Reconstruction of seasonal temperature variability in the tropical Pacific Ocean from the shell of the scallop, Comptopallium radula

We investigated the oxygen isotope composition (δ¹⁸O) of shell striae from juvenile Comptopallium radula (Mollusca; Pectinidae) specimens collected live in New Caledonia. Bottom-water temperature and salinity were monitored in-situ throughout the study period. External shell striae form with a 2-day periodicity in this scallop, making it possible to estimate the date of precipitation for each calcite sample collected along a growth transect. The oxygen isotope composition of shell calcite (δ¹⁸O_{shell calcite}) measured at almost weekly resolution on calcite accreted between August 2002 and July 2003 accurately tracks bottom-water temperatures. A new empirical paleotemperature equation for this scallop species relates temperature and δ¹⁸O_{shell calcite}:

t(°C)=20.00(±0.61)-3.66(±0.39)×(δ¹⁸O_{shell calcite VPDB}-δ¹⁸O_{water VSMOW})     

Particle fluxes and recent sediment accumulation on the Aquitanian margin of Bay of Biscay

As a part of the ANR-Forclim experiment, particle mass fluxes and sedimentation processes were investigated on the slope of Aquitanian margin of the Bay of Biscay, between the canyons of Cap-Breton and Cap-Ferret. Interface sediments were collected along a depth transect from 145 to 2000 m; simultaneously a mooring line was deployed at the deepest station (WH, 2000 m) with two traps (800 and 1700 m) for a 16-month period (June 2006–November 2007). ²¹⁰Pb activities of settling particles and of interface sediments were determined to study transport processes of particles. Sediment and mass accumulation rates, calculated from excess ²¹⁰Pb profiles in the sediment column, show the expected decreasing trend with depth, as usually observed on margins. Mean particulate mass fluxes at 800 and 1700-m depth at site WH are, respectively, 27 and 70 g m^?2 a^?1.The ²¹⁰Pb budget points out events of temporary high lateral input of particles. The comparison of mass and ²¹⁰Pb fluxes between the water column and the seabed indicates that lateral transport plays an important role in particle accumulation on the Aquitanian margin. Regarding the objectives of the ANR-Forclim program, which aims to improve significantly the interpretation of fossil foraminifera signals, as a proxy for hydrological changes in the North Atlantic ocean, these results highlight advection processes must be considered when interpreting fluxes of foraminifers on the Aquitanian margin.     

Lower and Middle Pleistocene human settlements recorded in fluvial deposits of the middle Loire River Basin,Centre Region,France

This paper records the findings from c. 80 prehistoric sites that have been discovered in the alluvial deposits of the rivers Creuse, Cher, and Loir, tributaries of the middle Loire River, over the period since 1981. These deposits comprise river terrace aggradations formed during successive glacial–interglacial cycles which have recorded climate and environment during Quaternary time. The systematic dating of these river deposits by Electron Spin Resonance (ESR) applied to optically bleached sedimentary quartz has resulted in the establishment of a chronological framework for the evolution of these rivers during Lower and Middle Pleistocene (between 1.7 Ma and 130 ka). Evidence for Early Palaeolithic (Mode 1) industries with an in situ context (workshops, soils) in the highest aggradations indicates that Hominins were present in the study area, near the geographical centre of France (47°N), around 1.1 Ma. Examination of the sites indicates that Human occupations were located along valley bottom sites during temperate episodes. Subsequently, after a gap of several hundred thousand years industries with handaxes appear in the Middle Loire Basin in the interval between 700 and 600 ka, and then continuously from 400 ka. These two phases of settlement produced industrial assemblages with clear differences in their responses to the supplies of raw materials and in the modes of making flakes.     

Enhanced Atlantic Meridional Overturning Circulation supports the Last Glacial Inception

The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the climate system. However, its role during climate change is still poorly constrained particularly during an Interglacial to Glacial climate transition and the associated global cooling. We present here the first reconstruction of the evolution of the vertical structure of the rate of the AMOC from the Last Interglaciation to the subsequent glaciation (128,000–60,000 years ago) based on sedimentary (²³¹Pa/²³⁰Th) records. We show a deep AMOC during the interglacial warmth Marine Isotope Stage (MIS) 5.5 and a shallower glacial one during glacial MIS 4. The change between these two patterns occurred mostly during the glacial inception, i.e. the transition from MIS 5.5 to MIS 5.4. Our data show that AMOC was enhanced during this latter transition as a consequence of a large increase of the overturning rate of the Intermediate Waters, above 2500 m. We suggest that this AMOC pattern required a reinforced Gulf Stream-North Atlantic Current system that ultimately supported ice-sheet growth by providing heat and moisture to the Northern high latitudes. From MIS 5.4 to MIS 5.1, the AMOC was broadly continuous below 2000 m and supported periods of ice-sheet growth. As a result, a glacial AMOC is triggered at the beginning of MIS 4 due to the extension of ice-sheet and the subsequent reorganization of deep-water formation. This study highlights the role of intermediate waters as a major player during climate change.     

