Glen Gawarkiewicz - Academia.edu (original) (raw)

Papers by Glen Gawarkiewicz

Research paper thumbnail of Frontal Studies in the South China Sea: High-Resolution Hydrographic Surveys at the Shelfbreak (ASIAEX)

The long-term goal is to understand thermohaline and velocity structure near a low-latitude shelf... more The long-term goal is to understand thermohaline and velocity structure near a low-latitude shelfbreak, and their effect on sound propagation between the continental shelf and slope.

Research paper thumbnail of Special Section:-Coastal Mixing and Optics/Primer-Observations of nonlinear internal waves on the outer New England continental shelf during the summer Shelfbreak Primer study (Paper 2000JC900124)

Research paper thumbnail of Gridded Oleander ADCP Data

Oleander acoustic Doppler current profiler (ADCP) from 1994-2018. These data are processed as des... more Oleander acoustic Doppler current profiler (ADCP) from 1994-2018. These data are processed as described in Forsyth et al., (in submission 2020). The product is quality controlled and detided. The gridding is done on a 4 km distance grid, and an 8 m depth grid. Velocity fields are rotated with U south-west, and V south-east.

Research paper thumbnail of A Survival Analysis of the Gulf Stream Warm Core Rings

Journal of Geophysical Research: Oceans, 2020

Rings was analyzed using Kaplan-Meier and Cox Hazard proportional models. • Ring survival depends... more Rings was analyzed using Kaplan-Meier and Cox Hazard proportional models. • Ring survival depends on the zone, season, latitude and proximity to New England Seamount at formation. • A pattern of higher survival was observed for rings formed within (70 •-65 • W) and then demised within (75 •-70 • W).

Research paper thumbnail of Mesoscale and Submesoscale Shelf‐Ocean Exchanges Initialize an Advective Marine Heatwave

Journal of Geophysical Research: Oceans, 2021

The global climate system has been undergoing profound changes in recent decades. As a key compon... more The global climate system has been undergoing profound changes in recent decades. As a key component of the climate system, the coastal ocean has been particularly affected. As the coastal ocean changes are significant in terms of impacts on fisheries, hazards, offshore wind energy, and defense, it is important to understand how the changes that occur on a global scale are manifested in the coastal ocean. In particular, it is imperative to understand the mechanisms connecting the large-scale climate variability with the changes and processes in the coastal oceans. The coastal ocean in the Northwest North Atlantic (Figure 1) off the Northeast US coast has been in the forefront of some of the most dramatic changes in recent years, including accelerated warming (e.g.,

Research paper thumbnail of RBR2020 Cohort Mentor Panel - SciComm & Group Mentoring

Research paper thumbnail of Forecasting the Gulf Stream Path Using Buoyancy and Wind Forcing Over the North Atlantic

Journal of Geophysical Research: Oceans, 2021

In the North Atlantic subtropical gyre, the Gulf Stream (GS) is the northward flowing geostrophic... more In the North Atlantic subtropical gyre, the Gulf Stream (GS) is the northward flowing geostrophic current that is topographically bound until it reaches the latitude of Cape Hatteras, where it separates from the coast and becomes a "free-wheeling" jet. The latitudinal excursion of the GS meanders from its mean path are on the order of 100-200 km after it departs from the coast (Cornillon, 1986). This path variability has been linked to multiple processes spanning from fisheries (Nye et al., 2011) to atmospheric events (Joyce et al., 2009) and is often interpreted as an indicator of climate change (Caesar et al., 2018; Zhang et al., 2019). In particular recent rapid changes in the northwest Atlantic water properties and ecosystem, responses have been linked to the variations of the GS path and its instabilities (

Research paper thumbnail of Interannual variability of the Eastern Indian Ocean with focus on the Ningaloo Niño and negative Indian Ocean Dipole event in 2010/2011

<p&amp... more <p>The dominant mode of sea surface temperature (SST) variability in the southeast Indian Ocean off the coast of Western Australia is called Ningaloo Niño/Niña. An unprecedented Ningaloo Niño, or marine heatwave, occurred during the austral summer of 2010/2011 with mean SSTs at 3°C above the long-term mean and had drastic impacts on the ecosystem. This event was attributed to a combination of an anomalous strong Leeuwin Current and high local air-sea heat fluxes. A number of local and remote forcing mechanisms have been investigated in recent years, however, little is known about the depth-structure of these ocean extremes and their general connections to large-scale ocean interannual to decadal variability. Using a suite of simulations with a high-resolution global Ocean General Circulation Model from 1958-2016, we investigate eastern Indian Ocean variability with focus on Ningaloo Niño and corresponding cold Ningaloo Niña events. In particular, we are interested in the impacts of large-scale ocean and climate variability, such as the Indonesian Throughflow, El Niño - Southern Oscillation and the Indian Ocean Dipole (IOD), on the study region. Spatial composites reveal large-scale surface and subsurface anomalies that extend from the western Pacific across the Indonesian Archipelago into the tropical eastern Indian Ocean. In particular, strong anomalies in temperature, salinity and mixed layer depth are found to the west of Sumatra and Java, a region that is generally strongly impacted by the IOD. We therefore investigate the connection with Ningaloo Niño/Niña events, at surface and subsurface, with a focus on 2010/2011 where a strong negative IOD event occurred prior to the unprecedented Ningaloo Niño. Furthermore, we find that major heatwaves in 2000 and 2011 are associated with pronounced fresh anomalies. Sensitivity experiments allow us to assess the relative role of buoyancy and wind-forcing as drivers of the observed patterns. Our work can provide valuable contributions for advancing the understanding of Ningaloo Niño/Niña drivers from surface to depth and regional to large scales.</p>

