144 research outputs found
Distinguishing the combined vegetation and soil component of Ξ΄13C variation in speleothem records from subsequent degassing and prior calcite precipitation effects
The carbon isotopic signature inherited from soil and epikarst processes may be modified by degassing and prior calcite precipitation (PCP) before its imprint on speleothem calcite. Despite laboratory demonstration of PCP effects on carbon isotopes and increasingly sophisticated models of the governing processes, to date, there has been limited effort to deconvolve the dual PCP and soilβepikarst components in measured speleothem isotopic time series. In this contribution, we explore the feasibility, advantages, and disadvantages of using trace element ratios and Ξ΄44Ca to remove the overprinting effect of PCP on measured Ξ΄13C to infer the temporal variations in the initial Ξ΄13C of drip water prior to degassing and PCP. In nine examined stalagmites, the most widely utilized PCP indicators Mg/Ca and Ξ΄44Ca covary as expected. However, Srββ/Ca does not show consistent relationships with Ξ΄44Ca so PCP is not the dominant control on Srββ/Ca. From Ξ΄44Ca and Mg/Ca, our calculation of PCP as fCa, the fraction of initial Ca remaining in solution at the time the stalagmite layer is deposited, yields multiple viable solutions depending on the assumed Ξ΄44Ca fractionation factor and inferred variation in DMg. Uncertainty in the effective fractionation of Ξ΄13C during degassing and precipitation contributes to uncertainty in the absolute value of estimated initial Ξ΄13C. Nonetheless, the trends in initial Ξ΄13C are less sensitive to these uncertainties. In coeval stalagmites from the same cave spanning the 94 to 82βka interval, trends in calculated initial Ξ΄13C are more similar than those in measured Ξ΄13C and reveal a common positive-anomaly initial Ξ΄13C during a stadial cooling event. During deglaciations, calculated initial Ξ΄13C implies a trend of greater respiration rates and higher soil CO2, although the higher interglacial drip water saturation favors more extensive PCP. Initial Ξ΄13C can be estimated for active and fossil speleothems from a range of settings, wherever there is confidence that Mg/Ca and/or Ξ΄44Ca provides a quantitative indication of past changes in PCP. Further study of Mg partitioning in speleothems will improve the robustness of Mg/Ca as a PCP proxy
ΠΡΠΎΠ΅ΠΊΡΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ ΡΠ»Π΅ΠΊΡΡΠΈΡΠ΅ΡΠΊΠΈΡ ΡΠΈΠ»ΠΎΠ²ΡΡ ΡΡΡΠ°Π½ΠΎΠ²ΠΎΠΊ ΠΏΡΠΈ ΠΏΠΎΠ΄Π΄Π΅ΡΠΆΠΊΠ΅ ΠΌΠ½ΠΎΠ³ΠΎΡΠ΅Π»Π΅Π²ΡΠΌΠΈ ΡΡΡΠ°ΡΠ΅Π³ΠΈΡΠΌΠΈ ΠΎΠΏΡΠΈΠΌΠΈΠ·Π°ΡΠΈΠΈ
