Showing papers on "Varve published in 1997"

A 40,000-year varve chronology from Lake Suigetsu, Japan: Extension of the 14C calibration curve

Abstract: A sequence of annually laminated sediments is a potential tool for calibrating the radiocarbon time scale beyond the range of the absolute tree-ring calibration (11 ka). We performed accelerator mass spectrometric (AMS) 14C measurements on >250 terrestrial macrofossil samples from a 40,000-yr varve sequence from Lake Suigetsu, Japan. The results yield the first calibration curve for the total range of the 14C dating method.

The relationship between glacial activity and sediment production: evidence from a 4450-year varve record of neoglacial sedimentation in Hector Lake, Alberta, Canada

Abstract: A 4450-year sequence of varves, spanning the entire Neoglacialinterval, has been recovered from Hector Lake, Alberta. The varve record is compared to records of regional glacial history toevaluate therelationship between alpine glacial activity and sediment production. Glacial controls on sediment production vary with the timescale considered. Long-term variations in sedimentation rate, of centuries to millennial duration, reflect changes in ice extent of the same timescale. Superimposed on these long-term changes is decadal-scale variability that is complexly related to upvalley ice extent. Over the short term, high sedimentation rates may be associated with glacier maximum stands, or with periods of glacier advance or recession. Overthe last millennium at least, highest sedimentation rates appear to have been associated with transitional periods, preceding or post-dating maximum ice stands, rather than with times of maximum ice extent.

δ18o and Trace Element Measurements as Proxy for the Reconstruction of Climate Changes at Lake Van (Turkey): Preliminary Results

Abstract: The sediments of Lake Van, the fourth largest terminal lake on earth, located at the eastern end of the Taurus Mountain Range show an undisturbed continuous record of chemically precipitated carbonate varves, which provide:

Rates, timing, and cyclicity of Holocene eolian activity in north-central United States: Evidence from varved lake sediments

Abstract: Most of the sediment components that accumulated in Elk Lake, northwestern Minnesota, during the Holocene are autochthonous or biogenic, delivered to the sediment-water interface on a seasonal schedule, preserved in distinct annual laminae (varves). The main allochthonous component is detrital clastic material, as measured by bulk-sediment concentrations of aluminum, sodium, potassium, titanium, and quartz, that enters the lake mostly as eolian dust. The eolian clastic influx to Elk Lake was considerably greater during the mid-Holocene (8–4 ka) than it has been for the past 4000 yr, when periods of increased eolian activity correspond to the time of the Little Ice age and the dust bowl. Geochemical records of eolian activity exhibit distinct cyclicities with dominant periodicities of 400 and 84 yr.

200-Year Record of Metals in Lake Sediments and Natural Background Concentrations

Abstract: Lake sediments conserve important information about past conditions of a lake and its environments. We present analyses of calcium, manganese, iron, copper, zinc, cadmium, mercury, and lead in dated (210Pb, 137Cs, varve-chronology) sediment cores from Zurichsee (Lake Zurich), Switzerland, covering a time span of the last 200 years and an additional time interval between 13 500 and 15 000 years before the present time. The concentrations of these elements varied very little in pre-anthropogenic sediments and represent geochemical background concentrations. With the beginning of industrialization in the early 19th century and the corresponding growth of population, significant changes occurred in the concentrations of the investigated metals. Copper, zinc, and cadmium increased until about 1960 and decreased sharply afterwards. The increase correlates to the growth of local industrial productivity (and population growth), whereas the decrease after about 1960 was caused by (i) the introduction of sewage tre...

