Donglai Gong | Woods Hole Oceanographic Institution (original) (raw)

Papers by Donglai Gong

Journal of Physical Oceanography

The ocean surface boundary layer is a gateway of energy transfer into the ocean. Wind-driven shea... more The ocean surface boundary layer is a gateway of energy transfer into the ocean. Wind-driven shear and meteorologically forced convection inject turbulent kinetic energy into the surface boundary layer, mixing the upper ocean and transforming its density structure. In the absence of direct observations or the capability to resolve subgrid-scale 3D turbulence in operational ocean models, the oceanography community relies on surface boundary layer similarity scalings (BLS) of shear and convective turbulence to represent this mixing. Despite their importance, near-surface mixing processes (and ubiquitous BLS representations of these processes) have been undersampled in high-energy forcing regimes such as the Southern Ocean. With the maturing of autonomous sampling platforms, there is now an opportunity to collect high-resolution spatial and temporal measurements in the full range of forcing conditions. Here, we characterize near-surface turbulence under strong wind forcing using the fi...

This data contains 125 geolocated water stable isotope, salinity, and temperature measurements fr... more This data contains 125 geolocated water stable isotope, salinity, and temperature measurements from niskin bottle samples at varying depths from 52 Conductivity, Temperature, Depth (CTD) casts along the RV Oden cruise track. The CTD rosette water sampling was conducted following the CLIVAR/GO-SHIP protocol with a 'water cop' keeping track of the sampling order. Sampling for gases goes first, followed by nutrients, water stable isotopes, and then microbiological and DNA sampling during each cast. Samples for water stable isotopes analyses were collected by filling 30-mL Nalgene bottles to the brim. Bottles were closed tightly, sealed with parafilm, and stored in a labeled sample bag. Sampling depths chosen were based on the profile, location, and whether samples were collected for nutrients. Two samples were collected per depth. A total of 250 samples were collected from the 52 CTD casts from 19 July – 04 August 2019. The corresponding salinity and temperature measurements pe...

The relationship between δ¹⁸O and salinity has been widely studied because it can provide crucial... more The relationship between δ¹⁸O and salinity has been widely studied because it can provide crucial information on the partitioning of isotopes through the hydrological cycle. Current understanding of δ¹⁸O-S characteristics has been used to constrain water cycle models, isotope-enabled atmospheric and ocean models as well as to monitor evaporation (E) and precipitation (P) changes in major ocean basins. However, in the polar regions, where large spatial and temporal variabilities in δ¹⁸O and salinity are expected due to the highly seasonal sea ice melting/formation, river runoff, E-P intensification and rapidly changing summer ice minimum, uncertainties still surround the δ¹⁸O-Salinity relationship. To observe the inputs of freshwater in a poorly-understood, but vastly changing region in the Arctic, we collected matching δ¹⁸O-Salinity data from discrete samples from the surface (bucket sampling) and from profiles (Conductivity, Temperature, Depth (CTD) casts) in the Canadian Arctic Ar...

This data contains 63 geolocated water stable isotopes and salinity measurements from the surface... more This data contains 63 geolocated water stable isotopes and salinity measurements from the surface of the ocean along the RV Oden cruise track. Surface seawater sampling was conducted using bucket sampling. This was done by throwing a weighted bucket offboard to sample the surface of the ocean every six (6) hours. Chosen times were 5:00, 11:00, 17:00, and 23:00. Multiple readings of sea surface salinity were recorded using a YSI professional series digital probe per sampling Water samples were transferred to a 30-mL Nalgene bottles that were filled to the brim. Bottles were tightly closed, sealed with parafilm, and placed inside sampling bags. Two samples were collected per sampling point, and all measurements were geolocated. A total of 126 samples were collected from 19 July – 04 August 2019. All water samples were transported to the Atmosphere, Climate, and Ecosystems lab at the University of Illinois at Chicago for processing. The δ¹⁸O and dD were measured using a Picarro l2130-I...

