Deep Sea Research Part II: Topical Studies in Oceanography
Seasonal and interannual dynamics of nutrients and phytoplankton pigments in the western Mediterranean Sea at the DYFAMED time-series station (1991–1999)
Introduction
To understand better the role of the ocean in the global biogeochemical carbon cycle is one of the challenges of the Joint Global Ocean Flux Study (JGOFS) project. Long-term time-series observations provide useful information on biogeochemical processes responsible of the seasonal and longer-term variability in the oceans (Lohrenz et al., 1992; Michaels et al., 1994; Michaels and Knap, 1996; Karl and Lukas, 1996).
In the framework of the France-JGOFS project, a long-term time-series investigation (DYFAMED program) has been undertaken since 1988 in the northwestern Mediterranean Sea. The “DYFAMED” site was first equipped with sediment traps mooring (Miquel et al., 1994; Marty et al., 1994), and visited punctually for hydrologic monitoring. Atmospheric deposition survey also was initiated in 1988 at the Cape Ferrat station. Since 1991, monthly cruises have been conducted and most of the JGOFS core parameters recorded. Among these parameters, pigments analyzed by HPLC provide a detailed examination of the algal stocks and distribution in relation to varying hydrological conditions.
The physical and chemical forcings and their related biological response are the main driving forces of the oceanic carbon cycle. The fate of the biogenic matter synthesized by phytoplankton is strongly related to the algae characteristics. The export of particulate carbon from the surface ocean is dependent on the production regime: low for oligotrophic systems where regenerated production is dominant, and high for mesotrophic areas where new production is high.
Using phytoplanktonic pigments (especially, chlorophylls and carotenoids) as specific markers of various phytoplanktonic groups, the chemotaxonomic approach provides very relevant information on the phytoplankton dynamics and fate. Claustre (1994) has shown that pigment signatures can even reveal the trophic status of the studied zone (proxy of the f-ratio).
The Mediterranean Sea is considered as oligotrophic, and characterized by low primary production (Margaleff, 1985; Minas et al., 1988). However, satellite imagery has exhibited the spatial and temporal heterogeneity of phytoplankton distribution (Morel and André, 1991). In the Liguro-provençal basin, spatial variations, as evidenced by multi-parametric measurements, are essentially related to the presence of the Ligurian Coastal Current (Béthoux and Prieur, 1983). However, the central part of the basin, where the DYFAMED site is located, constitutes a homogenous system isolated from direct coastal inputs by rivers. The continental inputs are significant only through the atmosphere. At this site, the seasonal succession of hydrologic conditions induces production systems varying from mesotrophy in spring to oligotrophy in summer and fall. The DYFAMED site is thus well situated for comprehensive studies of phytoplankton dynamics related to physical and chemical forcings.
Hereafter we report and discuss the seasonal and interannual variations of hydrography and pigment distribution after 9 years (1991–1999) of monthly measurements at the DYFAMED time-series site.
Section snippets
Material and methods
The DYFAMED site is located 52 km off Cape Ferrat, at 43°25′N, 07°52′E in the Ligurian Sea (Fig. 1) and has a water depth of 2350 m. The central zone of the Liguro-provençal basin is generally free of the influence of the Ligurian current, which separates the coastal zone from the open sea (Béthoux and Prieur, 1983; Sournia et al., 1990). The DYFAMED cruises were conducted on-board the R.V. Korotneff, Catherine-Laurence, Georges-Petit or Téthys II, every month, starting from January 1991. On a
Hydrology
According to Send et al. (1999), in their synthesis of the physical oceanography of the western Mediterranean Sea, there are three principal layers in the Liguro-Provençal basin. The surface layer, between 0 and 250 m, is strongly affected in the upper 100 m by the annual thermal cycle. The intermediate layer (of Levantine origin) is characterized by salinity and temperature maxima. The deeper, homogeneous layer, below about 700 m, is colder and less salty.
The temperature, salinity and density
Discussion
The 9 years of observation at the DYFAMED station reported here allow a unique description of seasonal and interannual dynamics of hydrology and trophic regimes in the northwestern Mediterranean Sea. The DYFAMED site was frequently visited in the past (Béthoux and Prieur, 1983; Béthoux et al., 1988) although with no regularity. Thus, the seasonal variation of the hydrological structure has not been detailed. Moreover, previous efforts have been particularly devoted to the description of the
Acknowledgments
This work has been funded by CNRS/INSU in the course of the French-JGOFS (now PROOF) program, and of the DYFAMED Observation Service. R.F.C. Mantoura and D.J. Repeta are thanked for their helpful comments and suggestions.
References (71)
- et al.
One-month study in the open NW Mediterranean Sea (DYNAPROC experiment, May 1995)overview of the hydrobiogeochemical structures and effects of wind events
Deep-Sea Research Part II
(2000) - et al.
