Finemed Rhode Campaign
FINEMED RHODE CAMPAIGN
INTRODUCTION & OBJECTIVES
The Mediterranean Sea (EMS) is known by its complex, mesoscale dynamic forced by geo-morphological and physical conditions specific to this basin. In the last decades, many campaigns have aimed the study of the Western region of the Mediterranean Sea, and very few reached the eastern part, leaving the dynamic of the whole Mediterranean uncomprehended; Siting the work done during the POEM cruise in the end of the 80s, and recently the studies performed during the BOUM campaign directed by the MIO in this region, both agreed on the complex situation of the EMS both geochemically and physically.
Noting that EMS is described as an ultra-oligotrophic ecosystem, physical variability in the region of Rhodes, south of Crete, grants this area an exceptional productivity; this feature is called the Rhodes cyclonic gyre (RG). Characterized as a cold core gyre, it brings cold and rich deeper water to the surface where the ecosystem strives as a response.
In addition, many important features are established near the RG, citing the Asian minor current (AMC), the Ierapetra anticyclonic eddy (IE), and the Levantine Intermediate water (LIW) formation zone. However, the interaction and the variability of these features are poorly studied.
For this aim, a campaign set up can be brought into action in this dynamic area, with many problematic to solve;
1- Understand the Eastern Mediterranean physical dynamics, by improving the knowledge on the Rhodes gyre and its variability and on the interaction with all the neighboring features.
2- Understand the effect of such variability on the biogeochemistry composition of this region of interest.
3- And resolve the forcing of each circulation features in the EMS, whether it is taken source from an atmospheric variability through an annual cycle scale, or in term of climate change effect.
The importance of this campaign is highlighted by the choice of this specific region to study, where many knowledge gaps reside. With this study continuous data sources are planned to be implemented. More opportunities to collect data by autonomous platforms are present (Mooring, Argo, etc.) Satellite SSH SST etc., and possibly by the end of this work, the circulation pattern of the EMS currents will be updated.
REGIONAL CONTEXT:
Rhodes Cyclonic Gyre (RG), takes place in the southeast corner of the Rhodes Basin is a one of the most intense and permanent feature of the EMS. It is the deepest part of the entire Eastern Mediterranean, and its circulation is highly affected by the bottom topography. Its circulation is also affected by the circulation patterns around the gyre, the most significant ones are eastward flowing Mid Mediterranean Jet (MMJ) in the middle of the Levantine Basin and westward flowing AMC near the Turkish coasts. Atmospheric conditions play a significant role in the location and intensity of the RG as well as the formation of the LIW in this area. RG is known as the major area of the formation of the LIW which is important water mass penetrating both into the EMS and the West Mediterranean Sea and characterized by the salinity maximum between depths 150 – 600 m of the water column. Owing to the upwelling movement of the deep waters, nutrients are carried into the upper water column which makes the Rhodes area is the most productive area in the EMS.
Since the location of the Gyre falls between territorial waters of several countries (Turkey, Greece, Cyprus?) it was not possible to study the area as individual institutions of both countries. In the past, with some collaborative efforts like POEM, LIWEX, monthly and seasonally in-situ data obtained and so much achieved on explaining the general characteristics of the area. However, these data do not cover enough resolution to explain lower scale circulation dynamics of the area. Even though general circulation patterns and interactions studied, there is not so much information on how the small scale patterns like IE and West Cyprus Gyre (WCG) affect the location and intensity of the RG. (IE intensifies in October – November. As it vanishes, in first three months of the year RG intensifies. Their dynamic affected by same forcing factors or are they interacting each other?)
LIW formation happens in a very short time (1-2 weeks) interval when atmospheric conditions are suitable, and time resolution of these studies were not enough to capture the formation process. Also the annual and inter-annual variations of LIW could not be extensively investigated through time since these studies did not continue until near past.
Figure 1 a) Proposed schema of general circulation from Munello et.al 2003 b) Rhode Gyre high chlorophyll concentration for 22 April 2017.
Productivity in the core of the RG has been evaluated in many studies in the past. Another important question is how LIW affects the productivity and the biogeochemical structure of intermediate layers the surrounding waters? This knowledge gap should be closed to estimate the future effects of LIW variations on biogeochemistry of the water not only in the EMS but also all the oceanographic areas where the LIW penetrates: Western Mediterranean Basin and the Atlantic Ocean.
After its penetration through the eastern and western basins, LIW spills into the Atlantic Ocean and has a contribution on salt budget of the deep circulation. The changes in its formation rate, volume and salinity would also affect the circulation and thermohaline processes of the Atlantic Ocean.
CAMPAIGN STRATEGY
- DATE OF THE CAMPAIGN:
Starting year: 2018, yearly campaign
In order to track the maximum intensity of the RG, LIW formation and the Phytoplankton bloom that occurs in this area, the campaign will be launched twice between 15 and 25 February and in April (1 April-10 April). The first time schedule choice for the campaign allows evaluating the LIW formation simultaneously with the deep mixing of the RG. While in April, the campaign will focus on the response of the ecosystem to such dynamic.
