INVESTIGATING THE ATLANTIC MERIDIONAL OVERTURNING CIRCULATION VARIABILITY IN THE ICELAND BASIN OVER THE HOLOCENE: A MULTI-PROXY APPROACH
Seminars
Semester 2
The Atlantic Meridional Overturning Circulation (AMOC) is a fundamental component of the global climate system, responsible for regulating the exchange of heat, carbon, and nutrients between the surface and deep ocean across latitudes. It is composed of three components: surface circulation, deep circulation, and deep water formation. Understanding the AMOC mechanisms and their variability is essential for predicting future climate behaviour. In this thesis, we reconstruct the past variations of the AMOC’s three components within the Iceland Basin, a critical region of the AMOC pathway. Using a multi-proxy approach that includes benthic and planktonic foraminifera assemblages, stable isotopic measurements (δ¹³C and δ¹⁸O), and transfer function reconstructions, we examine surface circulation, deep water formation, and deep circulation during the Holocene. Our findings highlight the dynamic role of the Subpolar Gyre (SPG) in influencing surface circulation in the Iceland Basin from the Mid to the Late Holocene. A strong SPG is marked by increased cold-water planktonic species, lower sea surface temperatures (SSTs), and lighter δ¹⁸O values of N. incompta, reflecting enhanced inflow of cold Labrador Sea water and potential vertical mixing in the upper layers. Interestingly, during notable Late Holocene climatic events, the Iceland Basin exhibited contrasting temperature trends than the rest of the Atlantic Ocean. To reconstruct deep circulation, we analysed benthic foraminiferal assemblages and the stable isotopic compositions of H. elegans and C. wuellerstorfi. Variations in the Iceland-Scotland Overflow Water (ISOW), a major component of the North Atlantic Deep Water (NADW), were identified. ISOW strength intensified during the early to mid-Holocene, supporting a more vigorous AMOC. This was followed by a gradual weakening after 6,500 years BP as Denmark Strait Overflow Water (DSOW) strengthened. Lastly, we tested a novel method of paleo-density reconstruction using planktonic foraminiferal abundances, δ¹⁸O, and transfer function calculations. Results confirmed vertical mixing impacting the subsurface in the Iceland Basin during the early to mid-Holocene. This thesis provides new insights into the past variability of the AMOC’s surface circulation, deep circulation, and deep water formation in the Iceland Basin.
Additional information: Mr. Mériadec Alain Guy LE PABIC, u3007783@connect.hku.hk