ALBERT

Description: The scientific work during SO242/2 (28. August - 01. October 2015) was part of the JPIO Pilot Action ‘Ecological Aspects of Deep-Sea Mining‘. The main goal was to study the potential long-term ecological impact of anthropogenic disturbances on the deep-sea floor from mining polymetallic Mn-nodules. The expedition SO242 built on studies of the former German TUSCH projects (1989-1996) with four RV SONNE cruises to the DISCOL Experimental Area in the Peru Basin, South Pacific (7°S, 88.5° W; 4150 m water depth) between 1989 and 1996 (DISCOL and ATESEPP projects). The integrated ecological studies were carried out within and next to plough tracks of the original DISCOL experiment 1989, which mimicked seafloor disturbances similar to those occurring during nodule mining. Leg 242/2 extended the investigations started during leg 242/1 with a focus on biogeochemical and biological sampling and observations, including comparative studies of the composition of benthic communities (all size classes) as well as of ecosystem functions (remineralization rates, transfer of matter and energy in food webs, ecotoxicology). In addition, observations were continued of the physicochemical characteristics of the DEA, including the overlying benthic boundary layer. The nodule fields surrounding the DEA were used as references for undisturbed areas. A large proportion of the work was based on autonomous instruments and sensor modules that were deployed by means of ROV and lander systems. In addition, ROV-manipulated and telemetryguided instruments such as the Ocean Floor Observatory System were used for targeted sampling and surveys. Food-web experiments including some small-scale disturbances were carried out and sampled directly at the seafloor by the ROV.

Description: The cruise SO239 EcoResponse took place between 11th of March and 30th of April 2015. Aim of the cruise was to study the biodiversity, geological and geochemical settings across a productivity gradient in the CCZ. Also to study the genetic connectivity between distant deepsea populations, to compare the fauna from seamounts with the fauna living attached to the nodules and to sample an APEI for the first time. The AUV was used to test the usefulness of photographic and side-scan sonar survey for future monitoring of mining activities. We visited 6 working areas in 4 ISA contractor areas (from BGR, IOM, DEME, Ifremer) and the APEI number 3. On all sites sediment samples were taken with the Multicorer, Box-Corer and Gravity Corer. Additionally epibenthic fauna and scavengers were sampled with the Epibenthic Sledge and Amphipod Trap, respectively. CTD cast and water samples were taken on each of the areas. An AUV was used to perform detail bathymetric mapping in addition to side-scan sonar and photographic surveys. ROV was used to sample megafauna organisms, to sample sediments inside dredge tracks, and to perform video transect.

Description: As a result of the raising CO2-emissions and the resultant ocean acidification (decreasing pH and carbonate ion concentration), the impact on marine organism that build their skeletons and protective shells with calcium carbonate (e.g., mollusks, sea urchins, coccolithophorids, and stony corals) becomes more and more detrimental. In the last few years, many experiments with tropical reef building corals have shown, that a lowering of the carbonate ion concentration significantly reduces calcification rates and therefore growth (e.g., Gattuso et al. 1999; Langdon et al. 2000, 2003; Marubini et al. 2001, 2002). In the middle of this century, many tropical coral reefs may well erode faster than they can rebuild. Cold-water corals are living in an environment (high geographical latitude, cold and deep waters) already close to a critical carbonate ion concentration below calcium carbonate dissolves. Actual projections indicate that about 70% of the currently known Lophelia reef structures will be in serious danger until the end of the century (Guinotte et al. 2006). Therefore L. pertusa was cultured at GEOMAR to determine its long-term response to ocean acidification. Our work has revealed that – unexpectedly and controversially to the majority of warm-water corals – this species is potentially able to cope with elevated concentrations of CO2. Whereas short-term (1 week) high CO2 exposure resulted in a decline of calcification by 26-29 % for a pH decrease of 0.1 units and net dissolution of calcium carbonate, L. pertusa was capable to acclimate to acidified conditions in long-term (6 months) incubations, leading to slightly enhanced rates of calcification (Form & Riebesell, 2012). But all these studies were carried out in the laboratory under controlled conditions without considering natural variability and ecosystem interactions with the associated fauna. Moreover, only very little is known about the nutrition (food sources and quantity) of cold-water corals in their natural habitat. In a multifactorial laboratory study during BIOACID phase II we could show that food availability is one of the key drivers that promote the capability of these organisms to withstand environmental pressures such as alterations in the carbonate chemistry and temperature (Büscher, Form & Riebesell, in prep.). To take into account the influences of natural fluctuations and interactions (e.g. bioerosion), we aim to merge in-situ results from the two research cruises POS455 and POS473 with laboratory experimental studies for a comprehensive understanding of likely ecosystem responses under past, present and future environmental conditions.

