Seim Harvey E.

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Seim

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Harvey E.

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0000-0002-1562-0849

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A shelf water cascading event near Cape Hatteras

(American Meteorological Society, 2021-06-01) Han, Lu ; Seim, Harvey E. ; Bane, John M. ; Todd, Robert E. ; Muglia, Michael

Carbon-rich Middle Atlantic Bight (MAB) and South Atlantic Bight (SAB) shelf waters typically converge on the continental shelf near Cape Hatteras. Both are often exported to the adjacent open ocean in this region. During a survey of the region in mid-January 2018, there was no sign of shelf water export at the surface. Instead, a subsurface layer of shelf water with high chlorophyll and dissolved oxygen was observed at the edge of the Gulf Stream east of Cape Hatteras. Strong cooling over the MAB and SAB shelves in early January led to shelf waters being denser than offshore surface waters. Driven by the density gradient, the denser shelf waters cascaded beneath the Gulf Stream and were subsequently entrained into the Gulf Stream, as they were advected northeastward. Underwater glider observations 80 km downstream of the export location captured 0.44 Sv (1 Sv ≡ 106 m3 s−1) of shelf waters transported along the edge of the Gulf Stream in January 2018. In total, as much as 7 × 106 kg of carbon was exported from the continental shelf to a greater depth in the open ocean during this 5-day-long cascading event. Earlier observations of near-bottom temperature and salinity at a depth of 230 m captured several multiday episodes of shelf water at a location that was otherwise dominated by Gulf Stream water, indicating that the January 2018 cascading event was not unique. Cascading is an important, yet little-studied pathway of carbon export and sequestration at Cape Hatteras.
Mixing in a coastal environment : 1. A view from dye dispersion

(American Geophysical Union, 2004-10-26) Ledwell, James R. ; Duda, Timothy F. ; Sundermeyer, Miles A. ; Seim, Harvey E.

Dye release experiments were performed together with microstructure profiling to compare the two methods of estimating diapycnal diffusivity during summer and fall stratification on the continental shelf south of New England. The experiments were done in 1996 and 1997 as part of the Coastal Mixing and Optics Experiment. During the 100 hours or so of the experiments the area of the dye patches grew from less than 1 km2 to more than 50 km2 [ Sundermeyer and Ledwell, 2001 ]. Diapycnal diffusivities inferred from dye dispersion range from 10−6 to 10−5 m2/s at buoyancy frequencies from 9 to 28 cycles/hour. Diffusivities estimated from the dye and those estimated from dissipation rates in the companion paper by Oakey and Greenan [2004] agree closely in most cases. Estimates of diffusivities from towed conductivity microstructure measurements made during the cruises by Duda and Rehmann [2002] and Rehmann and Duda [2000] are fairly consistent with the dye diffusivities. The dye diffusivities would be predicted well by an empirical formula involving shear and stratification statistics developed by MacKinnon and Gregg [2003] from profiling microstructure measurements obtained at the same site in August 1996. All of the measurements support the general conclusion that the diffusivity, averaged over several days, is seldom greater than 10−5 m2/s in the stratified waters at the site, and usually not much greater than 10−6 m2/s. Severe storms, such as a hurricane that passed over the CMO site in 1996, can dramatically increase the mixing at the site, however.
Overview of the Processes driving Exchange At Cape Hatteras Program

(Oceanography Society, 2022-05-12) Seim, Harvey E. ; Savidge, Dana ; Andres, Magdalena ; Bane, John M. ; Edwards, Catherine ; Gawarkiewicz, Glen G. ; He, Ruoying ; Todd, Robert E. ; Muglia, Michael ; Zambon, Joseph B. ; Han, Lu ; Mao, Shun

The Processes driving Exchange At Cape Hatteras (PEACH) program seeks to better understand seawater exchanges between the continental shelf and the open ocean near Cape Hatteras, North Carolina. This location is where the Gulf Stream transitions from a boundary-trapped current to a free jet, and where robust along-shelf convergence brings cool, relatively fresh Middle Atlantic Bight and warm, salty South Atlantic Bight shelf waters together, forming an important and dynamic biogeographic boundary. The magnitude of this convergence implies large export of shelf water to the open ocean here. Background on the oceanography of the region provides motivation for the study and gives context for the measurements that were made. Science questions focus on the roles that wind forcing, Gulf Stream forcing, and lateral density gradients play in driving exchange. PEACH observational efforts include a variety of fixed and mobile observing platforms, and PEACH modeling included two different resolutions and data assimilation schemes. Findings to date on mean circulation, the nature of export from the southern Middle Atlantic Bight shelf, Gulf Stream variability, and position variability of the Hatteras Front are summarized, together with a look ahead to forthcoming analyses.
CTD data from gliders on the R/V Savannah in the South Atlantic Bight (SAB) continental shelf off Long Bay (-79W, 32N; -77W, 34 N) collected from January to April 2012 (Long Bay Wintertime Bloom project)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2021-03-01) Nelson, James ; Edwards, Catherine ; Seim, Harvey E.

