Abstract
Abstract. One of the great challenges in ocean change research is to understand and forecast the effects of environmental changes on pelagic communities and the associated impacts on biogeochemical cycling. Mesocosms, experimental enclosures designed to approximate natural conditions, and in which environmental factors can be manipulated and closely monitored, provide a powerful tool to close the gap between small-scale laboratory experiments and observational and correlative approaches applied in field surveys. Existing pelagic mesocosm systems are stationary and/or restricted to well-protected waters. To allow mesocosm experimentation in a range of hydrographic conditions and in areas considered most sensitive to ocean change, we developed a mobile sea-going mesocosm facility, the Kiel Off-Shore Mesocosms for Future Ocean Simulations (KOSMOS). The KOSMOS platform, which can be transported and deployed by mid-sized research vessels, is designed for operation in moored and free-floating mode under low to moderate wave conditions (up to 2.5 m wave heights). It encloses a water column 2 m in diameter and 15 to 25 m deep (∼50–75 m3 in volume) without disrupting the vertical structure or disturbing the enclosed plankton community. Several new developments in mesocosm design and operation were implemented to (i) minimize differences in starting conditions between mesocosms, (ii) allow for extended experimental duration, (iii) precisely determine the mesocosm volume, (iv) determine air–sea gas exchange, and (v) perform mass balance calculations. After multiple test runs in the Baltic Sea, which resulted in continuous improvement of the design and handling, the KOSMOS platform successfully completed its first full-scale experiment in the high Arctic off Svalbard (78°56.2′ N, 11°53.6′ E) in June/July 2010. The study, which was conducted in the framework of the European Project on Ocean Acidification (EPOCA), focused on the effects of ocean acidification on a natural plankton community and its impacts on biogeochemical cycling and air–sea exchange of climate-relevant gases. This manuscript describes the mesocosm hardware, its deployment and handling, CO2 manipulation, sampling and cleaning, including some further modifications conducted based on the experiences gained during this study.
Highlights
Ocean ScienceOf the more than 260 scientific papers published until now on ocean acidification and its impacts on marine life less than 5 % have been conducted on communities or ecosystems, with the vast majority of studies performed on individual species (Gattuso and Hansson, 2011)
To allow mesocosm experimentation in a range of hydrographic conditions and in areas considered most sensitive to ocean change, we developed a mobile sea-going mesocosm facility, the Kiel Off-Shore Mesocosms for Future Ocean Simulations (KOSMOS)
Studies at volcanic CO2 vents have revealed drastic changes in benthic community composition and biodiversity when compared to adjacent areas not exposed to high CO2 (Barry et al, 2011)
Summary
Of the more than 260 scientific papers published until now on ocean acidification and its impacts on marine life less than 5 % have been conducted on communities or ecosystems, with the vast majority of studies performed on individual species (Gattuso and Hansson, 2011). Enclosure effects may influence food web dynamics to varying degrees, creating trophic interactions that can differ with mesocosm dimension and which may deviate from those of the natural system intended to be mimicked (Kuiper et al, 1983; French and Watts, 1989, Petersen et al, 2009). Despite these difficulties and the intense debate they have spurred over the past decades (e.g. Pilson and Nixon, 1980; Brockmann, 1990; Drenner and Mazumber, 1999), mesocosm enclosure studies still remain the most generally applicable means to experimentally manipulate and repeatedly sample multi-trophic planktonic communities. The new design in combination with new developments in mesocosm handling and sampling are intended to optimize mesocosm performance, prolong the duration of mesocosm experiments, and perform mass balance calculations by accounting for all relevant pools and fluxes of elements and compounds of interest
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