Varve formation since 1885 and high-resolution varve analyses in hypertrophic Baldeggersee (Switzerland)

Abstract: According to their microstratigraphical composition the laminated sediments of Baldeggersee are true varves. Two varve time-series from freeze cores taken in the deepest part (66 m) of Baldeggersee have been analysed for annual and seasonal layers. The varve time-series covers the period of 1885 to 1993. The two freeze-cores from Baldeggersee can be accurately correlated by means of distinct layers (e.g. marker varves, turbidites), lithological units, and varve measurements. The Baldeggersee varve chronology has been checked by independent high-resolution 137 Cs dating. Mobility of cesium has not been detected in Baldeggersee. A highly positive correlation between phosphorus concentration in the lake water and median grain size of calcite crystals has been observed and allows, together with the results of geochemical analyses, to hindcast the trophic state in Baldeggersee for periods where no limnological data are available. The main features of the Baldeggersee varve time-series can be summarized as follows: before 1885 there are packets of 5 ‐ 10 varves interrupted by massive, homogeneous marl beds, indicating oscillating hypolimnetic oxygen levels until the lake ultimately became anoxic in 1885. Between 1885 and 1905 varves are thin, with a high carbonate content. Between 1905 and 1910 the thickness of varves increased steadily, and an increase in calcite grain size suggests a major step in eutrophication. Median grain size values increase again at the end of the 1940s, whereas the thickness of the seasonal layers decreased between the early 1940s and the early 1960s. At the onset of the 1960s, during the time of highest epilimnetic phosphorus concentrations in Baldeggersee, the total phosphorus concentrations in the sediments as well as the varve thickness and the total accumulation rates all increased. At the beginning of the 1980s the median grain size decreased substantially as a result of lower phosphorus concentrations in Baldeggersee.

A high resolution proxy-climate record from an arctic lake with annually-laminated sediments on Devon Island, Nunavut, Canada

Abstract: Sediments from a 3 ha lake (75 °34.34′N, 89 °18.55′W) from the coastal region of northern Devon Island, Nunavut, Canada, contain discrete laminations in the deepest part of the basin. The laminations are varves as indicated by the correspondence between counts and thickness measurements of the couplets and 210Pb dating. A 14 cm core representing 150 years of sedimentation contained laminated couplets consisting of a lighter inorganic layer with a higher percentage of calcium and magnesium, alternating with fine darker bands, typically more cohesive, and comprising higher proportions of silica and carbon. A reddish oxidation zone with higher iron and aluminum frequently separates the laminations. The dark layer represents a biogenic component deposited in summer and is made cohesive by bacterial filaments among the other particles. The light inorganic layer represents clastic deposition from allochthonous sources. Deposition rates were relatively consistent through the core with an increase in varve thickness in the 1950s. Diatom concentrations in the sediments increased by two orders of magnitude in this century, with major increases in the 1920s and 1950s. The increase in varve thickness and diatom abundance coincides with an increase in summer melt percentage in an ice core from the Devon Island Ice Cap (Koerner, 1977). The relatively high sedimentation rate (0.15 cm yr-1) coupled with the consistency of deposition makes this lake a significant indicator for recent climate changes of the Canadian Arctic Archipelago.

Temperate Glacimarine Varves: An Example from Disenchantment Bay, Southern Alaska

Abstract: The sediment record of Disenchantment Bay, Southern Alaska, a large marine calving embayment, contains distinctive annual deposits. Each year a glacimarine couplet forms with a clast-rich stratified to massive diamicton deposited in winter by intense iceberg rafting and a summer, meltwater deposit of thinly laminated mud and turbidite sand beds. Although iceberg rafting occurs throughout the year, coarse debris is deposited in high concentrations and forms diamicton only during the winter because of minimal fine sediment from meltwater discharges and a longer residence time of icebergs in the Bay due to winter fjord circulation and meteorological factors. When meltwater discharge commences in summer, laminated mud with dropstones is deposited. Spring and fall conditions are recorded a transitional phases between winter and summer by clast-poor diamictons. Average sediment accumulation rates calculated from varve thicknesses range from 48 cm/yr, 3.4 km from Hubbard Glacier at the head of the Bay, to 14 cm/yr, 15 km away. Sediment accumulation rates estimated from 210Pb dating of core sediments are in the same range. Deposits from the 1986 Russell Fiord outburst flood are identified from anomalously high 210Pb activities in sediments indicating an alternative sediment source to Disenchantment Bay. Glacimarine varves are a dating tool for the barren proximal sediments commonly deposited near calving glacier termini. They yield paleoclimatic information because they are a product of both glacial ice in the sea and laminated sediments deposited from significant melt-water discharge found in a temperate to subpolar climate.

