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Estuarine Responses to Long‐Term Changes in Inlets, Morphology, and Sea Level Rise


Abstract and Figures

Pamlico Sound, a large back-barrier estuary in North Carolina, is under threat of climate change due to increased storm activity and sea-level rise. The response of this system is investigated by considering what has already happened during changes in sea-level over the late Holocene epoch. The hydrodynamic changes that occurred in response to geomorphic evolution are simulated using a 3D numerical model for four distinct ‘time-slice’ scenarios. To accomplish this, the present-day bathymetry was obtained from a high resolution digital elevation model, and paleo-bathymetric grids were developed from sediment cores and seismic observations. Using the same hydrodynamic forcing for each geomorphic scenario, the models are compared to assess the combined response to: different inlets connecting the back-barrier estuary to the ocean; changes in basin geomorphology due to sedimentation; and sea-level rise. The results indicate that these factors have a considerable effect on hydrodynamics, waves, and salinity in the estuary. The time-averaged tidal ranges were up to three times as high for the past environments in comparison with present day water level elevations, and maximum current velocities were over three times higher in regions close to paleo-inlets. The simulations for each time-slice suggest that the salinity distribution in Pamlico Sound is strongly influenced by the hydraulic connectivity with other estuaries, and the number and size of tidal inlets through the barrier island system. The results indicate that changes to barrier systems induce strong, non-uniform and complex responses in back-barrier estuaries with regime-shifts in hydrodynamic energy and water mass properties.
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Estuarine Responses to LongTerm Changes in Inlets,
Morphology, and Sea Level Rise
Ryan P. Mulligan
, David J. Mallinson
, Gregory J. Clunies
, Alexander Rey
, Stephen J. Culver
Nick Zaremba
, Eduardo Leorri
, and Siddhartha Mitra
Department of Civil Engineering, Queen's University, Kingston, Ontario, Canada,
Department of Geological Sciences,
East Carolina University, Greenville, NC, USA,
Department of Earth Sciences, Syracuse University, Syracuse, NY, USA
Abstract Pamlico Sound, a large backbarrier estuary in North Carolina, is under threat of climate
change due to increased storm activity and sea level rise. The response of this system is investigated by
considering what has already happened during changes in sea level over the late Holocene epoch. The
hydrodynamic changes that occurred in response to geomorphic evolution are simulated using a 3D
numerical model for four distinct timeslicescenarios. To accomplish this, the presentday bathymetry
was obtained from a highresolution digital elevation model, and paleobathymetric grids were developed
from sediment cores and seismic observations. Using the same hydrodynamic forcing for each geomorphic
scenario, the models are compared to assess the combined response to: different inlets connecting the
backbarrier estuary to the ocean, changes in basin geomorphology due to sedimentation, and sea level rise.
The results indicate that these factors have a considerable effect on hydrodynamics, waves, and salinity in
the estuary. The timeaveraged tidal ranges were up to 3 times as high for the past environments in
comparison with presentday water level elevations, and maximum current velocities were over 3 times
higher in regions close to paleoinlets. The simulations for each time slice suggest that the salinity
distribution in Pamlico Sound is strongly inuenced by the hydraulic connectivity with other estuaries and
the number and size of tidal inlets through the barrier island system. The results indicate that changes to
barrier systems induce strong, nonuniform, and complex responses in backbarrier estuaries with regime
shifts in hydrodynamic energy and water mass properties.
1. Introduction
Climate change has signicant implications for the coastal and marine ecosystems and associated socioeco-
nomic systems of coastal communities that depend on them (Harley et al., 2006). Lowlying coastal zones,
which contain a disproportionally high percentage of the world's population in a relatively small land area
(McGranahan et al., 2007), are at risk from climate change and associated sea level rise (SLR). Rising sea
level can lead to the inundation, erosion, and migration of natural coastal landforms and affect the salinity
distributions in coastal bays and estuarine systems (Scavia et al., 2002). Lowlying coastal areas are suscep-
tible to increasing frequency in barrier overwash and erosion due to SLR (Bernstein et al., 2007), in combi-
nation with projected increasing tropical cyclone frequency arising from climate change (Mann et al., 2009;
Smith, 1999). There is evidence of major geomorphological changes in the past along the U.S. East Coast, as
widespread barrier island segmentation coincides with a peak in Atlantic hurricane activity during the
Medieval Climate Anomaly (MCA) ~1,100 to 900 calibrated years before present (cal yr BP) (Culver et al.,
2007; Donnelly et al., 2015; Donnelly & Woodruff, 2007; Grand Pre et al., 2011; Mallinson et al., 2011;
Mann et al., 2009) and increased rate of SLR (González & Törnqvist, 2009; Kemp et al., 2009, 2011, 2017).
Understanding the impacts of climate change and SLR on these dynamic systems is critical to the manage-
ment of rapidly developing coastal communities.
Numerical models are tools that can be used to advance our understanding of the hydrodynamic conditions
that may likely have occurred corresponding to different geomorphic settings over long time scales of hun-
dreds to thousands of years. SLR has contributed to dramatic changes of the coastal landscape over the
Holocene and a review of hydrodynamic response of coastal systems to SLR is provided by Passeri et al.
(2015). To assess the impacts of SLR on storm surge ooding over a shorter time scale, Bilskie et al. (2014)
used the Advanced Circulation model at three modernday times (1960, 2005, and 2050) with alterations
to bathymetry, land use, and land cover of the coast to demonstrate the nonlinearity of coastal ooding
©2019. American Geophysical Union.
All Rights Reserved.
Key Points:
A modeling approach is developed
for simulating the response of an
estuary to different
geomorphological conditions over a
long time scale
Geological observations were used
to dene inlet locations, basin
morphology, and sea levels in the
hydrodynamic model
The results indicate controls on the
water levels, current velocities, and
salinity distributions in
paleoestuarine environments
Correspondence to:
R. P. Mulligan,
Mulligan, R. P., Mallinson, D. J.,
Clunies, G. J., Rey, A., Culver, S. J.,
Zaremba, N., et al. (2019). Estuarine
responses to longterm changes in
inlets, morphology and sea level rise.
Journal of Geophysical Research:
Received 31 OCT 2018
Accepted 17 NOV 2019
Accepted article online 28 NOV 2019
Oceans,124, https://
Published online 17 DEC 2019
driven by SLR and hurricanedriven storm surge. In the Wadden Sea, a large backbarrier estuarine system,
the sediment transport patterns have been simulated using the Delft3D model in response to extensive
coastal defense work over the last 400 yr (Elias & van der Spek , 2006) and in response to future SLR over
the next 100 yr (Wang et al., 2018). These studies highlight the interdependency between barrier island tidal
inlets and the backbarrier morphology. Moran et al. (2014) used the Delft3D model to investigate the geo-
logic evolution of Currituck Sound, a lagoon associated with the AlbemarlePamlico Estuarine System
(APES) in North Carolina, USA. The hydrodynamic model was used to simulate tidal ows at time intervals
spanning 4,000 yr using bathymetry developed from geologic observations, with results indicating that
strong tidal currents in Currituck Sound were constrained to the immediate surroundings of the inlets.
The North Carolina coast is dominated by ocean beaches along the Outer Banks barrier island chain that
protect the system of interconnected backbarrier estuaries. Previous geological studies have focused on
the Holocene geologic evolution of the APES, and it has been shown that signicant changes to the Outer
Banks barrier island chain have occurred in the past, based on geophysical and sediment core observations
(Culver et al., 2007; Grand Pre et al., 2011; Mallinson et el., 2010, 2011; Zaremba et al., 2016). A detailed ana-
lysis of marsh cores and SLR in the APES is given by Kemp et al. (2017). Morphological changes of this
coastal region began around 9,000 cal yr BP with the ooding of incised uvial valleys due to rapidly rising
relative sea level (~5 mm/yr; Horton et al., 2009) and formation of a broad estuary protected by lowlying
barrier islands (Mallinson et al., 2018; Zaremba et al., 2016). Grain sizes and foraminiferal assemblages in
sediment cores indicate that over time conditions in the system shifted regimes. The regime shifts are from
a lowenergy brackishsalinity estuarine environment with extensive barrier island protection and few inlets
to a higherenergy high salinity coastal marine environment and signicant segmentation of the barrier
islands (Culver et al., 2007; Grand Pre et al., 2011). Increased hurricane frequency during the MCA likely
resulted in a temporary segmentation due to breaching of the southern Outer Banks barrier islands allowing
for increased marine inuence in the backbarrier estuarine environment (Culver et al., 2007). Over the past
500 yr, estuarine deposits continued to accumulate (Peek et al., 2014) coinciding with a lower rate of relative
SLR from ~500 to 100 cal yr BP (Kemp et al., 2009) and the reestablishment of the barrier islands and low
energy backbarrier estuary of the present day. The presentday salinity distributions throughout the APES
have been described through observations and modeling studies. Wells and Kim (1989) synthesized histor-
ical observations and prescribed climatological mean surface salinity maps for the APES during both spring
(April) and fall (October) seasons. Jia and Li (2012) used the Regional Ocean Modeling System to determine
circulation dynamics and salt balance within the APES, nding that salinity is controlled by the relative
strength of inputs of freshwater from the four major rivers in comparison to the saltwater inows occurring
at inlets as a result of tidal pumping. Brown et al. (2014) used the Delft3D numericalmodel to simulate fresh-
water and dissolved organic carbon transport in the Neuse River Estuary, a subestuary of the APES, demon-
strating the importance of stratication in the Neuse River Estuary and indicating a wellmixed water
column at the estuary mouth in Pamlico Sound.
The objective of this study is to understand the responses in Pamlico Sound to periods of widespread barrier
island segmentation that have occurred in the past, in order to develop knowledge of potential future
changes that may occur as barrier island continuity and estuary morphology respond to SLR and storms.
