Geochemical tools and paleoclimate clues : multi-molecular and isotopic investigations of tropical marine sediments and alpine ice

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2006South American climate has undergone dramatic changes since the last glacial period, as evidenced from Cariaco Basin (Venezuelan coast) and Peru Margin marine sediment biomarker records. Compounds derived from vascular plant leaf waxes and delivered to the marine sedimentary environment, including long-chain (C24-C32) nalkanoic acids, were used as proxies for terrestrial vegetation type, aridity, and atmospheric circulation. Marine biomarkers, such as sterols and phytol, were used to reconstruct productivity in the Peru Margin upwelling zone, where sedimentary conditions are not conducive to the preservation of foraminifera. Through the use of organic molecular isotopic techniques and multi-molecular stratigraphy, a great deal can be learned about communities of marine organisms and terrestrial plants that existed in the past and the environments in which they lived. Vascular plant leaf wax carbon and hydrogen isotopic records were generated from n-alkanoic acids preserved in Cariaco Basin marine sediments. These records were compared to previously established pollen and climate records and were found to parallel local millennial-scale climate changes between the late Glacial and Preboreal periods, which were characterized by migrations of the inter-tropical convergence zone. Differences in δD between C16-C18 and C24-C30 n-alkanoic acids suggest a marine source for the shorter chain lengths and a terrestrial source for the longer chains. Stacked δD and δ13C records both exhibited isotopic enrichment during the late Glacial and Younger Dryas periods and depletion during the Bølling-Allerød and Preboreal periods. If interpreted as an aridity proxy, the δD record is in agreement with Cariaco Basin sediment grey scale records, suggesting that the late Glacial and Younger Dryas were more arid than the Bølling-Allerød and Preboreal periods. n-Alkanoic acid δ13C, which is a proxy for C3 versus C4 plant type, indicates that C3 plants predominated in this area of the tropics during warm and wet periods, such as the Bølling-Allerød and the Holocene, and C4 plants proliferated during cooler and more arid periods, such as the Glacial and Younger Dryas. The biomarker δ13C record agrees with pollen data previously developed from Cariaco Basin sediments, confirming that leaf wax compounds preserved in marine sediments can accurately record terrestrial vegetation changes. Analytical methods utilizing stir bar sorptive extraction (SBSE) and thermal desorption were developed and applied to investigate lipid organic matter in a suite of alpine ice cores. These methods permit use of small volume (10-30 ml) samples, as would be required for high-resolution down-core analyses. SBSE involves using a polymer coated stir bar to extract organic matter from aqueous samples, after which it is loaded directly into a thermal desorption unit and the organic matter transferred in its entirety to a gas chromatograph inlet. To test these methods and the organic content of tropical ice, post-industrial samples from two South American, two Asian, and one African ice core were analyzed. Compounds identified in the modern ice core samples included natural and anthropogenic biomarkers such as n-alkanes, n-alkanoic acids, nalkyl amides and nitriles, polycyclic aromatic hydrocarbons (PAHs), and diterpenoids. Variability in the distributions of these compounds between different cores demonstrated that the lipid organic fraction in each core was representative of mostly local inputs. To further investigate natural inputs, several pre-industrial samples were analyzed from the Sajama ice core in the Andes and The Puruogangri core on the Tibetan Plateau. Inputs of terrestrial vegetation combustion biomarkers such as PAHs, diterpenoids, and alkyl amides were consistent with periods of enhanced aridity in each core. The results of this investigation demonstrate the utility of the methodology, which could now be applied to generate very high-resolution biomarker records from tropical ice cores. Gas