Pigment signatures of the phytoplankton composition in the northeastern Atlantic during the 1990 spring bloom
Deep-Sea Research Part II
(1993) - et al.
Pigment chemotaxonomic distributions of phytoplankton during summer in the western Mediterranean
Deep-Sea Research Part II
(1997) - et al.
Monsoonal influence on the distribution of phytoplankton pigments in the Arabian sea
Deep-Sea Research Part II
(1999) - et al.
Temporal trends in nutrient ratiosChemical evidence of Mediterranean ecosystem changes driven by human activity
Deep-Sea Research II
(2002) - et al.
Nutrients in the Mediterranean Sea, mass balance and statistical analysis of concentrations with respect to environmental changes
Marine Chemistry
(1998) - et al.
Photosynthetic picoplankton community structure in the subtropical North Atlantic Ocean near Hawaii (station ALOHA)
Deep-Sea Research
(1993) - et al.
Specific phytoplantkon biomasses and their relation to primary production in the Tropical North Atlantic
Deep-Sea Research Part I
(1995) - et al.
Phytoplankton photoadaptation in relation to some frontal physical processes
Journal of Marine Systems
(1994) - et al.
Re-evaluation of the nutrient exchanges in the Strait of Gibraltar
Deep-Sea Research
(1988)
Phytoplankton community compositions in the western equatorial pacific determined from chlorophyll a and carotenoid pigment distributions
Deep-Sea Research
Potential role of large oceanic diatoms in new primary production
Deep-Sea Research
Effect of irradiances up to 2000 μE m−2 s–1 on marine Synechococcus WH7803-I. Growth, pigmentation, and cell composition
Deep-Sea Research
The Hawaii ocean time-series (Hot) programbackground, rationale and field implementation
Deep-Sea Research Part II
Seasonal and interannual variations in phytoplankton production at DYFAMED time-series station, northwestern Mediterranean Sea
Deep-Sea Research Part II
Particulate fluxes of organic compounds and their relationship to zooplankton fecal pellets in the northwestern Mediterranean Sea
Marine Chemistry
Overview of the US JGOFS Bermuda Atlantic time-series study and the hydrostation program
Deep-Sea Research Part II
Seasonal patterns of ocean biogeochemistry at the US JGOFS Bermuda Atlantic Time-series Study site
Deep-Sea Research Part I
Distribution of phytoplankton pigments in the North Pacific Ocean in relation to physical and optical variability
Deep-Sea Research
Recent advances in observing the physical oceanography of the western Mediterranean Sea
Progress in Oceanography
Phytoplankton pigment variations during the transition from spring bloom to oligotrophy in the northwestern Mediterranean sea
Deep-Sea Research
Modèles d’écosystèmes pélagiques des eaux côtières de la mer ligure
Oceanologica Acta
Ultrastructure and 18S rRNA gene sequence for Pelagomonas calceolate gen. et sp. nov. and the description of a new algal class, the Pelagophyceae classis nov
Journal of Phycology
Grazing, temporal changes of phytoplankton concentrations, and the microbial loop in the open sea
Source, transport and deposition of atmospheric phosphorus over the northwestern Mediterranean
Journal of Atmospheric Chemistry
Hydrologie et circulation en Méditerranée Nord-Occidentale
Pétroles et Techniques
Le courant Ligure au large de Nice
Oceanologica Acta
Evidence for phytoplankton succession and chromatic adaptation in the Sargasso Sea during spring 1985
Marine Ecology Progress Series
Specific phytoplankton signatures and their relationship to hydrographic conditions in the coastal northwestern Mediterranean Sea
Marine Ecology Progress Series
The trophic status of various oceanic provinces as revealed by phytoplankton pigment signatures
Limnology and Oceanography
Phytoplankton dynamics associated with a geostrophic frontecological and biogeochemical implications
Journal of Marine Research
Variability in particle attenuation and chlorophyll fluorescence in the tropical Pacificscales, patterns, and biogeochemical implications
Journal of Geophysical Research
Particulate organic matter flux and planktonic new production in the deep ocean
Nature
The phytoplanktonic ways of life
New Phytologist
Mediterranean deep water formation, baroclinic instability and oceanic eddies
Oceanologica Acta
Cited by (301)
Influence of oceanic mesoscale eddies on the deep chlorophyll maxima
2024, Science of the Total EnvironmentAssessment of pollutants in coastal waters, sediments, and biota of marine ecosystems in Algeria, North Africa
2024, Regional Studies in Marine ScienceNew insights on the <sup>7</sup>Be cycle in the ocean
2023, Deep-Sea Research Part I: Oceanographic Research PapersParticulate and dissolved fluorescent organic matter fractionation and composition: Abiotic and ecological controls in the Southern Ocean
2022, Science of the Total EnvironmentA year in the life of the Eastern Mediterranean: Monthly dynamics of phytoplankton and bacterioplankton in an ultra-oligotrophic sea
2022, Deep-Sea Research Part I: Oceanographic Research Papers