The SPURS (Salinity Processes in the Upper Ocean Regional Study) project is a series of science process studies and associated oceanographic field campaigns that aim to elucidate key mechanisms responsible for near-surface salinity variations in the oceans. In particular, SPURS seeks to quantify the relative significance of circulation, evaporation, precipitation over a range of scales for representative areas of the open ocean. In so doing, it addresses the fundamental role the ocean plays in global water cycle budgets and its relationship to climate.  Funded principally by NASA with support from other US agencies and European partners, the project involves two field campaigns and a series of cruises in regions of the Atlantic and Pacific Oceans exhibiting salinity and precipitation extremes (Figure 1).  SPURS employs a suite of state-of-the-art in-situ sampling technologies that, combined with remotely sensed salinity fields from the Aquarius/SAC-D and SMOS satellites, provide a detailed characterization of salinity structure over a continuum of spatio-temporal scales.  Coupling of resulting data with physical oceanographic models is a further distinguishing feature of SPURS synthesis activities which aim to understand underlying physical processes at work.

^{Figure 1: (Left) Global annual map of surface ocean salinity from Aquarius indicating SPURS-1 and 2 campaign sampling areas within salinity maximum and minimum regions of the subtropical N. Atlantic and Eastern Tropical Pacific respectively.(Middle) Global precipitation patterns showing the location of the SPURS-1 and 2 campaigns in low and high rainfall regions respectively.(Right) The SPURS sensor-web illustrating the integrated use of diverse sampling platforms and instrumentation to provide coverage over a continuum of scales.}

The SPURS-1 campaign involved a series of 5 cruises during 2012 - 2013 seeking to resolve the salinity structure and balance in a high salinity, high evaporation, and low rainfall region of the subtropical North Atlantic.  The specific purpose of the experiment was to examine the processes responsible for maintaining the subtropical surface salinity maximum in this region. An array of advanced sampling technologies were employed providing a detailed understanding of salinity structure within a 900 x 800-mile square study area centered at 25N, 38W. Figure 2 adjacent shows the location of the SPURS-1 study site in the salinity maximum region of the subtropical N. Atlantic with tracks for the R/V Knorr, Endeavor and Sarmiento cruises overlaid on a map of remotely sensed salinity data from Aquarius (salinity high values of 37 PSU represented in deeper orange).

Cruises

The table below summarizes the dates of the SPURS-1 cruises and research vessels involved.  Full cruise reports have been issued for the US cruises and the Sarmiento cruise.  These are available from here.

1. Research Vessels

RV Knorr (US)	RV Endeavor (US)	RV Sarmiento (Spain)	RV Thalassa (France)

