ORNL/CDIAC-154

NDP-089

CARBON DIOXIDE, HYDROGRAPHIC, AND CHEMICAL DATA OBTAINED DURING THE R/V
*Knorr* REPEAT HYDROGRAPHY CRUISES IN THE NORTH ATLANTIC OCEAN:

CLIVAR CO~2~ SECTIONS A20_2003 (22 SEPTEMBER--20 OCTOBER, 2003) AND

A22_2003 (23 OCTOBER--13 NOVEMBER, 2003)

Contributed by

R. A. Feely,^1^ C. L. Sabine,^1^ F. J. Millero,^2^ A. G. Dickson,^3^ R.
A. Fine,^2^ C. A. Carlson,^4^

J. Toole,^5^ T. M. Joyce,^5^ W. M. Smethie,^6^ A. P. McNichol,^5^ and R.
M. Key^7^

^1^ Pacific Marine Environmental Laboratory, NOAA, Seattle, WA

^2^Rosenstiel School of Marine and Atmospheric Science, University of
Miami, Miami, FL

^3^Scripps Institution of Oceanography, University of California, San
Diego

^4^University of California, Santa Barbara, CA

^5^Woods Hole Oceanographic Institution, Woods Hole, MA

^6^Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY

^7^Princeton University, Princeton, NJ

Prepared by

Alex Kozyr

Carbon Dioxide Information Analysis Center

Oak Ridge National Laboratory

Oak Ridge, Tennessee, USA

Date Published: September 2008

Prepared for the Climate Change Research Division

Office of Biological and Environmental Research

U.S. Department of Energy

Budget Activity Numbers KP 12 04 01 0 and KP 12 02 03 0

Prepared by the

Carbon Dioxide Information Analysis Center

OAK RIDGE NATIONAL LABORATORY

Oak Ridge, Tennessee 37831-6335

managed by

UT-BATTELLE, LLC

for the

U.S. DEPARTMENT OF ENERGY

under contract DE-AC05-00OR22725

# TABLE OF CONTENTS {#table-of-contents .TOC-Heading}

[LIST OF FIGURES v](#list-of-figures)

[LIST OF TABLES v](#list-of-tables)

[ABBREVIATIONS AND ACRONYMS vii](#abbreviations-and-acronyms)

[ABSTRACT ix](#abstract)

[1. BACKGROUND INFORMATION 1](#background-information)

[2. DESCRIPTION OF THE EXPEDITION 4](#description-of-the-expedition)

[2.1 R/V *Knorr:* Technical Details and History
4](#rv-knorr-technical-details-and-history)

[2.2 R/V *Knorr* A20_2003 and A22_2003 Cruise Information
4](#rv-knorr-a20_2003-and-a22_2003-cruise-information)

[2.3 Parameters Measured, Participating Institutions, and Responsible
Investigators
6](#parameters-measured-participating-institutions-and-responsible-investigators)

[3. DESCRIPTION OF VARIABLES AND METHODS
7](#description-of-variables-and-methods)

[3.1 Hydrographic Measurements 7](#hydrographic-measurements)

[3.2 Total CO~2~ Measurements 8](#total-co2-measurements)

[3.3 Total Alkalinity Measurements 9](#total-alkalinity-measurements)

[3.3.1 Section A20_2003 9](#section-a20_2003)

[3.3.2 Section A22_2003 12](#section-a22_2003)

[3.4 Dissolved Organic Carbon Measurements
25](#dissolved-organic-carbon-measurements)

[3.5 Total Dissolved Nitrogen Measurements
26](#total-dissolved-nitrogen-measurements)

[3.6 Chlorofluorocarbon Measurements
26](#chlorofluorocarbon-measurements)

[3.6.1 Sample Collection 26](#sample-collection)

[3.6.2 RSMAS Equipment and Technique 27](#rsmas-equipment-and-technique)

[3.6.3 Lamont-Doherty Earth Observatory Equipment and Technique
27](#lamont-doherty-earth-observatory-equipment-and-technique)

[3.6.4 Calibration 27](#calibration)

[3.7 ^14^C and ^13^C Measurements 28](#c-and-13c-measurements)

[4. HOW TO OBTAIN THE DATA AND DOCUMENTATION
33](#how-to-obtain-the-data-and-documentation)

[5. REFERENCES 35](#references)

# LIST OF FIGURES

1 Cruise tracks for the Atlantic Ocean sections A20_2003 and A22_2003 2

2 Plot of the deviations of analyses of reference materials (Batch 60
and Batch 61) from the

certified values (∆ = measured value -- certified value). Values
depicted by open circles are considered "outliers" 11

3 Auto-titration system used during the section A22_2003 Cruise 13

4 Titration cell diagram 14

5 Deviation between the TALK and CRM for both systems. 15

6 Deviation between the TCO~2~ and CRM for both systems 16

7 Deviation between the pH and CRM for both systems 16

8 Difference between the TCO~2~ of the SOMMA and TALK system results 17

9 Deviation of TALK on duplicate samples 18

10 Deviation of TCO~2~ on duplicate samples. 18

11 Deviation of pH on duplicate samples 19

12 Difference in calculated and measured TALK using an input of pH and
TCO~2~ 20

13 Difference in calculated and measured TCO~2~ using an input of TALK
and pH 20

14 Difference in calculated and measured pH using an input of TALK and
TCO~2~ 21

15 Surface measurements of salinity versus latitude from the 1997 and
2003 cruises 22

16 Surface measurements of temperature versus latitude from the 1997 and
2003 cruises. 22

17 Surface measurements of NTA versus latitude from the 1997 and 2003
cruises 23

18 Surface measurements of NTCO~2~ versus latitude from the 1997 and
2003 cruises 23

19 Surface measurements of in situ pH versus latitude from the 1997 and
2003 cruises 24

20 Surface measurements of in situ pCO~2~ versus latitude from the 1997
and 2003 cruises 24

21 Surface measurements of ^14^C versus longitude from the 1997 and 2003
cruises (A20) 29

22 Surface measurements of ^14^C versus longitude from the 1997 and 2003
cruises (A22) 30

23 Surface measurements of ^13^C versus longitude from the 1997 and 2003
cruises (A20) 30

24 Surface measurements of ^13^C versus longitude from the 1997 and 2003
cruises (A22) 31

# LIST OF TABLES

1 Technical characteristics of the R/V *Knorr* 5

2 Parameters measured, responsible investigator, and associated
institution 6

3 Listing of equipment used for alkalinity titrations for A20_2003
cruise 10

4 Summary of certified reference material measurements 15

5 Summary of duplicate measurements 17

6 Summary of internal consistency deviations 19

# ABBREVIATIONS AND ACRONYMS

AMC accelerator mass spectrometry

CDIAC Carbon Dioxide Information Analysis Center

CFC chlorofluorocarbon

CLIVAR Climate Variability (Program)

CO~2~ carbon dioxide

CRM certified reference material

CTD conductivity, temperature, and depth

DOC dissolved organic carbon

DOE U.S. Department of Energy

ECD electron capture detector

EXPOCODE expedition code

GC gas chromatograph

HCFC hydrochlorofluorocarbon

NDP numeric data package

NOAA National Oceanic and Atmospheric Administration

NO nitric oxide

NOSAMS National Ocean Sciences Accelerator Mass Spectrometry Facility

NSF National Science Foundation

ODF Oceanographic Data Facility

PMEL Pacific Marine Environmental Laboratory

RSMAS Rosenstiel School of Marine and Atmospheric Science

R/V research vessel

SIO Scripps Institution of Oceanography

SOMMA single-operator multi-parameter metabolic analyzer

TALK total alkalinity

TDN total dissolved nitrogen

TCO~2~ total inorganic carbon

WHP WOCE Hydrographic Program

WOCE World Ocean Circulation Experiment

#  {#section .unnumbered}

# ABSTRACT

Feely R. A., C. L. Sabine, F. J. Millero, A. G. Dickson , R. A. Fine, C.
A. Carlson, J. Toole,T. M. Joyce, W. M. Smethie, A. P. McNichol, and R.
M. Key. 2008. *Carbon Dioxide, Hydrographic, and Chemical Data Obtained
During the R/V Knorr Repeat Hydrography Cruise in the Atlantic Ocean:
CLIVAR CO~2~ Sections A20_2003 (22 September--20 October 2003) and
A22_2003 (23 October--13 November, 2003)*. Ed. A. Kozyr. ORNL/CDIAC-154,
NDP-089. Carbon Dioxide Information Analysis Center, Oak Ridge National
Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, 46 pp.

