Proxy Signals Research Articles

Volcanic ash reveals time-transgressive abrupt climate change during the Younger Dryas

Knowledge of regional variations in response to abrupt climatic transitions is essential to understanding the climate system and anticipating future changes. Global climate models typically assume that major climatic changes occur synchronously over continental to hemispheric distances. The last major reorganization of the ocean-atmosphere system in the North Atlantic realm took place during the Younger Dryas (YD), an ∼1100 yr cold period at the end of the last glaciation. Within this region, several terrestrial records of the YD show at least two phases, an initial cold phase followed by a second phase of climatic amelioration related to a resumption of North Atlantic overturning. We show that the onset of climatic amelioration during the YD cold period was locally abrupt, but time-transgressive across Europe. Atmospheric proxy signals record the resumption of thermohaline circulation midway through the Younger Dryas, occurring 100 yr before deposition of ash from the Icelandic Vedde eruption in a German varve lake record, and 20 yr after the same isochron in western Norway, 1350 km farther north. Synchronization of two high-resolution continental records, using the Vedde Ash layer (12,140 ± 40 varve yr B.P.), allows us to trace the shifting of the polar front as a major control of regional climate amelioration during the YD in the North Atlantic realm. It is critical that future climate models are able to resolve such small spatial and chronological differences in order to properly encapsulate complex regional responses to global climate change.

Masking of interannual climate proxy signals by residual tropical cyclone rainwater: Evidence and challenges for low‐latitude speleothem paleoclimatology

The anomalously low oxygen isotope ratio (δ18O values) of tropical cyclone rainfall can transfer proxy information about past tropical cyclone activity to stalagmite oxygen isotope records. Isotopically distinct stormwater reaches the growing crystal surface as a coherent slug, or after attenuation by mixing with isotopically normal vadose groundwaters. A high‐resolution micromilled stalagmite stable isotope record from Belize shows that residual tropical cyclone water from Hurricane Mitch masked the oxygen isotope record of a major El Niño event. On decadal time scales, measured δ18O values are affected by changes in local tropical cyclone frequency. Despite the tropical cyclone masking effect, the structure of the “missing” El Niño event is preserved in the ATM‐7 carbon isotope ratios (δ13C values). In tropical cyclone‐prone regions, the fidelity of stalagmite oxygen isotope proxy data to recording background climate signals is modulated by temporal variations in local tropical cyclone rainfall, and the sensitivity of individual stalagmites to tropical cyclone masking varies with hydrology. Speleothem δ13C values, unaffected by tropical cyclones, can preserve the underlying structure of climatic variability. For low‐latitude speleothems with C–O isotope covariance, intervals in which the δ18O values are significantly lower than δ13C values predict may indicate periods when local tropical cyclone masking of isotope‐derived precipitation records is enhanced by greater infiltration of tropical cyclone rain. The temporal structure in stalagmite C–O isotope covariance has paleoenvironmental meaning that may be revealed by exploring factors associated with independent behavior in each isotope ratio, respectively. Tropical cyclone masking presents new challenges to paleoclimatology and a source of hypotheses for paleotempestology.

Bunker Cave stalagmites: an archive for central European Holocene climate variability

Abstract. Holocene climate was characterised by variability on multi-centennial to multi-decadal time scales. In central Europe, these fluctuations were most pronounced during winter. Here we present a record of past winter climate variability for the last 10.8 ka based on four speleothems from Bunker Cave, western Germany. Due to its central European location, the cave site is particularly well suited to record changes in precipitation and temperature in response to changes in the North Atlantic realm. We present high-resolution records of δ18O, δ13C values and Mg/Ca ratios. Changes in the Mg/Ca ratio are attributed to past meteoric precipitation variability. The stable C isotope composition of the speleothems most likely reflects changes in vegetation and precipitation, and variations in the δ18O signal are interpreted as variations in meteoric precipitation and temperature. We found cold and dry periods between 8 and 7 ka, 6.5 and 5.5 ka, 4 and 3 ka as well as between 0.7 and 0.2 ka. The proxy signals in the Bunker Cave stalagmites compare well with other isotope records and, thus, seem representative for central European Holocene climate variability. The prominent 8.2 ka event and the Little Ice Age cold events are both recorded in the Bunker Cave record. However, these events show a contrasting relationship between climate and δ18O, which is explained by different causes underlying the two climate anomalies. Whereas the Little Ice Age is attributed to a pronounced negative phase of the North Atlantic Oscillation, the 8.2 ka event was triggered by cooler conditions in the North Atlantic due to a slowdown of the thermohaline circulation.

