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The abundance and distribution of biogenic, terrigenous and volcanic particles in the Panama Basin are markedly dependent on bottom topography and dissolution of calcite in the deeper parts of the basin. Of the coarse fraction (>62μ), foraminiferal tests and acidic volcanic glass shards are concentrated on the Cocos and Carnegie Ridges as lag deposits. Foraminiferal fragments are found on these ridge flanks and on the Malpelo Ridge due to reworking by bottom currents accentuated by dissolution of calcite with increasing depth. The finest calcite, probably coccoliths with fine foraminiferal fragments, together with the hydrodynamically light radiolarian skeletons are concentrated by bottom currents in the basin adjacent to the ridges. The foraminiferal calcite compensation depth in the basin is 3400 m. This relatively shallow depth probably reflects the high surface water productivity over the basin, although the pattern of productivity is not reflected in the pattern of biogenic sediments. Acidic volcanic glass appears to have been carried into the basin from Costa Rica, Colombia and Ecuador by easterly winds at altitudes of 1500 to 6000 m. Basaltic shards from the Galapagos Islands have been dispersed only over short distances to the west. Terrigenous sand-sized material is found on the edge of the continental shelf, where associated glauconite points to a relict origin, and along the northern Cocos Ridge, where contour currents may act as the dispersal mechanism. / Graduation date: 1973

In order to quantitatively examine the crustal structure of the Panama Basin without the benefit of local seismic refraction data, the following assumptions were made: (1) No significant lateral changes in density take place below a depth of 50 km. (2) The densities of the crustal layers are those of a 50-km standard section derived by averaging the results of 11 seismic refraction stations located in normal oceanic crust 10 to 40 million years (m. y. ) in age. (3) The density of the upper mantle is constant to a depth of SO km. (4) The thickness of the oceanic layer is normal in that region of the basin undergoing active spreading, exclusive of aseismic ridges. (5) The thickness of the transition layer is 1. 1 kin everywhere in the basin. Subject to these assumptions, the following conclusions are drawn from the available gravity, bathymetry, and sediment-thickness data: (1) Structurally, the aseismic ridges are surprisingly similar, characterized by a blocky, horst-like profile, an average depth of less than 2 km, an average depth to the Mohorovicic discontinuity of 17 km, and an average free-air anomaly of greater than +20 mgal. The fact that their associated free-air anomalies increase from near zero at their seaward ends to greater than +40 mgal at their landward ends suggests that the Cocos and Carnegie ridges are uplifted at their landward ends by lithospheric bending. (2) The centers of sea-floor spreading and fracture zones are characterized by a shoaling of the bottom and an apparent deepening of the Mohorovicic discontinuity. The only exception to this generalization is the northern end of the Panama fracture zone between the Cocos and Coiba ridges. (3) The Panama fracture zone and the fracture zone at 85°20'W longitude divide the Panama Basin into three provinces of different crustal thickness. Between these two fracture zones the crustal thickness is normal; west of 85°20W longitude it is greater than normal; and east of the Panama fracture zone it is less than normal. (4) In that part of the Panama Basin east of the Panama fracture zone there is a major discontinuity at 3°N latitude between a smooth, isostatically compensated crust to the south and an extremely rugged, uplifted crust to the north. An explanation for this discontinuity is the effect of the inflection in the shape of the continental margin at 3°N latitude on the eastward subductiori of the Nazca plate. / Graduation date: 1974

