Relative paleointensity (RPI) in the latest Pleistocene (10–45 ka) and implications for deglacial atmospheric radiocarbon

We report magnetic properties and relative paleointensity (RPI) proxies from a suite of 10 conventional piston cores and Kasten cores from the SW Iberian Margin collected during cruise JC089 of the RSS James Cook in August 2013. Mean sedimentation rates are in the 10-20 cm/kyr range. Age models were acquired by correlation of Ca/Ti and Zr/Sr XRF core-scanning data to L* reflectance from the Cariaco Basin that is, in turn, tied to the Greenland ice-core chronology. The natural remanent magnetization (NRM) is represented by a single magnetization component carried by a low-coercivity mineral (magnetite), although reflectance and bulk magnetic properties indicate the presence of a high-coercivity (hematitic) magnetic phase, possibly from eolian dust. The presence of fine-grained hematite means that the sediments are not ideal for RPI studies, however the detrital hematite does not appear to contribute to the NRM or anhysteretic remanent magnetization (ARM). In order to test the usefulness of the RPI data, we construct a stack of 12 RPI records from the SW Iberian Margin for the 0-45 ka interval and compare it with a stack of 12 globally distributed marine and lake records, chosen on the basis of mean sedimentation rates (>15 cm/kyr) and superior age models. The two stacks are similar, but different from published RPI stacks, particularly for the 10-30 ka interval, and imply a virtual axial dipole moment (VADM) high at ~15-18 ka followed by a drop in field strength from ~15 to 13 ka. A revised VADM estimate calculated from Greenland 10Be ice-core flux using a contemporary age model is remarkably consistent with the new overall RPI stack, based on Iberian Margin and global RPI records. The elevated atmospheric 14C levels of the last ice age cannot, however, be fully explained by this RPI stack although relative changes such as the long-term drop in atmospheric 14C from 30 to 15 ka are reproduced, supporting the hypothesis of a combined influence of production rate and ocean ventilation on 14C during the last ice age

Eccentricity signal in the nannofossil time-series across the Mid-Pleistocene Transition in the northwestern Pacific Ocean (ODP Site 1209)

The Mid-Pleistocene Transition (MPT; 1.25–0.6 million years ago, Ma) is one of the most important and still debated climate reorganizations during which the glacial/interglacial cycles switched from a 41-thousand years (kyr) cycle (i.e. obliquity) to a quasi-periodic 100-kyr cycle (associated with orbital eccentricity). Variations in the orbital geometry can affect the abundance and distribution of certain marine biota such as the coccolithophores, a group of unicellular calcifying phytoplankton, whose skeletal remains – called nannofossils – represent a valid tool within the geological archives to infer change in surface water conditions and/or coccolithophore productivity and how orbital variations may have impacted them. Here, we apply for the first time various time series analytical techniques to the nannofossil dataset from mid-latitudinal Ocean Drilling Program (ODP) Site 1209 in the northwest Pacific Ocean for the interval spanning the last 1.6 Myr. To better interpret the orbital signal recorded by different nannofossil species we used time series analyses (i.e. wavelet, autocorrelation and cross correlation) to identify the main periodicities by single nannofossil species during the MPT, and to investigate further their response timings to those orbital drivers. In addition, we investigated how the recorded periodicities can improve understanding of the paleoecological preferences of particular species. The combination of multiple time series analyses allowed identification of the 100-kyr periodicity as the main cyclicity recorded in most analyzed species at Site 1209, documenting the predominance of the eccentricity-related signal at mid-latitudes and a reduced or absent influence of the obliquity response. Thus, our data highlight how orbital influence varies by latitude impacting the nannofossil species. The lag between eccentricity and species abundance fluctuations was also investigated, identifying a fast response ranging between 20 and 40 kyr for the taxa Calcidiscus leptoporus subspecies leptoporus, Gephyrocapsa caribbeanica small, and Reticulofenestra spp. (>5 μm). This study corroborates the potential of nannofossils to deepen understanding of the dynamics and effects of variations in orbital geometry through time. It also underlines the need to extend the study of the responses of specific species through the use of different time series analysis techniques in order to return complementary information and detect clearer orbital signals

“Natural” stress patterns and dependencies between edge alignment and quantity sensitivity

We conducted an artificial language learning experiment to study learning asymmetries that might reveal latent preferences relating to, and any dependencies between, the edge alignment and quantity sensitivity (QS) parameters in stress patterning. We used a poverty of the stimulus approach to teach American English speakers an unbounded QS stress rule (stress a single CV: syllable) and either a left- or right-aligning QI rule if only light syllables were present. Forms with two CV: syllables were withheld in the learning phase and added in the test phase, forcing participants to choose between left- and right-aligning options for the QS rule. Participants learned the left- and right-edge QI rules equally well, and also the basic QS rule. Response patterns for words with two CV: syllables suggest biases favoring a left-aligning QS rule with a left-edge QI default. Our results also suggest that a left-aligning QS pattern with a rightedge QI default was least favored. We argue that stress patterns shown to be preferred based on evidence from ease-of-learning and participants’ untrained generalizations can be considered more natural than less favored opposing patterns. We suggest that cognitive biases revealed by artificial stress learning studies may have contributed to shaping stress typology.publishedVersio

Final Report. IUT No. B560420 with UC Berkeley. Organic Chemistry at High Pressures &Temperatures

We have successfully completed the research outlined in our proposal: Organic Chemistry at High Pressures and Temperatures. We have experimentally determined a phase diagram which documents the phases and reaction regimes of cyanuric acid , H{sub 3}C{sub 3}N{sub 3}O{sub 3} (1,3,5-triazine-2,4,6-trione), from 300 - 750 K and 0 - 8.1 GPa. We utilized a comparatively new technique to study thin samples of cyanuric acid in the diamond anvil cell in order to collect ambient temperature, high pressure FTIR and Raman data as well as the high-pressure, high-temperature data used in the phase diagram. These experiments made use of the CMLS High-pressure lab's diamond anvil facilities as well as the FTIR and Raman systems

