README FILE FOR 2023 BERING STRAIT CTD DATA             Version 24th Feb 2024
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This is an archive of CTD data from the 2023 Bering Strait mooring cruise.

The cruise was funded by the NSF-Arctic Observing Network grants:
- PLR-1758565 (PIs: Woodgate and Peralta-Ferriz). 
- PLR-2153942 (PIs: Woodgate and Peralta-Ferriz). 

The data are from a ~ 11 day cruise 
- on the US vessel Norseman II 
- from 4th-14th July 2023 
- sailing from and to Nome, Alaska, USA 
- to the Bering Strait and southern Chukchi Sea.
The cruise was also to service oceanographic moorings in the strait and those
data are archived separately. 

This is an archive of both hydrographic and bottle data.
A total of 78 casts were taken and are included in this archive.
Water samples were taken for salinity (6) and nutrients (194) from the CTD
rosette and these data are included in this archive.
A separate pumping system was used to take trace metal (and accompanying
nutrient) samples during this cruise (lead: Laramie Jensen).  These data
are archived separately.
 
Stations were taken in US waters near mooring locations and on sections
in the Bering Strait and southern Chukchi Sea.  See cruise report,
accompanying event log and data headers for map, station locations, 
calibration, and processing details. 

The data are taken using an SBE9-11plus system, recording 
- pressure 
- temperature (dual system)
- conductivity (dual system)
- oxygen (dual system)
- fluorescence
- turbidity
connected also to an
- SUNA nitrate sensor, recording both internally and with the CTD data. 

Bottle samples returned to the University of Washington (UW) for analysis post cruise.  

For an overview of previous and on-going Bering Strait mooring work,
please see http://psc.apl.washington.edu/BeringStrait.html.

For details of the measurements and their interpretation, please see:
   Woodgate, R.A., K.M.Stafford and F.G.Prahl (2015) A synthesis of
   year-round interdisciplinary mooring measurements in the Bering
   Strait (1990-2014) and the RUSALCA years (2004-2011), Oceanography
   28(3):46-67, doi:10.5670/oceanog.2015.57

Please cite that reference for the data. 

For queries, please contact:
   Rebecca Woodgate   woodgate@uw.edu   (206) 221-3268
   Polar Science Center, Applied Physics Lab, University of Washington
   1013 NE 40th, Seattle, WA  98105-6698   USA

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Meta data
=========

1) Platform: SBE9-11plus CTD rosette system (eleven 2.5l niskins) on board the RV Norseman II
  (one niskin place taken for the SUNA nitrate sensor)

2) Project title: Bering Strait

3) Data collection dates: 4th-14th July 2023

4) PI:   Rebecca Woodgate (woodgate@uw.edu)

5) Data collection method:
     Hydrographic casts with water samples for nutrients and salinity

6) Data calibration method:
     = CTD: 
       Instrument calibrated by manufacturers prior to deployment.
          Pressure calibrated June 2019
          Temperature calibrated December 2022
          Conductivity calibrated December 2022 and February 2023
          Oxygen calibrated February 2023
          Fluorescence / Turbidity calibrated  March 2010
      All times are given in GMT.
      All positions and times are from ship's aft-A-frame NMEA.
      For SBEs, calibration and processing details are in file header.

     = Salinity water samples:
	Collected to WOCE standards (3 rinses of bottle and cap)
	Analyzed at UW Marine Chemistry Lab to UNESCO 1994 JGOFS standards with
           resultant accuracy of 0.002psu
	Collected only to verify CTD salinity data.

     = Nutrient water samples:
	Collected to WOCE standards (3 rinses of bottle and cap).
	Samples filtered during collection (0.45micron 25mm Sterlitech filter)
	Samples frozen immediately after collection, and returned to UW frozen
           immediately after the cruise
	Analyzed at UW Marine Chemistry Lab to UNESCO 1994 JGOFS standards wth
           minimum detection limits of 
           0.03uM(PO4), 0.45uM(SO4), 0.18uM(NO3), 0.01uM(NO2), 0.09uM(NH4)
	See data header for more details.  

