We present the results obtained from continuous measurements

performed during two cruises with hemispherical courses. In this way, we obtained the latitudinal trend of CO2 in continuity of space and time along two hemispheric courses in 1994-95 and 1996-97 from Europe to Antarctica. The results are compared with measurements from the National Oceanic and Atmospheric Administration (NOAA) Climate Monitoring and Diagnostic Laboratory (CMDL) cooperative air

sampling network. The fitting of data recorded on board with the historical data sets recorded at Palmer Station is also presented, highlighting the current annual increase in atmospheric CO2 concentrations

Bonasoni, P.

Ciattaglia, L.

Colombo, T.

Giovanelli, G.

Lenaz, R.

Masarie, K.

Ori, C.

Ravegnani, F.

English

Scientific Open-access Literature Archive and Repository

IL NUOVO CIMENTO Settembre-Ottobre 2000VOL. 23 C, N. 5Ship-board report on atmospheric CO2 concentrations recordedon continuous from mediterranean sea to antarcticaR. LENAZ (1), G. GIOVANELLI (2), C. ORI (1), T. COLOMBO (3), K. MASARIE (4)L. CIATTAGLIA (5), F. RAVEGNANI (2) and P. BONASONI (2)(1) Istituto IGM-CNR - Via Gobetti 101, 40129 Bologna, Italy(2) Istituto ISAO-CNR - Via Gobetti 101, 40129 Bologna, Italy(3) Meteorological Service-Italian Air Force - Sestola (Mo), Italy(4) CMDL-NOAA - 325 Broadway, Boulder, CO 80303-3328, USA(5) IFA-CNR - Via Tiburtina, 770, 00159 Roma, Italy(ricevuto l’11 Febbraio 2000; approvato il 31 Marzo 2000)Summary. — We present the results obtained from continuous measurementsperformed during two cruises with hemispherical courses. In this way, we obtainedthe latitudinal trend of CO2 in continuity of space and time along two hemisphericcourses in 1994-95 and 1996-97 from Europe to Antarctica. The results are comparedwith measurements from the National Oceanic and Atmospheric Administration(NOAA) Climate Monitoring and Diagnostic Laboratory (CMDL) cooperative airsampling network. The fitting of data recorded on board with the historical data setsrecorded at Palmer Station is also presented, highlighting the current annualincrease in atmospheric CO2 concentrations.PACS 92.60 – Meteorology.PACS 92.60.Hp – Chemical composition and chemical interactions.1. – IntroductionFifty-five percent of the change in radiative forcing caused by greenhouse gasemissions from 1980 to 1990 is due to the anthropogenic increase in atmospheric carbondioxide [1]. The decline in the growth or stabilization of some greenhouse gases morerecently observed in the atmosphere underlines the importance of CO2 as a primaryagent of global climate change [2]. However, the incomplete understanding of thevariability of the global carbon budget makes it difficult to predict future levels ofatmospheric CO2. From the 1970s on, high-precision measurements of air collected inglass flasks from large global networks have documented the increase in atmosphericCO2 and the variability in its long-term growth [3, 4]. These observations are often usedwith 2- and 3-dimensional transport models to derive plausible distributions of thesources and sinks of CO2. The present knowledge of carbon dioxide concentrationvalues and the possible distribution of sources, sinks and trends is usually determinedG Società Italiana di Fisica 507T. COLOMBO, R. LENAZ, C. ORI, ETC.508from the weekly collection of air samples in glass flasks over a global network of sitessince the 1970s. Up to the 1990s, such measurements constituted the most accuratedata available [3, 4]. In spite of the importance of the rise in atmospheric CO2 expectedto lead the global climatic change, after thirty years of measurements in air and oceans,the variations of the global atmospheric CO2 budget remain uncertain [5].Nevertheless, any geographical distribution of CO2 is reflected in the spatial andtemporal variations of CO2 concentration patterns in the atmosphere.Numerical models of atmospheric transport can simulate these patterns and testhypotheses of the atmospheric CO2 budget. However, the sparseness of sampling sitesand the lack of temporal continuity among measurements at different locations areserious obstacles to this approach. The numerical forecasting models developed in the’70s and ’80s [6, 7] demonstrated that climatic changes are amplified in remote areas,such as the polar regions. Later on, the simulations based on a coupled ocean modelestablished that such amplifications are weaker than previously assumed. Hence, theneed to verify these models by means of direct measurements performed not only inpolar regions, but in surrounding oceanic areas. This is also necessary in order to verifythe extension of the phenomena observed at the poles and the likelihood of theirreaching intermediate latitudes. Recently, results obtained from direct measurementsperformed on board twice a day during cruises of limited shipping routes have beenpresented [8-12]. Continuous measurements along these two routes of hemisphericextension can now be used to further constrain models by providing the longitudinaland latitudinal gradient in oceanic areas.We were able to take advantage of two cruises organized by the Italian nationalresearch program in Antarctica (PNRA):– the EOLO 94 cruise with the ship R/V OGS EXPLORA bound for the Belling-shausen Sea through the Mediterranean Sea and North and South Atlantic ocean.