Bacterial dynamics on the surface of the Greenland Ice Sheet

Abstract

Bacteria play a key role in carbon cycling within every ecosystem on Earth and, despite the extremes in temperature, desiccation, irradiance and UV radiation, the surface (supraglacial) of ice sheets are no exception. Within the supraglacial environment of the Greenland Ice Sheet (GrIS), the surface ice represents one of the most expansive yet under-investigated habitats. This thesis aimed to assess heterotrophic bacterial community dynamics and interactions with glacier algal blooms within the surface ice environment of the GrIS. Three major investigations were employed to achieve this aim, addressing: i) in situ spatio-temporal patterning in bacterial abundance and production relative to glacier algal bloom progression, across different supraglacial habitats, and throughout an entire ablation season; ii) the nature of interactions between supraglacial bacterial, glacier algal, and dominant fungal communities within surface ice; and iii) the roles and relative importance of photo- and bio-degradation on the composition and quantity of dissolved organic matter in surface ice and the consequences for bacterial abundance and production. Data demonstrated that heterotrophic consumption of dissolved organic matter (DOM) produced by blooms of highly pigmented glacier algae within the surface ice stimulated bacterial production (BP) which ranged between 0.03 – 0.6 mg C L-1 h-1. However, BP was ~ 30 times lower than primary production highlighting that only a small proportion of algal-derived DOM was consumed by the in situ heterotrophic community, resulting in net organic carbon accumulation within the surface ice. Bacterial communities degraded a range of DOM substrates and consumption was not influenced by the photodegradation of surface ice DOM. Interactions were observed between dominant members of the surface ice community (i.e. glacier algae, bacteria and fungi) and bacterial growth was enhanced in the presence of glacier algae and fungi. However, nutrient limitation was found to change the nature of interactions between major functional groups within the surface ice. This data significantly advances knowledge on bacterial dynamics in the surface ice habitat and thus helps to constrain carbon flows through the supraglacial environment.

Date of Award	29 Sep 2020
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Martyn Tranter (Supervisor), Christopher J Williamson (Supervisor), Alexandre Anesio (Supervisor) & Marian Yallop (Supervisor)