Significance of non‐sinking particulate organic carbon and dark CO2 fixation to heterotrophic carbon demand in the mesopelagic northeast Atlantic

[EN] It is generally assumed that sinking particulate organic carbon (POC) constitutes the main source of organic carbon supply to the deep ocean's food webs. However, a major discrepancy between the rates of sinking POC supply (collected with sediment traps) and the prokaryotic organic carbon demand (the total amount of carbon required to sustain the heterotrophic metabolism of the prokaryotes; i.e., production plus respiration, PCD) of deep-water communities has been consistently reported for the dark realm of the global ocean. While the amount of sinking POC flux declines exponentially with depth, the concentration of suspended, buoyant non-sinking POC (nsPOC; obtained with oceanographic bottles) exhibits only small variations with depth in the (sub)tropical Northeast Atlantic. Based on available data for the North Atlantic we show here that the sinking POC flux would contribute only 4–12% of the PCD in the mesopelagic realm (depending on the primary production rate in surface waters). The amount of nsPOC potentially available to heterotrophic prokaryotes in the mesopelagic realm can be partly replenished by dark dissolved inorganic carbon fixation contributing between 12% to 72% to the PCD daily. Taken together, there is evidence that the mesopelagic microheterotrophic biota is more dependent on the nsPOC pool than on the sinking POC supply. Hence, the enigmatic major mismatch between the organic carbon demand of the deep-water heterotrophic microbiota and the POC supply rates might be substantially smaller by including the potentially available nsPOC and its autochthonous production in oceanic carbon cycling models.

Seismic tomographic full-waveform inversion for the Vrancea sinking lithosphere structure using the adjoint method.

The Vrancea region, at the south-eastern bend of the Carpathian Mountains in Romania, represents one of the most puzzling seismically active zones of Europe. Beside some shallow seismicity spread across the whole Romanian territory, Vrancea is the place of an intense seismicity with the presence of a cluster of intermediate-depth foci placed in a narrow nearly vertical volume. Although large-scale mantle seismic tomographic studies have revealed the presence of a narrow, almost vertical, high-velocity body in the upper mantle, the nature and the geodynamic of this deep intra-continental seismicity is still questioned. High-resolution seismic tomography could help to reveal more details in the subcrustal structure of Vrancea. Recent developments in computational seismology as well as the availability of parallel computing now allow to potentially retrieve more information out of seismic waveforms and to reach such high-resolution models. This study was aimed to evaluate the application of a full waveform inversion tomography at regional scale for the Vrancea lithosphere using data from the 1999 six months temporary local network CALIXTO. Starting from a detailed 3D Vp, Vs and density model, built on classical travel-time tomography together with gravity data, I evaluated the improvements obtained with the full waveform inversion approach. The latter proved to be highly problem dependent and highly computational expensive. The model retrieved after the first two iterations does not show large variations with respect to the initial model but remains in agreement with previous tomographic models. It presents a well-defined downgoing slab shape high velocity anomaly, composed of a N-S horizontal anomaly in the depths between 40 and 70km linked to a nearly vertical NE-SW anomaly from 70 to 180km.

Predicting State Allocation of Funds: The Case of John Rowland and his Hometown of Waterbury, Connecticut.

This study attempts to analyze the underlying factors and motives influencing the allocation of discretionary state expenditures. The fact that some cities receive more money than other cities begs the question of what accounts for this variation. After framing the provision of state money within the theoretical framework of political patronage, a case study of Governor Rowland’s tenure in office and the accompanying expenditures to Connecticut’s 17 largest cities from 1995 to 2004 was conducted to evaluate whether a disproportionate amount of money was given to Rowland’s hometown of Waterbury, Connecticut. Besides employing a statistical analysis that determined that cities with similar characteristics received different amounts of money, interviewing was conducted to identify reasons for such variation. The results indicate that Waterbury received a greater amount of money than was predicted based on the city’s economic and demographic characteristics, and that non-objective and biased factors such as favoritism, the need to reward political support, or the desire to increase political loyalty sometimes take precedence over more objective factors.

A four-year record of UK'37- and TEX86-derived sea surface temperature estimates from sinking particles in the filamentous upwelling region off Cape Blanc, Mauritania

Lipid biomarker records from sinking particles collected by sediment traps are excellent tools to study the seasonality of biomarker production as well as processes of particle formation and settling, ultimately leading to the preservation of the biomarkers in sediments. Here we present records of the biomarker indices UK'37 based on alkenones and TEX86 based on isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs), both used for the reconstruction of sea surface temperatures (SST). These records were obtained from sinking particles collected using a sediment trap moored in the filamentous upwelling zone off Cape Blanc, Mauritania, at approximately 1300 water depth during a four-year time interval between 2003 and 2007. Mass and lipid fluxes are highest during peak upwelling periods between October and June. The alkenone and GDGT records both display pronounced seasonal variability. Sinking velocities calculated from the time lag between measured SST maxima and minima and corresponding index maxima and minima in the trap samples are higher for particles containing alkenones (14-59 m/d) than for GDGTs (9-17 m/d). It is suggested that GDGTs are predominantly exported from shallow waters by incorporation in opal-rich particles. SST estimates based on the UK'37 index faithfully record observed fluctuations in SST during the study period. Temperature estimates based on TEX86 show smaller seasonal amplitudes, which can be explained with either predominant production of GDGTs during the warm season, or a contribution of GDGTs exported from deep waters carrying GDGTs in a distribution that translates to a high TEX86 signal.

Plutonium and americium concentrations in sea water and in sinking particles

Vertical fluxes of 239+240Pu and 241Am and temporal changes in their inventories in the northwestern Mediterranean Sea have been examined through high-resolution water column sampling coupled with direct measurements of the vertical flux of particle-bound transuranics using time-series sediment traps. Water column profiles of both radionuclides showed well-defined sub-surface maxima (2391240Pu between 100-400 m; 241Am at 100-200 m and 800 m), the depths of which are a result of the different biogeochemical scavenging behavior of the two radionuclides. Comparison of deep water column (0-2,000 m) transuranic inventories with those derived from earlier measurements demonstrate that the total 2391240Pu inventory had not substantially changed between 1976-1990 whereas 241Am had decreased by approximately 24%. Enhanced scavenging of 241Am and a resultant, more rapid removal from the water column relative to 239+240Pu was also supported by the observation of elevated Am/Pu activity ratios in sinking particles collected in sediment traps at depth. Direct measurements of the downward flux of particulate 239+240Pu and 241Am compared with transuranic removal rates derived from observed total water column inventory differences over time, show that particles sinking out of deep waters (1,000-2,000 m) could account for 26-72% of the computed total annual 239+240Pu loss and virtually all of the 241Am removal from the water column. Upper water column (0-200 m) residence times based on direct flux measurements ranged from 20-30 yr for 239+240Pu and 5-10 yr for 241Am. The observation that 241Am/239+240Pu activity ratios in unfiltered Mediterranean seawater are six times lower than those in the north Pacific suggests the existence of a specific mechanism for enhanced scavenging and removal of 241Am from the generally oligotrophic waters of the open Mediterranean. It is proposed that atmospheric inputs of aluminosilicate particles transported by Saharan dust events which frequently occur in the Mediterranean region could enhance the geochemical scavenging and resultant removal of 241Am to the sediments.