Two Webb Slocum gliders were used to measure salinity, temperature, and depth. Glider 'Pelagia' was deployed in Long Bay, S. Carolina, South Atlantic Bight and glider 'Ramses' was deployed along the upper slope of S. Carolina. in 2012. Data were collected in a time series from January to April, 2012. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/544615
Chlorophyll and pheopigments from filtered water samples from R/V Savannah cruises in the South Atlantic Bight (SAB) continental shelf off Long Bay, January-April 2012 (Long Bay Wintertime Bloom project)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2021-03-01) Nelson, James ; Edwards, Catherine ; Seim, Harvey E.

Chlorophyll and pheopigments from filtered water samples from R/V Savannah cruises in the South Atlantic Bight (SAB) continental shelf off Long Bay, January-April 2012. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/638203
Moored time-series records for chlorophyll and turbidity collected from the LB1 Mooring, LB2 Mooring, LB3 Mooring in the South Atlantic Bight (SAB) continental shelf off Long Bay from 2011-2012 (Long Bay Wintertime Bloom project)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2021-03-01) Nelson, James ; Edwards, Catherine ; Seim, Harvey E.

Time series of chlorophyll and turbidity measured every second on three moorings located at Long Bay, S. Carolina in the South Atlantic Bight, located at mid-shelf at 30 m, shelf break at 74 m and upper slope at 171 m along a central shelf/slope survey line SE of Myrtle Beach, SC between 33.17/-78.33 and 32.76/-77.91. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/638349
Moored time-series records for temperature collected from the LB1 Mooring, R/V Savannah (LB-2012-LB1, SAV-12-02) in the South Atlantic Bight (SAB) continental shelf off Long Bay during 2012 (Long Bay Wintertime Bloom project)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2023-03-09) Nelson, James ; Edwards, Catherine ; Seim, Harvey E.

Moored time-series records of temperature measured every 5 minutes (300sec) by 25 Onset HOBO Water Temperature Data Loggers mounted on a tautline mooring. Collected from the LB1 Mooring, R/V Savannah (LB-2012-LB1, SAV-12-02) in the South Atlantic Bight continental shelf off Long Bay during 2012. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/639382
Cold event in the South Atlantic Bight during summer of 2003 : model simulations and implications

(American Geophysical Union, 2007-05-11) Aretxabaleta, Alfredo L. ; Blanton, Brian O. ; Seim, Harvey E. ; Werner, Francisco E. ; Nelson, James R. ; Chassignet, Eric P.

A set of model simulations are used to determine the principal forcing mechanisms that resulted in anomalously cold water in the South Atlantic Bight (SAB) in the summer of 2003. Updated mass field and elevation boundary conditions from basin-scale Hybrid Coordinate Ocean Model (HYCOM) simulations are compared to climatological forcing to provide offshore and upstream influences in a one-way nesting sense. Model skill is evaluated by comparing model results with observations of velocity, water level, and surface and bottom temperature. Inclusion of realistic atmospheric forcing, river discharge, and improved model dynamics produced good skill on the inner shelf and midshelf. The intrusion of cold water onto the shelf occurred predominantly along the shelf-break associated with onshore flow in the southern part of the domain north of Cape Canaveral (29° to 31.5°). The atmospheric forcing (anomalously strong and persistent upwelling-favorable winds) was the principal mechanism driving the cold event. Elevated river discharge increased the level of stratification across the inner shelf and midshelf and contributed to additional input of cold water into the shelf. The resulting pool of anomalously cold water constituted more than 50% of the water on the shelf in late July and early August. The excess nutrient flux onto the shelf associated with the upwelling was approximated using published nitrate-temperature proxies, suggesting increased primary production during the summer over most of the SAB shelf.
Characteristics of an advective Marine Heatwave in the Middle Atlantic Bight in early 2017

