Benthic isopod species in the Ross Sea and their distribution in the Southern Ocean

In this study isopod species of the Ross Sea were investigated. Literature until May 2008 was checked to provide an overview of all known and described species in the Ross Sea. This species checklist was then enlarged through material of the 19th Italica expedition in 2004. During this expedition for the first time a small mesh net (500 µm) was used. Nine thousand four hundred and eighty one isopod specimens were collected during this expedition. Through this material the number of isopod species in the Ross Sea increased from 42 to 117 species, which belong to 20 families and 49 genera. Fifty-six percentage of the isopods species collected during the Italica expedition are new to science. The zoogeography of the 117 species was investigated. A non-transformed binary presence-absence data matrix was constructed using the Bray-Curtis coefficient. The results were displayed in a cluster analysis and by nonmetric multidimensional scaling (MDS). This paper gives a first insight into the occurrence and distribution of the isopod species of the Ross Sea.

Literature review of elasmobranch bycatch and retention rate

To address growing concern over the effects of fisheries non-target catch on elasmobranchs worldwide, the accurate reporting of elasmobranch catch is essential. This requires data on a combination of measures, including reported landings, retained and discarded non-target catch, and post-discard survival. Identification of the factors influencing discard vs. retention is needed to improve catch estimates and to determine wasteful fishing practices. To do this we compared retention rates of elasmobranch non-target catch in a broad subset of fisheries throughout the world by taxon, fishing country, and gear. A regression tree and random forest analysis indicated that taxon was the most important determinant of retention in this dataset, but all three factors together explained 59% of the variance. Estimates of total elasmobranch removals were calculated by dividing the FAO global elasmobranch landings by average retention rates and suggest that total elasmobranch removals may exceed FAO reported landings by as much as 400%. This analysis is the first effort to directly characterize global drivers of discards for elasmobranch non-target catch. Our results highlight the importance of accurate quantification of retention and discard rates to improve assessments of the potential impacts of fisheries on these species.

Geochemical analysis of nine sections from the Nama Group, Namibia

The first appearance of skeletal metazoans in the late Ediacaran (~550 million years ago; Ma) has been linked to the widespread development of oxygenated oceanic conditions, but a precise spatial and temporal reconstruction of their evolution has not been resolved. Here we consider the evolution of ocean chemistry from ~550 to ~541 Ma across shelf-to-basin transects in the Zaris and Witputs Sub-Basins of the Nama Group, Namibia. New carbon isotope data capture the final stages of the Shuram/Wonoka deep negative C-isotope excursion, and these are complemented with a reconstruction of water column redox dynamics utilising Fe-S-C systematics and the distribution of skeletal and soft-bodied metazoans. Combined, these inter-basinal datasets provide insight into the potential role of ocean redox chemistry during this pivotal interval of major biological innovation. The strongly negative d13C values in the lower parts of the sections reflect both a secular, global change in the C-isotopic composition of Ediacaran seawater, as well as the influence of 'local' basinal effects as shown by the most negative d13C values occurring in the transition from distal to proximal ramp settings. Critical, though, is that the transition to positive d13C values postdates the appearance of calcified metazoans, indicating that the onset of biomineralization did not occur under post-excursion conditions. Significantly, we find that anoxic and ferruginous deeper water column conditions were prevalent during and after the transition to positive d13C that marks the end of the Shuram/Wonoka excursion. Thus, if the C isotope trend reflects the transition to global-scale oxygenation in the aftermath of the oxidation of a large-scale, isotopically light organic carbon pool, it was not sufficient to fully oxygenate the deep ocean. Both sub-basins reveal highly dynamic redox structures, where shallow, inner ramp settings experienced transient oxygenation. Anoxic conditions were caused either by episodic upwelling of deeper anoxic waters or higher rates of productivity. These settings supported short-lived and monospecific skeletal metazoan communities. By contrast, microbial (thrombolite) reefs, found in deeper inner- and mid-ramp settings, supported more biodiverse communities with complex ecologies and large skeletal metazoans. These long-lived reef communities, as well as Ediacaran soft-bodied biotas, are found particularly within transgressive systems, where oxygenation was persistent. We suggest that a mid-ramp position enabled physical ventilation mechanisms for shallow water column oxygenation to operate during flooding and transgressive sea-level rise. Our data support a prominent role for oxygen, and for stable oxygenated conditions in particular, in controlling both the distribution and ecology of Ediacaran skeletal metazoan communities.

