Benthic and substrate cover data derived from a time series of photo-transect surveys for the Eastern Banks, Moreton Bay Australia, 2004-2015

This paper describes seagrass species and percentage cover point-based field data sets derived from georeferenced photo transects. Annually or biannually over a ten year period (2004-2015) data sets were collected using 30-50 transects, 500-800 m in length distributed across a 142 km**2 shallow, clear water seagrass habitat, the Eastern Banks, Moreton Bay, Australia. Each of the eight data sets include seagrass property information derived from approximately 3000 georeferenced, downward looking photographs captured at 2-4 m intervals along the transects. Photographs were manually interpreted to estimate seagrass species composition and percentage cover (Coral Point Count excel; CPCe). Understanding seagrass biology, ecology and dynamics for scientific and management purposes requires point-based data on species composition and cover. This data set, and the methods used to derive it are a globally unique example for seagrass ecological applications. It provides the basis for multiple further studies at this site, regional to global comparative studies, and, for the design of similar monitoring programs elsewhere.

Petrography, chemistry and magnetic properties of ODP Leg 115 basalts

A detailed study of the Fe-Ti oxides in four basalt samples-one from each of the four holes drilled into basement on Ocean Drilling Program Leg 115 (Sites 706, 707, 713, and 715) has been performed. Ilmenite is present only in samples from Sites 706 and 715. In the sample from Site 715, Ti-magnetite intergrowths are characteristic of subaerial (?) high-temperature oxy-exsolution; Ti-magnetite in the other three samples has experienced pervasive low-temperature oxidation to Ti-maghemite, as evidenced by the double-humped, irreversible, saturation magnetization vs. temperature (Js/T) curves. The bulk susceptibility of these samples, which are similar in terms of major element chemistry, varies by a factor of ~20 and correlates semiquantitatively with the modal abundance of Fe-Ti spinel, as determined by image analysis with an electron microprobe. The variation in Fe-Ti oxide abundance correlates with average grain size: fine-grained samples contain less Fe-Ti oxide. This prompts the speculation that the crystallization rate may also influence Fe-Ti oxide abundance.

Sedimentology of cores from the Iberian margin

Bioturbation in marine sediments has basically two aspects of interest for palaeo-environmental studies. First, the traces left by the burrowing organisms reflect the prevailing environmental conditions at the seafloor and thus can be used to reconstruct the ecologic and palaeoceanographic situation. Traces have the advantage over other proxies of practically always being preserved in situ. Secondly, for high- resolution stratigraphy, bioturbation is a nuisance due to the stirring and mixing processes that destroy the stratigraphic record. In order to evaluate the applicability of biogenic traces as palaeoenvironmental indicators, a number of gravity cores from the Portuguese continental slope, covering the period from the last glacial to the present were investigated through X-ray radiographs. In addition, physical and chemical parameters were determined to define the environmental niche in each core interval. A number of traces could be recognized, the most important being: Thalassinoides, Planolites, Zoophycos, Chondrites, Scolicia, Palaeophycus, Phycosiphon and the generally pyritized traces Trichichnus and Mycellia. The shifts between the different ichnofabrics agree strikingly well with the variations in ocean circulation caused by the changing climate. On the upper and middle slope, variations in current intensity and oxygenation of the Mediterranean Outflow Water were responsible for shifts in the ichnofabric. Larger traces such as Planolites and Thalassinoides dominated in coarse, well oxygenated intervals, while small traces such as Chondrites and Trichichnus dominated in fine grained, poorly oxygenated intervals. In contrast, on the lower slope where calm steady sedimentation conditions prevail, changes in sedimentation rate and nutrient flux have controlled variations in the distribution of larger traces such as Planolites, Thalassinoides, and Palaeophycus. Additionally, distinct layers of abundant Chondrites correspond to Heinrich events 1, 2, and 4, and are interpreted as a response to incursions of nutrient rich, oxygen depleted Antarctic waters during phases of reduced thermohaline circulation. The results clearly show that not one single factor but a combination of several factors is necessary to explain the changes in ichnofabric. Furthermore, large variations in the extent and type of bioturbation and tiering between different settings clearly show that a more detailed knowledge of the factors governing bioturbation is necessary if we shall fully comprehend how proxy records are disturbed. A first attempt to automatize a part of the recognition and quantification of the ichnofabric was performed using the DIAna image analysis program on digitized X-ray radiographs. The results show that enhanced abundance of pyritized microburrows appears to be coupled to organic rich sediments deposited under dysoxic conditions. Coarse grained sediments inhibit the formation of pyritized burrows. However, the smallest changes in program settings controlling the grey scale threshold and the sensitivity resulted in large shifts in the number of detected burrows. Therefore, this method can only be considered to be semi-quantitative. Through AMS-^C dating of sample pairs from the Zoophycos spreiten and the surrounding host sediment, age reversals of up to 3,320 years could be demonstrated for the first time. The spreiten material is always several thousands of years younger than the surrounding host sediment. Together with detailed X-ray radiograph studies this shows that the trace maker collects the material on the seafloor, and then transports it downwards up to more than one meter in to the underlying sediment where it is deposited in distinct structures termed spreiten. This clearly shows that age reversals of several thousands of years can be expected whenever Zoophycos is unknowingly sampled. These results also render the hitherto proposed ethological models proposed for Zoophycos as largely implausible. Therefore, a combination of detritus feeding, short time caching, and hibernation possibly combined also with gardening, is suggested here as an explanation for this complicated burrow.

Morphometrics of seagrasses at species level, Moreton Bay, Australia determined from core samples collected in 2012-2013

Seagrass meadows are important marine carbon sinks, yet they are threatened and declining worldwide. Seagrass management and conservation requires adequate understanding of the physical and biological factors determining carbon content in seagrass sediments. Here, we identified key factors that influence carbon content in seagrass meadows across several environmental gradients in Moreton Bay, SE Queensland. Sampling was conducted in two regions: (1) Canopy Complexity, 98 sites on the Eastern Banks, where seagrass canopy structure and species composition varied while turbidity was consistently low; and (2) Turbidity Gradient, 11 locations across the entire bay, where turbidity varied among sampling locations. Sediment organic carbon content and seagrass structural complexity (shoot density, leaf area, and species specific characteristics) were measured from shallow sediment and seagrass biomass cores at each location, respectively. Environmental data were obtained from empirical measurements (water quality) and models (wave height). The key factors influencing carbon content in seagrass sediments were seagrass structural complexity, turbidity, water depth, and wave height. In the Canopy Complexity region, carbon content was higher for shallower sites and those with higher seagrass structural complexity. When turbidity varied along the Turbidity Gradient, carbon content was higher at sites with high turbidity. In both regions carbon content was consistently higher in sheltered areas with lower wave height. Seagrass canopy structure, water depth, turbidity, and hydrodynamic setting of seagrass meadows should therefore be considered in conservation and management strategies that aim to maximize sediment carbon content.