Syndepositional tectonic activity in an epicontinental basin revealed by deformation of subaqueous carbonate laminites and evaporites: Seismites in Red River strata (Upper Ordovician) of southern Saskatchewan, Canada

Research Article| March 01, 2012 Syndepositional tectonic activity in an epicontinental basin revealed by deformation of subaqueous carbonate laminites and evaporites: Seismites in Red River strata (Upper Ordovician) of southern Saskatchewan, Canada Hussam El Taki; Hussam El Taki Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK S7N 5E2 Search for other works by this author on: GSW Google Scholar Brian R. Pratt Brian R. Pratt Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK S7N 5E2 Search for other works by this author on: GSW Google Scholar Bulletin of Canadian Petroleum Geology (2012) 60 (1): 37–58. https://doi.org/10.2113/gscpgbull.60.1.37 Article history received: 11 Mar 2011 accepted: 27 Apr 2012 first online: 12 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Hussam El Taki, Brian R. Pratt; Syndepositional tectonic activity in an epicontinental basin revealed by deformation of subaqueous carbonate laminites and evaporites: Seismites in Red River strata (Upper Ordovician) of southern Saskatchewan, Canada. Bulletin of Canadian Petroleum Geology 2012;; 60 (1): 37–58. doi: https://doi.org/10.2113/gscpgbull.60.1.37 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract The Yeoman and Herald formations of the Late Ordovician Red River succession of southeastern Saskatchewan comprise two carbonate–evaporite cycles in the epicontinental Williston Basin. Although these units possess an overall ‘layer-cake’ aspect across a broad area, thickness variations in the Herald Formation show that accumulation was affected by syndepositional flexure, differential subsidence, and displacement of basement faults thought to have been oriented orthogonally NE–SW and NW–SE. The dolomudstones and anhydrites of the Lake Alma and Coronach members host a variety of synsedimentary deformation features —seismites—interpreted to have been induced by earthquakes generated by movements of these faults, and the low-energy, subaqueous environmental setting was conducive to their preservation.Individual deformed intervals are <0.2 m thick. Folds and small-scale pinch-and-swell structures indicate plastic behaviour of both carbonate and evaporite sediment under compression and shear stress. Brittle failure of stiffer material from compression or extension is shown by microfaults, cracks, disrupted layers, pseudo-intraclasts, breccias and cataclastites. Dikelets in interlaminated dolomudstone and anhydrite record cyclically elevated pore pressure that caused dewatering and shrinkage with concomitant fluidization and injection of carbonate mud and primary granular gypsum. Enterolithic anhydrite exhibits compressed vertical dikes that likely represent injection of granular gypsum. Clay-filled shear-vein arrays occur rarely in dolomudstone. Seismites are absent in bioturbated limestones except for one horizon of molar-tooth structure.The different kinds of seismites are related to the varying rheology caused by the primary nature of the carbonate and evaporite sediment plus modifications due to deformation-induced dewatering, early diagenesis, and confinement under shallow burial, as well as earthquake magnitude. A minimum shaking intensity of MM=VI was probably required, meaning that events of lesser magnitude were not recorded. Some seismite-bearing horizons can be correlated across the study region. Within the limitations of core control, their geographic distribution varies, probably in relation to the basement faults. Seismites thus serve as proxy signals of syndepositional tectonic activity but also point to components of the basement structural fabric that, if reactivated later, might induce fracture porosity or influence subsurface fluid flow. Syndepositional tectonism undoubtedly had a much more profound influence on many successions than is presently thought, and its effects are more widespread than currently appreciated. You do not currently have access to this article.

The Failure of Lehman Brothers: Was it Preventable? If so, How? Recommendations for Going Forward

In determining whether the failure of Lehman Brothers was preventable, it is necessary to consider the several internal and external factors that contributed to the firm’s failure. Although there were many contributing factors, if the Federal Reserve and U.S. Treasury had chosen to prevent Lehman Brothers’ failure, they could have done so. Following so closely behind the government’s support for Bear Stearns, Freddie Mac and Fannie Mae, such an action would have created an expectation that the government was prepared to continue using taxpayer dollars to reward the failure of high risk financial institutions lying outside the reach of the state’s regulatory system. The failure of Lehman Brothers raises the larger question of whether government should provide liquidity support for financial institutions lying outside the Federal Reserve’s regulatory reach. The failure also points to weaknesses in proxy signals sent by third party Credit Rating Agencies, and weaknesses in Board governance.

