EcoMapper operations---KN209-1

This report describes the collection of water property data from EcoMapper AUVs during the R/V Knorr 209-1 cruise as part of the SPURS (Salinity Processes Upper-ocean Regional Study) project. Post-processing was required to improve the quality of the raw data, particularly salinity, and is documented herein. Initial results from temperature and salinity records are presented. The measurements are concentrated in the upper 10 meters of the mixed layer during calm conditions, and reveal significant diurnal warming (up to 3°C) and salinification (up to 0.1 psu) of the surface (< 1 meter) layer. The mixing promoted by the motion of the research vessel destroys this shallow stratification, so the ability of the AUVs to sample undisturbed water hundreds of meters from the ship was critical to the effort of accurately resolving it.Funding was provided by NASA under Grant No. NNX11AE82

North Brazil Current Rings Experiment : mooring S1 data report, November 1998 - June 2000

Nineteen months of temperature and salinity data were recovered from North Brazil Current (NBC) Rings Experiment Mooring S1. The mooring, located east of Barbados at 13º 00’N, 57º 53’W between November 1998 and June 2000, consisted of a vertical array of five temperature/conductivity recorders, five temperature recorders, one 150 kHz acoustic Doppler current profiler (ADCP), and one 260 Hz RAFOS sound source. This instrumentation was distributed over a depth interval (500-1100m) coincident with the low-salinity core of Antarctic Intermediate Water. Due to low concentration of scattering particles at 1000 m, the ADCP failed to return useful velocity data. Heading, pitch, and roll data were successfully recorded, however, and provide coarse measurement of current intensity. Four anomalously low temperature, low salinity, and (inferred) high-velocity events appear toward the end of the record. The temperature and salinity fluctuations observed during these events are most likely due to a combination of vertical instrument excursions due to current-induced mooring tilt and advection of anomalous NBC ring-core water past the mooring site. Anomalous conditions persist for a period of 2-3 weeks and appear, based on simultaneous surface drifter trajectories and satellite ocean color observations, to be associated with the passage of NBC Rings near Barbados.Funding was provided by the National Science Foundation under Grant No. OCE-9729765

The evolution and demise of North Brazil Current rings

Author Posting. © American Meteorological Society, 2006. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 36 (2006): 1241-1264, doi:10.1175/JPO2907.1.Subsurface float and surface drifter observations illustrate the structure, evolution, and eventual demise of 10 North Brazil Current (NBC) rings as they approached and collided with the Lesser Antilles in the western tropical Atlantic Ocean. Upon encountering the shoaling topography east of the Lesser Antilles, most of the rings were deflected abruptly northward and several were observed to completely engulf the island of Barbados. The near-surface and subthermocline layers of two rings were observed to cleave or separate upon encountering shoaling bathymetry between Tobago and Barbados, with the resulting portions each retaining an independent and coherent ringlike vortical circulation. Surface drifters and shallow (250 m) subsurface floats that looped within NBC rings were more likely to enter the Caribbean through the passages of the Lesser Antilles than were deeper (500 or 900 m) floats, indicating that the regional bathymetry preferentially inhibits transport of intermediate-depth ring components. No evidence was found for the wholesale passage of rings through the island chain.Funding was provided by National Science Foundation Grants OCE 97-29765 and OCE 01-36477

AUV observations of the diurnal surface layer in the North Atlantic salinity maximum

Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 44 (2014): 1595–1604, doi:10.1175/JPO-D-13-0140.1.Autonomous underwater vehicle (AUV) surveys of temperature, salinity, and velocity in the upper 10 m of the ocean were carried out in low-wind conditions near the North Atlantic surface salinity maximum as part of the Salinity Processes in the Upper Ocean Regional Study (SPURS) project. Starting from a well-mixed state, the development, deepening, and decay of a warm salty diurnal surface layer was observed at <1-h resolution. The evaporation rate deduced from the freshwater anomaly of the layer corroborates measurements at a nearby flux mooring. Profiles within a few hundred meters of the stationary research vessel showed evidence of mixing, highlighting the effectiveness of AUVs for collecting uncontaminated time series of near-surface thermohaline structure. A two-dimensional horizontal subsurface survey within the diurnal warm layer revealed coherent warm and cool bands, which are interpreted as internal waves on the diurnal thermocline.NASA supported this work under Grant NNX11AE82G.2014-12-0

