Silver as a Novel Tracer for Late Quaternary Southern Ocean Biological and Geophysical Processes.

The global air-sea CO2 balance is set within the Southern Ocean through deep water formation, upwelling, and the biological pump. Diatoms dominate Southern Ocean primary productivity and export large amounts of Corg. However, past changes in Southern Ocean biological pump strength are presently not well understood because conventional proxies for export production can be biased by particle degradation. This dissertation explores Ag as a novel, potentially more robust proxy for diatom (paleo)productivity. The reliability of Ag and its delivery mechanism to sediments are investigated in Southern Ocean sediments and by laboratory studies on pure diatom cultures. To test whether sedimentary Ag enrichment occurs underlying oceanic regions of high diatom productivity, Ag and redox-sensitive trace metal fluxes were measured alongside conventional productivity proxy fluxes in Southern Ocean surface sediments. In the open ocean Pacific sector, increased Ag and productivity proxy fluxes coincide with the highly productive opal belt. Along the West Antarctic Peninsula continental margin, high regional surface productivity and nonlithogenic trace metal concentrations strongly suggest suboxic sediments maintained by seasonally elevated export production. Having demonstrated that Ag records diatom productivity patterns, Ag and redox-sensitive trace metals were measured in two South Atlantic cores to determine whether glacial-age deep waters contained greater CO2/lower O2 concentrations. Results reveal a shift in pore water chemistry from poorly oxygenated during the Last Glacial Maximum and deglaciation, to well oxygenated during the late Holocene. Sedimentary suboxia resulting from high Corg flux and lower bottom water O2 concentrations implies that glacial Lower Circumpolar Deep Water was more isolated and stored more CO2 compared to present day. Accurately interpreting Ag as a paleoproxy requires understanding how diatom debris delivers Ag to sediments. To probe this mechanism, diatoms were fed Ag in culture and subsequently analyzed in bulk and as single cells to determine Ag storage location. Results indicate that diatoms store Ag in organic matter with little to no Ag in frustules. Although biogenic particle degradation and Ag scavenging during particle water column transit likely affect the amount of Ag delivered to sediments, Ag shows considerable potential to serve as a reliable qualitative proxy for diatom (paleo)productivity.PHDEarth and Environmental SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102468/1/megwagn_1.pd

ADAMTS13: A New Link Between Thrombosis and Inflammation

von Willebrand factor (VWF) levels are elevated and a disintegrin-like and metalloprotease with thrombospondin type I repeats–13 (ADAMTS13) activity is decreased in both acute and chronic inflammation. We hypothesized that by cleaving hyperactive ultralarge VWF (ULVWF) multimers, ADAMTS13 down-regulates both thrombosis and inflammation. Using intravital microscopy, we show that ADAMTS13 deficiency results in increased leukocyte rolling on unstimulated veins and increased leukocyte adhesion in inflamed veins. Both processes were dependent on the presence of VWF. Depletion of platelets in $Adamts13^{−/−}$ mice reduced leukocyte rolling, suggesting that platelet interaction with ULVWF contributes to this process. Increased levels of endothelial P-selectin and plasma VWF in $Adamts13^{−/−}$ compared with wild-type (WT) mice indicated an elevated release of Weibel-Palade bodies. ULVWF multimers released upon stimulation with histamine, a secretagogue of Weibel-Palade bodies, slowed down leukocyte rolling in $Adamts13^{−/−}$ but not in WT mice. Furthermore, in inflammatory models, ADAMTS13 deficiency resulted in enhanced extravasation of neutrophils, and this process was also dependent on VWF. Our findings reveal an important role for ADAMTS13 in preventing excessive spontaneous Weibel-Palade body secretion, and in the regulation of leukocyte adhesion and extravasation during inflammation

North American /l/ both darkens and lightens depending on morphological constituency and segmental context

It is uncontroversial that, in many varieties of English, the realization of /l/ varies depending on whether /l/ occurs word-initially or word-finally. The nature of this effect, however, remains controversial. Previous analyses alternately analyzed the variation as darkening or lightening, and alternately found evidence that the variation involves a categorical distinction between allophones or a gradient scale conditioned by phonetic factors. We argue that these diverging conclusions are a result of the numerous factors influencing /l/ darkness and differences between studies in terms of which factors are considered. By controlling for a range of factors, our study demonstrates a pattern of variability that has not been shown in previous work. We find evidence of morpheme-final darkening and morpheme-initial lightening when compared to a baseline of morpheme-internal /l/. We also find segmental effects such that, in segmental contexts which independently darken /l/, one can observe /l/ lightening, and contexts which independently lighten /l/ can make lightening effects undetectable. Morphological and prosodic effects are hence sometimes trumped by segmental context. Once contextual effects are controlled for, there is evidence both for morphologically-conditioned /l/-darkening and for morphologically-conditioned /l/-lightening, both of which can be understood as a result of prosodic differences reflecting morphological junctures

Equatorial Pacific productivity changes near the Eocene-Oligocene boundary

There is general agreement that productivity in high latitudes increased in the late Eocene and remained high in the early Oligocene. Evidence for both increased and decreased productivity across the Eocene-Oligocene transition (EOT) in the tropics has been presented, usually based on only one paleoproductivity proxy and often in sites with incomplete recovery of the EOT itself. A complete record of the Eocene-Oligocene transition was obtained at three drill sites in the eastern equatorial Pacific Ocean (ODP Site 1218 and IODP Sites U1333 and U1334). Four paleoproductivity proxies that have been examined at these sites, together with carbon and oxygen isotope measurements on early Oligocene planktonic foraminifera, give evidence of ecologic and oceanographic change across this climatically important boundary. Export productivity dropped sharply in the basal Oligocene (~33.7�Ma) and only recovered several hundred thousand years later; however, overall paleoproductivity in the early Oligocene never reached the average levels found in the late Eocene and in more modern times. Changes in the isotopic gradients between deep- and shallow-living planktonic foraminifera suggest a gradual shoaling of the thermocline through the early Oligocene that, on average, affected accumulation rates of barite, benthic foraminifera, and opal, as well as diatom abundance near 33.5�Ma. An interval with abundant large diatoms beginning at 33.3�Ma suggests an intermediate thermocline depth, which was followed by further shoaling, a dominance of smaller diatoms, and an increase in average primary productivity as estimated from accumulation rates of benthic foraminifera

