Principal Scientist: B. Manca (Osservatorio Geofisico Sperimentale, Trieste)
During the last decade the Eastern Mediterranean Sea has been the object of the international collaborative research program POEM (Physical Oceanography of the Eastern Mediterranean). A first intensive field program of 5 general multiship hydrographic surveys carried out in the period 1985-87 was dedicated to circulation and physical processes. The major results of POEM-Phase I led to a first definition of three predominant scales interacting in the general circulation pattern (Robinson et al., 1991; POEM Group, 1992; Robinson and Malanotte-Rizzoli, eds., 1993):
1. The basin-scale thermohaline circulation composed of two cells:
internal, single vertical cell of deep circulation, extending from the Ionian to the Levantine basin. In that period (1985-87) this closed cell was shown to be originated in the Southern Adriatic (Roether and Schlitzer, 1991) and spread into the Eastern Levantine, the Eastern Mediterranean “conveyor belt” formed by the Eastern Mediterranean Deep Water (EMDW);
external, upper open Mediterranean thermohaline cell, involving the exchange of water between the Eastern and Western Mediterranean through the Sicily Strait. The Atlantic Water (AW) flowing into the Mediterranean across the Gibraltar Strait, moving eastward spreads from the Sicily Strait through the Eastern Mediterranean as Modified Atlantic Water (MAW). It moves eastward as a surface layer 200 m thick; simultaneously the Levantine Intermediate Water (LIW), formed namely in the Northeastern Levantine, flows westward as a sub-surface layer between 200 and 600 m, finally exiting the Mediterranean across the Gibraltar Strait into the Northern Atlantic Ocean.
2. The sub-basin scale gyres and permanent, or quasi-permanent, cyclonic and anticyclonic structures interconnected by intense jets and meandering currents;
3. The most energetic meso-scale structures that interact with the sub-basin scale features.
In 1990 POEM evolved into the interdisciplinary POEM-BC including Biological and Chemical studies. Two major general surveys, fully interdisciplinary, were carried out: the first one in October-November 1991, the second one in January 1995. The 1995 general survey was also coupled with the execution of the Levantine Intermediate Water Experiment, carried out by five research vessels of Germany, Greece, Israel, Italy and Turkey which covered the Levantine basin from February through April 1995.
The upper thermocline circulation in the two periods 1985-87 and 1991-1995 presented the same overall general features. However very strong differences have been found between the two periods for the circulation in the intermediate and deep layers that confuse the two thermohaline cells of the Eastern Mediterranean. Both the intermediate LIW and the underlying dense water mass now showed the formation site to be the Aegean Sea (Roether, et al., 1996). Water mass tracer properties mapped on isopycnal surface in 1991 show LIW and EMDW to exit from the Aegean through the Western Cretan Arc Straits and to spread into the Ionian interior. In 1995 the Aegean Sea has confirmed to be the “driving engine” of the Eastern Mediterranean conveyor belt. This dramatic change in the deep thermohaline circulation suggests the intriguing possibility of two different configurations between which the deep cell has switched from 1987 to 1991.
The change in the deep circulation of the Eastern Mediterranean opens the question about the implications on the trophic status of the Eastern Mediterranean itself. In the oligotrophic regime of the Eastern Mediterranean it is possible to show occasional processes of fertilization of the photic layer, connected with the physical processes and water column instability. From the biochemical point of view the photic zone could receive more nutrients from the deeper layers, enhancing its biological productivity, thus reducing the oligotrophy of the basin. On the other hand, the lifting of deep nutrient rich water at intermediate layer could result in an increased export of nutrients through the Sicily Strait into the Western Mediterranean whose signal should be studied in the climate experiment described in Task B.1.2 (Study of long term trends in the Western Mediterranean Straits).
In this Task we propose to carry out different surveys of the Ionian basin with multidisciplinary data acquisition and analysis in order to explore the different aspects of the climate change event occurred in the Eastern Mediterranean deep circulation.