– the EOLO 96 cruise with the M/N ITALICA carrying instrumentation andsupplies to the Ross Sea Italian Base through the Mediterranean Sea, Red Sea, IndianOcean and the Southern Ocean.We used these two opportunities to carry out tropospheric O3 and CO2measurements and dust sampling.The present paper compares the data of CO2 concentration obtained during the twocruises with available measurements on the same days at Mt. Cimone (Italy),Seychelles Islands and the Jubany Station (Antarctica).Moreover, a comparison of February means obtained from data recorded during theroute in circum-Antarctic seas with the corresponding means at Palmer Station andSouth Pole Station allows us to assess the annual increase in the carbon dioxideconcentration from 1968 in this area.Finally, we compare data obtained on these cruises with values extracted at similartimes and latitudes from a marine boundary layer (MBL) reference surfaceconstructed using measurements from the NOAA CMDL cooperative air samplingnetwork [13].2. – Measurement methodologyThe measurements were carried out with a Siemens Ultramat 5E analyzer set upfor a marine use [14]. During the cruise EOLO 94 on the R/V OGS EXPLORA, the airSHIP-BOARD REPORT ON ATMOSPHERIC CO2 CONCENTRATIONS RECORDED ETC. 509inlet was mounted over the bows, ten meters above sea level. In the EOLO 96 cruise onthe M/N ITALICA, it was mounted on the upper deck (15 m above sea level). The inletwas protected from airborne particles and salt spray by two WHATMAN filters.The pipe connecting the inlet to the measurement equipment was made frompolyethylene, proven to be physically and chemically inert to CO2 by experimentscarried out at the Mt. Cimone Observatory. A single piece was employed in order toavoid leaks; the line was wrapped in a thermal insulating strip in order to avoid lightand warming from the sun. The WMO-X93 scale was used and calibrations wereperformed with two working standards (345 ppm and 375 ppm), whose CO2concentration was determined at Mt. Cimone Observatory, a baseline site of the ItalianMeteorological Service, with comparison against primary standards normally used atthe site itself: these standards were tested in the Round-Robin intercomparisonorganized by the NOAA in April 1996.The values measured using the working standards were almost always equal to theassumed concentration or different by no more than a decimal unit (0.1 ppm) even 24hours after the last true calibration; the tests were usually carried out at least twice aday.The meteorological monitoring system logged the wind direction (relative to theship’s axis) permitting us to flag as “suspect” those measurements made when the inletwas downwind from the ship’s funnel within a selected angle.3. – Data processingThe on-board data logger sampled the CO2 concentration every 4 seconds andrecorded 10 minutes means.It should be noted that, in the first days of the EOLO 94 cruise, the data logger wasunable to sample the decimal figures of the CO2 measurements.We processed the raw CO2 trying to eliminate data affected by anthropogenicinfluence in order to obtain a clean air selection conforming to the following criteria(fig. 1, 2):– Removal of the values measured when the inlet was downwind from the shipfunnel within an angle of 6 607 from the ship axis.– Removal of the EOLO 94 values recorded in proximity of South America(20–50 nm from the coast), when the true wind was blowing from the continent (from alatitude of 2 307 to 2 607 we accepted winds from 1507 to 2107; at latitudes less than2 607 we accepted winds from 07 to 2107).For the EOLO 94 cruise about 2000 values were rejected out of 5000 (70% below357S).For the EOLO 96 cruise about 500 values were rejected out of 7500 (60% below407S).– The use of a filter for the concentration values with the purpose of obtainingthe steady-state criteria proposed by Thoning [15] for processing the Mauna Loa CO2hourly data. We computed the moving average of the previous hour and eliminatedmeasurements differing by more than 0.5 ppm; special care was taken with the “first”data of a series; a data set starts after a calibration, a change of the humidity trap,some time downwind from the funnel or when the filter itself erases more than 40minutes of data.T. COLOMBO, R. LENAZ, C. ORI, ETC.510Fig. 1. – Latitudinal distribution of EOLO 94 CO2 concentration.For the EOLO 94 cruise about 700 values were filtered out, evenly spaced inlatitude.For the EOLO 96 cruise about 3000 values were rejected (50% below 607S).Fig. 2. – Latitudinal distribution of EOLO 96 CO2 concentrations.SHIP-BOARD REPORT ON ATMOSPHERIC CO2 CONCENTRATIONS RECORDED ETC. 511Fig. 3. – EOLO 94 CO2 concentrations against the MBL reference.