     = SUNA nitrate sensor data:
      In 2023, the SUNA nitrate data taken on the hydrographic sections were collected both on-board the SUNA 
(raw data) and with the CTD profile data via Seasave, the latter using a nominal calibration which is just a 
linear fit to the returned voltage.  While these raw two data sets are close in value, they are ~7uM higher 
than nitrate values from the bottle samples.  
      The on-board SUNA raw data were then processed using Seabird’s UCI software to apply a temperature and 
salinity correction to the bromide spectrum (see Sakamoto et al., 2009, doi: 10.4319/lom.2009.7.132), using 
temperature and salinity data from the CTD interpolated onto the times of the raw SUNA data.  This correction 
was run using both pre-cruise and post-cruise SUNA reference updates (i.e., short (order 1min) runs of the SUNA 
measuring in distilled water to correct the zero reading).  The two resultant data sets differ only by a 
constant (~2uM this year) and were closer to the bottle data   (rms error 2.3 or 0.7 uM, pre or post).  
     Since, compared to the bottle data, a significant drift in the SUNA data (~2uM) was evident over the 
course of the cruise, we combined the pre-cal and the post-cal SUNA data sets using a linear weighting by 
record number, such as to interpolate from the pre-cal at the start of the cruise to the post-cal by the end 
of the cruise.  This pre-post data set agreed with the bottle data to ~1uM (rms error). 
     Both before and after the cruise, we performed an extra calibration test at sea, making typically five 
to seven 1min SUNA runs, sampling either distilled water or a 20uM standard of nitrate solution made at UW 
(typically two or four distilled water runs, and three standard runs).  These runs showed the SUNA typically 
underestimated the standard by ~2uM, and some drift between pre-cruise and post-cruise still remained.  
Thus, for both pre and post at sea calibrations, we computed the offset between the pre-post data and at 
sea calibration and created a time-varying offset by interpolating between the pre and the post values 
weighted by record number, and applied a final correction by removing this time-varying offset from the 
pre-post data.  
      This final data set agreed with bottle samples to 0.6uM (rms error), with a mean offset to bottle 
data of -0.04uM (i.e., mean SUNA data are 0.04uM less than mean bottle data).    
      Note that these comparisons were all done comparing the SUNA data to the nitrate+nitrite of the 
bottle sample.  However, SUNA runs performed with a 20uM nitrite standard (made at UW), gave readings 
of 8uM instead of the 20uM expected.  This suggests that the SUNA reading is not nitrate+nitrite, but 
nitrate + (8/20)xnitrite, i.e., nitrate+0.4*nitrite, and thus the bottle values used for comparison 
were (1-0.4)*nitrite too high.   In this year, nitrite values were low, (maximum 0.14uM, mean 0.036uM), 
yielding a mean correction of only 0.02uM ((1-0.4)*0.036)).  While this implies the average fit of the 
SUNA is better than originally thought, (only 0.02uM less than the corrected bottle data), these 
differences are far smaller than the rms error of the data (0.6uM) and thus are not considered further, 
since this nitrite issue does not affect the final data (as ultimately that depends on the at sea 
calibrations, which were with a pure nitrate solution), but only affects the comparison to the bottle data.
     In summary, for 2023
- nitrate values in raw SUNA data (separate files) and .hex/xmlcon Seasave files are on average ~7uM 
greater than bottle data
- using Seabirds UCI temperature salinity correction and interpolating (by record number) between 
pre and post SUNA reference updates, this error can be reduced to ~1uM.
- by applying a further drift correction based on at-sea comparison to distilled water and a UW-made 
20uM nitrate standard solution, agreement of final data to bottle data is ~0.6uM
While .hex and .xmlcon files reflect the uncorrected SUNA data, the processed .cnv files archived 
here have been updated to contain corrected SUNA data, as indicated by ‘corSUNA’ in the file name.  


