M. A. St. John

Modelling the influences of atmospheric forcing conditions on Baltic cod early life stages: distribution and drift

Retention or dispersion of larvae from the spawning ground has been identified as one of the key processes influencing recruitment success in fish stocks. An exercise combining 3-D hydrodynamic model simulations and field data on spatial distributions of juvenile Baltic cod was utilised to investigate the potential drift of larvae from the centre of main spawning effort in the Bornholm Basin, Baltic Sea. In the simulations cod larvae were represented as Lagrangian drifters. Habitats in which larvae and juvenile cod potentially dwell and where juveniles settle were identified to ascertain the importance of predicting transport. The transport of Baltic cod larvae was investigated by detailed drift model simulations for the years 1986 to 1999. The results yielded a clear dependency on wind-induced drift of larval cod, which is mainly controlled by the local atmospheric conditions over the Baltic Sea. Seasonally averaged distributions of drifters were compared with actual distributions of 0-group cod, as determined from bottom and pelagic trawl surveys conducted in autumn of the years 1993 to 2000 in and around the Bornholm Basin. The results suggest that juveniles caught in different areas can be assigned to different times of the spawning season. Because of seasonal differences in the circulation patterns, the southern coastal environment is on average most important for early and late spawners, whereas larvae hatching in mid-summer were on average transported towards the north or to a higher degree remained in the spawning ground.

High export via small particles before the onset of the North Atlantic spring bloom

Sinking organic matter in the North Atlantic Ocean transfers 1-3 Gt carbon year?1 from the surface ocean to the interior. The majority of this exported material is thought to be in form of large, rapidly sinking particles that aggregate during or after the spring phytoplankton bloom. However, recent work has suggested that intermittent water column stratification resulting in the termination of deep convection can isolate phytoplankton from the euphotic zone, leading to export of small particles. We present depth profiles of large (>0.1mm equivalent spherical diameter, ESD) and small ( 300m depth, leading to deep mixing of particles as deep as 600m. Subsequent re-stratification could trap these particles at depth and lead to high particle fluxes at depth without the need for aggregation (‘mixed layer pump). Overall we suggest that pre-bloom fluxes to the mesopelagic are significant, and the role of small sinking particles requires careful consideration. This article is protected by copyright. All rights reserved.

Introduction to the BASIN Special Issue: State of art, past present a view to the future

The starting point for EURO-BASIN were discussions at the EurOcean conference in Hamburg (Germany) in 2000 focusing on perspectives for European and North American research cooperation in the North Atlantic. This conference resulted in a memorandum of understanding signed between the USA National Science Foundation (NSF) and the European Commission (EC), agreeing to support collaborative research in the North Atlantic. However, it was not until 2005 when funds from the USA NSF and the European network of excellence EURO-OCEANS allowed for European, USA and Canadian scientists to meet in Reykjavik, Iceland (Wiebe et al., 2009), to start the process leading to the development of an International North Atlantic Basin scale Science Plan. Subsequently, support for the BASIN community to hold three meetings in 2007–2008 was obtained from the US NSF and a EU 6th Framework Specific Support Action (SSA) BASIN. These meetings, which built upon the issues identified in Reykjavik, were held in Hamburg (Germany), Chapel Hill (USA), and Amsterdam (the Netherlands). The outcome of these meetings was the International BASIN Science Plan, published as a GLOBEC report (Wiebe et al., 2009). Alas, while the science needs were collectively agreed upon, the difficulty of funding coordinating research (both in time and in concept) from both sides of the Atlantic was not easily resolved. Moving ahead, the European Commission issued a call for proposals, which targeted some of the issues outlined in the International BASIN Science Plan. Specifically, the call was focused scientifically “on the need to improve the understanding of the variability, potential impacts, and feedbacks of global change and anthropogenic forcing on the structure, function and dynamics of the ecosystems of the North Atlantic Ocean and associated shelf seas and on their capacity to provide services”. The successful project needed to provide new data, analyses and the models necessary to: (1) Understand and simulate the population structure and dynamics of broadly distributed, and biogeochemically and trophically important plankton and fish species, to resolve the impacts of climate variability on marine ecosystems and the feedbacks to the earth system. (2) Develop understanding and strategies that would contribute to improving and advancing ocean management (ecosystem approach). In response to this call, the successful EURO-BASIN consortium was formed (European Basin Scale Analysis and Synthesis), using as its starting point the BASIN International Science plan. While a similar funding mechanism was not forthcoming from the North American side, North American scientists were able to take advantage of opportunities to participate in EURO-BASIN cruise programs, meetings and to publish joint articles (e.g., this Special Issue).