No description available.

Graduate

No description available.

The factors controlling primary production in the Southern Ocean were investigated over two years during two cruises of the South African National Antarctic Program (SANAP). The first cruise was conducted to the region of the eastern Atlantic sector of the Southern Ocean during the collaborative Scandinavian/South African Antarctic expedition conducted in austral summer (DecemberIFebruary) 1997-1998. Production studies were conducted in the vicinity of the Marginal Ice Zone (MIZ), Interfrontal Zone (IFZ) and Antarctic Polar Front(APF). The second cruise was conducted during the Third Marion Island Oceanographic Survey (MIOS III) to the region of the Sub-Antarctic Prince Edward Islands in austral autumn (April/May) 1998. Size-fractionated production rates were estimated by 14C incorporation using standard JGOFS protocols. Oceanographic data from the first cruise suggest that the three regions can be divided into two distinct regimes. Stations occupied in the vicinity of the MIZ and the APF were characterised by a shallow mixed layer depth « 40m) while at the IFZ-stations, the mixed layer depth exceeded the 1% light depth. Microphytoplankton dominated integrated chlorophyll-a biomass in the MIZ (total chlorophyll a ranged between 15.4 and 41.3 mg Chi-a. m-2) and at the APF (range between 10.7 and 31.4 mg Chi-a. m-2) , comprising > 50% of total chlorophyll-a at all these stations. Xl Within the IFZ (2 stations), nanophytoplankton dominated total integrated Chl-a biomass (range between 5.6 and 8.8 mg Chi-a. m-2) comprising, on average, 36% of the total. Picophytoplankton comprised an average of 12% of the total Chl-a biomass (range between 3.1 and 5.9 mg Chi-a. m-2) in the MIZ, 36% in the IFZ (range between 6.4 and 7.8 mg Chl-a . m-2) and 20% in the vicinity of the APF (range between 6.8 and 10.6 mg Chi-a. m-2). Total integrated primary production ranged between 316 and 729 mg C . m-2. d-1 at stations occupied in the vicinity of the MIZ, and between 292 and 317 mg C . m·2• d-l within the IFZ. At stations occupied in the region of the APF, total integrated production ranged between 708 and 926 mg C . m-2• dol. The contribution of various size fractions to total productivity generally displayed the same pattern as integrated Chl-a biomass. Microphytoplankton formed the most important contributor to total production at stations occupied in the MIZ and at the APF. Within the IFZ, nanophytoplankton dominated total daily production. Nutrient data suggest that concentrations of macro nutrients within the upper water column were above the threshold where growth would be limited. Preliminary results showed that concentrations of iron (Fe) were highest in the southern region of the MIZ and in the vicinity of the APF. During the second cruise, conducted in the vicinity of the Sub-Antarctic Front (SAF) and in the upstream, inter-island and downstream regions of the Prince Edward Islands, there was evidence of fresh water run-off from the islands, (i.e. decreased salinities and increased concentrations of ammonia and nitrate). Oceanographic data collected at the various production stations indicated that the upper water column was well mixed throughout the survey. Total integrated biomass during the study ranged between 8.5 and 20.1 mg Chi-a. m-2• No distinct patterns in total Chl-a biomass were evident. Picophytoplankton dominated total biomass comprising> 45 % of total pigment at all stations. Nanophytoplankton were the second most important contributor to total integrated biomass. Generally xu microphytoplankton contributed < 10 % of total ChI-a. Total daily integrated production was highest (442.6 mg Chi-a. m-2) at the single station occupied in the vicinity of the SAF. Outside this region, total areal production was lower, ranging from 94.5 to 353.0 mg C . m-2. d-1. With the exception of the station occupied in the vicinity of the SAF, total productivity was dominated by nanophytoplankton, which comprised between 48 and 66% of the total. Concentrations of macronutrients did not appear to be limiting to phytoplankton growth. The absence of a phytoplankton bloom in the vicinity of the islands appears to have been related to water column stability, which was influenced by the prevailing oceanographic regime during the survey. Previous studies have shown that when the SAF lies in close proximity to the islands, advecting forces prevail, resulting in the islands functioning as a flow-through system. During this study, the SAF lay immediately north of the islands. As a consequence no water was trapped in the leeward side of the islands. The results of the two cruises suggest that phytoplankton production in the four systems investigated: the Marginal Ice Zone (MIZ), Antarctic Polar Front (APF), Inter Frontal Zone (IFZ) and Prince Edward Islands (PEl), was largely controlled by water column stability. It is probable that the availability of iron, particularly in the region of the MIZ and APF, may have further contributed to the elevated production recorded in these two regions.

No description available.

Tropical cyclones in the Atlantic basin often undergo a process called extratropical transition (ET) and transform from warm-core to cold-core systems while retaining strong winds, heavy rainfall, and large ocean waves. Infrared satellite imagery from channels 2 and 4 of the Geostationary Operational Environmental Satellite (GOES) were used to examine key structural changes, synoptic interactions, and loss of deep centered convection in order to determine onset and completion of ET. The primary indicator for ET onset in 75% of cases was found to be a persistent increase in storm asymmetry along with the appearance of warm frontogenesis in its northern region. Cold frontogenesis in the southern portion of the storm was the secondary indicator for declaring onset of ET. Completion of ET was marked by the loss of centered deep convection for all cases. The average ET transition time was 18 hours for 60% of the cases.

No description available.

No description available.

Thesis advisor: Mark D. Behn / The global mid ocean ridge system is segmented by transform faults and non-transform discontinuities. Oceanic transform faults display distinct morphology characterized by a deep valley and shallow transverse ridges on either side of the valley. Although the morphology of oceanic transform faults is known to first order, there is no consensus on the processes that form the transform valley and/or the adjacent transverse ridges. To date, most models of transform morphology attribute these features to either transform-normal extension or to shear stresses induced by slip along the fault. In this thesis, I compile bathymetric data along 16 major transform faults on the Mid-Atlantic Ridge and identify the key morphological properties of each transform. Specifically, I estimate transform valley width, depth, and total relief measured from the valley floor to the adjacent transverse ridges. The strongest correlation is between the relief and maximum depth, but there is a weaker correlation between maximum depth and valley width. These morphologic properties are then compared to key fault parameters such as slip rate, fault-normal compression/extension rate, thermal area, and the seismic coupling ratio, which is defined as the fraction of total fault slip that occurs seismically. These comparisons are used to test models that describe mechanisms of the formation of the transform valley. The strongest correlation is between the fault thermal area and valley half width. This suggests that the width of the transform valley may be controlled by the shear stress applied to the fault as it slips. By contrast, the data are not consistent with a model in which the valley is created by extension across the fault, because our data show that the maximum transform valley depth increases with compression and not extension. / Thesis (MS) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

[The first purpose of this work is to present a literary history of the Atlantic Monthly between 1909 and 1929. The second is to observe the decline of the genteel tradition in American intellectual life. In 1909 Ellery Sedgwick began his twenty-eight year editorship of the magazine and gradually but thoroughly remade its editorial policy, emphasizing current affairs and supplementing belles-lettres with less formal narratives of personal experience. Sedgwick's literary tastes were relatively conservative and those of his readers, who included vieilles filles of both sexes, more so. But the magazine continued to attract serious writers. During Sedgwick's first decade he published fiction and essays by Edith Wharton, J.J. Chapman, Owen Wister, H.L. Mencken, Agnes Repplier, Gamaliel Bradford, John Galsworthy, Laurence Binyon, F.L. Lucas, John Buchan, Edward Garnett, Havelock Ellis, John Masefield, H.G. Wells and Bertrand Russell. The traditional English literary influence remained strong.]