Task B.5.1 Climate variability of deep and intermediate waters in the Ionian basin
Principal scientist: B.Manca (OGS, Trieste)
Background
The Ionian Sea is the transition basin for the spreading of deep thermohaline cell from its source, the Southern Adriatic Sea, to the Levantine basin. Moreover the Ionian receives the inflow of the Modified Atlantic Water (MAW) from the Sicily Strait and the inflow of LIW from the Levantine basin. In the period 1985-87 the LIW was shown to intrude the Ionian across the Cretan passage (Malanotte-Rizzoli et al., 1996) whereas the general survey carried out in October ‘91 showed that the major source of the intermediate salty water was the Cretan Sea (Manca et al., 1996a). These changes are similarly evident in the deep waters of the Ionian, where a warming trend and an associated increase in salinity have been found from the analysis of continuous observations in the Northern Ionian from 1986 to 1995 (Manca et al., 1996b).
The general circulation horizontal and vertical processes interact with the biochemical properties distribution at proper scales. From coupled hydrodynamic and ecological 3D modeling studies (Crise et al., 1996) the seasonal biochemical cycle shows marked spatial differences according to the prevailing cyclonic or anticyclonic regime. Moreover, the open ocean ecosystem response is influenced by coastal boundaries/open ocean exchanges as well as by Ekman pumping enrichment. Experimental evidences of the interaction between the general circulation as inferred by GCM and nitrogen cycle in the Ionian sea has been proved by Civitarese et al., 1996. However the experimental data exhibit more energetic dynamic features than those obtained by the climatological models, so further researches need to be addressed in order to investigate on the climate variability of the nutrient redistribution as induced by recent changes in the thermohaline deep circulation. Only recently, chemical investigations have been carried out in the Ionian Sea in the frame of the POEM-BC program. The October ‘91 and April ‘92 cruises showed that the upper layer can be supplied with advected new nitrogen after the primary production maximum occurring at the end of winter (Civitarese et al., 1996). This means that the annual cycle of biological production can be strongly influenced by the possible lifting of the nutricline due to the pushing action of the new deep circulation regime. Thus, the importance to monitor chemically the Ionian Sea becomes evident. Moreover the Ionian Sea is a good site to check and quantify not only the amount of Aegean deep waters intrusion and consequently the progress of the process, but also to monitor the modification of the chemical distributions in the water column and to study how the system adjusts itself in reply to this change.
Important water exchange occurs across the straits communicating with Ionian interior. In particular the outflow into the Ionian of dense Adriatic Deep Water (ADW) and the inflow into the Adriatic of LIW occur across the Otranto Strait. The recent measurements in the Otranto Strait revealed that the hydrodynamics is very complex due to the mesoscale activity as well as the transient phenomena associated with the passage of eddies traveling from the Ionian to the Adriatic Sea. Estimates of the volume transport through the Otranto Strait were obtained by means of direct current measurements. Both inflow and outflow total rates are revealed to be more than 1 Sv during winter (Gacic et al.,1996). Inflow is more stable than outflow. Comparing with the previous knowledge on water exchange regimes, which were obtained mainly from hydrographic measurements (Zore-Armanda M., Pucher-Petkovic T., 1976), the above mentioned results are three times greater. More investigations therefore are proposed to complement the detailed study of Deep Water Formation and transport pathways of Biogenic Materials across the Strait in the framework of EU MATER program, by the aim of additional current measurements over the sill of the Otranto Strait.
The dynamics controlling the transports in the Strait of Sicily is very complex because of the particular bottom topography. The large Sicily and Tunisia shelves make the area available to surface MAW (from Sicily to Cape Bon) very wide in comparison to the relatively narrow deepest part occupied by the LIW that enters the Western Mediterranean through two sills 365 and 430 m deep. Recent investigations reveal the importance of mesoscale phenomena on the transports. Direct current measurements showed velocities ranging up to 50 cm/s with events lasting from 2 to 10 days (low frequency). Of course, tidal phenomena and inertial component (high frequency) are also very important. Owing to their high variability long time series are needed to evaluate the residual currents, which are directly related to the salt, heat and mass budgets of the basins.