Journal of Atmospheric and Oceanic Technology, 2022

Finescale strain parameterization (hereafter, FSP) of turbulent kinetic energy dissipation rate h... more Finescale strain parameterization (hereafter, FSP) of turbulent kinetic energy dissipation rate has become a widely used method for observing ocean mixing, solving a coverage problem where direct turbulence measurements are absent but CTD profiles are available. This method can offer significant value, but there are limitations in its broad application to the global ocean. FSP often fails to produce reliable results in frontal zones where temperature-salinity (T/S) intrusive features contaminate the CTD strain spectrum, as well as where the aspect ratio of the internal wave spectrum is known to vary greatly with depth, as frequently occurs in the Southern Ocean. In this study we use direct turbulence measurements from DIMES (Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean) and glider microstructure measurements from AUSSOM (Autonomous Sampling of Southern Ocean Mixing) to show that FSP can have large biases (compared to direct turbulence measurement) below the mixed ...

Data analysis code used for Wallace et al. (2018): Multi-decadal trends and variability in temper... more Data analysis code used for Wallace et al. (2018): Multi-decadal trends and variability in temperature and salinity in the Mid-Atlantic Bight, Georges Bank, and Gulf of Maine This initial release is has only been tested on a macOS system.

OCEANS 2018 MTS/IEEE Charleston, 2018

A collaborative project to integrate a Laser In-Situ Scattering and Transmissometry (LISST) into ... more A collaborative project to integrate a Laser In-Situ Scattering and Transmissometry (LISST) into a Slocum glider was recently completed. This integrated system is capable of measuring particle size, concentration, and beam attenuation, among other standard LISST measurements from a single profiling sensor onboard an autonomous underwater glider coincident with a suite of additional integrated sensors. These integrated LISST-glider sensors provide the unique opportunity to measure suspended particle properties persistently at single locations or survey regional domains, and enable sampling during extreme events such as hurricanes or coastal storms. In this study we detail the sensor integration as well as preliminary data from instrument field tests.

OF THE DISSERTATION Mesoscale Variability on the New Jersey Shelf: Effects of Topography, Seasons... more OF THE DISSERTATION Mesoscale Variability on the New Jersey Shelf: Effects of Topography, Seasons, Winds, and Offshore Forcing on Circulation, Hydrography, and Transport

Frontiers in Marine Science, 2019

Journal of Marine Research, 2018

Increasing attention is being placed on the regional impact of climate change. This study focuses... more Increasing attention is being placed on the regional impact of climate change. This study focuses on the decadal scale variabilities of temperature and salinity in the Mid-Atlantic Bight (MAB), Georges Bank (GB), and Gulf of Maine (GOM) from 1977 to 2016 using hydrographic survey data from the National Oceanic and Atmospheric Administration (NOAA) Northeast Fisheries Science Center. The MAB (as defined by the shelf regions from Cape Hatteras to Cape Cod) experienced warming rates of 0.57 °C per decade during the Winter/Spring season (Jan–Apr) and 0.47 °C per decade during the Fall/Winter season (Sep–Dec). The GOM and GB, on the other hand, warmed at approximately half the rate of the MAB over the same time span (1977–2016). We found that rates of warming vary on decadal time scales. From 1977 to 1999, significant temperature increases (> 0.6 °C/decade) were found in the southern regions of the MAB during the Winter/Spring season. During the same period, significant freshening (st...

FEMS microbiology ecology, 2018

DNA stable isotope probing (SIP) was used to track the uptake of organic and inorganic carbon sou... more DNA stable isotope probing (SIP) was used to track the uptake of organic and inorganic carbon sources for TACK archaea (Thaumarchaeota/Aigarchaeota/Crenarchaeota/Korarchaeota) on a cruise of opportunity in the North Atlantic. Due to water limitations, duplicate samples from the deep photic (60-115 m), the mesopelagic zones (local oxygen minimum; 215-835 m) and the bathypelagic zone (2085-2835 m) were amended with various combinations of 12C- or 13C-acetate/urea/bicarbonate to assess cellular carbon acquisition. The SIP results indicated the majority of TACK archaeal operational taxonomic units (OTUs) incorporated 13C from acetate and/or urea into newly synthesized DNA within 48 h. A small fraction (16%) of the OTUs, often representing the most dominant members of the archaeal community, were able to incorporate bicarbonate in addition to organic substrates. Only two TACK archaeal OTUs were found to incorporate bicarbonate but not urea or acetate. These results further demonstrate th...