Research paper thumbnail of Seasonal Evolution of Oceanic Upper Layer Processes in the Northern Bay of Bengal Following a Single Argo Float

Geophysical Research Letters, 2019

Seasonal evolution of the barrier layer (BL) and temperature inversion in the northern Bay of Ben... more Seasonal evolution of the barrier layer (BL) and temperature inversion in the northern Bay of Bengal and their role on the mixed layer temperature (MLT) is examined using observations from a single Argo during December 2013 to July 2017. During fall, low salinity at surface generates BL in this region. It thickens to almost 80 m in winter enhanced by deepening of isothermal layer depth due to remote forcing. During winter, surface cooling lowers near-surface temperature, and thus, the subsurface BL experiences a significant temperature inversion (~2.5°C). This temperature inversion diffuses to distribute heat within ML and surface heating begins deep penetration of shortwave radiation through ML during spring. Hence, the ML becomes thermally well stratified, resulting in the warmest MLT. The Monin-Obukhov length attains its highest value during summer indicating wind dominance in the ML. During spring and fall, upper ocean gains heat allowing buoyancy to dominate over wind mixing. Plain Language Summary The northern Bay of Bengal is well known for its fresh ocean surface due to low salinity input from rivers. This study investigates the hydrography from the temperature and salinity profiles obtained from an Argo float, which drifted for 44 months in the northern Bay of Bengal. The mixed layer depends on the local processes and isothermal layer depth depends on the remote forcing through propagating Rossby waves. Thermal inversion within thick barrier layer is observed during winter. Wind stress is the dominant forcing in setting up the mixed layer during summer and winter. The barrier layer and temperature inversion play important roles on the mixed layer temperature. The state-of-the-art models failed to reproduce the temperature inversion layer due to low vertical resolution. While this is an integrated view from a single Argo, high-frequency high-resolution sampling would be necessary to understand turbulent mixed layer processes and quantify relative roles of haline buoyancy to thermal buoyancy.

Research paper thumbnail of Partnering with Fishing Fleets to Monitor Ocean Conditions

Annual Review of Marine Science, 2019

Engaging ocean users, including fishing fleets, in oceanographic and ecological research is a val... more Engaging ocean users, including fishing fleets, in oceanographic and ecological research is a valuable method for collecting high-quality data, improving cost efficiency, and increasing societal appreciation for scientific research. As research partners, fishing fleets provide broad access to and knowledge of the ocean, and fishers are highly motivated to use the data collected to better understand the ecosystems in which they harvest. Here, we discuss recent trends in collaborative research that have increased the capacity of and access to scientific data collection. We also describe common elements of successful collaborative research programs, including definition of a scientific problem and goals, choice of technology, data collection and sampling design, data management and dissemination, and data analysis and communication. Finally, we review four case studies that demonstrate the general principles of effective collaborative research as well as the utility of citizen-collecte...

Research paper thumbnail of Shelfbreak Frontal Structure and Gulf Stream Interaction north of Cape Hatteras: High resolution observations and regional modeling

The circulation over the shelf and slope in the vicinity of Cape Hatteras is complicated due to t... more The circulation over the shelf and slope in the vicinity of Cape Hatteras is complicated due to the presence of a number of fronts. The Cape Hatteras region marks the termination of the Shelfbreak Front and associated Cold Pool water masses, as Middle Atlantic Bight shelf water is entrained into the Gulf Stream. Also present within the region are the Hatteras Front, consisting of near surface buoyant water from the Middle Atlantic Bight which commonly moves southward past Diamond Shoals and into the South Atlantic Bight, as well as the Gulf Stream, which detaches from the continental slope in this region. In order to investigate the complex circulation in the region and the inter-relationship between the fronts, we performed high-resolution hydrographic observations in August, 2004 to investigate the southward evolution of the Cold Pool water mass and the shelfbreak front in the vicinity of Cape Hatteras. During the experiment, there were Gulf Stream waters directly abutting the she...

Research paper thumbnail of Impacts of the warming of the continental shelf in spring 2012 on acoustic propagation conditions and fish distributions north of Cape Hatteras

The Journal of the Acoustical Society of America, 2014

ABSTRACT During May 2012, we conducted hydrographic surveys in conjunction with studies of acoust... more ABSTRACT During May 2012, we conducted hydrographic surveys in conjunction with studies of acoustic scattering from fish schools north of Cape Hatteras. The waters of the continental shelf were greater than 4° Degrees C. warmer than prior observations during typical spring-time conditions in May 1996. In addition, the temperature gradients which normally exist across the shelfbreak front were absent, leading to intensification of the shelfbreak frontal jet. We relate the warming to large-scale atmospheric shifts and also report on the absence of cold water fish species, which were expected to be abundant in the study area.

