PMEL Programs and Plans
Accomplishments in FY 96 and Plans for FY 97
Figure. Depth sections of (a) Dissolved inorganic carbon and
(b) salinity for January - March 1996, at 170W.
Carbon Dioxide Program
Accomplishments in FY 96
The Carbon Dioxide Project
at PMEL supports the decadal to centenial component of
NOAA's Climate and Global Change (C&GC) Program, which addresses the need
to assess and predict changes in climate on time scales of 10 to 100 years. One
of the major components of this program concerns the climatic impact of the anthropogenic
production of "greenhouse gases" such as carbon dioxide (CO2). CO2 is estimated
to be responsible f or roughly one-half of the "greenhouse gas" effect resulting
from anthropogenic inputs of trace gases to the atmosphere. Because CO2 in the
atmosphere absorbs long-wave radiation emitted from the earth's surface, the post-industrial
increase of CO2 will have the effect of producing a higher equilibrium temperature
of the troposphere. Credible predction of the magnitude of this temperature increase
is a high priority scientific issue. Recent model predictions suggest an increase
of global mean s urface temperature of 1.5-4C in the next century for a doubling
of atmospheric CO2. Future decisions on regulating emissions of "greenhouse gases"
should be based on more accurate models which have been adequately tested against
a well-designed system of measurements.
Predicting global climate change as a consequence of CO2 emissions requires coupled
a tmosphere/ocean/biosphere carbon models that realistically estimate the rate
of growth of CO2 i n the
atmosphere, as well as its removal, redistribution and storage in the oceans
and terrestrial b iosphere. The primary objective of NOAA's
Ocean Atmosphere
Carbon Dioxide Exchange Study ( (OACES) is
to quantitatively assess the
fate of CO2 in the atmosphere and oceans. In order to accomplish t
his goal the natural sources and sinks of carbon dioxide must be determined.
During FY 96, the PMEL CO2 group developed a multi-parameter stepwise regression
model which quantitatively estimates the amount of anthropogenic CO2 that penetrates
into the oceans from changes in d
issolved inorganic carbon and other
physical and chemical data collected over decadal time s
cales. From
a comparison of the 1991 C&GC91 cruise data along 152W in
the North Pacific wi
th the 1973 GEOSECS data, the PMEL scientists determined that the North Pacific
accumulated anthropogenic CO2 in the mixed layer at an average rate of 1.3 ± 0.7 µmolk
g-1yr-1. T
he depth of penetration was approximately 800 m along 152W. These new model
results are comparable with previous estimates of anthropogenic CO2 inputs
into the North Pacific.
During the past year, the PMEL
and AOML CO2 groups also
completed a five-month cruise in the South Pacific under the auspices of NOAA's
Climate and Global Change (C&GC) Program . The multi-legged cruise, conducted
aboard NOAA research vessel Discoverer was a part of t he U.S.
JGOFS Program in the Southern Ocean and t he U.S.
WOCE Hydrographic Program (WOCE
Line P15S), supported jointly by NOAA, NSF, and the Department
of Energy. During the experiment, the NOAA scientists determined the
concentrations of carbon species and related physical and biological parameters
on several south-north transects. Over 4100 samples were collected coll
ected and analyzed for dissolved inorganic carbon (DIC), total alkalinity
(TAlk), CO2 partial p ressure (pCO2), pH, CFCs, carbontetrachloride, radiocarbon,
dissolved organic carbon and nitrogen, dissolved oxygen, nutrients and salinity.
Preliminary results from the cruise indicate that the southwestern Pacific
region is a large sink for atmospheric CO2. The sink regions are coincident
with regions of strong surface water stability induced by a salinity minimum
at the surface (Fig.
1). These so-called "barrier layers" prevent CO2 from vertically mixing
from below and enhance the invasion of CO2 across the air-sea interface.