Nature, Nov 1, 2017

Our growing awareness of the microbial world's importance and diversity contrasts starkly wit... more Our growing awareness of the microbial world's importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete ...

Limnology and Oceanography Letters, 2017

Deep Sea Research Part II: Topical Studies in Oceanography, 2016

Abstract Pacific water entering the Chukchi Sea through Bering Strait can be modified by physical... more Abstract Pacific water entering the Chukchi Sea through Bering Strait can be modified by physical processes such as surface heating and cooling, and internal mixing. Here we document the existence of a previously unobserved water mass in the eastern Chukchi Sea during the early-summer using hydrographic and velocity data from the June–July 2010 ICESCAPE survey. The water mass in question is as salty as Pacific Winter Water (PWW), but is much warmer with temperatures typical of summer waters. We label the water mass Dense Chukchi Summer Water (dCSW) which is dense enough to ventilate the upper halocline of the western Arctic Ocean, normally ventilated by the much colder PWW. Satellite sea surface temperature data, long-term mooring data from Bering Strait and the Beaufort Shelfbreak, and atmospheric reanalysis fields are used to characterize the spatial and temporal variability of the dCSW and explore potential forcing scenarios that can lead to its formation. In 2010 the dCSW did not enter the Chukchi Sea through Bering Strait, hence it had to be formed locally on the shelf. Two distinct forcing mechanisms are considered: (1) mixing of very warm Alaskan Coastal Water with the cold PWW when the two water masses come in contact in the energetic Alaskan Coastal Current; and (2) warming of PWW when it experiences solar heating within the coastal polynya in the northeastern Chukchi Sea during the spring melt season. Finally, we explore the conditions under which the springtime polynya has formed over the past three decades as it relates to the formation of dCSW.

Deep Sea Research Part II: Topical Studies in Oceanography, 2015

Hudson Canyon is the largest submarine canyon on the U. S. Atlantic continental margin. Having co... more Hudson Canyon is the largest submarine canyon on the U. S. Atlantic continental margin. Having completed a surface ship multi-beam bathymetric map of the Hudson Canyon region (resolution 100m; http://pubs.usgs.gov/of/2004/1441/index/html), we report preliminary results of mapping portions of the canyon head (75 square km, water depth 200-500 m) using the Eagle Ray autonomous underwater vehicle (Explorer 27- BO1-2200 AUV, ISE Ltd.) of the University of Southern Mississippi. The AUV was equipped with a Simrad EM2000 multi-beam sonar system and flown 50 m above the seafloor for resolution (3 m), and with a CTD to map water column properties. Shipboard CTD casts were also made and water sampled from the shelf break (depth 200 m) to the upper continental rise (3000 m) for detection of methane. The canyon head is of interest as an essential fish habitat (squid, hake, tilefish, and lobster) that may contribute to sustain a regional fishery and that may conduct sediment to the ocean basin. A shallow trough, the Hudson Shelf Valley, extends ~185 km across the continental shelf connecting the mouth of the Hudson River to the canyon head where it indents the seaward edge of the shelf. The canyon head bifurcates with branch 1 (6 km-long) oriented NW-SE aligned with the Shelf Valley, and branch 2 (4 km-long) oriented N-S. The two branches merge into a segment 10 km-long oriented NW-SE aligned with branch 1. Branch 1 has symmetric walls with mean inclinations of 10 degrees and smooth seafloor, suggesting that it is presently inactive and accumulating a cover of hemipelagic sediment. In contrast, the walls of both the N-S branch 2 and of the contiguous NW-SE segment are asymmetric. The walls of the NW-SE segment have a mean inclination of 15 degrees and exhibit semicircular escarpments 800-900 m long and 600-700 m wide, separated by narrow ravines perpendicular to the canyon axis. Slump blocks with sharp rims occur where N-S branch 1 joins the NW- SE segment. Two circular depressions (diameter 100 and 300 m; relief c.15 m; depths 345 m and 390 m) occur at the base of the SW wall of the segment and may be collapse features related to gas discharge evidenced by a high methane anomaly at the shelf edge. The head of Hudson Canyon encompasses diverse habitats and is a dynamic interface between shelf and slope processes. We thank NOAA's National Undersea Research Program for support.