Research paper thumbnail of Observations and modeling of acoustic intensity fluctuations seen during the 1996 summer New England shelfbreak PRIMER experiment

The Journal of the Acoustical Society of America, 2002

ABSTRACT

Research paper thumbnail of Slope water, Gulf Stream, and seasonal influences on southern Mid-Atlantic Bight circulation during the fall-winter transition

Journal of Geophysical Research, 2005

Observations from autumn 2000 near the shelfbreak front in the Middle Atlantic Bight are used to ... more Observations from autumn 2000 near the shelfbreak front in the Middle Atlantic Bight are used to describe the transition from stratified summer conditions to well-mixed winter conditions over the shelf. During the observational period, the front differed dramatically from climatological conditions, with buoyant Gulf Stream water found shoreward over the subsurface shelfbreak front. Water mass analysis shows a large number of separate water masses with shelf, slope, and Gulf Stream origins. The coolest shelf water was located at the shelfbreak and may be related to ''cold pool'' water masses observed to the north during summer. Shoreward of this shelfbreak water mass, a mid-shelf front was present which intersected the bottom at the 50-m isobath. High-volume transports were associated with both the shelfbreak and mid-shelf fronts. Transport estimates from the cross-shelf sections were approximately 1 Sverdrup, which is large relative to previous estimates of shelf transport. The foot of the front was near the 130-m isobath, much deeper than the climatological position near the 75-m isobath; however, this is consistent with a recent theory relating the magnitude of alongshelf transport to the depth at which the front intersects the bottom.

Research paper thumbnail of The coastal ocean off northeastern North America: A large-scale view

Research paper thumbnail of The Impact of Warm Core Rings on Middle Atlantic Bight Shelf Temperature and Shelf Break Velocity

Journal of Geophysical Research: Oceans, 2022

Warm Core Rings (WCRs) form from large meanders of the Gulf Stream that are pinched off, leaving ... more Warm Core Rings (WCRs) form from large meanders of the Gulf Stream that are pinched off, leaving an anti-cyclonic eddy of warm salty water north of the Gulf Stream. These rings can abut the Middle Atlantic Bight (MAB) shelf as they move westward through the Slope Sea until they are reabsorbed into the Gulf Stream. Disruptions to mean shelf break currents as well as large shelf temperature anomalies have been attributed to adjacent rings (e.g., Beardsley et al., 1985; Forsyth et al., 2020; Gawarkiewicz et al., 2019). Observations have shown that more rings have been formed annually since 2000, leading to the possibility that there are more frequent disruptions to the shelf system (Gangopadhyay et al., 2019). With this increase in the number of ring formations per year, understanding how rings are able to impact the shelf is increasingly important. Early studies of WCRs combined limited in-situ observations with satellite thermal imaging to study the properties of the rings and their interactions with the shelf (e.g., Bisagni, 1983; Churchill et al., 1986; Joyce, 1984; Morgan & Bishop, 1977). These studies quantified dynamical properties of the rings, and estimated cross-shelf fluxes associated with warm streamers which cross onto the shelf even as the ring core remains over the slope. Estimates of the ring-driven cross-shelf heat flux suggest that they play a key role in the yearly heat budget for the shelf (Morgan & Bishop, 1977). Individual shelf streamers were also observed to carry a significant fraction of the annual slope water transport to the shelf as estimated from salinity (Churchill et al., 1986). The cross-shelf water mass exchange is modified by both warm streamers moving onto the shelf, and also cold streamers pulled Abstract Warm Core Rings (WCRs) are known to disrupt the shelf flow as well as drive strong heat transport onto the Middle Atlantic Bight shelf. We examine 27 rings sampled by the container ship Oleander, 16 rings which have in-situ velocity data and 11 rings identified from satellite sea surface height but with in-situ temperature data, to study the variability in rings' impact on shelf break velocities and on the temperature of the adjacent shelf. WCRs that have higher rotational velocities and are closer to the shelf are found to exert greater influence on the along-shelf velocities, with the fastest and closest rings reversing the direction of flow at the shelf break. As rings approach the study site, the Shelfbreak Jet is faster than when the rings are about to exit the study site, likely due to first steepening then flattening of the isopycnals at the Shelfbreak Front. Rings also have lasting impacts on the shelf temperature: rings with faster rotational velocities cool the shelf and rings with slower rotational velocities warm the shelf. The evolution of temperature on the shelf as a ring passes is strongly tied to the season. During warmer seasons, when temperature stratification on the shelf is strong, a ring cools the shelf; during periods of weak thermal stratification, rings tend to warm the shelf. Rings which cool the shelf are additionally associated with increased upwelling as they pass the study site. Plain Language Summary Warm Core Rings are large rotating masses of Gulf Stream water that have been isolated from the Gulf Stream and move through the Slope Sea next to the shelf. We identify and study 16 rings from ship board observations off the coast of New Jersey, and additionally study 11 more rings using a combination of limited ship observations and satellite data. Typical velocities at the shelf break in this region are to the southwest. Rings which rotate more quickly tend to disrupt the normal velocities over the shelf and shelf break and can even reverse these currents. As a ring approaches the study site the southwest velocities over the shelf break are enhanced, and when a ring is exiting the study site the southwest velocities at the shelf break are reduced. Rings exert a lasting influence on the temperature on the shelf. During warmer seasons, rings tend to cool the shelf, while in cooler seasons rings tend to warm the shelf. FORSYTH ET AL.