‘Next-generation’ genome wide association studies

The first wave of cancer genome-wide association studies (GWAS) have revealed tens of independent loci marked by common variants of unknown or likely no functional significance that explain about 5-10% of familial risk for the particular disease. The approach taken to date has been conservative, and only a fraction of information has yet to be extracted from these expensive enterprises. For example, the Bonferroni procedure for selecting candidate phase II SNPs ignores many SNPs that happen to fail an extremely low p-value threshold. While this procedure does guarantee control of false positives, it seems counterintuitive to the purpose of phase I, which is to generate hypotheses based on promising candidates. Researchers have generally combined data from the discovery phase I and other phases and used ‘genome-wide thresholds’ based on assuming all SNPs are independent. Linkage disequilibrium (LD) makes it problematic to differentiate a real signal from highly correlated proxy signals. Most published GWAS do not examine SNP interactions due to: (a) the high computational complexity of computing pvalues for the interaction terms, and (b) the typically low power to detect significant interactions. It is plausible that more information should be extracted if: (i) higher order interactions are fitted, (ii) highly selected cases and controls are used in phase I, (iii) large replication studies are used, especially if involving existing GWAS data, (iv) the non-independence of SNPs is taken into account using, e.g. BEAGLE CALL or haplotype analyses, (v) focus is on candidate gene pathways, and/or functional SNPs, and (vi) rarer and more SNPs, such as is available from the Illumina 5M SNP chip, are used. We will illustrate these ideas using data from a GWAS of early-onset breast cancers, enriched for those with a family history, and a GWAS using extremes sample of extremes for mammographic density. We will also discuss the design of a large international breast cancer GWAS using the Illumina 5M SNP chip, phase I cases enriched for family history, population-based phase II cases and controls, population-based family study of candidate SNPs, and GxG analyses using ‘massively parallel’ super computing.

Climate on the southern Black Sea coast during the Holocene: implications from the Sofular Cave record

We present the updated Holocene section of the Sofular Cave record from the southern Black Sea coast (northern Turkey); an area with considerably different present-day climate compared to that of the neighboring Eastern Mediterranean region. Stalagmite δ 13C, growth rates and initial ( 234U/ 238U) ratios provide information about hydrological changes above the cave; and prove to be more useful than δ 18O for deciphering Holocene climatic variations. Between ∼9.6 and 5.4 ka BP (despite a pause from ∼8.4 to 7.8 ka BP), the Sofular record indicates a remarkable increase in rainfall amount and intensity, in line with other paleoclimate studies in the Eastern Mediterranean. During that period, enhanced summertime insolation either produced much stronger storms in the following fall and winter through high sea surface temperatures, or it invoked a regional summer monsoon circulation and rainfall. We suggest that one or both of these climatic mechanisms led to a coupling of the Black Sea and the Mediterranean rainfall regimes at that time, which can explain the observed proxy signals. However, there are discrepancies among the Eastern Mediterranean records in terms of the timing of this wet period; implying that changes were probably not always occurring through the same mechanism. Nevertheless, the Sofular Cave record does provide hints and bring about new questions about the connection between regional and large scale climates, highlighting the need for a more extensive network of high quality paleoclimate records to better understand Holocene climate.

Dating cave drip water by tritium

Summary Speleothems are increasingly used as an archive of past climate, but some of the proxy signals encoded in these deposits reflect hydrological characteristics of the karst aquifer (and not necessarily climate variability). A central aspect in karst hydrology is the time required for the rainwater to reach the point of discharge in a cave, e.g. the tip of the stalactite. One promising approach in determining this residence time is drip-water dating by tritium ( 3 H). In contrast to traditional tritium dating, we do not refer directly to tritium concentrations in precipitation as input function, but to an infiltration-weighted annual mean of the rainwater values. Using concentration differences between this infiltration-weighted mean and the drip water, an age is calculated from the radioactive decay law, assuming piston flow. The approach was tested in three adjacent caves in northwestern Germany which were monitored for about two years. All of the studied drip sites yielded drip water ages between 2 and 4 years with uncertainties on the order of 1 year. These results were confirmed at several drip sites by oxygen isotope data which show rather constant values with insignificant intra-annual variability. Attempts to apply the 3 H– 3 He method resulted in comparable ages, despite several complicating factors.