Electric drive systems consisting of battery, inverter, electric motor and gearbox are applied in hybridor purely electric vehicles. The layout process of such propulsion systems is performed on system level under consideration of various component properties and their interfering characteristics. In addition, different boundary conditions are taken under account, e. g. performance, efficiency, packaging, costs. In this way, the development process of the power train involves a broad range of influencing parameters and periphery conditions and thus represents a multi-dimensional optimization problem. Stateof-the-art development processes of mechatronic systems are usually executed according to the V-model, which represents a fundamental basis for handling the complex interactions of the different disciplines involved. In addition, stage-gate processes and spiral models are applied to deal with the high level of complexity during conception, design and testing. Involving a large number of technical and economic factors, these sequential, recursive processes may lead to suboptimal solutions since the system design processes do not sufficiently consider the complex relations between the different, partially conflicting domains. In this context, the present publication introduces an integrated multi-objective optimization strategy for the effective conception of electric propulsion systems, which involves a holistic consideration of all components and requirements in a multi-objective manner. The system design synthesis is based on component-specific Pareto-optimal designs to handle performance, efficiency, package and costs for given system requirements. The results are displayed as Pareto-fronts of electric power train system designs variants, from which decision makers are able to choose the best suitable solution. In this way, the presented system design approach for the development of electrically driven axles enables a multi-objective optimization considering efficiency, performance, costs and package. It is capable to reduce development time and to improve overall system quality at the same time.Π‘ΠΈΡΡΠ΅ΠΌΡ ΡΠ»Π΅ΠΊΡΡΠΎΠΏΡΠΈΠ²ΠΎΠ΄Π°, ΡΠΎΡΡΠΎΡΡΠΈΠ΅ ΠΈΠ· Π°ΠΊΠΊΡΠΌΡΠ»ΡΡΠΎΡΠ°, ΠΈΠ½Π²Π΅ΡΡΠΎΡΠ°, ΡΠ»Π΅ΠΊΡΡΠΎΠ΄Π²ΠΈΠ³Π°ΡΠ΅Π»Ρ ΠΈ ΠΊΠΎΡΠΎΠ±ΠΊΠΈ ΠΏΠ΅ΡΠ΅Π΄Π°Ρ, ΠΏΡΠΈΠΌΠ΅Π½ΡΡΡΡΡ Π² Π³ΠΈΠ±ΡΠΈΠ΄Π½ΡΡ
ΠΈΠ»ΠΈ ΡΠΈΡΡΠΎ ΡΠ»Π΅ΠΊΡΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΡΠ°Π½ΡΠΏΠΎΡΡΠ½ΡΡ
ΡΡΠ΅Π΄ΡΡΠ²Π°Ρ
. ΠΡΠΎΡΠ΅ΡΡ ΠΊΠΎΠΌΠΏΠΎΠ½ΠΎΠ²ΠΊΠΈ ΡΠ°ΠΊΠΈΡ
Π΄Π²ΠΈΠΆΠΈΡΠ΅Π»ΡΠ½ΡΡ
ΡΠΈΡΡΠ΅ΠΌ ΠΎΡΡΡΠ΅ΡΡΠ²Π»ΡΠ΅ΡΡΡ Π½Π° ΡΠΈΡΡΠ΅ΠΌΠ½ΠΎΠΌ ΡΡΠΎΠ²Π½Π΅ Ρ ΡΡΠ΅ΡΠΎΠΌ ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
ΡΠ²ΠΎΠΉΡΡΠ² ΠΊΠΎΠΌΠΏΠΎΠ½Π΅Π½ΡΠΎΠ² ΠΈ ΠΈΡ
ΠΈΠ½ΡΠ΅ΡΡΠ΅ΡΠΈΡΡΡΡΠΈΡ
Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊ. ΠΡΠΎΠΌΠ΅ ΡΠΎΠ³ΠΎ, ΡΡΠΈΡΡΠ²Π°ΡΡΡΡ ΡΠ°Π·Π½ΡΠ΅ Π³ΡΠ°Π½ΠΈΡΠ½ΡΠ΅ ΡΡΠ»ΠΎΠ²ΠΈΡ, Π½Π°ΠΏΡΠΈΠΌΠ΅Ρ ΡΠ΅Ρ
