Beryllium isotopes across Antarctica’s continental shelf: can they be used as a proxy for ice shelf environment, meltwater discharge, or upwelling?

Abstract

In recent times, changes in 10Be concentration or the 10Be/9Be ratio have been analysed from marine sediments to assess the presence or absence of ice shelves around Antarctica. But the sources of 10Be supplying the continental shelf sediments around Antarctica aren’t yet fully resolved. So, in this work, I investigate the distribution of Be-isotopes (10Be, 9Be, and the 10Be/9Be ratio) at three different scales: the sediment chemistry scale; the spatial scale, and the temporal scale. In doing so, I have been able to resolve the sources of 10Be around Antarctica, and its utility as a proxy for ice shelf presence or absence. By investigating each scale, I have shown that 10Be is a poor proxy for ice shelf presence or absence. Rather, improved resolution of the sources of 10Be in the Antarctic marine realm suggests that it is oceanic flux, opposed to meltwater or atmospheric flux, that best defines the distribution of 10Be around the continental shelf. 10Be as an ice shelf proxy relies on the idea that most 10Be in sediment is sourced from vertical deposition of 10Be from the atmosphere, the influence of currents and flux from oceanic sources creates intermediate signatures across the inflow and outflow environments of ice shelf cavities, making it hard to tease apart open marine from sub-ice shelf settings. Though, it may still aid interpretation in a multiproxy approach. While there is limited utility in the application of 10Be to ice shelves, I did find that 10Be/9Be ratio tracks the flow paths of upwelling circumpolar deep water (CDW). This is significant because most of the heat flux causing the basal melting of ice shelves is supplied by CDW. Thus, the ability to better track modern and past pathways using 10Be provides the opportunity to improve the ice ocean models. If those patterns can be related to ice shelf stability, then they offer the prospect of better predictions of the impact of ice shelf collapses in the future. Because 10Be/9Be ratio tracks the pathways of CDW derivatives, I was able to reconstruct a history of warm deep water (WDW) upwelling on the East Antarctic Peninsula continental shelf and its presence within different ice shelf cavities through the Holocene. I found that there was a southward migration of WDW interacting with the different East Antarctic Peninsula ice shelves. The crucial finding, however, is that there is an unprecedented increase the 10Be/9Be ratio within the Larsen C cavity, despite previous Holocene phases of grounding line retreat, which initiated only ~ 200 years ago, indicating a limited period of WDW influence at the Larsen C grounding line until then. Further north on the Peninsula, WDW has been influencing ice shelf systems for as long as 8000 years. Thus, and if ocean temperatures or fluxes increase into the Larsen C cavity, the future stability of Larsen C is in question.

Date of Award	2024
Original language	English
Supervisor	Duanne WHITE (Supervisor), Simon FOSTER (Supervisor), Tona SANCHEZ-PALACIOS (Supervisor) & Stephen SARRE (Supervisor)