共查询到20条相似文献，搜索用时 296 毫秒
1.
Ulrike Fallet Jenny E. Ullgren Hendrik M. van Aken Herman Ridderinkhof 《Geochimica et cosmochimica acta》2011,75(20):5834-5848
Accurate sea surface temperature (SST) proxies are important for understanding past ocean and climate systems. Here, we examine material collected from a deep-moored sediment trap in the Mozambique Channel (SW Indian Ocean) to constrain and compare both inorganic (δ18O, Mg/Ca) and organic (, TEX86) temperature proxies in a highly dynamic oceanographic setting for application in paleoceanography. High-resolution time-series current velocity data from long-term moorings (2003 - present) deployed across the Mozambique Channel reveal the periodic migration of four to six meso-scale eddies through the channel per year. These meso-scale eddies strongly influence water mass properties including temperature and salinity. Despite the dynamic oceanographic setting, fluxes of the surface-dwelling planktonic foraminifera Globigerinoidesruber and Globigerinoides trilobus follow a seasonal pattern. Temperatures reconstructed from G. ruber and G. trilobus δ18O and Mg/Ca closely mirror seasonal SST variability and their flux-weighted annual mean SSTs of 28.1 °C and 27.3 °C are in close agreement with annual mean satellite SST (27.6 °C). The sub-surface dwelling foraminifera Neogloboquadrina dutertrei and Globigerinoides scitula recorded high-frequency temperature variations that, on average, reflect conditions at water depths of 50-70 m and 200-250 m, respectively. Concentrations and fluxes of organic compounds (alkenones and crenarchaeol) display no or only moderate seasonality but flux weighted means of the associated temperature signatures, , and of 28.3 °C and 28.1 °C, respectively, also closely reflect mean annual SST. We analyzed all time-series data using multiple statistical approaches including cross-correlation and spectral analysis. Eddy variability was clearly expressed in the statistical analysis of physical oceanographic parameters (current velocity and sub-surface temperature) and revealed a frequency of four to six cycles per year. In contrast, statistical analysis of proxy data from the sediment trap did not reveal a significant coupling between eddy migration and organic compound fluxes or reconstructed temperatures. This is likely a result of the relatively low resolution (21 days) and short (2.5 years) duration of the time series, which is close to the detection limit of the eddy frequency. 相似文献
2.
Climatic and environmental controls on the occurrence and distributions of long chain alkenones in lakes of the interior United States 总被引：1，自引：0，他引：1
Jaime L. Toney Yongsong Huang Sherilyn C. Fritz Eric Grimm 《Geochimica et cosmochimica acta》2010,74(5):1563-7565
Long chain alkenones (LCA) are temperature-sensitive lipids with great potential for quantitative reconstruction of past continental climate. We conducted the first survey for alkenone biomarkers from 55 different lakes in the Northern Great Plains and Nebraska Sand Hills of the United States. Among those surveyed, we found 13 lakes that contain LCAs in the surface sediments. The highest concentrations of alkenones in sediments are found in cold (mean annual air temperature ∼11 °C versus 17 °C in our warmest sites), brackish to mesosaline (salinity = 8.5-9.7 g/L), and alkaline (pH = 8.4-9.0) lakes with high concentrations of sodium and sulfate. The dynamics of stratification and nutrient availability also appear to play a role in LCA abundance, as early spring mixing promotes a bloom of alkenone-producing haptophytes. Four of the alkenone-containing sites contain the C37:4 alkenone; however, we discovered an unprecedented lacustrine alkenone distribution in a cluster of lakes, with a total absence of C37:4 alkenone. We attribute this unusual composition to a different haptophyte species and show that the sulfate:carbonate ratio may control the occurrence of these two distinct populations. We created a new in-situ temperature calibration for lacustrine sites that contain C37:4 using a water-column calibration from Lake George, ND and show that is linearly correlated to lake water temperature (R2 = 0.74), but is not. A number of lakes contain an unidentified compound series that elutes close to the LCAs, highlighting the importance of routine GC-MS examination prior to using lacustrine LCAs for paleotemperature reconstructions. 相似文献
3.