- EXPERIMENTAL SETUP
The campaign will be organized in two legs, of 10 days each. The ship would ideally leave from the southern Turkish coast, allowing to track the Rhodes Gyre, as well as the Minor Asian current. The campaign is planned to be done once a year to be able to establish the climatology of the dynamics, including main currents and mid and small-scale features. The calculation of the climatology will allow us to distinguish between the permanent features and those one caused by decadal, annual or seasonal phenomena. The tracking of the Rhodes Gyre will also allow us to collect insitu data of biogeochemical parameters, including chlorophyll.
The personnel of the ship should include two teams, for the physical and biological parts, and an on-board laboratory to analyze water samples of oxygen, chlorophyll, nitrates and DIC. We will do physical and biogeochemical measurements during the 20 days of campaign and we will deploy moorings at key points to have a good time-resolution record of dynamical variables during all the year. Also, we will deploy two gliders around the center of the gyre, allowing us to have a high space-resolution record of the velocity field and salinity at different depths, and then to characterize the gyre and its seasonal variations.
During the campaign, measurements will be done with a CTD at 20 different stations (Fig 1) repeated in both legs, tracking the Rhodes Gyre and a part of the Asian Minor current. The CTD will make temperature, salinity, chlorophyll and oxygen records during all its diving and will also provide oxygen, DIC, chlorophyll, salinity and NO3 data at specific preset depths by analysis of water samples on the on-board laboratory. It is crucial to pay special attention to salinity, as it may allow us to identify different masses of waters and, in particular, identify the Rhodes Gyre.
Four moorings will be deployed and renewed every year at specific locations in the Gyre (Fig 2) and Asian Minor current to have a record of physical and biogeochemical parameters at a high time-resolution.
Western station M2 has been chosen for observing the interaction of RG with the IG. Northern one M1 is to see the contribution of the AMC to the RG where the easternmost station M4 is for both to observe the contribution of the MMJ and also the interaction between WCG. All of these stations also will help us to understand the periphery dynamics of the Gyre. One mooring is located in the center of the RG M1 which is aimed to see the upwelling of the deep waters, and to detect several biogeochemical, physical and meteorological parameters. The data will be taken in every 25 m.
We will deploy some drifters in the Asian Minor current, expecting them to follow the surface current until the Rhodes Gyre. We will, as well, deploy two gliders in the Gyre, making them tracking the Gyre from side to side to obtain a high space-resolution velocity field in the core of the gyre. In addition, nets of different grid sizes could be deployed to capture different species of zooplankton, whose collection may be interesting to study biological issues.
The two legs are set to be just before and after the spring bloom to pay special attention to chlorophyll in its growth and decay, as well as some physical parameters that may be a determinant effect on it.
Figure 2 Proposed Mooring stations.
Figure 3 Proposed CTD stations.
- MEASURED PARAMETERS
I- Physic and dynamics:
In order to evaluate the variability of the physical properties in this region, it is suggested to quantify the physical parameters listed below;
1- Oceanic measurement:
- SST (CTD)
- SSS (CTD derived from conductivity measurements)
- Dissolved Oxygen (for integration with profiling or moored CTDs)
- Current surface layer (SADCP)
- Velocity field (gliders/moorings)
- Thermosalinograph (Continuous SST/SSS measurement along the ship track)
- Radium isotopes (to determine the age of the water mass: LIW formation)
2- Meteorological measurement:
- Wind speed and direction at 2m above sea level
- Heat flux
3- Remote sensing data:
- Altimetric geostrophic velocity
- SST (MODIS-AVHRR)
II- Biogeochemical response:
Phytoplankton blooming cycle and community structure will be the second object of this study, while trying to understand the influence of changes in the physical dynamic on the ecosystem. For this aim, phytoplankton will be used as a biological tracer of surface physical dynamic;
Measured Parameters:
1- Geochemistry and nutrients
- Nitrates: Autonomous measurements/CTD
- Phosphates: Autonomous measurements/CTD
- Silicate (CTD)
2- Phytoplankton community structure:
- Total Chlorphyll-a (CTD)
- Diagnostic pigments (HPLC); (Fucoxanthin, Peridinin, 19Hex-Fucoxanthin, 19But-Fucoxanthin, Alloxanthin, Zeaxanthin, Chl-b, DVChl-a, DVChl-b, Chl-a) (Phytoplankton functional type identification)
- Flow Cytometer count for different Phytoplankton size fraction (Micro, Nano, Pico)
- Zooplankton identification and biomass
3- Remote sensing data:
- Total Chl-a (MODIS)
EXPECTED OUTCOMES
The outcome of the study will fill the gap about the LIW formation processes, interaction of Ierapetra and Rhodes gyres and interannual variability of Rhodes gyre. Also, the relation with physics and biology will be revealed. The data which are collected contribute the modeling studies for the study area. There will be one workshop at the end of the research in one of the contributing institutes. The workshops will provide a summary of the work which have been done and the opportunity to young scientist’s information about the campaign.
The integration of the data which is collected by the moorings and gliders will be published a paper about Levantine Intermediate Water formation processes. The second paper will be written with the coupling of physical and biochemical data and it will be about the effects of physics on the primary production in the study area.