7) Instrumentation used:
     Sea-Bird SBE9-11plus system sampling at 24Hz with
         two SBE3F temperature sensors
         two SBE4C conductivity sensors
         two SBE43 Oxygen sensors
         one Wetlabs FLNTURT fluorescence/turbidity sensor
         two SBE pumps
     Seabird 12 place, 2.5l rosette with eleven niskins
     Seabird SUNA nitrate sensor with 10mm pathlength

8) Quality control procedures:
     Basic quality control provided by Rebecca Woodgate.
     CTD processing by SBE software as described in cruise report and file headers. 
     SUNA processing as described above and in cruise report.
     Fluorescence/turbidity sensor cleaned prior to each cast. 

9) Data format:
     CTD: 
        Bstrait23nnn.hex data - as collected
        Bstrait23nnn.hdr data - as collected
        Bstrait23nnn.bl data - as collected  (not used by our processing)
        Bstrait23nnn.XMLCON - calibration coefficients
        Bstrait23nnnA00B15AdvOx2CTML7m4m18p5mndpDMF17corSUNA
                - processed data (at native time resolution) with corrected SUNA data
        Bstrait23nnnA00B15AdvOx2CTML7m4m18p5mndpDMF17corSUNABADCS010.cnv
                - processed data averaged to 1m bins from downcast with corrected SUNA data
        nnn gives cast number (see event log)
        Time (GMT), Latitude and longitude are recorded in the data files	
     SALINITY: 
	Ascii text, with header
     NUTRIENTS:
	Ascii text, with header
     SUNA:
        RAW SUNA files A00080.CSV to A0000116.CSV and instrument calibration and set up files.
        Time (GMT) is recorded in the data files.
        Corrected SUNA data have been added to the processed CTD data

      
10) Data collection problems:
     Altimeter data - no altimeter was used on the CTD.
     Issues with individual casts: 
	Cast 1 - has poor data, but was only for a bottle firing check
	Cast 8 - was yoyoed on the upcast
	Cast 16 - has problems with S2
	Cast 73 - has partial dropout of SUNA data
     Many casts struggle with sharpness of thermocoline giving erroneous signals in 
        salinity.  These issues appear to be resolved in the aligning process.
     Many casts struggle with sharpness of thermocoline giving erroneous signals in 
        oxygen.  These issues are somewhat but not entirely resolved in the aligning process.
     Salinity (from conductivity) senors agree to within 0.005psu.
	Salinity samples show 
        - both sensors to agree with bottle data to within manufacturer's specifications
        - S1 sensor has less noisey data, and a better match to bottle data (0.001psu)
        See cruise report for more details. 
     Oxygen sensors agree to ~4% saturation, within manufacturer's specifications

11) Other related data sets:
       This data set is a part of a suite of measurements made in the
       Bering Strait almost continuously since 1990.  Mooring data have
       already been archived via the SBI project (see JOSS/EOS)
       and at NODC/NCEI
       For details see
        http://psc.apl.washington.edu/BeringStrait.html
        http://www.eol.ucar.edu/projects/sbi/
        http://sbi.utk.edu/
        http://www.nodc.noaa.gov
        http://www.ncei.noaa.gov
       Since 2000, CTD sections have been run in the Bering Strait on
       the mooring cruises.  These data are also accessible via the http
       links above.

12) Conditions for use or citation:
       Data freely available
       Please, as a courtesy, contact the PIs before using these data and cite as
           Woodgate, R.A., K.M.Stafford and F.G.Prahl (2015) A synthesis of
             year-round interdisciplinary mooring measurements in the Bering
             Strait (1990-2014) and the RUSALCA years (2004-2011), Oceanography
             28(3):46-67, doi:10.5670/oceanog.2015.57

13) Data qualifications or warnings:
       See also Data collection problems.
       SBE data: Standard Sea-Bird limitations apply
           - pressure 0.015% of FSR (6800m), i.e., ~ 1m (calibration suggests 0.6m)
           - temperature 0.001degC
           - Conductivity 0.0003S/m
               Combined errors equivalent to salinity error of ~0.008psu

14) Grant numbers:
      Work funded by:
      - National Science Foundation (NSF) Arctic Observing Network (AON)
      grants PLR-1758565 (PI: Woodgate and Peralta-Ferriz) and
             PLR-2153942 (PIs: Woodgate and Peralta-Ferriz). 


