FortHjort on Climate effects
Location: Seminarroom K1, Institute of Biology (UiB), Thormøhlensgate 53A (Biologen) 1.etg.
Three presentations on climate effects.
Vidar S Lien (IMR):
Wind-driven Atlantic water flow as a direct mode for reduced Barents Sea ice cover
Variability in the Barents Sea ice cover on inter-annual and longer time-scales has previously been shown to be governed by oceanic heat transport. Based on analysis of observations and results from an ocean circulation model we show that the ocean also plays a direct role within seasons. Positive wind stress curl and associated Ekman divergence causes a coherent increase in the Atlantic water transport along the negative thermal gradient through the Barents Sea. The immediate response connected to the associated local winds in the north-eastern Barents Sea is a decrease in the sea-ice cover due to advection. Despite a subsequent anomalous ocean to air heat loss due to the open water, increased ocean heat content contributes to maintaining a reduced sea-ice cover. This may potentially affect productivity in the seasonal ice zone.
Çağlar Yumruktepe (NERSC):
Carbon export algorithm improvements in marine ecosystem models
Numerical models can be useful tools that can be used to improve our understanding of ecosystem dynamics and the global carbon cycle. A 1D lower trophic level pelagic ecosystem model, NAGEM, was developed to investigate processes moderating productivity, algal community structure and resulting carbon export at BATS, ESTOC and PAP time-series stations in the North Atlantic. Simulated carbon export rates were evaluated using in-situ sediment trap data collected at the 3 time series stations and model algorithms were modified in order to best represent observed differences in export rates between stations. This work highlighted the benefits of adequately describing plankton community structure in models to define the magnitude and structure of particle export. Modelled carbon export was highly sensitive to changes in particle sinking rates. Temporal and spatial variability was achieved when specific sinking rates were assigned to detritus from each community. This resulted in relatively higher export efficiency at PAP site due to the presence of larger plankton. Further improvements to model performance were achieved through adjusting aggregation, mineral ballasting, community specific remineralisation rates and diel vertical migration of zooplankton.
Anders Frugård Opdal (UiB):
Long term shift in cod phenology linked to water clarity and delayed spring bloom onset
Climate warming is known to promote earlier onset of spring activities such as plant flowering, animal migration and breeding. Contrary to these patterns, the high latitude spring bloom system of the North Sea and Norwegian Sea shelf areas appear to have experienced a delay in spring bloom onset by ca 0.5 days year-1 since the 1930s. At high latitudes the available window for timing life history events with resource availability is particularly narrow, and phenological shifts at lower trophic levels is hypothesised to promote trophical mismatch, such as that between food resources and early life stages. However, evidence for this is equivocal, and the role of individual plasticity to accommodate climate variability is poorly understood. Here we show that spawning phenology of the Northeast Arctic cod population is tracing the long-term shift in bloom timing, potentially as far back as the 1870s. Based on weekly fisheries catch and roe landing data we were able to reconstruct a 140 year long time series of seasonal development in female gonad size, which suggest a delay in spawning time matching that of the spring bloom onset. Our result indicate that cod are able to trace seasonal variation in multiple environmental ques and possibly time gonadal development and spawning to maximize overlap between offspring hatch date and predicted resource availability.