Description: Cruise SO242/1 ran from 28 July to 25 August 2015 starting and ending in Guayaquil, Ecuador. In total, 40 scientists from five European countries took part in this cruise of the JPIO project ‚Ecological Aspects of Deep‐Sea Mining‘ to study the ecological long‐term impact of deep sea disturbances. The working area, the DISCOL area in the Peru Basin, was ploughed in 1989 and thoroughly studied in the years thereafter, the last cruise, SO106, happened in 1996. SO242/2 aimed at mapping the DISCOL Experimental Area (DEA) in great detail using ship‐based and AUV‐based hydroacoustic and optical methods. To see changes between differently disturbed areas and study the possible recovery of the ecosystem, biological sampling occurred with TV‐guided multi‐coring (MUC), box coring (BC) and epi‐benthic sledge tracks (EBS). Additional biological sampling for scavenging animals occurred with baited Amphipod‐Traps within and further outside the DEA. For geochemical sampling, multi‐, box and gravity coring (BC) was used. Two lander systems equipped with physical sensors such as ADCPs and CTDs were used for current measurements and to monitor sediment plume dispersal created by the EBS. Additional visual studies of the fauna distribution occurred with camera tows (OFOS). Five main sampling areas were selected, two within the DEA targeting heavily disturbed (ploughed) locations and three reference areas 3 to 4 nmi outside the DEA. All five areas had been sampled in the past and can be directly compared concerning ecological changes. Despite a four‐day break due to medical reasons the work program could almost be completed. Four of the working areas were at least sampled with five BCs and MUCs each, and one GC. Box coring could not be performed in the western reference area. In total, 5 CTDs, 27 MUCs, 25 BCs, 7 GCs, 8 EBSs, 5 Amphipod‐Traps, 6 lander deployments and 6 OFOS tracks were successfully undertaken and one thermistor mooring was deployed. In addition, 16 AUV dives clearly showed that plough marks are still well visible after 26 years. There is a slight sediment cover next to the plough tracks, but first analyses of the faunal distribution show that the sessile fauna has not yet recolonised the tracks. Stalked sponges, corals and anemones can be found outside the tracks but still within the DEA. Their distribution patterns inside the DEA do not vary clearly from those on reference sites. The Mn‐nodule distribution is not homogenous; there are areas inside the DEA that do not have nodules at the seafloor surface; they are typically linked to depressions that show low backscatter intensity in the AUV side scan sonar data pointing towards less dense sediment infill. In gravity cores, nodules could be recovered even in 9m sediment depth, finding several more or less intact nodules throughout the entire sediment column was common. Water current measurements show slow currents (max. 6cm/s) and a strong tide‐influenced current direction, whereas no general direction could be observed. Two ‘disturbance experiments’ demonstrated that sediment plumes can be monitored using high frequency ADCPs (1200 kHz). The disturbance by the EBS created a sediment plume that stayed close to the seafloor. First analyses of current trajectories showed that the sediment resettled rather quickly. It became clear that plume behaviour during large‐scale mining cannot be extrapolated from these small‐scale and short‐term experiments. In resume, cruise SO242/1 was very successful and research should continue in the DEA area, which is undoubtedly the best studied long‐term deep sea disturbance site in the ocean.