Ramsey Andree L.

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A Deep Water Dispersion Experiment in the Gulf of Mexico

(American Geophysical Union, 2021-09-18) Meunier, Thomas ; Pérez-Brunius, Paula ; Rodríguez Outerelo, Javier ; García-Carrillo, Paula ; Ronquillo-Mendez, Argelia ; Furey, Heather H. ; Ramsey, Andree L. ; Bower, Amy S.

The Deep Water Horizon oil spill dramatically impacted the Gulf of Mexico from the seafloor to the surface. While dispersion of contaminants at the surface has been extensively studied, little is known about deep water dispersion properties. This study describes the results of the Deep Water Dispersion Experiment (DWDE), which consisted of the release of surface drifters and acoustically tracked RAFOS floats drifting at 300 and 1,500 dbar in the Gulf of Mexico. We show that surface diffusivity is elevated and decreases with depth: on average, diffusivity at 1,500 dbar is 5 times smaller than at the surface, suggesting that the dispersion of contaminants at depth is a significantly slower process than at the surface. This study also examines the turbulent regimes driving the dispersion, although conflicting evidences and large uncertainties do not allow definitive conclusions. At all depths, while the growth of dispersion and kurtosis with time supports the possibility of an exponential regime at very short time scales, indicating that early dispersion is nonlocal, finite size Lyapunov exponents support the hypothesis of local dispersion, suggesting that eddies of size comparable to the initial separation (6 km), may dominate the early dispersion. At longer time scales, the quadratic growth of dispersion is indicative of a ballistic regime, where a mean shear flow would be the dominating process. Examination of the along- and across-bathymetry components of float velocities supports the idea that boundary currents could be the source for this shear dispersion.
Mean conditions and seasonality of the West Greenland boundary current system near Cape Farewell

(American Meteorological Society, 2020-09-18) Pacini, Astrid ; Pickart, Robert S. ; Bahr, Frank B. ; Torres, Daniel J. ; Ramsey, Andree L. ; Holte, James W. ; Karstensen, Johannes ; Oltmanns, Marilena ; Straneo, Fiamma ; Le Bras, Isabela Astiz ; Moore, G. W. K. ; de Jong, Marieke Femke

The structure, transport, and seasonal variability of the West Greenland boundary current system near Cape Farewell are investigated using a high-resolution mooring array deployed from 2014 to 2018. The boundary current system is comprised of three components: the West Greenland Coastal Current, which advects cold and fresh Upper Polar Water (UPW); the West Greenland Current, which transports warm and salty Irminger Water (IW) along the upper slope and UPW at the surface; and the Deep Western Boundary Current, which advects dense overflow waters. Labrador Sea Water (LSW) is prevalent at the seaward side of the array within an offshore recirculation gyre and at the base of the West Greenland Current. The 4-yr mean transport of the full boundary current system is 31.1 ± 7.4 Sv (1 Sv ≡ 106 m3 s−1), with no clear seasonal signal. However, the individual water mass components exhibit seasonal cycles in hydrographic properties and transport. LSW penetrates the boundary current locally, through entrainment/mixing from the adjacent recirculation gyre, and also enters the current upstream in the Irminger Sea. IW is modified through air–sea interaction during winter along the length of its trajectory around the Irminger Sea, which converts some of the water to LSW. This, together with the seasonal increase in LSW entering the current, results in an anticorrelation in transport between these two water masses. The seasonality in UPW transport can be explained by remote wind forcing and subsequent adjustment via coastal trapped waves. Our results provide the first quantitatively robust observational description of the boundary current in the eastern Labrador Sea.
Pathways for the export of Arctic change into the North Atlantic

(Woods Hole Oceanographic Institution, 2018-01) Ramsey, Andree L. ; Straneo, Fiamma

The goal of the Pathways for the Export of Arctic Change into the North Atlantic project was to measure the exchange between the Hudson Bay System and the Labrador Sea, which occurs in the Hudson Strait. This exchange is of climactic relevance since a large amount of fresh water flows through the Hudson Strait into the Labrador Sea, where it can modulate the exchange of heat with the atmosphere. It is also of regional importance since the exchange influences the climate of Hudson Bay, which is home to a large indigenous population. The project consisted of deploying four subsurface moorings, over a one-year period, beginning August 2008 and ending September 2009. The moorings were positioned across the strait with Mooring A located on the south side and Moorings E, F, and G on the north side. The moorings were equipped with instruments to measure conductivity, temperature, pressure, ice draft and velocity.
Overturning of the Subpolar North Atlantic Program (OSNAP): RAFOS Float Data Report June 2014 - January 2019

(Woods Hole Oceanographic Institution, 2020-12) Ramsey, Andree L. ; Furey, Heather H. ; Bower, Amy S.

