The East Australian Current and Property Transport at 27°S from 2012 to 2013

Sloyan, Bernadette M.; Ridgway, K. R.; Cowley, Rebecca

doi:10.1175/jpo-d-15-0052.1

Cited by 63 publications

(114 citation statements)

References 28 publications

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“…In the northern part of the SR03 section, the area occupied by the STCW has high variability due to the encounter between the EAC and the ZC in the north of the section (Ridgway et al, 2007;Herraiz-Borreguero and Rintoul, 2011;Sloyan et al, 2016). The warming of the STCW layer found in this study (0.0335 ± 0.0130 • C yr −1 ) could be linked to variability in the extension of subtropical waters but it could also be related to atmospheric warming.…”

Section: Discussionmentioning

confidence: 48%

“…1) mix into the Subantarctic Zone, and also meet Zeehan Current (ZC, Fig. 1) waters transported down the west coast of Tasmania (Boland and Church, 1981;Baines et al, 1983;Speich et al, 2002;Davis, 2005;Ridgway et al, 2007;Sloyan et al, 2016). The EAC transported south of Tasmania forms a zonal jet towards the south-east Indian Ocean, known as the Tasman Outflow, that reaches the bottom of the Tasman slope and that is maintained all year round (Rintoul and Bullister, 1999;Ridgway et al, 2007).…”

Section: Hydrography Of the Regionmentioning

confidence: 99%

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Carbon uptake and biogeochemical change in the Southern Ocean, south of Tasmania

et al. 2017

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Abstract. Biogeochemical change in the water masses of the Southern Ocean, south of Tasmania, was assessed for the 16-year period between 1995 and 2011 using data from four summer repeats of the WOCE-JGOFS-CLIVAR-GO-SHIP (Key et al., 2015;Olsen et al., 2016) SR03 hydrographic section (at ∼ 140 • E). Changes in temperature, salinity, oxygen, and nutrients were used to disentangle the effect of solubility, biology, circulation and anthropogenic carbon (C ANT ) uptake on the variability of dissolved inorganic carbon (DIC) for eight water mass layers defined by neutral surfaces (γ n ). C ANT was estimated using an improved back-calculation method. Warming (∼ 0.0352 ± 0.0170 • C yr −1 ) of Subtropical Central Water (STCW) and Antarctic Surface Water (AASW) layers decreased their gas solubility, and accordingly DIC concentrations increased less rapidly than expected from equilibration with rising atmospheric CO 2 (∼ 0.86 ± 0.16 µmol kg −1 yr −1 versus ∼ 1 ± 0.12 µmol kg −1 yr −1 ). An increase in apparent oxygen utilisation (AOU) occurred in these layers due to either remineralisation of organic matter or intensification of upwelling. The range of estimates for the increases in C ANT were 0.71 ± 0.08 to 0.93 ± 0.08 µmol kg −1 yr −1 for STCW and 0.35 ± 0.14 to 0.65 ± 0.21 µmol kg −1 yr −1 for AASW, with the lower values in each water mass obtained by assigning all the AOU change to remineralisation. DIC increases in the Sub-Antarctic Mode Water (SAMW, 1.10 ± 0.14 µmol kg −1 yr −1 ) and Antarctic Intermediate Water (AAIW, 0.40 ± 0.15 µmol kg −1 yr −1 ) layers were similar to the calculated C ANT trends. For SAMW, the C ANT increase tracked rising atmospheric CO 2 . As a consequence of the general DIC increase, decreases in total pH (pH T ) and aragonite saturation ( Ar ) were found in most water masses, with the upper ocean and the SAMW layer presenting the largest trends for pH T decrease (∼ −0.0031 ± 0.0004 yr −1 ). DIC increases in deep and bottom layers (∼ 0.24 ± 0.04 µmol kg −1 yr −1 ) resulted from the advection of old deep waters to resupply increased upwelling, as corroborated by increasing silicate (∼ 0.21 ± 0.07 µmol kg −1 yr −1 ), which also reached the upper layers near the Antarctic Divergence (∼ 0.36 ± 0.06 µmol kg −1 yr −1 ) and was accompanied by an increase in salinity. The observed changes in DIC over the 16-year span caused a shoaling (∼ 340 m) of the aragonite saturation depth (ASD, Ar = 1) within Upper Circumpolar Deep Water that followed the upwelling path of this layer. From all our results, we conclude a scenario of increased transport of deep waters into the section and enhanced upwelling at high latitudes for the period between 1995 and 2011 linked to strong westerly winds. Although enhanced upwelling lowered the capacity of the AASW layer to uptake atmospheric CO 2 , it did not limit that of the newly forming SAMW and AAIW, which exhibited C ANT storage rates (∼ 0.41 ± 0.20 mol m −2 yr −1 ) twice that of the upper layers.