The separation of the influence of nutrients and climate on the varve time-series of Baldeggersee, Switzerland

Abstract: The varve data-set from a freeze-core taken in the deepest part of Baldeggersee was subjected to different multivariate statistical analyses in order to estimate the amount of variance in the varve thickness measures explicable by past climate and by the trophic state of the lake. A comparison of two different time-periods (1902 to1992 versus 1920 to 1980) revealed that the lake restoration programme since 1982 has had a significant impact on the formation of the seasonal layers. Results of the partitioning of the variance in the varve thickness measures showed that about two thirds of the variance are unexplained by a climate and trophic state model and that trophic state explains 6%, whereas climate accounts for about 28% of the variance before the effect of lake restoration had a strong impact on the varves. Among the climate parameters the amount of annual precipitation is a strong predictor for explaining the thickness of both dark layer and total couplet thickness, whereas summer precipitation is important for the thickness of the light layer.

A New 14C Calibration Data Set for the Last Deglaciation Based on Marine Varves

Abstract: Varved sediments of the tropical Cariaco Basin provide a new (super 14) C calibration data set for the period of deglaciation (10,000 to 14,500 years before present: 10-14.5 cal ka BP). Independent evaluations of the Cariaco Basin calendar and (super 14) C chronologies were based on the agreement of varve ages with the GISP2 ice core layer chronology for similar high-resolution paleoclimate records, in addition to (super 14) C age agreement with terrestrial (super 14) C dates, even during large climatic changes. These assessments indicate that the Cariaco Basin (super 14) C reservoir age remained stable throughout the Younger Dryas and late Allerod climatic events and that the varve and (super 14) C chronologies provide an accurate alternative to existing calibrations based on coral U/Th dates. The Cariaco Basin calibration generally agrees with coral-derived calibrations but is more continuous and resolves century-scale details of (super 14) C change not seen in the coral records. (super 14) C plateaus can be identified at 9.6, 11.4, and 11.7 (super 14) C ka BP, in addition to a large, sloping "plateau" during the Younger Dryas ( approximately 10 to 11 (super 14) C ka BP). Accounting for features such as these is crucial to determining the relative timing and rates of change during abrupt global climate changes of the last deglaciation.

A record of accelerated erosion in the recent sediments of Blelham Tarn in the English Lake district

Abstract: Two frozen cores from Blelham Tarn were subsampled and measured using mineral magnetic, loss-on-ignition (LOI), radiometric, granulometric and diatom analyses. A detailed chronology was established using varves, radioisotopes and diatoms. This has enabled an accurately dated reconstruction of sedimentation over the past forty years. Despite a large increase in lake productivity, evidence suggests that the observed exponential increase in sedimentation rates can be attributed to erosion within the catchment. The predominant sediment source has been identified as surface soil. A comparison between the trend of accelerated sedimentation and the record of increased sheep stocking density for the area within which the most of the catchment lies, as well as observations of contemporary surface processes within the catchment, both suggest that much of the recent erosion is a direct response to increased pressure from sheep grazing.