This report presents methods, and analytical and quality control
procedures for salinity, oxygen, nutrient, inorganic carbon, organic
carbon, chlorofluorocarbon (CFC), and bomb carbon-14 system parameters
performed during the A20_2003 and A22_2003 cruises, which took place
between September 22 and November 13, 2003, aboard research vessel (R/V)
*Knorr* under the auspices of the National Oceanic and Atmospheric
Administration (NOAA) and National Science Foundation (NSF). The R/V
*Knorr* departed Woods Hole, Massachusetts, on September 22 for the
Repeat Section A20, and ended this line in Port of Spain, Trinidad, on
October 20. The Repeat Section A22 started on October 23 in Port of
Spain, Trinidad, and finished on November 13, 2003, in Woods Hole,
Massachusetts. The research conducted was one of a series of repeat
hydrography sections jointly funded by NOAA and NSF as part of the
Climate Variability Program (CLIVAR)/CO2/repeat hydrography/tracer
program. Samples were taken from 36 depths at 88 stations on section A20
and 82 stations on section A22.

The data presented in this report include the analyses of water samples
for total inorganic carbon (TCO~2~), total alkalinity (TALK), dissolved
organic carbon (DOC), CFC, carbon-14, hydrographic, and other chemical
measurements.

The R/V *Knorr* A20_2003 and A22_2003 data sets are available free of
charge as a numeric data package (NDP) from the Carbon Dioxide
Information Analysis Center (CDIAC). The NDP consists of the
oceanographic data files and this printed documentation, which describes
the procedures and methods used to obtain the data.

**Keywords**: carbon dioxide, total CO~2~, total alkalinity, carbon
cycle, coulometry, potentiometry, hydrographic measurements, CLIVAR,
Atlantic Ocean

# BACKGROUND INFORMATION

The cruise of research vessel (R/V) *Knorr* along the World Ocean
Circulation Experiment (WOCE) designated sections A20 and A22 from Woods
Hole, Massachusetts, to Port of Spain, Trinidad, and back to Woods Hole
were the part of the Climate Variability (CLIVAR) Carbon Dioxide and
Repeat Hydrography Section Project, sponsored by the National Oceanic
and Atmospheric Administration (NOAA) and National Science Foundation
(NSF). The goal of the Repeat Hydrogaphy Project is to measure decadal
changes in circulation, heat and fresh water budgets, and carbon
inventory in the ocean. The cruises repeat a subset of the WOCE
Hydrographic Program (WHP) and Joint Global Ocean Flux Study lines
occupied in each major ocean basin in the 1990s.

The WOCE/WHP program is driven by the need to monitor the increases in
carbon dioxide (CO~2~) in the ocean and provide the necessary data to
support continuing model development that will lead to improved
forecasting skills for oceans and global climate. During the 1990s, the
WOCE/Joint Global Ocean Flux Study (JGOFS) provided a full-depth
baseline data set against which to measure future changes. By
integrating the scientific needs of programs requiring measurement of
the full water column, major synergies and cost savings are achieved.
These measurements are of importance both for major research programs,
such as CLIVAR and the U.S. Global Climate Research Project Ocean Carbon
and Climate Change Program, and for operational activities such as the
Global Ocean Observation System and the Global Climate Observing System.
As outlined in the program documentation, one component of a global
observing system for the physical climate/CO~2~ system should include
periodic observations of hydrographic variables, CO~2~ system
parameters, and other tracers. The large-scale observation component of
the Ocean Carbon and Climate Change Program needs systematic
observations of the invasion of anthropogenic carbon in the ocean that
is superimposed on a variable natural background. The five topical areas
addressed by the CO~2~/CLIVAR repeat hydrography program are

> 1\. carbon system studies;
>
> 2\. heat and freshwater storage and flux studies;
>
> 3\. deep and shallow water mass and ventilation studies;
>
> 4\. calibration of autonomous sensors; and
>
> 5\. data for model calibration.

R/V *Knorr* cruise 173 was conceived to reoccupy two meridional
hydrographic sections in the western North Atlantic as part of the
CLIVAR/Global Carbon Program of repeat hydrography. Section A20, which
lies nominally along 52° 20' W, was sampled during leg 1 of the cruise.
The return leg to Woods Hole reoccupied section A22 along 66° W (Fig.
1). Meridional hydrographic sections near 52° W had been made on three
occasions prior to this cruise: in the 1950s, 1980s, and in 1997. The
sampling plan for the 2003 occupation of both sections was simply to
make a full-depth hydrographic station at each site sampled in 1997 (see
NDP-082 at: http://cdiac.ornl.gov/oceans/ndp_082/ndp082.html). The
extremely tight station spacing at the northern end of the sections done
in 1997 was relaxed slightly in 2003.

This data report focuses on the measurements of total carbon dioxide
(TCO~2~), total alkalinity (TALK), dissolved organic carbon (DOC),
chlorofluorocarbons (CFC-11 and CFC-12), carbon-14 (^14^C), nitrate
(NO~3~), nitrite (NO~2~), phosphate (PO~4~), silicate (SiO~4~),
salinity, and dissolved oxygen (O~2~).

The methodology, instrumentation, and standardization of these
parameters have improved significantly during the WOCE/JGOFS era.
Notable developments include the release of manuals detailing the
analytical methods and operating protocols (DOE 1994, PICES 2007).
Certified reference materials (CRMs) are now available for TCO~2~ and
TALK, analyses for which are run interspersed with samples to determine
calibration offsets. For this cruise, the TALK and TCO~2~ values were
adjusted to account for the small difference between the CRMs run at sea
and the certified value determined at Scripps Institution of
Oceanography (SIO). The TCO~2~ coulometers were calibrated daily by
injecting aliquots of pure CO~2~ (99.995%). The stability of each
coulometer cell solution was confirmed with the analyses of several CRMs
each day.

![](media/image1.jpeg){width="6.290277777777778in"
height="6.426388888888889in"}

Fig. 1. Cruise tracks for the Atlantic Ocean sections A20_2003 and
A22_2003.

Instrumentation has improved in the last decade. Alkalinity measurements
can be done with better precision through automation and close checks of
the response of electrodes. Burettes are independently calibrated, and
the preparation of titrant (hydrochloric acid) has undergone improved
quality control and standardization (Millero et al. 1998). The TCO~2~
measurements are done by coulometry, a precise integrative method.
During the cruise two single-operator multiparameter metabolic analyzers
(SOMMAs) (Johnson et al. 1999) PMEL-1 and PMEL-2 were used for analyses,
which facilitated a sample throughput of up to 80 per day. Oxygen
measurements were performed by Winkler titrations (Carpenter 1965) with
photometric endpoint detection (Friederich, Sherman, and Codispoti
1984).

The data underwent careful quality assurance and quality control both
during and after the cruise. The precision of the measurements was
determined from duplicate sampling and comparison of data from deep
water, where little variability is expected. Outliers in the data were
flagged based on several methods using prior knowledge of the trends and
known relationships between parameters. Depth profiles for each
parameter were scrutinized for outliers. When deviations were observed,
other parameters were assessed to determine whether they showed
deviations as well.

This report describes procedures and methods for hydrographic
measurement and the analytical procedures, calculations, and assessment
of precision for nutrient, oxygen, TCO~2~, TALK, CFCs, ^14^C, and DOC
measurements.

# 2. DESCRIPTION OF THE EXPEDITION

## 2.1 R/V *Knorr:* Technical Details and History

The R/V *Knorr*, built in 1969 by the Defoe Shipbuilding Company in Bay
City, Michigan, is owned by the U.S. Navy. It was turned over to the
Woods Hole Oceanographic Institution (WHOI) in 1971 for operation under
a charter agreement with the Office of Naval Research. It was named for
E. R. Knorr, a hydrographic engineer and cartographer who in 1860 held
the title of Senior Civilian and Chief Engineer Cartographer of the U.S.
Navy Office. Its original length and beam were 245 and 46 ft,
respectively. Beginning on February 6, 1989, it underwent a major
midlife retrofit or "jumbo-izing" at the McDermott Shipyard in Amelia,
Louisiana. A midsection was added to the ship to stretch its length by
34 ft, to 279 ft, and fore and aft azimuthing propulsion systems were
added to make it one of the most maneuverable and stable ships in the
oceanographic fleet. By the time it was returned to WHOI in late 1991,
it had undergone retrofitting for 32 months. The WOCE section P6 was the
vessel's first post-retrofit scientific cruise. The R/V *Knorr* was
designed for a wide range of oceanographic operations and possesses
antiroll tanks and a strengthened bow for duty in icy waters. Like its
sister ship, the R/V *Melville*, it is used for ocean research and
routinely carries scientists from many different countries. Table 1
provides a list of technical characteristics of the R/V *Knorr*.

