07 Feb 2022
07 Feb 2022
Status: a revised version of this preprint is currently under review for the journal BG.

The influence of mesoscale climate drivers on hypoxia in a fjord-like deep coastal inlet and its potential implications regarding climate change and greenhouse gas production: examining a decade of water quality data

Johnathan Daniel Maxey1,2, Neil David Hartstein2, Aazani Mujahid3, and Moritz Müller1 Johnathan Daniel Maxey et al.
  • 1Faculty of Engineering, Computing and Science, Swinburne University of Technology, Kuching 93350, Malaysia
  • 2ADS Environmental Services, Kota Kinabalu, Sabah, 88400, Malaysia
  • 3Faculty of Resource Science & Technology, University Malaysia Sarawak, Kota Samarahan 94300, Sarawak, Malaysia

Abstract. Deep coastal inlets are sites of high sedimentation and organic carbon deposition that account for 11 % of the world's organic carbon burial. Australasia's mid to high latitude regions have many such systems. It is important to understand the role of climate forcings in influencing hypoxia and organic matter cycling in these systems, but many such systems, especially in Australasia, remain poorly described.

We analysed a decade of in-situ water quality data from Macquarie Harbour, Tasmania, a deep coastal inlet with more than 180,000 tons of organic carbon loading per annum. Monthly dissolved oxygen, total Kjeldhal nitrogen, dissolved organic carbon, and dissolved inorganic nitrogen concentrations were significantly affected by rainfall patterns. Increased rainfall was correlated to higher organic carbon and nitrogen loading, lower oxygen concentrations in deep basins, and greater oxygen concentrations in surface waters. Most notably, the Southern Annular Mode (SAM) significantly influenced oxygen distribution in the system. High river flow (associated with low SAM index values) impedes deep water renewal as the primary mechanism driving basin water hypoxia. Climate forecasting predicted increased winter rainfall and decreased summer rainfall, which may further exacerbate hypoxia in this system.

Currently, the Harbour basins experience frequent (up to 36 % of the time) and prolonged (up to 2 years) oxygen-poor conditions with the potential to promote greenhouse gas (CH4, N2O) production. Increased greenhouse gas production will alter the processing of organic matter entering the system. The increased winter rainfall predicted for the area will potentially increase greenhouse gas emissions due to increased spread and duration of hypoxia in the basins. Further understanding of these systems and how they respond to climate change will improve our estimates of future organic matter cycling (burial vs export) and greenhouse gas production.

Johnathan Daniel Maxey et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-20', Anonymous Referee #1, 21 Feb 2022
    • AC1: 'Reply on RC1', johnathan maxey, 01 Mar 2022
      • RC2: 'Reply on AC1', Anonymous Referee #1, 01 Mar 2022
        • AC3: 'Reply on RC2', johnathan maxey, 04 Apr 2022
  • RC3: 'Comment on bg-2022-20', Anonymous Referee #2, 11 Mar 2022

Johnathan Daniel Maxey et al.

Johnathan Daniel Maxey et al.


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Short summary
Deep Coastal Inlets are important sites for regulating land based organic pollution before it enters coastal oceans. This study focused on how large climate forces, rainfall, and river flow impact organic loading and oxygen conditions in a deep coastal inlet in Tasmania. Increases in rainfall were linked higher organic loading and lower oxygen in basin waters. Finally we observed a potential link between climate change and the conditions promoting greenhouse gas release from these systems.