Abstract

Jang-Geun Choi
Many marine ecosystem models assume that nitrogen is the limiting nutrient for primary production and that nutrient components follow Redfield stoichiometry. Research focus is often on resolving physical-ecological dynamics in large-scale pelagic ocean settings where primary production depends on nitrogen transport into the surface euphotic layer. However, many ecosystem models cannot resolve dynamics in the shallow coastal ocean. Observations show that coastal waters are productive and include high concentration of phytoplankton and nutrients; however, many model simulations predict that oligotrophic coastal waters will have low phytoplankton concentration, even if the model contains forcing by river discharge with large nitrogen loading. In this study, we use Nutrient-Phytoplankton-Zooplankton-Detritus model (NPZD; Franks et al., 1986) with the Regional Ocean Modeling System (ROMS; Shchepetkin and McWilliams, 2005), and show that the shallow water problem is caused by bottom boundary conditions for ecological tracers that poorly resolve interactions between seabed sediments and water. An idealized coastal ocean is simulated with the coupled physical-ecological ecosystem model to resolve the shallow water region. Sensitivity experiments are conducted for various bottom boundary conditions. Results show that proper parameterization for sediment-water mass exchange and sediment denitrification process is required to resolve coastal ecosystem dynamics.

Katie Kirk
Tidal currents in narrow inlets and channels can have horizontal velocity gradients that produce instabilities in the flow (so-called shear waves) that can lead to the spinoff of large eddies. The resulting vortices, or eddies, may impact transport of organic or inorganic matter and cause mixing of momentum in coastal estuaries. We analytically solved for linear shear instabilities of tidal currents in narrow estuarine channels following Bowen and Holman (1989), differing in boundary conditions that lead to an additional extremum in background vorticity. The characteristic frequencies, growth rates, and wavelengths of the fastest growing shear wave modes are determined as a function of the cross-channel structure and speed of the along-channel tidal current in this theoretical analysis.

Josh Humberston
Observations of currents and water pressure obtained at 7 locations within Oregon Inlet, NC, over a 40-day period in the spring of 2019 showed subtidal water level oscillations on the sound side of the inlet with magnitudes often exceeding typical tidal ranges. These oscillations, which are correlated with regional wind patterns, induce cross-shore gradients in sea surface slope from the back bay to the ocean that are strongly coupled to inlet current modulations at subtidal frequencies. Owing to their longer temporal scale, the sub-tidal gradients often combine with typical tidal flows to accelerate one phase while retarding or entirely reversing the other. Concurrent observations of bedform migration on the ebb-tidal delta, obtained with x-band radar, suggest these current modifications at sub-tidal frequencies may be important to sediment transport patterns in the inlet and on the ebb-tidal delta. The role of subtidal oscillations on large scale morphologic evolution is further examined through an idealized numerical model that couples hydrodynamics, waves, and sediment transport through the Delft3D modelling suite implemented at Oregon Inlet over observed bathymetry. The nature of the morphologic development of the inlet is discussed in terms of the presence or absence of subtidal oscillations. This work was supported by a DOD SMART Fellowship, UNH, the USACE CIRP program and the USACE Field Research Facility in Duck, NC.

Presenter Bio

Jang-Geun Choi
Jang is a graduate of Pusan Univeristy in South Korea. He is currently pursuing a Ph.D. in Oceanography at UNH with Dr. Thomas Lippmann.

Katie Kirk
Katie earned a B.Sc. in Science of Earth Systems with a concentration in Ocean Sciences from Cornell University. She went on to earn a Master of Engineering in Ocean Sciences & Technology in a joint program between Cornell University and Woods Hole Oceanographic Institution. Since graduation, Katie has participated in various oceanographic research cruises and worked as the Lead Engineer of the NOAA Chesapeake Bay Interpretive Buoy System. Katie currently works as an Oceanographer for NOAA National Ocean Service's Center for Operational Oceanographic Products and Services (CO-OPS) on the Coastal and Estuarine Circulation Analysis Team (CECAT) and Storm QuickLook team. On CECAT, she primarily works as a project lead of current surveys along the coastal U.S. in an effort to update the tidal current predictions. Katie supports the QuickLook team by generating products that provide near real-time oceanographic and meteorological observations during storm events. Katie is continuing her work with NOAA CO-OPS while pursuing a Ph.D. in Oceanography at UNH as an advisee to Dr. Tom Lippmann.

Josh Humberston
Josh completed his B.S. in geology with a concentration in coastal and marine geosciences at the University of Delaware. Through a NSF-funded Research Experience for Undergraduates (REU) and his senior thesis research project, he used naturally occurring radionuclides that adsorb to fine grain sediment to predict seasonal deposition patterns in the Delaware Estuary. He then completed an M.S. in oceanography at UNH through CCOM/JHC where his research focused on predicting surficial mud fraction in the Little Bay estuary using a statistical decomposition of single-beam sonar data. Following that, Josh spent some time on NOAA’s Okeanos Explorer as a hydrographer and then completed a year of Ph.D. work at Coastal Carolina University in Conway, South Carolina where he worked analyzing radar observations of surface waves. Josh spent a summer working with the US Army Corps of Engineers at their Coastal and Hydraulics field facility in Duck, NC through the PATHWAYS program. Josh then received a SMART scholarship through the Department of Defense (DoD) and has returned to UNH to complete his Ph.D. in oceanography. His research will take an interdisciplinary approach to better explain shore-oblique sandbars: how and where form and how they evolve. He will also explore tidal inlet ebb-shoals evolution and the varying sediment pathways hosted in these systems. Josh's research interests include coastal morphodynamics (sandbar and shoal evolution), coastal influence of ocean surface waves, coastal geologic influences, estuarine sediment dynamics, and remote sensing (acoustic and X-band radar).

Publication Date

2-14-2020

Document Type

Presentation

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