Red Sea Outflow Experiment (REDSOX) : DLD2 RAFOS float data report February 2001 - March 2003

This is the final data report of all acoustically tracked second-generation Deep Lagrangian Drifter (DLD2) RAFOS float data collected by the Woods Hole Oceanographic Institution in 2001-2003 during the Red Sea Outflow Experiment (REDSOX). The float component of REDSOX was comprised of two deployments on the R/V Knorr and R/V Ewing: the first in February-March 2001, with 26 floats, and the second in August-September 2001, with 27 floats. The isobaric floats were ballasted for 650 decibars to target the intermediate-depth, high-salinity outflow waters from the Red Sea. The objectives of the Lagrangian float study were (1) to identify the spreading pathways of the equilibrated Red Sea outflow, and to quantify the velocities and eddy variability typical of this outflow and of the background oceanic environment in the Gulf of Aden, and (2) to identify and describe the mesoscale processes which contribute to the seaward transport of Red Sea Overflow Water properties through the Gulf of Aden and into the western Indian Ocean. In addition to floats activated and launched during the two cruises, four time-series sites were chosen for dual-release float moorings. The dual-release floats were released every two months between cruises and every two months after the second cruise, with the final release in March 2002. A pirate attack on the R/V Ewing forced some modification of the float deployment plan during the second cruise.Funding was provided by the National Science Foundation under Grant Number OCE-9818464

AXIS—an Autonomous Expendable Instrument System

Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 34 (2017): 2673-2682, doi:10.1175/JTECH-D-17-0054.1.Expendable bathythermographs (XBT) to profile upper-ocean temperatures from vessels in motion have been in use for some 50 years now. Developed originally for navy use, they were soon adapted by oceanographers to map out upper-ocean thermal structure and its space–-time variability from both research vessels and merchant marine vessels in regular traffic. These activities continue today. This paper describes a new technology—the Autonomous Expendable Instrument System (AXIS)—that has been developed to provide the capability to deploy XBT probes on a predefined schedule, or adaptively in response to specific events without the presence of an observer on board. AXIS is a completely self-contained system that can hold up to 12 expendable probes [XBTs, XCTDs, expendable sound velocimeter (XSV)] in any combination. A single-board Linux computer keeps track of what probes are available, takes commands from ashore via Iridium satellite on what deployment schedule to follow, and records and forwards the probe data immediately with a time stamp and the GPS position. This paper provides a brief overview of its operation, capabilities, and some examples of how it is improving coverage along two lines in the Atlantic.Initial development of AXIS mechanical design elements wasmade possible by awards from the Cecil H. and Ida M. Green Technology Innovation Fund and the Sealark Foundation to the team of Dave Fratantoni, Keith von der Heydt (WHOI), and Terry Hammar (WHOI). Construction of the first full AXIS prototype was supported by a technology grant from the National Science Foundation (OCE-0926853) and the second one through an NSF-funded (OCE-1061185) subcontract from the University of Rhode Island.2018-06-2

North Brazil Current Rings Experiment : surface drifter data report, November 1998-June 2000

This data report summarzes 45 surface drifter trajectories collected between November 1998 and June 2000 as part of the North Brazil Current (NBC) Rings Experiment. NBC rings have been proposed as one of several important mechanisms for the transport of South Atlantic upper-ocean water across the equatorial-tropical gyre boundary and into the North Atlantic subtropical gyre. Such transport is required to complete the meridional overturning cell in the Atlantic forced by the high-latitude production and southward export of North Atlantic Deep Water. The goal of this program is to obtain, for the first time, comprehensive observations of the NBC retroflection, the NBC ring formation process, and the physical structure and properties of NBC rings as they translate northwestward along the low-latitude western boundary. A total of 45 drifters were deployed. Twenty-four of these looped anticyclonically within the five rings identified during this experiment. Seven of the looping ring drifters entered the Caribbean, while the rest moved northward along the eastern flank of the Lesser Antiles.Funding was provided by the National Science Foundation under Grant No. OCE-9729765

