SIZE-FRACTIONATED PARTICULATE ORGANIC CARBON (POC) EXPORT FLUXES ESTIMATED USING Th-234-U-238 DISEQUILIBRIA IN THE SARONIKOS GULF (GREECE) DURING WINTER BLOOM
Evangeliou, N; Florou, H; Psomiadou, C
| HERO ID | 2696377 |
|---|---|
| In Press | No |
| Year | 2013 |
| Title | SIZE-FRACTIONATED PARTICULATE ORGANIC CARBON (POC) EXPORT FLUXES ESTIMATED USING Th-234-U-238 DISEQUILIBRIA IN THE SARONIKOS GULF (GREECE) DURING WINTER BLOOM |
| Authors | Evangeliou, N; Florou, H; Psomiadou, C |
| Journal | Fresenius Environmental Bulletin |
| Volume | 22 |
| Issue | 7A |
| Page Numbers | 1951-1961 |
| Abstract | Activity concentrations of the naturally occurring, short-lived and highly particle-reactive radionuclide tracer Th-234 in the dissolved and particulate phase were determined at 3 shallow-water stations (maximum depths: 65 (S.3), 97 (S.5) and 220 m (S.7)) of the Saronikos Gulf (central Aegean Sea, Greece Eastern Mediterranean) during winter 2010 to assess the time scales of the dynamics and the depositional fate of particulate matter (POC, particulate Th-234). For that reason, the method of in situ pumping was performed previously used by many researchers. The fluxes of POC were estimated using radionuclides' disequilibrium. Specifically, the natural radionuclide Th-234 has been used as an indicator for export flux of particulate species from the euphotic zone. Its particle reactive and short half-life (t(1/2)=24.1 d) nature, in contrast to the conservative and long (t(1/2)=4.5 x 10(9) y) ones of its parent U-238 can be used to trace processes occurring over short timescales. Despite the wide application of Th-234, studies using (TH)-T-234/U-238 disequilibrium on export fluxes are still very limited, largely because of the demanding sampling and analyses. <br> <br>From the data obtained, the average activity concentrations of particulate and dissolved Th-234 were 5.4 +/- 0.8 and 18.4 +/- 7.4 Bq m(-3), respectively. Regarding the vertical profiles of Th-234 in comparison to the mother radionuclide U-238, a strong deficit of Th-234 was observed and as a result, rapid export of POC was estimated. The cumulative export fluxes of particulate Th-234 (after integration over the total depth of the stations) were estimated to be 52 +/- 7 in S.3, 180 +/- 19 in S.5 and 400 +/- 46 Bq m(-2) d(-1) in S.7. The respective cumulative scavenging rates of dissolved Th-234 onto particles were estimated to be 23 +/- 3 in S.3, 86 +/- 8 in S.5 and 172 +/- 19 Bq m(-2) d(-1) in S.7. Finally, the cumulative export fluxes of POC in the 3 stations examined were found 375 +/- 38, 311 +/- 34 and 300 +/- 33 Bq m(-2) d(-1), respectively. <br> <br>Large export fluxes of POC were observed here, over one order of magnitude compared to other areas of the Mediterranean Sea, attributed to the enhanced biological activity due to phytoplankton bloom in conjunction with the large amounts of organics that the gulf accepts for a long time period. At the stations S.5 and S.7 fine particles were found to sink rapidly in all depths examined except the bottom nepheloid layer. This is a result of aggregation processes due to the shallow depths of the sampling area or due to the instability of large aggregates during sampling that might induce uncertainty in particle sampling. Larger particles (> 25 mu m) of Th-234 were found increased at the surface, whereas smaller ones (0.6-25 mu m) increased or remained the same near the seabed. Increase of large Th-234 particles at the surface certifies the origin of surface Th-234 linked with the land-based atmospheric deposition and/or surface advective movements. The distribution of particulate Th-234 in both fractions is controlled by SPM, (SPM versus particulate Th-234: R-2 > 0.6), whereas POC follows a different trend attributed to the fact that POC is carried in the volume of a particle, whereas Th-234 sorbs to the surface. It is essential to mention that the Saronikos Gulf is still affected by the wide carbon discharges (domestic, industrial etc.) prior and after the construction of Psitalia WWTP as it is characterized by late renewal times of its waters. |
| Wosid | WOS:000327563300003 |
| Is Certified Translation | No |
| Dupe Override | No |
| Comments | Scopus URL: https://www.scopus.com/inward/record.uri?eid=2-s2.0-84885217277&partnerID=40&md5=49bd38b38f454d5f913c5a42b4ad9df1 |
| Is Public | Yes |
| Language Text | English |
| Keyword | POC; Particle Size; Th-234-U-238 Disequilibrium Approach; Export Flux; Scavenging Rate; Saronikos Gulf |