Stable isotope records for the last 10 000 years from Okshola cave (Fauske, northern Norway) and regional comparisons

Abstract. The sensitivity of terrestrial environments to past changes in heat transport is expected to be manifested in Holocene climate proxy records on millennial to seasonal timescales. Stalagmite formation in the Okshola cave near Fauske (northern Norway) began at about 10.4 ka, soon after the valley was deglaciated. Past monitoring of the cave and surface has revealed stable modern conditions with uniform drip rates, relative humidity and temperature. Stable isotope records from two stalagmites provide time-series spanning from c. 10 380 yr to AD 1997; a banded, multi-coloured stalagmite (Oks82) was formed between 10 380 yr and 5050 yr, whereas a pristine, white stalagmite (FM3) covers the period from ~7500 yr to the present. The stable oxygen isotope (δ18Oc), stable carbon isotope (δ13Cc), and growth rate records are interpreted as showing i) a negative correlation between cave/surface temperature and δ18Oc, ii) a positive correlation between wetness and δ13Cc, and iii) a positive correlation between temperature and growth rate. Following this, the data from Okshola show that the Holocene was characterised by high-variability climate in the early part, low-variability climate in the middle part, and high-variability climate and shifts between two distinct modes in the late part. A total of nine Scandinavian stalagmite δ18Oc records of comparable dating precision are now available for parts or most of the Holocene. None of them show a clear Holocene thermal optimum, suggesting that they are influenced by annual mean temperature (cave temperature) rather than seasonal temperature. For the last 1000 years, δ18Oc values display a depletion-enrichment-depletion pattern commonly interpreted as reflecting the conventional view on climate development for the last millennium. Although the δ18Oc records show similar patterns and amplitudes of change, the main challenges for utilising high-latitude stalagmites as palaeoclimate archives are i) the accuracy of the age models, ii) the ambiguity of the proxy signals, and iii) calibration with monitoring data.

Changes in atmospheric variability in a glacial climate and the impacts on proxy data: a model intercomparison

Abstract. Using four different climate models, we investigate sea level pressure variability in the extratropical North Atlantic in the preindustrial climate (1750 AD) and at the Last Glacial Maximum (LGM, 21 kyrs before present) in order to understand how changes in atmospheric circulation can affect signals recorded in climate proxies. In general, the models exhibit a significant reduction in interannual variance of sea level pressure at the LGM compared to pre-industrial simulations and this reduction is concentrated in winter. For the preindustrial climate, all models feature a similar leading mode of sea level pressure variability that resembles the leading mode of variability in the instrumental record: the North Atlantic Oscillation (NAO). In contrast, the leading mode of sea level pressure variability at the LGM is model dependent, but in each model different from that in the preindustrial climate. In each model, the leading (NAO-like) mode of variability explains a smaller fraction of the variance and also less absolute variance at the LGM than in the preindustrial climate. The models show that the relationship between atmospheric variability and surface climate (temperature and precipitation) variability change in different climates. Results are model-specific, but indicate that proxy signals at the LGM may be misinterpreted if changes in the spatial pattern and seasonality of surface climate variability are not taken into account.

Proxy calibration to instrumental data set: Implications for paleoceanographic reconstructions

High‐resolution proxy data analyzed on two high‐sedimentation shallow water sedimentary sequences (PO287‐26B and PO287‐28B) recovered off Lisbon (Portugal) provide the means for comparison to long‐term instrumental time series of marine and atmospheric parameters (sea surface temperature (SST), precipitation, total river flow, and upwelling intensity computed from sea level pressure) and the possibility to do the necessary calibration for the quantification of past climate conditions. XRF Fe is used as proxy for river flow, and the upwelling‐related diatom genus Chaetoceros is our upwelling proxy. SST is estimated from the coccolithophore‐synthesized alkenones and U37k′ index. Comparison of the Fe record to the instrumental data reveals its similarity to a mean average run of the instrumentally measured winter (JFMA) river flow on both sites. The upwelling diatom record concurs with the upwelling indices at both sites; however, high opal dissolution, below 20–25 cm, prevents its use for quantitative reconstructions. Alkenone‐derived SST at site 28B does not show interannual variation; it has a mean value around 16°C and compares quite well with the instrumental winter/spring temperature. At site 26B the mean SST is the same, but a high degree of interannual variability (up to 4°C) appears to be determined by summer upwelling conditions. Stepwise regression analyses of the instrumental and proxy data sets provided regressions that explain from 65 to 94% of the variability contained in the original data, and reflect spring and summer river flow, as well as summer and winter upwelling indices, substantiating the relevance of seasons to the interpretation of the different proxy signals. The lack of analogs and the small data set available do not allow quantitative reconstructions at this time, but this might be a powerful tool for reconstructing past North Atlantic Oscillation conditions, should we be able to find continuous high‐resolution records and overcome the analog problem.