Deep Sea Research Part II: Topical Studies in Oceanography, 2015

Journal of Physical Oceanography

The ocean surface boundary layer is a gateway of energy transfer into the ocean. Wind-driven shea... more The ocean surface boundary layer is a gateway of energy transfer into the ocean. Wind-driven shear and meteorologically forced convection inject turbulent kinetic energy into the surface boundary layer, mixing the upper ocean and transforming its density structure. In the absence of direct observations or the capability to resolve subgrid-scale 3D turbulence in operational ocean models, the oceanography community relies on surface boundary layer similarity scalings (BLS) of shear and convective turbulence to represent this mixing. Despite their importance, near-surface mixing processes (and ubiquitous BLS representations of these processes) have been undersampled in high-energy forcing regimes such as the Southern Ocean. With the maturing of autonomous sampling platforms, there is now an opportunity to collect high-resolution spatial and temporal measurements in the full range of forcing conditions. Here, we characterize near-surface turbulence under strong wind forcing using the fi...

This data contains 125 geolocated water stable isotope, salinity, and temperature measurements fr... more This data contains 125 geolocated water stable isotope, salinity, and temperature measurements from niskin bottle samples at varying depths from 52 Conductivity, Temperature, Depth (CTD) casts along the RV Oden cruise track. The CTD rosette water sampling was conducted following the CLIVAR/GO-SHIP protocol with a 'water cop' keeping track of the sampling order. Sampling for gases goes first, followed by nutrients, water stable isotopes, and then microbiological and DNA sampling during each cast. Samples for water stable isotopes analyses were collected by filling 30-mL Nalgene bottles to the brim. Bottles were closed tightly, sealed with parafilm, and stored in a labeled sample bag. Sampling depths chosen were based on the profile, location, and whether samples were collected for nutrients. Two samples were collected per depth. A total of 250 samples were collected from the 52 CTD casts from 19 July – 04 August 2019. The corresponding salinity and temperature measurements pe...

The relationship between δ¹⁸O and salinity has been widely studied because it can provide crucial... more The relationship between δ¹⁸O and salinity has been widely studied because it can provide crucial information on the partitioning of isotopes through the hydrological cycle. Current understanding of δ¹⁸O-S characteristics has been used to constrain water cycle models, isotope-enabled atmospheric and ocean models as well as to monitor evaporation (E) and precipitation (P) changes in major ocean basins. However, in the polar regions, where large spatial and temporal variabilities in δ¹⁸O and salinity are expected due to the highly seasonal sea ice melting/formation, river runoff, E-P intensification and rapidly changing summer ice minimum, uncertainties still surround the δ¹⁸O-Salinity relationship. To observe the inputs of freshwater in a poorly-understood, but vastly changing region in the Arctic, we collected matching δ¹⁸O-Salinity data from discrete samples from the surface (bucket sampling) and from profiles (Conductivity, Temperature, Depth (CTD) casts) in the Canadian Arctic Ar...

This data contains 63 geolocated water stable isotopes and salinity measurements from the surface... more This data contains 63 geolocated water stable isotopes and salinity measurements from the surface of the ocean along the RV Oden cruise track. Surface seawater sampling was conducted using bucket sampling. This was done by throwing a weighted bucket offboard to sample the surface of the ocean every six (6) hours. Chosen times were 5:00, 11:00, 17:00, and 23:00. Multiple readings of sea surface salinity were recorded using a YSI professional series digital probe per sampling Water samples were transferred to a 30-mL Nalgene bottles that were filled to the brim. Bottles were tightly closed, sealed with parafilm, and placed inside sampling bags. Two samples were collected per sampling point, and all measurements were geolocated. A total of 126 samples were collected from 19 July – 04 August 2019. All water samples were transported to the Atmosphere, Climate, and Ecosystems lab at the University of Illinois at Chicago for processing. The δ¹⁸O and dD were measured using a Picarro l2130-I...