## 2.2 R/V *Knorr* A20_2003 and A22_2003 Cruise Information

+----------------------+-----------------------------------------------+
| **Ship name**        | ***Knorr***                                   |
+----------------------+-----------------------------------------------+
| EXPOCODEs            | 316N20030922 and 316N20031023                 |
+----------------------+-----------------------------------------------+
| CLIVAR section       | A20_2003 and A22_2003                         |
+----------------------+-----------------------------------------------+
| Ports of call        | Woods Hole, MA→Port of Spain, Trinidad→Woods  |
|                      | Hole, MA                                      |
+----------------------+-----------------------------------------------+
| Dates                | September 22--October 20, 2003; October       |
|                      | 23--November 13, 2003                         |
+----------------------+-----------------------------------------------+
| Funding support      | NOAA, NSF                                     |
+----------------------+-----------------------------------------------+
| Chief scientists     | Dr. John Toole/WHOI                           |
|                      |                                               |
|                      | Dr. Terrence M. Joyce/WHOI                    |
+----------------------+-----------------------------------------------+

+-----------------------------------------------------------------------+
| **Table 1. Technical characteristics of the research vessel *Knorr*** |
+-----------------------------------------------------------------------+
| Ship name: R/V *Knorr*                                                |
|                                                                       |
| Call sign: KCEJ                                                       |
|                                                                       |
| Basic dimensions:                                                     |
|                                                                       |
| Gross registered tonnage 2518 T Displacement 2958 LT                  |
|                                                                       |
| Overall length 279 ft Beam 46 ft                                      |
|                                                                       |
| Draught (maximum) 16.5 ft Service speed 12 kn                         |
|                                                                       |
| Maximum speed 14.5 kn Minimum speed 0.1 kn                            |
|                                                                       |
| Main deck clear length 126 ft                                         |
|                                                                       |
| Personnel: Crew 24                                                    |
|                                                                       |
| Scientists 34                                                         |
|                                                                       |
| Main engine: 4 × Mak6M 322 = 4 × 1000 kW at 750 rpm                   |
|                                                                       |
| Propulsion: Twin lips diesel-electric, azimuthing stern thrusters,    |
| 1500 SHP                                                              |
|                                                                       |
| Bow thruster: Lips retractable azimuthing 900 SHP                     |
|                                                                       |
| Fuel capacity: 160,500 gal                                            |
|                                                                       |
| Maximum cruise duration: 60 days (12,000 nm)                          |
|                                                                       |
| Nautical equipment: Integrated navigation system                      |
|                                                                       |
| Potable water generator                                               |
|                                                                       |
| 2 instrument hangars                                                  |
|                                                                       |
| Winches: 1 heavy-duty trawl with 30,000 ft of ½-in. wire              |
|                                                                       |
| 2 hydrographic, both with 30,000 ft of hydrowire                      |
|                                                                       |
| Hydraulic cranes on the starboard side aft and midships               |
|                                                                       |
| Scientific storage space of 1,320 ft^2^                               |
|                                                                       |
| Portable van space                                                    |
|                                                                       |
| Machine shop                                                          |
|                                                                       |
| Fume hoods                                                            |
|                                                                       |
| Uninterruptible power supply                                          |
|                                                                       |
| Air conditioning                                                      |
|                                                                       |
| Library/lounge                                                        |
|                                                                       |
| 3680 ft^2^ of laboratory space for multidisciplinary research         |
+-----------------------------------------------------------------------+

## 2.3 Parameters Measured, Participating Institutions, and Responsible Investigators

Table 2 shows the parameters that were measured on the cruise of R/V
*Knorr* as part of the CLIVAR Carbon Dioxide and Repeat Hydrography
section project sponsored by NOAA and NSF.

**Table 2. Parameters measured listed with responsible investigator and
associated institution**

  ---------------------- ------------------------------ ------------------
  **Parameter**          **Institution**                **Responsible
                                                        Investigator**

  Conductivity,          Scripps Institution of         F. Delahoyd
  temperature, and depth Oceanography (SIO)             

  Acoustic and lowered   University of Hawaii           E. Firing/J.
  acoustic Doppler                                      Hummon
  current profile                                       

  Salinity               SIO                            J. Swift

  Nutrients              SIO                            J. Swift

  Dissolved oxygen       SIO                            J. Swift

  Chlorofluorocarbons    Lamont-Doherty Earth           W. Smethie/R. Fine
                         Observatory /University of     
                         Miami                          

  Tritium, helium        Woods Hole Oceanographic       W. Jenkins
                         Institution (WHOI)             

  Total carbon dioxide   Pacific Marine Environmental   R. Feely/C. Sabine
                         Laboratory (PMEL)              

  Total alkalinity       University of Miami/SIO        F. Millero /A.
                                                        Dickson

  Dissolved organic      University of California at    C. Carlson
  carbon                 Santa Barbara (UCSB)           

  Total dissolved        University of California at    C. Carlson
  nitrogen               Santa Barbara (UCSB)           

  Chromophoric dissolved University of California at    N. Nelson
  organic matter         Santa Barbara (UCSB)           

  ^13^C                  University of Washington       P. Quay

  ^14^C                  WHOI/Princeton University      A. McNichol/R. Key
  ---------------------- ------------------------------ ------------------

# 3. DESCRIPTION OF VARIABLES AND METHODS

## 3.1 Hydrographic Measurements

Samples for CFCs, helium isotopes (^3^He), oxygen (O~2~),
hydrochlorofluorocarbon (HCFCs), TCO~2~, TALK, radiocarbon (Δ^14^C),
tritium, DOC, chromophoric dissolved organic matter, TDN, salinity, and
nutrients were drawn in this sequence from a conductivity, temperature,
and depth (CTD) sampling package containing thirty-six 12-L Bullister
bottles. A detailed description of methods for the CTD data, lowered
acoustic Doppler current profile data, and bio-optical data are given in
the cruise reports at
<http://whpo.ucsd.edu/data_access?ExpoCode=316N200309> for the section
A20_2003 and <http://whpo.ucsd.edu/data_access?ExpoCode=316N200310> for
the section A22_2003.

In all, 2,530 bottle **salinity** samples were taken during the cruise
along A20 section and 2,493 samples measured along section A22. Samples
were drawn from the 12-L Bullister bottles into 250-mL Kimax
borosilicate bottles. The bottles were rinsed at least three times
before being filled to approximately 220 mL. A plastic insert and
Nalgene cap were used to seal the sample in the bottle. At the
conclusion of sampling, the time was noted and samples were placed into
the salinometer lab so they could equilibrate to room temperature.
Samples were analyzed after a period of at least 10 h and typically not
more than 24 h from the time of sampling. Two Guildline Autosal Model
8400A salinometers (S/N 57-263 and 57-266) were used on section A20, and
a single Guildline Autosal Model 8400A salinometer (S/N 48-266) was used
on section A22. They were located in the forward analytical lab and were
used for measuring salinity on all stations. The salinometers were
modified by SIO Oceanographic Data Facility (ODF) to contain an
interface for computer-aided measurement. The water bath temperatures
were set and maintained at a value near the laboratory air temperature
24°C for the entire leg. For more information on salinity measurements,
see the A20_2003 and A22_2003 cruise reports.

Dissolved **oxygen** analyses were performed with an ODF-designed
automated oxygen titrator using photometric end-point detection based on
the absorption of 365-nm wavelength ultra-violet light. The titration of
the samples and the data logging were controlled by PC software.
Thiosulfate was dispensed by a Dosimat 665 buret driver fitted with a
1.0-mL buret. ODF used a whole-bottle modified-Winkler titration
following the technique of Carpenter (1965) with modifications by
Culberson et al*.* (1991), but with higher concentrations of potassium
iodate standard (\~0.012N) and thiosulfate solution (\~65 gm/l). Samples
were collected soon after the rosette was brought on board using a Tygon
and silicone drawing tube. Nominal 125-mL volume-calibrated iodine
flasks were rinsed three times with minimal agitation, then filled and
allowed to overflow for at least three flask volumes. The sample draw
temperature was measured with a small platinum resistance thermometer
embedded in the drawing tube. Reagents were added to fix the oxygen
before stoppering. The flasks were shaken twice (10--12 inversions) to
ensure thorough dispersion of the precipitate, once immediately after
drawing, and then again after about 20 min. The samples were analyzed
within 1--6 h of collection, then the data were incorporated into the
cruise database. A total of 2,503 oxygen measurements were made during
section A20 and 2487 oxygen measurements were made during section A22.
For more information on salinity measurements, see the A20_2003 and
A22_2003 cruise reports.