Π½ΠΈΡΠ΅ΡΠΊΠΈΠ΅ Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊΠΈ, ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΡ, ΠΊΠΎΠΌΠΏΠ»Π΅ΠΊΡΠΎΠ²Π°Π½ΠΈΠ΅, ΡΡΠΎΠΈΠΌΠΎΡΡΡ. Π’Π°ΠΊΠΈΠΌ ΠΎΠ±ΡΠ°Π·ΠΎΠΌ, ΠΏΡΠΎΡΠ΅ΡΡ ΡΠ°Π·ΡΠ°Π±ΠΎΡΠΊΠΈ ΡΠΈΠ»ΠΎΠ²ΠΎΠΉ ΠΏΠ΅ΡΠ΅Π΄Π°ΡΠΈ Π²ΠΊΠ»ΡΡΠ°Π΅Ρ Π² ΡΠ΅Π±Ρ ΡΠΈΡΠΎΠΊΠΈΠΉ Π΄ΠΈΠ°ΠΏΠ°Π·ΠΎΠ½ Π²Π»ΠΈΡΡΡΠΈΡ
ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠΎΠ² ΠΈ ΠΏΠ΅ΡΠΈΡΠ΅ΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΡΠ»ΠΎΠ²ΠΈΠΉ ΠΈ ΡΠ΅ΠΌ ΡΠ°ΠΌΡΠΌ ΠΏΡΠ΅Π΄ΡΡΠ°Π²Π»ΡΠ΅Ρ ΡΠΎΠ±ΠΎΠΉ ΠΏΡΠΎΠ±Π»Π΅ΠΌΡ ΠΌΠ½ΠΎΠ³ΠΎΠΌΠ΅ΡΠ½ΠΎΠΉ ΠΎΠΏΡΠΈΠΌΠΈΠ·Π°ΡΠΈΠΈ. Π‘ΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΡΠ΅ ΠΏΡΠΎΡΠ΅ΡΡΡ ΡΠ°Π·ΡΠ°Π±ΠΎΡΠΊΠΈ ΠΌΠ΅Ρ
Π°ΡΡΠΎΠ½Π½ΡΡ
ΡΠΈΡΡΠ΅ΠΌ ΠΎΠ±ΡΡΠ½ΠΎ Π²ΡΠΏΠΎΠ»Π½ΡΡΡΡΡ Π² ΡΠΎΠΎΡΠ²Π΅ΡΡΡΠ²ΠΈΠΈ Ρ V-ΠΌΠΎΠ΄Π΅Π»ΡΡ, ΠΊΠΎΡΠΎΡΠ°Ρ ΠΏΡΠ΅Π΄ΡΡΠ°Π²Π»ΡΠ΅Ρ ΡΠΎΠ±ΠΎΠΉ ΡΡΠ½Π΄Π°ΠΌΠ΅Π½ΡΠ°Π»ΡΠ½ΡΡ ΠΎΡΠ½ΠΎΠ²Ρ Π΄Π»Ρ ΡΠΏΡΠ°Π²Π»Π΅Π½ΠΈΡ ΡΠ»ΠΎΠΆΠ½ΡΠΌΠΈ Π²Π·Π°ΠΈΠΌΠΎΠ΄Π΅ΠΉΡΡΠ²ΠΈΡΠΌΠΈ ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
Π΄ΠΈΡΡΠΈΠΏΠ»ΠΈΠ½. ΠΡΠΎΠΌΠ΅ ΡΠΎΠ³ΠΎ, ΠΏΡΠΈΠΌΠ΅Π½ΡΡΡΡΡ ΡΡΠ°ΠΏΠ½ΡΠ΅ ΠΏΡΠΎΡΠ΅ΡΡΡ ΠΈ ΡΠΏΠΈΡΠ°Π»ΡΠ½ΡΠ΅ ΠΌΠΎΠ΄Π΅Π»ΠΈ, ΡΡΠΎΠ±Ρ ΡΠΏΡΠ°Π²ΠΈΡΡΡΡ Ρ Π²ΡΡΠΎΠΊΠΈΠΌ ΡΡΠΎΠ²Π½Π΅ΠΌ ΡΠ»ΠΎΠΆΠ½ΠΎΡΡΠΈ ΠΏΡΠΈ ΡΠ°Π·ΡΠ°Π±ΠΎΡΠΊΠ΅, ΠΏΡΠΎΠ΅ΠΊΡΠΈΡΠΎΠ²Π°Π½ΠΈΠΈ ΠΈ ΡΠ΅ΡΡΠΈΡΠΎΠ²Π°Π½ΠΈΠΈ. ΠΠΎΠ²Π»Π΅ΠΊΠ°Ρ Π±ΠΎΠ»ΡΡΠΎΠ΅ ΠΊΠΎΠ»ΠΈΡΠ΅ΡΡΠ²ΠΎ ΡΠ΅Ρ
Π½ΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΈ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΠ°ΠΊΡΠΎΡΠΎΠ², ΡΡΠΈ ΠΏΠΎΡΠ»Π΅Π΄ΠΎΠ²Π°ΡΠ΅Π»ΡΠ½ΡΠ΅ ΡΠ΅ΠΊΡΡΡΠΈΠ²Π½ΡΠ΅ ΠΏΡΠΎΡΠ΅ΡΡΡ ΠΌΠΎΠ³ΡΡ ΠΏΡΠΈΠ²Π΅ΡΡΠΈ ΠΊ Π½Π΅ΠΎΠΏΡΠΈΠΌΠ°Π»ΡΠ½ΡΠΌ ΡΠ΅ΡΠ΅Π½ΠΈΡΠΌ, ΠΏΠΎΡΠΊΠΎΠ»ΡΠΊΡ ΠΏΡΠΎΡΠ΅ΡΡΡ ΠΏΡΠΎΠ΅ΠΊΡΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΡΠΈΡΡΠ΅ΠΌΡ Π½Π΅Π΄ΠΎΡΡΠ°ΡΠΎΡΠ½ΠΎ ΡΡΠΈΡΡΠ²Π°ΡΡ ΡΠ»ΠΎΠΆΠ½ΡΠ΅ ΠΎΡΠ½ΠΎΡΠ΅Π½ΠΈΡ ΠΌΠ΅ΠΆΠ΄Ρ ΡΠ°Π·Π»ΠΈΡΠ½ΡΠΌΠΈ, ΡΠ°ΡΡΠΈΡΠ½ΠΎ ΠΊΠΎΠ½ΡΠ»ΠΈΠΊΡΡΡΡΠΈΠΌΠΈ ΠΎΠ±Π»Π°ΡΡΡΠΌΠΈ. Π ΡΡΠΎΠΌ ΠΊΠΎΠ½ΡΠ΅ΠΊΡΡΠ΅ Π½Π°ΡΡΠΎΡΡΠ°Ρ ΠΏΡΠ±Π»ΠΈΠΊΠ°ΡΠΈΡ ΠΏΡΠ΅Π΄ΡΡΠ°Π²Π»ΡΠ΅Ρ ΠΈΠ½ΡΠ΅Π³ΡΠΈΡΠΎΠ²Π°Π½Π½ΡΡ ΠΌΠ½ΠΎΠ³ΠΎΡΠ΅Π»Π΅Π²ΡΡ ΡΡΡΠ°ΡΠ΅Π³ΠΈΡ ΠΎΠΏΡΠΈΠΌΠΈΠ·Π°ΡΠΈΠΈ Π΄Π»Ρ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΠΉ ΠΊΠΎΠ½ΡΠ΅ΠΏΡΠΈΠΈ ΡΠ»Π΅ΠΊΡΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΠΈΠ»ΠΎΠ²ΡΡ
ΡΡΡΠ°Π½ΠΎΠ²ΠΎΠΊ, Π²ΠΊΠ»ΡΡΠ°ΡΡΡΡ ΠΊΠΎΠΌΠΏΠ»Π΅ΠΊΡΠ½ΠΎΠ΅ ΡΠ°ΡΡΠΌΠΎΡΡΠ΅Π½ΠΈΠ΅ Π²ΡΠ΅Ρ
ΠΊΠΎΠΌΠΏΠΎΠ½Π΅Π½ΡΠΎΠ² ΠΈ ΡΡΠ΅Π±ΠΎΠ²Π°Π½ΠΈΠΉ Π½Π° ΠΌΠ½ΠΎΠ³ΠΎΡΠ΅Π»Π΅Π²ΠΎΠΉ ΠΎΡΠ½ΠΎΠ²Π΅. Π‘ΠΈΠ½ΡΠ΅Π· ΡΠΈΡΡΠ΅ΠΌΠ½ΠΎΠ³ΠΎ Π΄ΠΈΠ·Π°ΠΉΠ½Π° ΠΎΡΠ½ΠΎΠ²Π°Π½ Π½Π° ΠΠ°ΡΠ΅ΡΠΎ-ΠΎΠΏΡΠΈΠΌΠ°Π»ΡΠ½ΡΡ
ΠΊΠΎΠ½ΡΡΡΡΠΊΡΠΈΡΡ
ΡΠΎ ΡΠΏΠ΅ΡΠΈΡΠΈΡΠ΅ΡΠΊΠΈΠΌΠΈ ΠΊΠΎΠΌΠΏΠΎΠ½Π΅Π½ΡΠ°ΠΌΠΈ Ρ ΡΠ΅Π»ΡΡ ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠ΅Π½ΠΈΡ ΡΠ°Π±ΠΎΡΡ, ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ, ΠΊΠΎΠΌΠΏΠ»Π΅ΠΊΡΠ°ΡΠΈΠΈ ΠΈ Π·Π°ΡΡΠ°Ρ, ΠΏΡΠ΅Π΄ΡΡΠΌΠΎΡΡΠ΅Π½Π½ΡΡ
Π΄Π»Ρ Π΄Π°Π½Π½ΠΎΠΉ ΡΠΈΡΡΠ΅ΠΌΡ. Π Π΅Π·ΡΠ»ΡΡΠ°ΡΡ ΠΎΡΠΎΠ±ΡΠ°ΠΆΠ°ΡΡΡΡ Π² Π²ΠΈΠ΄Π΅ ΠΠ°ΡΠ΅ΡΠΎ-ΡΡΠΎΠ½ΡΠΎΠ² Π²Π°ΡΠΈΠ°Π½ΡΠΎΠ² ΡΠΈΡΡΠ΅ΠΌ ΡΠ»Π΅ΠΊΡΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΡΠ°Π½ΡΠΌΠΈΡΡΠΈΠΉ, ΠΈΠ· ΠΊΠΎΡΠΎΡΡΡ
