Variability in circulation and exchange in a sub-Antarctic island fjord.

Funding Bodies: NERC, Polar and Seaview Ltd.

Affiliations: University of Southampton, National Oceanography Centre (NOC), British Antarctic Survey (BAS), SAERI

PhD Project Overview

The overall aim of this PhD project is to investigate the drivers of variability in fjord water circulation, and the biological and physical consequences in a changing climate, using Cumberland Bay, South Georgia as a case study. Cumberland Bay is chosen as a study area for two main reasons. Firstly, the glaciers that terminate at the head of each arm have shown markedly different rates of retreat over the past century, aiding a strong comparative study of ocean forcing on glacier dynamics. Secondly, Cumberland Bay is an important spawning area for commercially fished mackerel icefish, which have seen significant reduction in annual catch in recent years. A high-resolution numerical model is developed using the Nucleus for European Modelling of the Ocean (NEMO) framework, and important forcing factors contributing to the circulation regime and the transport of heat to the glacier termini, such as winds and freshwater runoff, are assessed. An Individual Based Model (IBM) will then be used with the modelled flow fields to examine variability in retention of mackerel icefish larvae in the bay.

Project Objectives

The first objective is to use a combination of observations and numerical modelling to elucidate the ocean circulation in Cumberland Bay and to determine the dominating physical drivers of variability;
The second objective is to investigate how the circulation regime couples with associated glacier dynamics, the drivers of variability is glacier behaviour and expected responses in a changing climate;
The third objective is to investigate how the circulation regime impacts biological activity in and around Cumberland Bay, specifically the recruitment and retention of fish larvae and krill.

Highlights 2020- 2021

Completion of first year progression review (July 2020)
Organised, hosted and chaired first virtual BAS student symposium Oct 2020
Presented at the Challenger Society Ocean Modelling Conference (Sep 2020)
Winner of Best Student Poster Presentation at the Antarctic Science Conference (April 2021)
Joined BAS Net-Zero Communications and Awareness group as the student/early career researcher representative (April 2021)
Successfully implemented baseline Cumberland Bay model with NEMO4.0.6 on ARCHER2 (super-computer)

Joanna Zanker

Dates: October 2019 - April 2023

Bio
Jo has a BSc in Mathematics from the University of Surrey and an MSc in Pure Mathematics from the University of Manchester. In 2019 she completed an MSc (by research) in Polar and Alpine Change from the University of Sheffield where she used mathematical techniques to study the shape of tidewater glaciers in Greenland. She is interested in using her strong mathematical background to study ice-ocean interactions and the drivers of glacial retreat, and to further understand potential impacts on local ecosystems in a changing climate.

Highlights July 2021 to June 2022

Attended the Fluid Dynamics and Sustainability in the Environment summer school at Cambridge University (Sep ’21).
Second placement in the Falkland Islands, hosted at SAERI (Nov -Dec ‘21).
Second cruise to South Georgia on the Pharos SG to complete oceanographic surveys interrupted by the pandemic. A successful 3-week cruise was completed with Conductivity Temperature Depth (CTD) measurements taken in Cumberland Bay and in several other fjords on the northeast coast (Nov ’21) (see photos of CTD instrument and Pharos SG and crew in South Georgia).
Passed 2^nd year PhD confirmation review (Dec ‘21).
Delivered an oral presentation at the European Geosciences Union conference (May ’22).
Successfully implemented a new subglacial discharge parameterization improving the representation of this physical process in the model of Cumberland Bay.
Successfully ran tests of an Individual Based Model (IBM) that uses the Cumberland Bay model flow fields to track pathways of mackerel icefish larvae.

Highlights July 2022 to June 2023

Gave two oral presentations on the model development and initial results at the Challenger/Ocean modelling conference, London, UK, September 2022.
Submitted first paper from the PhD titled ‘Oceanographic Variability in Cumberland Bay, South Georgia and implications for glacier retreat’ to the Journal of Geophysical Research - Oceans.
Presented a poster on modelling mackerel icefish larval retention in Cumberland Bay at the Effects of Climate Change on the World’s Ocean conference in Bergen, Norway, April 2023.
Gave an oral presentation on the results of the submitted paper at the European Geosciences Union conference in Vienna, Austria, April 2023.
Submitted final PhD thesis June 2023. (Successfully defended thesis September 2023 earning my doctorate.)

Key findings

The new fjord circulation model of Cumberland Bay highlights the potential for the presence of a shallow inner sill to have contributed to the rapid retreat of Neumayer Glacier in Cumberland West Bay.
The Individual Based Model for tracking mackerel icefish larvae finds oceanographic variability can be significant in controlling the retention of larvae hatched in Cumberland Bay, which underpins their ability to survive and recruit to adult stock.

Variability in circulation and exchange in a sub-Antarctic island fjord.

Joanna Zanker

SAERI

COMPANY

OTHER

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