Journal of Atmospheric and Oceanic Technology, 2022

Finescale strain parameterization (hereafter, FSP) of turbulent kinetic energy dissipation rate h... more Finescale strain parameterization (hereafter, FSP) of turbulent kinetic energy dissipation rate has become a widely used method for observing ocean mixing, solving a coverage problem where direct turbulence measurements are absent but CTD profiles are available. This method can offer significant value, but there are limitations in its broad application to the global ocean. FSP often fails to produce reliable results in frontal zones where temperature-salinity (T/S) intrusive features contaminate the CTD strain spectrum, as well as where the aspect ratio of the internal wave spectrum is known to vary greatly with depth, as frequently occurs in the Southern Ocean. In this study we use direct turbulence measurements from DIMES (Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean) and glider microstructure measurements from AUSSOM (Autonomous Sampling of Southern Ocean Mixing) to show that FSP can have large biases (compared to direct turbulence measurement) below the mixed ...

Data analysis code used for Wallace et al. (2018): Multi-decadal trends and variability in temper... more Data analysis code used for Wallace et al. (2018): Multi-decadal trends and variability in temperature and salinity in the Mid-Atlantic Bight, Georges Bank, and Gulf of Maine This initial release is has only been tested on a macOS system.

OCEANS 2018 MTS/IEEE Charleston, 2018

A collaborative project to integrate a Laser In-Situ Scattering and Transmissometry (LISST) into ... more A collaborative project to integrate a Laser In-Situ Scattering and Transmissometry (LISST) into a Slocum glider was recently completed. This integrated system is capable of measuring particle size, concentration, and beam attenuation, among other standard LISST measurements from a single profiling sensor onboard an autonomous underwater glider coincident with a suite of additional integrated sensors. These integrated LISST-glider sensors provide the unique opportunity to measure suspended particle properties persistently at single locations or survey regional domains, and enable sampling during extreme events such as hurricanes or coastal storms. In this study we detail the sensor integration as well as preliminary data from instrument field tests.

OF THE DISSERTATION Mesoscale Variability on the New Jersey Shelf: Effects of Topography, Seasons... more OF THE DISSERTATION Mesoscale Variability on the New Jersey Shelf: Effects of Topography, Seasons, Winds, and Offshore Forcing on Circulation, Hydrography, and Transport

Frontiers in Marine Science, 2019

Journal of Marine Research, 2018

Increasing attention is being placed on the regional impact of climate change. This study focuses... more Increasing attention is being placed on the regional impact of climate change. This study focuses on the decadal scale variabilities of temperature and salinity in the Mid-Atlantic Bight (MAB), Georges Bank (GB), and Gulf of Maine (GOM) from 1977 to 2016 using hydrographic survey data from the National Oceanic and Atmospheric Administration (NOAA) Northeast Fisheries Science Center. The MAB (as defined by the shelf regions from Cape Hatteras to Cape Cod) experienced warming rates of 0.57 °C per decade during the Winter/Spring season (Jan–Apr) and 0.47 °C per decade during the Fall/Winter season (Sep–Dec). The GOM and GB, on the other hand, warmed at approximately half the rate of the MAB over the same time span (1977–2016). We found that rates of warming vary on decadal time scales. From 1977 to 1999, significant temperature increases (> 0.6 °C/decade) were found in the southern regions of the MAB during the Winter/Spring season. During the same period, significant freshening (st...

FEMS microbiology ecology, 2018

DNA stable isotope probing (SIP) was used to track the uptake of organic and inorganic carbon sou... more DNA stable isotope probing (SIP) was used to track the uptake of organic and inorganic carbon sources for TACK archaea (Thaumarchaeota/Aigarchaeota/Crenarchaeota/Korarchaeota) on a cruise of opportunity in the North Atlantic. Due to water limitations, duplicate samples from the deep photic (60-115 m), the mesopelagic zones (local oxygen minimum; 215-835 m) and the bathypelagic zone (2085-2835 m) were amended with various combinations of 12C- or 13C-acetate/urea/bicarbonate to assess cellular carbon acquisition. The SIP results indicated the majority of TACK archaeal operational taxonomic units (OTUs) incorporated 13C from acetate and/or urea into newly synthesized DNA within 48 h. A small fraction (16%) of the OTUs, often representing the most dominant members of the archaeal community, were able to incorporate bicarbonate in addition to organic substrates. Only two TACK archaeal OTUs were found to incorporate bicarbonate but not urea or acetate. These results further demonstrate th...