We investigated alkenones recorded in suspended particles and a settling particle time series collected at three stations, 40N (40°N, 165°E), KNOT (44°N, 155°E), and 50N (50°N, 165°E), in the northwestern North Pacific from December 1997 to May 1999. Emiliania huxleyi, the most abundant alkenone producer in this area, is present in surface to subsurface (to ∼50 m depth) waters. The alkenone concentrations recorded in the suspended particles indicated that the seasonal alkenone particle distribution differed significantly interannually. Alkenone export fluxes at the three sediment-trap stations ranged from 0.16 to 49.3 μg m−2 day−1, and the maximum export flux, which occurred in summer to fall (July-November), was associated with a high organic carbon export flux. The amount of alkenone produced during the maximum export season accounted for 60-80% of the total annual amount of alkenone, and the alkenones accumulated in the sediment below the traps had characteristics corresponding to subsurface waters during the summer-autumn season. Alkenone-derived temperatures recorded in suspended particles corresponded to the in situ temperature within ∼2 °C. Although alkenone-derived temperatures corresponded approximately to the temperatures observed in the stratified subsurface waters at the three trap stations during the high-export season, large differences were observed during the low-export (winter-spring) period. For example, the alkenone-derived temperatures observed at stations KNOT and 50N were much higher than the in situ subsurface temperatures reported in the World Ocean Atlas 2001. Relatively large differences between alkenone-derived temperatures and in situ temperatures in the subarctic might be due to (1) a low-light limitation or (2) contributions of allochthonous alkenones in particulate material transported from subtropical areas within a warm-core ring. 相似文献
4.
Alkenone paleothermometry: Biological lessons from marine sediment records off western South America
Fredrick G. Prahl Alan C. Mix Margaret A. Sparrow 《Geochimica et cosmochimica acta》2006,70(1):101-117
An empirical global core-top calibration that relates the alkenone unsaturation index to mean annual SST (maSST) is statistically the same as that defined for a subarctic Pacific strain of Emiliania huxleyi (CCMP1742) grown exponentially in batch culture under isothermal conditions. Although both equations have been applied widely for paleoSST reconstruction, uncertainty still stems from two key ecological factors: variability in the details of biosynthesis among genetically distinct alkenone-producing strains, and impacts of non-thermal physiological growth factors on . New batch culture experiments with CCMP1742 here reveal that diverge systematically from the core-top calibration in response to nutrient depletion and light deprivation, two physiological stresses experienced by phytoplankton populations in the real ocean. Other aspects of alkenone/alkenoate composition also respond to these stresses and may serve as signatures of such effects, providing an opportunity to detect, understand, and potentially correct for such impacts on the geologic record. A test case documents that sediments from the Southeast Pacific display the alkenone/alkenoate compositional signature characteristic of cells physiologically stressed by light deprivation. Such an observation could be explained if marine snow provided a major vector of sedimentation for these biomarkers. Late Pleistocene records in the Southeast Pacific yield plausible paleotemperature histories of ice-age cooling, but ice-age alkenone/alkenoate signatures fall outside the range of modern calibration samples of similar . They better match core-top samples deposited beneath waters characterized by much cooler maSST, suggesting key features of ice-age ecology for alkenone-producing haptophytes were different from today, and that the index taken alone may misgauge the total range of ice-age cooling at these locations. Analysis of the full spectrum of alkenone/alkenoate compositions preserved in sediments opens up a new opportunity that may improve the accuracy of paleotemperature estimates based on simple analysis and help resolve longstanding disagreements between various paleotemperature reconstruction methods. 相似文献
5.
Jung-Hyun Kim Jaap van der Meer Peer Helmke Francesca Sangiorgi Ellen C. Hopmans 《Geochimica et cosmochimica acta》2010,74(16):4639-4654
Several studies have shown that there is a strong relationship between the distribution of crenarchaeotal isoprenoid glycerol dibiphytanyl glycerol tetraethers (GDGTs) and sea surface temperature (SST). Based on this, a ratio of certain GDGTs, called TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms), was developed as a SST proxy. In this study, we determined the distribution of crenarchaeotal isoprenoid GDGTs in 116 core-top sediments mostly from (sub)polar oceans and combined these data with previously published core-top data. Using this extended global core-top dataset (n = 426), we re-assessed the relationship of crenarchaeal isoprenoid GDGTs with SST. We excluded data from the Red Sea from the global core-top dataset to define new indices and calibration models, as the Red Sea with its elevated salinity appeared to behave differently compared to other parts of the oceans. We tested our new indices and calibration models on three different paleo datasets, representing different temperature ranges. Our results indicate that the crenarchaeol regio-isomer plays a more important role for temperature adaptation in (sub)tropical oceans than in (sub)polar oceans, suggesting that there may be differences in membrane adaptation of the resident crenarchaeotal communities at different temperatures. We, therefore, suggest to apply two different calibration models. For the whole calibration temperature range (−3 to 30 °C), a modified version of TEX86 with a logarithmic function which does not include the crenarchaeol regio-isomer, called , is shown to correlate best with SST: (r2 = 0.86, n=396, p <0.0001). Application of on sediments from the subpolar Southern Ocean results in realistic absolute SST estimates and a similar SST trend compared to a diatom SST record from the same core. , which is defined as the logarithmic function of TEX86, yields the best correlation with SST, when the data from the (sub)polar oceans are removed: (r2 = 00.87, n = 255, p < 0.0001). Furthermore, gives the best correlation for mescosm data with temperatures ranging between 10 and 46 °C. For Quaternary sediments from the tropical Arabian Sea, both and yield similar trends and SST estimates. However, the extrapolation of calibration on a sediment record from a greenhouse world ocean predicts more reliable absolute SST estimates and relative SST changes in agreement with estimates based on the δ18O of planktonic foraminifera. Based on the comparison of and derived SSTs using the core top data, we recommend applying above 15 °C and below 15 °C. In cases where paleorecords encompass temperatures both below and above 15 °C, we suggest to use . 相似文献
6.