To achieve this, paleobathymetric data presented in Zaremba et al. (2016) were used with varying barrier
island/inlet congurations developed from sedimentary and geophysical data (Culver et al., 2006 , 2007;
Grand Pre et al., 2011; Mallinson et al., 2011). These data are used to dene four distinct geomorphic condi-
tions that occurred during the evolution of this coastal system and coupled numerical models are used to
numerically simulate the hydrodynamics and waves corresponding to each scenario. This investigation
demonstrates the signicance of geomorphic changes to physical processes that broadly affect erosion, sedi-
ment transport and accumulation, as well as ecosystems via changes from estuarine to marine salinity con-
ditions. The application of this method is important for a more thorough interpretation of the geological
record in coastal systems, as well as for understanding the range of possible future changes.
2. Observations
Presentday observations of winds, water levels, currents, river discharge, salinity, and sediment character-
istics were collected at various locations throughout Pamlico Sound (Figure 1a). Geophysical and core
Journal of Geophysical Research: Oceans
derived stratigraphic, lithologic, and micropaleontological observations (Figure 1b) were used to produce
paleobathymetric maps. These maps represent the estuarine geomorphology at four distinct times, herein
referred to as geomorphic timeslicescenarios, over the last 4,000 yr (Culver et al., 2007; Foley, 2007;
Metger, 2009; Grand Pre et al., 2011; Mallinson et al., 2010, 2011; Mallinson et al., 2018; Zaremba et al.,
2016) each referenced to the presentday mean sea level vertical datum. In particular, Culver et al. (2007)
provide the overall interpretation of sediment core data and describe the segmentation of the Outer Banks
barrier islands system twice during the late Holocene, with subsequent work (Grand Pre et al., 2011) that
describes the detailed geological observations, interpretations, and implications. Detailed descriptions of
the presentday hydrodynamic observations are presented in Clunies et al. (2017) and the geological
observations are presented in detail in Zaremba et al. (2016). Paleoinlet locations and size are based on
data from Culver et al. (2007), Grand Pre et al. (2011), and Mallinson et al. (2010, 2011). The approach
adopted in the present study is to use a numerical model with high temporal resolution to elucidate the
hydrodynamics over a short time scale that results from the major differences in bathymetry that are
dened by geologic interpretation over a long time scale.
A12month time period (corresponding to 1 October 2007 to 30 September 2008) is used to examine the
winds, ocean water levels, and inows from the four major rivers that drive the hydrodynamic conditions
in the APES. Hourly observations of wind components (u, v) observed at Diamond Shoals (DS; National
Data Buoy Center Buoy 41025) are shown in Figure 2a. Hourly water levels in the ocean were obtained from
National Data Buoy Center stations DUKN7 (FO) at Duck and BFTN7 (BF) at Beaufort (Figure 2b); locations
shown in Figure 1a. River discharges gauged at a temporal resolution of 15 min were obtained in the Neuse
River Estuary (NRE) at U.S. Geological Survey (USGS Station 02091814) near Fort Barnwell and in the Tar
Pamlico River Estuary (TPRE) near Washington (USGS Station 0204472) (shown in Figure 2c). Data for the
ow rates of the Roanoke and Chowan rivers are not shown for clarity; however, they are smaller than the
ows entering the NRE and TPRE and were input to the numerical model. Water levels and current
Figure 1. Bathymetry of the APES showing: (a) location of hydrodynamic observations (FO, BF, and P2), selected sediment cores (C1 and C2), wind observations
(DS), the TarPamlico River Estuary (TPRE), and the Neuse River Estuary (NRE); (b) constrained seismic grid (black lines) and sediment core sites (circles) in
Pamlico Sound.
Journal of Geophysical Research: Oceans
velocities were observed in Pamlico Sound using a Nortek Acoustic Doppler Velocimeter at P2 (5.0m mean
water depth), which burst sampled for 4 min out of every hour at a rate of 8 Hz and was deployed at selected
times in 20072008.
Salinity observations were obtained from three sources, discussed in more detail in sections 3.3 and 4.3. The
data sources include the University of North Carolina modeling and monitoring (MODMON) project with
observations throughout the water column at locations throughout the NRE; the North Carolina
Department of Environment and Natural Resources Pamlico River Water Quality Monitoring project
(PAMRIV) with measurements of the surface and nearbottom salinity in the TPRE; and the University of
North Carolina Ferry Monitoring (FerryMon) project with surface water quality data collected on North
Carolina Department of Transportation ferries crossing Pamlico Sound.
3. Numerical Model
Delft3D is a threedimensional (3D) numerical modeling system consisting of several integrated models that
simulate hydrodynamics, transport of waterborne constituents (e.g., salinity and heat), surface waves by
coupling with the SWAN (Simulating WAves Nearshore; Booij et al., 1999) spectral wave model, sediment
transport, and morphological changes. Delft3D has been used to simulate coastal hydrodynamics with con-
siderable success when compared to observations in different shallow coastal environments such as embay-
ments (Mulligan, Hay, et al., 2008), river deltas (Hu et al., 2009), and river mouths (Elias et al., 2012). It has
also been used to simulate storm surge in the APES (Mulligan et al., 2015), waves on estuarine shorelines in
Pamlico Sound (Eulie et al., 2016), and estuarine circulation in the NRE (Brown et al., 2014). Delft3D can be
run in 3D mode where topographyfollowing σlayers dene the vertical coordinate. In this study, a 3D
model with vertical layers is used which allows for prediction of stratication and vertical mixing that are
important for simulating salinity. A detailed description of the system of equations and numerical imple-
mentation is provided by Lesser et al. (2004).
Figure 2. Observations over a 12month period from 1 October 2007 to 30 September 2008 that are input to the model: (a) wind components at DS (Diamond Shoals
Buoy); (b) ocean water levels at FO (FRF Ocean side) and BF (Beaufort); and (c) selected river discharges at the head of the NRE and TPRE. Site locations are shown
in Figure 1.
Journal of Geophysical Research: Oceans
3.1. Model Setup
The model domain is a curvilinear grid, with an open boundary along the continental shelf that has higher
resolution in the narrow subestuaries of the APES and lower resolution in the Atlantic Ocean. The resolu-
tion of the ow model grid ranges from 250300 m, with the wave model grid having a resolution of
500600 m. Both model domains covered an area of 220 km in the eastwest direction and 295 km in the
northsouth direction. The presentday bathymetric grid was built using a highresolution digital elevation
model of Pamlico Sound, obtained from National Oceanic and Atmospheric Administration and the
USGS (Cross et al., 2005), at a resolution of 30 m. The vertical grid has eight vertical σlayers, and each layer
has a thickness equal to 12.5% of the local water depth. Since the APES has a maximum depth of 8 m and
typical depths of 15 m, this means the vertical resolution ranges from approximately 0.11.0 m in agree-
ment with other modeling studies in estuaries and inlets (e.g., Purkiani et al., 2015). Model simulations were
run for a 12month period from 1 October 2007 to 30 September 2008, with computations performed at a
time step of 30 s. Model spinup is an important consideration when initializing a numerical model. In this
case, the water levels and current speeds were near 0 at the start of the run and very good model agreement
with observations over the simulation period (Clunies et al., 2017). This indicates that the model spinup
time for water level elevations is very short (i.e., <2 days) for Pamlico Sound. The initial conditions for sali-
nity are very important since the system has a horizontal salinity gradient from fresh water to ocean water. A
realistic spatial distribution is used to initialize the model salinity eld, discussed further in section 3.3. All
model runs use the same hydrodynamic forcing from winds, tides, and river inows. Global tidal modeling
at 1,000yr intervals over the past 10,000 yr has shown that changes in the spatial patterns and amplitudes of
tidal constituents are small in the middle to late Holocene (Hill et al., 2011). It is therefore reasonable to
assume that tidal range at the ocean boundary has remained very similar over the last 4,000 yr, and any dif-
ferences in the ocean are signicantly smaller compared to changes to the coastal/estuarine system. In this
approach, the hydrodynamic responses to different morphology of the barrier islands and estuary
are isolated.
The model runs were forced using a spatially uniform wind eld, water levels at the open boundary, and
freshwater river discharges for the Neuse, TarPamlico, Chowan, and Roanoke Rivers (Figure 2c). The wind
eld, described by Clunies et al. (2017), was developed from observations made at DS (Figure 2a) with hourly
temporal resolution. The open boundary condition was developed from water level observations at BF and
FO (Figures 1 and 2b) by linearly interpolating along the open boundary to develop a spatially varying
boundary condition. The simulations were initialized with a water level of 0 m (mean sea level). Model para-
meters and sensitivity tests are described in detail by Clunies et al. (2017) and were validated using available
observations of water levels, waves, and currents for the presentday scenario. The bottom drag coefcient
) was set to the default value of 0.0023, and a kɛturbulence closure scheme was used with background
horizontal and vertical eddy viscosity coefcients of 1.0 and 1.0×10
, respectively. In SWAN, fre-
quency was dened using 49 logarithmically spaced bins from 0.053.00 Hz and directions were dened
using 36 bins with 10° spacing. Depthinduced breaking in shallow water was dened using the borebased
model of Battjes and Janssen (1978), with the rate of dissipation coefcient (α) set to 1.0 and the breaker
parameter (γ) set to 0.73. Bottom friction was parameterized using the semiempirical formulae from the
JONSWAP experiments (Hasselmann et al., 1973), using a bottom friction coefcient (c
) equal to 0.067
, appropriate for locally generated wind sea. Whitecapping was modeled based on the formulation
described by van der Westhuysen et al. (2007) and Mulligan, Bowen, et al. (2008).
