scholarly journals Biogeochemical characteristics of a long-lived anticyclonic eddy in the eastern South Pacific Ocean

2015 ◽  
Vol 12 (17) ◽  
pp. 14481-14506 ◽  
Author(s):  
M. Cornejo ◽  
L. Bravo ◽  
M. Ramos ◽  
O. Pizarro ◽  
J. Karstensen ◽  
...  
Keyword(s):  
Satellite Altimetry ◽  
Subsurface Layer ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
South Pacific ◽  
Biological Properties ◽  
Subsurface Water ◽  
Nitrite Accumulation ◽  
Source Water ◽  
Oxygen Utilization

Abstract. Eastern boundary upwelling systems are characterized by high productivity that often leads to subsurface hypoxia on the shelf. Mesoscale eddies are important, frequent, and persistent features of circulation in these regions, transporting physical, chemical and biological properties from shelves to the open ocean. In austral fall of 2011, during the Tara Oceans expedition, a subsurface layer (200–400 m) in which the concentration of oxygen was very low (< 2 μmol kg−1 of O2) was observed in the eastern South Pacific, ~ 900 km offshore (30° S, 81° W). Satellite altimetry combined with CTD observations associated the local oxygen anomaly with an intrathermocline, anticyclonic, mesoscale eddy with a diameter of about 150 km. The eddy contained Equatorial Subsurface Water (ESSW) that at this latitude is normally restricted near the coast. Undersaturation (44 %) of nitrous oxide (N2O) and nitrite accumulation (> 0.5 μM) gave evidence for denitrification in this water mass. Based on satellite altimetry, we tracked the eddy back to its region of formation on the coast of central Chile (36.1° S, 74.6° W). We estimate that the eddy formed in April 2010. Field studies conducted on the Chilean shelf in June 2010 provided approximate information on initial O2 and N2O concentrations of "source water" in the region at the time of eddy formation. Concentrations of both O2 and N2O in the oxygen minimum zone (OMZ) of the offshore eddy were lower than its surroundings or "source water" on the shelf, suggesting that these chemical species were consumed as the eddy moved offshore. Estimates of apparent oxygen utilization rates at the OMZ of the eddy ranged from 0.29 to 44 nmol L−1 d−1 and the rate of N2O consumption was 3.92 nmol L−1 d−1. Our results show that mesoscale eddies in the ESP not only transport physical properties of the ESSW from the coast to the ocean interior, but also export and transform biogeochemical properties, creating suboxic environments in the oligotrophic region of the eastern South Pacific. Suboxic water masses that are advected by eddies act as hotspots for denitrification and loss of fixed nitrogen from the system.

scholarly journals Biogeochemical characteristics of a long-lived anticyclonic eddy in the eastern South Pacific Ocean

2016 ◽  
Vol 13 (10) ◽  
pp. 2971-2979 ◽  
Author(s):  
Marcela Cornejo D'Ottone ◽  
Luis Bravo ◽  
Marcel Ramos ◽  
Oscar Pizarro ◽  
Johannes Karstensen ◽  
...  
Keyword(s):  
Nitrogen Loss ◽  
Subsurface Layer ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
South Pacific ◽  
Open Ocean ◽  
Subsurface Water ◽  
Nitrite Accumulation ◽  
Source Water ◽  
Surrounding Water

Abstract. Mesoscale eddies are important, frequent, and persistent features of the circulation in the eastern South Pacific (ESP) Ocean, transporting physical, chemical and biological properties from the productive shelves to the open ocean. Some of these eddies exhibit subsurface hypoxic or suboxic conditions and may serve as important hotspots for nitrogen loss, but little is known about oxygen consumption rates and nitrogen transformation processes associated with these eddies. In the austral fall of 2011, during the Tara Oceans expedition, an intrathermocline, anticyclonic, mesoscale eddy with a suboxic (< 2 µmol kg−1 of O2), subsurface layer (200–400 m) was detected  ∼  900 km off the Chilean shore (30° S, 81° W). The core of the eddy's suboxic layer had a temperature-salinity signature characteristic of Equatorial Subsurface Water (ESSW) that at this latitude is normally restricted to an area near the coast. Measurements of nitrogen species within the eddy revealed undersaturation (below 44 %) of nitrous oxide (N2O) and nitrite accumulation (> 0.5 µM), suggesting that active denitrification occurred in this water mass. Using satellite altimetry, we were able to track the eddy back to its region of formation on the coast of central Chile (36.1° S, 74.6° W). Field studies conducted in Chilean shelf waters close to the time of eddy formation provided estimates of initial O2 and N2O concentrations of the ESSW source water in the eddy. By the time of its offshore sighting, concentrations of both O2 and N2O in the subsurface oxygen minimum zone (OMZ) of the eddy were lower than concentrations in surrounding water and “source water” on the shelf, indicating that these chemical species were consumed as the eddy moved offshore. Estimates of apparent oxygen utilization rates at the OMZ of the eddy ranged from 0.29 to 44 nmol L−1 d−1 and the rate of N2O consumption was 3.92 nmol L−1 d−1. These results show that mesoscale eddies affect open-ocean biogeochemistry in the ESP not only by transporting physical and chemical properties from the coast to the ocean interior but also during advection, local biological consumption of oxygen within an eddy further generates conditions favorable to denitrification and loss of fixed nitrogen from the system.

