Observed multi-decadal trends in subsurface temperature adjacent to the East Australian Current
Michael P. Hemming1,2,Moninya Roughan1,2,Neil Malan1,2,and Amandine Schaeffer1,3Michael P. Hemming et al.Michael P. Hemming1,2,Moninya Roughan1,2,Neil Malan1,2,and Amandine Schaeffer1,3
Received: 25 Nov 2022 – Discussion started: 13 Dec 2022
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.
Observed multi-decadal trends in subsurface temperature adjacent to the East Australian Current
This paper utilizes temperature measurements near the surface of ocean waters to determine whether a trend exists. The East Australian Current is on the western side of the South Pacific subtropical gyre. There have been hints that this current may be strengthening over time. These changes along with the impact of these waters both regionally and for the globe makes this subject important for the scientific community.
Can the authors explain why the two particular sites are chosen? Are they selected because of their measurement quality? Because they are the only sites available? Because they are at particularly important locations? What is the reason?
I see a discussion about the accuracy of sensors that are on each of the observing platforms. But what about systematic biases?
I don’t see a reference or a discussion of figure 3 prior to the appearance of the figure. Perhaps I missed it?
In the second paragraph in Section 3.1, what I think are surprising results are discussed. That the warming rates at deeper layers exceed those at shallower layers. This behavior is discussed in depth in Section 4.1 with plausible physical mechanisms.
Did you mention any QC that is used on these measurements? If that was done, I missed it.
I also wonder how valuable it is to compare against quite old studies (Bindoff 1997 for example). I would think that limiting to studies done in the past decade or so would be wise. Perhaps they are not available?
We estimate subsurface linear and non-linear temperature trends at 5 coastal sites adjacent to the East Australian Current (EAC). We see accelerating trends at both 34.1° S and 42.6° S, and place our results in the context of previously reported trends, highlighting that magnitudes are depth-dependent and vary across latitude. Our results indicate the important role of regional dynamics, and show the necessity of subsurface data for the improved understanding of regional climate change impacts.
We estimate subsurface linear and non-linear temperature trends at 5 coastal sites adjacent to...
