Past warmer climate periods at the Antarctic margin detected from proxies and measurements of biogenic opal in the ABD-1B core: the XRF spectral silver (Ag) peak used as a new tool for biogenic opal quantification

• Main Authors: Kuhn, Gerhard, Helling, D., von Eynatten, H., Niessen, Frank, Magens, Diana
• Format: Conference Object
• Language: unknown
• Published: 2008
• Subjects: Antarc*; Antarctic; Ice Shelf; Ice Shelves; McMurdo Ice Shelf; Ross Ice Shelf
• Online Access: https://epic.awi.de/id/eprint/19860/; https://hdl.handle.net/10013/epic.32435

Quantification of biogenic opal in marine sediments is a time consuming job, but the results could indicate periods of higher bioproductivity and warmer conditions than today at the Antarctic margin. Within the international Antarctic Geological Drilling Program (ANDRILL), core AND-1B was drilled and recovered a 1285 m sequence from a flexural moat basin filled with glacimarine, terrigenous, volcanic and biogenic sediments below the McMurdo Ice Shelf. Our main goal is to study the variability and the stability of the Ross Ice Shelf from Miocene to Recent. The melting and collapse of large Antarctic ice shelves may cause a significant sea level rise because of accelerated inland ice glacier surges into the ocean. Biogenic opal content in sediments can be deduced indirectly from grain density measurements on single samples, or faster and more continuous by gamma ray attenuation measurements on the core, with subsequent wet bulk and grain density calculations. Spectral colour reflectance (b* value) measurements on the split core surface can also be a fast tool for opal content quantification. Of course, they all have disadvantages in comparison to direct measurement on samples using X-ray diffraction or geochemical leaching methods. Some major and minor chemical elements were measured directly on split core surfaces with a non- destructive X-Ray Fluorescence Core Scanner method (XRF-CS, Avaatech) in the field. Quantitative geochemical analyses like determination of total inorganic and organic carbon (TOC), biogenic opal as well as major and minor elements were done on core samples. We found a strong positive correlation between the counts per second of the XRF-CS Ag peak area and the biogenic opal content of the samples (r=0.81) not only in the AND-1B core but in others as well from the Antarctic margin. In literature, it is noted that diatoms could accumulate Ag in sediments, so at first we were pleased to find this Ag enrichment with our tool. But further geochemical analyses revealed that measuring these low Ag ...