Glacial Varve Thickness and 127 Years of Instrumental Climate Data: A Comparison

Abstract: Annually laminated sediments (glacial varves) from Lake Silvaplauna, a High Alpine proglacial lake in the Central Swiss Alps, were compared with glacier monitoring data and instrumental climate data from 1864 to 1990. Long-term and short-term responses to climatic change as well as anthropogenic influence can be traced separately in the varve succession. Economic development in the lake catchment has resulted in higher autochthonous production in recent years. Autochthonous components contribute around 10% to the total amount of sediment accumulated annually since 1960 but their contribution is negligible before this date. Decadal-scale varve thickness trends correlate with glacier size-variations. A stepwise, running multiple regression analysis demonstrates that interannual changes in varve thickness are strongly correlated with changes in mean summer temperatures, but cannot be sufficiently explained without considering summer precipitation and the number of days with snow per year. The wide range of observed correlation coefficients reveals the sensitivity of the archive to temporal variability of the climatic forcing factors and makes the development of transfer functions ambiguous.

AMS radiocarbon dating of organic fractions from varved lake sediments: an empirical test of reliability

Abstract: Replicate cores of annually laminated (varved) sediments have been used to test the accuracy and precision of chronologies of lake sediment accumulation over the last 1000 years, based on AMS 14C measurements. The internally consistent results show that in the case of the soft-water lake sediments studied (Kassjon, northern Sweden), all the organic fractions that include aquatic components give significantly older dates than expected. Only the single terrestrial macrofossil and the fine, unidentified residual particulate fraction provide dates close to the true age of the sediments. The results also show that age discrepancies for some fractions are not constant over time. The age discrepancies may arise from some carbon reservoir effect within the aquatic ecosystem, from resuspension and focusing of older marginal organic material into the deepest part of the lake or from some combination of these processes. More work is needed on the 14C ‘age’ of organic fractions in varve-dated sediments from a range of lake types.

Inter‐decadal signals during the last millennium (AD 1117–1992) in the Varve record of Santa Barbara Basin, California

Abstract: Annual varve thickness (AD 1117–1992) from Santa Barbara basin has been decomposed into orthogonal components using singular spectrum analysis (SSA) to identify and retrieve inter-decadal oscillations. After removing all variability with periods greater than 150 years, leading SSA eigenfunctions (EOFs) identify four oscillatory pairs with periods of ∼100, ∼58, ∼25, and ∼12 years respectively. Based on 2500 simulated series and on two-sided confidence intervals, EOFs 1–7 are significant at the 99% level and EOFs 8–9 are significant at the 90% level. Oscillatory signals retrieved from the marine varves show an abrupt change in frequency and amplitude near AD 1600. The largest contribution to this environmental shift is given by the interdecadal components, especially the ∼25 and the ∼12-year oscillation. The near-AD 1600 change may be related to multi-annual events reported in the stratigraphy of the nearby Santa Monica Basin and in dendrochronological records of the American Southwest.

Solar activity variations recorded in varved sediments from the crater lake of holzmaar - a maar lake in the westeifel volcanic field, germany

Abstract: Annually laminated sediments from Lake Holzmaar (Germany) provide high resolution sedimentological and palaeoenvironmental data of the last 22,500 years. Weichselian periglacial varves and Holocene organic varves indicate different depositional environments. For the best preserved sections from both parts, spectral analyses were performed in order to detect cyclic fluctuations in varve thickness. Weichselian varves are dominated by an 88 year periodicity. Linear spectral analysis of Holocene varves provides no significant cyclicity. But, supposing nonlinear transformations of the solar signal through the Lake Holzmaar ecosystem during the Holocene, an adequate nonlinear spectral analysis method was able to detect periodicities of 11, 88, and 208 years. The existence of these cyclicities, comparable to the solar activity fluctuations, give further evidence for the existence of a sun-climate relationship, based on a not yet completely understood mechanism.