scholarly journals Effect of mesoscale eddy on thermocline depth over the global ocean: deepen and uplift

2020 ◽  
Author(s):  
Xiaoyan Chen ◽  
Ge Chen
Keyword(s):  
Satellite Altimetry ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Vertical Displacement ◽  
Ring Structure ◽  
Global Ocean ◽  
Thermocline Depth ◽  
Strong Current ◽  
Current Systems ◽  
Northern And Southern Hemispheres

Abstract. Existing studies on the vertical displacement of thermoclines driven by mesoscale eddies are insufficient and rare. Using 17-year Argo dataset in combination with satellite altimetry, the deepening and uplifting of the depth of thermocline (DTC) by anticyclonic (AE) or cyclonic eddies (CE), respectively, were estimated globally. DTC shifts exhibited multiple geographic and seasonal trends, with the largest magnitude shifts occurring in March and September in the Northern and Southern Hemispheres, respectively. The more pronounced DTC shifts were concentrated in the midlatitudes, and the largest DTC displacements appeared along the western boundaries of strong current systems, with peak shifts of more than 40 m. In general, eddy-induced DTC shifts were linearly correlated with eddy radius and amplitude, suggesting that high intensity eddies induced larger DTC displacements. Finally, a normalized analysis revealed a monopole (ring) structure of DTC ringing the eddy center inside the AE (CE). The forces of AE and CE on the DTC were different, seen in the stronger deepening at the center of the AE (~ 30 m) than the uplifting at the center of the CE (~ 20 m). One possible mechanism for this asymmetry could stem from differential current shears in the thermoclines in AE and CE.

scholarly journals The impact of the planetary β-effect on the tilting vertical structure of a mesoscale eddy

2018 ◽  
Author(s):  
Shengmu Yang ◽  
Jiuxing Xing ◽  
Shengli Chen ◽  
Jiwei Tian ◽  
Daoyi Chen
Keyword(s):  
South China Sea ◽  
South China ◽  
General Circulation ◽  
Vertical Structure ◽  
Mesoscale Eddy ◽  
Maximum Velocity ◽  
Circulation Model ◽  
Mesoscale Eddies ◽  
China Sea ◽  
The Impact

Abstract. Tilting mesoscale eddies in the South China Sea have been reported recently from observed field data. The mechanism of the dynamic process of the tilt, however, is not well understood. In this study, the influence of planetary β on the vertical structure of mesoscale eddies and its mechanism is investigated using theoretical analysis and numerical model experiments based on the MIT General Circulation Model (MITgcm). The results of the both approaches show that vertical motion due to the planetary β effect and nonlinear dynamics causes a pressure anomaly in the horizontal domain which triggers the tilt of the eddy axis. The tilting distance extends to be the radius of the eddy maximum velocity. In addition, the vertical stratification is another key factor in controlling the tilt of a mesoscale eddy. External forcings such as wind and inflow current are not considered in this study, and topography is included only in a realistic South China Sea model. Therefore, mesoscale eddies with large vertical depth should have the similar axis tilt character in open oceans under the β-effect.

scholarly journals Extraction of Revolving Channels of Drifters around Mesoscale Eddy Centers Based on Spatiotemporal Trajectory Clustering

2019 ◽  
Vol 36 (9) ◽  
pp. 1903-1916
Author(s):  
Chunyong Ma ◽  
Siqing Li ◽  
Yang Yang ◽  
Jie Yang ◽  
Ge Chen
Keyword(s):  
Clustering Algorithm ◽  
Spatial Clustering ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Trajectory Clustering ◽  
Satellite Altimeter ◽  
Principal Mode ◽  
In Situ Data ◽  
Anticyclonic Eddies

The global oceanic transports of energy, plankton, and other tracers by mesoscale eddies can be estimated by combining satellite altimetry and in situ data. However, the revolving channels of particles entrained by mesoscale eddies, which could help explain the dynamic process of eddies entraining materials, are still unknown. In this study, satellite altimeter and drifter data from 1993 to 2016 are adopted, and the normalized trajectory clustering algorithm (N-TRACLUS) is proposed to extract the revolving channels of drifters. First, the trajectories of drifters are normalized and clustered by using the density-based spatial clustering of applications with noise (DBSCAN) algorithm. Next, the revolving channels of drifters around the eddy center are extracted. The ring or arc pattern in the middle of a normalized eddy appears when drifters are uninterruptedly entrained by eddies for more than 30 days. Moreover, the revolving channels of drifters in cyclonic eddies are relatively closer to the eddy center than those in anticyclonic eddies. These revolving channels suggest the principal mode of materials’ continuous motion processes that are inside eddies.