Research paper thumbnail of Autonomous Tracking of Salinity-Intrusion Fronts by a Long-Range Autonomous Underwater Vehicle

IEEE Journal of Oceanic Engineering

Shoreward intrusions of anomalously salty water along the continental shelf of the Middle Atlanti... more Shoreward intrusions of anomalously salty water along the continental shelf of the Middle Atlantic Bight are often observed in spring and summer. Exchange of heat, nutrients, and carbon across the salinity-intrusion front has a significant impact on the marine ecosystem and fisheries. In this article, we developed a method of using an autonomous underwater vehicle (AUV) to detect a salinity-intrusion front and track the front's movement. Autonomous front detection is based on the different vertical structures of salinity in the two distinct water types: the vertical difference of salinity is large in the intruding saltier water because of the salinity "tongue" at mid-depth, but is small in the nearshore fresher water due to absence of the salinity anomaly. Every time the AUV crosses and detects the front, the vehicle makes a turn at an oblique angle to cross the front, thus zigzagging through the front to map the frontal zone. The AUV's zigzags sweep back and forth to track the front as it moves over time. From June 25 to 30, 2021, a Tethys-class long-range AUV mapped and tracked a salinity-intrusion front on the southern New England shelf. The frontal tracking revealed the salinity intrusion's 3-D structure and temporal evolution with unprecedented detail.

Research paper thumbnail of A large-amplitude meander of the shelfbreak front in the Middle Atlantic Bight: Observations from the Shelfbreak Primer experiment

In order to examine spatial and temporal variability of the shelfbreak front during peak stratifi... more In order to examine spatial and temporal variability of the shelfbreak front during peak stratification, repeated surveys using a towed undulating vehicle (SeaSoar) are used to describe the evolution of shelfbreak frontal structure during 26 July to 1 August 1996 south of New England. Spatial correlation (e-folding) scales for the upper 60 m of the water column were generally between 8 and 15 km for temperature, salinity, and velocity. Temporal correlation scales were about 1 day. The frontal variability was dominated by the passage of a westward propagating meander that had a wavelength of 40 km, a propagation speed of 0.11 m s À1 , and an amplitude of 15 km (30 km from crest to trough). Along-front geostrophic velocities (referenced to a shipboard acoustic Doppler current profilers) were as large as 0.45 m s À1 , although subject to significant along-front variations. The relative vorticity within the jet was large, with a maximum 0.6 of the local value of the Coriolis parameter. Seaward of the front, a small detached eddy consisting of shelf water was present with a diameter of approximately 15 km. Ageostrophic contributions to the velocity field are estimated to be as large as 0.3 m s À1 in regions of sharp curvature within the meander. These observations strongly suggest that during at least some time periods, shelfbreak exchange is nonlinear (large Rossby number) and dominated by features on a horizontal scale of order 10 km.

Research paper thumbnail of Population Connectivity in Marine Systems Workshop Convenors

Research paper thumbnail of Seasonal and Tidal Variability of Surface Currents in the Western Andaman Sea Using HF Radars and Buoy Observations During 2016–2017

IEEE Transactions on Geoscience and Remote Sensing, 2021

The characteristics of surface currents during November 2016–October 2017 are studied using obser... more The characteristics of surface currents during November 2016–October 2017 are studied using observations from the high-frequency radars (HFRs) and a moored buoy (BD12) along the western Andaman Sea (WAnS). The comparison of HFR currents with the collocated currents from BD12 shows a high correlation (>0.78) on a daily scale for both the components. Moreover, the daily HFR currents compared reasonably well to the composite daily surface currents from multiple satellites for both the zonal and meridional components. The reversal of currents is observed during the northeast (November–February) and southwest (June–October) monsoons with the mean current magnitudes of 0.41 m/s northward and 0.22 m/s southward, respectively, which is predominantly influenced by the local wind stress. The seasonal reversal of currents leads to the exchange of waters between the WAnS and the Bay of Bengal through the 11° channel, which is primarily due to the Ekman mass transport. Harmonic analysis of the hourly data from HFRs shows the dominance of M2 tidal currents, followed by other semidiurnal (S2, N2), diurnal (K1, O1), and shallow water constituents (M4 and MS4). Also, the tidal constituents from both the current observations matched in their relative order of amplitudes with a reasonable correlation (0.95). Total tidal variance ranges between 10% and 50% in the WAnS, with the highest contributions from the M2 tidal currents (of 25%). Moreover, stronger M2 tidal currents are observed to skirt around Little Andaman (LA) Island extending out to 100-km offshore, with maximum amplitudes of 12 cm/s.

