İKLİM DEĞİŞKENLİĞİN KARADENİZ’DEKİ HAMSİNİN KIŞLAMA GÖÇÜ ÜZERİNE ETKİSİNİN MODELLENMESİ

Black Sea anchovy (Engraulis encrasicolus ponticus) undertake extensive (~1000km long) overwintering migration in autumn from northern spawning grounds to the overwintering areas located at the south-eastern coasts of the Black Sea. When arriving at the Anatolian coast, they support important fisheries in Turkey. Black Sea anchovy is known to experience stock variability quite frequently including stock collapses, which are believed to be closely linked with environmental conditions. Therefore, it is of importance to understand the mechanisms that set the scene for a successful migration and explore routes feasible for migration. To investigate anchovy overwintering migration, a fish behavior model embedded into a 2D Lagrangian particle tracking model is used. Particles are released into the surface circulation field calculated from AVISO sea level anomaly data. Model simulations are performed during years of very different physical conditions from 2001 to 2003. The results show that while advection by currents influences transport pathways, temperature used as a guide for migration is of more importance for high migration success. Simulations reveal highly variable migration pathways driven by the onset and course of winter cooling processes, cross-shelf transport, and variability in eddy formation and persistence.Karadeniz hamsisi (Engraulis encrasicolus ponticus) sonbaharda kuzeydeki yumurtlama alanlarından Karadeniz’in güneydoğu kıyılarındaki kışlama alanlarına doğru geniş çaplı (~1000 km.) bir kışlama göçü gerçekleştirir. Hamsi Anadolu kıyılarına vardığı zaman Türkiye balıkçılığı için önemli bir kaynak teşkil eder. Karadeniz hamsisi, çevresel koşullara bağlı olarak ani stok çökmelerine neden olan dalgalanmaları oldukça sık yaşar. Bu nedenle, başarılı bir göç için gereken mekanizmaların anlaşılması ve elverişli göç yollarının aydınlatılması önem arz etmektedir. Hamsi kışlama göçünü incelemek amacıyla 2D (iki boyutlu) Lagrangian parçacık izleme modeline bütünleşik balık davranış modeli kullanılmıştır. Parçacıklar AVISO deniz yüzey yüksekliği anomalisi veri seti kullanılarak hesaplanan jeostrofik yüzey akıntı sahasına bırakılmıştır. Simülasyonlar oldukça farklı fiziksel koşulların hakim olduğu 2001-2003 yılları arasında gerçekleştirilmiştir. Sonuçlarda adveksiyon taşınımının göç yolları üzerindeki etkili olduğu ortaya çıkarken, sıcaklığın göç davranışına kılavuz olarak dahil edildigi simülasyonların yüksek göç başarısı açısından daha önemli bir yere sahip olduğu görülmektedir. Simülasyonlar sonucunda, kış soğumasının başlama zamanı ve soğumanın süresi ile, kıta sahanlığından taşınım ve girdap oluşumu ve sürekliliğindeki değişkenlik mekanizmaları ile kontrol edilen yüksek derece degişkenlik gösteren göç yolları ortaya çıkarmıştır.Ph.D. - Doctoral Progra

Modeling the impact of climate variability on Black Sea anchovy recruitment and production

The connection of climate variability with anchovy spawning and recruitment in the Black Sea in particular, and other ecosystems in general, was studied using a two-way coupled lower trophic level and anchovy bioenergetics model. Climate variability was represented by a 50-yr time series of daily temperature and vertical mixing rates with stochastic variations. Temperature was found to be the dominant factor influencing early life stages and hence population dynamics of Black Sea anchovy as marked by a high correlation of anchovy egg production and recruitment success in response to changes in temperature. Each decrease of 2 degrees C in summer mean temperatures resulted in a delay in the timing of egg production of between 12 and 19 days. Water temperatures in the spawning season had a greater influence than the number of available spawning females on the intensity of egg production. Anchovy recruitment was similarly influenced by temperature, with decreased temperatures resulting in a significant delay in the onset of peak recruitment during the fall by 21-38 days. Also, recruitment numbers in December decreased by about 20% with decreasing temperatures. The impact of temperature on production was slightly diminished by the impact of vertical mixing. The strong linkage of climate variability with anchovy spawning and recruitment has an important prediction potential for short-term anchovy stock estimations, which may serve fisheries management purposes

Comparing the permanently anoxic Black Sea with the rapidly deoxygenating Marmara Sea: Distinct redox processes of sulfur, nitrogen and oxygen in the two interconnected basins.

Existing marine oxic-anoxic interfaces are expanding and new redox gradients are establishing themselves higher up in the water column in productive oceans and restricted marine basins. The feedback from these interfaces to euphotic zone can be diverse and can include higher internal loading of phosphorus and ammonium, as well as amplified oxygen consumption in cases of excessive hydrogen sulfide formation. There will be no single recipe to parametrize redox processes across these interfaces in next generation biogeochemical models, therefore, both existing and newly forming redox gradients need to be analyzed in a comparative fashion. Here we present the latest observations in two interconnected, but altogether restricted marine basins: Black Sea and Marmara Sea. Using latest water column and sediment microsensor biogeochemical profiles, we show that the Black Sea’s suboxic zone is likely to be sustained by high metal (manganese and iron) fluxes from especially southwestern shelf. The onset of sulfide in the Black Sea has not significantly changed, underpinning the likelihood that the control on the sulfide onset may not short-term physical forcing but a geochemical control sustained by benthic reactive metal stocks. Just to the south of Western Black Sea, connected by Bosporus, is the Marmara Sea (max. depth 1200 m) that is undergoing deoxygenation due to a number of poorly constrained anthropogenic and natural influences. Latest expeditions with R/V Bilim-2 revealed a thin (<40 m) oxic layer with a sharp oxycline. Trace levels (<10 microM) re-appear around 600-800 m in the water column. Biogeochemical profiles indicate that the sub-oxycline water column hypoxic region is dominated by respiratory processes using nitrate as electron acceptor. Only in the very eastern sub-basin of Marmara (Cinarcik Basin), beyond 1000 m depth, we have measured micromolar levels of hydrogen sulfide, indicating that a basin-wide switch to sulfate-reduction in deep Marmara can be likely within the near future. As will be demonstrated in this presentation, seas hosting dynamic redox interfaces will have their uniquely interacting processes and therefore response of each system to anthropogenic and natural forcing will be correspondingly distinct, posing a challenge to ecosystem modeling and subsequent management efforts