Su kolonunun oksijenli-oksijensiz arayüzey tabakasındaki fosfat ve nitrat döngülerinin modellemesi

TÜBİTAK ÇAYDAG15.07.2012Data collected extensively in the water of the central Baltic Sea show the development of nitrate deficits, likely caused by denitrification and anammox. Observations of temperature and salinity, oxygen, hydrogen sulfide and nutrient concentrations in the central Gotland Sea reveal the rate of formation of nitrate deficits to be largest in the oxic waters above and in the halocline. The reason that large accumulated deficits are observed in stagnant deeper waters is simply that there they can build up over years to decades of stagnation. The magnitude of the nitrate deficit formation varies between years, mainly depending on the annual maximum depth of the mixed layer and related late-winter nitrate concentration in surface water. The bulk of nitrogen losses is by denitrification (anamox maximum 12%?) in the oxic part of the Baltic where it is only possible in sediments. Deep waters turning anoxic can have very high rates of denitrification, but for short periods only. Therefore, and with the small water volume involved, this is of no importance for the Baltic N-balance. The results show that denitrification is not high in the Baltic Sea because it is prone to anoxia at depth. Especially, an often invoked negative feedback removing nitrogen (high nitrate - high production – high sedimentation – high oxygen consumption – anoxia – high denitrification, hence lowered nitrate delivery to the surface) is not at work here. On the contrary, oxic conditions of the water favour nitrogen removal. The stagnation period in the seventies had lower denitrification than the more oxic period of the nineties. Other processes than denitrification and burial in sediments contribute to bound-nitrogen removal in the Baltic Sea, since nitrate deficits are smaller than observed N2 supersaturation

Doğu Akdeniz'de mevcut farklı ekosistemlerin - upwelling bölgeleri, açık deniz ve kıta sahanlığı suları - dinamikleri, bakteriyel ve birincil üretim potansiyelleri, üst trofik seviyelere yansımaları

TÜBİTAK ÇAYDAG15.10.2014Türkiye denizleri, su bütçesi, atmosferik ve karasal girdiler, taban topoğrafyası, iklimsel evrim gibi temel etkenlerin belirlediği fiziksel, kimyasal, biyolojik özellikler bakımından büyük farklılıklar içeren zengin ve değişken deniz ekosistemlerini barındırmaktadır. Birincil üretim potansiyelleri açısından Karadeniz’in özellikle kuzeybatı kıta sahanlığı ötrofik, Marmara Denizi ve körfezleri ileri derecede ötrofik, Ege Denizi ve Doğu Akdeniz oligotrofik yapı sergilemektedir. Özgün bir dinamiği olan Doğu Akdeniz, genelde bir uç oligotrofik sistem olarak tanımlansa da, kendi içinde önemli bölgesel farklılıklar göstermektedir. Özellikle karasal tatlı su ve besin girdilerinden etkilenen kuzeydoğu kıta sahanlığı (Mersin ve İskenderun Körfezleri) ve ‘upwelling’ dinamiğinden etkilenen Rodos döngüsünde önemli düzeylerde birincil üretim potansiyeline sahiptirler ve daha yoksul olan açık denizden farklıdırlar. Aktif dinamik yapıya ve zengin biyolojik çeşitliliğe sahip kıyısal denizlerimizin sürekli gözlem, analiz ve model öngörüleri aracılığıyla araştırılmasının sürdürülmesi, büyük stratejik önemi haizdir. Çalışma O.D.T.Ü. Deniz Bilimleri Enstitüsü Araştırma Gemisi Bilim-2 ile anılan sahalarda ve istasyonlarda mevsimsel bazda gerçekleştirilmiştir. Bu çalışma ile fonksiyonel olarak üç farklı ekosistemi teşkil eden alanlarda bakteriden balıklara uzanan besin zincirinde olası yapısal farklılıklar, üretim potansiyelleri, dinamikleri karşılaştırılmış, toplanan diğer çevre faktörleri ile etkileşimleri irdelenmiştir.Turkish seas accommodate rich and varied marine ecosystems which are diverse in their physical, chemical, biological characteristics as a result of differences in basic driving factors such as the water budget, atmospheric and land-based inputs, bottom topography, climatic evolution. In terms of primary production potential, the Black Sea especially the northwestern continental shelf exhibits eutrophic characteristics, while Marmara Sea and its bays are highly eutrophic, and Aegean and Eastern Mediterranean Seas display oligotrophic structure. Although the Eastern Mediterranean with its rather unique characteristics is often defined as an ultra-oligotrophic system, there are significant regional differences within the system. The northeastern continental shelf (Mersin and İskenderun Bays) influenced by land-based fresh water and nutrient sources and the Rhodes Gyre influenced by ‘upwelling’ dynamics have potential for high primary production, while the open sea is relatively poor. Continued research through continuous observations, analyses and model predictions have immense strategic importance for the well being of our coastal seas possessing energetic dynamics and rich biological diversity. It is proposed that the physical-biochemical variability of the diverse northern Levantine Sea ecosystems be investigated through systematic observations during oceanographic cruises, as well as model-based predictions. Study has been conducted seasonally aboard Research Vessel Bilim-2 of the Institute of Marine Sciences of Middle East Technical University in the referred areas and stations. Throughout the study, in areas that represent the three different functional ecosystems, possible structural differences, productivity potential, and dynamics were compared in the food chain spanning bacteria to fish, and their interactions with the other environmental factors were investigated