Research paper thumbnail of Frontal Studies in the South China Sea: High-Resolution Hydrographic Surveys at the Shelfbreak (ASIAEX)

The long-term goal is to understand thermohaline and velocity structure near a low-latitude shelf... more The long-term goal is to understand thermohaline and velocity structure near a low-latitude shelfbreak, and their effect on sound propagation between the continental shelf and slope.

Research paper thumbnail of Special Section:-Coastal Mixing and Optics/Primer-Observations of nonlinear internal waves on the outer New England continental shelf during the summer Shelfbreak Primer study (Paper 2000JC900124)

Research paper thumbnail of Gridded Oleander ADCP Data

Oleander acoustic Doppler current profiler (ADCP) from 1994-2018. These data are processed as des... more Oleander acoustic Doppler current profiler (ADCP) from 1994-2018. These data are processed as described in Forsyth et al., (in submission 2020). The product is quality controlled and detided. The gridding is done on a 4 km distance grid, and an 8 m depth grid. Velocity fields are rotated with U south-west, and V south-east.

Research paper thumbnail of A Survival Analysis of the Gulf Stream Warm Core Rings

Journal of Geophysical Research: Oceans, 2020

Rings was analyzed using Kaplan-Meier and Cox Hazard proportional models. • Ring survival depends... more Rings was analyzed using Kaplan-Meier and Cox Hazard proportional models. • Ring survival depends on the zone, season, latitude and proximity to New England Seamount at formation. • A pattern of higher survival was observed for rings formed within (70 •-65 • W) and then demised within (75 •-70 • W).

Research paper thumbnail of Mesoscale and Submesoscale Shelf‐Ocean Exchanges Initialize an Advective Marine Heatwave

Journal of Geophysical Research: Oceans, 2021

The global climate system has been undergoing profound changes in recent decades. As a key compon... more The global climate system has been undergoing profound changes in recent decades. As a key component of the climate system, the coastal ocean has been particularly affected. As the coastal ocean changes are significant in terms of impacts on fisheries, hazards, offshore wind energy, and defense, it is important to understand how the changes that occur on a global scale are manifested in the coastal ocean. In particular, it is imperative to understand the mechanisms connecting the large-scale climate variability with the changes and processes in the coastal oceans. The coastal ocean in the Northwest North Atlantic (Figure 1) off the Northeast US coast has been in the forefront of some of the most dramatic changes in recent years, including accelerated warming (e.g.,

Research paper thumbnail of RBR2020 Cohort Mentor Panel - SciComm & Group Mentoring

Research paper thumbnail of Forecasting the Gulf Stream Path Using Buoyancy and Wind Forcing Over the North Atlantic

Journal of Geophysical Research: Oceans, 2021

In the North Atlantic subtropical gyre, the Gulf Stream (GS) is the northward flowing geostrophic... more In the North Atlantic subtropical gyre, the Gulf Stream (GS) is the northward flowing geostrophic current that is topographically bound until it reaches the latitude of Cape Hatteras, where it separates from the coast and becomes a "free-wheeling" jet. The latitudinal excursion of the GS meanders from its mean path are on the order of 100-200 km after it departs from the coast (Cornillon, 1986). This path variability has been linked to multiple processes spanning from fisheries (Nye et al., 2011) to atmospheric events (Joyce et al., 2009) and is often interpreted as an indicator of climate change (Caesar et al., 2018; Zhang et al., 2019). In particular recent rapid changes in the northwest Atlantic water properties and ecosystem, responses have been linked to the variations of the GS path and its instabilities (

Research paper thumbnail of Interannual variability of the Eastern Indian Ocean with focus on the Ningaloo Niño and negative Indian Ocean Dipole event in 2010/2011

<p&amp... more <p>The dominant mode of sea surface temperature (SST) variability in the southeast Indian Ocean off the coast of Western Australia is called Ningaloo Niño/Niña. An unprecedented Ningaloo Niño, or marine heatwave, occurred during the austral summer of 2010/2011 with mean SSTs at 3°C above the long-term mean and had drastic impacts on the ecosystem. This event was attributed to a combination of an anomalous strong Leeuwin Current and high local air-sea heat fluxes. A number of local and remote forcing mechanisms have been investigated in recent years, however, little is known about the depth-structure of these ocean extremes and their general connections to large-scale ocean interannual to decadal variability. Using a suite of simulations with a high-resolution global Ocean General Circulation Model from 1958-2016, we investigate eastern Indian Ocean variability with focus on Ningaloo Niño and corresponding cold Ningaloo Niña events. In particular, we are interested in the impacts of large-scale ocean and climate variability, such as the Indonesian Throughflow, El Niño - Southern Oscillation and the Indian Ocean Dipole (IOD), on the study region. Spatial composites reveal large-scale surface and subsurface anomalies that extend from the western Pacific across the Indonesian Archipelago into the tropical eastern Indian Ocean. In particular, strong anomalies in temperature, salinity and mixed layer depth are found to the west of Sumatra and Java, a region that is generally strongly impacted by the IOD. We therefore investigate the connection with Ningaloo Niño/Niña events, at surface and subsurface, with a focus on 2010/2011 where a strong negative IOD event occurred prior to the unprecedented Ningaloo Niño. Furthermore, we find that major heatwaves in 2000 and 2011 are associated with pronounced fresh anomalies. Sensitivity experiments allow us to assess the relative role of buoyancy and wind-forcing as drivers of the observed patterns. Our work can provide valuable contributions for advancing the understanding of Ningaloo Niño/Niña drivers from surface to depth and regional to large scales.</p>

