Abstract
Accelerated warming of western boundary currents due to the strengthening of subtropical gyres has had cascading effects on coastal ecosystems and is widely expected to result in further tropicalization of temperate regions. Predicting how species and ecosystems will respond requires a better understanding of the variability in ocean warming in complex boundary current regions. Using three ≥50 year temperature records we demonstrate high variability in the magnitude and seasonality of warming in the Southwest Pacific boundary current region. The greatest rate of warming was evident off eastern Tasmania (0.20 °C decade−1), followed by southern New Zealand (0.10 °C decade−1), while there was no evidence of annual warming in northeastern New Zealand. This regional variability in coastal warming was also evident in the satellite record and is consistent with expected changes in regional-scale circulation resulting from increased wind stress curl in the South Pacific subtropical gyre. Warming trends over the satellite era (1982–2016) were considerably greater than the longer-term trends, highlighting the importance of long-term temperature records in understanding climate change in coastal regions. Our findings demonstrate the spatial and temporal complexity of warming patterns in boundary current regions and challenge widespread expectations of tropicalization in temperate regions under future climate change.
Highlights
The redistribution of species due to human mediated climate change is having increasing impacts on ecosystems and human wellbeing[1]
This warming has been attributed to the intensification and pole-ward extension of the East Australian Current (EAC; Fig. 1)[8], resulting from increasing wind stress curl at mid-latitudes causing a strengthening of the South Pacific Ocean subtropical gyre[5]
The greatest warming trend was evident at Maria Island (+0.20 °C decade−1 from 1946–2016), followed by Portobello (+0.10 °C decade−1 from 1953–2016), and no trend was evident at Leigh over the last 50 years
Summary
The redistribution of species due to human mediated climate change is having increasing impacts on ecosystems and human wellbeing[1]. The long-term SST record from Maria Island, eastern Tasmania, has been pivotal in documenting and understanding the dynamics of warming that has occurred off the east coast of Tasmania, Australia, over the last 6–7 decades[8,21] This warming has been attributed to the intensification and pole-ward extension of the East Australian Current (EAC; Fig. 1)[8], resulting from increasing wind stress curl at mid-latitudes causing a strengthening of the South Pacific Ocean subtropical gyre[5]. Warming in this region has resulted in large-scale changes in coastal ecosystems[6,22] and similar changes are widely predicted in boundary current regions worldwide[4]. Subtropical waters from the southern Tasman flow around the southern tip of the South Island as part of the Southland Current[30,31] providing a potential mechanism for warming around southern New Zealand
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