**Nutrient** analyses (phosphate, silicate, nitrate and nitrite) were
performed on an ODF-modified 4-channel Technicon AutoAnalyzer II,
generally within 1 h after sample collection. Occasionally, samples were
refrigerated up to 4 h at \~4°C. All samples were brought to room
temperature prior to analysis. The methods used are described by Gordon
et al. (1992). The analog outputs from each of the four colorimeter
channels were digitized and logged automatically by computer (PC) at 2-s
intervals. Silicate was analyzed using the technique of Armstrong et al.
(1967). An acidic solution of ammonium molybdate was added to a seawater
sample to produce silicomolybdic acid, which was then reduced to
silicomolybdous acid (a blue compound) following the addition of
stannous chloride. Tartaric acid was also added to impede phosphate
(PO~4~) color development. The sample was passed through a 15-mm
flowcell and the absorbance measured at 660 nm. A modification of the
Armstrong et al. (1967) procedure was used for the analysis of nitrate
and nitrite. For the nitrate analysis, the seawater sample was passed
through a cadmium reduction column where nitrate was quantitatively
reduced to nitrite.

Sulfanilamide was introduced to the sample stream followed by
N-(1-naphthyl) ethylenediamine dihydrochloride, which coupled to form a
red azo dye. The stream was then passed through a 15-mm flowcell and the
absorbance measured at 540 nm. The same technique was employed for
nitrite analysis, except the cadmium column was bypassed, and a 50-mm
flowcell was used for measurement. Phosphate was analyzed using a
modification of the Bernhardt and Wilhelms (1967) technique. An acidic
solution of ammonium molybdate was added to the sample to produce
phosphomolybdic acid and was then reduced to phosphomolybdous acid (a
blue compound) following the addition of dihydrazine sulfate. The
reaction product was heated to \~55°C to enhance color development, then
passed through a 50-mm flowcell and the absorbance measured at 820 nm.
In all, 2,540 nutrient samples were analyzed along section A20 and 2,497
nutrient samples were analyzed during section A22. For more information
on salinity measurements, see the A20_2003 and A22_2003 cruise reports.

## 3.2 Total CO~2~ Measurements

The total carbon dioxide (TCO~2~) or dissolved inorganic carbon
analytical equipment was set up in a seagoing container modified for use
as a shipboard laboratory. The analysis was done by coulometry with two
analytical systems (PMEL-1 and PMEL-2) used simultaneously on the
cruise. Each system consisted of a coulometer (UIC, Inc.) coupled with a
SOMMA inlet system developed by Ken Johnson (Johnson et al. 1985, 1987,
1993; Johnson 1992) of Brookhaven National Laboratory. In the
coulometric analysis of TCO~2~, all carbonate species are converted to
CO~2~ gas by addition of excess hydrogen to the seawater sample, and the
evolved CO~2~ gas is carried into the titration cell of the coulometer,
where it reacts quantitatively with a proprietary reagent based on
ethanolamine to generate hydrogen ions. These are subsequently titrated
with coulometrically generated OH^-^. CO~2~ was measured by integrating
the total change required to achieve this.

The coulometers were each calibrated by injecting aliquots of pure CO~2~
(99.995%) by means of an 8-port valve outfitted with two sample loops.
The instruments were calibrated at the beginning and end of each station
with a set of the gas loop injections.

Secondary standards were run throughout the cruise on each analytical
system. These CRMs of seawater are poisoned and filtered and
ultra-violet-irradiated. The CRMs, supplied by Dr. A. Dickson of SIO,
have been certified in SIO's shore-based facility to have a known
concentration of TCO~2~. Although there were numerous small equipment
problems during the first third of the cruise on section A20, the
overall accuracy and precision of the at-sea analyses of the CRMs on
both instruments for this section was 1±1.7 µmol/kg (n=88) for both
systems combined and --0.05±1.01 µmol/kg (n=77) for both systems on
section A22. TCO~2~ data reported to the database have been recalculated
using the bottle salinities, and, although insignificant for this
cruise, corrected to the Batch 61 CRM value on a per-instrument basis.

Samples were drawn from the Niskin-type bottles into cleaned,
precombusted 500-mL Pyrex bottles using Tygon tubing. Bottles were
rinsed once and filled from the bottom, overflowing half a volume, and
care was taken not to entrain any bubbles. The tube was pinched off and
withdrawn, creating a 5-mL headspace, and 0.2 mL of saturated HgCl~2~
solution was added as a preservative. The sample bottles were sealed
with glass stoppers lightly covered with Apiezon-L grease and were
stored at room temperature for a maximum of 12 h prior to analysis.

In all, 1,640 samples were analyzed for TCO~2~ during section A20 and
1,600 samples were analyzed during section A22: full profiles were
completed on the even-numbered stations, with replicate samples taken
from the surface, oxygen minimum, and bottom Niskin-type bottles. At a
minimum, replicate surface samples were taken at every odd-numbered
station, and when time permitted, additional depths were sampled.
Approximately 120 replicates were collected in total. The replicate
samples were run at different times during the station analysis for
quality assurance of the integrity of the coulometer cell solutions. No
systematic differences between the replicates were observed and the
standard deviation of the differences was \~ 1.2 µmol/kg on both systems
during sections A20 and A22.

## 3.3 Total Alkalinity Measurements

###  3.3.1 Section A20_2003

**Method**

Dr. Andrew Dickson's group (SIO) was responsible for the TALK
measurements during section A22_2003. Samples for TALK were collected in
glass bottles made from Schott Duran^®^ glass. They were preserved by
the addition of 0.02% by volume of a saturated mercury (II) chloride
solution (DOE 1994 -- SOP 01), and analyzed---typically within 24 h---on
board ship.

TALK measurements were made using an open-cell, two-stage,
potentiometric titration procedure similar to that used to certify
reference materials for TALK (see Dickson et al. 2003), except that
samples were not weighed into the titration vessel but instead were
dispensed using a 120-mL glass syringe. A metal frame attached to the
syringe barrel and plunger controlled the maximum extent the plunger
could be withdrawn in the barrel. This ensured that a reproducible
amount of seawater was dispensed.

The analytical procedure was as follows:

1.  An aliquot of seawater was dispensed into the titration vessel (a
    jacketed glass beaker with its temperature controlled to ±0.02 °C at
    about 20.0 °C), a stirrer bar added, and the temperature probe and
    burette tip inserted in the solution.

2.  The solution was then acidified to a pH of about 3.6 with a single
    aliquot of the titration acid and stirred vigorously while
    CO~2~-free air was bubbled through for about 6 min to remove CO~2~.

3.  The main titration was then started and the solution was titrated
    using 0.05-mL increments to a pH of about 3.0. Data from the pH
    range 3.5--3.0 were used in a non-linear least squares process that
    corrects for the reactions with sulfate and fluoride ions to
    estimate the TALK of the sample---see Dickson et al. (2003) for more
    details.

The equipment used for this is listed in Table 3.

  -----------------------------------------------------------------------
  **Table 3. List of equipment used for alkalinity titrations for
  A20_2003 cruise**

  120-cm^3^ glass syringe with custom frame to ensure reproducible
  dispensing

  250-cm^3^ capacity glass jacketed beaker

  Thermostat bath (Fisher model 9110)

  Magnetic stirrer and stir bar

  Calibrated thermometer ± 0.01 °C for cell temperature (Guildline model
  9540)

  Digital voltmeter (Kethley model 199)

  Custom high-impedance voltage-follower amplifier

  Ross-Orion combination pH electrode (model 1802)

  Calibrated thermometer ± 0.1 °C for acid temperature (YSI model 4600)

  Metrohm Dosimat^®^ model 665 burette with calibrated 5 mL exchangeable
  burette unit and anti-diffusion tip
  -----------------------------------------------------------------------

The hydrochloric acid used for the titration was made up in bulk and
then stored in 1-L Pyrex bottles with greased ground-glass stoppers. The
acid strength was approximately 0.100 mol/kg. The acid was made up in a
0.6 mol/kg sodium chloride background so as to approximate the ionic
strength of seawater. Selected bottles of the acid were then analyzed
coulometrically (Dickson et al. 2003) to assign a concentration to the
batch.

**Quality Control and Calibration of Reported Results**

The at-sea repeatability of the method was estimated by analyzing
duplicate samples, collected on each cast. These results were used to
estimate a standard deviation using the standard expression (DOE 1994 --
SOP 23). The repeatability was 1.06 μmol/kg based on 89 pairs of
analyses.

In addition, analyses were made of the alkalinity of CO~2~ reference
material. These analyses were carried out regularly throughout the
cruise, typically a pair of analyses every 12 h. The results are shown
in Fig. 2.