A multi-proxy reconstruction of environmental change in the vicinity of the North Bay outlet of pro-glacial Lake Algonquin

This is the author accepted manuscriptWe present a multi-proxy study of environmental conditions during and after the recessional phases of pro-glacial Lake Algonquin in the vicinity of the North Bay outlet, Great Lakes Basin. Data presented comes from a new sedimentary profile obtained from the Balsam Creek kettle lake c. 34km north-east of the city of North Bay. This site lay close to the northeast margin of the maximum extent of the post-Algonquin lake sequence, which drained through the Ottawa-Mattawa valley system. Our data are presented against a Bayesian age-depth model, supporting and extending regional understanding of vegetation succession in this part of north-east Ontario. The core profile provides a minimum age for the formation of the glacial outwash delta in which the kettle is set, as well as a tentative timing for the Payette (post-Algonquin) lake phase. We highlight two discrete intervals during the Early Holocene, with modelled mean ages of: 8475-8040 cal. BP (332-316cm) and 7645 cal. BP (286cm), when climatic aridity affected the growth of vegetation within the kettle vicinity. Association with volcanic activity is posited. Cryptotephra dating to 7660-7430 cal. BP (mean age: 7580 cal. BP) is chronologically and geochemically assigned to the Mazama climactic eruption, while an earlier ash accumulation 8710-7865 cal. BP is tentatively sourced to an unknown eruption also in the Cascades region of Oregon. Outside of these periods, the Balsam Creek sequence shows considerable habitat stability and a character akin to that seen at more southerly latitudes. On this evidence we propose that access to reliable resources within kettle features could have aided the initial colonisation of northern Ontario’s environmentally dynamic early post-glacial landscape

Synthesis of Alkaline Earth Diazenides MAEN2 (MAE = Ca, Sr, Ba) by Controlled Thermal Decomposition of Azides under High Pressure

The alkaline earth diazenides MAEN2 with MAE = Ca, Sr and Ba were synthesized by a novel synthetic approach, namely, a controlled decomposition of the corresponding azides in a multianvil press at highpressure/ high-temperature conditions. The crystal structure of hitherto unknown calcium diazenide (space group I4/mmm (no. 139), a = 3.5747(6) Å, c = 5.9844(9) Å, Z = 2, wRp = 0.078) was solved and refined on the basis of powder X-ray diffraction data as well as that of SrN2 and BaN2. Accordingly, CaN2 is isotypic with SrN2 (space group I4/mmm (no. 139), a = 3.8054(2) Å, c = 6.8961(4) Å, Z = 2, wRp = 0.057) and the corresponding alkaline earth acetylenides (MAEC2) crystallizing in a tetragonally distorted NaCl structure type. In accordance with literature data, BaN2 adopts a more distorted structure in space group C2/c (no. 15) with a = 7.1608(4) Å, b = 4.3776(3) Å, c = 7.2188(4) Å, β = 104.9679(33)°, Z = 4 and wRp = 0.049). The N−N bond lengths of 1.202(4) Å in CaN2 (SrN2 1.239(4) Å, BaN2 1.23(2) Å) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N2]2−. Temperature-dependent in situ powder X-ray diffractometry of the three alkaline earth diazenides resulted in formation of the corresponding subnitrides MAE2N (MAE = Ca, Sr, Ba) at higher temperatures. FTIR spectroscopy revealed a band at about 1380 cm−1 assigned to the N−N stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides

A reference time scale for Site U1385 (Shackleton Site) on the SW Iberian Margin

Weproduced a composite depth scale and chronology for Site U1385 on the SWIberianMargin. Using log(Ca/Ti)measured by core scanning XRF at 1-cm resolution in all holes, a composite section was constructed to166.5 meter composite depth (mcd) that corrects for stretching and squeezing in each core. Oxygen isotopesof benthic foraminifera were correlated to a stacked d18O reference signal (LR04) to produce an oxygen isotopestratigraphy and age model.Variations in sediment color contain very strong precession signals at Site U1385, and the amplitude modulationof these cycles provides a powerful tool for developing an orbitally-tuned agemodel.We tuned the U1385 recordby correlating peaks in L* to the local summer insolation maxima at 37°N. The benthic d18O record of Site U1385,when placed on the tuned agemodel, generally agrees with other time scaleswithin their respective chronologicuncertainties.The age model is transferred to down-core data to produce a continuous time series of log(Ca/Ti) that reflectrelative changes of biogenic carbonate and detrital sediment. Biogenic carbonate increases during interglacialand interstadial climate states and decreases during glacial and stadial periods. Much of the variance in thelog(Ca/Ti) is explained by a linear combination of orbital frequencies (precession, tilt and eccentricity), whereasthe residual signal reflects suborbital climate variability. The strong correlation between suborbital log(Ca/Ti)variability and Greenland temperature over the last glacial cycle at Site U1385 suggests that this signal can beused as a proxy for millennial-scale climate variability over the past 1.5 Ma.Millennial climate variability, as expressed by log(Ca/Ti) at Site U1385, was a persistent feature of glacial climatesover the past 1.5Ma, including glacial periods of the early Pleistocene (‘41-kyrworld’)when boundary conditionsdiffered significantly from those of the late Pleistocene (‘100-kyr world’). Suborbital variability was suppressedduring interglacial stages and enhanced during glacial periods, especially when benthic d18O surpassed ~3.3–3.5‰. Each glacial inception was marked by appearance of strong millennial variability and each deglaciatio