– In order to relate our measurements to the CMDL-MBL data [13], wecomputed the mean of the data sharing the same 0.05 sin (latitude) interval and thesame “week” (7.6041 days). The time and latitude intervals are the same used incomputing the MBL (fig. 3, 4).Fig. 4. – EOLO 96 CO2 concentrations against the MBL reference.T. COLOMBO, R. LENAZ, C. ORI, ETC.5124. – DiscussionIn order to assess the quality of the data, we compared measurements obtained onboard the ships with those available to us recorded at the same time at differentstations using daily means:1) With respect to Mt. Cimone CO2 data [16, 17] the cruise values present asmoothed trend typical of a well-mixed marine site showing a mean difference of about2.7 ppm in the Western Mediterranean Sea (EOLO 94) and about 1.4 ppm in theEastern Mediterranean Sea.2) The mean difference of data recorded on board compared to those of theJubany station [18] is 0.7 ppm in the EOLO 94 cruise at a latitude below 557S and samelongitude (657–757W); in the EOLO 96 cruise the mean difference is 0.6 ppm at alatitude below 557S and a longitude around 1707W (more than 1007 from Jubany).The difference between average data recorded in February both on board duringEOLO 94 and EOLO 96 cruises in the Antarctic seas and at Palmer Station was 2.5 ppmand the rise was consistent with the value estimated in past records for the same stations.3) We related our February mean with the historical trends at PalmerStation [4, 5] (fig. 5); the trend seems to show an annual increase of more than1.6 ppm/year, normally indicated as global increase [19].4) Seychelles: only one flask was available in January 1997: the comparison ofthis sample analysis (361.9 ppm) agrees with the CO2 concentration measured on thesame day at sea (361.5 ppm).We also compared our data with the CMDL-MBL weekly interpolated values (seedata processing). This distribution is computed from sparse data and is independent ofcirculation models or specific hypotheses on CO2 sources and sinks whose latitude theauthors try to determine.We also see some differences probably due to local gradients, such as the oneFig. 5. – Palmer Station: historical CO2 February means.SHIP-BOARD REPORT ON ATMOSPHERIC CO2 CONCENTRATIONS RECORDED ETC. 513existing in the Mediterranean region which was evidenced by Mt. Cimone CO2data [16]. In this regard, the significant difference in longitude is relevant, bearing inmind that the MBL deal with CO2 data collected mostly in the Pacific Ocean. The MBLcurve presents a smoothed trend of the experimental CO2 data collected during the twocruises. Typical, for example, is the positive disagreement in the equatorial beltbetween 0.2 and 20.1 sin (lat) in the EOLO 94 cruise (fig. 3) in the Atlantic Ocean offcentral Africa and Southern America. The EOLO 96 data show a similar difference at ahigher latitude between 0.4 and 0.1 sin (lat) (fig. 4). The filtered CO2 data reveal anothersignificant positive disagreement between 20.6 and 20.9 sin (lat), during EOLO 94 (fig. 3).Overall, the difference between the meridian weekly CO2 distributions computedusing all the CMDL-MBL sites in a local strategy (far sites weigh less) and the shipdata measured on the same days seems to be less than 1 ppm.5. – ConclusionsThe activity exposed above was supported by the National Programme of Researchin Antarctica (PNRA) and the data were carried out during a survey of unusualhemispheric extension by direct and continuous measurements of CO2 concentration.The most important aim in measuring a CO2 latitudinal distribution is to obtain anidea of the trend and magnitude of the major sources and sinks of this gas, gainingfurther insight into the global carbon cycle.The results, compared with values recorded at different stations, confirm thevalidity of the measurement system that worked without interruption from Europe toAntarctica twice on two different ship-boardings.The criteria adopted for the data selection could permit the presentation of a steadyconcentration well representative of background data. The distribution obtained withCO2 in continuous measurements is particularly important because we have alatitudinal distribution of data.The other important consideration is that the measurements have been obtained atsea, where carbon dioxide measurements are rarer and sparse.We set up a filter for the concentration values with the purpose of obtaining steady-state data working on the steadiness of the data themselves.Although the routes for the different years are not the same, we obtained concentra-tion values at the same latitudes, that differ only in the annual increase in the Antarctic regions.The good quality of the data was validated by means of comparisons withsimultaneous measurements taken at other stations.The historical February means taken at the Palmer and South Pole Station,together with our February means, allowed us to estimate the current annual increasein the southern hemisphere as being higher than 1.6 ppm/year.