![](media/image2.jpeg){width="5.999305555555556in"
height="4.215972222222222in"}

> **Fig. 2.** **Plot of the deviations of analyses of reference
> materials (Batch 60 and Batch 61) from the certified values (∆ =
> measured value -- certified value).** Values depicted by open circles
> are considered "outliers."

An examination of Fig. 2 suggests that there was a change in the system
calibration at around the 100th reference material measurement (October
7, 2003). It seems from a review of contemporaneous notes that the
syringe that was being used to dispense the seawater samples for
analysis was changed on that date. It also appears that there may be an
error in calibrating the volume dispensed from the syringe (or perhaps
in the acid concentration value).

It thus seemed appropriate to treat the data in Fig. 2 as comprising two
groups: stations 1--37 and 38--88 (*i.e.*, before and after the syringe
change):

Δ~1--37~ = 3.92 ± 1.23 μmol/kg (86); Δ~38--88~ = 1.44 ± 0.74 μmol/kg
(66).

A decision was thus made to also treat the cruise data as being in the
same two groups, and to calibrate the reported data by adjusting the
measured results so as to correct these CRM results to a ∆ of zero. The
adjustment chosen was multiplicative (as would be expected if the
deviation was indeed due to a poorly calibrated dispensing system). The
reported data for stations 1--37 have thus been multiplied by a
calibration factor of 0.99822, and those for stations 38--88 by a factor
of 0.99935.

Finally, the adjusted alkalinity data results were multiplied by a
factor of 1.0002 to correct for the dilution inherent in adding mercuric
chloride to the sample to preserve it for analysis.

Once the at-sea alkalinity measurements had been adjusted in this
fashion, they were salinity normalized to a salinity of 35 and the
resulting values plotted in Ocean Data View to help identify any
questionable data. As a result of this analysis, 16 points were
identified as either questionable or bad, and flagged accordingly.

###  3.3.2 Section A22_2003

Dr. Frank Millero's group of Rosenstiel School of Marine and Atmospheric
Science (RSMAS), University of Miami, was responsible for the TALK
measurements during section A22_2003. The titration systems (Fig. 3)
used to determine TALK, TCO~2~, and pH consisted of a Metrohm 665
Dosimat titrator and an Orion 720A pH meter that is controlled by a
personal computer (Millero et al. 1993b). Both the acid titrant in a
water jacketed burette and the seawater sample in a water jacketed cell
were controlled to a constant temperature of 25 ± 0.1°C with a Neslab
constant temperature bath. The Plexiglas water jacketed cell used is
shown in Fig. 3. These cells had fill-and-drain valves that increased
the reproducibility of the cell volume.

The TALK system consisted in a manifold which allows the automated
measurement of eight samples. A set of pumps, valves and relays are used
to rinse, fill and drain the TALK cell (Fig. 3). The titration is
controlled programmatically using National Instrument's Labwindows/CVI
environment. The titration is made by adding HCl to seawater past the
carbonic acid end point. A typical titration records the
electro-magnetic fields (emf) reading after the readings become stable
(± 0.05 mV) and adds enough acid to change the voltage to a pre-assigned
increment (10 mV). In contrast to the delivery of a fixed volume
increment of acid, this method gives more data points in the range of
rapid increase in the emf near the endpoint. A full titration (25
points) takes about 20 min. Using two automated systems a 32-bottle
station cast can be completed in 8 h.

The electrodes used to measure the emf of the sample during a titration
consisted of a ROSS 8101 glass pH electrode and an Orion 90-02 double
junction Ag/AgCl reference electrode.

The HCl used throughout the cruise were made, standardized, and stored
in 500 cm3 glass bottles in the laboratory for use at sea. The 0.23202 M
HCl solutions were made from 1 M Mallinckrodt standard solutions in 0.45
M NaCl to yield an ionic strength equivalent to that of average seawater
(0.7 M). The acid was standardized using a coulometric technique by our
group and Dickson (Taylor and Smith, 1959; Marinenko and Taylor, 1968).
Both results agree to 0.0001 M.

The volumes of the cells used at sea were determined in the laboratory
by assuming a volume of 200cm^3^, then running many measurements of
seawater with a known TALK. Once the TALK values agree to ± 1 mol/kg,
the known TALK of the sample is used to back-calculate the volume of the
cell. The volume is reproducible to ± 0.01 cm^3^. Measurements of the
TALK of CRM throughout the cruise are used to confirm the volume on each
cell.

The volume of HCl delivered to the cell is traditionally assumed to have
small uncertainties (Dickson 1981) and equated to the digital output of
the titrator. Calibration of the burette of the Dosimat with Milli-Q
water at 25°C indicate that the system delivers 3.000 cm3 (the value for
a titration of seawater) to a precision of ± 0.0004 cm3. This
uncertainty results in an error of ± 0.4 μmol/kg in TALK and TCO2. The
accuracy of the volume of acid delivered by the Dosimat, however, is ten
times bigger than the precision. Since the titration systems are
calibrated using standard solutions, this error in the accuracy of
volume delivery will be partially canceled and included in the value of
cell volumes assigned.

The TALK of seawater was evaluated from the proton balance at the
alkalinity equivalence point, pHequiv = 4.5, according to the exact
definition of TALK (Dickson 1981)

TALK = \[HCO3-\] + 2\[CO32-\] + \[B(OH)4-\] + \[OH-\] + \[HPO42-\] +
2\[PO43-\]

\+ \[SiO(OH)3-\] - \[H+\] - \[HSO4-\] - \[HF\] - \[H3PO4\] (1)

At any point of the titration, the TALK of seawater can be calculated
from the equation

(V~0~ TA - VN)/(V~0~ + V) = \[HCO3-\] + 2\[CO32-\] + \[B(OH)4-\] +
\[OH-\]

\+ \[HPO42-\] + 2\[PO43-\] + \[SiO(OH)3-\] - \[H+\] - \[HSO4-\] -
\[HF\] - \[H3PO4\] (2)

where V~0~ is the volume of the cell, N is the normality of the acid
titrant, and V is the volume of acid added. In the calculation all the
volumes are converted to mass using the known densities of the
solutions.

A computer program has been developed in Labwindows/CVI to calculate the
carbonate parameters (pHsw, E\*, TALK, TCO~2~, and pK1) in seawater
solutions. The program is patterned after those developed by Dickson
(1981), Johansson and Wedborg (1982) and DOE 1994. The fitting is
performed using the STEPIT routine (J.P. Chandler, Oklahoma State
University, Stillwater, OK 74074). The STEPIT software package minimizes
the sum of squares of residuals by adjusting the parameters E\*, TALK,
TCO2 and pK1. The computer program is based on equation (2) and assumes
that nutrients such as phosphate, silicate and ammonia are negligible.
This assumption is valid only for surface waters. Neglecting the
concentration of nutrients in the seawater sample does not affect the
accuracy of TALK, but does affect the carbonate alkalinity.

![](media/image3.jpeg){width="5.749305555555556in" height="3.5in"}

**Fig. 3. Auto-titration system used during the section A22_2003
cruise.**

The pH and pK of the acids used in the program are on the seawater
scale, \[H+\]sw = \[H+\] + \[HSO4-\] + \[HF\] (Dickson, 1984). The
dissociation constants used in the program were taken from Dickson and
Millero (1987) for carbonic acid, from Dickson (1990a) for boric acid,
from Dickson and Riley (1979) for HF, from Dickson (1990b) for HSO4- and
from Millero (1995) for water. The program requires as input the
concentration of acid, volume of the cell, salinity, temperature,
measured emf (E) and volume of HCl (VHCl). To obtain a reliable TALK
from a full titration at least 25 data points should be collected (9
data points between pH 3.0 to 4.5). The precision of the fit is better
than 0.4 μmol/kg when pK1 is allowed to vary and 1.5 μmol/kg when pK1 is
fixed. The titration program has been compared to the titration programs
used by others (Johansson and Wedborg 1982, Bradshaw and Brewer 1988)
and the values of TALK agree to within ± 1 μmol/kg.

