Evolution Of The NW Indian Ocean Carlsberg Ridge And Response Of Global Change

The Mid-OceanRidge, as the plant boundary, is one of the important place to study the interaction of the earth system, with the exchanges of energy and material from the interior and surface of the earth. Some recent studies have proposed that the bathymetric fabric of the seafloor formed at mid-ocean ridges records rapid fluctuations in accordance with the astronomical orbital period (23,41, and 100 kyr). Glacial cycles redistribute water between oceans and continents, causing pressure changes in the upper mantle, with consequences for the melting of earth’s interior. Some studies have reported the seafloor abyssal hills could be studied for the past sea level changes as a paleoclimatic proxy. However, the relationship between the sea-level changes and the seafloor bathymetry is not clear perfectly. The published researches almost studied about the intermediate or fast-spreading ocean ridges, but rare study for slow-spreading ridges.The 1500 km-long Carlsberg Ridge, North West Indian Ocean, is a slow-spreading ridge, with the full spreading rate of 24.6-34.4 mm/a. Our samples, the multibeam bathymetry, are from the hydrothermal sulfide investigation voyage, DY125-33. This study chooses two sections (vertical the ocean ridge) in the construct stable area (66°E,3°N). With the magnetic chronology constraint, the study ofchronology of the two sections has these results and conclusions:1.The spectra of sections under magnetic chronology constrains show 500-300 kyr and 100 kyr cycles, which correspond to the 405 kyr and 100 kyr eccentricity cycles. As a result, this thesis thought that the expansion of the mid-ocean Ridge might be controlled by the eccentricity cycles.2. Using the Astrochronology theory, this study tunes the high-value of bathymetry to the low-value eccentricity by every 100 kyr cycles. The spectra of tuned sections show prominent 400 kyr and 100 kyr cycles, and the weak 54 kyr cycles. The 100 kyr cycle is remarkable in the 800 ka in according with the 100 kyr dominated Middle Pleistocene climate.3. The spreading rates of the two sections show faster in the mid-ocean rift valley and slower the two outer sides. And, the high resolution spreading rates have ～2.4 Myr and 405 kyr cycles. The same variation trends of the 400 kyr filters of bathymetry and spreading rates indicate the expansion of mid-ocean ridge in the both lateral (spreading rate) and vertical (bathymetry) at the same time.4. Compared with the eccentricity, the Carlsberg Ridge sections and the sea-level change, this thesis shows the anti-phase relation between the 100 kyr cycles of the Carlsberg Ridge sections and the sea-level change curve. When the period of the low eccentricity, the sea-level stayed minimal value and the mid-ocean ridge expanded rapidly. The low sea-level appeared at the glacial period and controlled by the eccentricity; at the meantime, the reduce of the sea-level could reduce the press of the mid-ocean ridge, promote the magma upwelling and accelerate the mid-ocean ridgeexpansion. So the mid-ocean ridge expansion also controlled by the astronomical cycles.5. In the glacial period, the mid-ocean ridge intensively expanded and released a large quantity of heat and carbon dioxide to cause negative feedback for the glacial climate and regulate climate.