OC449-09 Data Report : St. Thomas, USVI to Bermuda, December 1-10, 2008

Data collected during multiple surveys of hydrography, velocity, and biological quantities are presented from a 9-day cruise aboard the R/V Oceanus near the island of St. Thomas, USVI and a subsequent transit to Bermuda during December, 2008. This cruise (OC449-09) was undertaken primarily to field test a newly acquired towed-undulating body, the Scanfish. The Scanfish and a second towed body, the Video Plankton Recorder (VPR), were used to survey hydrographic, optical, and biological properties north and south of St. Thomas. Conductivity-Temperature-Depth (CTD) casts and plankton net-tows were made at locations along the survey transects for inter-comparison. The VPR was also used to profile conditions between St. Thomas and Bermuda during transit. An overview of the cruise is given along with descriptions of the data collection methods, processing steps taken, and data products available for distribution.Funding for this research was provided by the King Abdullah University of Science and Technology (KAUST) under a cooperative research agreement with Woods Hole Oceanographic Institution

Updated bathymetry of the Anegada-Jungfern Passage complex and implications for Atlantic inflow to the abyssal Caribbean Sea

Recent bathymetric, hydrographic and direct velocity measurements indicate that a previously unexplored deep passage in the northeastern Caribbean Sea may play a significant role in the abyssal ventilation of this basin. The Anegada-Jungfern Passage complex has long been recognized as the sole pathway for deep Atlantic inflow to the eastern Caribbean. The Anegada Passage (sill depth 1915 m) connects the Atlantic Ocean with the small Virgin Islands Basin, while Jungfern Passage (sill depth 1815 m) connects the latter with the large and deep Venezuela Basin comprising the eastern third of the Caribbean Sea. In the region of Jungfern Passage recent bathymetric measurements reveal additional, shallower routes for Atlantic inflow at depths between 1710 and 1630 m. Despite the relatively shallow controlling depths of these passages, direct measurements of velocity and watermass properties reveal an active inflow of water of Atlantic origin. Bathymetric and other oceanographic observations indicate that the previously unexplored Grappler Channel (sill depth 1710 m; located just west of Jungfern Passage) is responsible for up to 20% of the total inflow to the abyssal Caribbean from the mid-depth Atlantic (about 0.2 Sv)

A thin layer of phytoplankton observed in the Philippine Sea with a synthetic moored array of autonomous gliders

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): C10020, doi:10.1029/2009JC005317.A synthetic moored array composed of five buoyancy-propelled autonomous underwater gliders was used to characterize mesoscale variability and phytoplankton distribution in a 100 km × 100 km domain in the Philippine Sea east of Luzon Strait for 10 days in May 2004. The study area, located east of the Kuroshio near the subtropical front, is dominated by strong internal tides, by energetic westward-propagating mesoscale eddies with azimuthal velocities exceeding 50 cm/s, and by a deep (130 m) maximum in chlorophyll fluorescence. Each glider in the array was instructed to maintain geographic position while repeatedly profiling to 200-m depth. Good station-keeping performance enabled the resulting series of vertical profiles to be interpreted in the same manner as a physically moored chain of instruments. Although organized primarily as a demonstration of glider capabilities, this field exercise provides a unique data set for examining biological-physical interactions in the open ocean. Here we report on the evolution of a thin layer of phytoplankton observed near the deep chlorophyll maximum. Coincident observations of fine structure in temperature and salinity suggest that the thinning process of this layer was driven primarily by physical forcing, most probably vertical shear associated with energetic diurnal internal waves, as opposed to a biological mechanism, such as convergent swimming, grazing, or spatial variation in growth rate.The Office of Naval Research provided support for fieldwork and analysis through grants N-00014-00-1-0256 and N-00014-05-1-0367