Supplementary material to "Seasonal and interannual variability of the pelagic ecosystem and of the organic carbon budget in the Rhodes Gyre (Eastern Mediterranean): influence of winter mixing (original) (raw)
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The Rhodes Gyre is a cyclonic persistent feature of the general circulation of the Levantine Basin in the eastern Mediterranean Sea. Although it is located in the most oligotrophic basin of the Mediterranean Sea, it is a relatively high primary production area due to strong winter nutrient supply associated with the formation of Levantine Intermediate Water. In this study, a 3D coupled hydrodynamic-biogeochemical model (SYMPHONIE/Eco3M-S) was used to characterize the seasonal and interannual variability of the Rhodes Gyre's ecosystem and to estimate an annual organic carbon budget over the 2013-2020 period. Comparisons of model outputs with satellite data and compiled in situ data from cruises and BioGeoChemical-Argo floats revealed the ability of the model to reconstruct the main seasonal and spatial biogeochemical dynamics of the Levantine Basin. The model results indicated that during the winter mixing period, phytoplankton first progressively grow sustained by nutrient supply. Then, short episodes of convection driven by heat loss and wind events, favoring nutrient injections, organic carbon export and inducing light limitation on primary production, alternate with short episodes of phytoplankton growth. The estimate of the annual organic carbon budget indicated that the Rhodes Gyre is an autotrophic area with a positive net community production in the upper layer (0-150 m) amounting to 31.2 ± 6.9 g C m-2 year-1. Net community production in the upper layer is almost balanced over the seven year period by physical transfers, (1) via downward export (16.8 ± 6.2 g C m-2 year-1) and (2) through lateral transport towards the surrounding regions (14.1 ± 2.1 g C m-2 year-1). The intermediate layer (150-400 m) also appears to be a source of organic carbon for the surrounding Levantine Sea (7.5 ± 2.8 g C m-2 year-1) mostly through the subduction of Levantine Intermediate Water following winter mixing. The Rhodes Gyre shows high interannual variability with enhanced primary production, net community production and exports during years marked by intense heat losses and deep mixed layers. However,
Eastern Mediterranean biogeochemical flux model- Simulations of the pelagic ecosystem
2009
Abstract. During the second phase (2003–2006) of the Mediterranean ocean Forecasting System Project (MFS) named Toward Environmental Predictions (MFSTEP) one of the three major aims was the development of numerical forecasting systems. In this context a generic Biogeochemical Flux Model (BFM) was developed and coupled with hydrodynamic models already operating at basin scale as well as in regional areas.
Anthropogenic inputs of nutrient phosphorus (P) and nitrogen (N) to the Eastern Mediterranean Sea (EMS) increased significantly after 1950. Nonetheless, the EMS remained ultra-oligotrophic, with eutrophication only affecting a restricted number of nearshore areas. To better understand this apparent contradiction, we reconstructed the external inputs of reactive P and N to the EMS for the period 1950 to 2000. Although the inputs associated with atmospheric deposition and river discharge more than doubled, the inflow of surface water from the Western Mediterranean Sea (WMS) remained the dominant source of nutrient P and N to the EMS during the second half of the 20th century. The combined external input of reactive P rose by 24% from 1950 to 1985, followed by a slight decline. In contrast, the external reactive N input increased continuously from 1950 to 2000, with a 62% higher input in 2000 compared to 1950. When imposing the reconstructed inputs to the dynamic model of P and N cycling in the EMS developed in the companion paper, a maximum increase of primary production of only 16% is predicted. According to the model, integrated over the period 1950-2000, outflow of Levantine Intermediate Water (LIW) to the WMS exported the equivalent of about one third of the P supplied in excess of the 1950 input, while another one third was translocated to the Eastern Mediterranean Deep Water (EMDW). Together, both mechanisms efficiently counteracted enhanced P input to the EMS, by drawing nutrient P away from primary producers in the surface waters. Furthermore, between 1950 and 2000, inorganic and organic dissolved N:P ratios increased in all water masses. Thus, the EMS became even more P limited because of anthropogenic nutrient inputs. A model simulation incorporating the circulation changes accompanying the Eastern Mediterranean Transient (EMT) between 1987 and 2000 yielded a 4% increase of EMS primary productivity relative to the baseline scenario.