3.2. Paleobathymetric Grids
Zaremba et al. (2016) describe the geological observations corresponding to the late Holocene stratigraphic
record and paleoenvironmental evolution of Pamlico Sound, with a focus on time periods of increased mar-
ine inuence. These periods are interpreted to be the result of extensive barrier island segmentation synchro-
nous with periods of rapid climate change, indicating the highly dynamic character of the coastal system in
response to sea level changes and interactions with paleotopography. In the present numerical study, the
hydrodynamic and wave models are applied to four different geomorphic scenarios characterized by changes
to the bathymetry and inlet congurations and corresponding to distinct time intervals (present day, 500,
1,000, and 4,000 cal yr BP) during the evolution of Pamlico Sound as described by Zaremba et al. (2016).
The paleobathymetric grids were created using agedepth relationships developed from cores in Pamlico
Journal of Geophysical Research: Oceans
Sound in combination with the timeconstrained seismic grid data with locations shown in Figure 1b. The
paleosurfaces implemented in the numerical model are therefore derived from the presentday surface,
after modication based on observations from the sediment cores and geophysical surveys. Relative sea
level curves developed from geological sea level reconstructions (Kopp et al., 2015) were used as a
reference for water depth at the time of formation of signicant stratigraphic horizons. SLR corrections
for the 500, 1,000, and 4,000 cal yr BP bathymetric grids were 0.61, 1.35, and 3.06 m, respectively in
comparison to the presentday sea level. In the present, Pamlico Sound has three inlets shown in Figure 3
Figure 3. Bathymetry of Pamlico Sound for four different geomorphic scenarios: (a) present day; (b) 500 cal yr BP; (c) 1,000 cal yr BP; and (d) 4,000 cal yr BP
(adapted from the observations described by Zaremba et al., 2016). The 3and 5m depth contours are indicated by black lines, and the inlet locations are indi-
cated by red boxes. The vertical datum is presentday mean sea level (MSL) for all scenarios.
Journal of Geophysical Research: Oceans
a: Ocracoke Inlet, Hatteras Inlet, and Oregon Inlet. In addition to changes made to the Pamlico Sound basin
morphology, the grids were modied to account for paleoinlets occurring during the different time intervals
based on the work of Culver et al. (2007), Grand Pre et al. (2011), and Mallinson et al. (2010, 2011)
(Figures 3b3d). Paleoinlet dimensions (i.e., the active inlet throat channels) are difcult to estimate
based on geological data, because of the migration tendencies of the channel within the overall ll
sequence, as well as difculties in imaging with ground penetrating radar greater than 4 m below the
subsurface because of the effects of salt water. Thus, for model purposes inlet dimensions utilized a
modern analogue (Drum Inlet) with an inlet throat channel width of 0.5 km and maximum depth of 6 m.
This is consistent with geological constraints provided by ground penetrating radar data (Mallinson et al.,
2010). Based on the inletthroat area to tidal prism relationship (Hughes, 2002; Jarrett, 1976), each inlet
would accommodate a tidal prism of 4.6 × 10
, which is approximately half of the average (19881989)
tidal prism at Oregon Inlet (1.1 × 10
; Nichols & Pietrafesa, 1997). Thus, model results likely represent
minimum expected changes within the Sound, given the relatively small size of modeled inlets. The
bathymetry in each geomorphic scenario is assumed to be in morphodynamic equilibrium since it is
derived from the geological record.
3.3. Initial Salinity Conditions
Advectiondiffusion of salinity is simulated using the 3D transport equation (Lesser et al., 2004) in horizon-
tal (x,y) and vertical topographyfollowing (σ) coordinates to determine the salt concentration in the model
domain. The horizontal and vertical diffusion coefcients have values of D
= 0.1 m
and D
= 1.0×10
. The predicted salinity is compared to available data in September from the MODMON, PAMRIV,
and FerryMon monitoring projects at the stations shown in Figure 4a.
Simulating salinity in the estuaries requires the initial salinity conditions to be specied throughout the
model domain. Initial salinity values in the APES were developed for the model using typical fall salinity
values described by Wells and Kim (1989) that compare well with the model results of Jia and Li (2012).
These are shown in Figure 4b, with a strong horizontal gradient from the river inows (0 psu) to central
Pamlico Sound (~20 psu). Ocean salinity outside the Outer Banks and along the offshore boundary was
set to a value of 34 psu to represent the North Carolina shelf water, and the initial salinity conditions
Figure 4. Estuarine salinity: (a) observation sites from the FerryMon, MODMON, and PAMRIV monitoring projects and (b) model domain and initial conditions at
the start of each model run.
Journal of Geophysical Research: Oceans
were depthuniform throughout the model domain. For computational efciency, eight vertical σlayers are
used in this shallow system (average depth is 5 m), and therefore, each layer has an average thickness of 0.6
m. After initializing the model with the salinity distribution, it was determined that the spinup time is
approximately 6 months indicated by the adjustment to steadystate salinity over the 12month
simulations. There is a marked difference in model spinup time scales for water levels (2 days) and for
salinity (6 months). This is because the tidal inuence on water level elevations in Pamlico Sound is very
small compared to the larger winddriven water level uctuations. However, salinity, as an indicator of
water mass transport, requires a much longer time to achieve a steadystate balance between the
freshwater discharge from rivers that enter on the west side and tidal pumping of marine water through
inlets on the east side of the Sound.
4. Results
4.1. Hydrodynamics
Model validation for the presentday scenario is explained in detail in Clunies et al. (2017), where water
level statistics including the correlation coefcients (R= 0.800.93) and rootmeansquare errors (RMSE
= 0.060.10 m) are provided over a 35day simulation at six sites. For the signicantly longer model
Figure 5. Model validation over the 12month simulation period in Pamlico Sound (Site P2): (a) water level elevation (RMSE = 0.08 m), with selected period shown
by the gray shaded box; (b) current magnitude (RMSE = 0.04 m/s); and (c and d) detail of water levels and currents during selected period in September 2008.
Journal of Geophysical Research: Oceans
simulation in the present study, validation for water levels and currents in Pamlico Sound is presented in
Figure 5 using observations at Site P2 over a 1yr period. These results have low errors for water levels
(RMSE = 0.08 m) and for currents (RMSE = 0.04 m/s), which indicates high condence in the
hydrodynamic numerical results. The water levels and currents in Pamlico Sound have a minimal tidal
inuence and the variability is almost exclusively wind driven, in agreement with other studies
(Clunies et al., 2017; Luettich et al., 2002).
Figure 6. Simulated water level elevations above mean sea level at high tide (corresponding to the conditions on 25 September at 1230, for the four different geo-
morphic scenarios: (a) present day; (b) 500 cal yr BP; (c) 1,000 cal yr BP; and (d) 4,000 cal yr BP.
Journal of Geophysical Research: Oceans
The response of Pamlico Sound to wind and ocean water level forcing is investigated for distinct scenarios,
and the inuence of the different morphological conditions is evaluated through the comparison between
the model results for each time slice. Simulated water levels are shown in Figure 6 at a time with high tidal
elevations in the ocean, and the differences between the four time slices indicate the inuence of the differ-
ent inlet congurations on water levels in the Sound. Similar to the water level results, current velocity pre-
dictions indicate a different tidal signal in each case. Maximum simulated current velocities in the 4,000 cal
Figure 7. Simulated velocities during maximum ood tidal current (corresponding to the conditions on 2 August at 0030) for the four different geomorphic scenar-
ios: (a) present day; (b) 500 cal yr BP; (c) 1,000 cal yr BP; and (d) 4,000 cal yr BP.
Journal of Geophysical Research: Oceans
yr BP model are strongest near the inlets (e.g., near Site C2), reaching approximately 0.8 m s
, 3 times
higher than current velocities in the presentday model at C2 and indicating the importance of inlets on
circulation in the backbarrier estuary.
The ows during maximum oodtidal currents with calm winds (U
) are shown in Figure 7. The
greater number of inlets (500 cal yr BP, Figure 3b) and wider inlets (1,000 cal yr BP, Figure 3c) result in
higher current velocities in Pamlico Sound, with a noticeable increase in velocity in central Pamlico
Sound (1,000 and 4,000 cal yr BP) and the mouths of the TPRE and NRE (4,000 cal yr BP, Figure 3d). The
ow during maximum ebbtidal currents (Figure 8) through the inlets indicates higher current velocities
Figure 8. Simulated velocities during maximum ebb tidal current (corresponding to the conditions on 22 September at 1230) for four different geomorphic scenar-
ios: (a) present day; (b) 500 cal yr BP; (c) 1,000 cal yr BP; and (d) 4,000 cal yr BP.
Journal of Geophysical Research: Oceans
in Pamlico Sound than in the presentday case, even at considerable distances from the inlets. This is caused
by higher ow rates through the system due to the different inlet congurations, since the inlets are either
wider (e.g., 21 km wide at 1,000 cal yr BP) or there is a greater number of smaller inlets (e.g., nine inlets at
500 cal yr BP) and is not restricted to the three inlets in the presentday scenario (Figure 3a).
Currents in central Pamlico Sound are also inuenced by the mean water depth change, particularly over the
shallow northsouth oriented sand ridge called Bluff Shoal. Bluff Shoal is a relic interuvial divide between
the Neuse River and Pamlico/Tar River systems, dating prior to 7,500 cal yr BP (Zaremba et al., 2016) and is a
good example of the role of antecedent topography on hydrodynamics (Mallinson et al., 2010). SLR of
approximately 3 m over the last 4,000 yr (Horton et al., 2009; Kemp et al., 2009, 2017) has increased the depth
over Bluff Shoal and decreased the current magnitude over this feature. In the 4,000 and 1,000 cal yr BP
cases, with lower sea level, a deviation in ow direction occurs at Bluff Shoal during the ebb tide. Bluff
Shoal impedes the ow of water driven by winds and tides, and water from Pamlico Sound is able to exit
the backbarrier environment through the closest paleoinlets near the presentday site of Ocracoke Island.