Late Holocene sedimentation in Saanich Inlet, British Columbia, and its paleoseismic implications

Abstract: Eight piston cores of sediment spanning the last 1500 years were collected from Saanich Inlet, an anoxic fiord on southern Vancouver Island, to obtain information on sedimentation and prehistoric earthquake activity. The cores consist mainly of fine-grained varved sediments, but include massive layers deposited by subaqueous debris flows. The debris flows may have been triggered by earthquakes or by the buildup of fine sediment on the walls of the inlet. Cesium-137 and 2BoPb data, I4C ages, and varve counts were used to date and correlate massive layers in the eight cores. The uppermost massive layer in two cores may record a magnitude 7.2 earthquake that occurred in 5946 near Comox, British Columbia: 200 km north-northwest of Saanich Inlet. Seven older layers are found in two or more cores and are about 200, 440, 550, 800-850, 1050- 1100, 1100- 1150, and 1450- 1500 years old. Two of these older layers may correlate with previously documented earthquakes in the region. There is an average of one massive layer per 116 varves in the core with the greatest number of such layers, which is broadly consistent with the expected periodicity of moderate to large earthquakes in the region, on average, one earthquake producing local Modified Mercalli Intensity VII or VIII per century. Saanich Inlet may contain a proxy record of all moderate and large earthquakes that have affected southwestern British Columbia during Holocene time, but some of the massive layers do not appear to correlate from core to core and undoubtedly are nonseismically generated deposits.

The glacilacustrine sedimentary environment of Bowser Lake in the northern Coast Mountains of British Columbia, Canada

Abstract: Bowser Lake, a fiord lake in the northern Coast Mountains of British Columbia, contains a thick Holocene fill consisting mainly of silt and clay varves These sediments were carried into the lake by proglacial Bowser River which drains a high-energy, heavily glacierized basin Sedimentation in the lake is controlled by seasonal snow and ice melt, by autumn rainstorms, and by rare, but very large jokulhlaups from glacier-dammed lakes in the upper Bowser River basin which complicate environmental inferences from the sedimentary record Sediment is dispersed through the deep western part of the lake by energetic turbidity currents The turbidity currents apparently do not overtop a sill that separates the western basin from much shallower areas to the east Large amounts of silt and clay are deposited from suspension in the eastern part of the lake, but sediment accumulation rates there are much lower than to the west Several strong acoustic reflectors punctuate the varved fill in the western basin; these may be thick or relatively coarse beds deposited during jokulhlaups or exceptionally large storms The contemporary sediment yield to Bowser Lake, estimated from sediments in the lake, is about 360 t km-2a-1 This is a relatively high value, but it is less than yields insome other, similar montane basins with extensive snow and ice coverThe most likely explanation for the difference is that large amounts of sediment have been, and continue to be, stored on the Bowser delta andin small proglacial lakes

High-resolution varve studies in Baldeggersee (Switzerland): Project overview and limnological background data

Abstract: This introduction to a series of high-resolution varve studies in Baldeggersee provides both an overview of the different subprojects as well as background information on relevant limnological trends. The project was based on a new method of in-situ freezing of unconsolidated surficial sediments in deep lakes. With this freeze-core technique a detailed, high-resolution stratigraphy of the varved sediments at the deepest point of Baldeggersee has been established for the period of 1885–1993. Annual and seasonal sediment samples were analyzed. Concentrations of redox active metals in sediments were calibrated as proxy indicators for the reconstruction of hypolimnetic oxygen conditions. Particle size analysis and varve measurements were used to discriminate between the influence of nutrients and climate on sediment formation and accumulation. Baldeggersee is an ideal system for calibrating indicators of deep-water oxygen concentrations because it underwent dramatic changes in nutrient loading and redox conditions during this century. The hypolimnion has been seasonally anoxic for the last 100 years and phosphorus content decreased by a factor of five in the last 20 years. Meromixis was observed between 1960 and 1980. Since 1983 the deep water has been artificially oxygenated. This well documented change in deep-water oxygen concentration represents a unique whole-lake experiment that can be used to analyze the geochemical response of the sediments.