chromatography/time-of-flight mass spectrometry (GC/TOF-MS) was used to generate a high-resolution, multi-molecular organic biomarker record from Peru Margin sediments (~11oS, 252 m water depth) for the last 15 ka. Because of their position beneath the oxygen minimum zone of a productive upwelling region, these sediments contain a wealth of compounds that can be exploited as paleoclimate indicators. TOF-MS and fast GC techniques allowed me to generate this record in a short amount of time and without employing the traditional suite of purification techniques. Before about 9 ka, organic carbon and biomarker concentration records exhibited similar variability, implying a forcing mechanism that affected input and/or preservation of both marine and terrestrial organic matter, such as large-scale climate change. Organic carbon and biomarker abundances then systematically increased throughout the Holocene and exhibited higher frequency variability, suggesting overall enhanced productivity from rapidly evolving planktonic communities. Similar patterns of variability between bacterial hopanol, sterol degradation product, and primary productivity biomarker records suggest that the productivity biomarkers are recording sea surface and water column processes, and are not significantly biased by sedimentary diagenesis. Low bound sulfur content in lipid extracts and a lack of observed sulfur-containing compounds argue against significant sulfurization and resultant biomarker sequestration in 1228D sediments. Factor analysis provided a statistical means of separating terrestrial and marine organic inputs, and reinforced the interpretations that very long chain n-alkanoic acids (C30-C32) are terrestrially derived and sterol compounds primarily represent marine algal inputs. In all, the biomarker records suggest millennial-scale changes in upwelling strength superimposed on longer-term trends, with additional variability in contributions from specific precursors, such as dinoflagellates. Terrestrial leaf wax compounds also exhibited high-amplitude, millennial-scale variability, but with a different pattern of change than the marine inputs. GC/TOF-MS was shown to be a useful tool for generating high-resolution records of the type necessary to understand the relationships between biomarkers in a complex and sensitive depositional environment such as the Peru Margin. Climate signals embedded in the Peru Margin biomarker records provided clues as to the productivity and upwelling histories of the Peru Margin, as well as regional terrestrial vegetation. Elevated concentrations of marine biomarkers suggest enhanced upwelling and productivity from about 6.5 ka to the present on the Peru Margin, with lower-amplitude millennial-scale variations occurring throughout this period. Enhanced dinosterol abundances after 6.5 ka are consistent with greater occurrences and/or strength of El Niño, while concurrently enhanced upwelling suggests a parallel increase in La Niña activity. Similar timing of mid to late Holocene variability between Peru Margin marine biomarker records, a faunal sea surface temperature record from the eastern tropical Atlantic, and Andean paleoclimate records suggests strong climate links between these regions of the tropics, likely driven by broad-scale changes in El Niño and the Southern Oscillation (ENSO) and trade wind strength. The C30 n-alkanoic acid, which is representative of vascular plant leaf wax inputs, exhibited millennial-scale variability superimposed on longer-term trends that may be related to aridity, assuming fluvial transport of terrestrial material. n-Alkanoic acid δ13C is generally enriched during periods of enhanced leaf wax abundance, consistent with increased inputs of C4 plant material at these times.Funding for this research was provided by a Schlanger Ocean Drilling Fellowship, which is part of the NSF-sponsored U.S. Science Support Program (USSSP). An NSF grant to TIE (OCE-0402533) provided additional funding for the research presented in Chapters 3-5. Funding for the Cariaco Basin isotopic analyses was provided by the Frank and Lisina Hoch Endowed Fund and the Woods Hole Oceanographic Institution Director’s General Discretionary Fund

