Prospects for Using Historical Transmissometer Data in Large-Scale Assessment of Particular Organic Carbon A.V. Mishonov, W.D. Gardner, & M.J. Richardson Department of Oceanography, Texas A & M University, College Station, TX, USA,

2 Data Set n Transmissometer data have been collected using instruments provided by our group over the last decade in collaboration with WOCE, JGOFS, and other large-scale hydrographic programs. n These data include basin-wide transects in the North and South Atlantic, North and South Pacific, Indian, and Southern Oceans. n We have proposed to analyze these data and convert the beam attenuation values to POC using the beam attenuation:POC relationships derived by our group during JGOFS Process studies.

3 Approach n Stramski et al. (1999, Science, 285: ) have introduced algorithms to estimate POC from satellite backscatter data for the Southern Ocean for both surface values and euphotic zone integrations. n In a similar manner, our basin-wide data will be compared with satellite backscattering data on appropriate seasonal and space scales to establish region-specific algorithms. n A compilation of historic hydrographic/optical data has been compared by season with recent satellite data by Mishonov et al. (1999, IUGG-99, Vol. B., p. 242) and the results further validate our proposed global synthesis of POC in Case I waters (non-coastal) using satellite-derived data.

4 Comparison of SeaWiFS & in-situ Sampling Data: 37 th cruise of RV Academician Vernadsky, Aug - Sep 1988 Sep’98 SeaWiFS chlorophyll Dominant Wavelength Forele-Ule Scale Secchi Disk Chlorophyll-a Calculated by regression Sep’98 Data from

5 DominantWavelength Chlorophyll-a Forele-UleScale Secchi Disk Feb’98 SeaWiFS chlorophyll Data: 41 st cruise of RV Academician Vernadsky, Feb - May 1990 Feb’98 Data from Comparison of SeaWiFS & in-situ Sampling

6 Initial Data Set n 15 cruises from February 1992 till June 1997; n 2027 Stations in Pacific, Indian and Atlantic oceans; n 1817 Transmissometer Casts; n Accompanied hydrological data on Temperature, Salinity and Dissolved Oxygen; n More data will be added from JGOFS, SAVE, WOCE, etc. legs.

7 Partial WOCE Cruise List

8 Station Coverage: WOCE, JGOFS & other data Loaded Not loaded

9 Transmissometer Data Set Monthly Distribution

10 Pacific Ocean Section Th.Thompson, Jul-Aug.93, p14n line Beam Attenuation Distance, nm Depth, m South North

AVHRR SST July 1993 Data from t, °C S, p.s.u. Stations Position Temperature Salinity Upper 500 meters Pacific Ocean Section Th.Thompson, Jul-Aug.93, p14n line

12 SeaWiFS CHL July 1998 Data from Kg/m 3 C m -1 Stations Position Density Beam Attenuation Upper 500 meters Pacific Ocean Section Th.Thompson, Jul-Aug.93, p14n line

13 Indian Ocean Section Knorr, Feb. 95, i09s line Distance, nm Depth, m Beam Attenuation N S Stations Position

AVHRR SST Feb 1995 t, °C S, p.s.u. Stations Position Temperature Salinity Upper 500 meters Indian Ocean Section Knorr, Feb. 95, i09s line Data from North

SeaWiFS CHL Feb, 1998 Stations Position Upper 500 meters Indian Ocean Section Knorr, Feb. 95, i09s line Data from Density Beam Attenuation C m -1 North Kg/m 3

16 Future plans: 1 n Transmissometer database: –Process 17 WOCE cruises of transmissometer data; – Add processed transmissometer & POC data from 19 JGOFS cruises; – Add processed transmissometer data from other basin-scale cruises where we have data (9 + ). n Beam attenuation / POC relationship: –Use algorithms developed during JGOFS, NABE, EqPAC, Indian Ocean and Southern Ocean expeditions;

17 Future plans: 2 n Compile SeaWiFS back-scatter data for comparable times of POC + Beam attenuation measurements; n Refine algorithms for predicting POC from SeaWiFS data; n Examine hydrography of each area: –Mixed layer depth; –Subsurface maxima. n Correlate POC standing stock by ocean basin & season; n Analyse data in context of JGOFS Synthesis & Modelling Program.

18 Thank You!

19 Transmissometer Data Set Year Distribution

20 Data: 36 th cruise of RV Academician Vernadsky, June - July 1987 Forele-Ule Scale Chlorophyll-a Dominant Wavelength Secchi Disk June 1998 SeaWiFS chlorophyll Data from Comparison of SeaWiFS & in-situ Sampling