Differential sedimentation versus coring artifacts: a comparison of two widely used piston-coring methods

Abstract: In order to compare two widely used piston-coring techniques, parallel cores were taken with both a Kullenberg and a Livingstone corer in the deepest part of Soppensee (25 m), a small eutrophic Swiss lake containing varved sediments The cores were taken within a horizontal distance of 3 m and yield comparable stratigraphic records Differences in millimetre-scale microstructure are attributed to primary sedimentation processes at the water/sediment interface Sediment thin-sections, as well as sediment x-radiograph investigations, reveal no difference in microstructure that could unequivocally be attributed to one of the coring methods used The differences in deposition are therefore thought to reflect the inherent variability of lacustrine sedimentation in Soppensee Major differences in overall core recovery do occur, however, in organic-rich, highly porous sediments These variations are primarily attributed to differential gas expansion Actual sediment-accumulation rates can therefore only be correctly estimated if the sedimentary record can be constrained within a high-resolution temporal framework, eg by annual laminations

Clay varve chronology in the Eastern Baltic area

Abstract: The clay varve chronologies of the Eastern Baltic and NW Russia are discussed, and an attempt is made on the basis of the revised Swedish Time Scale and direct correlation with the Swedish and Finnish clay varve chronologies, to date Markov's chronologies for the St. Petersburg area and southern Karelia via Sauramo's chronology for Finland. A mean annual rate of ice recession is used to overcome the distance of 100 km between the sites investigated by Sauramo and Markov. It is proposed that the area north of L. Onega was deglaciated approximately between 13,940 and 13,140 varve years BP, the Neva basin between 12,600 and 12,520 varve years BP and the Luga basin between 12,440 and 12,360 varve years BP. Accordingly, the Weichselian ice sheet would have retreated from the Pandivere/Neva ice marginal zone about 12,330 varve years BP. The weakness of some of the arguments used in correlating the chronologies for NW Russia means that the deglaciation chronology of the Eastern Baltic remains open for f...

A Late Weichselian geomagnetic record from Lake Tamula, SE Estoniah

Abstract: A Late Weichselian palaeomagnetic record has been obtained from sediments deposited in Lake Tamula in SE Estonia, and detailed mineral magnetic studies have been undertaken to identify the carriers of remanence. The palaeomagnetic record can be compared to records from southern Sweden and Karelia in NW Russia. A westerly declination swing in the Swedish and Russian records, between 13,300 and 12,100 calender years BP is also found in the Lake Tamula sediments. Based on a floating varve chronology in the varved clay unit the deglaciation can be dated to 14,400 calender years or 12,600 radiocarbon years BP. The palaeomagnetic evidence supports the presently accepted deglaciation chronology of southeastern Estonia, which is based on radiocarbon dates of the Haanja and Otepaa ice‐marginal stages. Sandgren, P., Hang, T. & Snowball, I.F., 1997: A Late Weichselian geomagnetic record from Lake Tamula, SE Estonia. GFF, Vol. 119 (Pt. 4, December), pp. 279–284. Stockholm. ISSN 1103–5897.

14C ages of terrestrial macrofossils from Lago Grande di Monticchio (Italy)

Abstract: Lago Grande di Monticchio (Italy) contains long sedimentary records of >75 ka (Zolitschka and Negendank 1996). In a joint European project (Creer and Thouveny 1996), vegetation history and climatic changes for this part of the Mediterranean have been reconstructed (Watts, Allen and Huntley 1996; Watts et al. 1996). In addition to the time scale based on annual laminations and sedimentation rate, tephra layers and pollen spectra, radiocarbon dating was applied for the last 40 ka. Previous studies have shown that the age of bulk sediment from Lago Grande di Monticchio, which is a maar lake at the flanks of Mt. Vulture, was influenced by "dead carbon" of volcanic origin dissolved in the lake water. Thus, (super 14) C dating of the record is problematic and must be limited to dating macrofossils of terrestrial origin. From a set of sediment samples, macrofossils were selected and dated using accelerator mass spectrometry (AMS). A (super 14) C time scale based on seven data points between 9000 and 24,000 BP is compared with other dating of the record based on varve counting and tephrochronology (Zolitschka 1996).

