Low-latitude western north atlantic climate variability during the past millennium : insights from proxies and models

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 September 2009Estimates of natural climate variability during the past millennium provide a frame of reference in which to assess the significance of recent changes. This thesis investigates new methods of reconstructing low-latitude sea surface temperature (SST) and hydrography, and combines these methods with traditional techniques to improve the present understanding of western North Atlantic climate variability. A new strontium/calcium (Sr/Ca) - SST calibration is derived for Atlantic Montastrea corals. This calibration shows that Montastrea Sr/Ca is a promising SST proxy if the effect of coral growth is considered. Further analyses of coral growth using Computed Axial Tomography (CAT) imaging indicate growth in Siderastrea corals varies inversely with SST on interannual timescales. A 440-year reconstruction of low-latitude western North Atlantic SST based on this relationship suggests the largest cooling of the last few centuries occurred from ~1650-1730 A.D., and was ~1ºC cooler than today. Sporadic multidecadal variability in this record is inconsistent with evidence for a persistent 65-80 year North Atlantic SST oscillation. Volcanic and anthropogenic radiative forcing are identified as important sources of externally-forced SST variability, with the latter accounting for most of the 20th century warming trend. An 1800-year reconstruction of SST and hydrography near the Gulf Stream also suggests SSTs remained within about 1ºC of modern values. This cooling is small relative to other regional proxy records and may reflect the influence of internal oceanic and atmospheric circulation. Simulations with an atmospheric general circulation model (AGCM) indicate that the magnitude of cooling estimated by proxy records is consistent with tropical hydrologic proxy records.Funding for this research was provided by a National Science Foundation Graduate Student Fellowship, National Science Foundation grants OCE-0402728, OCE-0623364, ATM-033746, the WHOI Ocean and Climate Change Institute, the WHOI Ocean Ventures Fund, the WHOI Ocean Life Institute, the MIT Student Assistance Fund, award number USA-0002, made by King Abdullah University of Science and Technology (KAUST), and the Inter-American Institute for Global Change Research

The John Brewer Reef floating hotel : a case-study in marine environmental monitoring : proceedings of a GBRMPA workshop reviewing the environmental monitoring program, held in Townsville, Australia in December 1989

Although the John Brewer Reef Floating Hotel remained in operation for only one year from March 1988, its construction and installation triggered a major environmental assessment and monitoring program which was innovative in many ways. First, the hotel was the first of its kind in the world so the potential impacts were largely unknown and, second, there was increasing community pressure for comprehensive assessments of environmental impacts given the high conservation value placed on the Great Barrier Reef Marine Park - a World Heritage Area. As a result, the environmental impact assessment and monitoring procedure which was implemented was probably the most complex that had been attempted for a project of that scale in Australia and proved, in many ways, to be a pilot for studies within the Great Barrier Reef Marine Park since then. The program involved many individuals and several institutions working in areas such as oceanography, water quality, biological monitoring and social impact studies, with the program coordinated by the Centre for Coastal Management at the University of New England - Northern Rivers (then known as the Northern Rivers College of Advanced Education) on behalf of the proponent

DNA nanotweezers studied with a coarse-grained model of DNA

We introduce a coarse-grained rigid nucleotide model of DNA that reproduces the basic thermodynamics of short strands: duplex hybridization, single-stranded stacking and hairpin formation, and also captures the essential structural properties of DNA: the helical pitch, persistence length and torsional stiffness of double-stranded molecules, as well as the comparative flexibility of unstacked single strands. We apply the model to calculate the detailed free-energy landscape of one full cycle of DNA 'tweezers', a simple machine driven by hybridization and strand displacement.Comment: 4 pages, 5 figure

Natural history of the Hogan Group - 2. Some marine algae from Hogan Island, Bass Strait, with an account of the marine zonation

The marine zonation of Hogan Island was studied as part of the McCoy Society expedition early in 1968. The composition of the supra-littoral zone is similar to that in Tasmania and Wilson's Promontory while the composition of the littoral zone and the sublittoral fringe has greater resemblance to South Australian coasts. A list of the algae collected is appended