Productivity cycles in Lake Hovsgol, NW Mongolia, during the last 1 Ma and the age model of the HDP-04 drill core record

Repetitive patterns in the records of total organic carbon (TOC), total nitrogen (TN) and δ 13C org observed in the Lake Hovsgol sediment section from HDP-04 drill core reflect past changes in productivity of Lake Hovsgol and in the isotopic composition of the lake's carbon pool. Lake Hovsgol productivity proxy signals are interpreted to represent the response of the Hovsgol lacustrine system to glacial–interglacial cycles of the Pleistocene. This interpretation is supported by the apparent orbitally-forced pattern in the TOC, TN and δ 13C org records of the past 250 ka in the BDP-96-2 drill core from neighboring Lake Baikal. The intervals with independent age control, such as the radiocarbon-dated last glacial–interglacial transition and the paleomagnetic reversals, make it evident that productivity proxy signals are reliable indicators of past cold-to-warm and warm-to-cold climate transitions, as seen from the agreement with the pattern of global climate change in marine δ 18O records. The Brunhes/Matuyama reversal during the MIS 19 interglacial coincides with a distinct peak of TOC and TN in the Hovsgol record, similar to the signal during the Holocene interglacial. By contrast, the upper Jaramillo reversal in the Lake Hovsgol record occurs in a diatom-free calcareous interval characterized by minima in TOC, TN and by a ‘glacial’-type range of δ 13C org values. In both Lake Baikal and Lake Hovsgol records, peaks in TOC and TN contents help distinguishing past interglacials and interstadials, and isotopically-heaviest δ 13C org values help identify past glacial intervals. An age model for the HDP-04 drill core section is proposed based on recognizing the repetitive patterns in Lake Hovsgol productivity and lithologic records as regional paleoclimate cycles of middle to late Pleistocene. Absolute dates and diatom biostratigraphic correlation ties to the Lake Baikal record are used as key controls. In the proposed age model, the interval 81–24 m in the HDP-04 sediment section below the major unconformity is correlated to MIS 27 through late MIS 13, whereas the upper 24 m of the HDP-04 section is suggested to have recovered the sedimentary record of late MIS 7 to MIS 1.

Lake Hovsgol basin as a new study site for long continental paleoclimate records in continental interior Asia: General context and current status

Lacustrine sedimentary strata in the Lake Hovsgol rift basin, NW Mongolia, preserved an important regional archive with new powerful proxies for climate change in continental interior Asia. Two scientific drilling campaigns of the Hovsgol Drilling Project (HDP) recovered the most complete and best resolved mid-late Pleistocene paleoclimate archive in Mongolia. With the basal age of ca. 1 Ma, Lake Hovsgol drill core section complements those obtained previously in the neighboring Lake Baikal, and contains regional paleoclimate proxy records on a timescale comparable to that of marine sedimentary records and the longest Antarctic ice core record. Works in this volume discuss changes in lake chemistry, biota and environment, closely linked with drill core lithology and depositional trends apparent from sediment facies. The current collection of works illustrates the potential of proxy signals in the Hovsgol record and highlights new important constraints on their interpretation. Because of a nearly continuous record of endogenic carbonate accumulation in Lake Hovsgol, a wealth of paleoclimate proxy data is preserved in carbonate mineralogy, elemental geochemistry and stable isotope composition; such a unique long record was not previously available in this part of the world. The repetitive pattern of changes in the lake's water budget in response to the climatic cycles of the Pleistocene is established and constrained by absolute dating and the robust paleomagnetic event/reversal timescale. The new proxy records from the HDP sediment sections are both relevant and timely contributions to the discussion of the nature of paleoclimate changes in continental interior Asia during prior glacial and interglacial intervals of the Pleistocene. These records help establish the early timing of the post-glacial changes in atmospheric circulation and effective moisture budget in the region and resolve the previously proposed scenarios of extreme precipitation gradients during glacial periods. The key primary data presented in this volume make a compelling case for further in-depth studies of the available records and for future deeper drilling into the early Pleistocene and the Pliocene strata in this basin.

