Periodic Reporting for period 2 - SHARP (Southern Ocean and Antarctic Climatic Phasing:Tephrochronological Correlation of Southern Ocean Marine Records and Antarctic Ice-cores)
Berichtszeitraum: 2018-09-01 bis 2019-08-31
This project aimed to address these challenges by ascertaining the rate, timing and phasing of Southern Hemisphere climatic changes between 40-10 kyr BP. Using tephrochronology to independently synchronise the palaeoclimatic sequences using common horizons of volcanic ash as time-synchronous tie-lines. Recognition of ash horizons not visible upon core inspection (cryptotephras) within sequences increasingly distal from volcanic regions has increased the scope of this technique. As such, a prime objective of this project was applying recently developed techniques and protocols for cryptotephra identification and assessment to several marine sequences from the South Atlantic sector of the Southern Ocean to build a framework of isochronous volcanic events present in these records. To achieve this high-resolution profiles of tephra shard concentration were gained and any identified deposits were robustly geochemically characterised. These physical characteristics were then be used to assess whether the deposits were deposited via primary airfall, and can be utilised as isochronous markers, or if secondary processes, which would affect their temporal integrity, were responsible for tephra delivery.
A combined assessment of the tephra shard concentration profiles and the geochemical analyses from deposits identified in two marine records (MD07-3076CQ and TN057-21) shows that the dominant mechanisms for tephra delivery to the region are secondary processes. This is shown by the wide spread of tephra in the sequences and the heterogeneous geochemical signature of deposits, indicative of the mixing of tephra shards from several eruptions. Secondary processes that could have been depositing tephra shards at the sites include iceberg or sea-ice rafting and bottom current reworking through the migration of currents or variations in their velocity. These processes cause ‘non-isochronous’, i.e. delayed, deposition of material and as such these deposits can not be used as time-synchronous markers to synchronise the marine records to the Antarctic ice-cores. Therefore, it has not been possible to address the research questions regarding providing better constraints on the rate, timing and phasing of past climatic and CO2 changes in the region. Work is ongoing to identify the primary drivers of the tephra deposition and assess the relationship between deposits in the two cores and assessing whether the processes driving tephra deposition were local-scale, i.e. site-specific, or regional-scale, i.e. oceanwide.
One potential tie-line was further investigated as in one core a more discrete peak in tephra shard concentration, more characteristic of primary deposition, was identified. Geochemical analysis of that tephra peak did display some homogeneity in composition, again potentially indicative of primary deposition. Ice-core samples with a similar timing were investigated to see if a correlation could be defined, however, these samples did not contain volcanic glass shards to allow an isochronous tie-line to be defined.
Results are currently being prepared for publication and dissemination.