2. Sensor Platforms

Moorings
Device	Description	Device	Description
	The SPURS central mooring consisted of a surface meteorological package, surface oceanographic instruments, and subsurface, non-realtime oceanographic instruments including CTD, ADCP sensors and current meters providing continuous series of temperature, salinity and current profile data. Meteorological observations included wind speed, air temperature, precipitation, and radiative flux. The mooring was deployed in 5,535 meters of water at 24° 34.867'N, 38°W on 14 September 2012, was serviced on 25 March 2013 and recovered on 30 September 2013.		Two PICO moorings (PICO-1000 & 3000) were deployed on the Knorr cruise in September 2012 in northern and eastern domain quadrants at 24.74°N, 37.95°W and 24.51°N,37.81°W respectively. These moorings contained a surface meteorological package and a "prawler", a CTD that crawls up and down the mooring line from the near-surface down to about 500m, yielding time series of salinity and temperature profile data at fixed locations. The moorings were recovered on the Endeavor-2 cruise.
SPURS Mooring	Contributor: T.Farrarr (WHOI) Data Access	PICO Moorings	Contributors: WS.Kessler (NOAA/PMEL) Data Access
Ship-based Samplers
Device	Description	Device	Description
	Shipboard lowered CTD probes provide continuous conductivity, salinity, and temperature vertical profile observations at fixed sampling stations. There were 100, 52, 17, 22 and 94 CTD casts made during the Knorr, Endeavor-1, Endeavor-2, Sarmiento, and Thalassa cruises respectively. All CTD data were calibrated using shipboard salinometers according to IAPSO standard seawater, and processed to 1 meter bin depth intervals.		Acoustic Doppler Current Profilers (ADCP) provide water column current velocity profile observations.  Shipborne ADCP data were collected during the 3 US cruises, using the Knorr and Endeavor 300 kHz Workhorse, 75 khz broadband and 75 khz narrowband instruments, and during the Sarmiento cruise using a 76.8 khz broadband ADCP.  Additionally, lowered ADCP (L-ADCP) measurements were made during the Knorr cruise on every CTD cast and during the Sarmiento cruise.
CTD	Contributors: F.Bingham, G.Riverdin, J.Font (UNCW, IFREMER, CSIC) Data Access	ADCP	Contributors: F.Bingham, J.Schanze (UNCW, ESR) Data Access
	Underway-CTD (UCTD) is a towed CTD instrument providing salinity and temperature profile observations while underway at up to 20kts. 771 UCTD casts occurred during the Knorr and Endeavor-I cruises utilizing an Oceanscience instrument.		Microstructure profilers are lowered probes measuring small-scale (cm) variations in vertical water turbulence, temperature, and salinity. Numerous microstructure profiles were collected on the Knorr and Endeavor-1 cruises.  This work was NSF funded.
Underway-CTD	Contributors: T.Farrar (WHOI) Data Access	Microstructure Profiler	Contributors: R.Schmitt, L.St.Laurent (WHOI) Data Access
	A thermosalinograph (TSG) is an automated measurement system that is coupled to a research vessel's water intake and GPS systems to provide continuous, along-track surface temperature and salinity measurements. Each SPURS cruise had a TSG instrument, with measurements calibrated against onboard salinometers.		A ship mast meteorological sensor package was set up on all SPURS-1 cruises, with an additional set of sophisticated sensor, including a direct covariance flux package, installed on the Knorr.  These provided georeferenced, along-track atmospheric pressure, temperature, humidity, IR/visible radiation, rain, wind speed and direct covariance flux measurements.
Thermosalinograph	Contributors: Multiple Data Access	Meteorology	Contributors: Multiple Data Access
	A SeaSoar is a towed vehicle equipped with impeller-forced wings that can be rotated on command to allow the vehicle to undulate in the upper ocean. Generally, SeaSoar operates between the surface and about 400 meters depth while being towed on faired cable at about eight knots. A typical dive cycle takes about 12 minutes to complete, providing an up- and down profile every 3 km.  For SPURS-1, a SeaSoar was deployed exclusively during the Sarmiento cruise over the period 22 Mar-8 Apr, 2013 and to a maximum depth of 312m.  The SeaSoar towed sensor system was equipped with dual pumped temperature/conductivity sensors.  The SeaSoar data, in netCDF form here, contains a highly processed 1-meter gridded version of the original source dataset, which is comprised of temperature, conductivity, salinity, pressure observations from 1144 casts during 2013 Spring SPURS Cruise.
SeaSoar	Contributors: J.Busecke   (Columbia U.) Data Access
Autonomous Samplers
Device	Description	Device	Description
	The Tenuse (Slocum) glider is an autonomous undulating profiler measuring salinity and temperature.  It was deployed from the Thalassa on 21-August and recovered by the Knorr on 4-October-2012. It made a total of about 1400 profiles during that period (1-2 profiles/hour), going from the surface to 200 m.		The Seaglider is an autonomous profiler measuring salinity and temperature. Three Seagliders were deployed on the Knorr cruise in September 2012. These were retrieved during the first Endeavor cruise, and then redeployed. The Seagliders typically made loops or butterfly patterns around the central SPURS mooring, diving to 1000 m.
Slocum/Tenuse Gliders	Contributor: G Reverdin (IFREMER) Data Access	Seaglider	Contributors: C.Eriksen, C Lee (U. Washington) Data Access
	A Waveglider is an autonomous platform propelled by the conversion of ocean wave energy into forward thrust and employing solar panels to power instrumentation. For SPURS-1, sensors included a CTD at the near-surface and another at 6 m depth, providing continuous salinity and temperature observations. Three wavegliders (ASL2, ASL3 and ASL4) were deployed from the Knorr in September 2012, redeployed in April 2013 (ASL22, ASL32 and ASL42) with final recovery in September. Waveglider trajectories followed a square loop or butterfly pattern around the central SPURS mooring.		The Ecomapper or IVER is a portable autonomous underwater vehicle (AUV) capable carrying a range of sensor payloads.  For SPURS-1 these included CTD, chlorophyll, oxygen and turbidity sensors. Ecomapper was deployed on two days during the Knorr cruise, 29 and 30 September 2012.
Waveglider	Contributors: D.Fratantoni, B.Hodges (WHOI, Horizon Marine,) Data Access	Ecomapper	Contributors:  D.Fratantoni, B.Hodges (WHOI, Horizon Marine) Data Access
	Part of the Argo global network of autonomous, self-reporting samplers, Argo floats drift horizontally and move vertically through the water column generally on 10 day cycles, collecting high-quality temperature and salinity profiles from the upper 2000m. Approximately 24 floats were deployed during SPURS-1, mainly on the Knorr cruise. These were standard Argo floats with the addition of surface temperature and salinity (STS) sensors and acoustic rain gauges (PAL). Data accessible here only include the standard ARGO profiles, not the STS or PAL data.		Neutrally buoyant floats drift and move through the water column providing continuous temperature and salinity profiles via 2 integrated CTDs and GPS surface position location data. Two floats were deployed during SPURS-1, one during the Knorr cruise in September 2012 another deployed during the April 2013 Endeavor cruise.  Recoveries were in April and September 2013 respectively.
Argo Float	Contributor: S. Riser (U.Washington) Data Access	Neutrally Buoyant Float	Contributors: E.d'Asaro, A.Shcherbina (U.Washington) Data Access
	A drifter is passive Lagrangian platform consisting of a surface buoy and tethered subsurface drogue. Buoys contain GPS and satellite data transmitters, with sensors measuring temperature and other properties. Approximately 83 drifters were deployed during SPURS-1. These were standard Surface Velocity Program (SVP) drifters with salinity sensors added (SVP/S).  Drifter data available here in netCDF format include data from both the US and European driifter deployments during the SPURS-1 campaign.
Drifter	Contributors: L.Centurioni, G.Reverin (USCD, IFREMER) Data Access
Satellite Observations Complementary, broad-scale measurements of remotely sensed sea surface salinity over the SPURS-1 domain are provided by the AQUARIUS/SAC-D and SMOS satellite missions.
Device	Description	Device	Description
	The Aquarius/SAC-D satellite mission launched in June 2011, providing over 3 years of global sea surface salinity   and wind speed observations in  390 km swaths with a 7 day repeat cycle.  The Aquarius instrument has 3 radiometer beams in push-broom alignment with footprint resolutions of 76 km (along-track) x 94 km (cross-track), 84 km x 120 km and 96km x 156 km and a sampling frequency of 1.44sec/block.  SSS accuracy is about 0.2 PSU RMS (1degree Lat/Lon, monthly average).  Both orbital/swath L2 and gridded L3 products are available from the PO.DAAC.		ESA’s SMOS (Soil Moisture & Ocean Salinity) satellite mission launched November 2009, providing over 5 years of global sea surface salinity observations. The SMOS MIRAS radiometer is an L-band passive microwave 2D-interferometer, with a, spatial resolution of 35 km (at center of the 1000km field of view) and a 3 day Equatorial temporal repeat cycle. SMOS salinity L2, L3 and L4 products are available.
Aquarius/SAC-D	Agency: NASA/CONAE Data Access	SMOS	Agency: ESA Data Access

