scholarly journals Turbulence and Diapycnal Mixing in Drake Passage

2012 ◽  
Vol 42 (12) ◽  
pp. 2143-2152 ◽  
Author(s):  
L. St. Laurent ◽  
A. C. Naveira Garabato ◽  
J. R. Ledwell ◽  
A. M. Thurnherr ◽  
J. M. Toole ◽  
...  
Keyword(s):  
Drake Passage ◽  
Global Ocean ◽  
Mixing Enhancement ◽  
Turbulent Dissipation ◽  
Dissipation Rates ◽  
Direct Measurements ◽  
Order Of Magnitude ◽  
Frontal Zones ◽  
Circumpolar Current ◽  
The Antarctic

Abstract Direct measurements of turbulence levels in the Drake Passage region of the Southern Ocean show a marked enhancement over the Phoenix Ridge. At this site, the Antarctic Circumpolar Current (ACC) is constricted in its flow between the southern tip of South America and the northern tip of the Antarctic Peninsula. Observed turbulent kinetic energy dissipation rates are enhanced in the regions corresponding to the ACC frontal zones where strong flow reaches the bottom. In these areas, turbulent dissipation levels reach 10−8 W kg−1 at abyssal and middepths. The mixing enhancement in the frontal regions is sufficient to elevate the diapycnal turbulent diffusivity acting in the deep water above the axis of the ridge to 1 × 10−4 m2 s−1. This level is an order of magnitude larger than the mixing levels observed upstream in the ACC above smoother bathymetry. Outside of the frontal regions, dissipation rates are O(10−10) W kg−1, comparable to the background levels of turbulence found throughout most mid- and low-latitude regions of the global ocean.

scholarly journals A Microscale View of Mixing and Overturning across the Antarctic Circumpolar Current

2016 ◽  
Vol 46 (1) ◽  
pp. 233-254 ◽  
Author(s):  
Alberto C. Naveira Garabato ◽  
Kurt L. Polzin ◽  
Raffaele Ferrari ◽  
Jan D. Zika ◽  
Alexander Forryan
Keyword(s):  
Antarctic Circumpolar Current ◽  
Large Scale ◽  
Drake Passage ◽  
Small Scale ◽  
Overturning Circulation ◽  
Order Of Magnitude ◽  
Circumpolar Current ◽  
Scale Turbulence ◽  
Microstructure Measurements ◽  
The Antarctic

AbstractThe relative roles of isoneutral stirring by mesoscale eddies and dianeutral stirring by small-scale turbulence in setting the large-scale temperature–salinity relation of the Southern Ocean against the action of the overturning circulation are assessed by analyzing a set of shear and temperature microstructure measurements across Drake Passage in a “triple decomposition” framework. It is shown that a picture of mixing and overturning across a region of the Antarctic Circumpolar Current (ACC) may be constructed from a relatively modest number of microstructure profiles. The rates of isoneutral and dianeutral stirring are found to exhibit distinct, characteristic, and abrupt variations: most notably, a one to two orders of magnitude suppression of isoneutral stirring in the upper kilometer of the ACC frontal jets and an order of magnitude intensification of dianeutral stirring in the subpycnocline and deepest layers of the ACC. These variations balance an overturning circulation with meridional flows of O(1) mm s−1 across the ACC’s mean thermohaline structure. Isoneutral and dianeutral stirring play complementary roles in balancing the overturning, with isoneutral processes dominating in intermediate waters and the Upper Circumpolar Deep Water and dianeutral processes prevailing in lighter and denser layers.

scholarly journals Intrinsic variability of the Antarctic Circumpolar Current system: low- and high-frequency fluctuations of the Argentine Basin flow

Ocean Science ◽  
2014 ◽  
Vol 10 (2) ◽  
pp. 201-213 ◽  
Author(s):  
G. Sgubin ◽  
S. Pierini ◽  
H. A. Dijkstra
Keyword(s):  
High Frequency ◽  
Antarctic Circumpolar Current ◽  
Current System ◽  
Low Frequency ◽  
Drake Passage ◽  
Ocean Model ◽  
Intrinsic Variability ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Argentine Basin

