Bottom water production at the Antarctic Peninsula, ODP Site 1101

• Main Author: Condon, Donna
• Other Authors: Ohneiser, Christian
• Format: Thesis
• Language: English
• Published: University of Otago 2020
• Subjects: New Zealand; Antarctic; Antarctic Peninsula; The Antarctic; Antarc*; Antarctica; Ice Shelf; Iceberg*; Sea ice
• Online Access: http://hdl.handle.net/10523/10486

During the Pleistocene period Antarctica underwent cyclic variations in ice volume known as glacial and interglacial stages. Bottom water production is intricately linked to changes in ice volume, climate, and particularly wind. However, high resolution reconstructions of bottom water generation or export from Antarctica are lacking. This project aims to build the first high resolution record of changes in bottom water production and identify the relationship with changing ice volume for the Pleistocene period (between ~0.7 Ma and 2 Ma) from a sedimentary succession; ODP Site 1101. Site 1101 from Leg 178 of the International Ocean Discovery Program is located on the western side of the Antarctic Peninsula, a 218 m core drilled into a sediment drift at the base of the continental shelf. Due to its lower latitude, this area of Antarctica is particularly sensitive to changes in climate. Fast flowing glaciers along the peninsula terminate in the ocean providing a plentiful supply of sediment to the site. This provides perfect conditions for a high-resolution multifaceted study to be conducted on changing currents, iceberg rafted debris episodes and ocean productivity. Eighty-five m of sediment (48 – 133 mbsf) spanning between ~0.7 Ma and 2 Ma were measured at centimetre intervals using an Avaatech XRF core scanner for a range of elements which were used to determine the terrigenous vs carbonate content within the sediment. These clearly identify glacial and interglacial cycles which are correlated to the Marine Isotope Stages (MIS) identified in the LR04 δ18O stack. A further 430 discrete cubes were collected at ~10 cm intervals to determine the magnetic fabric (a proxy for ancient current strength) and also for paleomagnetic studies to construct a magnetostratigraphy and paleomagnetic age model. Three facies are identified in the ODP Site 1101 succession; 1) laminated facies; finely laminated silty clay representing glacials 2) massive foraminifera bearing facies; massive greenish grey silty clay with white foraminifera representing warm interglacials and 3) massive facies; massive brown silty clay representing transitions between glacials and interglacials. During interglacials Ca is high indicating high ocean productivity. Magnetic susceptibility and Ti are low indicating less terrigenous input from ice rafted debris (IRD) and magnetic fabric is weak which is interpreted as weakened or non-existent bottom current. During glacial periods Ca is supressed and MS and Ti are elevated indicating high terrigenous sediment input with little to no ocean productivity. Magnetic fabrics are well developed which indicates deep circulation was strong. A comparison of glacial-interglacial cycles from ODP Site 1101 with the benthic LR04 δ18O stack indicates that not all Marine Isotope Stages are present as carbonate rich intervals at Site 1101. Absent interglacials are MIS 33, MIS 39, MIS 41 and MIS 59. The missing or cooler interglacials coincide with eccentricity nodes and low amplitude of insolation. It is possible that this orbital setting which produced successive long winters and mild summers enhanced sea-ice production and survival which may have acted as a protective buffer preventing ice shelf retreat.