To compare the hydrodynamic results for each scenario, water levels and current velocities for a short time
near the end of the simulations are presented in Figure 9 at three locations (P2, C1, and C2; Figure 1a) in
Pamlico Sound for morphological conditions corresponding to each geomorphic scenario. During each time
period a strong northerly wind event drives a storm surge into southwestern Pamlico Sound and the wind
driven water levels are signicantly greater than the tides in the estuary. The results of the presentday run
are in good agreement with the water level and current observations at P2, indicating microtidal conditions
Figure 9. Comparison of selected time series of model results (water level elevation, depthaveraged current magnitude, and salinity) for the four simulations at
Sites P2, C1, and C2 corresponding to the conditions over a 10day period in September 2008.
Journal of Geophysical Research: Oceans
with a tidal range of <0.10 m, storm surge of 0.60 m, and maximum current speeds of 0.10 m s
. The inlets
along the Outer Banks have a signicant effect on the simulated water levels and current velocities in
Pamlico Sound at C1 and C2 (Figure 9). The water levels indicate higher tidal energy in Pamlico Sound,
in comparison to the presentday model since tides are able to propagate farther into the backbarrier envir-
onment. The tidal signal is strongest at the observation sites (C1 and C2) in the 4,000 cal yr BP scenario due
to the proximity of these sites to inlets at this time. The average tidal range, the residual after removing the
larger winddriven surge, in Pamlico Sound (at P2) is approximately 0.30, 0.20, 0.15, and 0.10 m for the 4,000,
1,000, 500, and presentday geomorphic scenarios, respectively.
4.2. Surface Waves
Validation of the wave model for the presentday scenario (Clunies et al., 2017) in Albemarle Sound indi-
cated the wave climate is fetch or depth limited in the estuarine system depending on the wind direction.
Signicant wave height (H
) for the present day and 1,000 cal yr BP geomorphic scenarios, for strong winds
blowing from the south (Figures 10a and 10c) and the north (Figures 10b and 10d), indicate differences in
wave energy of 1020%. For winds from the south, the 1,000 cal yr BP simulation had the largest signicant
wave heights, with waves up to H
= 1.5 m in Pamlico Sound near the mouths of the NRE and TPRE, with
some wave energy from the ocean that is transmitted into the sound through two inlets. Similarly, the trans-
mission of wave energy from the ocean into Pamlico Sound also occurs in the 1,000 cal yr BP run through an
inlet west of Cape Hatteras, increasing the wave height in eastern Pamlico Sound. Wave energy is also trans-
mitted through the wide inlet in the 1,000 cal yr BP geomorphic scenario into central Pamlico Sound but is
reduced by depthlimited breaking in the shallow sound. Wave energy from the ocean through these two
inlets during south winds results in H
= 1.4 m in the western region of the northern basin of Pamlico
Sound. The smaller inlets in the presentday case and the relatively shallow inlets in the 500 cal yr BP geo-
morphic scenario limit wave energy in Pamlico Sound to approximately H
< 1.2 m for these wind condi-
tions. For winds from the north, the presentday geomorphic scenario has the largest H
, reaching 1.5 m
in a signicant portion of Pamlico Sound due to the greater water depth. The smaller number of narrower
inlets in the presentday case results in negligible transmission of wave energy from Pamlico Sound to the
ocean. The wider and deeper inlets in the paleobathymetric model runs allow a higher amount of wave
energy transmission from the sound to the ocean.
4.3. Salinity
To assess the changes in salinity distributions in Pamlico Sound and exchange between the ocean and the
backbarrier environment, the model was used to simulate the salt concentration for each geomorphic sce-
nario. The simulations do not intend to predict the exact salinity distributions but highlight important differ-
ences in circulation for the different inlet congurations. However, the salinity predictions are rst validated
using observations in the present day in three regions of the estuary: the NRE, the TPRE, and Pamlico Sound
along a ferry route (Figure 4a). Observations and model results are shown in the NRE and TPRE for one day
(29 September 2008) at the end of the simulation. These results indicate that the salinity eld has some rea-
listic aspects that match the eld measurements. First, the lowest simulated salinity values occur at the
heads of the subestuaries near the freshwater sources from the Neuse and Tar Rivers with the estuaries
becoming higher in salinity eastward toward Pamlico Sound. Second, stratication is much stronger in
the NRE than in the TPRE due to higher discharge in the NRE, indicated by the observed and predicted sur-
face (Figure 11a) and near bed level (Figure 11b) salinity values. The vertical structure of salinity in the NRE
is apparent in the model (Figure 11c), although the halocline is slightly deeper and salinity values are lower
near the bottom in the model. Overall, the error of the salinity at the NRE surface has a spatially averaged
RMSE = 2.4 psu and at the bottom RMSE = 9.6 psu. This error in nearbottom salinity after 1 yr of simulation
could possibly be reduced by increasing the vertical resolution and improving the simulation of baroclinic
processes; however, this is computationally intensive and the surface layer has lower error in both the
NRE and the TPRE. The TPRE is vertically well mixed (Figure 11d) and the surface salinity error in the
TPRE is RMSE = 3.4 psu, and at the bottom it is lower with RMSE = 1.5 psu. Observations and model results
indicate that the water column is well mixed in Pamlico Sound indicated by the near identical salinity at the
NRE and TPRE estuary mouths in Figure 11.
The variation in the simulated surface salinity distribution and the FerryMon observations on 12 different
days in September 2008 are shown in Figure 12. The model results for surface salinity are not in perfect
Journal of Geophysical Research: Oceans
agreement with FerryMon measurements across the southeastern part of Pamlico Sound, likely due to the
highly dynamic exchange of water masses in this region. However, the model results capture the
exchange of high salinity ocean water with the brackish estuarine water through Ocracoke Inlet and
variability over time. For example, export of lower salinity water (2630 psu) through the inlet to the
ocean occurs in the model on several days (e.g., Figure 12a) and plumes of higher salinity water (3135
psu) occur inside the sound in the model and observations (e.g., Figure 12d). The model predicts the
Figure 10. Simulated signicant wave height in Pamlico Sound for (a) 17ms
winds from the south (6 September at 1230) and (b) 16ms
winds from the north
(24 September at 0030) for basin morphology corresponding to the present day; and the same winds from (c) the south and (d) the north for basin morphology
corresponding to the 1,000 cal yr BP scenario.
Journal of Geophysical Research: Oceans
Figure 11. Salinity observations and model results in the NRE and TPRE on 29 September 2008: (a) nearsurface model results and observations (colored circles);
(b) nearbottom model results and observations; (c) transect along the TPRE; and (d) transect along the NRE.
Journal of Geophysical Research: Oceans
variability in salinity distribution across the region with differences from observations that have RMSE
ranging from 1.43.6 psu for a given day and an average RMSE = 2.1 psu for all data shown. This suggests
that the model is a useful tool to investigate salinity differences and identify important trends between the
geomorphic scenarios, though modeled salinity values may not be precise. The model is applied to each
geomorphic scenario to determine realizations of the salinity distribution over a 12month period with the
same realistic hydrodynamic forcing conditions.
Timeaveraged (6month) spatial distributions of nearbed salinity in the estuary are shown in Figure 13.
These model results indicate that the lowest salinity (2025 psu) in central Pamlico Sound occurs in the
presentday geomorphic scenario (Figure 13a), due to the fewer and smaller inlets. Results for the 500 and
1,000 cal yr BP geomorphic scenarios indicate higher salinity (2534 psu) in central Pamlico Sound, the
strong inuence of the very shallow Bluff Shoal in dividing Pamlico Sound into two basins, and lower sali-
nity in western regions of Pamlico Sound with marine salinity water in the eastern region near the paleo
inlets open along the Outer Banks (Figures 13b and 13c). Results for the 4,000 cal yr BP time slice also
Figure 12. Simulated estuary surface salinity compared to FerryMon salinity observations (colored circles) on 12 days in September 2008. The RMSE ranges from
1.43.6 psu for each day, and the average RMSE of all data shown is 2.1 psu.
Journal of Geophysical Research: Oceans
indicate high salinity in Pamlico Sound compared to the presentday case. The southern inlet at this time
also allows greater transport of estuarine water to the ocean. Salinity ranges developed from observed
foraminiferal assemblages in sediment cores are superimposed on the salinity distributions in Figure 13.
Variability in salinity is also shown in the time series at selected sites in Figure 9. Although the salinity
values interpreted from core data represent longterm environmental averages and the model results
indicate changes over a 6month average period, this approach demonstrates the effect of different inlets
on water mass properties in the estuary and exchange with the ocean.
Figure 13. Sixmonth averaged (AprilSeptember) maps of simulated nearbed salinity for four geomorphic scenarios: (a) present day; (b) 500 cal yr BP; (c) 1,000 cal
yr BP; and (d) 4,000 cal yr BP (see color bar). Longterm approximate mean salinity values determined from foraminiferal assemblages at sediment cores in Pamlico
Sound are shown by the colored circles (see legend).
Journal of Geophysical Research: Oceans
5. Discussion
5.1. Hydrodynamic Responses to LongTerm Changes in Basin Morphology
Model simulations for the three geomorphic scenarios indicate that more inlets or wider inlets result in
higher currents even at large distances from the inlets. Wider inlets allow more tidal energy to enter the
basin and therefore increase velocities in the basin (farther from the inlets); however, wider inlets would
have lower currents in the inlet channels for the same tidal conditions. Although the 1,000 cal yr BP geo-
morphic scenario has the largest inlet (21 km), the highest water levels and currents in central Pamlico
Sound occur in the 4,000 cal yr BP simulation. SLR and inlet dynamics (breaching and closure) have also
changed the wave climate in Pamlico Sound over the last 4,000 yr. In the present day, waves from the ocean
are unable to propagate into the backbarrier system due to the relatively small size of the inlets (Figure 3a).