Π»ΠΈΡΠ°, ΠΏΡΠΈΠ½ΠΈΠΌΠ°ΡΡΠΈΠ΅ ΡΠ΅ΡΠ΅Π½ΠΈΡ, ΠΌΠΎΠ³ΡΡ Π²ΡΠ±ΡΠ°ΡΡ Π½Π°ΠΈΠ±ΠΎΠ»Π΅Π΅ ΠΏΠΎΠ΄Ρ
ΠΎΠ΄ΡΡΠ΅Π΅ ΠΈΠ· Π½ΠΈΡ
. Π’Π°ΠΊΠΈΠΌ ΠΎΠ±ΡΠ°Π·ΠΎΠΌ, ΠΏΡΠ΅Π΄ΡΡΠ°Π²Π»Π΅Π½Π½ΡΠΉ ΠΏΠΎΠ΄Ρ
ΠΎΠ΄ ΠΊ ΠΏΡΠΎΠ΅ΠΊΡΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΡΠΈΡΡΠ΅ΠΌΡ Π΄Π»Ρ ΡΠ°Π·ΡΠ°Π±ΠΎΡΠΊΠΈ ΠΎΡΠ΅ΠΉ Ρ ΡΠ»Π΅ΠΊΡΡΠΈΡΠ΅ΡΠΊΠΈΠΌ ΠΏΡΠΈΠ²ΠΎΠ΄ΠΎΠΌ ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΠ²Π°Π΅Ρ ΠΌΠ½ΠΎΠ³ΠΎΡΠ΅Π»Π΅Π²ΡΡ ΠΎΠΏΡΠΈΠΌΠΈΠ·Π°ΡΠΈΡ Ρ ΡΡΠ΅ΡΠΎΠΌ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ, ΡΡΠ½ΠΊΡΠΈΠΎΠ½ΠΈΡΠΎΠ²Π°Π½ΠΈΡ, ΡΡΠΎΠΈΠΌΠΎΡΡΠΈ ΠΈ ΠΊΠΎΠΌΠΏΠ»Π΅ΠΊΡΠ°ΡΠΈΠΈ. ΠΠ°Π½Π½ΡΠΉ ΠΏΠΎΠ΄Ρ
ΠΎΠ΄ ΠΏΠΎΠ·Π²ΠΎΠ»ΡΠ΅Ρ ΡΠΎΠΊΡΠ°ΡΠΈΡΡ Π²ΡΠ΅ΠΌΡ ΡΠ°Π·ΡΠ°Π±ΠΎΡΠΊΠΈ ΠΈ ΠΎΠ΄Π½ΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΠΎ ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΡΡ ΡΠ»ΡΡΡΠ΅Π½ΠΈΠ΅ ΠΊΠ°ΡΠ΅ΡΡΠ²Π° ΡΠΈΡΡΠ΅ΠΌΡ
The role of microorganisms in the formation of a stalactite in Botovskaya Cave, Siberia β paleoenvironmental implications
Calcitic speleothems in caves can form through abiogenic or biogenic processes, or through a combination of both. Many issues conspire to make the assessment of biogenicity difficult, especially when focusing on old speleothem deposits. This study reports on a multiproxy analysis of a Siberian stalactite, combining high-resolution microscopy, isotope geochemistry and microbially enhanced mineral precipitation laboratory experiments. The contact between growth layers in a stalactite exhibits a biogenic isotopic signature; coupled with morphological evidence, this supports a microbial origin of calcite crystals. SIMS Ξ΄<sup>13</sup>C data suggest that microbially mediated speleothem formation occurred repeatedly at short intervals before abiotic precipitation took over. The studied stalactite also contains iron and manganese oxides that have been mediated by microbial activity through extracellular polymeric substance (EPS)-influenced organomineralization processes. The latter reflect paleoenvironmental changes that occurred more than 500 000 yr ago, possibly related to the presence of a peat bog above the cave at that time. Microbial activity can initiate calcite deposition in the aphotic zone of caves before inorganic precipitation of speleothem carbonates. This study highlights the importance of microbially induced fractionation that can result in large negative Ξ΄<sup>13</sup>C excursions. The microscale biogeochemical processes imply that microbial activity has only negligible effects on the bulk Ξ΄<sup>13</sup>C signature in speleothems, which is more strongly affected by CO<sub>2</sub> degassing and the host rock signature
Distinguishing the vegetation and soil component of δ13C variation in speleothem records from degassing and prior calcite precipitation effects