ADAMTS13: a new link between thrombosis and inflammation

von Willebrand factor (VWF) levels are elevated and a disintegrin-like and metalloprotease with thrombospondin type I repeats–13 (ADAMTS13) activity is decreased in both acute and chronic inflammation. We hypothesized that by cleaving hyperactive ultralarge VWF (ULVWF) multimers, ADAMTS13 down-regulates both thrombosis and inflammation. Using intravital microscopy, we show that ADAMTS13 deficiency results in increased leukocyte rolling on unstimulated veins and increased leukocyte adhesion in inflamed veins. Both processes were dependent on the presence of VWF. Depletion of platelets in Adamts13−/− mice reduced leukocyte rolling, suggesting that platelet interaction with ULVWF contributes to this process. Increased levels of endothelial P-selectin and plasma VWF in Adamts13−/− compared with wild-type (WT) mice indicated an elevated release of Weibel-Palade bodies. ULVWF multimers released upon stimulation with histamine, a secretagogue of Weibel-Palade bodies, slowed down leukocyte rolling in Adamts13−/− but not in WT mice. Furthermore, in inflammatory models, ADAMTS13 deficiency resulted in enhanced extravasation of neutrophils, and this process was also dependent on VWF. Our findings reveal an important role for ADAMTS13 in preventing excessive spontaneous Weibel-Palade body secretion, and in the regulation of leukocyte adhesion and extravasation during inflammation

Exploring the influence of ancient and historic megaherbivore extirpations on the global methane budget

Globally, large-bodied wild mammals are in peril. Because “megamammals” have a disproportionate influence on vegetation, trophic interactions, and ecosystem function, declining populations are of considerable conservation concern. However, this is not new; trophic downgrading occurred in the past, including the African rinderpest epizootic of the 1890s, the massive Great Plains bison kill-off in the 1860s, and the terminal Pleistocene extinction of megafauna. Examining the consequences of these earlier events yields insights into contemporary ecosystem function. Here, we focus on changes inmethane emissions, produced as a byproduct of enteric fermentation by herbivores. Although methane is ∼200 times less abundant than carbon dioxide in the atmosphere, the greater efficiency of methane in trapping radiation leads to a significant role in radiative forcing of climate. Using global datasets of late Quaternary mammals, domestic livestock, and human population from the United Nations as well as literature sources, we develop a series of allometric regressions relating mammal body mass to population density and CH4 production, which allows estimation of methane production by wild and domestic herbivores for each historic or ancient time period. We find the extirpation ofmegaherbivores reduced global enteric emissions between 2.2–69.6 Tg CH4 y−1 during the various time periods, representing a decrease of 0.8–34.8% of the overall inputs to tropospheric input. Our analyses suggest that large-bodied mammals have a greater influence on methane emissions than previously appreciated and, further, that changes in the source pool from herbivores can influence global biogeochemical cycles and, potentially, climate

High-resolution fMRI of content-sensitive subsequent memory responses in human medial temporal lobe

Abstract & The essential role of the medial temporal lobe (MTL) in long-term memory for individual events is well established, yet important questions remain regarding the mnemonic functions of the component structures that constitute the region. Within the hippocampus, recent functional neuroimaging findings suggest that formation of new memories depends on the dentate gyrus and the CA 3 field, whereas the contribution of the subiculum may be limited to retrieval. During encoding, it has been further hypothesized that structures within MTL cortex contribute to encoding in a content-sensitive manner, whereas hippocampal structures may contribute to encoding in a more domain-general manner. In the current experiment, highresolution fMRI techniques were utilized to assess novelty and subsequent memory effects in MTL subregions for two classes of stimuli-faces and scenes. During scanning, participants performed an incidental encoding (target detection) task with novel and repeated faces and scenes. Subsequent recognition memory was indexed for the novel stimuli encountered during scanning. Analyses revealed voxels sensitive to both novel faces and novel scenes in all MTL regions. However, similar percentages of voxels were sensitive to novel faces and scenes in perirhinal cortex, entorhinal cortex, and a combined region comprising the dentate gyrus, CA 2 , and CA 3 , whereas parahippocampal cortex, CA 1 , and subiculum demonstrated greater sensitivity to novel scene stimuli. Paralleling these findings, subsequent memory effects in perirhinal cortex were observed for both faces and scenes, with the magnitude of encoding activation being related to later memory strength, as indexed by a graded response tracking recognition confidence, whereas subsequent memory effects were scene-selective in parahippocampal cortex. Within the hippocampus, encoding activation in the subiculum correlated with subsequent memory for both stimulus classes, with the magnitude of encoding activation varying in a graded manner with later memory strength. Collectively, these findings suggest a gradient of content sensitivity from posterior (parahippocampal) to anterior (perirhinal) MTL cortex, with MTL cortical regions differentially contributing to successful encoding based on event content. In contrast to recent suggestions, the present data further indicate that the subiculum may contribute to successful encoding irrespective of event content. &amp