The results in Figure 10 indicate that for different wind directions, barrier segmentation (in combination
with geomorphic changes due to longterm sediment transport and deposition in the basin) has a strong
inuence on the estuarine wave climate. The results suggest that changes in water depth due to SLR have
an impact on the wave climate for winds from the north, with the largest signicant wave heights in the east-
ern basin of Pamlico Sound for the presentday setting (Figure 10a). For winds blowing from the south, the
barrier island conguration and basin morphology become stronger controls on the wave climate. When
compared to the present day, the 4,000 and 1,000 cal yr BP cases have smaller basins in central Pamlico
Sound and a shallower depth over Bluff Shoal, which cause depthlimited breaking. The wave height results
also suggest that the inlets in the 1,000 cal yr BP geomorphic scenario, in comparison to smaller inlets in the
presentday case, have a greater effect on the wave climate. These results provide an example of the syner-
gistic effects of barrier segmentation and longterm bathymetric changes on signicant wave heights in a
backbarrier estuary such as Pamlico Sound. The wider Ocracoke Inlet in the 1,000 cal yr BP case allows a
higher amount of wave energy to enter the backbarrier estuary from the ocean, resulting in higher signi-
cant wave heights in Pamlico Sound (Figure 10d) than occur in the presentday (Figure 10b) barrier island
conguration. Greater wave heights would likely enhance estuarine shoreline erosion rates, increasing sedi-
ment ux to the basin, and also more effectively winnowing those sediments and preferentially exporting
mud from the system to the shelf via the inlets. This agrees with the observed increase in the sand/mud ratio
of sediments corresponding approximately to the 1,000 cal yr BP time interval (Zaremba et al., 2016).
5.2. Controls on Salinity Distributions
The model results represent relatively short (1yr) duration realizations of the hydrodynamic response to the
different bathymetry in each geomorphic scenario. The simulations include freshwater inows from the
major rivers using measured data (Figure 2) but do not include uctuations in salinity resulting from
longerterm changes in rainfall or runoff patterns. This is apparent when comparing the foraminifera
derived salinity to the salinity model for the present day (Figure 13a). The foraminiferal data in this case
are from near the top of the various cores and reect conditions between approximately 70 and 400 yr ago
(based on average accumulation rates of 1 mm/yr). Geochemical and microfossil data indicate that marine
inuence within Pamlico Sound has increased over the last century (Abbene, 2004; Abbene et al., 2006);
thus, the foraminiferal assemblages reect lower salinity conditions of the last several centuries, whereas
the model reects modern conditions. An additional complicating factor is that, because of salinity toler-
ances, the foraminiferabased salinity estimates reect conditions within a range of approximately 5 to 10
psu. Furthermore, the values can be considered as minima as the presence and relative abundance of the
species involved are limited more by lower (estuarine) rather than higher (i.e., estuarine, but closer to nor-
mal marine, or normal marine) salinity values. This demonstrates that the models are not directly compar-
able with the centennialto millennialscale changes inferred from the depositional record preserved in the
sediment cores but are still useful for interpreting the response of the estuary to the different geomorpholo-
gical conditions. With these caveats in mind, the models generally support the higher salinity trends sug-
gested by distributions of foraminifera during the 4,000 (in particular) and 1,000 cal yr BP time intervals
and lower salinities of the present day (Figure 13; Foley, 2007; Metger, 2009; Grand Pre et al., 2011). An
exception to this is the simulated high salinity conditions within Pamlico Sound during the 500 cal yr BP sce-
nario, which are not supported by microfossil data (Figure 13b), in contrast to the salinity conditions during
the 4,000 and 1,000 cal yr BP periods. This suggests that tidal exchange was not as high at 500 cal yr BP as
during earlier and more segmented scenarios; thus, inlets were likely smaller and more ephemeral and
Journal of Geophysical Research: Oceans
the number of inlets open at one time in the geomorphic reconstruction may be an overestimate. Salinities
were higher at 1,000 cal yr BP than present by 510 psu and at 4,000 cal yr BP salinities were slightly lower
than at 1,000 cal yr BP, suggesting differences in connections with the ocean during these periods.
The simulated surface salinity distributions suggest that water properties in Pamlico Sound are controlled by
mixing due to winds and waves, the degree of connectivity (i.e., owthrough area) between the higher sali-
nity Pamlico Sound and lower salinity Albemarle Sound, and the number and size of inlets and the strength
of the currents that inuence ows in Pamlico Sound. Albemarle Sound is connected to Pamlico Sound via
the shallow Roanoke and Croatan Sounds, with Albemarle Sound having considerably lower salinity water
than Pamlico Sound (Wells & Kim, 1989). Apart from the net seaward ow that occurs as a result of the dis-
charge from river inputs, wind is the governing force that controls the salinity distribution in Pamlico Sound.
Changes in monthly, seasonal, decadal, or longer time scale winds as a result of climate change could dras-
tically affect the transport of water between Albemarle and Pamlico Sound and inuence the
salinity distribution.
Connectivity between Albemarle and Pamlico Sounds was likely nonexistent during lower sea level condi-
tions prior to ~500 cal yr BP due to the occurrence of an interuvial divide and an extensive marsh system,
in the location of modernday Croatan Sound (Figure 1a). Connectivity increased greatly during the early
nineteenth century when inlet closure along the northern Outer Banks forced water south through
Croatan Sound, removing the marshes and rapidly expanding this connection (Riggs et al., 2000; Riggs &
Ames, 2003). The lack of this connectivity between the sounds at lower sea levels relative to the present
day is illustrated in Figures 13b13d, where salinity along the northern shoreline of Pamlico Sound was
much greater during the three paleoscenarios compared to the present day.
In all geomorphic scenarios, a net seaward transport of water from Pamlico Sound into the Atlantic Ocean
through the inlets occurs as a result of ows from the major rivers. Changes in the size, number, and location
of inlets along the Outer Banks create alternative ow paths for water through the estuary, leading to higher
ushing rates and shorter residence times relative to the present day. Plumes of lower salinity water that are
typically conned to the northern region of Pamlico Sound in the presentday case are able to exit the back
barrier environment via paleoinlets located along Hatteras Island (e.g., in the 500 and 1,000 cal yr BP geo-
morphic scenarios). The paleobathymetric model results indicate that morphological changes, including
changes to the bathymetry, shoreline position, opening of new inlets, changes to inlet size, or changes to
inlet location have a signicant and complex inuence on the hydrodynamic energy and salinity distribution
in Pamlico Sound. The changes are complex and include morphodynamic feedbacks via sediment transport
such that they are not easily forecast without a numerical modeling approach. Sediment transport modeling
is an important next step; however, it would require a different method consisting of signicantly longer
model runs or morphologic upscaling(e.g., Ranasinghe et al., 2011) over long time scales.
5.3. Insight From New Results and Comparison With Other BackBarrier Systems
Studies of other large backbarrier systems indicate the sensitivity of these regions to SLR. For example,
Beets and van der Spek (2000) investigated the evolution of the backback barrier evolution of estuaries in
Belgium and the Netherlands during the sea level changes over the Holocene. Their study importantly found
differences in the balance between accommodation space and the sediment supply that led to stabilization of
the barrier islands and deposition in the Belgian basin, while higher tidal energy and sediment transport
capacity have kept the Netherlands large inlets and Wadden Sea open to present. Basin evolution in the
Wadden Sea has also been investigated numerically using Delft3D by Dissanayake et al. (2012) using an
idealized modeling approach over a 110yr future period to determine possible erosion/accretion rates.
This system has also been studied by Wang et al. (2018) for future SLR corresponding to various climate
change scenarios, to determine rates of sand sediment import into the tidal basins by tidal currents. In other
systems, Leorri et al. (2011) investigated multiple static sea level conditions in Delaware Bay, nding that
signicant changes in the tidal range occur due to amplication or attenuation of the tides over different
bathymetry. Passeri et al. (2016) used a numerical model to simulate the tidal hydrodynamics of different
backbarrier bays in the Gulf of Mexico for different SLR scenarios and emphasized the need to consider
the coevolution of morphology in conjunction with SLR for comprehensive evaluations of hydrodynamics.
Passeri et al. (2018) considered hurricane storm surge combined with SLR, quantifying the higher inunda-
tion and overwash that occurs when sea levels are higher in the Gulf of Mexico.
Journal of Geophysical Research: Oceans
Taken together with the new results of the present study, it is apparent that barrier systems are sensitive to
change (e.g., SLR or storms) and backbarrier estuaries respond strongly and with great complexity, causing
regime shifts in hydrodynamics (water levels, currents, and waves) and water mass properties such as sali-
nity. The present method allows for an understanding of the mechanisms responsible for past changes that
are fundamentally grounded in reality and have several important implications for future changes. First, our
results indicate that relatively small perturbations to the morphology of the system such as opening a new
inlet or changing the depth can have major impacts on water levels that would drive ooding of the main-
land. This would have signicant implications on the sediment distribution and dynamics within the sound
as circulation patterns and current strength drive sediment transport in the backbarrier system. In the event
of barrier segmentation caused by new inlet formation in the future, reworking of the presentday sediment
distribution within Pamlico Sound is expected. The results of this study improve understanding of the hydro-
dynamic response of the system to the changes in morphology that have already occurred as interpreted
from the geological record, and may also help inform studies of future change and management decisions.
Second, our results suggest that SLR could further increase the connectivity between Albemarle and
Pamlico Sounds in the future. This could result in a systemwide shift in the salinity distribution with
impacts on habitat and the organisms that reside within the backbarrier environment, for example, sh spe-
cies dependent on this region for spawning, larval, and juvenile stages of life. Third, with the possibility of
potentially accelerating SLR (Bernstein et al., 2007; Jevrejeeva et al., 2010, 2012; Rahmstorf et al., 2012),
in combination with projected increasing tropical cyclone intensity (Elsner et al., 2008; Emanuel, 2005),
the Outer Banks barrier islands and similar barrierisland systems are at an increased risk for overwash, ero-
sion, and breaching.
