Carbonate chemistry of the North Pacific Ocean

Graduation date: 1986This thesis covers a wide area of the North Pacific Ocean, latitudinally from 10° to 55°N and longitudinally from Japan to the U.S. coast. With two longitudinal cruises as the main data sources and selected literature data sets as supplementary data source, the distribution of physical and chemical properties in the North Pacific Ocean is presented. AOU, pH, total CO₂, and nutrients (nitrate and phosphate) are interrelated parameters. Along our two longitudinal sections they all show a core structure underlying the salinity minimum layer. From these oxidation related parameters we obtain a conclusion that the subsurface water of the eastern North Pacific Ocean is older than that of the western North Pacific Ocean. Alkalinity,\ud calcium, and silicate show a monotonically increasing trend with depth to the deepest sampling depth. The alkalinity data can be used as a water mass tracer. Different water masses which show their own mixing trends can be identified when the correlation of normalinzed alkalinity with temperature is scrutinized. The vertical distribution of the normalized alkalinity shows a maximum core at a depth of about 2500 m in the .North Pacific Ocean. Not only the calcium carbonate dissolution but also the circulation in the deep and bottom layer plays a role in\ud this normalized alkalinity maximum core. Our analysis of carbonate data shows that about 257. of the increase in total inorganic CO₂ of deep water, after leaving from the Southern Ocean to the North Pacific, is contributed by inorganic CaCO₃ dissolution. There is no significant difference of inorganic carbon/organic carbon ratio between our two sections. However, it was found that the eastern section has a higher total TCO₂ input than that of the western section.\ud The degree of saturation with respect to calcite and aragonite was calculated from all the available data sets. Mr. Ahmed Rushdi and Professor R.M. Pytkowicz are working on the effect of Mg on the formation and the properties of magnesian calcites. There are metastable forms of these compounds which may have been interpreted as stable ones in solubility determinations. Some revision of degree of saturation may be called for in the future. Four selected cross-sections, three longitudinal and one latitudinal, show that a large volume of the North\ud Pacific is undersaturated with respect to CaCO₃. The saturation horizon generally shows a shoaling from the west to the east and from the south to the north in the North Pacific Ocean. It was found that lysocline falls on a depth much deeper (about 2500 m deeper) than the saturation horizon of calcite and several hundred meters shallower than the CCD (calcium carbonate compensation depth) depth. Our results support the kinetic point of view on the CaCO₃\ud dissolution mechanisms. The direct approach on the fossil fuel increase signal in seawater is adopted in this thesis. A new set of preformed equations of alkalinity and total CO₂ was obtained from a more updated GEOSECS data. Our results show that the penetration depth of fossil fuel CO₂ is strongly related to the surface oceanographic circulation. The shallowest\ud penetration depth is less than 300 m found in the eastern equatorial region where the upwelling prevails and the deepest penetration depth is deeper than 2000 m off Japan where an interaction of Oyashio and Kuroshio currents is found