Holocene bulk sediment and component accumulation rates were measured in twenty-eight piston and gravity cores taken from the floor of the western Panama Basin and on the surrounding ridges. Radiocarbon ages and oxygen isotope curves provided Holocene age control in nine cores. Time datums in nineteen other cores were inferred by correlation of calcium carbonate curves to the dated cores. Dry bulk densities were measured in ten cores and were estimated in the others by an empirical relationship between dry bulk density and the percentages of sand, clay, and calcium carbonate. Other studies of the textural, mineralogical and sand fraction composition of near surface sediments in these cores provided analyses which could be used to obtain accumulation rates for these components. A general similarity between the map pattern of surface productivity and the patterns of carbonate and opal accumulation rates suggests a first order control of biogenic sedimentation by fertility of surface waters. Accumulation rates of terrigenous components are highest near the continents; the map and depth patterns suggest dispersal by currents shallower than 2000 m or by winds. It is inferred from textural component accumulation rate patterns that no significant regional redistribution of sediment by winnowing occurred during the Holocene. Deposition from deep thermohaline circulation probably increased the accumulation rates of silt, clay, and opaline components in the gaps between the western and eastern troughs. Calcium carbonate accumulation rates at equal depths are generally lower within 250 km of the edge of the continental shelf. Below 2000 m in high productivity regions > 250 km from the shelf calcium carbonate accumulation rates decrease linearly with depth according to a gradient of -3.3 gm CaCO₃/cm²/1000 yrs/ km. From this gradient, two independent estimates of the lysocline in this region, and a model of calcium carbonate accumulation, the average Holocene rate of supply of calcite from the surface is calculated to be 5-10 gm/cm²/1000 yrs. / Graduation date: 1976

The Cocos Gap is a deeper portion, or saddle, of the Cocos Ridge and forms part of the western boundary of the Panama Basing It is probably typical of saddles within most submarine ridges, In order to determine the mechanisms controlling sediment dispersal, the nature and sources of the sediments at 23 core locations were defined by hydrodynamic size separation (> 63, 2- 63, <2 micron) and microscopic or X-ray diffraction analysis of the individual fractions. In addition, calcium carbonate, organic carbon, opal and quartz determinations were made for the total sediment. The silt sized fraction was resolved into eight textural modes, The coarse modes reflect the progressive breakage and winnowing of the corase fraction (foraminifera) under the influence of bottom currents and gravity. Above 2000 m mechanical breakdown, winnowing and relocation by bottom currents mask the effects of depth related dissolution of the carbonate fraction, Intermediate modes in general represent a transitional facies with both biogenic and terrigenous influences, while the finest modes characterize a distal regime of clay deposition, The clay fraction is amorphous material with very low percentages of well crystallized clays. Three main sources and transport paths were recognized, including one associated with the circulation of the Panama Basin. Sedimentation within the Gap is controlled by local processes, predominantly the interaction between tidally induced intensification of bottom water flow and directional (thermohaline) flow. The steep' ness of the sea floor slope is a major factor controlling the efficiency of winnowing of the sediment away from certain higher elevations (biogenic source areas) to the sheltered parts and flanks of the ridge. Superimposed upon this sediment dispersal is the influx of terrigenous material carried by directional bottom currents that operate as postulated upper and lower contour currents along the flanks of the ridge. The crest of the Cocos Gap acts as a catchment area for the biogenic components, while the adjacent more sloping region, the sub-plateau, acts as a source area. The extreme breakage of the foraminifera is most likely a function of the tidally induced intensification of the bottom water flow, characteristic of many shallow ridges, and is probably most significant in the subplateau. Hydrographic data indicates that there is no significant transport of bottom water across the Cocos Gap into the Panama Basin, but downslope transport of carbonate and siliceous fragments and minerals from the Gap into the basin is associated with cyclical tidal bottom water flow. / Graduation date: 1976

Age-model derived sediment mass accumulation rates (MARs) are consistently higher than 230Th-normalized MARs in the Equatorial Pacific Ocean during the past 25 ka. The offset, being highest in the Panama Basin, suggests sediment redistribution in this region is prominent. I test the hypothesis that downslope transport of sediments from topographically highs that surround the Panama Basin is the cause of higher-than-expected xs230Th inventories in the deeper parts of the basin. There is little difference in xs230Th inventories between the highest and lowest reaches of the basin suggesting that the topographic highs did not serve as a source of xs230Th. A spatial analysis suggests that there may be an enhanced scavenging of xs230Th closest to the equator in productive waters. To examine whether lateral mixing of productive equatorial waters with adjacent waters delivers xs230Th to the Panama Basin, I measured dissolved 230Th in eight deep-water casts within the Guatemala, Panama, and Peru Basins along a meridional transect at ~86°W. Below 1000 m, the Panama Basin shows the highest deficit (~50%) of 230Th in deep waters assuming a reversible exchange of 230Th between dissolved and sinking particulate matter. Peru Basin waters have a larger range of dissolved 230Th concentrations (7.9-16.5 fg/kg) than that within Panama Basin waters (5.7-7.1 fg/kg). There is a progressive decrease, suggesting advection, in average dissolved deep-water (>1000 m) 230Th concentrations from the southernmost sites in the Peru Basin toward the Panama Basin. My calculations suggest that advected 230Th is between 15-30% of the total 230Th being produced within waters of the Panama Basin itself. In the Panama Basin, the averaged biogenic barium and opal MARs suggest that productivity was greater during the Holocene (0-13000 years) than that during the last glacial (13000-25000 years) suggesting higher productivity during the Holocene. Uauth, however, is higher in sediments deposited during the last glacial than in those deposited during the Holocene, suggesting that low bottom water oxygen contents rather than respiration of organic matter drives Uauth enrichment. This oxygen depletion during the last glacial suggests that bottom waters were enriched in respired carbon, which, in turn, could be a driver of lower glacial atmosphere pCO2 values.

