1 / 28

Alexandra Gogou 1 , S. Stavrakakis 1 , V. Lykousis 1 ,

Seasonal and interannual variability of sinking particulate matter in the deep Ionian Sea: ecological and biogeochemical perspectives. Alexandra Gogou 1 , S. Stavrakakis 1 , V. Lykousis 1 , E. Krasakopoulou 1,3 , A. Karageorgis 1 , M. Triantaphyllou 2 ,

albertm
Download Presentation

Alexandra Gogou 1 , S. Stavrakakis 1 , V. Lykousis 1 ,

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Seasonal and interannual variability of sinking particulate matter in the deep Ionian Sea: ecological and biogeochemical perspectives Alexandra Gogou1, S. Stavrakakis1, V. Lykousis1, E. Krasakopoulou1,3, A. Karageorgis1, M. Triantaphyllou2, C. Parinos1, M. Dimiza2 , F. Paraschos1, E. Skampa2, H. Kontoyiannis1, G. Rousakis1, D. Velaoras1, G. Kambouri1, I. Stavrakaki1 1. Hellenic Centre for Marine Research, Institute of Oceanography, Greece 2. Department of Historical Geology and Palaeontology, Faculty of Geology and Geoenvironment, University of Athens, Greece 3. Department of Marine Sciences, University of the Aegean, Greece

  2. Chl-a (mg/m3) W Med: generally oligotrophic, evident seasonality and relevant blooms E Med: ultra-oligotrophic, low seasonality Ten years (1997–2007) of SeaWiFS ocean color observations in the Mediterranean Sea D’Ortenzio & Ribera d’Alcala, 2010

  3. Distribution of Chl-a, pico-, nano- and micro-phytoplankton TChl a Ras et al., 2011

  4. Phytoplankton = C106N16P1 Redfield ratio or Redfield stoichiometry is the atomic ratio of carbon, nitrogen and phosphorus found in phytoplankton and throughout the deep oceans. This empirically developed stoichiometric ratio was originally found to be C:N:P = 106:16:1 (and has more recently been revised to 117:14:1[1]). This term is named after the American oceanographerAlfred C. Redfield, who first described this ratio in an article written in 1934 (Redfield 1934). As a Harvard physiologist, Redfield participated in several voyages on board the research vessel Atlantis. Alfred Redfield analyzed thousands of samples of marine biomass across all of the ocean regions. From this research he found that globally the elemental composition of marine organic matter (dead and living) was remarkably constant across all of the regions. The stoichiometric ratios of carbon, nitrogen, phosphorus remain relatively consistent from both the coastal to open ocean regions. (Redfield 1934) Alfred C. Redfield Relationship of Phosphate to Nitrate Uptake for photosynthesis in various regions of the ocean. Note that nitrate is more often limiting than phosphate

  5. Eastern Mediterranean: An Ultra-Oligotrophic Marine System N : P > 20:1 (~ 28:1) • P-limited • No significant denitrification P-limitation could be attributed to: • High N/P ratio in all inputs (mainly atmospheric where N/P≈100) Herut et al., 1999, 2002; Kouvarakis et al., 2002. • Enhanced N-fixation ? Bethoux & Copin-Montegut, 1986; Pantoja et al., 2005. Further increase of N/P ratio in time due to: • Atmospheric input of N increase due to anthropogenic influenceHastings et al., 2003; Duce et al., 2007; Mara et al., 2009 GBC • P riverine inputs have decreased (e.g. Po River, Krom et al., 2004).

  6. Aims of our study • Examine the seasonal/ interannual variabilityin marine productivity and vertical distributions of sinking particles (mass flux) in respect to the prevailing physical and biogeochemical dynamics in the Ionian Sea (Pylos Deep site). • Obtain a comprehensive view of the chemical composition (OC, CaCO3, N, biogenic Si, C & N stable isotopes) of the exported matter and the extent of degradation vs. export at various depths of the water column. • Characterization of sinking particles in the epipelagic, mesopelagic and bathypelagic zones provide valuable information on sources, budgets and the biogeochemical processes that shape deep-sea heterotrophic communities.

  7. ‘NESTOR’ site Pylos Deep, Ionian Sea, NE Mediterranean

  8. Mooring line NESTOR Deep-Sea Site Deep-sea regions have been generally considered as stable environments, not subjected to the strong and rapid modifications related to human influence that characterize the coastal regions. More recent studies have demonstrated, however, that deep-sea regions are subject to strong variations of the trophic and sedimentation rate, even on a seasonal scale. The aim of Nestor Project (funded by KM3Net/ ESONet, Hermione and EUROSITES Projects) is to construct an observatory able to monitor the deep-sea environment by measuring in situ biological, chemical and physical parameters. Two mooring lines, NESTOR4.5 and NESTOR5.2, are deployed from February 2006 in the area of Calypso Deep (5264 m depth), the deepest part of Mediterranean Sea, SW Peloponnese, Greece. Area of Study: Pylos, Ionian Sea