Abstract. In this paper, the variability of the Antarctic Circumpolar Current system produced by purely intrinsic nonlinear oceanic mechanisms is studied through a sigma-coordinate ocean model, implemented in a large portion of the Southern Ocean at an eddy-permitting resolution under steady surface heat and momentum fluxes. The mean transport through the Drake Passage and the structure of the main Antarctic Circumpolar Current fronts are well reproduced by the model. Intrinsic variability is found to be particularly intense in the Subantarctic Front and in the Argentine Basin, on which further analysis is focused. The low-frequency variability at interannual timescales is related to bimodal behavior of the Zapiola Anticyclone, with transitions between a strong and collapsed anticyclonic circulation in substantial agreement with altimeter observations. Variability on smaller timescales shows clear evidence of topographic Rossby-wave propagation along the eastern and southern flanks of the Zapiola Rise and of mesoscale eddies, also in agreement with altimeter observations. The analysis of the relationship between the low- and high-frequency variability suggests possible mechanisms of mutual interaction.

scholarly journals Interannual response of global ocean hindcasts to a satellite-based correction of precipitation fluxes

2012 ◽  
Vol 9 (2) ◽  
pp. 611-648 ◽  
Author(s):  
A. Storto ◽  
I. Russo ◽  
S. Masina
Keyword(s):  
Ocean Circulation ◽  
Surface Current ◽  
Global Ocean ◽  
Surface Salinity ◽  
Near Surface ◽  
Convergence Zones ◽  
Circumpolar Current ◽  
The Tropics ◽  
Spatially Varying ◽  
The Antarctic

Abstract. We present a methodology to correct precipitation fluxes from the ECMWF atmospheric reanalysis (ERA-Interim) for oceanographic applications. The correction is performed by means of a spatially varying monthly climatological coefficient, computed within the period 1989–2008 by comparison between ERA-Interim and a satellite-based passive microwave precipitation product. ERA-Interim exhibits a systematic over-estimation of precipitation within the inter-tropical convergence zones (up to 3 mm d−1) and under-estimation at mid- and high- latitudes (up to −4 mm d−1). The correction has been validated within eddy-permitting resolution global ocean hindcasts (1989–2009), demonstrating the ability of our strategy in attenuating the 20-yr mean global EMP negative imbalance by 16%, reducing the near-surface salinity fresh bias in the Tropics up to 1 psu and improving the representation of the sea level interannual variability, with an SSH error decrease of 8%. The ocean circulation is also proved to benefit from the correction, especially in correspondence of the Antarctic Circumpolar Current, where the error in the near-surface current speed decreases by a 9%. Finally, we show that the correction leads to volume and freshwater transports that better agree with independent estimates.

scholarly journals Coupling Influences of ENSO and PDO on the Inter-Decadal SST Variability of the ACC around the Western South Atlantic

2019 ◽  
Vol 11 (18) ◽  
pp. 4853
Author(s):  
You-Lin Wang ◽  
Yu-Chen Hsu ◽  
Chung-Pan Lee ◽  
Chau-Ron Wu
Keyword(s):  
Antarctic Circumpolar Current ◽  
Water Mass ◽  
Southern Oscillation ◽  
Drake Passage ◽  
South Atlantic ◽  
Sst Variability ◽  
The Pacific ◽  
Circumpolar Current ◽  
The Antarctic

The Antarctic Circumpolar Current (ACC) plays an important role in the climate as it balances heat energy and water mass between the Pacific and Atlantic Oceans through the Drake Passage. However, because the historical measurements and observations are extremely limited, the decadal and long-term variations of the ACC around the western South Atlantic Ocean are rarely studied. By analyzing reconstructed sea surface temperatures (SSTs) in a 147-year period (1870–2016), previous studies have shown that SST anomalies (SSTAs) around the Antarctic Peninsula and South America had the same phase change as the El Niño Southern Oscillation (ENSO). This study further showed that changes in SSTAs in the regions mentioned above were enlarged when the Pacific Decadal Oscillation (PDO) and the ENSO were in the same warm or cold phase, implying that changes in the SST of higher latitude oceans could be enhanced when the influence of the ENSO is considered along with the PDO.

scholarly journals Coccolithophore populations and their contribution to carbonate export during an annual cycle in the Australian sector of the Antarctic zone

2018 ◽  
Vol 15 (6) ◽  
pp. 1843-1862 ◽  
Author(s):  
Andrés S. Rigual Hernández ◽  
José A. Flores ◽  
Francisco J. Sierro ◽  
Miguel A. Fuertes ◽  
Lluïsa Cros ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ocean Acidification ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Global Ocean ◽  
Field Observations ◽  
Scotia Sea ◽  
Allochthonous Species ◽  
Circumpolar Current ◽  
The Antarctic