Scientific Objectives
The major scientific objectives of the proposed study are:
to monitor the deep internal thermohaline cell as well as the external one in the Ionian Sea , Sicily and Otranto Straits as a consequence of the recent changes in the EMDW;
to study the thermohaline circulation of the Ionian interior, including interannual variability;
to evaluate the thermohaline structures that influence the pathway and the exchange of the water masses in the Sicily and Otranto Straits (baroclinic control);
to study the upper-layer distribution of a number of biochemical parameters in presence of dynamic features;
to evaluate the barotropic component of the flow across the Straits and the biogeochemical exchange among the Adriatic, the Eastern and the Western Mediterranean;
to determine the horizontal and vertical flux of nutrients, organic matter and tracer elements through the Ionian Sea as a consequence both of dynamic features and of the lifting of deep waters, bringing nutrient-rich waters at the intermediate layer and closer to the surface;
to estimate biological production and particles transport by measuring the downward fluxes of particulate matter and characterizing its biogenic and inorganic components;
to analyze and form a well documented climatological data set in the Eastern Mediterranean to assess the seasonal and interannual variability of the thermohaline properties and of the concentration of major inorganic nutrients and biological markers.
Workplan
The major activities are concerned with field measurements. The first scientific goal points out that the Ionian, in proximity of the Western Cretan Arc Straits, the Sicily and Otranto Straits are the preferred areas of investigation. A basin-wide survey is proposed to cover the Ionian interior and Sicily Channel to fill in the gaps in physics and to achieve basic information on the basin-wide distribution of chemical and biological parameters as well as to evaluate the correlation with physical processes. The intensive hydrographic survey should be planned to complement the field activities in the framework of EU MATER programme. The basin-wide, multidisciplinary coordinated survey should be carried out in April-May 1998 as a continuity of spreading phase of Adriatic Deep Water formation experiment planned for March-April 1998, which will occupy the Region marked 1 in the enclosed Figure (Southern Adriatic, Otranto Strait and Northern Ionian down to 39.5° N). A two-legs general survey is required in the Ionian basin (Calabrian rise, Malta escarpment, Ionian abyssal plain and Hellenic trench) and the Sicily Strait (Malta plateau, Sicily and Tunisia shelves, Pantelleria trough with some extensions to the Tyrrenian sea) marked as regions 2 and 3 respectively. A general station grid of half a degree resolution along the longitudinal transects spaced of one degree in latitude, or possibly 0.5 degree, will be performed in the Ionian basin. A coarser station grid will be occupied in the Southern portion of the Ionian, whereas a denser station grid will be performed in proximity of the main continental margin (Calabrian rise and Malta escarpment) as well as in the Sicily Channel.
The basic parameters to be measured at each station will be: temperature, salinity, dissolved oxygen (by means of in situ probe and classical Winkler method), turbidity, fluorimetry, nutrients (ammonia, nitrite, nitrate, phosphate and silicate) and chlorophyll. Additional parameters to be measured at selected stations will be: TDN (Total Dissolved Nitrogen), TDP (Total Dissolve Phosphorus), PN (Particulate Nitrogen), POP (Particulate Organic Phosphorus), BSi (Biogenic Silica), DOC (Dissolved Organic Carbon), POC (Particulate Organic Carbon), phytoplankton composition, biomass, primary productivity (14C and 15N), CO2, alkalinity and tracers. The CTD observations, as well as oxygen and nutrients determinations will serve objectives 1, 2 and 3. Emphasis in the XBT observations, launched every 10 nautical miles along the ship track, will provide upper-ocean mesoscale resolution and will serve the goal 4. The current measurements in the Otranto and Sicily Straits will serve the goal 5. The deployment of the moorings will be positioned to complement the current time series that will be collected in the framework of EU MATER program.
Within the EU MATER program downward fluxes of particulate suspended solids will be also assessed and characterized for their biological and abiotic components. This investigation will be based on deployment of a mooring array provided with traps and current meters at one station located on the main pathway of the water mass outflowing the Southern Adriatic westwards into the Ionian Sea. The time series from EU MATER task will complement the spatial distribution of microbiological properties measured in the framework of SINAPSI and will serve the goals 6 and 7.
The physical and biochemical data which have already been collected during the POEM phase I and II, as well as those collected in the framework of MAST/MTP, although not systematic, should be analyzed and synthesized to have great insight into the interaction between the physical and biochemical processes. The analyses mentioned above will be achieved regionally and interdisciplinary according to the space/time coverage. More than 10 years of data collected recently since the half of the eighties, not yet included in MODB data base, must be globally analyzed. Special emphasis will be given to the analysis of the Southern Adriatic, Ionian interior, Sicily Strait and its exchanges with the remainder of the Western Mediterranean Sea. In order to enable us to understand the climate variability the following topics should be addressed:
physical and chemical characteristics of water masses;
water column processes;
dynamics of the euphotic zone;
residence time estimates for the major water masses;
flow through the Sicily and Otranto Straits;
sources and sinks of nutrients;
variability in biological and chemical parameters;
variability of biological production and associated fluxes of biotic and abiotic particulate suspended matter.
