Oxygen isotope ratios of organic matter in arctic lakes as a paleoclimate proxy: field and laboratory investigations

Paleoclimate research based on the stable isotopic composition of lake sediments is often hampered by the lack of preservation of suitable material for isotopic analysis. We examined organic material as a proxy for past water isotopic composition in a series of experiments. First, we cultured aquatic moss under constant illumination, temperature, and water ¹⁸O, and show that new cellulose records source water ¹⁸O precisely (r² = 0.9997). Second, we analyzed paired lakewater and vegetation samples collected from sites spanning strong climatic gradients. In field conditions, the relationship between organic ¹⁸O and water ¹⁸O is more variable, though it is still controlled by environmental water isotopic composition. However, terrestrial mosses in the arctic are often significantly enriched in ¹⁸O relative to aquatic mosses in nearby lakes due to their use of different water sources. Third, we measured ¹⁸O of cellulose extracted from disseminated sedimentary organic material. In the majority of the middle- to high-arctic lakes in this study, the ¹⁸O of disseminated sediment cellulose is greatly enriched relative to the expected values based on lakewater ¹⁸O, suggesting a significant component of terrestrial cellulose. This interpretation is supported by radiocarbon dates from a Holocene sediment core in which ¹⁴C ages of sediment cellulose are 700-5000 yrs older than the enclosing sediments. We conclude that aquatic cellulose can be used as a reliable tracer of lakewater isotope ratios, but terrestrial cellulose often dominates the sedimentary cellulose pool in places such as Baffin Island where sedimentation rates are low enough to allow the degradation of aquatic cellulose. Care must be taken when interpreting sediment cellulose ¹⁸O records where diagenesis has played a role, because terrestrial cellulose is more resistant to degradation, and therefore can predominate in environments with low organic carbon burial.     

Lacustrine organic matter and the Holocene paleoenvironmental record of Lake Albano (central Italy)

A combined bulk and detailed geochemical study of the sedimentary organic matter in Lake Albano, central Italy, provides critical data to track the response of this aquatic system to the environmental changes of variable amplitude that occurred during the Holocene. RockEval pyrolysis of this predominantly laminated, organic carbonrich sedimentary sequence shows changes in hydrogen and oxygen indices that are related to variations in the dominance of the primary producers. These variations are further confirmed by the pigments and the carbon isotopic composition of bulk organic matter showing that cyanobacteria dominated the lake waters during the early and late Holocene whereas diatoms have been the main producers during the middle Holocene. Sharp decreases in productivity, 2–3 centuries long, are identified at ca. 8.2, 6.4 and 3.8 ka. B.P. Changes in temperature and/or effective moisture are suggested as the most probable causes, although human impact cannot be ruled out for the latest part of the Holocene.     

Accelerator mass spectrometry radiocarbon dating of 1994 Lake Winnipeg cores

Conventional radiocarbon dating of Lake Winnipeg core samples has produced erroneously old ages due to the incorporation of pre-Quaternary carbon derived from carbonaceous rocks, soils and sediments in the watershed, as well as a hard-water effect resulting from leaching of calcareous rocks and soils. To circumvent these problems and develop a reliable chronology for the Lake Winnipeg core series, a total of 64 samples from the Lake Winnipeg core series were processed to isolate well preserved macrofossils suitable for Accelerator Mass Spectrometry (AMS) radiocarbon dating. Here we report six radiocarbon ages derived from plant macrofossils and ostracodes, and reconstruct aspects of the depositional environment of each sample based on the associated macrofossil assemblage.     

Stable isotopic compositions of sulfur in PIRLA sediment cores

Stable isotopic compositions of total sedimentary sulfur were determined for cores from eight of the PIRLA study lakes. Preindustrial sulfur deposited prior to 1800 had roughly constant isotopic compositions within a 1–2 range in each core. In more recent sediments, large 5–10 decreases in ³⁴S content occurred and likely resulted from the addition of anthropogenic sulfur. These isotopic changes began at the same time that lead concentrations increased in sediments, suggesting a close linkage between lead and sulfur deposition in the mid and late 1800s.This is the ninth of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D.F. Charles and D.R. Whitehead are guest editors for this series.     

