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Origin and mechanism of Subantarctic Mode Water formation and transformation in the Southern Indian Ocean 总被引:1,自引:0,他引:1
The sources and pathways of mode waters and lower thermocline waters entering the subtropical gyre of the Indian Ocean are
examined. A Lagrangian analysis is performed on an eddy-admitting simulation of the Global Ocean performed by the DRAKKAR
Group (NEMO/OPA), which captures the main observed features. We trace the subducted mode water’s pathways, identify their
formation regions and trace whether their source waters come from the Atlantic, Pacific or Indian sectors of the Southern
Ocean. Three main sites for mode waters ventilation in the Indian sector are identified with different circulation pathways
and source water masses: (a) just north of Kerguelen, where 4.2 Sv of lighter Subantarctic Mode Waters (SAMW); σ
0 ∼ 26.5) are exported—originating in the Atlantic and Agulhas Retroflection regions; (b) SW of Australia, where 6.5 Sv of
medium SAMW (σ
0 ∼ 26.6) are ventilated—originating in the southern and denser Agulhas Retroflection region; (c) SW of Tasmania and along
the South Australian coast, where 3 Sv of denser SAMW (σ
0 ∼ 26.75) are ventilated—originating from three sources: Leeuwin Current waters, Tasman Sea (Pacific) waters and Antarctic
Surface Waters. In all cases, modelled mode waters were last ventilated in the Indian Ocean just north of the deepest winter-mixed
layers. For the waters subducted SW of Australia, the last ventilation site extends even further north. Waters ventilated
in the deepest mixed layers north of the Subantarctic Front are then re-ventilated 5 years later southwest of Australia. The
model results raise new hypotheses that revisit the classical picture of the SAMW formation and transformation, where a large
homogeneous mixed layer is subducted and ‘slides’ equatorward, essentially maintaining the T/S characteristics acquired at
the surface. Firstly, the last ventilation of the modelled mode waters is not in the region of the deepest mixed layers, as
previously thought, but further north in regions of moderate meso-scale eddy activity. Secondly, the model shows for the first
time a significant source region for Indian Ocean mode waters coming from deep winter-mixed layers along the south Australian
coast. Finally, this analysis shows how the mode water characteristics are modified after subduction, due to internal eddy
mixing. The simulation shows that resolved eddies have a strong impact on the mixed layer properties and that isopycnal eddy
mixing also contributes to the generation of more homogeneous mode water characteristics in the interior. 相似文献
2.
Audrey Hasson Ariane Koch-Larrouy Rosemary Morrow Mélanie Juza Thierry Penduff 《Ocean Dynamics》2012,62(3):335-354
Understanding the origin and fate of mode and intermediate waters (MW) in the subtropical Pacific Ocean is critical for climate,
as MW store and export a large volume of CO2, heat, nutrients and salinity to lower latitudes at depths isolated from the atmosphere. A realistic 4D simulation has been
used to track and quantify the MW routes and their property characteristics at the last region of subduction. It also allows
us to quantify the water transformation after subduction. The simulation has been compared to available observations using
a collocation method that interpolated model data onto observations in time and space. The comprehensive comparisons gave
us confidence in the model’s capacity to reproduce MW characteristics. A quantitative Lagrangian analysis was performed on
the model output to depict the origin, the fate and the route of MW circulating in the southern Pacific Ocean, selected in
the density range of 26.8–27.4 kg m−3. We found 18 Sv of MW were transported northward in patches through the 42° S section, mostly between 200 and 800 m depth.
Of this transport, 8 Sv enters the Pacific Ocean in the upper layer south of Tasmania and subducts in the Pacific. The remainder
is not ventilated in the Pacific sector: 4 Sv is advected from the Indian Ocean south of Tasmania at intermediate depth and
finally 6 Sv is part of an intermediate depth recirculation within the Pacific Ocean. Particles take up to 30 years to travel
northward through our domain before crossing the 42° S section. Southward transport branches also exist: 3 Sv flows southward
following the eastern New Zealand coast and then exits through Drake Passage. An additional 4 Sv passes southward in the Tasman
Sea, following the eastern Tasmanian coast and enters the Indian Ocean south of Tasmania, as part of the Tasman Leakage. Four
different formation sites have been identified, where the MW are last ventilated. These formation sites have different water
masses with specific salinity ranges. A study on the evolution of the physical characteristics of each of these water masses
has been performed. All MW characteristics become more homogeneous at 42° S than they were when they left the mixed layer.
This study confirms the homogenisation of mode waters at intermediate depth in the Pacific Ocean as previously revealed in
the Indian Ocean using the same methodology. Transformations are shown to be mostly isopycnal in the Tasman Sea and diapycnal
farther east. 相似文献
3.
Aguiar Eva Mourre Baptiste Juza Mélanie Reyes Emma Hernández-Lasheras Jaime Cutolo Eugenio Mason Evan Tintoré Joaquín 《Ocean Dynamics》2020,70(2):273-288
Ocean Dynamics - In numerical ocean modeling, dynamical downscaling is the approach consisting in generating high-resolution regional simulations exploiting the information from coarser resolution... 相似文献
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