  9. CTD profiles & Nutrient distributions Inorganic nutrients NO3- PO43- NH4+ NO3- PO43- NH4+ Kontoyiannis et al., 2009 Stavrakakis et al., 2009 Salinity (red), potential temperature (purple), density (black), water transparency (blue) and dissolved oxygen (green) profiles Stavrakakis et al., Biogeosciences 2013 Theodosiet al., Biogeosciences2013 Parinos et al., Biogeosciences, 2013 Gogou et al., JMS, 2014 Gogou et al., in preparation

  10. Mass and major constituent fluxes Total mass flux OC flux IC (Carbonate) flux Biogenic Si flux Stavrakakis et al., Biogeosciences 2013

  11. Organic carbon flux vs. (a) lithogenic flux; (b) carbonate flux; (c) opal flux; (d) organic carbon content vs. total mass flux Stavrakakis et al., Biogeosciences 2013

  12. δ13Corg Gogou et al., in preparation

  13. δ13Corg vs. Corg/N ratio Gogou et al., in preparation

  14. OC flux and major planktonic groups contributions – lipid biomarkers Diatoms Coccos Diatoms Dinoflag Coccos Dinoflag Dinoflag Silicoflagellates Gogou et al., in preparation

  15. Coccolithophore flux from the shallower trap (700 m) for an overall interval between 6/2010 and 8/2012, reveals a peak during late spring-early summer (max. May 2012; 1.43 x106 coccospheres m-2 day-1) that is in accordance with the peak of total mass flux, and is directly correlated with the primary productivity signal. Gogou et al., in preparation

  16. What are the factors driving/ influencing seasonal and interannual variability of mass export at the NESTOR site?

  17. Corg flux at 700 m & satellite Chl-a

  18. Lithogenic flux at 700 m & satellite deposition

  19. Salinity profile – 500 m

  20. Oceanographic setting 38.80 38.76 38.72 avg. Salinity @ 200-800 m 38.68 38.64 38.60 cyclonic anticyclonic cyclonic anticyclonic The Adriatic-Ionian BiOS (Gačić et al., GRL, 2010) MAW MAW MAW MAW Eastern Mediterranean waters enter the Adriatic S (and density) increases in the Adriatic MAW enters the Adriatic  S (and density) decreases in the Adriatic LIW LIW LIW LIW ADW ADW ADW ADW upwelling at the border more nutrients into the Adriatic downwelling at the border less nutrients into the Adriatic Anticyclonic mode Cyclonic mode Adopted from Civitarese et al., 2010 NO3 in north eastern Ionian NO3 in Southern Adriatic S in Southern Adriatic

  21. Schematic representation of the two EMED upper thermohaline cell circulation modes Mode 1: Following DWF in the Adriatic Sea, the outflowing dense masses cause the deflection of the AIS pathway (cyan) towards the North Ionian with reduced eastward flow which consequently results in the recirculation of the LIW (red) in the Levantine, finally favouring DWF in the Aegean Sea and consequent Aegean dense outflow (blue). Mode 2:Following DWF in the Aegean Sea, the outflowing dense masses cause the re-establishment of the AW eastward flow (cyan) which consequently results in the restoration of the LIW westward return flow (red), finally favouring DWF in the Adriatic Sea and consequent Adriatic dense outflow (blue). Yellowdotted circles shown in both modes, portray the respective North Ionian Gyre reversals as proposed by the BiOS theory. Velaoraset al., 2014

  22. Major conclusions on the biogeochemical functioning of the Ionian Sea – Nestor site • The Ionian Sea, as one of the most oligotrophic Mediterranean sites, displays seasonal variability with maximum productivity rates observed during the late winter/spring convective mixing period. • Our flux study proposes two additional processes, potentially of high importance for fuelling surface waters at the NESTOR site: (1) the upwelling of intermediate waters in late spring-early summer, causing nutrient uplift in the euphotic layer which may lead to episodes of increased productivity, as witnessed by the organic carbon, carbonate, opal, coccolithophorid and organic biomarker fluxes and (2) the influence of episodic dust input events, leading to enhanced fluxes of lithogenicmatter. • A pronounced increase of all biogenic fluxes was recorded in spring 2012, when atmospheric conditions involving particularly strong cold and dry northerly winds triggered intense winter convection mixing and thus enhanced productivity and carbon export to the deep layers. • Further research is needed in order to get deeper insight to the mechanism influencing the export of C, N and ballast minerals to the deep Ionian Sea.

  23. Thank you for your attention!

  24. Nitrate to phosphate ratio in the main external sources of nutrients Durrieu de Madron et all, 2011

  25. The Eastern Mediterranean Transient The thermohaline cells of the Mediterranean Sea: (a) before the EMT (1987) and (b) after the EMT Tsimplis et al., 2006

  26. Vertical profiles of salinity (1987-2002) in three regions of the EMS • The most impressive change caused by the EMT was: • The uplifting of the EMDW of Adriatic origin • Thesalinity increase in the bottom layer of the whole EMS Manca et al., 2003

More Related