4 results on '"Giddings, Sarah N."'
Search Results
2. Estuary‐enhanced upwelling of marine nutrients fuels coastal productivity in the U.S. Pacific Northwest
- Author
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Davis, Kristen A, Banas, Neil S, Giddings, Sarah N, Siedlecki, Samantha A, MacCready, Parker, Lessard, Evelyn J, Kudela, Raphael M, and Hickey, Barbara M
- Subjects
Life Below Water ,estuarine circulation ,primary productivity ,Pacific Northwest ,Strait of Juan de Fuca ,Columbia River ,nitrogen ,Geophysics ,Oceanography ,Physical Geography and Environmental Geoscience - Abstract
The Pacific Northwest (PNW) shelf is the most biologically productive region in the California Current System. A coupled physical-biogeochemical model is used to investigate the influence of freshwater inputs on the productivity of PNW shelf waters using realistic hindcasts and model experiments that omit outflow from the Columbia River and Strait of Juan de Fuca (outlet for the Salish Sea estuary). Outflow from the Strait represents a critical source of nitrogen to the PNW shelf-accounting for almost half of the primary productivity on the Vancouver Island shelf, a third of productivity on the Washington shelf, and a fifth of productivity on the Oregon shelf during the upwelling season. The Columbia River has regional effects on the redistribution of phytoplankton, but does not affect PNW productivity as strongly as does the Salish Sea. A regional nutrient budget shows that nitrogen exiting the Strait is almost entirely (98%) of ocean-origin - upwelled into the Strait at depth, mixed into surface waters by tidal mixing, and returned to the coastal ocean. From the standpoint of nitrogen availability in the coastal euphotic zone, the estuarine circulation driven by freshwater inputs to the Salish Sea is more important than the supply of terrigenous nitrogen by rivers. Nitrogen-rich surface waters exiting the Strait follow two primary pathways - to the northwest in the Vancouver Island Coastal Current and southward toward the Washington and Oregon shelves. Nitrogen flux from the Juan de Fuca Strait and Eddy Region to these shelves is comparable to flux from local wind-driven upwelling.
- Published
- 2014
3. Generation of Low‐Latitude Seamount‐Trapped Waves: A Case Study of the Seychelles Plateau
- Author
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Arzeno‐Soltero, Isabella B., Giddings, Sarah N., Pawlak, Geno, McClean, Julie L., Wang, He, Rainville, Luc, and Lee, Craig M.
- Abstract
Baroclinic seamount‐trapped waves are thought to influence their surrounding ecosystem; however, trapped waves are not well‐studied in near‐equatorial settings, where stratification is strong and Burger numbers (S=N2H2f2LH2)are large. Motivated by observations, we use daily output (2005–2009) from the global Parallel Ocean Program Model (POP) to examine topographically trapped baroclinic waves around the Seychelles Plateau (S>400) in the tropical Indian Ocean. These trapped waves are associated with velocity and temperature oscillations at periods of 15–16 days, similar to the dominant period of some equatorial Yanai waves. Energy flux maps using POP output suggest that quasi‐biweekly equatorial Yanai waves excite trapped waves on the western and south‐western flanks of the Seychelles Plateau, near the surface. The anticyclonic energy flux associated with the trapped wave extends vertically throughout the water column and around most of the plateau circumference, diminishing on the eastern flank of the plateau. This work highlights the role that equatorial planetary waves and trapped waves play in facilitating energy redistribution, dissipation, and mixing in the tropical ocean. Oceanic internal waves (waves in the interior of the ocean) that propagate around seamounts are thought to contribute to ecological productivity, yet there is a lack of research on the dynamics of these processes in the tropics. We refer to these particular internal oscillations as “trapped waves” because they propagate along a topographic slope, rather than radiating away in the ocean as free waves. Motivated by observations, we use five years (2005–2009) of daily output from a global numerical model (POP) to study trapped waves around the Seychelles Plateau in the tropical Indian Ocean. These oscillations cause changes in the velocity and temperature at periods of 15–16 days, resembling the dominant periods of some waves along the equator (Yanai waves). We created maps of energy pathways using POP output; these suggest that Yanai waves excite the plateau‐trapped waves near the surface, along the western and south‐western flanks of the plateau. The trapped waves propagate energy vertically throughout the water column and around the plateau until they reach the eastern side of the plateau, where the energy decays. This work highlights the role of equatorial waves and trapped waves in redistributing energy, and facilitating turbulence and mixing in the tropical ocean. Model output suggests Yanai waves generate trapped waves around the Seychelles PlateauYanai wave energy flux is surface‐intensified along the western and south‐western plateau edgesTrapped waves flux energy throughout the water column and around the plateau circumference Model output suggests Yanai waves generate trapped waves around the Seychelles Plateau Yanai wave energy flux is surface‐intensified along the western and south‐western plateau edges Trapped waves flux energy throughout the water column and around the plateau circumference
