Assimilation von ð13C-Daten aus marinen Sedimentbohrkernen in das LSG zur Rekonstruktion der Ozeanzirkulation während des letzten glazialen Maximums

• Main Author: Winguth, A.
• Format: Doctoral or Postdoctoral Thesis
• Language: German
• Published: University of Hamburg 1997
• Subjects: Antarctic; Pacific; Antarc*; NADW; North Atlantic Deep Water; North Atlantic
• Online Access: http://hdl.handle.net/21.11116/0000-0009-E30C-A; http://hdl.handle.net/21.11116/0000-0009-E50A-A

Measurements of stable carbon isotope ratios (ôttC) from foraminiferal shells indicate that during the last glacial maximum (LGM) the Atlantic thermohaline circulation was significantly different from the present day circulation. It has been suggested that during the LGM the flow of North Atlantic Deep Water (NADW) ** reduced, while the com- pensating Antarctic Bottom Water (AABW) penetrated further northward. Assimilation of ô13C data by using the adjoint technique into a global ocean general circulation model (OGCM) can evaluate an optimal circulation patterns providing consistency between the dynamics of the model and the analysis of the ô13C data. In this study assimilation experiments with the Hamburg large scale geostrophic model (LSG) are examined to investigate the extent to which ô13C as a paleotracer constrains the simulation of the North Atlantic circulation during the LGM. The prescribed wind stress and 2 m air temperatures \ryere taken from the ice age ïesponse of an atmospheric general circulation model (AGCM). The first guess LGM salinity anomalies were calculated from salinity reconstructions adapted from stable oxygen isotope ratios (ô18O) in foraminiferal shells. The optimized model state was obtained by varying the salinities of the sea surface. This simulated glacial circulation is closer to the observed ô13C distribution than flow pattern of previous OGCMs of comparable resolution. The results of the assimilation experiments confirm that during the LGM the production of NADW was substantially reduced. An increased salinity difference between the tropical Atlantic and Pacific supports earlier suggestions of a higher water vapor transfer from the Atlantic to the Pacific. The glacial changes in the circulation indicate also an increased outflow from the Mediterranea¡r Sea as a consequence of increased surface salinities in this area. However, the optimized model simulation is only partially consistent with error estimates from the observations and large deviations still exist. Sensitivity ...