scholarly journals Mesoscale Eddy Energy Locality in an Idealized Ocean Model

2013 ◽  
Vol 43 (9) ◽  
pp. 1911-1923 ◽  
Author(s):  
Ian Grooms ◽  
Louis-Philippe Nadeau ◽  
K. Shafer Smith
Keyword(s):  
Energy Budget ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Spatial Filter ◽  
Ocean Model ◽  
Energy Budgets ◽  
Subgrid Scale ◽  
Common Time ◽  
Local Functions ◽  
The Mean

Abstract This paper investigates the energy budget of mesoscale eddies in wind-driven two-layer quasigeostrophic simulations. Intuitively, eddy energy can be generated, dissipated, and fluxed from place to place; regions where the budget balances generation and dissipation are “local” and regions that export or import large amounts of eddy energy are “nonlocal.” Many mesoscale parameterizations assume that statistics of the unresolved eddies behave as local functions of the resolved large scales, and studies that relate doubly periodic simulations to ocean patches must assume that the ocean patches have local energetics. This study derives and diagnoses the eddy energy budget in simulations of wind-driven gyres. To more closely approximate the ideas of subgrid-scale parameterization, the authors define the mean and eddies using a spatial filter rather than the more common time average. The eddy energy budget is strongly nonlocal over nearly half the domain in the simulations. In particular, in the intergyre region the eddies lose energy through interactions with the mean, and this energy loss can only be compensated by nonlocal flux of energy from elsewhere in the domain. This study also runs doubly periodic simulations corresponding to ocean patches from basin simulations. The eddy energy level of ocean patches in the basin simulations matches the level in the periodic simulations only in regions with local eddy energy budgets.

Colder and smaller : 10 years of observations of surface salinity by SMOS, Aquarius and SMAP to study mesoscale eddies in the Southern Ocean

2020 ◽  
Author(s):  
Audrey Hasson ◽  
Cori Pegliasco ◽  
Jacqueline Boutin ◽  
Rosemary Morrow
Keyword(s):  
Soil Moisture ◽  
Southern Ocean ◽  
European Space Agency ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Global Ocean ◽  
Surface Salinity ◽  
Sst Anomalies

&lt;p&gt;Since 2010, space missions dedicated to Sea Surface Salinity (SSS) have been providing observations with almost complete coverage of the global ocean and a resolution of about 45 km every 3 days. The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) mission was the first orbiting radiometer to collect regular SSS observations from space. The Aquarius and SMAP (Soil Moisture Active-Passive) missions of the National Aeronautics and Space Administration (NASA) then reinforced the SSS observing system between mid-2011 and mid-2015 and since mid-2015, respectively.&lt;/p&gt;&lt;p&gt;Using the most recent SSS Climate Change Initiative project dataset merging data from the 3 missions, this study investigates the SSS signal associated with mesoscale eddies in the Southern Ocean. Eddies location and characteristics are obtained from the daily v3 mesoscale eddy trajectory atlas produced by CLS. SSS anomalies along the eddies journey are computed and compared to Sea Surface Temperature (SST) anomalies (v4 Remote Sensing Systems) as well as the SubAntarctic Front (SAF) position (CTOH, LEGOS). The vertical structure of the eddies is further investigated using profiles from colocated Argo autonomous floats.&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;This study highlights a robust signal in SSS depending on both the eddies rotation (cyclone/anticyclone) and latitudinal position with respect to the SAF. Moreover, this dependence is not found in SST. These observations reveal oceanic the interaction of eddies with the larger scale ocean water masses. SSS and SST anomalies composites indeed show different patterns either bi-poles linked with horizontal stirring of fronts, mono-poles from trapping water or vertical mixing changes, or a mix of the two.&lt;/p&gt;&lt;p&gt;This analysis gives strong hints for the erosion of subsurface waters, such as mode waters, induced by enhanced mixing caused by the deep-reaching eddies of the southern ocean.&lt;/p&gt;

Mesoscale eddies, satellite altimetry, and new production in the Sargasso Sea

1999 ◽  
Vol 104 (C6) ◽  
pp. 13359-13379 ◽  
Author(s):  
David A. Siegel ◽  
Dennis J. McGillicuddy ◽  
Erik A. Fields
Keyword(s):  
Satellite Altimetry ◽  
Mesoscale Eddies ◽  
Sargasso Sea ◽  
New Production

scholarly journals Transport, properties, and life cycles of mesoscale eddies in the eastern tropical South Pacific