Budget allocated to each Team and breakdown of costs
1997
Institution
Consum.
Travel
Personnel
Total
OGS
25 1)
5
20 5)
50
IBM
15 2)
5
20
ISDGM
10
5
15
ITT
10
5
15
IUN-IMO
20 3)
5
25
SZ
10
5
15
ENEA-CRAM
10 3)
5
15
1998
Institution
Consum.
Travel
Personnel
Total
OGS
651),4)
23
20 5)
108
IBM
15 2)
10
20 5)
45
ISDGM
15
10
25
ITT
15
10
20 5)
45
IUN-IMO
25 3)
15
40
SZ
15
15
30
ENEA-CRAM
15 3)
10
25
1) costs include the mooring at Otranto Strait (to be added to EU MATER moorings)
2) costs include the complement of mooring into the Ionian (EU MATER mooring)
3) costs include the mooring at Sicily Strait (to be added to EU MATER moorings)
4) costs include 270 XBT probes
5) costs for the Fellowship at OGS, IBM and ITT
Task B.5.2 Characterization of dissolved organic matter in different water masses of the Ionian by means of the optical properties of its chromophoric component
Responsible: Dr. Alfredo Seritti (IB-CNR, Pisa)
Background
The study of the physical and chemical properties of the non living organic matter (NLOM) in surface waters, water column, water-sediment interface and pore waters is a crucial point for understanding the reactivity and transport processes of organic compounds in the sea. In addition it could be used as a tracer of its recent history and origin, so as to improve our knowledge on the relationship between environmental forcing and the fate of DOC in the marine environment.
The development of suitable analytical methods for determining the low concentrations of dissolved organic carbon (DOC) in open sea waters as well as the application of physical (Ultrafiltration, Dialysis) and physico-chemical (Molecular Spectroscopy) techniques allowed some important information on the molecular characteristics of such a wide pool of organic compounds to be obtained. In this context, fluorescence spectroscopy has been proposed as an useful tool for getting information on the main fluorophoric groups occurring in natural waters (Seritti et al., 1994; Green & Blough, 1994). The combination of absorption, fluorescence and DOC measurements and the relationships occurring among these data allow to get information on parameters as aromaticity, molecular weight and main functional groups(Seritti et al., 1996) as well as their capability of binding metals (Seritti et al., 1996).
Scientific Objectives
1) Study of the molecular characteristics of marine NLOM, to shed light on its origin and its temporal dynamics
2) Assessment of carbon reactivity of different local and seasonal environments.
Workplan
On the samples collected in the surveys proposed by Task B.5.1, different spectral regions will be investigated for fluorescence of NLOM. Absorbance values will be collected at the same wavelengths used for excitation the fluorescence. The fluorescence data (Fn) will be normalized by using the Raman band as internal standard and a reference compound, chosen in the same spectral region, as external standard. This double normalization will allow the comparison of different data obtained with different instruments and settings to be performed. Parameters such as quantum yields (), molar absorptivities(), slope of the log-linearized absorption spectra (S) will also be calculated and compared in the different stations and seasons. This will provide a first data set on fluorescence and absorption characteristics of different european coastal waters; further these data will represent the background step for laboratory experiments.
Basically fluorescence measurements will be performed using two approaches:
i) the conventional one based on the recording of one fluorescence spectra for one wavelength of excitation;
ii) the three dimension synchronous spectra (3DSS) approach based on the recording of 3D spectra obtained by recording the intensity versus the wavelength of excitation and versus the wavelength offset between the wavelength of excitation and that of emission. This last technique which combines total fluorescence and synchronous spectroscopic technique will be applied in this study for the first time. It will allow to reveal with the most efficiency and clarity the presence and variation of the fluorescent components responsible of the fluorescence properties of the studied samples.
Conventional fluorescence : three fluorescence parameters will be used to characterize DOM in sea water, each one giving access to information which could be used to follow the temporal variation of the DOM in the sea surface waters.