The carbon isotopic signature inherited from soil/epikarst processes may be modified by degassing and prior calcite precipitation (PCP) before its imprint on speleothem calcite. Despite laboratory demonstration of PCP effects on carbon isotopes and increasingly sophisticated models of the governing processes, to date, there has been limited effort to deconvolve the dual PCP and soil/epikarst components in measured speleothem isotopic time series. In this contribution, we explore the feasibility, advantages, and disadvantages of using trace element ratios and δ44Ca to remove the overprinting effect of PCP on measured δ13C to infer the temporal variations in the initial δ13C of dripwater. In 8 examined stalagmites, the most widely utilized PCP indicators Mg/Ca and δ44Ca covary as expected. However, Sr/Ca does not show consistent relationships with δ44Ca so PCP is not universally the dominant control on Sr/Ca. From δ44Ca and Mg/Ca, our calculation of PCP as fCa, fraction of initial Ca remaining at the deposition of the stalagmite layer, yields multiple viable solutions depending on the assumed δ44Ca fractionation factor and inferred variation in DMg. Uncertainty in the effective fractionation of δ13C during degassing and precipitation contributes to uncertainty in the absolute value of estimated initial δ13C. Nonetheless, the trends in initial δ13C are less sensitive to these uncertainties. In coeval stalagmites from the same cave spanning 94 to 82 ka interval, trends in calculated initial δ13C are more similar than those in measured δ13C, and reveal a common positive anomaly initial δ13C during a stadial cooling event. During deglaciations, the trend of greater respiration rates and higher soil CO2 is captured in the calculated initial δ13C, despite the tendency of higher interglacial dripwater situation to favor more extensive PCP.</p
Local and Regional Indian Summer Monsoon Precipitation Dynamics During Termination II and the Last Interglacial
To date Indian summer monsoon (ISM) dynamics have been assessed by changes in stalagmite Ξ΄18O. However, stalagmite Ξ΄18O is influenced by multiple environmental factors (e.g., atmospheric moisture transport, rainfall amount at the study site, and ISM seasonality), precluding simple and clear reconstructions of rainfall amount or variability. This study aims to disentangle these environmental factors by combining Ξ΄18O, Ξ΄44Ca, and elemental data from a stalagmite covering Termination II and the last interglacial from Mawmluh Cave, NE India, to produce a semiquantitative reconstruction of past ISM rainfall. We interpret Ξ΄18O as a mixed signal of rainfall source dynamics and rainfall amount and