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

[摘要] Deep coastal inlets are sites of high sedimentation and organic carbondeposition that account for 11 % of the world's organic carbon burial.Australasia's mid- to high-latitude regions have many such systems. It isimportant to understand the role of climate forcings in influencing hypoxiaand 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 t of organic carbonloading per annum. Monthly dissolved oxygen, total Kjeldahl nitrogen,dissolved organic carbon, and dissolved inorganic nitrogen concentrationswere significantly affected by rainfall patterns. Increased rainfall wascorrelated to higher organic carbon and nitrogen loading, lower oxygenconcentrations in deep basins, and greater oxygen concentrations in surfacewaters. Most notably, the Southern Annular Mode (SAM) significantlyinfluenced oxygen distribution in the system. High river flow (associatedwith low SAM index values) impedes deep water renewal as the primarymechanism driving basin water hypoxia. Climate forecasting predictsincreased winter rainfall and decreased summer rainfall, which may furtherexacerbate hypoxia in this system. Currently, Macquarie Harbour's basins experience frequent (up to 36 % ofthe time) and prolonged (up to 2 years) oxygen-poor conditions that maypromote greenhouse gas (CH 4 , N 2 O) production altering theprocessing of organic matter entering the system. The increased winterrainfall predicted for the area will likely promote the increased spread andduration of hypoxia in the basins. Further understanding of these systemsand how they respond to climate change will improve our estimates of futureorganic matter cycling (burial vs. export).

[学科分类] 大气科学