Impacts of Subglacial Meltwater Discharge on Biological Production in the fjord

1. Key Points

• Subglacial meltwater discharge into fjords^※1 is known to enhance the proliferation of phytoplankton, resulting in rich fjords’ marine ecosystems. This process gives subglacial discharge an important role in fisheries and other ecosystems. However, global warming in recent years has led to the progressive retreat and disappearance of glaciers, raising concerns about their impact on ecosystems.

• We have developed a marine ecosystem model for the lower trophic level^※2 applied to a Greenlandic fjord. We successfully quantified the nutrient^※3 supply processes for primary production^※4 initiated by subglacial discharge during summer. The results showed that subglacial discharge plays a crucial role in primary production by stirring and mixing the entire fjord water system, transporting nutrients to the surface and enhancing primary production (figure).

• Sensitivity experiments to estimate the effects of variability in subglacial discharge and glacier recession due to global warming showed that conditions of increasing subglacial discharge led to increased primary production, while conditions of retreating glaciers and large discharge of suspended sediment led to significantly lower primary production.

• Developing the model used here and applying the results to other fjords should allow us to predict changes in biological production in fjords that affect the ecosystems of polar regions, which will lead to an assessment of the impact of global warming on marine ecosystems.

Fig: Schematic representation of the nutrient budget in the fjord during the summer.
All the numbers represent the difference between with and without subglacial meltwater discharge for 60-day model runs, and the numbers enclosed in the circles around “PHY bloom” indicate the primary productions of each nutrient source.

2. Overview

Project Researcher Yasuhiro Hoshiba of the Earth Surface System Research Center, Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, in collaboration with Assistant Professors Yoshimasa Matsumura and Naoya Kanna from the University of Tokyo, Project Researcher Yoshihiko Ohashi of the National Institute of Polar Research, and Professor Shin Sugiyama of Hokkaido University, used a newly developed lower-trophic level marine ecosystem model to successfully quantify the process by which subglacial meltwater discharge affects the primary production at the fjord surface. The researchers also conducted sensitivity experiments on the changes in subglacial discharge and glacier recession due to global warming. The results showed that extreme global warming could lead to an increased subglacial discharge in the fjord area, with biological production dramatically decreasing under conditions of significant glacial retreat.

Many glaciers worldwide are currently shrinking, and further changes are predicted to occur in the coming decades. The knowledge gained in the present study must to be used as a basis for the development of integrated research with continuous field observations and numerical modelling to deepen our understanding of the biogeochemical cycle between terrestrial and marine areas.

This research will be published in Scientific Reports on July 30 (Japan time). This study was supported by the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) (JP21K17875, JP22H05204, JP23H05411), as well as the Arctic Challenge for Sustainability Project and the Arctic Challenge for Sustainability II.