Paleo-redox conditions during OAE 2 reflected in Demerara Rise sediment geochemistry (ODP Leg 207)

Cretaceous black shales deposited under severe oxygen-depletion are carriers of proxy signals for paleoenvironmental conditions. Using high-resolution patterns of iron and sulfur speciation, stable sulfur isotope discrimination, and trace element enrichment from black shale sequences of Sites 1258 and 1260 we identified alterations of the depositional environment during the Cenomanian/Turonian boundary Event (OAE 2) in the southern North Atlantic (ODP Leg 207, Demerara Rise). Changes in redox-conditions are suggested by high ratios of reactive to total iron which indicate that pyrite was formed both in the water column and within the sediment. This corresponds to euxinic paleoenvironmental conditions with at least temporarily free dissolved sulfide in the water column, a situation similar to the modern deep Black Sea. In addition, besides fixation of sulfide as iron sulfide, organic matter acted as an important sulfur trap during early diagenesis. Stable sulfur isotope fractionation went through a minimum within the OAE 2 interval indicating enhanced sulfur isotope discrimination during highest burial of organic matter (OM) potentially due to lower burial efficiency of reduced sulfur and/or a higher contributions from the oxidative part of the sulfur cycle (e.g., in the water column or the surface sediments). Elevated Fe/Al and Co/Al values within the Cenomanian/Turonian interval confirm euxinic conditions but, at the same time, require a zone where reducing but non-sulfidic conditions prevail, allowing reductive Fe and Co mobilization in oxygen-depleted nearshore sediments. The existence of an expanded oxygen-minimum-zone (OMZ) is demonstrated by extremely low Mn/Al ratios. A change in the trace metal (TM) inventory of seawater is postulated from a decline in seawater derived TM enrichment. Because hypoxic or even euxinic environments form an important sink for TM, the enlargement of euxinic depositional areas at the global onset of black shale deposition during OAE 2 have likely led to a drawdown of the seawater TM reservoir.

Bias in foraminiferal multispecies reconstructions of paleohydrographic conditions caused by foraminiferal abundance variations and bioturbational mixing: A model approach

A simple box model was applied to study the combined effect of bioturbation and foraminiferal abundance variations using synthetic isotope records constructed from the Greenland oxygen isotope record (GISP2). Apart from the well known general smoothing of the signal, the attenuation of peak heights, and the up- or downwards shift of the proxy records at intervals of changing abundance, the modeling results draw attention to two effects of special importance to climatic reconstructions based on the comparison of proxy signals from two or more planktonic foraminifer species. First, the bioturbational mixing of tests out of abundance maxima and into over- and underlying sediment can lead to the introduction of stratigraphic shifts between different species when species with opposing abundance patterns are used. This shifting of the signals can easily result in apparent increases or decreases in the isotopic gradients between different species, especially at intervals of rapidly changing climate conditions. Second, in intervals with rapidly changing environmental conditions, such as Dansgaard–Oeschger cycles, where species with different preferences often show opposing abundance patterns, the mixing of foraminifer tests out of their respective abundance maxima can result in a general, but artificial, offset between the two species. This offset then may disappear during intervals of slower variability. These artifacts have the potential of seriously biasing any paleoceanographic and paleoclimatic reconstructions based on multispecies analysis where the studied species show opposing abundance patterns. It is therefore highly recommended that species with as low abundance variations as possible, or at least with similar abundance variations, are used whenever multispecies reconstructions are attempted.