Two-thirds of submarine volcanism in the Earth's ocean basins is manifested along mid-ocean ridges and the remaining one-third is revealed along intraoceanic arcs and seamounts. Hydrothermal systems and the circulation patterns associated with these volcanic settings remove heat from the solid Earth into the deep ocean. Hydrothermal circulation continues to remove and redistribute heat in the crust as it ages. The heat and mass fluxes added to the deep ocean influence mixing in the abyssal ocean thereby affecting global thermohaline circulation. In addition to removing heat, hydrothermal processes extract chemical components from the oceanic and carry it to the surface of the ocean floor, while also removing certain elements from seawater. The resulting geochemical cycling has ramifications on the localized mineral deposits and also the biota that utilize these chemical fluxes as nutrients. In this dissertation, I analyze observed conductive heat flow measurements in the Panama Basin and borehole thermal measurements in Brothers Volcano and use mathematical models to estimate advective heat and mass fluxes, and crustal permeability. In the first manuscript, I use a well-mixed aquifer model to explain the heat transport in a sediment pond in the inactive part of the Ecuador Fracture Zone. This model yields mass fluxes and permeabilities similar to estimates at young upper oceanic crust suggesting vigorous convection beneath the sediment layer. In the second manuscript, I analyze the conductive heat flow measurements made in oceanic between 1.5 and 5.7 Ma on the southern flank of the Costa Rica Rift. These data show a mean conductive heat deficit of 70%, and this deficit is explained by various hydrothermal advective transport mechanisms, including outcrop to outcrop circulation, transport through faults, and redistribution of heat by flow of hydrothermal fluids in the basement. In the third manuscript, I analyze the borehole temperature logs for two sites representative of recharge and discharge areas of hydrothermal systems in the Brothers Volcano. I develop upflow and downflow models for fluids in the borehole and formation resulting in estimated of flow rates and permeabilities. All three independent research works are connected by the common thread of utilizing relatively simple mathematical concepts to get new insights into hydrothermal processes in oceanic crust. / PHD / Two-thirds of underwater volcanic activity in the Earth’s ocean basins is exhibited in areas where new material for Earth’s outer shell is created and the remaining one-third is displayed along areas where the outer shell is destroyed. In these areas, hot springs that are under water and their water movement patterns remove heat from the solid outer shell and puts it into the deepest parts of the ocean. Hot water circulation continues to remove and redistribute heat and various chemical elements in the shell as it grows old. This heat and chemical elements, which get added to the deep ocean water, influences the way water mixes and forms layers in the world oceans. This also affects the movement of ocean currents. The chemical elements removed from the shell by hot water gets deposited as minerals on the ocean floor in places where hot springs arise. This variety of minerals provides nutrients for different marine organisms. In this work done during my PhD studies, I examine the heat and temperature that was measured in the Panama Basin and Brothers Volcano. I utilize these examinations to build simple math models to find out how much heat and chemical components are being added to the deep ocean water. I also find out the methods in which the hot water springs appear on the ocean floor and the patterns in which the hot water circulates in the Earth’s outer shell. All of these estimates will help the scientists who are studying the patterns and changes in ocean currents by giving them a number on how much heat is released from the inside of the Earth.