coupled Ξ΄44Ca and X/Ca ratios as indicators of local infiltration rate and prior calcite precipitation in the karst zone. The wettest conditions in our studied interval (135 and 100 kyrs BP; BP = before present, with the present being 1950 CE) occurred during Marine Isotope Stage 5e. Our multiproxy data set suggests a likely change in seasonal distribution of Marine Isotope Stage 5e rainfall compared to the Holocene; the wet season was longer with higherβthanβmodern dry season rainfall. Using the last interglacial as an analogue for future anthropogenic warming, our data suggest a more erratic ISM behavior in a warmer world
A novel approach for construction of radiocarbon-based chronologies for speleothems
Robust chronologies are crucial for the correct interpretation of climate proxy records and for detailed reconstructions of palaeoclimate. Stalagmites have garnered strong interest as recorders of past climate in part due to their amenability to U-series dating. However, many stalagmites are not dateable using this technique due to low 238U and/or high detrital Th concentrations (e.g., many tropical cave systems (Adkins et al., 2013)), and occasionally these issues affect stalagmites across wide geographical regions (e.g., large parts of Australia (Green et al. 2013)) complicating the use of stalagmites in these areas. Radiocarbon (14C) offers an alternative method of dating stalagmites, but issues associated with the βdead carbon fractionβ (DCF) have historically hindered this approach. Here, a novel 14C-based method for dating stalagmites is presented and discussed. The technique calculates a best-fit growth rate between a time-series of stalagmite 14C data and known atmospheric 14C variability. The new method produces excellent results for stalagmites that satisfy four requirements: i) the absence of long-term secular variability in DCF (i.e., stalagmite DCF varies around a mean value with no long-term trend), ii) stalagmite growth rate does not vary significantly (the technique identifies stalagmites with substantial growth rate variability), iii) the stalagmite record is long enough that measurable 14C decay has occurred, and iv) one βanchorβ point exists where the calendar age is known. The model produces good results for a previously UβTh dated stalagmite from Heshang Cave, China, and is then applied to an undated stalagmite from southern Poland. The new method will not replace high-precision UβTh measurements, because the precision of the technique is difficult to quantify. However, it provides a means for dating certain stalagmites undateable by conventional UβTh methods and for refining coarse UβTh chronologies
Permafrost-related hiatuses in stalagmites: Evaluating the potential for reconstruction of carbon cycle dynamics