-The protein-like signature due to the presence of tryptophan and/or tyrosine chromophores. It is well known that these chromophores display highly variable fluorescence spectra (ex 280, em max 300-340 nm) which depend on the medium and the molecular forms they are associated with.
- the wavelength of the fluorescence spectrum maximum for excitation at 360 nm which correlates with the mean molecular weight of the humic substances (Ewald et al. 1988; Belin et al. 1993) and whose intensity allows a fast and a more precise estimate of the concentration in humic substances than the DOC content.
- the spectral profile of the fluorescence spectra for excitation in the range 310-320 nm which is suitable to differentiate between marine and continental material and which may be used to follow the evolution of organic matter having different origins (humic substances, algal exudates).
- the fluorescence quantum efficiency which reflect both electronic properties and interaction of the aromatic chromophores. In connection with the absorbance which allows a quantitative estimate of the content in aromatic carbon.
Three dimension synchronous spectra : the technique will be applied to all samples and will served, in a qualitative point of view, to emphasize the spectroscopic difference and changes of the fluorescence properties of the samples.
Tangential ultrafiltration technique will be carried out with the aim of investigating the respective reactivity and fluorometric characteristic of the DOM with respect to their mean molecular weights (MW). From literature it appears that a large part of the marine DOM has MW larger than 1500 Daltons while we noticed that the protein-like signature is observed mainly in fraction of less than 1000 Daltons. In order to assess variations of the high (HMW) and low (LMW) molecular weight substances fractions, two different types of membranes with nominal cut-offs respectively 1000 and 10.000 Daltons will be used.
Generally, a 600 mL Amicon TCF10 apparatus will be used. Ultrafiltration will be performed in a continuous way which greatly improve the reliability and the efficiency of the procedure.
Correlations occurring among the different parameters and oceanographic data will the investigated.
Task B.5.3 Recent hystory of Mediterranean water masses analyzed through the determination of in-situ microbial activity
Responsible: Dr. Renata Zaccone (IST-CNR, Messina)
Background
In the context of climatic global changes, the increase of carbon dioxide concentration in the atmosphere can be dampen by CO2 removal from the surface layers and its sequestering in the deep sea and sediments.
Three mechanisms are involved in the removal of atmopsheric CO2 in the ocean: the carbonate pump, the solubility pump and the biological pump that regulates biogeonic carbon fluxes in the sea.
Microbial activity plays a key role in the last process, yet microbial metabolism characteristics are still not well-defined and need further investigation.
Oxidation of organic matter, both dissolved and particulated, to CO2 occurs through the following steps:
decomposition of polymeric organic compounds by bacterial exoenzymatic activity;
incorporation of organic substrata and biomass production;
respiration of organic matter and consequent CO2 production.
Scientific Objective
Study of the different steps of Organic Carbon Transformation in different water masses of the Ionian Sea basin.
Workplan
Samples collected along the water column will be handled and stored in order to:
determine the exoenzymatic activity (EEA) (aminopeptidase and glucosidase);
evaluate the bacterial production;
quantify the oxygen utilization rates (OUR) and the metabolic production of carbon dioxide (CDPR) by ETS assays;
detrmine the physiolagical groups of bacterial population;
determine the cell abundance differentiating between bacterioplankton and pico-phytoplankton.
Coordinator: M. Ribera D’Alcala’ (Stazione Zoologica, Napoli)
Scientific background
Marine communities of mid and high latitudes undergo large seasonal changes in total biomass and species composition principally due to seasonal variability in physical forcing (light and vertical mixing to first order). In addition, episodic and multiannual events of abrupt changes in species abundance have regularly been observed, as well as long term variations, both periodic and aperiodic at the observed time scales, in the structure of communities at least at the key species level.
A strict correlation between observed trends in marine ecosystems and climate variability of physical forcing on a short time scale (e.g. years) can hardly be assumed as unequivocal. By contrast, the dependence of marine production on the long term climate oscillations (e.g. thousand of years) certainly holds true. Apparently something is missing in our way of interpreting experimental data or, alternatively, the signal to noise ratio in short time series is too low to easily allow for the detection of coherence in trends. Because of the foremost importance of global changes in marine ecosystems forced by mid-term fluctuations in climate, both geophysically and anthropogenically induced, a significant effort in the project must be devoted to improving our understanding of the response of biota to environmental variability due to the climate. Furthermore, it is very likely that biota do in fact trace climate dynamics so as to be potentially usable as bio-sensors on a mid term scale.