Modeling the influence of hydrodynamic processes on anchovy distribution and connectivity in the black sea Karadeniz'deki hamsi dağılımı ve bölgeler arası bağlantısı üzerine hidrodinamik proseslerin etkisinin modellenmesi

Dispersal mechanisms of Black Sea anchovy larvae (Engraulis encrasicolus ponticus) across the Black Sea were studied with an individual based anchovy larvae model embedded in a Lagrangian model using surface currents calculated from daily dynamic height topography maps of altimeter data during a period of three years (2001-2003). Particles representing anchovy eggs were released at different sites during June to August and their movement was tracked over time. Drifters were advected for 36 days, representing the time it generally takes for anchovy eggs to develop into juveniles. Each individual was subject to somatic growth whose temperature dependence was calculated from satellite derived sea surface temperature data. Model results indicate that larval dispersal in the Black Sea is strongly controlled at the basin scale by the Rim Current circulation and its two cyclonic basin-wide gyres. It is locally controlled by mesoscale eddies. Consistent with the observed circulation fields, a strong meridional transport exists from the northern to the southern coastal zone along the western coast and the central basin. The peripheries of both the western and the eastern cyclonic gyres are also associated with strong larval transport from the southern coast to offshore areas. Elsewhere the connectivity between different regions is not as well pronounced due to weaker and patchy current fields. Variability in the dispersal of larvae is considerable when comparing different years and seasons and should be taken into account when designing networks of Marine Protected Areas in the Black Sea

Trophic controls in the Black Sea ecosystem (BLACK MODE)

The study proposed here aims to understanding the functioning of the Black Sea ecosystem in terms of the "trophic cascade" control and "regime shift" mechanisms using retrospective data analysis and interdisciplinary modelling approach. The main focus of the proposal is on understanding the long-term ecological changes within the pelagic interior Black Sea ecosystem during its transformation from the pre-eutrophication phase of the 1960s to the post-eutrophication phase of the 1990s. It is devoted to model the structural changes took place in the Black Sea ecosystem under concurrent effects of climatic changes, anthropogenic nutrient enrichment, temporal outburst of gelatinous species, overexploitation of small pelagic stocks in terms of the identification of regime shifts, alternative states, and trophic controls. The second objective is to elaborate individual role of each forcing mechanism on the structural changes of the Black Sea ecosystems, and predict its possible future states under some specific scenarios. The proposed study integrates various aspects of physical oceanography, climate-change research, ocean biogeochemistry, fisheries oceanography, and therefore represents a truly multi-disciplinary research approach based on the analysis of avail able data and simulations.EIF - Marie Curie actions-Intra-European Fellowships (FP6-2005-MOBILITY-5

Invasion dynamics of the alien ctenophore Mnemiopsis leidyi and its impact on anchovy collapse in the Black Sea