Abstract. The Southern Ocean is experiencing rapid and relentless change in its physical and biogeochemical properties. The rate of warming of the Antarctic Circumpolar Current exceeds that of the global ocean, and the enhanced uptake of carbon dioxide is causing basin-wide ocean acidification. Observational data suggest that these changes are influencing the distribution and composition of pelagic plankton communities. Long-term and annual field observations on key environmental variables and organisms are a critical basis for predicting changes in Southern Ocean ecosystems. These observations are particularly needed, since high-latitude systems have been projected to experience the most severe impacts of ocean acidification and invasions of allochthonous species. Coccolithophores are the most prolific calcium-carbonate-producing phytoplankton group playing an important role in Southern Ocean biogeochemical cycles. Satellite imagery has revealed elevated particulate inorganic carbon concentrations near the major circumpolar fronts of the Southern Ocean that can be attributed to the coccolithophore Emiliania huxleyi. Recent studies have suggested changes during the last decades in the distribution and abundance of Southern Ocean coccolithophores. However, due to limited field observations, the distribution, diversity and state of coccolithophore populations in the Southern Ocean remain poorly characterised. We report here on seasonal variations in the abundance and composition of coccolithophore assemblages collected by two moored sediment traps deployed at the Antarctic zone south of Australia (2000 and 3700 m of depth) for 1 year in 2001–2002. Additionally, seasonal changes in coccolith weights of E. huxleyi populations were estimated using circularly polarised micrographs analysed with C-Calcita software. Our findings indicate that (1) coccolithophore sinking assemblages were nearly monospecific for E. huxleyi morphotype B/C in the Antarctic zone waters in 2001–2002; (2) coccoliths captured by the traps experienced weight and length reduction during summer (December–February); (3) the estimated annual coccolith weight of E. huxleyi at both sediment traps (2.11 ± 0.96 and 2.13 ± 0.91 pg at 2000 and 3700 m) was consistent with previous studies for morphotype B/C in other Southern Ocean settings (Scotia Sea and Patagonian shelf); and (4) coccolithophores accounted for approximately 2–5 % of the annual deep-ocean CaCO3 flux. Our results are the first annual record of coccolithophore abundance, composition and degree of calcification in the Antarctic zone. They provide a baseline against which to monitor coccolithophore responses to changes in the environmental conditions expected for this region in coming decades.

scholarly journals Detecting and Characterizing Ekman Currents in the Southern Ocean

2015 ◽  
Vol 45 (5) ◽  
pp. 1205-1223 ◽  
Author(s):  
Christopher J. Roach ◽  
Helen E. Phillips ◽  
Nathaniel L. Bindoff ◽  
Stephen R. Rintoul
Keyword(s):  
Southern Ocean ◽  
Classical Theory ◽  
Geographical Area ◽  
Drake Passage ◽  
Current Decay ◽  
Common Value ◽  
Constant Viscosity ◽  
Circumpolar Current ◽  
Reasonable Description ◽  
The Antarctic

AbstractThis study presents a unique array of velocity profiles from Electromagnetic Autonomous Profiling Explorer (EM-APEX) profiling floats in the Antarctic Circumpolar Current (ACC) north of Kerguelen. The authors use these profiles to examine the nature of Ekman spirals, formed by the action of the wind on the ocean’s surface, in light of Ekman’s classical linear theory and more recent enhancements. Vertical decay scales of the Ekman spirals were estimated independently from current amplitude and rotation. Assuming a vertically uniform geostrophic current, decay scales from the Ekman current heading were twice as large as those from the current speed decay, indicating a compressed spiral, consistent with prior observations and violating the classical theory. However, if geostrophic shear is accurately removed, the observed Ekman spiral is as predicted by classical theory and decay scales estimated from amplitude decay and rotation converge toward a common value. No statistically robust relationship is found between stratification and Ekman decay scales. The results indicate that compressed spirals observed in the Southern Ocean arise from aliasing of depth-varying geostrophic currents into the Ekman spiral, as opposed to surface trapping of Ekman currents associated with stratification, and extends the geographical area of similar results from Drake Passage (Polton et al. 2013). Accounting for this effect, the authors find that constant viscosity Ekman models offer a reasonable description of momentum mixing into the upper ocean in the ACC north of Kerguelen. These results demonstrate the effectiveness of a new method and provide additional evidence that the same processes are active for the entire Southern Ocean.