Previous attempts on this path have been conducted for significant ocean areas to understand fluctuations and/or declines in fisheries (see McGowan, 1990 and references therein). While clear response of food web functioning to episodic events can easily be detected, much more difficult is coping drift in climate and changing in populations and communities structure. Different components of the pelagic communities react in a different ways (which is quite obvious) though rarely showing significant cross-correlation among them (which is much less trivial). The difficulty in interpreting such results certainly resides in the lack of knowledge on the biological compartment, even at the ecophysiological level of the species involved, but it is also due to the still loose definition of climatic changes. The Mediterranean Sea stands as a very peculiar system for studying mutual interaction between short-term climatic variability and marine biota response. It is quite responsive and well studied at the physical level (see preceding sections); it should be equally responsive at biological level, but, it is for sure, much less studied and understood. Shelf-open sea interactions, spring bloom events in the Western basin and weak seasonality in the Eastern basin seem to coexist in the Mediterranean Sea, but the time evolution of the system at biological level is largely under-explored.
Leading hypotheses of this sub-project are:
1. the response of Mediterranean communities to climate variations should be detectable on a time/space scale of the same order of magnitude as geophysical trends;
2. the smaller extension, if any, of continental shelves should result in the readability of direct climate signals even in perturbed coastal areas;
3. the reduced size of the basin and sub-basins makes feasible the use of ecological models coupled with 3-D general circulation models, thus allowing for reconstruction of different scenarios and validation of hypotheses on covariance of geophysical and biological changes;
4. the response of the biota to geophysical forcing variability and its feedback, which are intrinsically non-linear, occur at both quantitative (biomass, size, numbers) and qualitative (occurrence, cycles, structure) levels.
Not too much progress has been achieved in recent years in understanding how, for example, species composition reflects bio-physical interaction in the water column. Moreover, the definition of the most informative descriptors and the development and tuning of the mathematical/statistical tools to analyze these trends is in itself a major scientific achievement, that would significantly improve our capability of monitoring environmental trends. We propose to revisit existing bio-oceanographic data, spanning from one to three decades at most, to outline their temporal structure, to quantify variations using different descriptors, to compare objectively defined variations with geophysical variables at different space and time scales. This, in order to outline and quantify covariances among biological and meteorological processes in the available data sets; define typical seasonal community structures, if any, especially for planktonic organisms; calibrating existing modeling approaches so as to reproduce and predict typical Mediterranean scales and processes; improve predictability of fluctuating marine resources; obtaining comparable, readable and easy to access data bases encompassing the presently disseminated biological information.
This approach will be followed for the study on the three main compartments of marine ecosystems, plankton, nekton and benthos, according to the schemes synthetically reported under the specific tasks. The division of the working groups according to the three realms of marine environment reflects both different temporal and spatial scales of these subsystems and differences in methodologies and expertise among scientists. A major Task of the subproject will therefore be to coalesce concepts and approaches of groups that normally do not interact and to merge the long term observational as well as synthetic results within a modeling approach.
The group is aware that two major problems, common to both planktonic and benthic systems, could hinder the final goal of the subproject. They are: 1) the complex interactions between the physical and the biological scales, and 2) the superposition of anthropogenic signals, particularly in coastal area where most of the available data have been collected, with the climatic signature. However, it is believed that a discrimination will be possible by comparing the same descriptors at the numerous sites sampled and over the time. On the other hand, coastal areas are certainly characterized by a stronger signal-to-noise ratio because of their more intense production and frequently higher diversity.
At the same time it is worth noticing that the subproject will not deal in this first phase with the analysis of the processes responsible for the feedback of marine organisms (plankton in particular) on the atmosphere-ocean interaction (Charlson et al., 1987) even being aware of their importance and of their forefront character in contemporary research. Tracing this intersection and testing hypothesis on this subject would imply a much greater process-oriented experimental effort that is out of the scope of the present study. In fact field work will be quite limited in this first phase. Basic processes will indeed be accounted for in the project through a coupled modeling approach and the process study described under task C.2.