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Section: Discussionmentioning

confidence: 48%

Section: Hydrography Of the Regionmentioning

confidence: 99%

Carbon uptake and biogeochemical change in the Southern Ocean, south of Tasmania

et al. 2017

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“…Remote wind forcing, communicated via first mode baroclinic Rossby waves, has been shown to affect the annual cycle in volume transport (Domingues et al, 2016), but for the data presented here at 25-26°N, the Bahamas island chain blocks most of this direct mid-ocean influence (Archer, Shay, et al, 2017). At 30-31°S, the EAC has a mean core speed between 0.6 and 1.35 m s À1 (Archer, Roughan, et al, 2017;Mata et al, 2000;Schaeffer et al, 2017) and a volume transport of~22 Sv with an STD of~5-7 Sv (Mata et al, 2000;Sloyan et al, 2016). The EAC closes the South Pacific subtropical gyre, flowing poleward along SE Australia (Figure 1b).…”

Section: Introductionmentioning

confidence: 76%

The Kinematic Similarity of Two Western Boundary Currents Revealed by Sustained High‐Resolution Observations

Archer

Keating

Roughan

et al. 2018

Geophysical Research Letters

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Western boundary currents (WBCs) modulate the global climate and dominate regional ocean dynamics. Despite their importance, few direct comparisons of the kinematic structure of WBCs exist, due to a lack of equivalent sustained observational data sets. Here we compare multiyear, high‐resolution observations (1 km, hourly) of surface currents in two WBCs (Florida Current and East Australian Current) upstream of their separation point. Current variability is dominated by meandering, and the WBCs exhibit contrasting time‐mean velocities in a Eulerian coordinate frame. By transforming to a jet‐following coordinate frame, we show that the time‐mean surface velocity structure of the WBC jets is remarkably similar, considering their distinct local wind, bathymetry, and meandering signals. Both WBCs show steep submesoscale kinetic energy wavenumber spectra with weak seasonal variability, in contrast to recent findings in other ocean regions. Our results suggest that it is the mesoscale flow field that controls mixing and ocean dynamics in these regions.

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“…Mesoscale anticyclonic eddies intermittently pinch off the EAC retroflection and propagate to the south and east, sometimes propagating as far south as Tasmania in what is termed the EAC extension (Everett et al, ; Godfrey et al, ; Nilsson & Creswell, 1980). Most recently, Sloyan et al () quantified the cross‐sectional profile of the EAC from six moorings at 27°S, and calculated an 18 month poleward‐only mean volume transport above 2,000 m to be 22.1 ± 7.5 Sv (Sv = 10 6 m 3 s −1 ). This mean poleward transport agrees with Mata et al (), who at 30°S obtained a 2.5 year mean transport of 22.1 ± 4.6 Sv, from nine hydrographic stations and six moorings.…”

Section: Introductionmentioning

confidence: 99%

On the Variability of the East Australian Current: Jet Structure, Meandering, and Influence on Shelf Circulation

et al. 2017

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Given the importance of western boundary currents over a wide range of scales in the ocean, it is crucial that we understand their dynamics to accurately predict future changes. For this, we need detailed knowledge of their structure and variability. Here we investigate the jet structure of the East Australian Current (EAC), using observations from HF radars and moorings deployed at 30°S–31°S. Meandering, core velocity, width, and eddy kinetic energy (EKE) are quantified from 4 years of hourly 1.5 km resolution surface current maps (2012–2016), to obtain the most detailed representation of the surface EAC jet to date. The EAC flows predominantly over the ∼1,500 m isobath 50 km offshore but makes large amplitude displacements eastward every 65–100 days—the time scale associated with mesoscale eddy shedding at the EAC separation. Smaller‐amplitude, higher‐frequency meanders occur every 20–45 days. Using a coordinate frame that follows the jet, we show core velocity and EKE exhibit seasonality in both magnitude and variance, being maximum in summer (1.55 m s−1 mean core velocity), minimum in winter (0.8 m s−1). However, it is the eddy‐shedding time scale that dominates jet variability. As the EAC moves shoreward, shelf temperature and along‐stream velocity vary linearly with jet movement, within ∼35 km of the core. The EAC is within this range 75% of the time, demonstrating its importance to the shelf circulation. Temperature and velocity fluctuations at the 70 m (100 m) isobath are more influenced by wind (EAC encroachment), with the strongest response occurring when wind and EAC act constructively.

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The East Australian Current and Property Transport at 27°S from 2012 to 2013

Cited by 63 publications

References 28 publications

Carbon uptake and biogeochemical change in the Southern Ocean, south of Tasmania

Carbon uptake and biogeochemical change in the Southern Ocean, south of Tasmania

The Kinematic Similarity of Two Western Boundary Currents Revealed by Sustained High‐Resolution Observations

On the Variability of the East Australian Current: Jet Structure, Meandering, and Influence on Shelf Circulation

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