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A high-resolution multiproxy geochemical approach was applied to the sediments of Laguna Potrok Aike in an attempt to reconstruct moist and dry periods during the past 16 000 years in southeastern Patagonia. The age-depth model is inferred from AMS 14 C dates and tephrochronology, and suggests moist conditions during the Lateglacial and early Holocene (16 000-8700 cal. BP) interrupted by drier conditions before the beginning of the Holocene (13 200-11 400 cal. BP). Data also imply that this period was a major warm phase in southeastern Patagonia and was approximately contemporaneous with the Younger Dryas chronozone in the Northern Hemisphere (12 700-11 500 cal. BP). After 8650 cal. BP a major drought may have caused the lowest lake level of the record. Since 7300 cal. BP, the lake level rose and was variable until the 'Little Ice Age', which was the dominant humid period after 8650 cal. BP.

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Particulate (POM) and dissolved organic matter (DOM) released by the cold water corals Lophelia pertusa (L.) and Madrepora oculata (L.) was collected, analysed and quantitatively compared to that released by warm water reef-building corals. Particulate nitrogen (PN) and particulate organic carbon (POC) release rates of L. pertusa were 0.14 ± 0.07 mg N m -2 h -1 and 1.43 ± 1.22 mg C m -2 h -1, respectively, which is in the lower range of POM release rates measured for warm water corals, while dissolved organic carbon (DOC) release was 47 ± 19 mg C m -2 h -1. The resulting high DOC:POC ratio indicates that most cold water coral-derived organic matter immediately dissolved in the water column. Cold water corals, similar to their warm water counterparts, produced large amounts of nitrogen-rich coral mucus with C:N ratios of 5 to 7 for Lophelia-and 7 to 9 for Madrepora-derived mucus. A 7-fold increase in the oxygen consumption rates in cold water coral mucus-amended seawater containing the natural microbial assemblage indicates that this organic matter provided an attractive food source for pelagic microbes. In situ investigations at Røst Reef, Norway, showed that microbial activity in the seawater closest to the reef was 10 times higher than in the overlying water column. This suggests that cold water corals can stimulate microbial activity in the direct reef vicinity by the release of easily degradable and nutrient-rich organic matter, which may thereby function as a vector for carbon and nutrient cycling via the microbial loop in cold water coral reef systems. KEY WORDS: Coral reefs · Cold water corals · Lophelia pertusa · Madrepora oculata · Organic matter release · Microbial ecology · Fauna-microbe interaction Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 372: [67][68][69][70][71][72][73][74][75] 2008 products and mucus (e.g. Harrison et al. 1984, Crossland 1987, in dissolved (Ferrier-Pages et al. 1998) or particulate form into their surroundings. The release of organic matter by corals makes an important contribution to the ecological functioning of tropical coral reefs by controlling key processes such as the transport of organic matter. This, in turn, may influence planktonic and benthic metabolism as well as the associated recycling of essential elements. Mass release of eggs and sperm during the annual coral spawning event can have extensive biogeochemical consequences (Wild et al. 2004c, Eyre et al. 2008, Glud et al. 2008. Furthermore, mucus continuously released by tropical corals can act as an energy carrier and particle trap (Wild et al. 2004a) and consequently initiates element cycling and interaction between fauna and microorganisms in tropical reef ecosystems. Within this context, coral-derived mucus can strongly influence planktonic microbial metabolism (Ferrier-Pages et al. 2000), microbial abundance (Wild et al. 2004b) and microbial community composition (Allers et al. 2008).Cold water coral reefs exist in different environmental sett...