README FILE FOR 2025 BERING STRAIT CTD DATA            Version 19th Feb 2026
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This is an archive of CTD data from the 2025 Bering Strait mooring cruise.

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

The data are from a ~ 9 day cruise 
- on the US vessel Norseman II 
- from 2nd-10th July 2025 
- sailing from and to Nome, Alaska, USA 
- to the Bering Strait, southern Chukchi Sea, and northern Bering 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 162 casts were taken and are included in this archive.
Water samples were taken for salinity (6) and nutrients (194) from the CTD
rosette.  Nutrient data are included in this archive. 
Salinity samples were only to confirm sensor/bottle discrepancies but
are included in the cruise report (copy 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, southern Chukchi Sea and northern Bering 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: 2nd-10th July 2025

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 Feb/March 2025
          Conductivity calibrated Jan/Feb 2025
          Oxygen calibrated Mar/Apr 2025
          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. Included in the cruise report.

     = 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 2025, 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 ~5-8uM 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 (~2.1uM this year) and were closer to the bottle data (-1.1uM and -3.2uM, pre or post).  
     Since, compared to the bottle data, a significant drift in the SUNA data (~4uM) 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 slightly worse (-1.8uM), but without any trend in error.
Thus, by adding a constant offset to these data (1.8uM), we could reduce the mean discrepancy to the bottle to 
zero, although an rms error of 0.13uM remains. 
     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). In past years, a correction to these
distilled water runs has been used to improve the SUNA-bottle fit.  However, this year, such a correction
would have increase the bias.  
      While to the bottle data, this suggests an accuracy of 0.1uM, we feel this is over optimistic, given
the variability, and the final accuracy is nearer 1-2uM.     
      Note that these comparisons were all done comparing the SUNA data to the nitrate of the 
bottle sample.  Previously, 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 affected by nitrite, but 
in this year (as in past years), nitrite values were low, and thus this would only
have a small effect <0.3uM) on the SUNA readings. 
     Finally, please note that the extreme gradients in temperature and salinity severely challenged the
extraction of the SUNA data using the UCI software, and resulted in artifacts (both positive and
negative) around these regions of high gradient.  It was not possible to reduce these errors to
zero using time-offsets in UCI.  However, this only affected SUNA data where the water column reading
was generally near zero - higher concentrations did not show this problem.
     See cruise report for details and figures. 
     In summary, for 2025
- nitrate values in raw SUNA data (separate files) and .hex/xmlcon Seasave files are on average ~5-8uM 
greater than bottle data
- using Seabirds UCI temperature salinity correction and interpolating (by record number) between 
pre and post SUNA reference updates, and applying a further offset correction based on comparison 
to bottle samples, agreement of final data to bottle data is ~1-2uM
- strong temperature and salinity gradients produced erroneous small vertical scale artifacts in
the SUNA profiles that were near zero, and these should be excluded in analysis of the data.

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. 
The SUNA data appears in the Seabird-named column, User Poly 2.  


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: 
        Bstrait25nnn.hex data - as collected
        Bstrait25nnn.hdr data - as collected
        Bstrait25nnn.bl data - as collected  (not used by our processing)
        Bstrait25nnn.XMLCON - calibration coefficients
        (all as per BStrait2025_CalsToFeb2025_SUNA_withNMEA_BOTTLES.XMLCON) 
        Bstrait25nnnA00B15AdvOx2CTML7m2m18p5mndpDMF17corSUNA
                - processed data (at native time resolution) with corrected SUNA data
        Bstrait25nnnA00B15AdvOx2CTML7m2m18p5mndpDMF17corSUNABADCS010.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: 
	In the cruise report
     NUTRIENTS:
	Ascii text, with header
     SUNA:
        RAW SUNA files A000191.CSV to A0000252.CSV and D2025015 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.
     Overall - the most reliable data is from T1, S1 and Ox1,
      although bottle samples show S1 may be 0.01psu too fresh. 