![](media/image4.jpeg){width="4.147222222222222in"
height="4.368055555555555in"}

**Fig. 4. Titration cell diagram.**

The spectroscopic pH and potentiometric TALK of CRM used during the
cruise have been measured in the laboratory before the cruise to
characterize the pH of the standard and ensure the titration systems
were performing to the desired precision. During the cruise, titrations
on CRM were made to ensure that the two titration systems were giving
consistent values. The values of pH, TCO~2~, and TALK for CRM No. 61 are
summarized in Table 4. The precision of the measurements was ± 3.6
µmol/kg for TALK, ± 3.4 µmol/kg for TCO~2~, and ± 0.009 for pH. The
average values agreed to the certified values to ± 1.8 µmol/kg in TALK,
± 4.7 µmol/kg in TCO~2~, and ± 0.009 for pH. The deviations in TALK,
TCO~2~ and pH for all the CRMs are shown in Figs. 5--7. The deviations
are within 2σ for most of the measurements. Since the average offset
between the TALK measurements of CRM agreed within experimental error,
no corrections were made in our field measurements of TALK. A small
correction factor was made for TCO~2~ (a factor of 0.9951 was multiplied
to System 2) and pH (a factor of 0.004 was added to System 1 and 0.015
to System 2) to the values for each titration system. The TCO~2~
measurements made on the titrations system have been compared to the
values measured with the SOMMA system on the same samples. These results
are shown in Fig. 8. The average differences of the adjusted values of
the titration TCO~2~ on all the measurements made on the cruise agree
with the SOMMA values to ± 3.0 µmol/kg, which is within the precision of
the measurements. These comparisons indicate that the titration values
of TCO~2~ from the alkalinity systems can yield reasonable values if the
system is calibrated with CRM in agreement with earlier studies (Millero
et al. 1993b). **Note:** the TCO~2~ and pH values that have been
measured on the alkalinity system are not present in the dataset for
section A22_2003.

  ----------------- ------------ --------------- -------------- -----------
  **Table 4.                                                    
  Summary of                                                    
  certified                                                     
  reference                                                     
  material                                                      
  measurements**                                                

                    **TA         **TCO~2~        **pH @         **Total
                    µmol/kg**    µmol/kg**       25^o^C**       runs**

  **Leg 1**                                                     

  System 1          2203.4 ± 2.8 1999.4 ± 3.5    7.887 ± 0.008  43

  System 2          2204.2 ± 4.4 2008.1 ± 3.4    7.876 ± 0.010  47

  Combined          2203.8 ± 3.6 2003.9 ± 3.4    7.881 ± 0.009  90

                                                                

  **Certified                                                   
  Values**                                                      

  CRM Batch 61      2202.04      1998.2          7.891          
  ----------------- ------------ --------------- -------------- -----------

![](media/image5.wmf)

**Fig. 5. Deviation between the TALK and CRM for both systems.**

![](media/image6.wmf)

**Fig. 6. Deviation between the TCO~2~ and CRM for both systems.**

![](media/image7.wmf)

**Fig. 7. Deviation between the pH and CRM for both systems.**

![](media/image8.wmf)

**Fig. 8. Difference between the TCO~2~ of the SOMMA and TALK system
results.**

The precision of the instruments was also tested by making duplicate
measurements of samples throughout the cruise. These duplicates were
taken from the same niskin bottle, equilibrated for an equal amount of
time, and then measured on the same instrument. A total of 117 duplicate
samples was made, and the results showed that the average delta was 0.2
± 1.8 mol/kg for TALK, 0.2 ± 1.3 mol/kg for TCO~2~, and 0.000 ± 0.003
for pH. Table 5 and Figs. 9--11 summarize these results.

+-----------+--------------+----------------+------------+------------+
| **Table   |              |                |            |            |
| 5.        |              |                |            |            |
| Summary   |              |                |            |            |
| of        |              |                |            |            |
| duplicate |              |                |            |            |
| measu     |              |                |            |            |
| rements** |              |                |            |            |
+-----------+--------------+----------------+------------+------------+
|           | **TALK       | **TCO~2~**     | **pH**     | **Total    |
|           | µmol/kg**    |                |            | runs**     |
|           |              | **µmol/kg**    |            |            |
+-----------+--------------+----------------+------------+------------+
| System 1  | 0.0 ± 1.1    | 0.3 ± 1.5      | 0.000 ±    | 62         |
|           |              |                | 0.003      |            |
+-----------+--------------+----------------+------------+------------+
| System 2  | 0.5 ± 2.6    | 0.1 ± 1.1      | 0.000 ±    | 55         |
|           |              |                | 0.003      |            |
+-----------+--------------+----------------+------------+------------+
| Combined  | 0.2 ± 1.8    | 0.2 ± 1.3      | 0.000 ±    | 117        |
|           |              |                | 0.003      |            |
+-----------+--------------+----------------+------------+------------+

![](media/image9.wmf)

**Fig. 9. Deviation of TALK on duplicate samples.**

![](media/image10.wmf)

**Fig. 10. Deviation of TCO~2~ on duplicate samples.**

![](media/image11.wmf)

**Fig. 11. Deviation of pH on duplicate samples.**

The carbonate system is characterized by four parameters: TALK, TCO~2~,
partial pressure of carbon dioxide (pCO~2~), and pH. Knowing two of
these parameters, one can calculate the other two. If more than two
parameters are known, a comparison of calculated and measured values
will tell if the measured value is internally consistent with the two
used in the calculation. We have examined the internal consistency of pH
and TALK measurements and the SOMMA values of TCO~2~. The "CO~2~sys.bas"
basic program used to make these calculations was written by Lewis and
Wallace (1998) and modified by Denis Pierrot to run in Excel. We used
the carbonic acid constants of Mehrbach (1973) and refit by Dickson and
Millero (1987) for all calculations, as well as the constant of Dickson
(1990b) for bisulfate all on the seawater pH scale. We examined an input
of pH and TALK to calculate TCO~2~, pH and TCO~2~ to calculate TALK, and
TALK and TCO~2~ to calculate pH. The results of these calculations are
summarized in Table 6 and the deviations are shown in Figs. 12--14.

  -------------- ---------------- ---------------- -------------- -------------
  **Table 6.                                                      
  Summary of                                                      
  internal                                                        
  consistency                                                     
  deviations**                                                    

  **Input**      **pH and         **TALK and       **pH and       **SOMMA -
                 TCO~2~**         TCO~2~**         TALK**         Titrator**

  **Output**     **∆ TALK**       **∆ pH**         **∆ TCO~2~**   **∆ TCO~2~**

                                                                  

                 1.1 ± 3.9        0.002 ± 0.008    1.1 ± 3.7      2.6 ± 3.0

  Runs           1375             1375             1375           1394

                                                                  
  -------------- ---------------- ---------------- -------------- -------------

![](media/image12.wmf)

**Fig. 12. Difference in calculated and measured TALK using an input of
pH and TCO~2~.**

![](media/image13.wmf)

**Fig. 13. Difference in calculated and measured TCO~2~ using an input
of TALK and pH.**

![](media/image14.wmf)

**Fig. 14. Difference in calculated and measured pH using an input of
TALK and TCO~2~.**

Once the data have been proven accurate and precise, as well as
internally consistent, a comparison of the 1997 and 2003 cruises were
made.

In looking at the changes in the carbonate system of the ocean, the
surface measurements are of the greatest concern. These values change
much more than do the deep water values. The following figures are a
comparison between the 1997 and 2003 cruises along section A22 showing a
variety of measurements versus latitude. Fig. 15 details the salinity
measurements that were obtained from the ship's CTD measurements. The
overall trend of salinity seems to remain fairly consistent. Fig. 16
shows the values for temperature, which were also obtained from the
ship's CTD measurements. The overall trend for the temperature is
slightly askew because the 1997 cruise took place in late summer and the
2003 cruise took place in the fall. Fig. 17 compares the normalized TALK
of the two cruises (normalized TALK meaning corrected to a salinity of
35, or NTA = TA × 35/S, see Millero 1996). The overall trend of NTA
remains fairly consistent between the two cruises. Fig. 18 shows the
normalized TCO~2~ (normalized meaning corrected to a salinity of 35, or
NTCO~2~ = TCO~2~ × 35/S, see Millero 1996). The trend has remained
consistent, but the concentration of TCO~2~ has increased due to the
uptake of anthropogenic carbon dioxide from industrialized countries.
This effect is more predominant in colder or northern waters as these
waters are able to hold more dissolved gases. Figures 19 and 20 show the
in situ pH and in situ pCO~2~ of the two cruises, respectively. These
values were calculated from the temperatures and pressures at which the
samples were taken, with pCO~2~ being calculated from the TALK and
TCO~2~. The figures are basically inverses of one another, because
carbon dioxide acts as a weak acid; therefore, as the concentration of
pCO~2~ increases, the pH decreases and vice versa.