(Frontiers Media, 2019-11-22) Gawarkiewicz, Glen G. ; Chen, Ke ; Forsyth, Jacob S. T. ; Bahr, Frank B. ; Mercer, Anna Malek ; Ellertson, Aubrey ; Fratantoni, Paula S. ; Seim, Harvey E. ; Haines, Sara ; Han, Lu

There has been wide interest in Marine Heatwaves and their ecological consequences in recent years. Most analyses have focused on remotely sensed sea surface temperature data due to the temporal and spatial coverage it provides in order to establish the presence and duration of Heatwaves. Using hydrographic data from a variety of sources, we show that an advective Marine Heatwave was initiated by an event in late December of 2016 south of New England, with temperature anomalies measuring up to 6°C and salinity anomalies exceeding 1 PSU. Similar features were observed off of New Jersey in February 2017, and are associated with the Shelfbreak Front migrating from its normal position to mid-shelf or further onshore. Shelf water of 34 PSU was observed just north of Cape Hatteras at the 30 m isobath and across the continental shelf in late April 2017. These observations reveal that the 2017 Marine Heatwave was associated with a strong positive salinity anomaly, that its total duration was approximately 4 months, and its advective path extended roughly 850 km along the length of the continental shelf in the Middle Atlantic Bight. The southward advective velocity implied by the arrival north of Cape Hatteras is consistent with previous estimates of alongshelf velocity for the region. The origin of this Marine Heatwave is likely related to cross-shelf advection driven by the presence of a Warm Core Ring adjacent to the shelfbreak south of New England.
Time series of dissolved oxygen measured on an undulating glider collected from the South Atlantic Bight (SAB) cruises along the continental shelf off Long Bay from January to April in 2012 (Long Bay Wintertime Bloom project)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2021-03-04) Nelson, James ; Edwards, Catherine ; Seim, Harvey E.

Two Webb Slocum gliders were used to measure salinity, temperature, and depth. Glider 'Pelagia' was deployed in Long Bay, S. Carolina, South Atlantic Bight and glider 'Ramses' was deployed along the upper slope of S. Carolina. in 2012. Data were collected in a time series from January to April, 2012. NOTE: This is a very large dataset (1.53 million records). It takes a while to serve and may not display entirely depending on your browser. You can download all the data from the Data Files section on this metadata page. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/636636
Long Bay ship macronutrient concentrations from R/V Savannah (SAV-12-03, SAV-12-05, SAV-12-11) cruises in the South Atlantic Bight (SAB) continental shelf off Long Bay during 2012 (Long Bay Wintertime Bloom project)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2021-03-01) Nelson, James ; Edwards, Catherine ; Seim, Harvey E.

Long Bay ship macronutrient concentrations from R/V Savannah (SAV-12-03, SAV-12-05, SAV-12-11) cruises in the South Atlantic Bight (SAB) continental shelf off Long Bay during 2012. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/638156
Ocean circulation near Cape Hatteras: observations of mean and variability

(American Geophysical Union, 2022-11-19) Han, Lu ; Seim, Harvey ; Bane, John ; Savidge, Dana ; Andres, Magdalena ; Gawarkiewicz, Glen ; Muglia, Mike

The convergence of different water masses on the shelf and along the shelfbreak, and cross‐isobath shelf‐open ocean exchanges contribute to the complex circulation near Cape Hatteras. We examine the mean and variability of these circulations using data from nine bottom‐mounted acoustic Doppler current profilers, deployed over the mid‐ to outer‐continental shelf north and south of Cape Hatteras as part of the Processes driving Exchange At Cape Hatteras program. The 18‐month‐mean depth‐averaged shelf flows are mostly aligned with isobaths and oriented toward Cape Hatteras. At two sites just north of Cape Hatteras, mean flows have a strong cross‐shelf component. Two dominant spatial patterns in the velocity field are obtained from an empirical orthogonal function analysis. The two leading modes contain 61% of the total variance. The spatial variation of Mode 1 exhibits an along‐shelf flow pattern, while that of Mode 2 shows a convergent flow pattern. The principal component (PC) series of Mode 1 is significantly correlated with the local wind stress, confirming that the along‐shelf flow is wind‐driven as expected. The PC of Mode 2 is highly correlated with the Gulf Stream lateral position as inferred from the current‐ and pressure‐sensor‐equipped inverted echo sounders over the slope south of Cape Hatteras, which indicates that Gulf Stream movement drives time‐varying shelf flow convergence. Conditionally averaged sea‐surface temperature and high‐frequency radar‐measured surface currents based on PC1 and PC2 confirm these relationships and further illustrate how the wind and Gulf Stream forcing work together to influence the flow regime in this region.
Observations of Shelf-Ocean Exchange in the Northern South Atlantic Bight Driven by the Gulf Stream