Organo-geochemical and stable isotope indicators ofenvironmental change in a marl lake, Malham Tarn, North Yorkshire,U.K.

Sediments of the marl lake Malham Tarn located in NW Englandpreserve an environmental record since 12 Ka. Eight Holocene pollen zones wereidentified, and the ¹³C of total organic carbon (TOC) showsthree stratigraphic divisions. The basal clay unit and overlayingsand/clay/marl unit have ¹³C of –24which decreases at the base of the principal marl unit to a mean value around–30, whilst the topmost black marl unit ¹³Cincreases to –28 at the surface. Representative samples of theseunits were selected for analysis of n-alkanes andn-fatty acids and their ¹³C.Samples of modern Chara and peat were analysed forcomparison. The clay unit has a minor contribution of redeposited matureorganic matter and autochthonous algae, the marl unit a high contribution ofChara, and the dark marl unit has a high contribution fromhigher plants. Compound-specific ¹³C revealssystematic differences between alkanes and fatty acids of different chainlength. The major shift in ¹³C in the short and medium chainfatty acids are probably due to the decreasing influence of carbonate rockflour as source of DIC. The major shift in ¹³C in the longchain n-fatty acids andn-alkanes could reflect the lower atmosphericCO₂ concentration at Last Glacial. The negative shift of short chainfatty acids in organic rich dark marls reflects introduction of detrital peatinto the lake. The ¹³C results show a dramatic change fromdominance of autochthonous plus eroded sources up to Pollen Zone IV, then slowcolonisation of the hinterland by higher plants, followed by constantChara contributions throughout the deposition of the marl,and a further increase of higher plant material after the rise in water levelin 1791.     

Anthropogenic changes in the sediment composition of Lake Gości& aogon;ż (central Poland), during the last 330 yrs*

According to historical sources, the development of settlement around Lake Goci& aogon; during the last 330 yrs was intense at two time periods: the second half of the 1700's, and from ca. 1880 until 1944. The small farms were then abandoned, following which the lake surroundings were planted with forest trees. The presented study of human influence on the lake ecosystem and surrounding vegetation has been based on analyses of general sediment composition and its chemistry, pollen, Cyanobacteria, Chlorophyceae, Rotatoria, Cladocera, and a preliminary diatom survey. The history of human impact has been divided into four phases: 1. Phase of small local hamlets (before ca. 1770): The human impact was rather moderate then, but the cultivation of Canabis sativa, Secale cereale and later of Fagopyrum is evidenced from that time. 2. Phase of Hollandii settlement (ca. 1770-1863). Its influence is indicated first by the recession of deciduous wood (Corylus, Carpinus) stands, which triggered drastic drop of calcium in sediments. The development of rural economy in the area, including, an extension of agriculture (Secale and other cereals, crucifers, potatoes), and animal breeding based partly on grazing in the forest, is evidenced only after 1820. 3. Phase of German colonization (1863-1944): In the early periods (before 1910) the pollen spectra do not document any essential change in the type of farming, however, a serious disturbance of the lake ecosystem and sediment chemistry is evidenced by the blooms of Araphidinae diatoms and Tetraedron minimum, a maximum frequency of Bosmina longirostris, disturbances of the regular spring blooms of Chrysophyceae, appearance of vivianite, distinct maxima of organic matter, potassium, and iron concentration in sediments and an increase of the sedimentation rate. An intensification of agricultural activities commenced around 1910; woods, including also pinewoods, were then heavily devastated, and farming extended on poor soils, what was symptomatic for the general poverty of population. Coincidently in the lake, Centriceae showed blooms, Araphidinae diatoms and Tetraedron minimum developed, and the content of potassium, iron and phosphorus increased substantially, indicating altogether rising eutrophication. 4. Phase of restoration of the natural landscape (after 1945): The farm degradation from ca. 1944 is very weakly expressed in pollen data, which show a substantial fall of farming indicators from 1953/6 only, when the whole area was used for forest plantation. It was accompanied by a certainly spontaneous development of Betula and Alnus woods, this process progressing till recent time. The gradual extinction of farming activity near Lake Goci was accompanied by abrupt changes in the lake ecosystem, expressed by the restored blooms of Chrysophyceae expansion of planktonic Cladocera, rapid decline of phosphorus and extinction of vivianite from sediments. As documented by the drop of Cu/Zn ratio, lake hypolimnion has been weakly oxidized since 1949, what was probably responsible for the drop of Fe and Mn content in sediments. Increasing strength of overturns affected preservation of laminae in sediments, which almost completely disappeared after 1966.     