Permafrost is widely present throughout the Northern Hemisphere high latitudes, and stores large amounts of carbon in the form of frozen soil organic matter. The response of permafrost regions to anthropogenic climate change remains uncertain, in part because of a lack of information on their response to past changes in global climate. Here we test the use of stalagmites from two caves in Siberia as a novel, precisely dated, and highly localised archive of past permafrost carbon cycle dynamics. Stalagmite growth at these sites is controlled by the presence/absence of permafrost above the cave over glacial-interglacial time scales. We target the transition layer between two subsequent growth phases (interglacials) and the interval directly following growth resumption after the last glacial in three stalagmites, as this is where a geochemical imprint of thaw-related processes in the frozen zone between surface and cave would be recorded. We apply a multi-proxy approach including carbon isotopes (Ξ΄13C and 14C) and trace element concentrations, combined with petrographic analyses and high-resolution U-Th chronology. Our dataset indicates complex growth patterns and possible intervals of microbial colonisation of the stalagmite surface in the transition layers. High-resolution U-Th ages confirm that the transition layer is not a single, long growth hiatus, but rather a period of extremely slow or episodic growth phases, possibly during βskippedβ interglacials. However, we find no conclusive evidence for a geochemical signature related to permafrost degradation and related local carbon cycle dynamics, which might be related to insufficient sensitivity of the archive for high-frequency processes and/or insufficient measurement resolution
Aerosol forcing of the position of the intertropical convergence zone since AD1550
The position of the intertropical convergence zone is an important control on the distribution of low-latitude precipitation. Its position is largely controlled by hemisphere temperature contrasts1, 2. The release of aerosols by human activities may have resulted in a southward shift of the intertropical convergence zone since the early 1900s (refs 1, 3, 4, 5, 6) by muting the warming of the Northern Hemisphere relative to the Southern Hemisphere over this interval1, 7, 8, but this proposed shift remains equivocal. Here we reconstruct monthly rainfall over Belize for the past 456 years from variations in the carbon isotope composition of a well-dated, monthly resolved speleothem. We identify an unprecedented drying trend since ad 1850 that indicates a southward displacement of the intertropical convergence zone. This drying