SPURS-2 is a follow-on field campaign slated for 2016-2017 and currently in the planning stage.  It aims to better understand physical processes that influence upper-ocean salinity in a low-salinity, precipitation dominated region of the eastern tropical Pacific (ETP).  The field sampling will cover an annual cycle and will be centered at 10N, 125W.  This area is heavily influenced by rainfall associated with the intertropical convergence zone (ITCZ; Figure 4). It has a shallow thermocline and strong seasonally-varying currents, making sampling a challenge.  SPURS will leverage satellite measurements from Aquarius/SAC-D, SMOS and other remote sensing datasets. A suite of in-situ (field) observations will be guided by a data-assimilating numerical model.  A nested sampling design will examine processes on three different scales:

• Large Scale: The purpose here is to characterize processes that freshen and salinity the upper ocean in the ITCZ region and connect it to the eastern Pacific fresh pool.
• Mesoscale: A smaller observational region surrounding the central SPURS-2 site will resolve scales from 10-300 km.  This scale includes eddies which act to stir the salinity field.  Numerical modeling studies will be especially important at this scale.
• Small-scale: The smallest scales to be observed are less than 10 km. Precipitation is expected to be locally patchy at this scale. SPURS-2 especially focuses on how intense rainfall bursts are dispersed vertically and horizontally.