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Aim: The Western Antarctic Peninsula is challenged by climate change and increasing maritime traffic that together facilitate the introduction of marine non‐native species from warmer regions neighbouring the Southern Ocean. Ballast water exchange has been frequently reported as an introduction vector. This study uses a Lagrangian approach to model the passive drift of virtual propagules departing from Ballast water hypothetic exchange zones, at contrasting distances from the coasts. Location: Western Antarctic Peninsula. Methods: Virtual propagules were released over the 2008–2016 period and at three distances from the nearest coasts: 200 (convention for the management of Ballast Water, 2004), 50 or 11 nautical miles (NM). Results: Results show that exchanging Ballast water at 200 NM considerably reduces the arrival of propagules in proposed marine protected areas of the western side of the Antarctic Peninsula. On the eastern side, propagules can reach north‐eastern marine protected areas within a few days due to strong currents for all tested scenarios. Seasonal and yearly variations indicate that exceptional climate events could influence the trajectory of particles in the region. Ballast water should be exchanged at least 200 NM offshore on the western side of the Antarctic Peninsula and avoided on the eastern side to limit particle arrival in proposed marine protected areas. Focusing on Deception Island, our results suggested that the Patagonian crab (Halicarcinus planatus) observed in 2010 could have been introduced in case of Ballast water exchange at 50 NM or less from the coast. Main conclusions: This study highlights the importance of respecting Ballast water exchange convention to limit the risk of non‐native species introduction. Ballast water exchange should be operated at least at 200 NM from the coasts, which further limits particle arrival in shallow water areas. This is especially important in the context of a more visited and warmer Southern Ocean. [ABSTRACT FROM AUTHOR]

The potential for biological colonization of Antarctic shores is an increasingly important topic in the context of anthropogenic warming. Successful Antarctic invasions to date have been recorded exclusively from terrestrial habitats. While non‐native marine species such as crabs, mussels and tunicates have already been reported from Antarctic coasts, none have as yet established there. Among the potential marine invaders of Antarctic shallow waters is Halicarcinus planatus (Fabricius, 1775), a crab with a circum‐Subantarctic distribution and substantial larval dispersal capacity. An ovigerous female of this species was found in shallow waters of Deception Island, South Shetland Islands in 2010. A combination of physiological experiments and ecological modelling was used to assess the potential niche of H. planatus and estimate its future southward boundaries under climate change scenarios. We show that H. planatus has a minimum thermal limit of 1°C, and that its current distribution (assessed by sampling and niche modelling) is physiologically restricted to the Subantarctic region. While this species is presently unable to survive in Antarctica, future warming under both 'strong mitigation' and 'no mitigation' greenhouse gas emission scenarios will favour its niche expansion to the Western Antarctic Peninsula (WAP) by 2100. Future human activity also has potential to increase the probability of anthropogenic translocation of this species into Antarctic ecosystems. [ABSTRACT FROM AUTHOR]

Aim: The species of the genus Chionodraco (Notothenioidei) are the most abundant icefish on the continental shelf of the Weddell Sea. While previous studies indicated that only Chionodraco hamatus and Chionodraco myersi inhabit the Weddell Sea, the third Chionodraco species, Chionodraco rastrospinosus, was recently sampled in the area. As C. rastrospinosus is supposed to be found only at the Antarctic Peninsula and Scotia Arc, this study aimed at confirming the species classification of C. rastrospinosus by molecular methods and identifying its putative source population. Given the documented evidence of introgression among the three species, we tested whether the newly found C. rastrospinosus shared any genetic variability with the other Chionodraco species. To explain the pattern of distribution of the Chionodraco species, we aimed at estimating the hydrodynamic connectivity between the Antarctic Peninsula and the Weddell Sea. Location: Antarctic Peninsula, southern Scotia Arc and the south‐eastern Weddell Sea. Methods: We genotyped 19 microsatellites and sequenced the mitochondrial D‐loop for 560 Chionodraco individuals. We simulated the dispersal of more than 3 million drifters (Lagrangian model). Results: The molecular analyses support the presence of C. rastrospinosus in the Weddell Sea and its homogeneity with C. rastrospinosus from the Antarctic Peninsula. Bayesian clustering identifies three putative hybrids among C. rastrospinosus and the other congenerics. Lagrangian simulations do not support connectivity driven by the oceanographic features of the Antarctic Peninsula and Weddell Sea via passive larval dispersal only. Main conclusions: This study documents, for the first time, the presence of C. rastrospinosus in the Weddell Sea unveiling more biodiversity than previously known in this region. The sympatry of the three Chionodraco species explains the occurrence of occasional, ongoing events of hybridization in the genus. Alternative possible hypotheses need to be tested in future studies about the mechanisms maintaining the interspecific connectivity in Chionodraco spp. [ABSTRACT FROM AUTHOR]

Over the last decades, nutrients loading to the sea have significantly increased due to the growing anthropogenic pressure in the river watersheds. Some areas of the English Channel and Southern Bight of the North Sea are particularly affected by the resulting eutrophication nuisances. Establishing the link between these nuisances and anthropogenic activities requires (1) the identification of the major nutrient sources and (2) the assessment of the ecosystem response to these nutrient alterations. A nutrient tracking approach has been implemented in the marine ecological model MIRO&CO to allow tracing marine nitrogen back to its continental sources over 2000–2010. On average, nitrogen atmospheric deposition contributes between 1 and 10 mmol N/m3 to marine nutrients concentrations in the English Channel and Southern Bight of the North Sea. This corresponds to relative contributions between 10 and 30%. River contributions remained localized except for the Seine and small French rivers. Different geographical patterns of sources contribution were found for wet and dry periods. Results also showed different contribution systems between offshore and coastal areas. Relative contributions from nitrogen sources to nutrients and phytoplankton biomass are similar. This study provides useful information to help identifying the causes of marine eutrophication and mitigating its nuisances. [ABSTRACT FROM AUTHOR]