Biogeochemical tracers and fluxes in the Western Mediterranean Sea, spring 2005
Journal of Marine Systems, 2010
Only few studies about biogeochemical properties' distributions in wide areas of the Mediterranean Sea are available. We present a new biogeochemical dataset for the Western Mediterranean, collected in spring 2005. The paper presents a general description of the vertical and horizontal variability of dissolved inorganic nutrients and of the anomalous stoichiometric ratios. Nutrients are subsequently used as water mass tracers, comparing non-conservative with conservative tracers. The biogeochemical footprint of waters of different origin and ages has been revealed by the conservative parameters NO and PO, which combine oxygen and nutrients to cancel the alteration of both due to respiration. Using mass transports estimated with an inverse box model, the biogeochemical fluxes between different regions are computed. Our results confirm previous findings, i.e. that the eastern basin is a nutrient source for the western one. In addition we provide quantitative estimates of cross-basin biogeochemical fluxes. In the vertical, generally the surface layers act as a nutrient sink, to which corresponds a deep source. Finally, the biogeochemical fluxes were used to estimate the export production. A comparison with an independent measurement, confirms that this method is a valuable tool to obtain information about the CO 2 removal and the functioning of pelagic ecosystems.
A biogeochemical model for phosphorus and nitrogen cycling in the Eastern Mediterranean Sea
Journal of Marine Systems, 2014
Anthropogenic inputs of nutrient phosphorus (P) and nitrogen (N) to the Eastern Mediterranean Sea (EMS) increased significantly after 1950. Nonetheless, the EMS remained ultra-oligotrophic, with eutrophication only affecting a restricted number of nearshore areas. To better understand this apparent contradiction, we reconstructed the external inputs of reactive P and N to the EMS for the period 1950 to 2000. Although the inputs associated with atmospheric deposition and river discharge more than doubled, the inflow of surface water from the Western Mediterranean Sea (WMS) remained the dominant source of nutrient P and N to the EMS during the second half of the 20th century. The combined external input of reactive P rose by 24% from 1950 to 1985, followed by a slight decline. In contrast, the external reactive N input increased continuously from 1950 to 2000, with a 62% higher input in 2000 compared to 1950. When imposing the reconstructed inputs to the dynamic model of P and N cycling in the EMS developed in the companion paper, a maximum increase of primary production of only 16% is predicted. According to the model, integrated over the period 1950-2000, outflow of Levantine Intermediate Water (LIW) to the WMS exported the equivalent of about one third of the P supplied in excess of the 1950 input, while another one third was translocated to the Eastern Mediterranean Deep Water (EMDW). Together, both mechanisms efficiently counteracted enhanced P input to the EMS, by drawing nutrient P away from primary producers in the surface waters. Furthermore, between 1950 and 2000, inorganic and organic dissolved N:P ratios increased in all water masses. Thus, the EMS became even more P limited because of anthropogenic nutrient inputs. A model simulation incorporating the circulation changes accompanying the Eastern Mediterranean Transient (EMT) between 1987 and 2000 yielded a 4% increase of EMS primary productivity relative to the baseline scenario.