Nature, Nov 1, 2017

Our growing awareness of the microbial world's importance and diversity contrasts starkly wit... more Our growing awareness of the microbial world's importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete ...

Limnology and Oceanography Letters, 2017

Deep Sea Research Part II: Topical Studies in Oceanography, 2016

Abstract Pacific water entering the Chukchi Sea through Bering Strait can be modified by physical... more Abstract Pacific water entering the Chukchi Sea through Bering Strait can be modified by physical processes such as surface heating and cooling, and internal mixing. Here we document the existence of a previously unobserved water mass in the eastern Chukchi Sea during the early-summer using hydrographic and velocity data from the June–July 2010 ICESCAPE survey. The water mass in question is as salty as Pacific Winter Water (PWW), but is much warmer with temperatures typical of summer waters. We label the water mass Dense Chukchi Summer Water (dCSW) which is dense enough to ventilate the upper halocline of the western Arctic Ocean, normally ventilated by the much colder PWW. Satellite sea surface temperature data, long-term mooring data from Bering Strait and the Beaufort Shelfbreak, and atmospheric reanalysis fields are used to characterize the spatial and temporal variability of the dCSW and explore potential forcing scenarios that can lead to its formation. In 2010 the dCSW did not enter the Chukchi Sea through Bering Strait, hence it had to be formed locally on the shelf. Two distinct forcing mechanisms are considered: (1) mixing of very warm Alaskan Coastal Water with the cold PWW when the two water masses come in contact in the energetic Alaskan Coastal Current; and (2) warming of PWW when it experiences solar heating within the coastal polynya in the northeastern Chukchi Sea during the spring melt season. Finally, we explore the conditions under which the springtime polynya has formed over the past three decades as it relates to the formation of dCSW.

Deep Sea Research Part II: Topical Studies in Oceanography, 2015

Hudson Canyon is the largest submarine canyon on the U. S. Atlantic continental margin. Having co... more Hudson Canyon is the largest submarine canyon on the U. S. Atlantic continental margin. Having completed a surface ship multi-beam bathymetric map of the Hudson Canyon region (resolution 100m; http://pubs.usgs.gov/of/2004/1441/index/html), we report preliminary results of mapping portions of the canyon head (75 square km, water depth 200-500 m) using the Eagle Ray autonomous underwater vehicle (Explorer 27- BO1-2200 AUV, ISE Ltd.) of the University of Southern Mississippi. The AUV was equipped with a Simrad EM2000 multi-beam sonar system and flown 50 m above the seafloor for resolution (3 m), and with a CTD to map water column properties. Shipboard CTD casts were also made and water sampled from the shelf break (depth 200 m) to the upper continental rise (3000 m) for detection of methane. The canyon head is of interest as an essential fish habitat (squid, hake, tilefish, and lobster) that may contribute to sustain a regional fishery and that may conduct sediment to the ocean basin. A shallow trough, the Hudson Shelf Valley, extends ~185 km across the continental shelf connecting the mouth of the Hudson River to the canyon head where it indents the seaward edge of the shelf. The canyon head bifurcates with branch 1 (6 km-long) oriented NW-SE aligned with the Shelf Valley, and branch 2 (4 km-long) oriented N-S. The two branches merge into a segment 10 km-long oriented NW-SE aligned with branch 1. Branch 1 has symmetric walls with mean inclinations of 10 degrees and smooth seafloor, suggesting that it is presently inactive and accumulating a cover of hemipelagic sediment. In contrast, the walls of both the N-S branch 2 and of the contiguous NW-SE segment are asymmetric. The walls of the NW-SE segment have a mean inclination of 15 degrees and exhibit semicircular escarpments 800-900 m long and 600-700 m wide, separated by narrow ravines perpendicular to the canyon axis. Slump blocks with sharp rims occur where N-S branch 1 joins the NW- SE segment. Two circular depressions (diameter 100 and 300 m; relief c.15 m; depths 345 m and 390 m) occur at the base of the SW wall of the segment and may be collapse features related to gas discharge evidenced by a high methane anomaly at the shelf edge. The head of Hudson Canyon encompasses diverse habitats and is a dynamic interface between shelf and slope processes. We thank NOAA's National Undersea Research Program for support.

Deep Sea Research Part II: Topical Studies in Oceanography, 2015