The Overturning in the Subpolar North Atlantic Program (OSNAP) is an international effort started in 2014 dedicated to achieving a better understanding of the link between dense-water formation and the meridional overturning circulation in the high-latitude North Atlantic. Moorings, gliders, and subsurface acoustically-tracked RAFOS floats have been used to collect temperature, salinity, and current data across the Labrador Sea, Irminger Sea, Reykjanes Ridge, Iceland Basin, Rockall-Hatton Plateau, and Rockall Trough. The specific objective of the OSNAP float program is to gather information on the pathways of the dense overflow waters transported by the deep limb of the overturning circulation and assess the connection of those pathways with currents observed crossing the OSNAP mooring line. This data report details the observations collected by 148 floats that were deployed for OSNAP during the summers of 2014, 2015, 2016 and 2017. Deployment locations were in the Iceland Basin, Irminger Sea, and in the Charlie-Gibbs Fracture Zone. Mission lengths ranged from 540-730 days, and the floats were ballasted to passively drift at a fixed pressure of either 1800, 2000, 2200, 2500, or 2800 dbar to tag the deep overflow water masses of the subpolar North Atlantic (Iceland-Scotland and Denmark Strait Overflow Waters).
CLIMODE Subsurface Mooring Report : November 2005 - November 2007

(Woods Hole Oceanographic Institution, 2013-03) Lund, John M. ; Davis, Xujing Jia ; Ramsey, Andree L. ; Straneo, Fiamma ; Torres, Daniel J. ; Palter, Jaime B. ; Gary, Stefan F. ; Fratantoni, David M.

Two years of temperature, salinity, current, and nutrient data were collected on four subsurface moorings as part of the 2 year field component of the CLIMODE experiment. The moorings were located in North Atlantic’s subtropical gyre, south-east of the Gulf Stream. Two moorings, the most heavily instrumented, were close to the Gulf Stream, in the region where cold air outbreaks force large air-sea fluxes and where Eighteen Degree Water outcrops. Two other moorings were located farther south and carried more limited instrumentation. The moorings were initially deployed in November of 2005, turned around in November of 2006 and finally recovered in November of 2007. During the first year, the moorings close to the Gulf Stream suffered considerable blow down, and some of the instruments failed. During the second year, the blow down was greatly reduced and most instruments collected a full year worth of data.
Overturning of the Subpolar North Atlantic Program (OSNAP): RAFOS Float Data Report June 2014 - January 2019

(Woods Hole Oceanographic Institution, 2020-12) Ramsey, Andree L. ; Furey, Heather H. ; Bower, Amy S.

The Overturning in the Subpolar North Atlantic Program (OSNAP) is an international effort started in 2014 dedicated to achieving a better understanding of the link between dense-water formation and the meridional overturning circulation in the high-latitude North Atlantic. Moorings, gliders, and subsurface acoustically-tracked RAFOS floats have been used to collect temperature, salinity, and current data across the Labrador Sea, Irminger Sea, Reykjanes Ridge, Iceland Basin, Rockall-Hatton Plateau, and Rockall Trough. The specific objective of the OSNAP float program is to gather information on the pathways of the dense overflow waters transported by the deep limb of the overturning circulation and assess the connection of those pathways with currents observed crossing the OSNAP mooring line. This data report details the observations collected by 148 floats that were deployed for OSNAP during the summers of 2014, 2015, 2016 and 2017. Deployment locations were in the Iceland Basin, Irminger Sea, and in the Charlie-Gibbs Fracture Zone. Mission lengths ranged from 540-730 days, and the floats were ballasted to passively drift at a fixed pressure of either 1800, 2000, 2200, 2500, or 2800 dbar to tag the deep overflow water masses of the subpolar North Atlantic (Iceland-Scotland and Denmark Strait Overflow Waters).
Bight Fracture Zone Experiment Moored Instrument Data

(Woods Hole Oceanographic Institution, 2024-03-25) Furey, Heather H. ; Ramsey, Andree L. ; Bower, Amy S.

Two 2-year moorings were placed in the Bight Fracture Zone (BFZ), one in the north channel and one in the south channel, between July 2015 to July 2017. Each mooring was instrumented at four depths with a pair of instruments comprised of an SBE MicroCAT and a Nobska MAVS-4 Acoustic Current Meter. The four pairs of instruments were placed at 1500, 1750, 2000 meters depth and 22 meters above the bottom of the channel (2440 meters depth in the north channel and 2115 meters depth in the south channel). The initial processing for both the MicroCAT and MAVS-4 consisted of removing data collected while out of water, replacing data outliers with NaNs, and correcting drifts in the data. In addition, the MAVS-4 data were transformed from instrument coordinates to earth coordinates and magnetic declination was correction was applied.
Bight Fracture Zone Experiment: Moored Instrument Data Report, July 2015 - July 2017

(Woods Hole Oceanographic Institution, 2024-04) Furey, Heather H. ; Ramsey, Andree L. ; Bower, Amy S.