![](media/image15.wmf)

**Fig. 15. Surface measurements of salinity versus latitude from the
1997 and 2003 cruises.**

![](media/image16.wmf)

**Fig. 16. Surface measurements of temperature versus latitude from the
1997 and 2003 cruises.**

![](media/image17.wmf)

**Fig. 17. Surface measurements of NTA versus latitude from the 1997 and
2003 cruises.**

![](media/image18.wmf)

**Fig. 18. Surface measurements of NTCO~2~ versus latitude from the 1997
and 2003 cruises.**

![](media/image19.wmf)

**Fig. 19. Surface measurements of in situ pH versus latitude from the
1997 and 2003 cruises.**

![](media/image20.wmf)

**Fig. 20. Surface measurements of in situ pCO~2~ versus latitude from
the 1997 and 2003 cruises.**

After reviewing the accuracy, precision and internal consistency of the
data, we feel very confident in the level of quality of these data. In
comparison with the 1997 cruise, it is very clear that the anthropogenic
output of CO~2~ has been increasing in the atmosphere, and in turn, has
increased the concentration of TCO~2~ and pCO~2~ in the surface of the
ocean. This effect is more pronounced in northern latitudes where there
is colder water, but the increase is also noticeable in the equatorial
regions. The increase in CO~2~ has caused a slight decrease in the pH,
because CO~2~ acts as a weak acid, effectively lowering the pH. However,
there were no significant findings in increase or decrease of the TALK.
Such changes in the oceans need to be constantly monitored to better
understand and predict what may happen due to human activity on earth.

## 3.4 Dissolved Organic Carbon Measurements

All samples were collected directly from the Niskin Bottles. Because
particulate organic carbon concentrations in the surface waters can be
elevated all samples collected from the upper 500 m were filtered. Water
was filtered through a combusted GF/F housed in an acid washed
polycarbonate filter cartridge attached directly the Niskin bottle
spigot. All samples were collected directly into an acid washed and
Nanopure flushed high density polyethylene (HDPE) bottles (60ml).
Samples were immediately placed upright in a -20°C freezer and samples
were shipped to shore laboratory packed in dry ice. All samples were
kept frozen at -20°C in an organic (volatile) free environment.

All DOC samples were analyzed via high temperature combustion using
Shimadzu TOC-V in shore based laboratory at the University of
California, Santa Barbara. The operating conditions of the Shimadzu
TOC-V were slightly modified from the manufacturer's model system. The
condensation coil was removed and the head space of an internal water
trap was reduced to minimize the system's dead space. The combustion
tube contained 0.5 cm Pt pillows placed on top of Pt alumina beads to
improve peak shape and to reduce alteration of combustion matrix
throughout the run. CO~2~ free carrier gas was produced with a Whatman®
gas generator (Carlson et al. 2004). Samples were drawn into 5 mL
injection syringe and acidified with 2M HCl (1.5%) and spared for 1.5
min with CO~2~ free gas. Three to five replicate 100 µL of sample were
injected into combustion tube heated to 680° C. The resulting gas stream
was passed though a several water and halide traps, the CO~2~ in the
carrier gas was analyzed with a non-dispersive infrared detector and the
resulting peak area was integrated with Shimadzu chromatographic
software. Injections continued until the at least three injection meet
the system specified range of a SD of 0.1 area counts, CV ≤2% or best 3
of 5 injections.

Extensive conditioning of the combustion tube with repeated injections
of low-carbon water and deep seawater was essential to minimize the
machine blanks. After conditioning, the system blank was assessed with
ultra-violet oxidized low carbon water. The system response was
standardized with a four-point calibration curve of potassium hydrogen
phthalate solution in low-carbon water. All samples were systematically
referenced against low-carbon water, deep Sargasso Sea reference waters
(2600 m) and surface Sargasso Sea water every 6--8 analyses (Hansell and
Carlson 1998). The standard deviation of the deep and surface references
analyzed throughout a run generally have a coefficient of variation
ranging between 1--3% over the 3--7 independent analyses (number of
references depends on size of the run) (see Hansell 2005). Daily
reference waters were calibrated with DOC CRM provided by D. Hansell
(University of Miami). The UCSB DOC laboratory exchanges references and
samples with the Hansell DOC laboratory to ensure similar performance of
DOC systems and comparability of data.

DOC calculation:

µMC = (average sample area -- average machine blank area) / (slope of
std curve)

## 3.5 Total Dissolved Nitrogen Measurements

Total dissolved nitrogen samples were analyzed via high temperature
combustion using a Shimadzu TOC-V with attached Shimadzu TNM1 unit at an
in-shore based laboratory at the University of California, Santa
Barbara. The operating conditions of the Shimadzu TOC-V were slightly
modified from the manufacturer's model system. The condensation coil was
removed and the headspace of an internal water trap was reduced to
minimize the system's dead space. The combustion tube contained 0.5 cm
Pt pillows placed on top of Pt alumina beads to improve peak shape and
to reduce alteration of combustion matrix throughout the run. Carrier
gas was produced with a Whatman® gas generator (Carlson et al. 2004) and
ozone was generated by the TNM1 unit at 0.5 L/min flow rate. Three to
five replicate 100 µL of sample were injected at 130 mL/min flow rate
into the combustion tube heated to 680° C, where the total dissolved
nitrogen in the sample was converted to nitric oxide (NO). The resulting
gas stream was passed through an electronic dehumidifier. The dried NO
gas then reacted with ozone producing an excited chemiluminescence NO~2~
species (Walsh 1989) and the fluorescence signal was detected with a
Shimadzu TNMI chemiluminescence detector. The resulting peak area was
integrated with Shimadzu chromatographic software. Injections continued
until at least three injections meet the specified range of a SD of 0.1
area counts, CV ≤2% or best 3 of 5 injections.

Extensive conditioning of the combustion tube with repeated injections
of low nitrogen water and deep seawater was essential to minimize the
machine blanks. After conditioning, the system blank was assessed with
ultra-violet oxidized low nitrogen water. The system response was
standardized daily with a four-point calibration curve of potassium
nitrate solution in blank water. All samples were systematically
referenced against low nitrogen water and deep Sargasso Sea reference
waters (2600 m) and surface Sargasso Sea water every 6--8 analyses
(Hansell and Carlson 1998). Daily reference waters were calibrated with
deep CRM provided by D. Hansell (University of Miami; Hansell 2005).

Total dissolved nitrogen calculation:

µMN = (average sample area -- average machine blank area) / (slope of
std curve)

## 3.6 Chlorofluorocarbon Measurements

###  3.6.1 Sample Collection

All samples were collected from depth using 10-L Niskin bottles. None of
the Niskin bottles used showed a CFC contamination throughout the
cruise. All bottles in use remained inside the CTD hanger between casts.

Both the Lamont-Doherty Earth Observatory and RSMAS analytical
instruments were on board so each group sampled and analyzed every other
station. Each system was capable of analyzing CFC-11, CFC-12, and
CFC-113. The RSMAS system was also capable of analyzing CCl~4~. CFC
sampling was conducted first at each station, according to WOCE
protocol. This avoids contamination by air introduced at the top of the
Niskin bottle as water was being removed. A water sample was collected
directly from the Niskin bottle petcock using a 100 mL ground glass
syringe which was fitted with a three-way stopcock that allowed flushing
without removing the syringe from the petcock. Syringes were flushed
several times and great care was taken to avoid contamination by air
bubbles. Two duplicate samples were taken on most stations from random
Niskin bottles, one duplicate was for same analytical system analysis,
to calculate precision and the other was for cross analytical system
comparison. Air samples, pumped into the system using an Air Cadet pump
from a Dekoron air intake hose mounted high on the foremast were run
when time permitted.

###  3.6.2 RSMAS Equipment and Technique

The RSMAS system analyzed 46 complete stations out of 88 for a total of
1357 samples on A20, and 42 complete stations out of 82 for a total of
1298 samples on A22. Halocarbon analyses were performed on a gas
chromatograph (GC) equipped with an electron capture detector. Samples
were introduced into the GC-EDC via a purge and dual trap system. The
samples were purged with nitrogen and the compounds of interest were
trapped on a main Porapack N trap held at \~ -15^o^C with a Vortec Tube
cooler. After the sample had been purged and trapped for several minutes
at high flow, the gas stream was stripped of any water vapor via a
magnesium perchlorate trap prior to transfer to the main trap. The main
trap was isolated and heated by direct resistance to 140^o^C. The
desorbed contents of the main trap were back-flushed and transferred,
with helium gas, over a short period of time, to a small volume focus
trap in order to improve chromatographic peak shape. The focus trap was
also Porapak N and is held at \~ −15 ^o^C with a Vortec Tube cooler. The
focus trap was flash heated by direct resistance to 155 ^o^C to release
the compounds of interest onto the analytical pre-column. The pre-column
was the first 5 meters of a 60 m Gaspro capillary column with the main
column consisting of the remaining 55 meters. The analytical pre-column
was held in-line with the main analytical column for the first 2 min of
the chromatographic run. After 2 min, all of the compounds of interest
were on the main column and the pre-column was switched out of line and
back-flushed with a relatively high flow of nitrogen gas. This prevented
later eluting compounds from building up on the analytical column,
eventually eluting and causing the detector baseline signal to increase.