The mechanisms governing the unprecedented 1989-90 anchovy-Mnemiopsis shift event in the Black Sea were evaluated with a coupled model of bioenergetic-based anchovy population dynamics and lower trophic food web structure. Simulations showed that a combination of direct and density-dependent effects of overfishing, eutrophication-induced nutrient enrichment, climate-induced over-enrichment and temperature-controlled Mnemiopsis spring production were involved in the shift. Eutrophication made the system vulnerable to further enrichment through the change of regional climate to a severe winter regime during 1985-87. While Mnemiopsis was acclimating to its new environment, increasing nitrate flux into the euphotic layer enhanced the carrying capacity of the system, but a disproportionate Mnemiopsis biomass increase was delayed until spring temperature conditions returned to normal in 1988-89. Enhanced carrying capacity provided a competitive advantage of food consumption to Mnemiopsis compared with anchovy, and warm spring temperature conditions promoted their spring-summer production. Prevalent high fishery pressure and increasing impact of Mnemiopsis on the food web further induced the anchovy stock collapse. However, the shift event did not result in alternation of the system to a new totally Mnemiopsis-invaded quasi-stable regime. Instead, anchovy started recovering when the subsequent strong 1991-93 cooling regime limited the Mnemiopsis population growth. Our analysis indicated that the switch of a large marine ecosystem to a totally gelatinous invader-dominated state requires extremely strong environmental perturbations. More often, environmental disturbances create a suitable niche for an alien gelatinous invader to become a member of the food web structure, and to share food resources with the native small pelagic fish community

Control mechanisms on the ctenophore Mnemiopsis population dynamics: A modeling study

A comprehensive understanding of the mechanisms that control the ctenophore Mnemiopsis blooms in the Black Sea is gained with a zero-dimensional population based model. The stage resolving model considers detailed mass and population growth dynamics of four stages of model-ctenophore. These stages include the different growth characteristics of egg, juvenile, transitional and adult stages. The dietary patterns of the different stages follow the observations given in the literature. The model is able to represent consistent development patterns, while reflecting the physiological complexity of a population of Mnemiopsis species. The model is used to analyze the influence of temperature and food variability on Mnemiopsis reproduction and outburst. Model results imply a strong temperature control on all stages of Mnemiopsis and that high growth rates at high temperatures can only be reached if food sources are not limited (i.e. 25 mg C m(-3) and 90 mg C m(-3) mesozooplankton and microplankton, respectively). A decrease of 5 degrees C can result in considerable decrease in biomass of all stages, whereas at a temperature of 25 degrees C a 40% decrease in food concentrations could result in termination of transfer between stages. Model results demonstrate the strong role of mesozooplankton in controlling the adult ctenophore biomass capable of reproduction and that different nutritional requirements of each stage can be critical for population growth. The high overall population growth rates may occur only when growth conditions are favorable for both larval and lobate stages. Current model allows the flexibility to assess the effect of changing temperature and food conditions on different ctenophore stages. Without including this structure in end-to-end models it is not possible to analyze the influence of ctenophores on different trophic levels of the ecosystem

A coupled plankton-anchovy population dynamics model assessing nonlinear controls of anchovy and gelatinous biomass in the Black Sea

A coupled model of lower trophic levels and anchovy Engraulis encrasicolus ponticus population dynamics was developed to analyze the mechanisms controlling sharp anchovy and gelatinous zooplankton biomass transitions from the 1960s to the 1980s in the Black Sea. An increase in anchovy stocks from estimated low (similar to 300 kt) to moderate (similar to 700 kt) in the late 1960s was related to weakening piscivore predation pressure, slight nutrient enrichment of the basin during an early eutrophication phase, and competitive exclusion of gelatinous carnivores. The transition to high stocks (similar to 1500 kt) from 1979 to 1980 was caused by additional nutrient enrichment. With enhanced enrichment, gelatinous carnivores started to coexist with anchovy at low biomass levels (<1.0 gC m(-2)), but they did not yet exert a strong control on anchovy because of their competitive disadvantage of consuming prey at low carrying capacity. The third transition (1989-1990) returned the anchovy stock to the low regime and increased the biomass of the alien gelatinous species Mnemiopsis leidyi (hereafter Mnemiopsis) to 3.0 gC m(-2). The anchovy-Mnemiopsis shift was pre-conditioned by nutrient accumulation in the subsurface layer and triggered by their more effective transport into the productive surface layer following the switch of regional climate into a severe winter phase during 1985-1987. The resulting enhanced resource carrying capacity, together with decreasing adult anchovy stocks, led to a competitive advantage of Mnemiopsis in food exploitation relative to anchovy, growth and reproductive advantages relative to the native gelatinous species Aurelia aurita, and stronger predation on anchovy eggs and larvae. The anchovy stock depletion was caused by increasing fishing pressure and by competition with and predation by Mnemiopsis. While nonlinear coupling of these 2 independent processes amplified the anchovy collapse, neither would be able to individually impose such a severe anchovy stock change under the observed environmental conditions of the Black Sea