The effects of altered freshwater inflows on catch rates of non-estuarine-dependent fish in a multispecies nearshore linefishery

In KwaZulu-Natal on the east coast of South Africa, the commercial and recreational boat-based linefishery is the largest fishery accounting for 1235 t (40%) of the total landed mass there. In particular, the Thukela Banks are where most fishing takes place. Numerous developments ranging from dams to inter-basin transfer schemes either exist or have been proposed for the Thukela River, which is the largest of 17 catchments entering the sea in the region and provides over 40% of the mean annual runoff. Exploratory analyses of the relationships between monthly flows and catch-per-unit-effort were performed using spectral analysis and general linear models on a data set comprising 17 years of monthly commercial catch-and-effort data for 140 species and monthly flow data from 17 catchments. Catchments having a significant influence on catches were those providing the bulk of the runoff volume (75%) reaching the sea. Significant relationships existed between flow and the catches of 14 species, which provided over 90% of the total linefish catch on the Thukela Banks. Time lags between flow events (wet and drought periods) and changes in catch-per-unit-effort corresponded in many cases to age at 50% maturity and/or age-at-first-capture of the species concerned. Under a future maximum-development scenario, corresponding to a 44% reduction in flow from the Thukela River, catches of slinger Chrysoblephus puniceus and squaretail kob Argyrosomus thorpei are forecast to decline by 36% and 28% respectively. These two species currently provide over 50% of the landed mass on the Thukela Banks. Some species should respond positively to a reduction in flow, but any increases in their catches will be negligible, falling within natural variability, and will be insufficient to offset losses of other species because their abundance is naturally low or has been fished down to low levels. National legislation requires that sufficient freshwater flows be set aside to protect ecosystems, so these findings have important management implications, as marine needs for freshwater flows have not previously been addressed.     

Recruitment patterns of young-of-the-year mugilid fishes in a West African estuary impacted by climate change

With the persistence of the sub-Saharan drought since the 1970s, the Sine Saloum estuary (Senegal) – the second largest coastal Biosphere Reserve of West-Africa – has become an “inverse estuary” and hypersaline (salinity > 60) in its upstream part. A one-year survey was conducted from April 2007 to March 2008 at eight sites distributed along the salinity gradient, to investigate the recruitment patterns of young-of-the-year mugilids in such an impacted ecosystem. Fishes were sampled monthly with a conical net and a beach seine in salinities ranging from 31 to 104. Samples were identified to the species level. For the smallest individuals (<20 mm SL) a PCR–RFLP technique, developed on the mitochondrial 16S ribosomal RNA region, was used for identification. A total of 8438 juveniles belonging to six of the eight species of mugilids known for the tropical Eastern Atlantic were collected: Mugil bananensis, Mugil cephalus, Mugil curema, Liza dumerili, Liza falcipinnis and Liza grandisquamis. One species, L. dumerili, represented 89% of the total catch. Length–frequency distributions revealed that M. cephalus and L. dumerili preferentially recruited during the dry season whereas the recruitment of M. curema, M. bananensis and L. falcipinnis generally occurred during the wet season. Minimal size at recruitment ranged from 9 to 19 mm SL depending on the species, the smallest size being that of L. dumerili. Despite the general salinity increase in the estuary, most parts of the Sine Saloum were suitable for the juveniles. Only the hypersaline area in the uppermost part of the estuary presented very low fish abundance for all species. According to the species, small recruits (12–20 mm SL) were collected at salinities up to 47–78, suggesting that osmoregulatory capacities had been gained early during ontogenesis, possibly resulting from an adaptation of these populations to changing environmental conditions.     

Cryptic metasomatic agent measured in situ in Variscan mantle rocks: Melt inclusions in garnet of eclogite,Granulitgebirge, Germany

Garnet of eclogite (formerly termed garnet clinopyroxenite) hosted in lenses of orogenic garnet peridotite from the Granulitgebirge, NW Bohemian Massif, contains unique inclusions of granitic melt, now either glassy or crystallized. Analysed glasses and re-homogenized inclusions are hydrous, peraluminous, and enriched in highly incompatible elements characteristic of the continental crust such as Cs, Li, B, Pb, Rb, Th, and U. The original melt thus represents a pristine, chemically evolved metasomatic agent, which infiltrated the mantle via deep continental subduction during the Variscan orogeny. The bulk chemical composition of the studied eclogites is similar to that of Fe-rich basalt and the enrichment in LILE and U suggest a subduction-related component. All these geochemical features confirm metasomatism. In comparison with many other garnet+clinopyroxene-bearing lenses in peridotites of the Bohemian Massif, the studied samples from Rubinberg and Klatschmühle are more akin to eclogite than pyroxenites, as reflected in high jadeite content in clinopyroxene, relatively low Mg, Cr, and Ni but relatively high Ti. However, trace elements of both bulk rock and individual mineral phases show also important differences making these samples rather unique. Metasomatism involving a melt requiring a trace element pattern very similar to the composition reported here has been suggested for the source region of rocks of the so-called durbachite suite, that is, ultrapotassic melanosyenites, which are found throughout the high-grade Variscan basement. Moreover, the Th, U, Pb, Nb, Ta, and Ti patterns of these newly studied melt inclusions (MI) strongly resemble those observed for peridotite and its enclosed pyroxenite from the T-7 borehole (Staré, České Středhoři Mountains) in N Bohemia. This suggests that a similar kind of crustal-derived melt also occurred here. This study of granitic MI in eclogites from peridotites has provided the first direct characterization of a preserved metasomatic melt, possibly responsible for the metasomatism of several parts of the mantle in the Variscides.