6. Conclusions
Pamlico Sound is a large backbarrier estuary that has evolved over the late Holocene in response to SLR,
similarly to other large systems such as the Wadden Sea in the Netherlands and many smaller backbarrier
bays along the northern Gulf of Mexico coast and other parts of the world. The present study uses a coupled
numerical ow (Delft3D) and wave model (SWAN) with different bathymetric grids corresponding to four
distinct times during the geomorphic evolution of Pamlico Sound to assess the hydrodynamic, surface wave,
and salinity response to longterm changes in geomorphology, barrier segmentation, and SLR. The presence
of inlets along the Outer Banks and changes to bathymetry in the model runs had a signicant effect on the
water levels and current velocities in Pamlico Sound. Increasing the number and size of the inlets in the
paleobathymetric simulations resulted in increased tidal range in Pamlico Sound. Tidal signals were stron-
gest in the 4,000 cal yr BP scenario, with current magnitudes up to 3 times higher (0.78 m s
) in comparison
to presentday maximum currents of 0.25 m s
. Higher current velocities in Pamlico Sound occurred due to
a greater number of inlets and due to wider inlets, and stronger currents were not limited to the areas adja-
cent to the inlets. Current velocities increased throughout the estuary in all three paleobathymetric simula-
tions during both ood and ebb tides suggesting a higher transport rate in the sound and exchange rate
between the sound and the ocean. Changes in inlet size and water depth due to sediment inlling and
SLR also impact the wave climate in Pamlico Sound, which would also inuence erosion and transport of
estuarine sands and muds. Mean water level change due to SLR and sedimentation factors can therefore
inuence the wave climate when winds are from the north as the waves are fetch and depth limited for
winds from this direction. Barrier segmentation and longterm bathymetry changes more strongly affect
the wave climate when winds are from the south due to incident wave energy from the Atlantic Ocean that
is regulated by inlet size, depth, and abundance. Overall, the results indicate that with greater segmentation
comes greater tidal range and higher wave energy in the backbarrier environment, which will accelerate
ooding and shoreline erosion.
The distribution of salinity throughout the estuarine system was computed for each geomorphic scenario.
The presentday simulated salinity distribution was compared with observations from three monitoring pro-
jects and errors quantied that indicate high condence in the model results for salinity. The comparisons
between each geomorphic scenario suggest that transport and mixing due to winds and waves, hydraulic
connectivity between Albemarle and Pamlico Sounds, and the number and size of inlets are three major fac-
tors inuencing salinity in Pamlico Sound. The model results are not directly comparable with the 100to
1,000yr changes inferred from the microfossils (i.e., foraminiferal assemblages) preserved in the sediment
Journal of Geophysical Research: Oceans
cores since the models are shortduration averages of the evolving hydrodynamics associated with each geo-
morphic scenario. Nevertheless, the modeling approach is useful for interpreting and comparing the bulk
response of the estuary to the different geomorphological conditions that occurred in the past. In the present,
Pamlico Sound grades from a partially mixed to a wellmixed brackish estuary from east to west. The geolo-
gical observations and hydrodynamic modeling indicate that at certain times in the past, Pamlico Sound had
greater marine inuence with greater current velocities, tidal ranges, and salinities. Given likely future sce-
narios of coastal evolution, for example, changes in water depth and inlets due to SLR and storms, Pamlico
Sound could return to a more marineinuenced system. The introduction of greater tidal range, stronger
tidal currents, and increased wave energy will accelerate mainland ooding and shoreline erosion and have
profound impacts on estuarine shorelines and ecosystems, which will require a numerical modeling
approach for forecasting future changes.
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Journal of Geophysical Research: Oceans
Thanks to J. P. Walsh and D. Reide
Corbett at ECU for providing
hydrodynamic observations and
Benjamin Peierls at the University of
North Carolina at Chapel Hill and Jill
Paxson at the NC Department of
Environment and Natural Resources
for providing salinity data. The data
used in this study are archived in the
Department of Civil Engineering at
Queen's University and are available in
a data repository accessible online (doi:
10.5683/SP2/I6XNB8). The model
simulations were run using advanced
research computing resources provided
by Compute Canada. This study of
Coastal Hydrodynamics and Natural
Geologic Evolution (CHaNGE) was
funded by the U.S. National Science
Foundation under grant number OCE
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Journal of Geophysical Research: Oceans
... The integration of field data and numerical modelling also helps to test, quantify and visualize the spatio-temporal changes in tidal processes resulting from changes in basin configuration (Collins et al., 2021). For instance, in depositional basins, the sedimentary record can be interpreted and numerical models can be used to confirm or enhance knowledge of these systems (Mallinson et al., 2018;Mulligan et al., 2019b). This increased knowledge of past basins will improve understanding of how tidal processes will evolve in response to today's sea-level rise, including assisting coastal areas in their planning by demonstrating how and where the tidal regime will significantly change (Hayden et al., 2020). ...
... The geological record from the innermost Curtis Sea is relatively well-constrained (Gilluly & Reeside, 1928;Pipiringos & O'Sullivan, 1978;Kreisa & Moila, 1986;Caputo & Pryor, 1991;Wilcox & Currie, 2008;Doelling et al., 2013;Danise & Holland, 2017Zuchuat et al., 2018Zuchuat et al., , 2019aDanise et al., 2020) and was used to inform and interpret series of numerical modelling experiments in Delft3D. The methods employed in this study followed common practice for hydrodynamic modelling in present-day tidal basins (Hu et al., 2009;Elias et al., 2012;Brown et al., 2014;Mulligan et al., 2015;Mulligan et al., 2019b); however, the lack of observations of water levels and currents necessitate the use of geological interpretations of palaeoenvironmental conditions. The modelling of tides in the Upper Jurassic Sundance and Curtis seas used the Oxfordian palaeogeographical map ( Fig. 1) from Deep Time MapsÔ (Colorado Plateau Geosystems Inc. Maps), which was palaeogeoreferenced using GPlates and projected on a Lambert Conformal Conic projection. ...
... Various palaeophysiographies were generated by converting the maps to a physiographic raster (Python code; Appendix A) and importing them into Deltares open-source Delft3D numerical modelling software. Delft3D is a three-dimensional hydrodynamic simulation suite used for solving hydrostatic and nonhydrostatic equations (see Delft3D user manual for details), and it has been used to model a variety of coastal systems, including river deltas, beaches, estuaries, lagoons and barrier islands− inlet systems (Hu et al., 2009;Elias et al., 2012;Brown et al., 2014;Mulligan et al., 2015;Mulligan et al., 2019b). Due to the unknown true water depths and the need to investigate different realistic palaeophysiographies (Byrne et al., 2020), a series of different depth grids were generated using the colour-gradient in the original palaeogeographical map. ...
Simulating hydrodynamic conditions in palaeo‐ocean basins is needed to better understand the effects of tidal forcing on the sedimentary record. When combined with sedimentary analyses, hydrodynamic modelling can help inform complex temporal and spatial variability in the sediment distribution of tide‐dominated palaeo‐ocean basins. Herein, palaeotidal modelling of the epicontinental Upper Jurassic (160 Ma, lower Oxfordian) Sundance and Curtis Seas of North America reveals possible regional‐scale variations in tidal dynamics in response to changes in ocean tidal forcing, physiographic configuration and bottom drag coefficient. A numerical model forced with an M2 tidal constituent at the open boundary shows that the magnitude and location of tidal amplification, and the variability in current velocity and bed shear stress in the basin, were controlled by palaeophysiography. Numerical results obtained using a depth of 600 m at the ocean boundary of the system enable the prediction of major facies trends observed in the lower Curtis Formation. The simulation results also highlight that certain palaeophysiographic configurations can either permit or prevent tidal resonance, leading to an overall amplification or dampening of tides across the basin. Furthermore, some palaeophysiographic configurations generated additional tidal harmonics in specific parts of the basins. Consequently, similar sedimentary successions can emerge from a variety of relative sea‐level scenarios, and a variety of sedimentary successions may be deposited in different parts of the basin in any given relative sea‐level scenario. These results suggest that the interpretation of sedimentary successions deposited in strongly tide‐influenced basins should consider changes in tidal dynamics in response to changing sea level and basin physiography.
... A growing body of literature indicates that SLR induces variations to estuarine tidal structure, including tidal range, currents, and asymmetry, and thereby to water quality (e.g., salinity), eco-geomorphology, and associated feedback loops (Dessu et al., 2018;Khojasteh et al., 2023;Mulligan et al., 2019;Rayner et al., 2021). Understanding SLR-induced changes to the tidal range (i.e., the difference between high water and low water levels), is a useful proxy to learn about the response of estuarine processes to climate change (Haigh et al., 2020;Khojasteh et al., 2021b;Talke and Jay, 2020). ...
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Climate change induced sea level rise (SLR) is one of the greatest challenges threatening the sustainable management of estuaries worldwide. Current knowledge regarding SLR and estuarine hydrodynamics is primarily focused on individual case studies, which provides limited guidance on how different estuary typologies will respond to SLR. To expand the current knowledge, this research used an idealised hydrodynamic approach to analyse the tidal range dynamics of 25 real-world estuaries with diverse shapes and boundary conditions, providing insights into estuarine response to SLR-induced tidal variations. Under present-day conditions, short length estuaries with wide entrances, deep waters, strong convergence, macro-tidal conditions, low values of roughness, and low upland river inflows are likely to experience amplified tidal range patterns; whereas lengthy estuaries with narrow entrances, shallow water depths, micro/meso-tidal conditions, high values of roughness, and high upland river inflows often exhibit a mix of dampened-amplified or fully dampened tidal range patterns. Under the effects of SLR, estuarine tidal range dynamics change depending on their present-day tidal range patterns. Where the present-day tidal range pattern is either dampening, a mix of dampening/amplification, or amplification, SLR increases (up to 61 %), moderately increases (up to 26 %), and slightly decreases/increases (up to 5 %) the tidal range of estuaries, respectively. Considering the relationship between an estuary's present-day tidal range pattern and its response to SLR, the presented approach may be useful in providing an initial assessment of SLR effects in estuaries worldwide. This may help to identify sites most impacted by future SLR, and to direct decision-making towards evidence-based management approaches.
