Abstract
Abstract. There is a general scarcity of oceanic observations that concurrently examine air–sea interactions, coastal–open-ocean processes and physical–biogeochemical processes, in appropriate spatiotemporal scales and under continuous, long-term data acquisition schemes. In the Mediterranean Sea, the resulting knowledge gaps and observing challenges increase due to its oligotrophic character, especially in the eastern part of the basin. The oligotrophic open Cretan Sea's biogeochemistry is considered to be representative of a greater Mediterranean area up to 106 km2, and understanding its features may be useful on even larger oceanic scales, since the Mediterranean Sea has been considered a miniature model of the global ocean. The spatiotemporal coverage of biogeochemical (BGC) observations in the Cretan Sea has progressively increased over the last decades, especially since the creation of the POSEIDON observing system, which has adopted a multiplatform, multivariable approach, supporting BGC data acquisition. The current POSEIDON system's status includes open and coastal sea fixed platforms, a Ferrybox (FB) system and Bio-Argo autonomous floats that remotely deliver fluorescence as a proxy of chlorophyll-a (Chl-a), O2, pH and pCO2 data, as well as BGC-related physical variables. Since 2010, the list has been further expanded to other BGC (nutrients, vertical particulate matter fluxes), ecosystem and biodiversity (from viruses up to zooplankton) variables, thanks to the addition of sediment traps, frequent research vessel (R/V) visits for seawater–plankton sampling and an acoustic Doppler current profiler (ADCP) delivering information on macrozooplankton–micronekton vertical migration (in the epipelagic to mesopelagic layer). Gliders and drifters are the new (currently under integration to the existing system) platforms, supporting BGC monitoring. Land-based facilities, such as data centres, technical support infrastructure, calibration laboratory and mesocosms, support and give added value to the observatory. The data gathered from these platforms are used to improve the quality of the BGC-ecosystem model predictions, which have recently incorporated atmospheric nutrient deposition processes and assimilation of satellite Chl-a data. Besides addressing open scientific questions at regional and international levels, examples of which are presented, the observatory provides user-oriented services to marine policy makers and the society, and is a technological test bed for new and/or cost-efficient BGC sensor technology and marine equipment. It is part of European and international observing programs, playing a key role in regional data handling and participating in harmonization and best practices procedures. Future expansion plans consider the evolving scientific and society priorities, balanced with sustainable management.
Highlights
International need for observatoriesOceans are complex dynamic systems embracing various physical, chemical and biological processes interacting on a wide range of timescales and space scales
POSEIDON is being developed in accordance to the policy framework suggested by Intergovernmental Oceanographic Commission (IOC)/GOOS, EuroGOOS, the Mediterranean Operational Network for the Global Ocean Observing System (MonGOOS) and the Group on Earth Observations (GEO)
The present (2018) status of the Cretan Sea’s coastal openocean biogeochemistry, ecosystem and biodiversity observatory includes (a) an open sea fixed platform with a multisensor array, (b) a coastal fixed platform with a multi-sensor array, (c) open sea sediment traps, (d) an open sea acoustic Doppler current profiler (ADCP) (e) open sea sampling through regular research vessel (R/V) visits, (f) coastal sampling through regular R/V visits, (g) a Ferrybox (FB) and (h) a glider (Figs. 1 and 2)
Summary
Oceans are complex dynamic systems embracing various physical, chemical and biological processes interacting on a wide range of timescales and space scales. The International GeosphereBiosphere Programme (IGBP) (led by the Intergovernmental Oceanographic Commission – IOC of UNESCO), since its first projects (JGOFS – Joint Global Ocean Flux Study), as well as with its current ones (IMBER – Integrated Marine Biosphere Research), has realized that key biogeochemical variables and ecosystems must be systematically and long-term observed, in order to study marine biogeochemical cycles and their interactions with the ecosystems, at the seasonal and decadal scales, as well as in shortterm episodic events (http://www.imber.info, last access: 26 September 2018). Biogeochemical-ecosystem long-term data are, available only from few locations worldwide (Karl, 2010) and scarcity increases when considering only open (deep) ocean observatories (Ruhl et al, 2011). The European Marine Board (EMB) has published a position paper on critical challenges of deep-sea research, stressing that a current limitation of observatories is that they mainly monitor almost exclusively abiotic variables (Rogers et al, 2015)
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