Ocean Science ◽  
2018 ◽  
Vol 14 (4) ◽  
pp. 731-750 ◽  
Author(s):  
Rena Czeschel ◽  
Florian Schütte ◽  
Robert A. Weller ◽  
Lothar Stramma
Keyword(s):  
Satellite Data ◽  
Water Mass ◽  
Mesoscale Eddies ◽  
South Pacific ◽  
Life Cycles ◽  
Open Ocean ◽  
Reference Station ◽  
Formation Region ◽  
Mass Properties ◽  
Lateral Mixing

Abstract. The influence of mesoscale eddies on the flow field and the water masses, especially the oxygen distribution of the eastern tropical South Pacific, is investigated from a mooring, float, and satellite data set. Two anticyclonic (ACE1/2), one mode-water (MWE), and one cyclonic eddy (CE) are identified and followed in detail with satellite data on their westward transition with velocities of 3.2 to 6.0 cm s−1 from their generation region, the shelf of the Peruvian and Chilean upwelling regime, across the Stratus Ocean Reference Station (ORS; ∼20∘ S, 85∘ W) to their decaying region far west in the oligotrophic open ocean. The ORS is located in the transition zone between the oxygen minimum zone and the well oxygenated South Pacific subtropical gyre. Velocity, hydrographic, and oxygen measurements at the mooring show the impact of eddies on the weak flow region of the eastern tropical South Pacific. Strong anomalies are related to the passage of eddies and are not associated with a seasonal signal in the open ocean. The mass transport of the four observed eddies across 85∘ W is between 1.1 and 1.8 Sv. The eddy type-dependent available heat, salt, and oxygen anomalies are 8.1×1018 J (ACE2), 1.0×1018 J (MWE), and -8.9×1018 J (CE) for heat; 25.2×1010 kg (ACE2), -3.1×1010 kg (MWE), and -41.5×1010 kg (CE) for salt; and -3.6×1016 µmol (ACE2), -3.5×1016 µmol (MWE), and -6.5×1016 µmol (CE) for oxygen showing a strong imbalance between anticyclones and cyclones for salt transports probably due to seasonal variability in water mass properties in the formation region of the eddies. Heat, salt, and oxygen fluxes out of the coastal region across the ORS region in the oligotrophic open South Pacific are estimated based on these eddy anomalies and on eddy statistics (gained out of 23 years of satellite data). Furthermore, four profiling floats were trapped in the ACE2 during its westward propagation between the formation region and the open ocean, which allows for conclusions on lateral mixing of water mass properties with time between the core of the eddy and the surrounding water. The strongest lateral mixing was found between the seasonal thermocline and the eddy core during the first half of the eddy lifetime.

scholarly journals Random movement of mesoscale eddies in the global ocean

2020 ◽  
Author(s):  
Xiaoming Zhai ◽  
Qinbiao Ni ◽  
Guihua Wang ◽  
David Marshall
Keyword(s):  
Isotropic Turbulence ◽  
Mesoscale Eddy ◽  
Lateral Diffusion ◽  
Mesoscale Eddies ◽  
Global Ocean ◽  
Altimeter Data ◽  
High Latitudes ◽  
Turbulence Regime ◽  
Low Latitudes ◽  
Baroclinic Rossby Wave

&lt;p&gt;In this study we track and analyze eddy movement in the global ocean using 20 years of altimeter data and show that, in addition to the well-known westward propagation and slight polarity-based meridional deflections, mesoscale eddies also move randomly in all directions at all latitudes as a result of eddy-eddy interaction. The speed of this random eddy movement decreases with latitude and equals the baroclinic Rossby wave speed at about 25&amp;#176; of latitude. The tracked eddies are on average isotropic at mid and high latitudes, but become noticeably more elongated in the zonal direction at low latitudes. Our analyses suggest a critical latitude of approximately 25&amp;#176; that separates the global ocean into a low-latitude anisotropic wavelike regime and a high-latitude isotropic turbulence regime. One important consequence of random eddy movement is that it results in lateral diffusion of eddy energy. The associated eddy energy diffusivity, estimated using two different methods, is found to be a function of latitude. The zonal-mean eddy energy diffusivity varies from over 1500 m&lt;sup&gt;2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt; at low latitudes to around 500 m&lt;sup&gt;2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt; at high latitudes, but significantly larger values are found in the eddy energy hotspots at all latitudes, in excess of 5000 m&lt;sup&gt;2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;. Results from this study have important implications for recently-developed energetically-consistent mesoscale eddy parameterization schemes which require solving the eddy energy budget. &amp;#160;&lt;/p&gt;

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