* * *Contribution n. 1102 of IGM - CNR - Bologna.R E F E R E N C E S[1] Intergovernmental Panel on Climate Changes (IPCC), Climate Change. The IPCC ScientificAssessment (Cambridge University Press) 1990, 365 pp.T. COLOMBO, R. LENAZ, C. ORI, ETC.514[2] CONWAY T. J., TANS P. P., WATERMAN L. S., THONING K. W., KITZIIS D. R., MASARIE K. A. andZHANG N., Evidence for interannual variability of the carbon cycle from NOAA/ClimateMonitoring and diagnostic laboratory global air sampling network, J. Geophys. Res., 99(1994) 22831-22855.[3] KEELING C. D., WHORF T. P., WONG C. S. and BELLAGAY R. D., The Concentration of CarbonDioxide at Ocean Weather Station P, 1969-1981, J. Geophys. Res., 90 (1985) 10511-10528.[4] CONWAY T. J., TANS P. P. and WATERMAN L. S., Atmospheric CO2 records from sites in theNOAA/CMDL air sampling network, in BODEN T. A., KAISER D. P., SEPANSKI R. J. andSTOSS F. W. (Editors), Trends 93: A Compendium of Data on Global Change.ORNL/CDIAC-65 Carbon Dioxide Information Analysis Center, Oak Ridge NationalLaboratory, Oak Ridge, Tenn. USA, pp. 41-119.[5] TANS P. P., FUNG I. Y. and TAKAHASHI T., Observational constraints on the globalatmospheric CO2 budget, Science, 247 (1990) 1431-1438.[6] MANABE S. and WETHERALD T., The effects of doubling the CO2 concentration on the climateof a general circulation model, J. Geophys. Res., 32, No. 1 (1975) 3-15.[7] WASHINGTON W. M. and MEEHL G., Seasonal cycle experiment on the climate sensitivity dueto a doubling of CO2 with an atmospheric general circulation model coupled to a simplemixed-layer ocean model, J. Geophys. Res., 89, N. D6 (1984) 9475-9503.[8] OUDOT C., TERNON J. F. and LECOMPTE J., Measurements of atmospheric and oceanic CO2in the tropical Atlantic: ten years after the 1982-84 FOCAL Cruises, Tellus B, 47 (1995)70-85.[9] METZL N., POISSON A., LOUANCHI F., BRUNET C., SCHAUER B. and BRES B., Spatio-temporaldistribution of air-sea fluxes of CO2 in the Indian and Antarctic oceans. A first step, TellusB, 47 (1995) 56-69.[10] NOAA CMDL 1996, N7 23, Summary Report 1994-1995, 30-31.[11] INOUE H., SUGIMURA Y. and FUSHIMI K., PCO2 and delta 13C in the air and surface sea waterin the western North Pacific, Tellus B, 39 (1987) 228-242.[12] MURPHY P. P., FEELY R. A., GAMMON R. H., KELLY K. C. and WATERMAN L. S., Autumnair-sea disequilibrium of CO2 in the South Pacific Ocean, Marine Chemistry, 35 (1991)77-84.[13] MASARIE K. A. and TANS P. P., Extension and integration of atmospheric carbon dioxidedata into a globally consistent measurement record, J. Geophys. Res., 100 (1995)11593-11610.[14] ORI C., LENAZ R., COLOMBO T. and GIOVANELLI G., Atmospheric CO2 concentrationmeasured continuously from the Mediterranean to the Bellingshausen sea: technology andmethodology, in Proceedings of the 6th Workshop Italian Research On AntarcticAtmosphere, Firenze 1995, edited by M. COLACINO, G. GIOVANELLI and L. STEFANUTTI, Conf.Proc. SIF, Vol. 5 (Editrice Compositori, Bologna) 1996, pp. 361-367.[15] THONING K. W., TANS P. P. and KOMHYR W. D., Atmospheric carbon dioxide at Mauna LoaObservatory: II. Analysis of the NOAA/GMCC data, 1974-1985, J. Geophys. Res., 94 (1989)8549-8567.[16] COLOMBO T. and R. SANTAGUIDA, Atmospheric CO2 record from in situ measurements at Mt.Cimone (Italy), in Trends 93: A Compendium of Data on Global Change, ORNL/CDIAC 65,Oak Ridge Lab., USA, edited by T. A. BODEN, D. P. KAISER, R. J. SEPANSKI and W.STOSS.[17] CUNDARI V., COLOMBO T. and CIATTAGLIA L., Thirteen years of Atmospheric Carbon DioxideMeasurements at Mt. Cimone Station, Italy, Nuovo Cimento C, 18 (1995) 33-48.[18] CIATTAGLIA L., GUERRINI A. and COLOMBO T., Atmospheric CO2 Monitoring in an AntarcticRemote Site, Jubany Station (South Shetland), Proceedings of the Italian Research onAntarctic Atmosphere, edited by M. COLACINO, G. GIOVANELLI and L. STEFANUTTI, Conf.Proc. 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Ship-board report on atmospheric CO2 concentrations recorded on continuous from Mediterranean sea to Antarctica

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Ship-board report on atmospheric CO2 concentrations recorded on continuous from Mediterranean sea to Antarctica

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