7.
8.
Sunita R. Shah Gesine Mollenhauer Timothy I. Eglinton 《Geochimica et cosmochimica acta》2008,72(18):4577-4594
Understanding the supply and preservation of glycerol dibiphytanyl glycerol tetraethers (GDGTs) in marine sediments helps inform their use in paleoceanography. Compound-specific radiocarbon measurements of sedimentary alkenones from multiple environments have been used to gain insight into processes that affect paleotemperature reconstructions. Similar analyses are warranted to investigate how analogous processes affecting GDGTs impact TEX86 paleotemperatures. Here we present radiocarbon measurements on individual GDGTs from Bermuda Rise and Santa Monica Basin sediments and discuss the results in the context of previous studies of co-depositional alkenones and foraminifera. The 14C contents of GDGTs and planktonic foraminifera in Bermuda Rise are very similar, suggesting a local source; and TEX86-derived temperatures agree more closely with foraminiferal temperatures than do temperatures. In contrast, GDGTs in Santa Monica Basin are depleted in 14C relative to both alkenones and foraminifera, and TEX86 temperatures agree poorly with known surface water values. We propose three possible factors that could explain these results: (i) GDGTs may be labile relative to alkenones during advective transport through oxic waters; (ii) archaeal production deep in the water column may contribute 14C-depleted GDGTs to sediments; and (iii) some GDGTs also may derive from sedimentary archaeal communities. Each of these three processes is likely to occur with varying relative importance depending on geographic location. The latter two may help to explain why TEX86 temperature reconstructions from Santa Monica Basin do not appear to reflect actual sea surface temperatures. Terrigenous GDGTs are unlikely to be major contributors to Bermuda Rise or Santa Monica Basin sediments, based on values of the BIT index. The results also indicate that the crenarchaeol regioisomer is governed by processes different from other GDGTs. Individual measurements of the crenarchaeol regioisomer are significantly depleted in 14C relative to co-occurring GDGTs, indicating an alternative origin for this compound that presently remains unknown. Re-examination of the contribution of crenarchaeol regioisomer to the TEX86 index shows that it is a significant influence on the sensitivity of temperature reconstructions. 相似文献
9.
10.
Isotopic composition of nitrate in five German rivers discharging into the North Sea 总被引：6，自引：0，他引：6
We determined concentrations and isotopic composition of nitrate in five German rivers (Rhine, Elbe, Weser, Ems, and Eider) that discharge into the North Sea. Samples were obtained on a biweekly to monthly basis and chemical and isotopic analyses were conducted for the period January 2006 to March 2007 at sampling stations situated before estuarine mixing with North Sea water. We observed maximum nitrate loads in winter and fall, when both discharge and concentration of nitrate are highest. Mean annual isotope values in nitrate ranged from 8.2‰ to 11.3‰ for and 0.4‰ to 2.2‰ for . The ranges of isotope values suggest that nitrate in these rivers derives from soil nitrification, sewage, and/or manure. These and published data on other rivers in northern Europe and northern America reveal a correlation between agricultural land use (>60% in the catchment areas of rivers examined) and values. The rivers Rhine, Elbe, Weser and Ems show similar seasonal patterns of the isotopic fractionation of nitrate with increasing values and simultaneously decreasing concentrations during summer months, indicating that assimilation of nitrate is the main fractionation process of riverine nitrate. Isotopic signals in winter are more depleted than the mean summer isotope values, attributed to less microbial activity and assimilative processes. Load weighted nitrate δ15N of the riverine input to the German Bight Coastal Water mass before estuarine mixing and processing is between 8‰ and 12‰. The high δ15N value of river nitrate is matched by high δ15N of nitrate in surface sediments in the German Bight. 相似文献
11.
12.
13.
14.
15.
