Mortality rates in by-caught loggerhead turtle Caretta caretta in the Mediterranean Sea and implications for the Atlantic populations

Reliable estimates of the post-release mortality probability of marine turtles after incidental by-catch are essential for assessing the impact of longline fishing on these species.Large numbers of loggerhead turtles Caretta caretta from rookeries in the northwestern Atlantic Ocean have been by-caught annually in the southwestern Mediterranean Sea since the 1980s, but nothing is known about their post-release mortality probability under natural conditions. Pop-up archival transmitting tags were attached to 26 loggerhead turtles following incidental capture by Spanish longliners. Hooks were not removed, and 40 cm of line was left in place. The post-release mortality probability during the 90 d following release ranged from 0.308 to 0.365, and was independent of hook location. When the post-release mortality probability was combined with previously reported estimates of the mortality probability before hauling, the aggregated by-catch mortality probability ranged from 0.321 to 0.378. Assuming a total annual by-catch of 10656 loggerhead turtles by the Spanish longline fleet operating in the southwestern Mediterranean, by-catch results in 3421 to 4028 turtle deaths annually. This range is equivalent to 8.5−10.1% of the approximately 40000 turtles inhabiting the fishing grounds used by Spanish longliners, most of them from rookeries in the northwestern Atlantic. As a consequence, the accumulated mortality during the oceanic stage is expected to be larger for those loggerhead turtles of Atlantic origin that spend several years in the Mediterranean Sea than for turtles of the same cohort that remain in the Atlantic. For this reason, the Mediterranean can be considered a dead end for loggerhead turtle populations nesting in the Atlantic, although the actual demographic relevance of by-catch mortality of loggerhead turtles in the Mediterranean remains unknown.

Reexposure and advection of C-14-depleted organic carbon from old deposits at the upper continental slope

Outcrops of old strata at the shelf edge resulting from erosive gravity-driven flows have been globally described on continental margins. The reexposure of old strata allows for the reintroduction of aged organic carbon (OC), sequestered in marine sediments for thousands of years, into the modern carbon cycle. This pool of reworked material represents an additional source of C-14-depleted organic carbon supplied to the ocean, in parallel with the weathering of fossil organic carbon delivered by rivers from land. To understand the dynamics and implications of this reexposure at the shelf edge, a biogeochemical study was carried out in the Gulf of Lions (Mediterranean Sea) where erosive processes, driven by shelf dense water cascading, are currently shaping the seafloor at the canyon heads. Mooring lines equipped with sediment traps and current meters were deployed during the cascading season in the southwestern canyon heads, whereas sediment cores were collected along the sediment dispersal system from the prodelta regions down to the canyon heads. Evidence from grain-size, X-radiographs and Pb-210 activity indicate the presence in the upper slope of a shelly-coarse surface stratum overlying a consolidated deposit. This erosive discontinuity was interpreted as being a result of dense water cascading that is able to generate sufficient shear stress at the canyon heads to mobilize the coarse surface layer, eroding the basal strata. As a result, a pool of aged organic carbon (Delta C-14 = -944.5 +/- 24.7%; mean age 23,650 +/- 3,321 ybp) outcrops at the modern seafloor and is reexposed to the contemporary carbon cycle. This basal deposit was found to have relatively high terrigenous organic carbon (lignin = 1.48 +/- 0.14 mg/100 mg OC), suggesting that this material was deposited during the last low sea-level stand. A few sediment trap samples showed anomalously depleted radiocarbon concentrations (Delta C-14 = -704.4 +/- 62.5%) relative to inner shelf (Delta C-14 = -293.4 +/- 134.0%), mid-shelf (Delta C-14 = -366.6 +/- 51.1%), and outer shelf (Delta C-14 = -384 +/- 47.8%) surface sediments. Therefore, although the major source of particulate material during the cascading season is resuspended shelf deposits, there is evidence that this aged pool of organic carbon can be eroded and laterally advected downslope.

Geofluid behaviour in successive extensional and compressional events: a case study from the southwestern end of the Vallès-Penedès Fault (Catalan Coastal Ranges, NE Spain)

The structural position of the Upper Jurassic-Lower Cretaceous carbonates located in the central part of the Catalan Coastal Ranges corresponds to the southwestern end of the Vallès-Penedès Fault. This fault was reactivated at different times during successive extensional and compressional events and several generations of fractures and cementations were formed.

The summer North Atlantic Oscillation in CMIP3 models and related uncertainties in projected summer drying in Europe

This paper discusses uncertainties in model projections of summer drying in the Euro-Mediterranean region related to errors and uncertainties in the simulation of the summer NAO (SNAO). The SNAO is the leading mode of summer SLP variability in the North Atlantic/European sector and modulates precipitation not only in the vicinity of the SLP dipole (northwest Europe) but also in the Mediterranean region. An analysis of CMIP3 models is conducted to determine the extent to which models reproduce the signature of the SNAO and its impact on precipitation and to assess the role of the SNAO in the projected precipitation reductions. Most models correctly simulate the spatial pattern of the SNAO and the dry anomalies in northwest Europe that accompany the positive phase. The models also capture the concurrent wet conditions in the Mediterranean, but the amplitude of this signal is too weak, especially in the east. This error is related to the poor simulation of the upper-level circulation response to a positive SNAO, namely the observed trough over the Balkans that creates potential instability and favors precipitation. The SNAO is generally projected to trend upwards in CMIP3 models, leading to a consistent signal of precipitation reduction in NW Europe, but the intensity of the trend varies greatly across models, resulting in large uncertainties in the magnitude of the projected drying. In the Mediterranean, because the simulated influence of the SNAO is too weak, no precipitation increase occurs even in the presence of a strong SNAO trend, reducing confidence in these projections.