Coastal management and maritime safety strongly rely on accurate representations of the sea state. Both dynamical models and observations provide abundant pieces of information. However, none of them provides the complete picture. The assimilation of observations into models is one way to improve our knowledge of the ocean state. Its application in coastal models remains challenging because of the wide range of temporal and spatial variabilities of the processes involved. This study investigates the assimilation of temperature profiles with the ensemble Kalman filter in 3-D North Sea simulations. The model error is represented by the standard deviation of an ensemble of model states. Parameters' values for the ensemble generation are first computed from the misfit between the data and the model results without assimilation. Then, two square root algorithms are applied to assimilate the data. The impact of data assimilation on the simulated temperature is assessed. Results show that the ensemble Kalman filter is adequate for improving temperature forecasts in coastal areas, under adequate model error specification. [ABSTRACT FROM AUTHOR]

Trends in extreme temperature and precipitation in two regional climate model simulations forced by two global climate models are compared with observed trends over the western United States. The observed temperature extremes show substantial and statistically significant trends across the western United States during the late twentieth century, with consistent results among individual stations. The two regional climate models simulate temporal trends that are consistent with the observed trends and reflect the anthropogenic warming signal. In contrast, no such clear trends or correspondence between the observations and simulations is found for extreme precipitation, likely resulting from the dominance of the natural variability over systematic climate change during the period. However, further analysis of the variability of precipitation extremes shows strong correspondence between the observed precipitation indices and increasing oceanic Niño index (ONI), with regionally coherent patterns found for the U.S. Northwest and Southwest. Both regional climate simulations reproduce the observed relationship with ONI, indicating that the models can represent the large-scale climatic links with extreme precipitation. The regional climate model simulations use the Weather Research and Forecasting (WRF) Model and Hadley Centre Regional Model (HadRM) forced by the ECHAM5 and the Hadley Centre Climate Model (HadCM) global models for the 1970-2007 time period. Comparisons are made to station observations from the Historical Climatology Network (HCN) locations over the western United States. This study focused on temperature and precipitation extreme indices recommended by the Expert Team on Climate Change Detection Monitoring and Indices (ETCCDMI). [ABSTRACT FROM AUTHOR]

Surface temperature, precipitation, specific humidity and wind anomalies associated with the warm and cold phases of ENSO simulated by WRF and HadRM are examined for the present and future decades. WRF is driven by ECHAM5 and CCSM3, respectively, and HadRM is driven by HadCM3. For the current decades, all simulations show some capability in resolving the observed warm-dry and cool-wet teleconnection patterns over the PNW and the Southwest U.S. for warm and cold ENSO. Differences in the regional simulations originate primarily from the respective driving fields. For the future decades, the warm-dry and cool-wet teleconnection patterns in association with ENSO are still represented in ECHAM5-WRF and HadRM. However, there are indications of changes in the ENSO teleconnection patterns for CCSM3-WRF in the future, with wet anomalies dominating in the PNW and the Southwest U.S. for both warm and cold ENSO, in contrast to the canonical patterns of precipitation anomalies. Interaction of anomalous wind flow with local terrain plays a critical role in the generation of anomalous precipitation over the western U.S. Anomalous dry conditions are always associated with anomalous airflow that runs parallel to local mountains and wet conditions with airflow that runs perpendicular to local mountains. Future changes in temperature and precipitation associated with the ENSO events in the regional simulations indicate varying responses depending on the variables examined as well as depending on the phase of ENSO. [ABSTRACT FROM AUTHOR]

This work compares the Weather Research and Forecasting (WRF) and Hadley Centre Regional Model (HadRM) simulations with the observed daily maximum and minimum temperature (Tmax and Tmin) and precipitation at Historical Climatology Network (HCN) stations over the U.S. Pacific Northwest for 2003–07. The WRF and HadRM runs were driven by the NCEP/Department of Energy (DOE) Atmospheric Model Intercomparison Project (AMIP)-II Reanalysis (R-2) data. The simulated Tmax in WRF and HadRM as well as in R-2 compares well with the observations. Predominantly cold biases of Tmax are noted in WRF and HadRM in spring and summer, while in winter and fall more stations show warm biases, especially in HadRM. Large cold biases of Tmax are noted in R-2 at all times. The simulated Tmin compares reasonably well with the observations, although not as well as Tmax in both models and in the reanalysis R-2. Warm biases of Tmin prevail in both model simulations, while R-2 shows mainly cold biases. The R-2 data play a role in the model biases of Tmax, although there are also clear indications of resolution dependency. The model biases of Tmin originate mainly from the regional models. The temporal correlation between the simulated and observed daily precipitation is relatively low in both models and in the reanalysis; however, the correlation increases steadily for longer averaging times. The high-resolution models perform better than R-2, although the nested WRF domains do have the largest biases in precipitation during the winter and spring seasons. [ABSTRACT FROM AUTHOR]