     GENERIC ISSUES
     Jelly fish were a persisent problem, often fouling the sensors, more often S2.
     Surface soaks were sometimes long to allow jellyfish to clear
     On the SBS line, the outercasing of the conducting wire started to fray
      and upcasts were interrupted to allow for whipping of the line.
      At the end of the SBS line, the bad wire was cut off and the wire reterminated

     For more details see cruise report.  Issues reported here only for T1,S1, Ox1
     ISSUES BY CHANNEL: 
	SALINITY (barring odd spike) 
	S1 gives good data on almost all downcasts. Maybe 0.01 psu fresh 
	-- S1 bad on down for casts 124, 126 (SBSnn5.5 and cast off the SBS line) – use S2
	-- S1 bad on up for those and for cast 101 (BS15.5) - use S2
	S2 bad on more casts (see cruise report) 
	OXYGEN 
        Ox1 ok on all casts, and in agreement with Ox2 to 1-2%.  

     ISSUES BY CAST:
	1 - in water test, can be discarded
	19 - T2, S2, Ox2 bad
	21 - aborted - discard
	23 - yoyoed at surface
	59 - S2 bad on upcast
	60 - S2 bad all cast
        83 - S2 bad on up, Ox2 bad on all
	84 - Ox2 bad on all 
	101 - S1 bad at pt in up cast
	117 - S2 bad on down
	124 - S1 suspect all cast
	125 - cast hit bottom and wire wrapped on drum
	(next station, 126, is off the line in deeper water to rewrap wire correctly
	127 - upcast yoyoed
     Many casts struggle with sharpness of thermocline giving erroneous signals in 
        salinity.  These issues appear to be resolved in the aligning process.
     Many casts struggle with sharpness of thermocline giving erroneous signals in 
        oxygen.  These issues are somewhat but not entirely resolved in the aligning process.
     Many casts struggle with sharpness of thermocline giving erroneous signals in 
        the SUNA.  These issues are not entirely resolved in processing.
     Salinity (from conductivity) senors do not always agree to within 0.005psu.
        See cruise report for more details. 
     Oxygen sensors agree to within manufacturer's specifications (2% per sensor)

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)
      grant  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:  881 including 5 subdirectories.
Total number of casts:   162  
Total number of salinity samples:   6 (data included in cruise report)
Total number of nutrient samples: 194

Size (b)   Name
---------  ----
= Metadata file (1 file)
    Bering_Strait_CTD_July2025_NSFAON_ReadMe_versFeb2026.txt

= Cruise report (1 file)
  BeringStrait2025CruiseReport_Norseman2_versFeb2026withlogs.pdf

= Separate copy of event log (1 file)
    BeringStrait2025_EventLog_final_19thAug2025.xlsx

.. and the 5 subdirectories: 

== One subdirectory of SBE .hex, .hdr, .bl and .XMLcon calibration files (487 files)
./BeringStrait2025CTD_hexhdrblandXMLCON:
Bstrait25nnn.hex, .hdr, .bl files (one per cast) where nnn is cast number, e.g.
      Bstrait25001.bl
      Bstrait25001.hdr
      Bstrait25001.hex
and one XMLCON calibration file (which yields uncorrected SUNA data)
      BStrait2025_CalsToFeb2025_SUNA_withNMEA_BOTTLES.xmlcon

== One subdirectory of processed data at native time resolution (162 files),
including corrected SUNA data 
./BeringStrait2025CTD_processed:
      Bstrait25nnnA00B15AdvOx2CTML7m2m18p5mndpDMF17corSUNA.cnv where nnn is cast number,

== One subdirectory of processed data averaged to 1m bins from the down cast (162 files)
including corrected SUNA data
./BeringStrait2025CTD_Binaveraged:
Bstrait25nnnA00B15AdvOx2CTML7m2m18p5mndpDMF17corSUNABADCS010.cnv, where nnn is cast number,

== One subdirectory of nutrient bottle data (1 files) 
./BeringStrait2025CTD_Bottledata_nutrients:
with nutrient files with individual file header
      BeringStrait_2025_NutrientSampleswithCTDdata_CorrSUNA_vers19thFeb2026.txt

== One subdirectory of raw (uncorrected) SUNA data and calibration files (66 files)
./BeringStrait2025CTD_RawSUNAdata:
two reference update files (S=precruise, T=postcruise)
     SNA1916S.cal
     SNA1916T.CAL
one instrument package file
     SUNA_1916_001.xml
and 62 data files for pre cruise calibrations, cruise data and post cruise calibrations
    A0000mmm.CSV, with mmm from 191 to 252 inclusive,
and D2025015.CSV

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