The Cenozoic tectonic evolution of the Scotia Sea area

2020 ◽  
Author(s):  
Anne Oldenhage ◽  
Anouk Beniest ◽  
Wouter P. Schellart
Keyword(s):  
Tectonic Evolution ◽  
Drake Passage ◽  
Sea Level Changes ◽  
Scotia Sea ◽  
Scotia Ridge ◽  
The North ◽  
Reconstruction Software ◽  
Circumpolar Current ◽  
Global Sea Level ◽  
The Antarctic

<p>The breakup of the southern edge of Gondwanaland resulted in the formation of the Scotia Plate and the opening of Drake Passage throughout the Cenozoic. During the same period, the Tasman Seaway opened, although the timing of this opening is much better constrained. Rapid cooling of the Antarctic continent followed the openings of Drake Passage and the Tasman Seaway. The opening of Drake Passage or the Tasman seaway allowed the onset of the Antarctic Circumpolar Current, which is held responsible for the late Miocene global cooling, but discussions about the most important opening are still ongoing.</p><p>The opening of Drake Passage and the development of the Scotia plate have been studied in multitude, but paleogeographic reconstructions show many differences and inconsistencies in both timing of opening Drake Passage as well as paleo-locations of crustal segments. The paleogeographic or tectonic reconstructions of the opening of Drake Passage and the formation of the Scotia plate are hard to compare, because differences in shapes of crustal segments, geographic projections and relative movements of segments chosen by previous authors make it difficult to observe similarities and differences between the different reconstructions.</p><p>We present a thorough analysis of the previously published paleogeographic reconstructions with the aim to identify agreements and inconsistencies between these reconstructions. We re-defined the crustal segments that formed after the break-up of Gondwanaland by re-interpreting the bathymetry and magnetic anomalies of the study area. We re-modelled and compared georeferenced reconstructions from earlier studies in GPlates plate reconstruction software using our own defined crustal segments.</p><p>This comparison shows that the different reconstructions agree quite well along the South Scotia Ridge, but that the North Scotia Ridge shows significant variations between different reconstructions or is not even considered in the reconstructions. Also, the nature and age of the crust of the Central Scotia Sea is heavily discussed, resulting in different opening scenarios. We argue that the tectonic evolution of the North Scotia Ridge and Central Scotia Sea is a crucial factor in identifying the timing of the development of an ocean gateway. We made a new tectonic reconstruction of the North Scotia Ridge crustal segments with less overlaps and gaps between the reconstructed crustal segments.</p><p>The next step would be to compare the global sea-level changes and paleo-bathymetry with the different opening scenarios. Because we standardized all scenarios with the same crustal segments, we will then be able to provide opening ages of Drake Passage for the different scenarios that can be compared in a quantitative way.</p>

Jets of the Antarctic Circumpolar Current in the Drake Passage Based on Hydrographic Section Data

2020 ◽  
Author(s):  
Roman Tarakanov ◽  
Alexander Gritsenko
Keyword(s):  
Antarctic Circumpolar Current ◽  
Basic Research ◽  
Drake Passage ◽  
Section Data ◽  
Temporal And Spatial ◽  
Circumpolar Current ◽  
Basic Research Grant ◽  
The Antarctic ◽  
Jet Structure ◽  
Satellite Altimetry Data

<p>We have analyzed the fine structure of Antarctic Circumpolar Current jets in the Drake Passage based on CTD and SADCP measurements over two hydrographic sections in January 2010 and October–November 2011. Eleven jets with a local horizontal velocity maximum were revealed in 2010, and nine jets were in 2011. These individual jets were various combinations of 12 jets of the Antarctic Circumpolar Current, which we revealed earlier in the region south of Africa on the basis of the section data in December 2009. Daily satellite altimetry data available at http://www.aviso.altimetry.fr were also used to interpret the synoptic patterns of currents over the sections. These results allow us to suggest that the multi-jet structure with a number of jets exceeding nine reported by Sokolov&Rintoul, 2009 is common for the entire circumpolar circle and even for regions with significant contraction of the ACC, such as the Drake Passage. However, the question about the number of jets and its temporal and spatial permanency remains open. Investigation was supported by Russian Foundation of Basic Research grant No 18-05-00283.</p>

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