15) Sample repository locations:
        National Ocean Data Center/National Centers for Environmental
          Information (http://www.nodc.noaa.gov)
        University of Washington (http://psc.apl.washington.edu/HLD)

16) Please use the following citation for these data:
   Woodgate, R.A., K.M.Stafford and F.G.Prahl (2015) A synthesis of
       year-round interdisciplinary mooring measurements in the Bering
       Strait (1990-2014) and the RUSALCA years (2004-2011), 
       Oceanography, 28(3):46-67, doi:10.5670/oceanog.2015.57

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FILE LISTING
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Total number of files:  436 including 5 subdirectories.
Total number of casts:   78  
Total number of salinity samples:   6
Total number of nutrient samples: 194

Size (b)   Name
---------  ----
= Metadata file (1 file)
    16238 Bering_Strait_CTD_July2023_NSFAON_ReadMe_versFeb2024.txt

= Cruise report (1 file)
  6446350 BeringStrait2023CruiseReport_Norseman2_vers10thDec2023wELsmall.pdf

= Separate copy of event log (1 file)
    69652 BeringStrait2023_EventLog_final.xlsx

.. and the 5 subdirectories: 

== One subdirectory of SBE .hex, .hdr, .bl and .XMLcon calibration files (235 files)
./BeringStrait2023CTD_hexhdrblandXMLCON:
Bstrait23nnn.hex, .hdr, .bl files (one per cast) where nnn is cast number, e.g.
       562 Bstrait23001.bl
       853 Bstrait23001.hdr
    891925 Bstrait23001.hex
and one XMLCON calibration file (which yields uncorrected SUNA data)
     10068 BSTRAIT23xxxwithox.XMLCON

== One subdirectory of processed data at native time resolution (78 files),
including corrected SUNA data 
./BeringStrait2023CTD_processed:
Bstrait23nnnA00B15AdvOx2CTML7m4m18p5mndpDMF17corSUNA.cnv where nnn is cast number, e.g.,
   3197699 Bstrait23001A00B15AdvOx2CTML7m4m18p5mndpDMF17corSUNA.cnv

== One subdirectory of processed data averaged to 1m bins from the down cast (78 files)
including corrected SUNA data
./BeringStrait2023CTD_Binaveraged:
Bstrait23nnnA00B15AdvOx2CTML7m4m18p5mndpDMF17corSUNABADCS010.cnv, where nnn is cast number, e.g.,
     15751 Bstrait23001A00B15AdvOx2CTML7m4m18p5mndpDMF17corSUNABADCS010.cnv

== One subdirectory of nutrient and salinity bottle data (2 files) 
./BeringStrait2023CTD_Bottledata_nutrientsandsalinity:
with separate salinity and nutrient files with individual file headers
      5815 BeringStrait2023_BottleSalinitySamples.txt
     48052 BeringStrait_2023_NutrientSampleswithCTDdata_vers23rdFeb2024.txt

== One subdirectory of raw (uncorrected) SUNA data and calibration files (40 files)
./BeringStrait2023CTD_RawSUNAdata:
two reference update files (I=precruise, J=postcruise)
     16269 SNA1916I.cal
     16374 SNA1916J.CAL
one instrument package file
   1049248 SUNA_1916_001.xml
and 37 data files for pre cruise calibrations, cruise data and post cruise calibrations
    A0000mmm.CSV, with mmm from 80 to 116 inclusive, e.g.,
    940067 A0000080.CSV

+++++++++ END OF FILE LISTING ++++++++++++++++++++++++++++++ 