... Several high-quality bathymetric and topographic data for this study have been combined in implementing the Delft3D FM. The entire western North Atlantic Ocean built using global SRTM15_PLUS bathymetry (Tozer et al. 2019), while NCEI Bathymetric Digital Elevation Model (30 m resolution) data has been utilized to enhance the representation of the bathymetry of the barrier island and Pamlico sound (Mulligan et al. 2019). These data are merged to create an unstructured grid mesh that spans much of the west Atlantic-the model domain extends from latitude 34.0° N and longitude 78.0° W to latitude 36.5° ...
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Prediction and reanalysis of storm surge rely on wind and pressure fields from either parametric tropical cyclone wind models or numerical weather model reanalysis, and both are subject to large errors during landfall. This study assesses two sets of wind/pressure fields for Hurricane Florence that made landfall along the Carolinas in September 2018, and appraises the impacts of differential structural errors in the two suites of modeled wind fields on the predictive accuracy of storm surge driven thereby. The first set was produced using Holland 2010 (H10), and the second set is the Hurricane Weather Research and Forecasting (HWRF) reanalysis created by the NWS National Centers for Environmental Prediction (NCEP). Each is validated using a large surface data set collected at public and commercial platforms, and then is used as input forcing to a 2-D coastal hydrodynamic model (Delft3D Flexible Mesh) to produce storm surge along the Carolina coasts and major sounds. Major findings include the following. First, wind fields from HWRF are overall more accurate than those based on H10 for the periphery of the storm, though they exhibit limitations in resolving high wind speeds near the center. Second, applying H10 to the best track data for Florence yields an erroneously spike in wind speed on September 15th when the storm reduced to a tropical depression. Third, HWRF wind fields exhibit a progressively negative bias after landfall, likely due to deficiencies of the model in representing boundary layer processes, and to the lack of assimilation of surface product after landfall for compensating for these deficiencies. Fourth, using HWRF reanalysis as the forcings to Delft3D yields more accurate peak surges simulations, though there is severe underestimation of surge along the shoreline close to the track center. The peak surge simulations by Delft3D are biased low when driven by H10, even though over several locations the H10 model clearly overpredicts surface wind speeds. This contrast highlights the importance of resolving wind fields further away from the center in order to accurately reproduce storm surge and associated coastal flooding.
... While the SLR effects on salinity is a well-studied issue and general patterns are being elucidated (Ross et al., 2015), other important variables for benthic macroinvertebrates such as sediment still have high uncertainty. Numerical simulations of SLR influence on estuarine sediments transport suggest that for moderate scenarios (i.e., 30 cm in 2050) there is no expected change in the distribution of sediments, while for extreme scenarios (i.e., 100 cm in 2100) there is still great uncertainty about such changes due to the complexity of erosion and deposition processes (Mulligan et al., 2019). ...
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The sea-level rise induced by climate change has caused impacts (e.g., floods and saline intrusion) in estuaries. In this work, we used monitoring data (salinity, sediment and taxa occurrence), simulated saline intrusion and Species Distribution Model to predict the spatial distribution of families in the estuary at two levels of SLR (0.5 m and 1 m) for two scenarios (moderate and extreme). For the simulation, we used the ensemble method applied to five models (MARS, GLM, GAM, RF and BRT). High AUC and TSS values indicated “good” to “excellent” accuracy. RF and GLM obtained the best and worst values, respectively. The model predicted local extinctions and new colonization in the upper estuarine zones. With the effects of climate change intensifying, it is extremely important that managers consider the use of predictive tools to anticipate the impacts of climate change on a local scale on species migration.
... Estuarine processes are largely controlled by the interaction between climate-related changes in sea level, environmental factors, such as the oceanographic regime, sediment availability, and tectonics, as well as anthropogenic impacts [14][15][16][17][18][19]. The interplay of these factors results in a variety of different estuarine settings, ranging from wavedominated, microtidal estuaries to macrotidal estuaries with extensive gently sloping coastal plains [14]. ...
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The rapid advance of remote sensing technology during the last few decades provides a new opportunity for measuring detectable estuarine spatial change. Although estuarine surface area and convergence are important hydraulic parameters often used to predict long-term estuarine evolution, the majority of automated analyses of channel plan view dynamics have been specifically written for riverine systems and have limited applicability to most of the estuaries in the world. This study presents MorphEst, a MATLAB-based collection of analysis tools that automatically measure estuarine planform geometry. MorphEst uses channel masks to extract estuarine length, convergence length, estuarine shape, and areal gain and loss of estuarine surface area due to natural or human factors. Comparisons indicated that MorphEst estimates closely matched with independent measurements of estuarine surface area (r = 0.99) and channel width (r = 0.92) of 39 estuaries along the South Korean coast. Overall, this toolbox will help to improve the ability to solve research questions commonly associated with estuarine evolution as it introduces a tool to automatically measure planform geometric features from remotely sensed imagery.
Salinity distributions and gradients within an estuary are of great socioeconomic and ecological importance. In this study, a well-validated and process-based hydrodynamic model (Delft3D) was applied to investigate the salinity distributions and variations in the Yangtze Estuary subject to river discharge regulation by the Three Gorges Reservoir and morphological evolution of the estuary. The results indicate that the regulation of river discharge is the controlling factor for salinity variations in the estuary. Following construction of the Three Gorges Reservoir, the salinity significantly decreased during the dry season and slightly increased during the flood season. The morphological evolution of the estuary induced spatial salinity variations and affected the salinity in the estuarine wetlands (the Jiuduansha Shoal and East Chongming Mudflat). The salinity in the Jiuduansha Shoal increased from 1998 to 2010, whereas it decreased from 2010 to 2018. During the period 1998 to 2018, the salinity in the East Chongming Mudflat exhibited an increasing trend. These findings provide implications for management of water resources and wetlands in the Yangtze and other similar estuaries.
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O presente trabalho analisa as alterações morfológicas ocorridas no Complexo Estuarino Lagunar Mundaú-Manguaba (CELMM), através de técnicas de geoprocessamento e da modelagem computacional. Inicialmente realizou-se uma análise multitemporal das variações das linhas de costa entre o período de 1986 até 2017 a partir de imagens dos satélites Landsat 5-TM e Landsat 8-OLI. As imagens foram vetorizadas em ambiente de Sistema de Informações Geográficas (SIG) para a posterior realização do cálculo das taxas de erosão e acreção. Após isso, algumas simulações foram realizadas com o auxílio do Sistema Base de Hidrodinâmica Ambiental (SisBaHiA®) para os parâmetros tempo de residência e idade da água, considerando três cenários com configurações de embocaduras distintas (2006, 2014 e 2017). Os resultados indicaram o predomínio da deposição de sedimentos na região da embocadura, com a dinâmica migratória no sentido sudoeste-nordeste. O tempo de residência apontou possíveis áreas de estagnação na região noroeste da laguna Manguaba e nas porções noroeste e sudeste da laguna Mundaú. O cenário de 2014 apresentou menores idades das águas, mostrando que as diferentes configurações de embocaduras interferem na renovação das águas do complexo estuarino lagunar.
This article summarizes the state of knowledge and emerging trends in coastal geomorphology seeking to understand coastal responses to climate and sea level changes. The roles of climate, storminess, vertical land motion, and geologic framework are assessed as dynamic forces acting upon coasts and forcing changes. The article surveys various types of coastal responses and presents short case studies to emphasize concepts. Advances in data, methodologies, sensors and platforms to measure and predict changes are also presented, including Earth observation platforms, unmanned systems, and integrated modeling of coupled human-natural systems on coasts.
Saltmarsh area is decreasing globally from natural and anthropogenic stressors. Accelerating relative sea-level rise (SLR) is projected to exacerbate losses if not offset by upland saltmarsh migration (transgression). In the absence of coastal upland development, saltmarsh transgression rates increase with accelerating SLR and lower upland surface gradients. Storm wind and surge stress coastal upland forests causing defoliation, uprooting, and soil salinization, which makes upland areas more habitable for saltmarsh species and can promote transgression. This study aims to elucidate the contribution of storms to saltmarsh transgression by reconstructing transgression rates over the past 600 years during stormy and non-stormy conditions and fast and slow SLR rates. Our reconstructions are based on the stratigraphic record and historical aerial photography at three sites in North Carolina, U.S.A. where low-gradient pocosin upland grades into expansive saltmarsh. When sea level was rising <0.9 mm yr⁻¹, saltmarsh transgression rates at the two sites where saltmarsh is > 100 years were an average of 2 and 10 times faster during a paleo-stormy period (1400–1675 CE) than a subsequent non-stormy period. After 1865 CE when SLR accelerated to 2.4 mm yr⁻¹, transgression rates were an average of 7 times faster than the preceding slow SLR non-stormy period. The two sites where the historical record was not confounded by dredging show transgression was 7 times faster and saltmarsh areas increased an average of 28% during stormy decades than non-stormy decades; however, the rate of transgression only increased at the site with greatest surge during the stormy period characterized by strong northeast winds. Modeled transgression rates, using the paleo-upland slope and a sea level curve, do not match observed transgression rates for the paleo-stormy and rapid SLR periods. Furthermore, the thickness of saltmarsh peat younger than 1957 CE is greater than what would be predicted from independent records of SLR. Changes in the elevation of the upland surface, which is composed of peat, contributes to the disparity between predicted and observed transgression rates. The upland surface elevation can keep pace with some rates of SLR through vertical accretion; however, salinization and decomposition of upland vegetation from storm surge plus SLR decreases the elevation of the paleo-upland surface and increases accommodation and transgression rates. Along low-gradient coastlines with pocosin upland areas, SLR, subsidence, and storminess are coupled in modulating transgression rates and those processes need to be included in forecasts of saltmarsh response to climate change.