Research paper thumbnail of Seasonal Evolution of Oceanic Upper Layer Processes in the Northern Bay of Bengal Following a Single Argo Float

Geophysical Research Letters, 2019

Seasonal evolution of the barrier layer (BL) and temperature inversion in the northern Bay of Ben... more Seasonal evolution of the barrier layer (BL) and temperature inversion in the northern Bay of Bengal and their role on the mixed layer temperature (MLT) is examined using observations from a single Argo during December 2013 to July 2017. During fall, low salinity at surface generates BL in this region. It thickens to almost 80 m in winter enhanced by deepening of isothermal layer depth due to remote forcing. During winter, surface cooling lowers near-surface temperature, and thus, the subsurface BL experiences a significant temperature inversion (~2.5°C). This temperature inversion diffuses to distribute heat within ML and surface heating begins deep penetration of shortwave radiation through ML during spring. Hence, the ML becomes thermally well stratified, resulting in the warmest MLT. The Monin-Obukhov length attains its highest value during summer indicating wind dominance in the ML. During spring and fall, upper ocean gains heat allowing buoyancy to dominate over wind mixing. Plain Language Summary The northern Bay of Bengal is well known for its fresh ocean surface due to low salinity input from rivers. This study investigates the hydrography from the temperature and salinity profiles obtained from an Argo float, which drifted for 44 months in the northern Bay of Bengal. The mixed layer depends on the local processes and isothermal layer depth depends on the remote forcing through propagating Rossby waves. Thermal inversion within thick barrier layer is observed during winter. Wind stress is the dominant forcing in setting up the mixed layer during summer and winter. The barrier layer and temperature inversion play important roles on the mixed layer temperature. The state-of-the-art models failed to reproduce the temperature inversion layer due to low vertical resolution. While this is an integrated view from a single Argo, high-frequency high-resolution sampling would be necessary to understand turbulent mixed layer processes and quantify relative roles of haline buoyancy to thermal buoyancy.

Research paper thumbnail of Partnering with Fishing Fleets to Monitor Ocean Conditions

Annual Review of Marine Science, 2019

Engaging ocean users, including fishing fleets, in oceanographic and ecological research is a val... more Engaging ocean users, including fishing fleets, in oceanographic and ecological research is a valuable method for collecting high-quality data, improving cost efficiency, and increasing societal appreciation for scientific research. As research partners, fishing fleets provide broad access to and knowledge of the ocean, and fishers are highly motivated to use the data collected to better understand the ecosystems in which they harvest. Here, we discuss recent trends in collaborative research that have increased the capacity of and access to scientific data collection. We also describe common elements of successful collaborative research programs, including definition of a scientific problem and goals, choice of technology, data collection and sampling design, data management and dissemination, and data analysis and communication. Finally, we review four case studies that demonstrate the general principles of effective collaborative research as well as the utility of citizen-collecte...

Research paper thumbnail of Shelfbreak Frontal Structure and Gulf Stream Interaction north of Cape Hatteras: High resolution observations and regional modeling

The circulation over the shelf and slope in the vicinity of Cape Hatteras is complicated due to t... more The circulation over the shelf and slope in the vicinity of Cape Hatteras is complicated due to the presence of a number of fronts. The Cape Hatteras region marks the termination of the Shelfbreak Front and associated Cold Pool water masses, as Middle Atlantic Bight shelf water is entrained into the Gulf Stream. Also present within the region are the Hatteras Front, consisting of near surface buoyant water from the Middle Atlantic Bight which commonly moves southward past Diamond Shoals and into the South Atlantic Bight, as well as the Gulf Stream, which detaches from the continental slope in this region. In order to investigate the complex circulation in the region and the inter-relationship between the fronts, we performed high-resolution hydrographic observations in August, 2004 to investigate the southward evolution of the Cold Pool water mass and the shelfbreak front in the vicinity of Cape Hatteras. During the experiment, there were Gulf Stream waters directly abutting the she...

Research paper thumbnail of Impacts of the warming of the continental shelf in spring 2012 on acoustic propagation conditions and fish distributions north of Cape Hatteras

The Journal of the Acoustical Society of America, 2014

ABSTRACT During May 2012, we conducted hydrographic surveys in conjunction with studies of acoust... more ABSTRACT During May 2012, we conducted hydrographic surveys in conjunction with studies of acoustic scattering from fish schools north of Cape Hatteras. The waters of the continental shelf were greater than 4° Degrees C. warmer than prior observations during typical spring-time conditions in May 1996. In addition, the temperature gradients which normally exist across the shelfbreak front were absent, leading to intensification of the shelfbreak frontal jet. We relate the warming to large-scale atmospheric shifts and also report on the absence of cold water fish species, which were expected to be abundant in the study area.