In the high southern latitudes the barrier layers are maintained by melting
ice during the austral summer; whereas, in the tropical and subtropical
latitudes the barrier layers are maintained by an excess of precipitation
over evaporation, which is common over large regions of the western Pacific.
The data collected from this cruise represents the most comprehensive set
of chemical and hydrographic measurements of its kind for the southwestern
Pacific Ocean. The DIC measurements were accurate to within ± 1. 5 µmol/kg,
based upon a nalysis of reference materials and replicate samples. The
data from this cruise will be combined with other data sets from the WOCE
Hydrographic Program to constrain models of basinwide circulation and carbon
distributions in the South Pacific Ocean. We plan to use this data set
in combination with CO2 data from the same region in 1973 to determine
the amount of anthropogenic CO2 that is stored in t he South Pacific Ocean
since the middle of the last century. .
Carbon Dioxide Program
Plans for FY 97
During FY 97, the Ocean-Atmosphere Carbon Exchange Study will provide
data reduction and synthesis of the current field data in the Atlantic, Pacific, and Indian Oceans, in collaboration with the participants
of the DOE-CO2 Survey Science Team. In particular, the group will compare datasets with data obtained on other WOCE-WHP cruises and will provide internally consistent datasets encompassing roughly sixteen cruises in the Pacific Ocean, fifteen cruises in the Indian Ocean, and ten cruises in the Atlantic. These data will be used by the modeling community for setting boundary conditions for general
ocean circulation models, to determine the DIC inventory in each basin using several independent methods as outlined in Wallace (1995), and to estimate anthropogenic CO2 increases in the ocean (Goyet and Brewer, 1993; Gruber and Sarmiento; in press; Slansky et al., submmitted). To facilitate comparisons of models and observations, the data will be gridded into similar box sizes as currently used in
the models.
CO2 fluxes between air and water are poorly constrained because of lack of
seasonal and geographic coverage of pCO2 (air-water disequilibrium) values
and incomplete understanding of factors controlling the air-sea exchange.
In addition to intensive monitoring of carbon parameters and parameters influencing
pCO2 levels in surface water on dedicated cruises sponsored by OACES, PMEL,
and AOML have outfitted the NOAA Ship Ka'imimoana with a new automated CO2
system to monitor surface water pCO2 on a continuous basis. While this effort
has been a success we need more CO2 systems on NOAA ships to obtain the large
area coverage. The new shipboard design (Fig.
2), patterned after the systems recently built at AOML and PMEL, uses
stop-flow technology to reduce the amount of gas required for analysis by
the LICOR detector. It will be improved to facilitate fully autonomous operation.
The improvements will include automating draining of water traps, comprehensive
self diagnostics by the program running the computer, and automatic rebooting
capabilities of the system if errors are detected. The underway system will
be an integrated package for measurement of pCO2 in air and water and support
sensors necessary to reduce the data (such as equilibrator temperature,
location, salinity, sea surface temperature, and barometric pressure). The
comprehensive automated package will facilitate operations on ships of opportunity.
The NOAA Ship Ka'imimoana,
used to maintain the TAO
moorings on six month intervals, offers an excellent opportunity to determine
seasonal and secular trends in the region.
In addition to this activity, we will continue our pCO2 instrument development
activities with the group at MBARI , directed by Francisco Chavez, to provide
a suite of chemical and biological sensors deployed on the 155W and 170W TAO
morring array in the equatorial Pacific in November of 1996. The work leverages
on developmental efforts carried out by MBARI (with support from NOAA, NASA, and PMEL) over the past several years. The primary
objectives of this project are: (1) to determine the relationships
between physical forcing, primary production and the exchange of carbon dioxide between ocean and atmosphere; (2) to determine the biological and chemical responses to climatic and ocean variability in the
equatorial Pacific; (3) to determine the spatial, seasonal and interannual variability in primary production, carbon dioxide, and nutrient distributions; and (4) to determine the spatial, seasonal and interannual variability of sea surface pigment distributions to groundtruth sattelite measurements of ocean color.
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