Simulations of biological production in the Rhodes and Ionian basins of the eastern Mediterranean
Journal of Marine Systems, 2000
The biological production characteristics of the Rhodes and western Ionian basins of the eastern Mediterranean are studied by a one-dimensional, coupled physical-biological model. The biological model involves single aggregated compartments of phytoplankton, zooplankton, detritus as well as ammonium and nitrate forms of the inorganic nitrogen. It interacts with the physical model through the vertical eddy diffusivity which is calculated using the Mellor-Yamada level 2.5 turbulence parameterization. The model simulations demonstrate the importance of the contrasting physical oceanographic characteristics of these two basins on affecting their yearly planktonic structures. The annual primary production in the Rhodes basin is estimated as ; 97 g C m 2 yr y1 which is comparable with the northwestern Mediterranean. The western Ionian basin, on the contrary, possesses only 10% of the Rhodes' productivity and therefore represent a most oligotrophic site in the eastern Mediterranean. The Rhodes basin reveals a strong bloom in early spring, typically in March, a weaker bloom in early winter, typically in January, and a subsurface production below the seasonal thermocline during summer. This structure is slightly modified in the western Ionian basin, and the early winter and early spring blooms are merged to cover the entire winter. These results are supported favorably by the available observations both in their magnitudes and timing. q
Biogeosciences, 2011
A coupled hydrodynamic-biogeochemical modelling is developed to address main mechanisms that drive the particulate organic carbon (POC) deposition in the Gulf of Lions (NW-Mediterranean). Low-salinity water (LSW, salinity <37.5) lenses detached from the Rhone River plume under specific wind conditions tend to favour the biological productivity and provide a good opportunity for validating a planktonic ecosystem modelling. A specific calibration dedicated to river plume ecosystems is then proposed and validated using in situ measurements within such LSW lens (BIOPRHOFI cruise-May 2006) and on the Gulf of Lions. During spring 2006, the POC deposition is maximal on the prodelta area and within the coastal area in the Gulf of Lions. Organic detritus mostly contribute to the total POC deposition (82-92 %) whereas the contribution of living organisms (microphytoplankton) appears lower than 17 %. Exploring both influences of terrestrial inputs from the Rhone River and planktonic ecosystems on the POC deposition on the shelf, we estimated that the contribution of terrestrial POM inputs to the total POC deposition is lower than 17 % at the shelf scale during the study period, with maxima during peak discharges of the Rhone River. The main deposition area of terrestrial POC is found in the vicinity of the river mouth in agreement with sediment data. On the other hand, a remarkable influence of marine biological processes on the POC deposition is highlighted further on the shelf (from 60 to 80 m depth). A tight feedback between zooplankton and POM contents in the water column is proposed to explain
Biogeochemical fluxes through the Strait of Otranto (Eastern Mediterranean
Continental Shelf Research, 1998
A series of seasonal cruises and Eulerian current measurements in the Otranto Strait were carried out to study the biogeochemical characteristics of the strait and to estimate the exchange of water, dissolved and particulate matter between the Adriatic and the Ionian Sea. Analysis of data shows that on an annual scale, the Adriatic Sea exports dissolved nutrients (nitrate and phosphate) to the Ionian, and imports particulate organic carbon and nitrogen. Estimate of the mean annual water flux for the first time based on direct Eulerian current measurements gives value of 0.9 Sv that is appreciably higher than those found in literature. Calculations of the ratio of new and total primary production based on an annual phosphate subsurface export suggest that the trophic status of the Adriatic Sea on the whole is close to that of an oligotrophic sea. From the biogeochemical distributions obtained, an active role for the Adriatic in supporting the well-known N:P ratio anomaly of the Mediterranean is hypothesized. Further studies are needed to estimate the contribution of the dissolved organic forms to the nutrient exchanges through the strait, and to establish the total budget of N and P in the Adriatic Sea.
Deep Sea Research Part I: Oceanographic Research Papers, 1999
A one year study of downward particle #uxes conducted in the northwestern Mediterranean Sea is presented. Two mooring lines equipped with sediment traps and current meters were deployed at around 1000 m depth on the northeastern continental slope of the Gulf of Lions, one inside the Grand-Rho( ne canyon and the other outside on the adjacent open slope. Mean total mass #uxes increased slightly with trap depth inside the canyon, a feature quite typical of #uxes in continental margin environments. The near-bottom trap inside the canyon collected more material than its counterpart deployed at equivalent depth on the open slope, indicating a preferential transport of material within the canyon. Major biogeochemical constituents (organic and inorganic carbon, opal, and siliciclastic residue) revealed a marked di!erence in particle composition between the sub-surface (80 m) and deeper traps, suggesting the existence of at least two sources of material. The two shallower traps showed a clear biological signal: #ux peaks were related to periods of surface biological production, especially perceptible in summer and autumn. The particulate matter trapped at deeper levels in the canyon and on the open slope was characterized by a more stable composition with a major lithogenic contribution, originating from sedimentary material most probably resuspended on the upper-or mid-slope. The seasonal variability was dominated by the summer/winter alternation; the latter period was characterized by a weak strati"cation of the water column and an enhanced current variability favoring vertical exchanges. The present results are compared with those obtained previously in the Lacaze-Duthiers canyon on the southwestern side of the Gulf of Lions. The comparison shows strong di!erences between the NE entrance and the SW exit of the gulf, with respect to 0967-0637/99/$ -see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 7 -0 6 3 7 ( 9 9 ) 0 0 0 1 4 -X the general along-slope circulation of water masses, both in terms of intensity of particulate #uxes and transport processes.