Species abundance and water and sediment characteristics for three ANDEEP stations on Maud Rise and the Weddell Sea

The benthic fauna was investigated during the expedition ANT-XXIV/2 (2007/08) in relation to oceanographic features, biogeochemical properties and sediment characteristics, as well as the benthic, pelagic and air-breathing fauna. The results document that Maud Rise (MR) differs distinctly from surrounding deep-sea basins investigated during previous Southern Ocean expeditions (ANDEEP 2002, 2005). Considering all taxa, the overall similarity between MR and adjacent stations was low (~20% Bray-Curtis-Similarity), and analyses of single taxa show obvious differences in species composition, abundances and densities. The composition and diversity of bivalves of MR are characterised by extremely high abundances of three species, especially the small sized Vesicomya spp. Exceptionally high gastropod abundance at MR is due to the single species Onoba subantarctica wilkesiana, a small brooder that may prey upon abundant benthic foraminiferas. The abundance and diversity of isopods also show that one family, Haplomunnidae, occurs with a surprisingly high number of individuals at MR while this family was not found at any of the 40 bathyal and abyssal ANDEEP stations. Similarly, polychaetes, especially the tube-dwelling, suspension-feeder fraction, are represented by species not found at the comparison stations. Sponges comprise almost exclusively small specimens in relatively high numbers, especially a few species of Polymastiidae. Water-column sampling from the surface to the seafloor, including observations of top predators, indicate the existence of a prospering pelagic food web. Local concentrations of top predators and zooplankton are associated with a rich ice-edge bloom located over the northern slope of MR. There the sea ice melts, which is probably accelerated by the advection of warm water at intermediate depth. Over the southern slope, high concentrations of Antarctic krill (Euphausia superba) occur under dense sea ice and attract Antarctic Minke Whales (Balaenoptera bonaerensis) and several seabird species. These findings suggest that biological prosperity over MR is related to both oceanographic and sea-ice processes. Downward transport of the organic matter produced in the pelagic realm may be more constant than elsewhere due to low lateral drift over MR.

North Atlantic IODP Site 303-U1308 Middle Pleistocene Heinrich Events record

Heinrich events are well documented for the last glaciation, but little is known about their occurrence in older glacial periods of the Pleistocene. Here we report scanning XRF and bulk carbonate d18O results from Integrated Ocean Drilling Program Site U1308 (reoccupation of Deep Sea Drilling Project Site 609) that are used to develop proxy records of ice-rafted detritus (IRD) for the last ~1.4 Ma. Ca/Sr is used as an indicator of IRD layers that are rich in detrital carbonate (i.e., Heinrich layers), whereas Si/Sr reflects layers that are poor in biogenic carbonate and relatively rich in detrital silicate minerals. A pronounced change occurred in the composition and frequency of IRD at ~640 ka during marine isotope stage (MIS) 16, coinciding with the end of the middle Pleistocene transition. At this time, "Hudson Strait" Heinrich layers suddenly appeared in the sedimentary record of Site U1308, and the dominant period of the Si/Sr proxy shifted from 41 ka prior to 640 ka to 100 ka afterward. The onset of Heinrich layers during MIS 16 represents either the initiation of surging of the Laurentide Ice Sheet (LIS) off Hudson Strait or the first time icebergs produced by this process survived the transport to Site U1308. We speculate that ice volume (i.e., thickness) and duration surpassed a critical threshold during MIS 16 and activated the dynamical processes responsible for LIS instability in the region of Hudson Strait. We also observe a strong coupling between IRD proxies and benthic d13C variation at Site U1308 throughout the Pleistocene, supporting a link between iceberg discharge and weakening of thermohaline circulation in the North Atlantic.