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A description is given of a model developed for the prediction of the dissipation of energy in random waves breaking on a beach. The dissipation rate per breaking wave is estimated from that in a bore of corresponding height, while the probability of occurrence of breaking waves is estimated on the basis of a wave height distribution with an upper cut-off which in shallow water is determined mainly by the local depth. A comparison with measurements of wave height decay and set-up, on a plane beach and on a beach with a bar-trough profile, indicates that the model is capable of predicting qualitatively and quantitatively all the main features of the data.
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The Wadden Sea is a unique coastal wetland containing an uninterrupted stretch of tidal flats that span a distance of nearly 500km along the North Sea coast from the Netherlands to Denmark. The development of this system is under pressure of climate change and especially the associated acceleration in sea-level rise (SLR). Sustainable management of the system to ensure safety against flooding of the hinterland, to protect the environmental value and to optimise the economic activities in the area requires predictions of the future morphological development. The Dutch Wadden Sea has been accreting by importing sediment from the ebb-tidal deltas and the North Sea coasts of the barrier islands. The average accretion rate since 1926 has been higher than that of the local relative SLR. The large sediment imports are predominantly caused by the damming of the Zuiderzee and Lauwerszee rather than due to response to this rise in sea level. The intertidal flats in all tidal basins increased in height to compensate for SLR. The barrier islands, the ebb-tidal deltas and the tidal basins that comprise tidal channels and flats together form a sediment-sharing system. The residual sediment transport between a tidal basin and its ebb-tidal delta through the tidal inlet is influenced by different processes and mechanisms. In the Dutch Wadden Sea, residual flow, tidal asymmetry and dispersion are dominant. The interaction between tidal channels and tidal flats is governed by both tides and waves. The height of the tidal flats is the result of the balance between sand supply by the tide and resuspension by waves. At present, long-term modelling for evaluating the effects of accelerated SLR mainly relies on aggregated models. These models are used to evaluate the maximum rates of sediment import into the tidal basins in the Dutch Wadden Sea. These maximum rates are compared to the combined scenarios of SLR and extraction-induced subsidence, in order to explore the future state of the Dutch Wadden Sea. For the near future, up to 2030, the effect of accelerated SLR will be limited and hardly noticeable. Over the long term, by the year 2100, the effect depends on the SLR scenarios. According to the low-end scenario, there will be hardly any effect due to SLR until 2100, whereas according to the high-end scenario the effect will be noticeable already in 2050.
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Sea level rise (SLR) has the potential to exacerbate the impacts of extreme storm events on the coastal landscape. This study examines the coupled interactions of SLR on storm-driven hydrodynamics and barrier island morphology. A numerical model is used to simulate the hydrodynamic and morphodynamic impacts of two Gulf of Mexico hurricanes under present-day and future sea levels. SLR increased surge heights and caused overwash to occur at more locations and for longer durations. During surge recession, water level gradients resulted in seaward sediment transport. The duration of the seaward-directed water level gradients was altered under SLR; longer durations caused more seaward-directed cross-barrier transport and a larger net loss in the subaerial island volume due to increased sand deposition in the nearshore. Determining how SLR and the method of SLR implementation (static or dynamic) modulate storm-driven morphologic change is important for understanding and managing longer-term coastal evolution.
Kinetic energy (KE) in the Arctic Ocean's Beaufort Gyre is dominated by the mesoscale eddy field that plays a central role in the transport of freshwater, heat, and biogeochemical tracers. Understanding Beaufort Gyre KE variability sheds light on how this freshwater reservoir responds to wind forcing and sea ice and ocean changes. The evolution and fate of mesoscale eddies relate to energy pathways in the ocean (e.g., the exchange of energy between barotropic and baroclinic modes). Mooring measurements of horizontal velocities in the Beaufort Gyre are analyzed to partition KE into barotropic and baroclinic modes and explore their evolution. We find that a significant fraction of water column KE is in the barotropic and the first two baroclinic modes. We explain this energy partitioning by quantifying the energy transfer coefficients between the vertical modes using the quasi-geostrophic potential vorticity conservation equations with a specific background stratification observed in the Beaufort Gyre. We find that the quasi-geostrophic vertical mode interactions uphold the persistence of KE in the first two baroclinic modes, consistent with observations. Our results explain the specific role of halocline structure on KE evolution in the gyre and suggest depressed transfer to the barotropic mode. This limits the capacity for frictional dissipation at the sea floor and suggests that energy dissipation via sea ice-ocean drag may be prominent.
It is now evident that noncoding RNAs play key roles in regulatory networks determining cell fate and behavior, in a myriad of different conditions, and across all species. Among these noncoding RNAs are short RNAs, such as microRNAs, snoRNAs, and piRNAs, and the functions of those are relatively well understood. Other noncoding RNAs are longer, and their modes of action and functions are also increasingly explored and deciphered. Short RNAs and long noncoding RNAs (lncRNAs) interact with each other with reciprocal consequences for their fates and functions. LncRNAs serve as precursors for many types of small RNAs and, therefore, the pathways for small RNA biogenesis can impinge upon the fate of lncRNAs. In addition, lncRNA expression can be repressed by small RNAs, and lncRNAs can affect small RNA activity and abundance through competition for binding or by triggering small RNA degradation. Here, I review the known types of interactions between small and long RNAs, discuss their outcomes, and bring representative examples from studies in mammals. This article is protected by copyright. All rights reserved.
Large estuaries are influenced by winds over adjacent coastal ocean and land areas causing significant spatial variations in water levels, currents and surface waves. In this study we apply a numerical model to simulate hydrodynamics and waves in the Albemarle-Pamlico Estuarine System, a large and shallow back-barrier basin in eastern North Carolina, over a one-month study period (September, 2008) with observations from several storm wind events of differing time scales and directions. Model performance is evaluated for a spatially varying wind field from the North American Regional Reanalysis (NARR) dataset in comparison to spatially uniform forcing from wind observations at offshore, coastal and land-based sites across the region. A spatially uniform wind field from offshore winds observations results in statistically better hydrodynamic simulations of water levels (R = 0.88) in the estuaries than NARR (R = 0.48) after comparison with measurements and indicates the importance of strong marine winds over most of the estuary surface area.
Barrier islands and associated back-barrier estuaries and lagoons interact via hydrodynamic and sedimentary processes, affecting the evolution of both systems. Understanding coupled dynamic processes between both systems is vital to forecasts of future coastal morphologic and hydrodynamic changes in response to such factors as sea-level rise and storm patterns. The Pamlico Sound and the Outer Banks barrier islands of North Carolina, USA have co-evolved in response to Holocene climate and sea-level change, and autogenic processes. Recent data and models illustrate the dynamic response of this system to minor, but rapid, climate changes occurring throughout the Holocene, including the Medieval Climate Anomaly and Little Ice Age. Periods of extreme barrier segmentation occurred during times of rapid climate change, affecting tidal energy and salinity conditions within the Pamlico Sound. Hydrodynamic models aid in understanding the magnitude of changes, and the impact on barrier morphology. Future changes to coastal systems may be anticipated based upon changes that have occurred in the past.
We produced ∼3000-year long relative sea-level (RSL) histories for two sites in North Carolina (USA) using foraminifera preserved in new and existing cores of dated salt-marsh sediment. At Cedar Island, RSL rose by ∼2.4 m during the past ∼3000 years compared to ∼3.3 m at Roanoke Island. This spatial difference arises primarily from differential GIA that caused late Holocene RSL rise to be 0.1–0.2 mm/yr faster at Roanoke Island than at Cedar Island. However, a non-linear difference in RSL between the two study regions (particularly from ∼0 CE to ∼1250 CE) indicates that additional local- to regional-scale processes drove centennial-scale RSL change in North Carolina. Therefore, the Cedar Island and Roanoke Island records should be considered as independent of one another. Between-site differences on sub-millennial timescales cannot be adequately explained by non-stationary tides, sediment compaction, or local sediment dynamics. We propose that a period of accelerating RSL rise from ∼600 CE to 1100 CE that is present at Roanoke Island (and other sites north of Cape Hatteras at least as far as Connecticut), but absent at Cedar Island (and other sites south of Cape Hatteras at least as far as northeastern Florida) is a local-to regional-scale effect of dynamic ocean and/or atmospheric circulation.
Many shoreline studies rely on historical change rates determined from aerial imagery decades to over 50 years apart to predict shoreline position and determine setback distances for coastal structures. These studies may not illustrate the coastal impacts of short-duration but potentially high-impact storm events. In this study, shoreline change rates (SCRs) are quantified at five different sites ranging from marsh to sediment bank shorelines around the Albemarle-Pamlico estuarine system (APES) for a series of historical (decadal to 50-year) and short-term (bimonthly) time periods as well as for individual storm events. Long-term (historical) SCRs of approximately −0.5 ± 0.07 m year⁻¹ are observed, consistent with previous work along estuarine shorelines in North Carolina. Short-term SCRs are highly variable, both spatially and temporally, and ranged from 15.8 ± 7.5 to −19.3 ± 11.5 m year⁻¹ at one of the study sites. The influence of wave climate on the spatial and temporal variability of short-term erosion rates is investigated using meteorological observations and coupled hydrodynamic (Delft3D) and wave (SWAN) models. The models are applied to simulate hourly variability in the surface waves and water levels. The results indicate that in the fetch-limited APES, wind direction strongly influences the wave climate at the study sites. The wave height also has an influence on short-term SCRs as determined from the wave simulations for individual meteorological events, but no statistical correlation is found for wave height and SCRs over the long term. Despite the significantly higher rates of shoreline erosion over short time periods and from individual events like hurricanes, the cumulative impact over long time periods is low. Therefore, while the short-term response of these shorelines to episodic forcing should be taken into account in management plans, the long-term trends commonly used in ocean shoreline management can also be used to determine erosion setbacks on estuarine shorelines.