Organic carbon dynamics in the Mediterranean Sea: An integrated study

Abstract

[1] Total (TOC) and dissolved (DOC) organic carbon vertical profiles were analyzed from 11 stations located in various regions of the Mediterranean Sea, together with the distribution of other physical, chemical and biological parameters. TOC showed the highest concentrations (68-83 mM) above the pycnocline, followed by a marked decrease to values of 45-48 mM at 100-200 m. Below 200 m, values of 40-45 mM were observed. The excess TOC and DOC occurring at each station was calculated by subtracting 48 mM from the observed concentrations. The stock of the excess TOC and DOC increased eastward; while surface DOC mineralization rates decreased from 1.The integrated average of the biological parameters in the above-pycnocline layer showed a bacterial production versus particulate primary production (BP/PPP) ratio ranging from 22% in the Ionian Sea (MIO station) to 31% in the Ligurian Sea (Dyfamed station), while bacterial carbon demand versus PPP was higher than 100%, considering a bacterial growth efficiency of both 15% and 30%. The data here reported indicate various scenarios of carbon dynamics. At the stations west of the Sardinian Channel, the microbial loop was very active, and a high flux of carbon to the microbial loop (large bacterial and protist abundance) may be hypothesized, which would result in a low DOC concentration. At the stations east of the Sardinian Channel, no significant longitudinal variation was found in DOC and BP. DOC accumulated at these stations, possibly due to bacteria P-limitation, to DOC chemical composition and/or to the occurrence of different prokaryotic populations with a different ability to consume the available DOC.

DOC in the Mediterranean Sea

“…In the West Med, LIW shows minima in both DOC (36-44 μM) and DO (155-200 μM) (Figures 13.3 and 13.4). The same pattern has been observed using DOC data collected in the whole basin in September 1999 (Santinelli et al, 2012a) as well as DOC data collected over 8 years (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) during ten oceanographic cruises (Santinelli et al, 2010). The good relationship between DOC and apparent oxygen utilization (AOU = oxygen at saturation minus observed oxygen concentration) expressed as C equivalent (AOU-C eq = AOU × 0.72, Doval and Hansell, 2000) suggests that DOC FIGURE 13.4 DOC and dissolved oxygen (DO) in the core of the LIW.…”

“…The multiple regression between DOC, AOU_Ceq, and salinity allows for the removal of the effect of mixing from the relationship. It shows a slope of −0.38, −0.49, indicating that during LIW route from the Levantine Basin to the Tyrrhenian Sea, 38-49% of oxygen consumption is due to DOC mineralization (Santinelli et al, 2010(Santinelli et al, , 2012a. These values are slightly higher than those reported for the North Atlantic Ocean (5-14%, Carlson et al, 2010), the South Pacific (15%, 34%), and the Indian Ocean (13%, 31%) (Doval and Hansell, 2000).…”

“…These values are slightly higher than those reported for the North Atlantic Ocean (5-14%, Carlson et al, 2010), the South Pacific (15%, 34%), and the Indian Ocean (13%, 31%) (Doval and Hansell, 2000). If the DOC removal is in fact biotic, then it may be inferred that the semi-labile fraction of DOC is exported and mineralized while the LIW travels from the Levantine Basin to the Sicily Channel, with mineralization rates of 2.2-2.3 μM DOC year −1 (Santinelli et al, 2010(Santinelli et al, , 2012a.…”

“…It is worth noting that DOC always accumulates above the pycnocline, and the amount of accumulated DOC is a function of the strength of stratification. Finally, an eastward increase in DOC is usually observed, with values >65 μM in the easternmost part of the basin (Figure 13.3) (Pujo-Pay et al, 2011;Santinelli et al, 2012a).…”

“…The basin-scale DOC and DO distributions result from the merger of various data sets collected in the salinity maximum ( Figure 13.4) (Santinelli et al, 2010(Santinelli et al, , 2012a.…”