Pérez-Hernández
M. Dolores
Pérez-Hernández
M. Dolores
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ArticleCharacteristics and evolution of an Agulhas ring(John Wiley & Sons, 2017-09-01) Casanova-Masjoan, Maria ; Pelegrí, Josep ; Sangrà, Pablo ; Martínez-Marrero, Antonio ; Grisolía-Santos, Diana ; Pérez-Hernández, M. Dolores ; Hernández-Guerra, AlonsoA South Atlantic ring is studied through remote sensing altimetry, hydrographic stations, and drifters' trajectories. The ring's core was characterized by warmer and saltier Indian Ocean waters. At the time of the cruise, the ring's signature extended radially out to 124 km and vertically down to 2000 m, and its core absolute dynamic topography (ADT) exceeded the surrounding Atlantic Ocean waters in 0.4 m. The geostrophic velocities were anticyclonic with maximum speeds about 35 cm s−1 at 100 m and reaching negligible values near 4500 m. The rotational transport inside the ring was 33 Sv in the thermocline and intermediate layers. The drifters' data distinguish a 30-km core revolving as a solid body with periodicity near 5 days and a transitional band that revolves with constant tangential velocity, resembling a Rankine vortex. The ADT data identify the ring's track, showing that it was shed by the Agulhas Current retroflection in November 2009 and propagated northwest rapidly during the first 2 months (mean speed of about 10 cm s−1) but slowed down substantially (3–4 cm s−1) between March and July 2010, when it was last detected. The altimetry data also outlines the evolution of the ring's core ADT, radius, vorticity, and, through a simple calibration with the cruise data, rotational transport. In particular, the ring surface and vertical-mean vorticity decay with time scales of 373 and 230 days, respectively, indicating that most of the property anomalies contained by the ring are diffused out to the subtropical gyre before it reaches the western boundary current system.
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ArticleVariability and redistribution of heat in the Atlantic Water boundary current north of Svalbard(John Wiley & Sons, 2018-09-12) Renner, Angelika H. H. ; Sundfjord, Arild ; Janout, Markus A. ; Ingvaldsen, Randi B. ; Beszczynska-Möller, Agnieszka ; Pickart, Robert S. ; Pérez-Hernández, M. DoloresWe quantify Atlantic Water heat loss north of Svalbard using year‐long hydrographic and current records from three moorings deployed across the Svalbard Branch of the Atlantic Water boundary current in 2012–2013. The boundary current loses annually on average 16 W m−2 during the eastward propagation along the upper continental slope. The largest vertical fluxes of >100 W m−2 occur episodically in autumn and early winter. Episodes of sea ice imported from the north in November 2012 and February 2013 coincided with large ocean‐to‐ice heat fluxes, which effectively melted the ice and sustained open water conditions in the middle of the Arctic winter. Between March and early July 2013, a persistent ice cover‐modulated air‐sea fluxes. Melting sea ice at the start of the winter initiates a cold, up to 100‐m‐deep halocline separating the ice cover from the warm Atlantic Water. Semidiurnal tides dominate the energy over the upper part of the slope. The vertical tidal structure depends on stratification and varies seasonally, with the potential to contribute to vertical fluxes with shear‐driven mixing. Further processes impacting the heat budget include lateral heat loss due to mesoscale eddies, and modest and negligible contributions of Ekman pumping and shelf break upwelling, respectively. The continental slope north of Svalbard is a key example regarding the role of ocean heat for the sea ice cover. Our study underlines the complexity of the ocean's heat budget that is sensitive to the balance between oceanic heat advection, vertical fluxes, air‐sea interaction, and the sea ice cover.
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ArticleOrganic carbon budget for the eastern boundary of the North Atlantic subtropical gyre : major role of DOC in mesopelagic respiration(Nature Publishing Group, 2017-08-31) Santana-Falcón, Yeray ; Álvarez-Salgado, Xosé Antón ; Pérez-Hernández, M. Dolores ; Hernández-Guerra, Alonso ; Mason, Evan ; Arístegui, JavierTransports of suspended particulate (POCsusp) and dissolved (DOC) organic carbon are inferred from a box-model covering the eastern boundary of the North Atlantic subtropical gyre. Corresponding net respiration rates (R) are obtained from a net organic carbon budget that is based on the transport estimates, and includes both vertical and lateral fluxes. The overall R in the mesopelagic layer (100–1500 m) is 1.6 ± 0.4 mmol C m−2 d−1. DOC accounts for up to 53% of R as a result of drawdown of organic carbon within Eastern North Atlantic Central Water (ENACW) that is entrained into sinking Mediterranean Overflow Water (MOW) that leads to formation of Mediterranean water (MW) at intermediate depths (~900 m). DOC represents 90% of the respired non-sinking organic carbon. When converted into oxygen units, the computed net respiration rate represents less than half the oxygen utilization rates (OUR) reported for the mesopelagic waters of the subtropical North Atlantic. Mesoscale processes in the area, not quantified with our approach, could account in part for the OUR differences observed between our carbon budget and other published studies from the North Atlantic, although seasonal or interannual variability could also be responsible for the difference in the estimates.