Stalagmite stable isotope record of recent tropical cyclone events

Research Article| February 01, 2007 Stalagmite stable isotope record of recent tropical cyclone events Amy Benoit Frappier; Amy Benoit Frappier 1Department of Geology & Geophysics, Boston College, Chestnut Hill, Massachusetts 02467, USA Search for other works by this author on: GSW Google Scholar Dork Sahagian; Dork Sahagian 2Environmental Initiative and Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA Search for other works by this author on: GSW Google Scholar Scott J. Carpenter; Scott J. Carpenter 3Center for Global and Regional Environmental Research and Department of Geoscience, University of Iowa, Iowa City, Iowa 52242, USA Search for other works by this author on: GSW Google Scholar Luis A. González; Luis A. González 4Department of Geology, University of Kansas, Lawrence, Kansas 66045, USA Search for other works by this author on: GSW Google Scholar Brian R. Frappier Brian R. Frappier 5Department of Natural Resources, University of New Hampshire, Durham, New Hampshire 03857, USA Search for other works by this author on: GSW Google Scholar Geology (2007) 35 (2): 111–114. https://doi.org/10.1130/G23145A.1 Article history received: 28 Jun 2006 rev-recd: 12 Sep 2006 accepted: 16 Sep 2006 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Amy Benoit Frappier, Dork Sahagian, Scott J. Carpenter, Luis A. González, Brian R. Frappier; Stalagmite stable isotope record of recent tropical cyclone events. Geology 2007;; 35 (2): 111–114. doi: https://doi.org/10.1130/G23145A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We present a 23 yr stalagmite record (1977–2000) of oxygen isotope variation, associated with 11 tropical cyclones (TCs), from Actun Tunichil Muknal cave in central Belize. High-resolution microsampling yielded a record of monthly to weekly temporal resolution that contains abrupt decreases (negative excursions) in calcite δ18O values that correspond with recent TC rain events nearby. A logistic discriminant model reliably identified TC proxy signals using the measurable parameters δ18O and δ13C values, and single point changes in δ18O value. The logistic model correctly identified 80% of excursions as TC events and incorrectly classified only 1 of nearly 1200 nonstorm sampling points. In addition to enabling high-resolution TC frequency reconstruction, this geologic proxy also provides information about the intensity of individual TCs. A multiple regression predicted TC intensity (R2 = 0.465, p = 0.034) using sampling frequency and excursion amplitude. Consistent with previous low-resolution studies, we found that the decadal average δ18O value was lower during the 1990s when several TCs produced rainfall in the area, but higher during the 1980s when only one TC struck. Longer, accurately dated, high-resolution speleothem stable isotope records may be a useful new tool for paleotempestology, to clarify associations between highly variable TC activity and the dynamic range of Quaternary climate. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Monitoring of a methane-seeping pockmark by cabled benthic observatory (Patras Gulf, Greece)

A new seafloor observatory, the gas monitoring module (GMM), has been developed for continuous and long-term measurements of methane and hydrogen sulphide concentrations in seawater, integrated with temperature (T), pressure (P) and conductivity data at the seafloor. GMM was deployed in April 2004 within an active gas-bearing pockmark in the Gulf of Patras (Greece), at a water depth of 42 m. Through a submarine cable linked to an onshore station, it was possible to remotely check, via direct phone connection, GMM functioning and to receive data in near-real time. Recordings were carried out in two consecutive campaigns over the periods April–July 2004, and September 2004–January 2005, amounting to a combined dataset of ca. 6.5 months. This represents the first long-term monitoring ever done on gas leakage from pockmarks by means of CH4+H2S+T+P sensors. The results show frequent T and P drops associated with gas peaks, more than 60 events in 6.5 months, likely due to intermittent, pulsation-like seepage. Decreases in temperature in the order of 0.1–1°C (up to 1.7°C) below an ambient T of ca. 17°C (annual average) were associated with short-lived pulses (10–60 min) of increased CH4+H2S concentrations. This seepage “pulsation” can either be an active process driven by pressure build-up in the pockmark sediments, or a passive fluid release due to hydrostatic pressure drops induced by bottom currents cascading into the pockmark depression. Redundancy and comparison of data from different sensors were fundamental to interpret subtle proxy signals of temperature and pressure which would not be understood using only one sensor.

Analysis of late Palaeozoic glacial to postglacial sedimentary successions in South Africa by geochemical proxies – Response to climate evolution and sedimentary environment

