Work

Warming temperatures and prevalence of marine heatwaves in a temperate fjord

Year: 2025

Type: article

Abstract: Climate change is causing shifts to thermal regimes in coastal marine environments often expressed as alarming marine heat waves, however, such changes are not well understood or observed in fjord environments. Ongoing exposure to intensifying marine heatwaves is becoming increasingly likely and could cause significant and even catastrophic outcomes on the unusual and sensitive ecosystems that characterize fjords. Here we identify spatial and temporal changes in temperature and salinity in the surface waters (0.5-19 m) of a temperate fjord, Doubtful Sound, New Zealand, utilising high resolution data. Data was collected between 2005 and 2023 and recorded at 15-minute intervals at three sites, an outer-, mid- and inner-fjord site. Trends of increasing temperature anomalies, including two marine heatwave events were superimposed on seasonal and interannual temperature and salinity. We detect both increasing temperatures through time, from the surface to 19 m and a notable freshening of the near surface low salinity layer. Annual mean temperatures increased at a rate of 0.39 to 0.67°C per decade, with the deeper waters warming more than shallow waters. This is one of the first studies to document the temporal oceanic progression of a heatwave into a fjord, taking mere hours for the most intense temperatures to travel from the outermost site to the innermost site, about 30 km. The documented heatwaves in this temperate fjord caused increases of 2-3°C above mean summer temperatures throughout the rest of the time series. Marine heatwaves are emerging as a pervasive threat to marine communities hence the ecological implications of these findings are considered.

Source: Continental Shelf Research

DOI: 10.1016/j.csr.2025.105603

Authors: Claire T. Shellem, Karin R. Bryan, Conrad A. Pilditch, Chris D. Cornelisen, Joanne I. Ellis

Institutions: University of Waikato, University of Auckland, Cawthron Institute

Language: English

Topic: Oceanographic and Atmospheric Processes

Subfield: Oceanography

Field: Earth and Planetary Sciences

Domain: Physical Sciences

SDGs: Life below water, Climate action

Open Access status: hybrid

Estimated APC paid: $3,260