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ArticleStructure, transport, and seasonality of the Atlantic Water boundary current north of Svalbard: Results from a yearlong mooring array(American Geophysical Union, 2019-02-15) Pérez-Hernández, M. Dolores ; Pickart, Robert S. ; Torres, Daniel J. ; Bahr, Frank B. ; Sundfjord, Arild ; Ingvaldsen, Randi B. ; Renner, Angelika H. H. ; Beszczynska-Möller, Agnieszka ; von Appen, Wilken‐Jon ; Pavlov, VladimirThe characteristics and seasonality of the Svalbard branch of the Atlantic Water (AW) boundary current in the Eurasian Basin are investigated using data from a six‐mooring array deployed near 30°E between September 2012 and September 2013. The instrument coverage extended to 1,200‐m depth and approximately 50 km offshore of the shelf break, which laterally bracketed the flow. Averaged over the year, the transport of the current over this depth range was 3.96 ± 0.32 Sv (1 Sv = 106 m3/s). The transport within the AW layer was 2.08 ± 0.24 Sv. The current was typically subsurface intensified, and its dominant variability was associated with pulsing rather than meandering. From late summer to early winter the AW was warmest and saltiest, and its eastward transport was strongest (2.44 ± 0.12 Sv), while from midspring to midsummer the AW was coldest and freshest and its transport was weakest (1.10 ± 0.06 Sv). Deep mixed layers developed through the winter, extending to 400‐ to 500‐m depth in early spring until the pack ice encroached the area from the north shutting off the air‐sea buoyancy forcing. This vertical mixing modified a significant portion of the AW layer, suggesting that, as the ice cover continues to decrease in the southern Eurasian Basin, the AW will be more extensively transformed via local ventilation.
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ArticleZonal circulation in the North Atlantic ocean at 52°W from WOCE-WHP and CLIVAR sections: 1997, 2003 and 2012(Elsevier, 2023-06-17) Santana-Toscano, Daniel ; Perez-Hernandez, M. Dolores ; Macdonald, Alison M. ; Arumi-Planas, Cristina ; Cainzos, Veronica ; Hernandez-Guerra, AlonsoThe A20 line is a meridional hydrographic section located at 52°W that cuts through the western North Atlantic Subtropical Gyre (NASG). It encloses the main paths of the Atlantic Meridional Overturning Circulation (AMOC). Using data from three A20 hydrographic cruises carried out in 1997, 2003 and 2012 together with Acoustic Doppler Current Profiler data and the velocities from an inverse box model, the circulation of the western NASG is estimated. The Gulf Stream is the main poleward path of the AMOC, carrying 155.3 ± 11.1, 102.7 ± 13.5 and 181.1 ± 14.9 Sv in 1997, 2003 and 2012, respectively (1 Sv = 106 m3/s ∼ 109 kg/s). In opposite direction, the Deep Western Boundary Current crosses the section at the northern/southern boundaries with a mass transport of −21.2 ± 8.9/29.0 ± 9.1, −14.4 ± 10.8/14.2 ± 8.1 and −37.9 ± 10.2/44.5 ± 9.8 Sv in 1997, 2003 and 2012, respectively. A net heat exchange from the ocean to the atmosphere is estimated to be −0.7 ± 0.1 PW and −0.6 ± 0.1 PW in 1997 and 2012, respectively, but is negligible in 2003 (0.1 ± 0.1 PW). The freshwater flux is significantly lower in 2003 (0.3 ± 0.1 Sv) than in 1997 (0.6 ± 0.1 Sv) and 2012 (0.6 ± 0.1 Sv). Ocean numerical models such as ECCO, GLORYS and MOM are used to address the interannual variability between the three surveys, but only the GLORYS output roughly agrees with the hydrographic data. GLORYS suggests a heat transport from the ocean to the atmosphere throughout the year and a net freshwater flux supported by precipitation plus river runoff higher than evaporation in all seasons except the spring.