Effect of shear force on the separation of double stranded DNA

Using the Langevin Dynamics simulation, we have studied the effects of the shear force on the rupture of short double stranded DNA at different temperatures. We show that the rupture force increases linearly with the chain length and approaches to the asymptotic value in accordance with the experiment. The qualitative nature of these curves almost remains same for different temperatures but with a shift in the force. We observe three different regimes in the extension of covalent bonds (back bone) under the shear force.Comment: 4 pages, 4 figure

Interaction of Tet Repressor with Operator DNA and with Tetracycline Studied by Infrared and Raman Spectroscopy

AbstractTet repressor (TetR) is involved in the most abundant mechanism of tetracycline (Tc) resistance of Gram-negative bacteria. Raman spectra were measured for the class D TetR protein, for an oligodeoxyribonucleotide with sequence corresponding to operator site O1, and for the TetR:oligonucleotide complex. TetR forms a complex with [Ni-Tc]+, which does not bind to operator DNA. Raman and infrared measurements indicate nearly identical conformations of TetR with and without [Ni-Tc]+. Differences between the experimental spectrum of the TetR:operator DNA complex and the computed sum of the component spectra provide direct spectroscopic evidence for changes in DNA backbone torsions and base stacking, rearrangement of protein backbone, and specific contacts between TetR residues and DNA bases. Complex formation is connected with intensity decrease at 1376cm−1 (participation of thymine methyl groups), intensity increase at 1467cm−1 (hydrogen bond formation at guanine N7), decreased intensity ratio I854/I823 (increased hydrophobicity of tyrosine environment), increased intensity at 1363cm−1 (increased hydrophobicity of tryptophan ring environment), differences in the range 670–833cm−1 (changes in B-DNA backbone torsions and base stacking), and decreased intensity of the amide I band (structural rearrangement of TetR backbone consistent with a reduction of the distance between the two binding helices)

A physico-chemical survey of inland lakes and saline ponds: Christmas Island (Kiritimati) and Washington (Teraina) Islands, Republic of Kiribati

The equatorial Pacific Ocean atoll islands of Kiritimati and Teraina encompass great physical, chemical and biological variability within extreme lacustrine environments. Surveys of lake chemistry and sediments revealed both intra- and inter-island variability. A survey of more than 100 lakes on Kiritimati found salinities from nearly fresh to 150 ppt with the highest values occurring within the isolated, inland portions of the island away from the influence of groundwater or extreme tides. Dissolved oxygen (DO) and pH values also showed considerable variability with a less regular spatial pattern, but were both generally inversely related to salinity. Series of lakes, progressively more isolated from marine communication, present a modern analog to the chemical and morphologic evolution of presently isolated basins. Sediments on both islands consist of interbedded red and green silt, possibly degraded bacterial mat, overlying white, mineralogenic silt precipitate. Variability may be indicative of shifts in climatological parameters such as the El Niño Southern Oscillation (ENSO) or the Pacific Intertropical Convergence Zone (ITCZ)

Logging activities in mangrove forests: A case study of Douala Cameroon

The Cameroon mangroves are exploited by local communities through fishing, hunting, and especially logging for fuel-wood and charcoal. The changing demographic patterns in the region have increased the need of citizens in the urban centres, which in turn, has accelerated the pressure on the neighbouring forests. The objective of these studies was to assess the impact of local communities on the mangroves’ development. Through an eight point semi-structured questionnaire, 120 mangrove loggers were interviewed in the local markets in Douala. The survey data show that 61% of respondents are permanent workers and do not envisage quitting this mode of employment. The surface area destroyed annually approximates 1000 ha. Species of the genus Rhizophora are mostly exploited, with about 200,000 trees cut down per year. The declared revenues are about 400,000 Euros per year. Further analysis of information from different sources suggests that the total annual income could amount to four millions euros. These estimates show that the mangroves have a significant economic value and require significant improvement in modes of exploitation to include strategies for sustainable management.Key words: Anthropogenic impact, deforestation, Douala-Cameroon, economic value, loggers, mangroves,  Rhizophora