a later time should it become necessary.The high-temperature reduction technique for analyzing delta(18)O and delta(2)H is not as widely applicable as the well-established combustion technique for carbon and nitrogen stable isotope determination. To obtain the most reliable stable isotope data, materials should be treated in an identical fashion; within the same sequence of analyses, samples should be compared with working reference materials that are as similar in nature and in isotopic composition as feasible.

Status report : The Groningen AMS facility

The Groningen AMS facility has been in operation since 1994. The AMS is based on a 2.5 MV tandetron accelerator. It is an automatic mass spectrometer, dedicated to C-14 analysis. Thus far, a grand total of about 16 000 C-14 targets have been measured. We report here on the status and performance of the facility, technical improvements and a precision study on atmospheric samples

Simultaneous Determination of the 2H/1H, 17O/16O, and 18O/16O Isotope Abundance Ratios in Water by Means of Laser Spectrometry

We demonstrate the first successful application of infrared laser spectrometry to the accurate, simultaneous determination of the relative (2)H/(1)H, (17)O/(16)O, and (18)O/(16)O isotope abundance ratios in water. The method uses a narrow line width color center laser to record the direct absorption spectrum of low-pressure gas-phase water samples (presently 10 μL of liquid) in the 3-μm spectral region. It thus avoids the laborious chemical preparations of the sample that are required in the case of the conventional isotope ratio mass spectrometer measurement. The precision of the spectroscopic technique is shown to be 0.7‰ for δ(2)H and 0.5‰ for δ(17)O and δ(18)O (δ represents the relative deviation of a samples isotope abundance ratio with respect to that of a calibration material), while the calibrated accuracy amounts to about 3 and 1‰, respectively, for water with an isotopic composition in the range of the Standard Light Antarctic Precipitation and Vienna Standard Mean Ocean Water international standards.

A three-dimensional synthesis study of δ18O in atmospheric CO2: 2. Simulations with the TM2 transport model

In this study, using a three-dimensional (3-D) tracer modeling approach, we simulate the •80 of atmospheric CO2. In the atmospheric transport model TM2 we prescribe the surface fluxes of •80 due to vegetation and soils, ocean exchange, fossil emissions, and biomass burning. The model simulations are first discussed for each reservoir separately, then all the reservoirs are combined to allow a comparison with the atmospheric •80 measurements made by the National Oceanic and Atmospheric Administration-University of Colorado, Scripps Institution of Oceanography-Centrum Voor Isotopen Onderzoek (United States-Netherlands) and Commonwealth Scientific and Industrial Research Organisation (Australia) air sampling programs. Insights into the latitudinal differences and into the seasonal cycle of •80 in CO2 are gained by looking at the contribution of each source. The isotopic exchange with soils induces a large isotopic depletion over the northern hemisphere continents, which overcomes the concurrent effect of isotopic enrichment due to leaf exchange. Compared to the land biota, the ocean fluxes and the anthropogenic CO2 source have a relatively minor influence. The shape of the latitudinal profile in •80 appears determined primarily by the respiration of the land biota, which balances photosynthetic uptake over the course of a year. Additional information on the phasing of the terrestrial carbon exchange comes from the seasonal cycle of •80 at high northern latitudes.

Radiocarbon analyses along the EDML ice core in Antarctica

Trend analyses were performed on several indicators of Arctic haze using data from sites located in the North American, Norwegian, Finnish and Russian Arctic for the spring months of March and April. Concentrations of nonseasalt (nss) SO4= in the Canadian, Norwegian and Finnish Arctic were found to have decreased by 30–70% from the early 1990s to present. The magnitude of the decrease depended on location. The trend in nss SO4= at Barrow, Alaska from 1997 to present, is unclear. Measurements at Barrow of light scattering by aerosols show a decrease of about 50% between the early 1980s and the mid-1990s for both March and April. Restricting the analysis to the more recent period of 1997 to present indicates an increase in scattering of about 50% during March. Aerosol NO3- measured at Alert, Canada has increased by about 50% between the early 1990s and 2003. Nss K+ and light absorption, indicators of forest fires, have a seasonal maximum during the winter and spring and minimum during the summer and fall at both Alert and Barrow. Based on these data, the impact of summertime forest fire emissions on low-altitude surface sites within the Arctic is relatively small compared to winter/spring emissions. Key uncertainties about the impact of long range transport of pollution to the Arctic remain including the certainty of the recent detected trends; sources, transport and trends of soot; and radiative effects due to complex interactions between aerosols, clouds and radiation in the Arctic.