Reconstruction of the water mass circulation patterns in the Labrador Sea based on radiogenic isotopes and alkenone composition from the present day up to the Late Quaternary (35 kyrs)

• Main Author: Filippova, Alexandra
• Format: Thesis
• Language: English
• Published: 2016
• Subjects: Labrador Sea; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/35354/; https://oceanrep.geomar.de/id/eprint/35354/1/Filippova_%20Thesis.pdf

The Labrador Sea plays a crucial role in influencing the strength of the Atlantic Meridional Overturning Circulation (AMOC), as it is one of the main deep water formation sites. Numerous studies have been carried out in the Labrador Sea, covering different aspects and time scales. This thesis presents an investigation of the complex processes that prevail in the Labrador Sea covering surface, intermediate and deep waters using a combination of organic (alkenone paleothermometry) and inorganic (radiogenic isotopes) geochemical proxies. Over the past decades it has been debated, whether or not the alkenone unsaturation ratio can reliably be used as a paleo sea surface temperature proxy, especially in cold environments. Many studies have been published presenting contradicting results. In Chapter 4 an investigation of the proxy reliability was carried out based on available and newly obtained data from the western North Atlantic region. The results show that if certain conditions are met, such as appropriate age control of sediment samples, sufficient distance from the main ocean frontal systems characterized by high SST gradients, low risk of allochthonous input, alkenone-derived temperatures can be reliably used even in the cold regions of the North Atlantic. These results were applied to reconstruct sea surface temperatures in the Labrador Sea over the last 35 kyrs based on alkenone unsaturation ratio of marine sediment samples from four cores (Chapter 5). The motivation of this study was to reconstruct the variability of sea surface conditions in the area and correlate it to presence or absence of cold/warm surface water currents. The sediment cores used in this study were recovered from around the Labrador Sea following the flow path of the main alongshore currents. Prior to 10 ka the record was only partially preserved and indicated significantly cold temperatures and negative ????37???? values, suggesting that these data are unreliable. However, alkenone unsaturation ratios provided reliable sea surface ...