Natural and anthropogenic influences on the geochemistry of Quaternary lake sediments from Holzmaar, Germany

Abstract: The accumulation of heavy metals and trace elements has been investigated in a well laminated sequence of Holocene and late Pleistocene lake sediments composed of diatomaceous gyttja, tuff and silt and clay sediments. Varve chronology of the annually deposited gyttja yielded a continuous high-resolution time sequence and allowed the absolute age dating of the sediment.

A Spacio-Temporal Pattern of Pollen Sedimentation in a Dimictic Lake with Laminated Sediments

Abstract: Resuspension in the main basin of Lake Gościąz results approximately a doubling of the total sedimentation rate in the deepest region. The increase pollen flux in bottom traps during overturn was more four times higher than in the upper traps. The most intensive pollen sedimentation was recorded before and just after freeze-up. This could only have been the result of previous sediment resuspension. Mechanisms of sedimentation in the studied lake showed that resuspension and resedimentation can change “the environmental record” of events even in a lake with laminated sediments. Higher sedimentation of pollen during autumn circulation confumed that in the sediment layers (varves or laminae) particles from previous seasons also could have been found. In the bay pollen sedimentation was lower and depended on plant flowering, there was no resuspension.

Varves and solar variability (Lake Holzmaar, Eifel, Germany)

Abstract: Annually-laminated sediments from Lake Holzmaar are a high resolution archive of palaeoenvironmental changes in the Eifel region (Germany). During a selected time window of the early Holocene, organic sedimentation is mainly controlled by biological productivity and seems to depend on temperature and solar radiation. Applying a non-linear phase-oriented analysis to varve thickness measurements, 11-, 88- and 208-year solar periodicities were detected. We therefore propose to use these sediments as a proxy for solar activities. Additionally, we suspect planetary revolution and lap frequencies in this record, which might indicate a relationship between solar-activity variations and solar-system dynamics.

Climate Change at the End of the Third Millennium BC — Evidence from Varved Lacustrine Sediments

Abstract: The sedimentary record of Lake Holzmaar provides an absolute varve chronology confirmed by AMS-14C data. Before 2500 BC and after 1800 BC depositional processes were controlled by both human and palaeoclimatic influences. Between the end of the Neolithic and the onset of the Bronze Age no anthropogenic interference with the environment is suggested by the archaeological data. An increase in dry density and magnetic susceptibility during the period 2500 to 1800 BC (in sideral years) is therefore, attributed to palaeoclimatic causes. These sediment changes are interpreted to be the result of increased runoff related to an increase of precipitation and/or colder temperatures which is in agreement with other proxy records from northern and central Europe, indicating cold and wet conditions at this time.

The near-AD 1600 multi-proxy puzzle

Abstract: EXTRACT (SEE PDF FOR FULL ABSTRACT): A varve chronology with annual resolution (AD 1117-1992) has been developed recently for Santa Barbara Basin. Varve thickness and water content show an exponential trend consistent with expected patterns in the presence of sediment compaction over time. Annual varve thickness was decomposed into orthogonal components using singular spectrum analysis (SSA) to identify and retrieve inter-decadal oscillations. ... This suggests a connection with global-scale decadal cycles identified in the subtropical Pacific gyre circulation and, possibly, with solar-driven phenomena. The near-1600 AD event coincides with (a) a similarly sudden change of state in nearby Santa Monica Basin that triggered the onset of anoxic conditions and the preservation of laminated sediments, (b) an extreme drought over the American Southwest, (c) a transformation of the age structure in a number of forest populations throughout Arizona and New Mexico. Total organic carbon burial flux in Santa Barbara Basin varves also shows a marked change after AD 1600. A possible climatic link is proposed that involves pathways for moisture transport in the Southwest at decadal and longer time scales.