coincides with increasing aerosol emissions in the Northern Hemisphere and also marks a breakdown in the relationship between Northern Hemisphere temperatures and the position of the intertropical convergence zone observed earlier in the record. We also identify nine short-lived drying events since ad 1550 each following a large volcanic eruption in the Northern Hemisphere. We conclude that anthropogenic aerosol emissions have led to a reduction of rainfall in the northern tropics during the twentieth century, and suggest that geographic changes in aerosol emissions should be considered when assessing potential future rainfall shifts in the tropics
Evaluating model outputs using integrated global speleothem records of climate change since the last glacial
Although quantitative isotope data from speleothems has been used to evaluate isotope-enabled model simulations, currently no consensus exists regarding the most appropriate methodology through which to achieve this. A number of modelling groups will be running isotope-enabled palaeoclimate simulations in the framework of the Coupled Model Intercomparison Project Phase 6, so it is timely to evaluate different approaches to using the speleothem data for dataβmodel comparisons. Here, we illustrate this using 456 globally distributed speleothem Ξ΄18O records from an updated version of the Speleothem Isotopes Synthesis and Analysis (SISAL) database and palaeoclimate simulations generated using the ECHAM5-wiso isotope-enabled atmospheric circulation model. We show that the SISAL records reproduce the first-order spatial patterns of isotopic variability in the modern day, strongly supporting the application of this dataset for evaluating model-derived isotope variability into the past. However, the discontinuous nature of many speleothem records complicates the process of procuring large numbers of records if dataβmodel comparisons are made using the traditional approach of comparing anomalies between a control period and a given palaeoclimate experiment. To circumvent this issue, we illustrate techniques through which the absolute isotope values during any time period could be used for model evaluation. Specifically, we show that speleothem isotope records allow an assessment of a model's ability to simulate spatial isotopic trends. Our analyses provide a protocol for using speleothem isotope data for model evaluation, including screening the observations to take into account the impact of speleothem mineralogy on Ξ΄18O values, the optimum period for the modern observational baseline and the selection of an appropriate time window for creating means of the isotope data for palaeo-time-slices
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