Palaeolimnological evidence for recent climatic change in lakes from the northern Urals, arctic Russia

The recent sediments from two deep arctic lakes, Mitrofanovskoe and Vanuk-ty, situated in the permafrost belt within the Bolshezemelskaya Tundra in the northern Ural region, were studied for diatoms, chironomids, spheroidal carbonaceous particles and stable lead isotopes. The magnitudes and rates-of-change in diatom and chironomid assemblages were numerically estimated. Instrumental climate records were used to assess statistically the amount of variance in diatom and chironomid data explained by temperature. August and September air temperatures have a statistically significant effect on diatom composition at both lakes. At Mitrofanovskoe Lake, major compositional changes in diatom and chironomid assemblages occurred at the turn of the 20th century and might be related to the regional increase in temperature. Chironomid-inferred air temperature also increased by approximately 1 °C since the early 1900s. At both lakes diatom compositional changes, coincident with the increase in June and September temperatures, also occurred in the late 1960s. These compositional changes are correlated with the increase in diatom production, sediment organic content and diatom species richness, and are likely to be a diatom response to the lengthening of the growing season. These changes are also correlated with the circum-Arctic temperature increase from the 1960s. A chironomid response to the late 1960s temperature increase was less pronounced at both lakes. Pollution levels are relatively low and pollution history is unrelated to ecological changes. Both lead isotopes and spheroidal carbonaceous particles show a clear atmospheric pollution signal, peaking in the 1980s.     

Sub-sampling unconsolidated sediments: A solution for the preparation of undistrubed thin-sections from clay‐rich sediments

Using the principles of electroosmosis, a subsampling technique for clay-rich sediments is introduced that produces undisturbed thinsections from sediment cores. The fragile sample remains in the same disposable box throughout the process, preventing collapse of its structure during subsampling, manipulation and impregnation, as well as other potential problems.     

On the red coloration of saltern crystallizer ponds. II. Additional evidence for the contribution of halobacterial pigments

In a previous paper we attempted to assess the contribution of red bacteria of theHalobacterium — Haloferax — Haloarcula group and of the -carotene-rich green algaDunaliella salina to the red colour of saltern crystallizer ponds. By means of light absorption measurements, we showed that bacterioruberin contained in the bacteria was mainly responsible for the colour of the brines, in spite of the fact that -carotene derived fromDunaliella was the pigment present in the greatest amount. This apparent discrepancy was explained by the very smallin vivo optical cross-section of -carotene, which is densely packed in globules inside theD. salina cells. We recently observed that the centrifugation technique used in the previous study to collect biomass from the ponds was unsuitable for this type of measurements, as a substantial part of theDunaliella cells present did not sediment upon centrifugation due to the low specific gravity caused by the high -carotene content. Therefore similar measurements were performed with biomass collected by filtration. Again,in vivo absorption spectra were dominated by the absorption peaks of bacterioruberin. The results reported here show that, in spite of the methodological problem associated with the earlier study, all views and conclusions expressed in our earlier paper retain their validity.     