Research paper thumbnail of Observations and modeling of acoustic intensity fluctuations seen during the 1996 summer New England shelfbreak PRIMER experiment

The Journal of the Acoustical Society of America, 2002

ABSTRACT

Research paper thumbnail of Slope water, Gulf Stream, and seasonal influences on southern Mid-Atlantic Bight circulation during the fall-winter transition

Journal of Geophysical Research, 2005

Observations from autumn 2000 near the shelfbreak front in the Middle Atlantic Bight are used to ... more Observations from autumn 2000 near the shelfbreak front in the Middle Atlantic Bight are used to describe the transition from stratified summer conditions to well-mixed winter conditions over the shelf. During the observational period, the front differed dramatically from climatological conditions, with buoyant Gulf Stream water found shoreward over the subsurface shelfbreak front. Water mass analysis shows a large number of separate water masses with shelf, slope, and Gulf Stream origins. The coolest shelf water was located at the shelfbreak and may be related to ''cold pool'' water masses observed to the north during summer. Shoreward of this shelfbreak water mass, a mid-shelf front was present which intersected the bottom at the 50-m isobath. High-volume transports were associated with both the shelfbreak and mid-shelf fronts. Transport estimates from the cross-shelf sections were approximately 1 Sverdrup, which is large relative to previous estimates of shelf transport. The foot of the front was near the 130-m isobath, much deeper than the climatological position near the 75-m isobath; however, this is consistent with a recent theory relating the magnitude of alongshelf transport to the depth at which the front intersects the bottom.

Research paper thumbnail of The coastal ocean off northeastern North America: A large-scale view

Research paper thumbnail of The Impact of Warm Core Rings on Middle Atlantic Bight Shelf Temperature and Shelf Break Velocity

Journal of Geophysical Research: Oceans, 2022

Warm Core Rings (WCRs) form from large meanders of the Gulf Stream that are pinched off, leaving ... more Warm Core Rings (WCRs) form from large meanders of the Gulf Stream that are pinched off, leaving an anti-cyclonic eddy of warm salty water north of the Gulf Stream. These rings can abut the Middle Atlantic Bight (MAB) shelf as they move westward through the Slope Sea until they are reabsorbed into the Gulf Stream. Disruptions to mean shelf break currents as well as large shelf temperature anomalies have been attributed to adjacent rings (e.g., Beardsley et al., 1985; Forsyth et al., 2020; Gawarkiewicz et al., 2019). Observations have shown that more rings have been formed annually since 2000, leading to the possibility that there are more frequent disruptions to the shelf system (Gangopadhyay et al., 2019). With this increase in the number of ring formations per year, understanding how rings are able to impact the shelf is increasingly important. Early studies of WCRs combined limited in-situ observations with satellite thermal imaging to study the properties of the rings and their interactions with the shelf (e.g., Bisagni, 1983; Churchill et al., 1986; Joyce, 1984; Morgan & Bishop, 1977). These studies quantified dynamical properties of the rings, and estimated cross-shelf fluxes associated with warm streamers which cross onto the shelf even as the ring core remains over the slope. Estimates of the ring-driven cross-shelf heat flux suggest that they play a key role in the yearly heat budget for the shelf (Morgan & Bishop, 1977). Individual shelf streamers were also observed to carry a significant fraction of the annual slope water transport to the shelf as estimated from salinity (Churchill et al., 1986). The cross-shelf water mass exchange is modified by both warm streamers moving onto the shelf, and also cold streamers pulled Abstract Warm Core Rings (WCRs) are known to disrupt the shelf flow as well as drive strong heat transport onto the Middle Atlantic Bight shelf. We examine 27 rings sampled by the container ship Oleander, 16 rings which have in-situ velocity data and 11 rings identified from satellite sea surface height but with in-situ temperature data, to study the variability in rings' impact on shelf break velocities and on the temperature of the adjacent shelf. WCRs that have higher rotational velocities and are closer to the shelf are found to exert greater influence on the along-shelf velocities, with the fastest and closest rings reversing the direction of flow at the shelf break. As rings approach the study site, the Shelfbreak Jet is faster than when the rings are about to exit the study site, likely due to first steepening then flattening of the isopycnals at the Shelfbreak Front. Rings also have lasting impacts on the shelf temperature: rings with faster rotational velocities cool the shelf and rings with slower rotational velocities warm the shelf. The evolution of temperature on the shelf as a ring passes is strongly tied to the season. During warmer seasons, when temperature stratification on the shelf is strong, a ring cools the shelf; during periods of weak thermal stratification, rings tend to warm the shelf. Rings which cool the shelf are additionally associated with increased upwelling as they pass the study site. Plain Language Summary Warm Core Rings are large rotating masses of Gulf Stream water that have been isolated from the Gulf Stream and move through the Slope Sea next to the shelf. We identify and study 16 rings from ship board observations off the coast of New Jersey, and additionally study 11 more rings using a combination of limited ship observations and satellite data. Typical velocities at the shelf break in this region are to the southwest. Rings which rotate more quickly tend to disrupt the normal velocities over the shelf and shelf break and can even reverse these currents. As a ring approaches the study site the southwest velocities over the shelf break are enhanced, and when a ring is exiting the study site the southwest velocities at the shelf break are reduced. Rings exert a lasting influence on the temperature on the shelf. During warmer seasons, rings tend to cool the shelf, while in cooler seasons rings tend to warm the shelf. FORSYTH ET AL.

