ALBERT

Description: The relationship of Barents-Kara sea ice concentration in October and November with atmospheric circulation in the subsequent winter is examined using reanalysis and observational data. The analyses are performed on data with the 5-year running means removed to reduce the potential effects of slowly-varying external driving factors, such as global warming. We show that positive (negative) Barents-Kara sea ice concentration anomaly in autumn is associated with a positive (negative) North Atlantic Oscillation-like (NAO) pattern with lags of up to 3 months. The month-to-month variations in the lag relationships of the atmospheric anomalies related to November sea ice concentration are presented. Further analysis shows that the stratosphere-troposphere interaction may provide the memory in the system: positive (negative) sea ice concentration anomaly in November is associated with a strengthened (weakened) stratospheric polar vortex and these anomalies propagate downward leading to the positive (negative) NAO-like pattern in the late December to early January. This stratosphere mechanism may also play a role for Barents-Kara sea ice anomaly in December, but not for September and October. Consistently, Eliassen-Palm, eddy heat and momentum fluxes suggest that there is strong forcing of the zonal winds in November.

Description: In aquatic ecosystems, body size has a remarkable influence on the hierarchical structure of food webs and trophic interactions. The trophic relationship between mosquito larvae and copepods offers an exception to the conspicuous feature that the bigger consumes the smaller. We here address this ecological question by investigating the predation impact of the epibenthic cyclopoid copepod Megacyclops formosanus on a 30-h old mosquito larvae Aedes aegypti in a controlled environment. Our quantitative assessment depicted the effect of M. formosanus on 30-h old mosquito larvae. We found that copepod captured mosquito larvae on an average 1.6 ± 0.20 larvae ind−1 h−1 with an attack speed 22.80 ± 8.52 mm s−1. In addition, copepod predation dramatically affected mosquito behavior. In the presence of predator, mosquito larvae significantly decreased browsing and filtering paths, while using mixed foraging tactics and shifting the habitat use from the bottom to surfacing or air–water interfacing. These results provide a mechanistic understanding of the interaction between mosquito and cyclopoid copepods, and show that copepod predation constrains the habitat use of mosquito larvae. Copepod predation pressure results in reduced facultative behavioral responses that challenge mosquito life history and ultimately percolate its population fitness.

Description: The data from six zonal sections in the World Ocean Circulation Experiment (WOCE) in the tropical and southem Atlantic are used to describe the distribution of water masses. Due to the high spatial resolution, the structure oftemperature, salinity, oxygen, silicate and nitrate displays details related to transport and mixing in this region. Temperature-salinity diagrams are also presented which indicate the effects ofbranching and recirculation loops in the water mass flow.

Description: A set of ensemble integrations from the Coupled Model Intercomparison Project phase 5, with historical forcing plus RCP4.5 scenario, are used to explore if state-of-the-art climate models are able to simulate previously reported linkages between sea-ice concentration (SIC) anomalies over the eastern Arctic, namely in the Greenland–Barents–Kara Seas, and lagged atmospheric circulation that projects on the North Atlantic Oscillation (NAO)/Arctic Oscillation (AO). The study is focused on variability around the long-term trends, so that all anomalies are detrended prior to analysis; the period of study is 1979–2013. The model linkages are detected by applying maximum covariance analysis. As also found in observational data, all the models considered here show a statistically significant link with sea-ice reduction over the eastern Arctic followed by a negative NAO/AO-like pattern. If the simulated relationship is found at a lag of one month, the results suggest that a stratospheric pathway could be at play as the driving mechanism; in observations this is preferentially shown for SIC in November. The interference of a wave-like anomaly over Eurasia, accompanying SIC changes, with the climatological wave pattern appears to be key in setting the mediating role of the stratosphere. On the other hand, if the simulated relationship is found at a lag of two months, the results suggest that tropospheric dynamics are dominant, presumably due to transient eddy feedback; in observations this is preferentially shown for SIC in December. The results shown here and previous evidence from atmosphere-only experiments emphasize that there could be a detectable influence of eastern Arctic SIC variability on mid-latitude atmospheric circulation anomalies. Even if the mechanisms are robust among the models, the timing of the simulated linkages strongly depends on the model and does not generally mimic the observational ones. This implies that the atmospheric sensitivity to sea-ice changes largely depends on the mean-flow and parameterizations, which could lead to misleading conclusions elsewhere if a multi-model ensemble-mean approach is adopted. It might also represent an important source of uncertainty in climate prediction and projection. Modelling efforts are hence further required to improve representation of the background atmospheric circulation and reduce biases, in order to attain more accurate covariability.