Hubbert’s petroleum production model: an evaluation and implications for World Oil Production Forecasts

Following Hubberts successful prediction of the timing of US peak oil production, Hubberts model has been used extensively to predict peak oil production elsewhere. However, forecasts of world and regional peak oil and natural gas production using Hubberts methodology usually have failed, leading to the implicit belief that such predictions always will fail and that we need not worry about finite resources. A careful examination of Hubberts approach indicates that the most important reasons for his success in the US were stable markets, the high growth rate of demand, ready availability of low cost imports, and a reasonable estimate of easily extractable reserves. This analysis also shows that his model cannot predict ultimate oil reserves and that it should be considered an econometric model. Building on Hubberts vital insight, that cheap fossil fuel reserves are knowable and finite, one can state that for world peak oil production, political constraints should be much more important than resource constraints.     

Late-Holocene equatorial environments inferred from deposition processes,carbon isotopes of organic matter,and pollen in three shallow lakes of Gabon,west-central Africa

Seven vibro-cores were collected from three shallow lakes of the Gabon (Kamalété, Nguène, Maridor) along a 300-km west–east transect close to the Equator. These lakes are located in very distinct landscapes: coastal forest-savanna mosaic, rain forest and savanna with colonising forest, respectively. Core chronologies were established by radiocarbon dating. Study of these lacustrine archives (textural variables, clay minerals, organic matter components, δ¹³C, pollen) allowed comparison of late Holocene environmental changes recorded at each site and with results from other studies. Lake Kamalété indicates minor climatic deterioration (increased drying and greater seasonality) between 1,410 and 500 cal. years BP, which is also recognised in southern Cameroon and east-central Africa. Lake Nguène was surrounded by dense moist forest throughout the last 4,110 years, but shows significant deterioration from ~2,800 cal. years BP, a phenomenon seen at nearby sites. Lake Maridor shows a decline of forest initiated a little after 3,800 cal. years BP, which indicates timing that is distinct from the two other sites. This was probably a response to local conditions (i.e. outlet damming). Although the three lakes display generally parallel climatic trends perhaps linked to SST oscillations, there is not perfect coherence between these three sites. Differences among the three basins may be attributable to local factors like groundwater hydrology and slope instabilities of such shallow lake systems in this equatorial region.     

Zipf’s Law: A Viable Geological Paradigm?

Zipfs Law originally was proposed as a guide to a statistical distribution in social studies. The law describes a relationship between size and rank of discrete phenomena. It is a variant of Paretos 1927 Law known as the 80/20 rule and is similar to Bodes Law in concept. The relationship described by Zipfs Law is a succession of order data with the largest followed by half the size for the next largest, which in turn, the next is half that size, and so on. In geology, it has been used with moderate success in resource assessment of mining and petroleum. In essence, it predicts how many entities of a certain size may be left in a sequence of decreasing size assuming the largest has been ascertained. Examples of applications would be plotting the rank and size of ore deposits or oil fields to determine how many deposits remained undiscovered and their size. After a flurry of papers in the 1970s and 1980s, application of the law apparently either was successful and thus not reported in way the literature or was determined to be ineffectual and its use discontinued, but either way the law lapsed into obscurity. Examples of oil- and gas-field size in Kansas, the occurrence of historic earthquakes that affected the state, and size of anticlines (plains-type folds) are presented to illustrate application and limits of Zipfs Law.     

Late glacial environment and climate development in northeastern China derived from geochemical and isotopic investigations of the varved sediment record from Lake Sihailongwan (Jilin Province)