Research paper thumbnail of Autonomous Tracking of Salinity-Intrusion Fronts by a Long-Range Autonomous Underwater Vehicle

IEEE Journal of Oceanic Engineering

Shoreward intrusions of anomalously salty water along the continental shelf of the Middle Atlanti... more Shoreward intrusions of anomalously salty water along the continental shelf of the Middle Atlantic Bight are often observed in spring and summer. Exchange of heat, nutrients, and carbon across the salinity-intrusion front has a significant impact on the marine ecosystem and fisheries. In this article, we developed a method of using an autonomous underwater vehicle (AUV) to detect a salinity-intrusion front and track the front's movement. Autonomous front detection is based on the different vertical structures of salinity in the two distinct water types: the vertical difference of salinity is large in the intruding saltier water because of the salinity "tongue" at mid-depth, but is small in the nearshore fresher water due to absence of the salinity anomaly. Every time the AUV crosses and detects the front, the vehicle makes a turn at an oblique angle to cross the front, thus zigzagging through the front to map the frontal zone. The AUV's zigzags sweep back and forth to track the front as it moves over time. From June 25 to 30, 2021, a Tethys-class long-range AUV mapped and tracked a salinity-intrusion front on the southern New England shelf. The frontal tracking revealed the salinity intrusion's 3-D structure and temporal evolution with unprecedented detail.

Research paper thumbnail of A large-amplitude meander of the shelfbreak front in the Middle Atlantic Bight: Observations from the Shelfbreak Primer experiment

In order to examine spatial and temporal variability of the shelfbreak front during peak stratifi... more In order to examine spatial and temporal variability of the shelfbreak front during peak stratification, repeated surveys using a towed undulating vehicle (SeaSoar) are used to describe the evolution of shelfbreak frontal structure during 26 July to 1 August 1996 south of New England. Spatial correlation (e-folding) scales for the upper 60 m of the water column were generally between 8 and 15 km for temperature, salinity, and velocity. Temporal correlation scales were about 1 day. The frontal variability was dominated by the passage of a westward propagating meander that had a wavelength of 40 km, a propagation speed of 0.11 m s À1 , and an amplitude of 15 km (30 km from crest to trough). Along-front geostrophic velocities (referenced to a shipboard acoustic Doppler current profilers) were as large as 0.45 m s À1 , although subject to significant along-front variations. The relative vorticity within the jet was large, with a maximum 0.6 of the local value of the Coriolis parameter. Seaward of the front, a small detached eddy consisting of shelf water was present with a diameter of approximately 15 km. Ageostrophic contributions to the velocity field are estimated to be as large as 0.3 m s À1 in regions of sharp curvature within the meander. These observations strongly suggest that during at least some time periods, shelfbreak exchange is nonlinear (large Rossby number) and dominated by features on a horizontal scale of order 10 km.

Research paper thumbnail of Population Connectivity in Marine Systems Workshop Convenors

Research paper thumbnail of Seasonal and Tidal Variability of Surface Currents in the Western Andaman Sea Using HF Radars and Buoy Observations During 2016–2017

IEEE Transactions on Geoscience and Remote Sensing, 2021

The characteristics of surface currents during November 2016–October 2017 are studied using obser... more The characteristics of surface currents during November 2016–October 2017 are studied using observations from the high-frequency radars (HFRs) and a moored buoy (BD12) along the western Andaman Sea (WAnS). The comparison of HFR currents with the collocated currents from BD12 shows a high correlation (>0.78) on a daily scale for both the components. Moreover, the daily HFR currents compared reasonably well to the composite daily surface currents from multiple satellites for both the zonal and meridional components. The reversal of currents is observed during the northeast (November–February) and southwest (June–October) monsoons with the mean current magnitudes of 0.41 m/s northward and 0.22 m/s southward, respectively, which is predominantly influenced by the local wind stress. The seasonal reversal of currents leads to the exchange of waters between the WAnS and the Bay of Bengal through the 11° channel, which is primarily due to the Ekman mass transport. Harmonic analysis of the hourly data from HFRs shows the dominance of M2 tidal currents, followed by other semidiurnal (S2, N2), diurnal (K1, O1), and shallow water constituents (M4 and MS4). Also, the tidal constituents from both the current observations matched in their relative order of amplitudes with a reasonable correlation (0.95). Total tidal variance ranges between 10% and 50% in the WAnS, with the highest contributions from the M2 tidal currents (of 25%). Moreover, stronger M2 tidal currents are observed to skirt around Little Andaman (LA) Island extending out to 100-km offshore, with maximum amplitudes of 12 cm/s.