Master Thesis Defense by Hongli Wu

Title: From time fixing of foraminifera data towards NAO reconstruction over the last two millennia

The Green-Planning Project proposes the envisage of attempting to use the foraminifera data derived from Disco Bay in the West Greenland Region to reconstruct the NAO in the last two millennia. However, the foraminifera data from four different cores in this region all exhibit relatively low time resolution with significant time uncertainty, indicating they possess floating age models and can’t be directly utilized in NAO reconstruction. Hence, this thesis aims to try establishing fixed age models for these foraminifera data to enhance their reliability for further NAO reconstruction purposes. Considering that the foraminifera data with reliable time stamps is supposed to demonstrate notably similar variability as the Greenland temperature data at GISP2, three different methods (statistical correlation method, DTW method, manually moving method) are attempted in this thesis to fix the time of these foraminifera data through identifying new time stamps that make them best fit with the Greenland temperature data at GISP2.

The results indicate that all of these foraminifera data can be time-fixed through the statistical correlation method, and the time-fixed foraminifera data all show significantly higher correlations with temperature data at GISP2. However, the other two methods are only able to generate fixed age models for some of the cores and the time-fixed results produced by them are less accurate than the corresponding results from the statistical correlation method. Thus, the statistical correlation method is a relatively more appropriate method for time fixing. Moreover, though the foraminifera data with new time history is regarded as more reliable than the data with original time stamps, it still remains inevitable uncertainty due to the limitations in methodology and internal noise of the data, and may exhibit challenges when applied in NAO reconstruction. Future efforts should consider further improving the accuracy as well as the reliability of time fixing and conducting further researches to better assess the applicability of the time-fixed foraminifera data in NAO reconstruction.

Supervisor: Jens Hesselbjerg Christensen