Total organic carbon (TOC) content, total nitrogen (TN) content, stable nitrogen isotope (δ¹⁵N) and stable organic carbon isotope (δ¹³C_org) ratios were continuously analysed on a high resolution sediment profile from Lake Sihailongwan (SHL), covering the time span between 16,500 and 9,500 years BP. Strong variations of the investigated proxy parameters are attributed to great climatic fluctuations during the investigated time period. Variations in organic carbon isotope ratios and the ratio of TOC/TN (C/N ratio) are discussed with respect to changing proportions of different organic matter (OM) sources to bulk sedimentary OM. Phases of high TOC content, high TN content, depleted δ¹³C_org values and high δ¹⁵N values are interpreted as times with increased productivity of lacustrine algae in relation to input of terrigenous organic matter. Two distinct phases of enriched nitrogen isotope ratios from 14,200 to 13,700 and 11,550 to 11,050 years BP point towards a reduced phytoplankton discrimination against ¹⁵N due to a diminished dissolved inorganic nitrogen pool. The combination of geochemical (TOC, TN, C/N ratio) and isotopic (δ¹³C_org, δ¹⁵N) proxy parameters points to a division of climate development into four stages. A cold and dry stage before 14,200 years BP, a warm optimum stage with high phytoplankton productivity from 14,200 to 12,450 BP, a colder and drier stage from 12,450 to 11,600 BP and a stage of climatic amelioration with high variability in TOC and TN contents after 11,600 BP. These results are discussed in relation to monsoon variability and Northern Hemisphere climate development of the late glacial.     

Late Quaternary palaeohydrological changes in the large playa Lake Frome in central Australia, recorded from the Mg/Ca and Sr/Ca in ostracod valves and biotic remains

The last 42,000 years of hydrological history of Lake Frome, a large playa located in the arid part of northern South Australia, which is hypersaline and most often dry today, is reconstructed using a combination of ostracod assemblages, other microfossil remains, and the trace elemental composition of the selected halobiont ostracod species of Diacypris and Reticypris.The Mg/Ca and Sr/Ca of ostracod valves from 2 cores relate to significant hydrological changes that affected the lake over time. The reconstruction of the Sr/Ca of the lake’s waters, based on the Sr/Ca of ostracod shells, shows that when the lake fills the waters originate mostly from runoff, not from hypersaline waters located below the lake or the surrounding aquifers. The Last Glacial Maximum saw gypsum deflation from the lake.Prior to 25K yBP, Frome had a stable hydrological regime, permanent water and low salinities, with occasional freshwater conditions between 42 and 33K yBP. From 25 to 20.3K yBP, salinities fluctuated and ephemeral conditions operated. After that, until ∼14.8K yBP, a brine pool was located below the lake and was therefore under a different hydrological regime. Between 13 and 11.2K yBP, wet conditions occurred, but such conditions were not seen again during the Holocene.     

30种藜科C_4植物同化器官解剖结构及δ~(13)C值

观测了藜科滨藜族(Atripliceae)、樟味藜族(Camphorosmeae)、碱蓬族(Suaedeae)和猪毛菜族(Salsoleae)30种C4植物的同化器官的解剖结构和δ13 C值,共见到12种解剖结构类型。滨藜族包含2种类型,Atriplicoid-Ⅰ型和Atriplicoid-Ⅱ型,它们的差异仅在于结构中是否含有皮下组织。樟味藜族包括3种解剖结构类型,即含有皮下组织的Kochioid-Ⅰ型、叶肉细胞和维管束鞘细胞形成近似于环形的Kochioid-Ⅱ型和不含有皮下组织的Kochioid-Ⅲ型。碱蓬族包含3种类型,Kranz-Suaedoid-Ⅰ型和Kranz-Suaedoid-Ⅱ型结构中具有皮下组织,但是Kranz-Suaedoid-Ⅱ型结构中只具有一层叶肉细胞,这种结构存在于异子蓬属的异子蓬(Borszczowia aralocaspica),而Kranz-Suaedoid-Ⅲ型结构中不具有皮下组织。猪毛菜族植物叶片/同化枝的解剖结构类型有4种,它们的差异在于结构中是否含有皮下组织、次要的较小的维管束的位置以及环形的维管束鞘细胞是否被打断。30种植物的δ13 C值范围-11.1‰~-14.5‰,显示为C4植物,与其同化器官解剖结构相对应。