This document describes the steps used for the initial processing of the Bight Fracture Zone mooring data, collected between July 2015 – July 2017. The data were collected using SBE MicroCATs and Nobska MAVS- 4 Acoustic Current Meters. The initial processing for both the MicroCAT and MAVS-4 consisted of removing data collected while out of water, replacing data outliers with NaNs, and correcting drifts in the data. In addition, the MAVS-4 data were transformed from instrument coordinates to earth coordinates and magnetic declination was correction was applied.
The Deep Water Dispersion Experiment: RAFOS float data report June 2016 - January 2019

(Woods Hole Oceanographic Institution, 2019-12) Ramsey, Andree L. ; Furey, Heather H. ; Bower, Amy S. ; Pérez-Brunius, Paula ; García-Carrillo, Paula

This is the final data report for all acoustically-tracked subsurface RAFOS floats deployed for the “Deep Water Dispersion Experiment: RAFOS Float Study in Support of Analysis of Possible Consequences of Large Scale Oil-Spills under Various Scenarios” (DWDE). This study is part of the larger program “Deep and Shallow Particle Dispersion and Biological Connectivity over the Continental Slope in the Western Gulf of Mexico”, of the Gulf of Mexico Research Consortium (CIGoM). The objective of the DWDE project was to measure and evaluate the ocean circulation at various depths in order to estimate the rates and pathways by which a passive tracer (e.g. pollutant, nutrients, etc.) would spread. The experiment consisted of the deployment 93 RAFOS floats and five sound source moorings (needed for tracking the floats underwater) over the course of five cruises, between June 2016 and January 2019, in the Perdido region of the Gulf of Mexico. The floats were deployed nearly simultaneously at stacked depths of 300 and 1500 dbar, in sets of 2-4 instruments per station, for calculating dispersion statistics. Mission lengths for the floats were set to ~12 to 18 months. Included in this report are cruise summaries, statistics and notes on sound source and float performance, sound source drift calculations, description of the RAFOS float data processing steps, and figures.
Pathways to the Denmark Strait Overflow: A Lagrangian Study in the Iceland Sea

(Woods Hole Oceanographic Institution, 2019-09) de Jong, Marieke Femke ; Bower, Amy S. ; Søiland, Henrik ; Furey, Heather H. ; Ramsey, Andree L.

The goal of this project was to directly measure the dense water pathways upstream of the Denmark Strait in the Iceland Sea and compare the results to existing ideas about the dynamics of the circulation by deploying 45 acoustically tracked RAFOS floats over a two year time period (24-Jul-2013 to 29-May-2015). The floats were ballasted to drift at a target depth of 500m, recording pressure, temperature, and Times Of Arrivals (TOAs) every six hours or every 12 hours.
Overturning in the Subpolar North Atlantic Program (OSNAP) RAFOS Float Data collected between June 2014 to January 2019

( 2019-08) Furey, Heather H. ; Ramsey, Andree L.

As part of the Overturning in the Subpolar North Atlantic Program (OSNAP), 137 acoustically tracked RAFOS floats, using 13 moored sound sources, were deployed at five deployment locations (four around the Reykjanes Ridge and one east of Greenland), between 2014 and 2019. The floats were deployed within 200m of the sea floor (1800-2800m) and with density greater than 27.8. They recorded position, temperature, and pressure once a day.
Variability of Iceland Scotland overflow water across the Reykjanes Ridge: 2-years of moored observations in the Bight Fracture Zone

(American Geophysical Union, 2024-05-29) Furey, Heather H. ; Bower, Amy S. ; Ramsey, Andree L. ; Houk, Adam ; Meunier, Thomas

This study presents the first continuous observations of Iceland Scotland Overflow Water (ISOW) passing through the Bight Fracture Zone (BFZ), the northernmost deep bathymetric channel across the Reykjanes Ridge between the Iceland and Irminger Basins in the subpolar North Atlantic. Data from two 2-year moorings, measuring temperature, salinity, and current velocity from 2015 to 2017, along with a set of deep ISOW-embedded RAFOS floats, are used to investigate ISOW transport and water property variability through the BFZ, as well as advective pathways between the Iceland and Irminger Basins. The mooring-derived record-mean ISOW transport through the BFZ was −0.59 ± 0.27 × 1e6 m3/s (westward) and varied seasonally with weaker transport in winter and stronger transport in summer. Flow direction of ISOW through the BFZ was consistently westward except in winter, when week-long flow reversals were frequently observed. The previously reported subpolar North Atlantic freshening event of the 2010s is evident in the BFZ mooring records beginning about January 2017. About one-quarter of floats deployed in ISOW at 1800-m depth upstream in the Iceland Basin show a direct advective pathway into the BFZ that appears to be primarily determined by bathymetry. Another quarter of the floats crossed over the ridge to the Irminger Sea through other gaps prior to reaching the Charlie-Gibbs Fracture Zone.

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