- Published
- 2021
- Full Text
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4. Observations and Modeling of Ocean Circulation in the Seychelles Plateau Region
- Author
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Castillo‐Trujillo, Alma Carolina, Arzeno‐Soltero, Isabella B., Giddings, Sarah N., Pawlak, Geno, McClean, Julie, and Rainville, Luc
- Abstract
The ocean circulation around and over the Seychelles Plateau (SP) is characterized using 35 months of temperature and velocity measurements along with a numerical model. The results here provide the first documented description of the ocean circulation atop the SP. The SP is an unusually broad (∼200 km), shallow (∼50 m) plateau, dropping off steeply to the abyss. It is situated in a dynamic location (3.5–5.5°S, 54‐57°E) in the south‐western tropical Indian Ocean where northwesterly winds are present during austral summer and become southeasterly in austral winter, following the reversal of the western Indian ocean monsoon winds. Measurements around the Inner Islands, on the SP, have been carried out since 2015. Velocity measurements show that most of the depth‐averaged current variance on the SP arises from near‐inertial oscillations and lower‐frequency variability. Lower‐frequency variability encompasses seasonal and intraseasonal variability, the latter of which includes the effects of mixed Rossby‐gravity waves and mesoscale eddies. A global 0.1° numerical ocean simulation is used in conjunction with these observations to describe the regional circulation around the SP. Atop the SP, circulation is dominated by ageostrophic processes consistent with Ekman dynamics, while around the SP, both geostrophic and ageostrophic processes are important and vary seasonally. Stratification responds to the sea surface height semiannual signal which is due to Ekman pumping‐driven upwelling (related to the Seychelles‐Chagos Thermocline Ridge) and the arrival of an annual downwelling Rossby wave. This study characterizes the Seychelles Plateau (SP) circulation using 35 months of temperature and velocity measurements and a global numerical model. The SP is an unusually broad shallow plateau (∼50 m), situated in the south‐western tropical Indian Ocean. In this region, ocean and climate dynamics are strongly modulated by the western Indian Ocean monsoon signal, with northwesterly winds from December to March, and southeasterly winds from April to November. Model results show that the seasonal circulation is dominated by local wind‐driven processes at the peak of the monsoons (December to February and June to August), while the rest of the year, circulation is controlled by a combination of local and remote atmospheric and oceanic processes. Atop the Plateau, oscillations with periods similar to the rotation rate of the earth at this latitude (∼6 days) and planetary‐scale waves traveling along the equator are important contributors to the ocean circulation. Temperature observations taken near the island of Mahé, show the warmest water in April and May (>29° C) and the coldest water in July and August (<26° C). The results here will aid regional navigation and will contribute to an improved understanding of regional models and biogeochemical cycles and fisheries over the SP region. Circulation around and atop the broad, shallow Seychelles Plateau is described using a series of observations and a numerical modelCirculation on the Plateau is dominated by near‐inertial oscillations and intraseasonal variability connected to the mesoscale circulationSea surface height seasonal variations atop the Plateau are modulated by Ekman pumping and an annual downwelling Rossby wave Circulation around and atop the broad, shallow Seychelles Plateau is described using a series of observations and a numerical model Circulation on the Plateau is dominated by near‐inertial oscillations and intraseasonal variability connected to the mesoscale circulation Sea surface height seasonal variations atop the Plateau are modulated by Ekman pumping and an annual downwelling Rossby wave
- Published
- 2021
- Full Text
- View/download PDF
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