Observed multi-decadal trends in subsurface temperature adjacent to the East Australian Current

Abstract

Abstract. Sea surface temperature observations have shown that western boundary currents, such as the East Australian Current (EAC), are warming faster than the global average. However, we know little about coastal temperature trends inshore of these rapidly warming regions, particularly below the surface. In addition to this, warming rates are typically estimated linearly, making it difficult to know how these rates have changed over time. Here we use long-term in situ temperature observations through the water column at five coastal sites between approximately 27.3–42.6° S to estimate warming trends between the ocean surface and the bottom. Using an advanced trend detection method, we find accelerating warming trends at multiple depths in the EAC extension region at 34.1 and 42.6° S. We see accelerating trends at the surface and bottom at 34.1° S, but similar trends at 3 depths in the top 50 m at 42.6° S. We compare several methods, estimate uncertainty, and place our results in the context of previously reported trends, highlighting that magnitudes are depth-dependent, vary across latitude, and are sensitive to the data time period chosen. The spatial and temporal variability in the long-term temperature trends highlight the important role of regional dynamics against a background of broad-scale ocean warming. Moreover, considering that recent studies of ocean warming typically focus on surface data only, our results show the necessity of subsurface data for the improved understanding of regional climate change impacts.

Exploring multi-decadal time series of temperature extremes in Australian coastal waters

“…Little is known about marine extremes in Australian coastal waters, particularly below the surface. Here we introduce a multi-decadal observational record of extreme ocean temperature events starting in the 1940s and 1950s between the surface and the bottom (50-100 m) at four long-term coastal sites around Australia: the Australian Multi-Decadal Ocean Time Series EXTreme (AMDOT-EXT) data products (https://doi.org/10.26198/wbc7-8h24, Hemming et al, 2024). The data products include indices indicating the timing of extreme warm and cold temperature events, their intensity and the corresponding temperature time series and climatology thresholds.…”