High-sensitivity measurement of diverse vascular plant-derived biomarkers in high-altitude ice cores

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L13501, doi:10.1029/2009GL037643.Semi-volatile organic compounds derived from burned and fresh vascular plant sources and preserved in high-altitude ice fields were detected and identified through use of recently developed analytical tools. Specifically, stir bar sorptive extraction and thermal desorption coupled with gas chromatography/time-of-flight mass spectrometry allowed measurement of multiple biomarkers in small sample volumes (≤30 ml). Among other compounds of interest, several diterpenoids, which suggest inputs from conifers and conifer burning, were identified in post-industrial era and older Holocene ice from the Sajama site in the Bolivian Andes, but not in a glacial period sample, consistent with aridity changes. Differences in biomarker assemblages between sites support the use of these compounds as regionally constrained recorders of vegetation and climate change. This study represents the first application of these analytical techniques to ice core research and the first indication that records of vegetation fires may be reconstructed from diterpenoids in ice.This project was supported in part by NSF-OCE (0402533), and NSF-EAR (0094475)

Murine factor H co-produced in yeast with protein disulfide isomerase ameliorated C3 dysregulation in factor H-Deficient mice

Recombinant human factor H (hFH) has potential for treating diseases linked to aberrant complement regulation including C3 glomerulopathy (C3G) and dry age-related macular degeneration. Murine FH (mFH), produced in the same host, is useful for pre-clinical investigations in mouse models of disease. An abundance of FH in plasma suggests high doses, and hence microbial production, will be needed. Previously, Pichia pastoris produced useful but modest quantities of hFH. Herein, a similar strategy yielded miniscule quantities of mFH. Since FH has 40 disulfide bonds, we created a P. pastoris strain containing a methanol-inducible codon-modified gene for protein-disulfide isomerase (PDI) and transformed this with codon-modified DNA encoding mFH under the same promoter. What had been barely detectable yields of mFH became multiple 10s of mg/L. Our PDI-overexpressing strain also boosted hFH overproduction, by about tenfold. These enhancements exceeded PDI-related production gains reported for other proteins, all of which contain fewer disulfide-stabilized domains. We optimized fermentation conditions, purified recombinant mFH, enzymatically trimmed down its (non-human) N-glycans, characterised its functions in vitro and administered it to mice. In FH-knockout mice, our de-glycosylated recombinant mFH had a shorter half-life and induced more anti-mFH antibodies than mouse serum-derived, natively glycosylated, mFH. Even sequential daily injections of recombinant mFH failed to restore wild-type levels of FH and C3 in mouse plasma beyond 24 hours after the first injection. Nevertheless, mFH functionality appeared to persist in the glomerular basement membrane because C3-fragment deposition here, a hallmark of C3G, remained significantly reduced throughout and beyond the ten-day dosing regimen

An extended mini-complement factor H molecule ameliorates experimental C3 glomerulopathy.

Abnormal regulation of the complement alternative pathway is associated with C3 glomerulopathy. Complement factor H is the main plasma regulator of the alternative pathway and consists of 20 short consensus repeat (SCR) domains. Although recombinant full-length factor H represents a logical treatment for C3 glomerulopathy, its production has proved challenging. We and others have designed recombinant mini-factor H proteins in which ‘non-essential’ SCR domains have been removed. Here, we report the in vitro and in vivo effects of a mini-complement factor H protein, FH1–5^18–20, using the unique factor H–deficient (Cfh-/-) mouse model of C3 glomerulopathy. FH1–5^18–20 is comprised of the key complement regulatory domains (SCRs 1–5) linked to the surface recognition domains (SCRs 18–20). Intraperitoneal injection of FH1–5^18–20 in Cfh-/- mice reduced abnormal glomerular C3 deposition, similar to full-length factor H. Systemic effects on plasma alternative pathway control were comparatively modest, in association with a short half-life. Thus, FH1–5^18–20 is a potential therapeutic agent for C3 glomerulopathy and other renal conditions with alternative pathway-mediated tissue injury

South Atlantic intermediate water mass geometry for the last glacial maximum from foraminiferal Cd/Ca

Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 25 (2010): PA4101, doi:10.1029/2010PA001962.Paleoceanographic studies using benthic foraminiferal Cd as a nutrient tracer have provided a robust means of reconstructing glacial Atlantic Ocean water mass geometry, but a paucity of data from the South Atlantic above 1200 m has limited investigation of Antarctic Intermediate Water (AAIW) configuration and formation. A new Cd depth profile from Brazil margin sediments suggests that AAIW penetrated northward at 1100 m to at least 27°S in the glacial Atlantic. It exhibited substantially reduced δ13Cas values, confirming preliminary evidence that this AAIW was unique to the glacial Atlantic and that it formed differently than today, with less atmospheric contact