Gypsum precipitation kinetics were examined from a wide range of chemical compositions , ionic strengths (4.75-10 m) and saturation state with respect to gypsum (1.16-1.74) in seeded batch experiments of mixtures of Ca2+-rich Dead Sea brine and -rich seawater. Despite the variability in the experimental solutions, a single general rate law was formulated to describe the heterogeneous precipitation rate of gypsum from these mixtures:
16.
17.
18.
We investigated the characteristics of the alkenones produced by a bloom of Emiliania huxleyi in the eastern Bering Sea in 2000. Alkenones were detected in surface waters between 57°N and 63°N, where phosphate concentrations were low and the ammonium/nitrate ratio was high. The total alkenone content (C37:2, C37:3, and C37:4) ranged from 22.0 to 349 μg g−1 in suspended particles and from 0.109 to 1.42 μg g−1 in surface sediments. This suggests that a large proportion of the particulate alkenones synthesized in the surface water rapidly degraded within the water column and/or at the water-sediment interface of the Bering Shelf. The change in the stable carbon isotopic composition (δ13C) of C37:3 alkenone could not be explained only by variation in [CO2(aq)] in the surface water but also depended on the growth rate of E. huxleyi. The alkenone unsaturation index (UK′37) was converted into an alkenone “temperature” with three equations
[Prahl et al 1988],
[Sikes et al 1997] and [Müller et al 1998]; Sikes et al.’s (1997) equation gave the best correlation with the observed sea surface temperature (SST) in the eastern Bering Sea. However, some temperatures estimated by Sikes et al.’s (1997) equation from the UK′37 varied from the observed SST, possibly because of the rapidly changing rate of alkenone synthesis in the logarithmic growth stage or the low rate of alkenone synthesis when nutrients were limiting. Temperatures estimated from UK′37 in the surface sediments (6.8-8.2°C) matched the observed SST in September (7-8°C) but differed from the annual average SST of 4 to 5°C, suggesting that most of the alkenone in the eastern Bering Sea was synthesized during limited periods, for instance, in September. The relative amounts of C37:4 alkenone as proportions of the total alkenones (referred to as C37:4%) were high, ranging from 18.3 to 41.4%. Low-salinity water (<32 psu) within the study area would have contributed to the high C37:4% because a negative linear relationship between C37:4% and salinity was found in this study. 相似文献
19.
We investigated relationships between sedimentary solvent-extractable long-chain alkenone (LCA) concentration and composition and environmental factors in a suite of endorheic lakes from inland Spain. LCAs were found in 14 of the 54 lakes examined, with concentrations comparable with those from previously published lacustrine settings. The composition of LCAs in our sites, however, contrast from the majority of those previously reported from lake environments; in our study the tri-unsaturated component is the most abundant component at most sites where LCAs are detected, and C38:3 is the most abundant LCA in the majority of sites. LCA occurrence appears to be restricted to brackish-hypersaline sites and C37 LCAs are absent above a salinity of ∼40 g L−1 suggesting a salinity control on LCA-producing organisms in these sites. Low concentrations of C37 LCA components means and temperature indices are generally not applicable. Instead we find good relationships between C38 components and (in particular mean autumn) temperature and the strongest LCA-temperature relationships are found when using a combination of all C37 and C38 compounds. We propose a new alkenone temperature index for lakes with elevated salinity and where the C38 components dominate the LCA distributions. This is expressed as (r2 = 0.80, n = 13). In this paper, we provide the first account of sedimentary LCA distributions from lakes in inland Spain, extending the range of environments within which these compounds have been found and highlighting their significance as indicators of both salinity and temperature in saline, endorheic lake environments. This has important implications for extending the potential role of LCAs as palaeoclimatic indicators in lacustrine environments. 相似文献
20.
The speciation of cobalt (II) in Cl− and H2S-bearing solutions was investigated spectrophotometrically at temperatures of 200, 250, and 300 °C and a pressure of 100 bars, and by measuring the solubility of cobaltpentlandite at temperatures of 120-300 °C and variable pressures of H2S. From the results of these experiments, it is evident that CoHS+ and predominate in the solutions except at 150 °C, for which the dominant chloride complex is CoCl3−. The logarithms of the stability constant for CoHS+ show moderate variation with temperature, decreasing from 6.24 at 120 °C to 5.84 at 200 °C, and increasing to 6.52 at 300 °C. Formation constants for chloride species increase smoothly with temperature and at 300°C their logarithms reach 8.33 for , 6.44 for CoCl3−, 4.94 to 5.36 for , and 2.42 for CoCl+. Calculations based on the composition of a model hydrothermal fluid (Ksp-Mu-Qz, KCl = 0.25 m, NaCl = 0.75 m, ΣS = 0.3 m) suggest that at temperatures ?200 °C, cobalt occurs dominantly as CoHS+, whereas at higher temperatures the dominant species is . 相似文献