Dişa, Deniz
The ocean has a crucial role in global carbon cycle. Marine ecosystems are responsible for storing the carbon within the ocean body by means of uptaking atmospheric carbon into the ocean, transforming it into organic carbon through photosynthesis and transporting to the profound depths of the ocean. Playing a significant role in the marine food webs, grazing on plankton and providing nutrient to ecosystem by its metabolic activities, fish is thought to have a considerable impact on carbon export. For this reason, having regard to its increasing trend especially after 1950s, fishing is expected to impact carbon cycle directly by changing the fish biomasses. However, how fish impacts the biogeochemistry of marine ecosystems is not known clearly and to be assessed quantitatively. In this regard, this study aims to analyze the impact of fish and fisheries on marine biogeochemical processes by setting up an end-to-end model that simulates lower and higher tropic levels of marine ecosystems simultaneously. For this purpose, a biogeochemical model, which simulates lower tropic level dynamics (e.g. carbon export, nutrient cycles) and an ecosystem model, which simulates fisheries exploitation and higher tropic level dynamics (e.g. food web) were online and two-way coupled. Simulating the ecosystem from one end to the other with a holistic approach, the coupled model provided a more realistic representation of the ecosystem. It served as a tool for the analysis of fishing impacts on marine biogeochemical dynamics. Coupled model resolved the inefficiencies of biogeochemical model, which was because of being “closed” by zooplankton. Results pointed out 56% decrease in the mesozooplankton biomass due to higher trophic level predation. Simulations estimated an approximately 24% increase in the carbon export compared to the biogeochemical model simulations, which had no fish compartment. This increase was due to the change in the plankton compositions and enhanced outflows to detritus. The changes in the lower trophic level dynamics were statistically more consistent with the empirical data. Moreover, results obtained by applying different fishing intensities indicated that changes in fisheries exploitation levels directly influence the marine nutrient cycles and hence, the carbon export. Depending on the target and the intensity of fisheries, considerable changes in the biogeochemical responses obtained. For example, in the scenario where new potential target mesopelagics harvested in addition to the current fisheries revealed 12% decrease in the carbon export. The same scenario also indicated 11-15% changes in the remineralization flows. As a result of this study, unlike the models that do not represent the fish explicitly, how marine biogeochemical processes are impacted by the activity of fish assemblages and fisheries exploitation was delineated.


Comparison of Productivity Plankton Types and Carbon Export Mechanisms in two Different Regimes of Subtropical North Atlantic a Modeling Study
Salihoğlu, Barış (2016-02-15)
Improved structure and mechanisms of carbon export and sequestration within marine ecosystem models is vital to better understand and predict changes in the global carbon cycle. We have implemented a 1D lower trophic ecosystem model at long-term time-series stations (BATS and ESTOC) in the North Atlantic for the years 1996-2000. We have investigated the dynamics of the productivity and carbon export, and mechanisms regulating them. Our simulations agree with the previous observations that show similar produ...
Potential impacts of climate change on the primary production of regional seas: A comparative analysis of five European seas
Holt, Jason; Schrum, Corinna; Cannaby, Heather; Daewel, Ute; Allen, Icarus; Artioli, Yuri; Bopp, Laurent; Butenschon, Momme; Fach Salihoğlu, Bettina Andrea; Harle, James; Pushpadas, Dhanya; Salihoğlu, Barış; Wakelin, Sarah (2016-01-01)
Regional seas are potentially highly vulnerable to climate change, yet are the most directly societally important regions of the marine environment. The combination of widely varying conditions of mixing, forcing, geography (coastline and bathymetry) and exposure to the open-ocean makes these seas subject to a wide range of physical processes that mediates how large scale climate change impacts on these seas' ecosystems. In this paper we explore the response of five regional sea areas to potential future cl...
European Union Basin-scale Analysis, Synthesis and Integration (EURO-BASIN)
Salihoğlu, Barış(2014-12-30)
EURO-BASIN is designed to advance our understanding on the variability, potential impacts, and feedbacks of global change and anthropogenic forcing on the structure, function and dynamics of the North Atlantic and associated shelf sea ecosystems as well as the key species influencing carbon sequestering and ecosystem functioning. The ultimate goal of the program is to further our capacity to manage these systems in a sustainable manner following the ecosystem approach. Given the scope and the international ...
Challenges in integrative approaches to modelling the marine ecosystems of the North Atlantic: Physics to fish and coasts to ocean
Holt, Jason; Allen, J. Icarus; Anderson, Thomas R.; Brewin, Robert; Butenschoen, Momme; Harle, James; Huse, Geir; Lehodey, Patrick; Lindemann, Christian; Memery, Laurent; Salihoğlu, Barış; Senina, Inna; Yool, Andrew (2014-12-01)
It has long been recognised that there are strong interactions and feedbacks between climate, upper ocean biogeochemistry and marine food webs, and also that food web structure and phytoplankton community distribution are important determinants of variability in carbon production and export from the euphotic zone. Numerical models provide a vital tool to explore these interactions, given their capability to investigate multiple connected components of the system and the sensitivity to multiple drivers, incl...
The Biological Carbon Pump in the North Atlantic
Sanders, Richard; Henson, Stephanie A.; Koski, Marja; De la Rocha, Christina L.; Painter, Stuart C.; Poulton, Alex J.; Riley, Jennifer; Salihoğlu, Barış; Visser, Andre; Yool, Andrew; Bellerby, Richard; Martin, Adrian P. (2014-12-01)
Mediated principally by the sinking of organic rich particles from the upper ocean, the Biological Carbon Pump (BCP) is a significant component of the global carbon cycle. It transfers roughly 11 Gt C yr(-1) into the ocean's interior and maintains atmospheric carbon dioxide at significantly lower levels than would be the case if it did not exist. More specifically, export by the BCP in the North Atlantic is similar to 0.55-1.94 Gt C yr(-1). A rich set of observations suggests that a complex set of processes...
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