The syringes were stored in a flow-through seawater bath and analyzed
within 8--12 h after collection. Bath temperature was recorded every
time a sample was analyzed for use in calculating the mass of water
analyzed. Every 12 to 18 measurements were followed by a purge blank and
a standard. The surface sample was held after the initial measurement
and was sent through the process again in order to "restrip" it to
determine the efficiency of the purging process.

###  3.6.3 Lamont-Doherty Earth Observatory Equipment and Technique

Water was transferred from the syringe into a purge and trap system
interfaced to a Hewlett Packard 5890 gas chromatograph with an electron
capture detector. The gas chromatography was carried out using a 40 inch
x 1/8 inch diameter pre-column of porasil B, a 60 in. × 1/8 in. diameter
main column of carbograph-1AC and a 4 in. × 1/8 in. diameter post column
of molecular sieve 5A. The molecular sieve 5A column separated CFC-12
from nitrous oxide and was valved out of the gas stream before CFC-11
eluted from the main column. The combination of the pre-column and main
column provided excellent separation of CFCs 11, 12, and 113 as well as
separation of CFC-113 from methyl iodide. The gas chromatograph was
calibrated against a known gas standard and concentrations are reported
on the SIO98 scale. The precision of this technique was the larger of 1%
or 0.01 pmol/kg.

###  3.6.4 Calibration 

A gas phase standard, ALM35078, was used for calibration. The
concentrations of the CFCs in this standard are reported on the SIO 1998
absolute calibration scale. Multiple calibration curves were run over
the course of the cruise on each analytical system. Estimated accuracy
is ± 2%. Precision for CFC-12, CFC-11, CFC-113 and CCl~4~ was less than
1%. Estimated limit of detection is 0.010 pM/kg for CFC-12 and CFC-113,
and 0.005 pM/kg for CFC-11 and CCl~4~.

**3.6.5 Technical Problems**

In large part, sample collection and measurement were very successful.
The integration of the computer software with the GC-EDC system hardware
made the procedure almost completely automated. There were no incidents
that caused significant instrument down time.

**3.6.6 Processing of External Duplicates**

External duplicates are defined as samples where RSMAS and Lamont both
sampled the same station/bottle. The Lamont and Miami systems were
compared throughout the A20 and A22 legs by running duplicate samples
from stations on both systems.

For A20 the agreement between these duplicates was within the
measurement error for CFC-11 and CFC-12. For CFC-11 and CFC-12 external
duplicates, the CFC values were averaged if both RSMAS and Lamont
samples had QB=2. If one of the lab's samples had a questionable (QB=3)
or bad (QB=4) quality designation, then the other lab's sample was used
for that CFC value for that particular station/bottle.

For A22 the Lamont CFC-11 and CFC-12 data were higher than the Miami
data and were believed to be in error because the surface waters
measured by the Lamont system were consistently supersaturated by about
10% and the Miami data were close to 100% saturation. A correction was
applied to the Lamont data to bring it in line with the Miami data. All
of the Lamont data for A22 was reduced by 5.5% and a further correction
was applied to stations 38-82 to correct for a small leak that
apparently developed in the Lamont system for these stations. Comparison
of the duplicates run on the Lamont and Miami systems after the
corrections yielded an error of the larger of 0.01 pmol kg^-1^ or 1.7 %
for CFC-11 and CFC-12 and 0.01 pmol/kg for CFC-113.

Following the offset correction made by Lamont on their data, the CFC-11
and CFC-12 external duplicates (with QB=2) were compared to determine
whether they were within 5% of each other. If the RSMAS and Lamont
values were within 5% of each other, they were averaged. If they were
not, then the value that most closely fit with the remainder of the
station and surrounding stations was chosen. This was determined by
examining plots of CFCs and Pressure.

For CFC113, there was a \~10% difference between the RSMAS and Lamont
values. The external duplicates were not averaged. The CFC113 sample
from the lab that sampled the remainder of the station was used instead.

RSMAS sampled CCl~4~. Lamont did not analyze water samples for CCl~4~.

## 3.7 ^14^C and ^13^C Measurements 

A small number of samples (34 surface and 3 depth profiles) were
collected directly from the Niskin bottles for measurement of
radiocarbon in dissolved inorganic ^14^C using the procedures described
at http://nosams.whoi.edu/clients/submissions_sample_prep.html#dic.
Samples were poisoned with mercuric chloride and shipped to National
Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) for
analysis. For radiocarbon analyses, the procedures used are described in
McNichol et al. (1994), McNichol and Jones in WHP 91-1 (accessible at
<http://whpo.ucsd.edu/manuals.htm>), and McNichol et al. 2000, 2001.
Briefly, the carbon is first extracted in a sample as CO~2~ and then
reduced from a gas to solid carbon. Samples are acidified with
phosphoric acid and CO~2~ gas is stripped out with a nitrogen carrier
gas. After conversion to CO~2~, samples are reduced to "graphite" on Fe
powder with hydrogen gas as the reducing agent. Sample graphite
compacted into target cartridges is loaded into a multi-sample wheel
mounted in the accelerator mass spectrometry (AMS) Cs-sputter ion
source. The graphite (pure carbon) derived from a sample is compressed
by the target press and inserted into the cathode of the AMS ion source
where the ratio of ^14^C to ^12^C is measured and compared to that of
known standards. Shipboard duplicates, i.e., two separate AMS samples
collected from the same water depth but measured separately, continue to
show a high level of precision (Elder et al. 1998). Fifteen paired
analyses from samples collected along 150°W in the North Pacific
demonstrate reproducibility of ± 3.3% for dissolved inorganic ^14^C and
± 0.04% for dissolved inorganic ^13^C, consistent with results we have
obtained in the past. This precision is obtained through careful
preparation in the laboratory, increased counting statistics on the
accelerator, and careful quality screening after analysis. Long-term
reproducibility of results over time is demonstrated by periodically
re-running entire water profiles from randomly selected stations.

![](media/image21.jpeg){width="6.631944444444445in"
height="4.367361111111111in"}

**Fig. 21. Surface measurements of ^14^C versus longitude from the 1997
and 2003 cruises (A20).**

Comparing the surface values obtained in 1997 with those measured here
(Figs. 21 and 22 below for ^14^C and Figs. 23 and 24 for ^13^C) shows no
obvious patterns of change. There is a hint of an increase near the
equator, but the sparse data set makes it challenging to consider this a
robust feature.

![](media/image22.jpeg){width="6.122916666666667in"
height="4.125694444444444in"}

**Fig. 22. Surface measurements of ^14^C versus longitude from the 1997
and 2003 cruises (A22).**

![](media/image23.jpeg){width="5.804166666666666in"
height="3.904861111111111in"}

**Fig. 23. Surface measurements of ^13^C versus longitude from the 1997
and 2003 cruises (A20).**

![](media/image24.jpeg){width="6.498611111111111in"
height="4.334722222222222in"}

**Fig. 24. Surface measurements of ^13^C versus longitude from the 1997
and 2003 cruises (A22).**

#  {#section-1 .unnumbered}

# 4. HOW TO OBTAIN THE DATA AND DOCUMENTATION

This database (NDP-089) is available free of charge from CDIAC. The
complete documentation and data can be obtained from the CDIAC
oceanographic web site (http://cdiac.ornl.gov/oceans/doc.html), through
CDIAC's online ordering system
(http://cdiac.ornl.gov/pns/how_order.html) or by contacting CDIAC.

The data are also available from CDIAC's anonymous file transfer
protocol (FTP) area via the Internet. (Please note that your computer
needs to have FTP software loaded on it. It is included in most newer
operating systems.) Use the following commands to obtain the database:

ftp cdiac.ornl.gov or \>ftp 160.91.18.18

Login: "anonymous" or "ftp"

Password: your e-mail address

ftp\> cd pub/ndp089/

ftp\> dir

ftp\> mget (files)

ftp\> quit

The full datasets from the cruise, including bottle and CTD data, can be
found at the CLIVAR repeat hydrography website:
http://ushydro.ucsd.edu/cruise_data_links.html.

Contact information:

Carbon Dioxide Information Analysis Center

Oak Ridge National Laboratory

P.O. Box 2008

Oak Ridge, Tennessee 37831-6335

USA

Telephone: (865) 574-3645

Telefax: (865) 574-2232

E-mail: cdiac@ornl.gov

Internet: <http://cdiac.ornl.gov/>

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