Records of incisive climate changes during the late Palaeozoic Era are best documented in sedimentary basins of South Africa. Glacial (Upper Carboniferous–Early Permian Dwyka Group and equivalents) and postglacial deposits (Early to Middle Permian Ecca and Beaufort Groups) are known from the Main Karoo Basin in South Africa, from the Kalahari Basin (Namibia and Botswana) and other late Palaeozoic Basins of south Gondwana. Glacial deposits comprise diamictites and tillites followed by postglacial shales with variable organic matter contents and intercalated carbonate horizons. This study covers the final glaciation phase (Upper Pennsylvanian–Asselian/Sakmarian) and the transition into the postglacial stage of the Middle to Late Permian. For sedimentary successions from the Karoo and eastern Kalahari Basin element geochemical proxies (Chemical Index of Alteration, Zr/Ti, Rb/K, V/Cr and organic carbon content) supported by mineralogical data record pronounced variation in sedimentary conditions. These took place in the course of glacier retreat at the Dwyka/Ecca boundary where climate and weathering processes are known to have changed. The proxy signals indicate an increase in sea level and salinity, and a shift in redox conditions from oxygenated to temporary anoxic/euxinic conditions. Due to the synchronicity of these events, distant sampling localities in the Karoo Basin can be correlated. Despite facies differences between the Eastern Kalahari and Karoo Basin, the geochemical proxies point to a comparable climatic evolution during the postglacial phase. For the Early Permian, proxy signals indicate warm–humid conditions in the Karoo and Kalahari Basin. During the Middle Permian increased aridity hampered chemical weathering processes as indicated by decreasing CIA values. Results show that: (i) proxies reflect provenance, synsedimentary redox regime and late diagenetic alteration, (ii) by combination of different independent geochemical proxies primary conditions of sedimentation and climate can be deduced, (iii) the geochemical proxies applied are independent of local environments and (iv) the data reveal supra-regional or even hemispherical changes in climate and sedimentary conditions. Thus geochemical proxies can be used as reliable markers for basin wide correlations. Knowledge about synchronicity on basin scale contributes to an improved understanding of SW Gondwana's interaction with and influence on global climatic evolution.

Intercolony variability of skeletal oxygen and carbon isotope signatures of cultured Porites corals: Temperature-controlled experiments

The skeletal oxygen isotope ratio of Porites corals is the most frequently used proxy of past seawater temperature and composition for tropical and subtropical oceans. However, field calibration of the proxy signals is often difficult owing to the dual dependence of skeletal oxygen isotope ratio on temperature and the oxygen isotope composition of water. We conducted tank experiments in which we grew Porites spp. colonies for 142 d in thermostated seawater at five temperature settings between 21°C and 29°C under moderate light intensity of 250 μmol m −2 s −1 with a 12:12 light:dark photoperiod. A skeletal isotope microprofiling technique applied along the major growth axis of each colony revealed that the oxygen isotope ratios of newly deposited skeleton in most colonies remained almost constant during tank incubation, thus providing an ideal situation for precise calibration of oxygen isotope ratio proxy signals. However, the oxygen isotope ratios displayed an unusually large intercolony variability (∼1‰) at each temperature setting although the mean slope (∼0.15‰ °C −1) obtained for the temperature–skeletal oxygen isotope ratio relationship was close to previous results. The intercolony variations in the oxygen isotope ratios were apparently caused by kinetic isotope effects related to variations in the skeletal growth rate rather than by species-specific variability or genetic differences within species. No correlation was found between skeletal carbon isotope ratios and temperature. The carbon isotope ratios showed significantly inverse correlation with linear growth rates, suggesting a kinetic isotope control at low growth rates. Observed intercolony variability in skeletal carbon isotope ratios (∼5‰) can be partly attributed to growth-rate-related kinetic isotope effects.

Neodymium isotopic composition of Ordovician conodonts as a seawater proxy: Testing paleogeography

To evaluate recent Ordovician paleogeographic reconstructions, εNd values were determined in conodonts as a proxy for the isotopic variations in ancient seawater using samples from the major cratons and microplates. Isotopic variations reveal the existence of distinct oceanic masses and epeiric seas that constrain the position of plates and terranes relative to these water masses and hence constrain models of regional and global paleogeography. The isotopic patterns show a consistent picture of the changes in the Ordovician oceans. The εNd values for water masses associated with Laurentia are strongly negative (−28 to −18) in the Early Ordovician, evolving over time to higher values in the range −13 to −5. The Early Ordovician signature of Laurentia is in marked contrast to other cratons and microplates, which have a range of values from −10 to −5. Samples from South China show interesting signals that reflect a greater similarity to Laurentia than other peri‐Gondwana terranes. The isotopic variations are a function of both regional geology and global tectonic processes, the most obvious being the Taconic Orogeny and onset of the closure of the Iapetus Ocean. Regional and global models of paleogeography are considered in light of these proxy signals. This study also reveals that conodonts are powerful geochemical tools for obtaining information on ancient water masses. The use of the Nd isotopic signatures from conodonts provides a method independent of paleomagnetism and biogeography to test paleogeographic models. By integrating such information, a more multidisciplinary approach is possible.