Premium
Variability and Long‐Term Trends in the Shelf Circulation Off Eastern Tasmania
Author(s) -
Oliver Eric C. J.,
Holbrook Neil J.
Publication year - 2018
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2018jc013994
Subject(s) - oceanography , climatology , boundary current , ocean current , current (fluid) , temperature salinity diagrams , sea surface temperature , pacific decadal oscillation , environmental science , ocean general circulation model , geology , salinity , climate change , general circulation model
This study investigates trends and interannual variability of the marine climate across the continental shelf off eastern Tasmania for 1993–2016. This region is a hotspot for global warming and biodiversity. Eastern Tasmania lies at the boundary between two ocean currents (the East Australian Current Extension, or EAC Extension, and the Zeehan Current, ZC) leading to the local marine climate exhibiting trends and variability from both boundary currents. A numerical ocean model is used to provide high‐resolution (∼2 km) estimates of the temperature, salinity, and circulation for the region. Results indicate significant positive trends in temperature, salinity, and southward flow over the shelf, consistent with an increasing EAC Extension. These trends are particularly strong in autumn, indicating a lengthening of the warm season. The interannual variability in the EAC Extension and ZC was quantified by a simple index, based on a modal analysis of surface circulation, indicating the relative dominance of each current. Strong EAC years were related to significantly more summertime marine heat wave days. Large‐scale remote drivers of variability were considered, and we found weak but significant links with El Niño–Southern Oscillation and Tasman Sea Blocking. El Niño–Southern Oscillation was found to modulate the EAC Extension in summer with a El Niño leading to enhanced southward flow and warming over the shelf. Tasman Sea Blocking was found to drive enhanced southward surface flow, particularly in winter. Nonetheless, large‐scale forcing modes explain less than 25% of the total variability in the EAC‐ZC system indicating that most of the variability is internally generated.