(American Geophysical Union, 2023-07-07) Andres, Magdalena ; Muglia, Michael ; Seim, Harvey E. ; Bane, John M. ; Savidge, Dana

Between Florida and Cape Hatteras, North Carolina, the Gulf Stream carries warm, salty waters poleward along the continental slope. This strong current abuts the edge of the South Atlantic Bight (SAB) continental shelf and is thought to influence exchange of waters between the open ocean and the shelf. Observations from a pair of instruments deployed for 19 months in the northern SAB are used here to examine the processes by which the Gulf Stream can impact this exchange. The instrument deployed on the SAB shelf edge shows that the time-averaged along-slope flow is surface-intensified with only few flow reversals at low frequencies (>40-day period). Time-averaged cross-slope flow is onto the SAB shelf in a lower layer and off-shelf above. Consistent with Ekman dynamics, the magnitude of lower-layer on-shelf flow is correlated with the along-slope velocity, which is in turn controlled by the position and/or transport of the Gulf Stream that flows poleward along the SAB continental slope. In the frequency band associated with downstream-propagating wave-like meanders of the Gulf Stream jet (2-15 day period), currents at the shelf-edge are characterized by surface-intensified flow in the along- and cross-slope directions. Estimates of maximum upwelling velocities associated with cyclonic frontal eddies between meander crests occasionally reach 100 m/day.
Global perspectives on observing ocean boundary current systems

(Frontiers Media, 2019-08-08) Todd, Robert E. ; Chavez, Francisco P. ; Clayton, Sophie A. ; Cravatte, Sophie ; Goes, Marlos Pereira ; Graco, Michelle ; Lin, Xiaopei ; Sprintall, Janet ; Zilberman, Nathalie ; Archer, Matthew ; Arístegui, Javier ; Balmaseda, Magdalena A. ; Bane, John M. ; Baringer, Molly O. ; Barth, John A. ; Beal, Lisa M. ; Brandt, Peter ; Calil, Paulo H. R. ; Campos, Edmo ; Centurioni, Luca R. ; Chidichimo, Maria Paz ; Cirano, Mauro ; Cronin, Meghan F. ; Curchitser, Enrique N. ; Davis, Russ E. ; Dengler, Marcus ; deYoung, Brad ; Dong, Shenfu ; Escribano, Ruben ; Fassbender, Andrea ; Fawcett, Sarah E. ; Feng, Ming ; Goni, Gustavo J. ; Gray, Alison R. ; Gutiérrez, Dimitri ; Hebert, Dave ; Hummels, Rebecca ; Ito, Shin-ichi ; Krug, Marjolaine ; Lacan, Francois ; Laurindo, Lucas ; Lazar, Alban ; Lee, Craig M. ; Lengaigne, Matthieu ; Levine, Naomi M. ; Middleton, John ; Montes, Ivonne ; Muglia, Michael ; Nagai, Takeyoshi ; Palevsky, Hilary I. ; Palter, Jaime B. ; Phillips, Helen E. ; Piola, Alberto R. ; Plueddemann, Albert J. ; Qiu, Bo ; Rodrigues, Regina ; Roughan, Moninya ; Rudnick, Daniel L. ; Rykaczewski, Ryan R. ; Saraceno, Martin ; Seim, Harvey E. ; Sen Gupta, Alexander ; Shannon, Lynne ; Sloyan, Bernadette M. ; Sutton, Adrienne J. ; Thompson, LuAnne ; van der Plas, Anja K. ; Volkov, Denis L. ; Wilkin, John L. ; Zhang, Dongxiao ; Zhang, Linlin

Ocean boundary current systems are key components of the climate system, are home to highly productive ecosystems, and have numerous societal impacts. Establishment of a global network of boundary current observing systems is a critical part of ongoing development of the Global Ocean Observing System. The characteristics of boundary current systems are reviewed, focusing on scientific and societal motivations for sustained observing. Techniques currently used to observe boundary current systems are reviewed, followed by a census of the current state of boundary current observing systems globally. The next steps in the development of boundary current observing systems are considered, leading to several specific recommendations.

Seim Harvey E.

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