Table of Contents

• Dataset Description
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

Full resolution profiles of temperature, potential temperature, salinity, and dissolved oxygen from Seaglider equipped with CTD, oxygen, and optical sensors. 

Modification history:

28 March 2011:  original Matlab-format data files reformatted for database to include higher accuracy for bbp variables (from four decimal places to six)

Latitude and longitude (parameter names lat and lon) were measured at the surface and interpolated when the glider was at depth.  Parameter name GPS value id indicates measurements while glider was at the surface (value=1) or interpolated while diving (value=0).  No interpolation or smoothing was performed on other data. 

Temperature and salinity (parameter names temp and sal):  Temperature and salinity data were calculated using pre deployment calibration coefficients.  Further correction to temperature and conductivity was applied to NAB08 SG140 dataset based on the R/V Knorr calibration cast.  A first-order lag correction was applied to raw measurements of temperature and conductivity (due to temperature latency).  For each dive, out of range measurements and spikes (3 interquartile ranges above or below the median in windows of 15 contiguous measurements) were flagged and replaced with NaNs, which were repopulated by linear interpolation.  Data were smoothed with an 11-point median filter.  Parameters potemp and sigma_0 were calculated from the smoothed temp and sal datasets.  For more details, see Seaglider_CTD_Calibration-NAB08.pdf.

Dissolved oxygen, O2 (parameter name O2_cal):  Oxygen data from the Aanderaa optode were corrected for time lags in oxygen and temperature.  Winkler oxygen bottle data from glider – ship and float-ship calibration profiles, as well as concurrent glider – float profiles were used to determine the appropriate gain and offset.  The resulting oxygen has an error of ±2 µmol kg-1.  For more details, see Oxygen_glider_float_Calibration-NAB08.pdf. 

Particulate backscattering coefficients, bbp (parameter names bbp470, bbp700): Backscattering digital counts were converted to β at 117° by subtracting factory-provided dark counts and multiplying by factory calibration scale factors, modified based on measurements and calculations of Sullivan et al. (subm.)  Sensors were calibrated before the experiment and after the experiment. β at 117° was converted to bbp (m-1) by subtracting β of seawater (Zhang et al., 2009) and multiplying by 2πβ (where β = 1.132).  Ship-glider calibration profiles were used to produce fully cross calibrated data sets only for bbp at 700 nm (m-1).  The other backscattering coefficient (bbp at 470 (m-1)) is calculated using the factory calibrations only since the ship had only one backscatter sensor, i.e., bbp700.  For more details, see Backscatter_Calibration-NAB08.pdf.

Particulate organic carbon (POC) derived from bbp(700) (parameter name POC_bbp):  The regression to convert ship downcast bbp at 700 nm to POC is:
POC (mg C m-3) = bbp (700)_downcast  (m-1) * 35800 (mg C m-2) – 16.2 (mg C m-3); r2 = 0.81.
Because all backscatter sensors were cross calibrated with the ship CTD downcast, this regression was directly applied to glider bbp at 700 nm to compute glider POC.  For more details, see KN193-03 BOTTLE metadata and POC_cp_bbp_Calibration-NAB08.pdf.

Chlorophyll fluorescence (parameter names chl_raw):  Chlorophyll fluorescence measured by glider ECOPuck BB2F was cross-calibrated with other chlorophyll fluorometers by ship-glider calibration profiles and converted to volts.  Dark voltage (median in situ dark voltage = 0.083 volts) was subtracted from cross-calibrated values to obtain chlorophyll fluorescence in volts. The ECOPuck was calibrated before and after the experiment. For more details: Seaglider_chl_Calibration.pdf.

NAB2008 was a process experiment designed to study an important component of the oceanic carbon system - the North Atlantic spring bloom. The phytoplankton bloom occurring each spring in the North Atlantic, drives the uptake of carbon dioxide and is an important component of the biological pump (Bagniewski et al., 2010). Previous studies in this region have shown the importance of small temporal and spatial scales, i.e. ecosystem patchiness, during the bloom, but were restricted by the limitations of ship-based sampling. Recent advances in autonomous platforms and sensors presented an opportunity to study this important event in a new way. In addition to deployment of a diverse suite of in situ sampling devices, NAB2008 was also a test-bed for developing the strategies and knowledge needed to successfully use new methods to drive the next generation of ocean observations.

In 2008, a coordinated deployment of 1 float, 4 Seagliders and 2 research vessels sampled the evolution of the North Atlantic spring bloom along and surrounding the nearly Lagrangian path followed by the float. The autonomous measurements were continuous through the experimental period, and included CTD, chlorophyll fluorescence, optical backscatter, and oxygen on all platforms; and nitrate, optical attenuation, and various radiance measurements on the float. Velocities were determined from the vehicle motion, with the float extending to a depth of 230 meters and gliders to 1,000 meters. The autonomous vehicles were deployed, rescued, and recovered on three cruises of the Icelandic vessel Bjarni Saemundsson. A 21-day cruise of the R/V Knorr conducted more detailed measurements during the peak of the bloom in May. The R/V Knorr sampling program included optical profiles, ADCP data and analysis of water samples for nutrients, particulate organic carbon, pigments, micro-plankton composition, complemented by guest investigator analyses. Data from both ships were used to calibrate and validate the autonomous measurements.

References:
Bagniewski, W., Fennel, K., Perry, M. J., and D'Asaro, E. A. (2010) Optimizing models of the North Atlantic spring bloom using physical, chemical and bio-optical observations from a Lagrangian float, Biogeosciences Discuss., 7, pp. 8477-8520, doi:10.5194/bgd-7-8477-2010

NAB08 preprints

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The Ocean Carbon and Biogeochemistry (OCB) program focuses on the ocean's role as a component of the global Earth system, bringing together research in geochemistry, ocean physics, and ecology that inform on and advance our understanding of ocean biogeochemistry. The overall program goals are to promote, plan, and coordinate collaborative, multidisciplinary research opportunities within the U.S. research community and with international partners. Important OCB-related activities currently include: the Ocean Carbon and Climate Change (OCCC) and the North American Carbon Program (NACP); U.S. contributions to IMBER, SOLAS, CARBOOCEAN; and numerous U.S. single-investigator and medium-size research projects funded by U.S. federal agencies including NASA, NOAA, and NSF.

The scientific mission of OCB is to study the evolving role of the ocean in the global carbon cycle, in the face of environmental variability and change through studies of marine biogeochemical cycles and associated ecosystems.

The overarching OCB science themes include improved understanding and prediction of: 1) oceanic uptake and release of atmospheric CO2 and other greenhouse gases and 2) environmental sensitivities of biogeochemical cycles, marine ecosystems, and interactions between the two.

The OCB Research Priorities (updated January 2012) include: ocean acidification; terrestrial/coastal carbon fluxes and exchanges; climate sensitivities of and change in ecosystem structure and associated impacts on biogeochemical cycles; mesopelagic ecological and biogeochemical interactions; benthic-pelagic feedbacks on biogeochemical cycles; ocean carbon uptake and storage; and expanding low-oxygen conditions in the coastal and open oceans.