Dissolved iron(III) speciation in the high latitude North Atlantic Ocean

On voyages in the Iceland Basin in 2007 and 2009, we observed low (ca. 0.1 nM) total dissolved iron concentrations [dFe] in surface waters (<150 m), which increased with depth to ca. 0.2–0.9 nM. The surface water [dFe] was low due to low atmospheric Fe inputs combined with biological uptake, with Fe regeneration from microbial degradation of settling biogenic particles supplying dFe at depth. The organic ligand concentrations [L_T] in the surface waters ranged between 0.4 and 0.5 nM, with conditional stability constants (log K′_FeL) between 22.6 and 22.7. Furthermore, [L_T] was in excess of [dFe] throughout the water column, and dFe was therefore largely complexed by organic ligands (>99%). The ratio of [L_T]/[dFe] was used to analyse trends in Fe speciation. Enhanced and variable [L_T]/[dFe] ratios ranging between 1.6 and 5.8 were observed in surface waters; the ratio decreased with depth to a more constant [L_T]/[dFe] ratio in deep waters. In the Iceland Basin and Rockall Trough, enhanced [L_T]/[dFe] ratios in surface waters resulted from decreases in [dFe], likely reflecting the conditions of Fe limitation of the phytoplankton community in the surface waters of the Iceland Basin and the high productivity in the Rockall Trough.Below the surface mixed layer, the observed increase in [dFe] resulted in a decrease of the [L_T]/[dFe] ratios (1.2–2.6) with depth. This indicated that the Fe binding ligand sites became occupied and even almost saturated at enhanced [dFe] in the deeper waters. Furthermore, our results showed a quasi-steady state in deep waters between dissolved organic Fe ligands and dFe, reflecting a balance between Fe removal by scavenging and Fe supply by remineralisation of biogenic particles with stabilisation through ligands.     

Geodynamics and plume tectonics of the Azore-Gibraltar fault zone (North Atlantic)

Maps of the principal structures and geological-geophysical knowledge for the Azores-Gibraltar and Icelandic regions have been made. The geodynamic conditions of the Azores archipelago formation have been analyzed. It has been noted that the uplifting of the Azores plume (as well as the Icelandic one) might have been triggered by near-surface tectonic processes. The computer modeling has been performed with respect to the coefficients of the geodynamic sinking rates for the Azores fragment of the Mid-Atlantic Ridge. Based on the modeling results, this rate was ∼1.5 times higher than the average sinking rate for the mid-ocean ridges of the World Ocean in general. The high sinking rate of the Azores fragment is caused by the influence of the plume material on the sinking process. Based on the complex analysis of the seismicity, thermal flow, and seismic tomography data distribution, as well as the implemented numerical calculations, the European (northern) part of the diffuse boundary between the Eurasian and African plates has been identified for the first time. Along with the African (southern) boundary, it outlines the identified by the authors West Mediterranean plate.     

Reactive mercury in the eastern North Atlantic and southeast Atlantic

The vertical distribution of reactive mercury has been measured at two stations in the eastern North Atlantic and one station in the southeast Atlantic in conjunction with the IOC Open Ocean Baseline Survey. The average concentrations of reactive Hg in vertical profiles ranged from 0.70 to 1.07 pM with the highest values found at the northeast Atlantic stations and the lowest at the southeast station. No significant concentration gradients were found below the surface mixed layer at the two stations in the eastern North Atlantic. At station 7, in the southeast Atlantic, an increase in reactive Hg was noted in the water adjacent to the mixed layer (35–200 m) which was coincident with an oxygen depletion, down to 20% saturation at 200 m. The concentration of reactive Hg in the North Atlantic Deep Water (0.48–1.34 pM), the Antarctic Intermediate Water (0.47 pM), the Antarctic Bottom Water (0.67–1.25 pM), and the Mediterranean Outflow Water (0.83–1.06 pM) were noted. The trends in Hg concentration in the water masses between stations showed the concentration decreasing with distance from the water mass source except for Hg in the Antarctic Bottom Water. The increase noted in this water mass was attributed to mixing with North Atlantic Deep Water and or release from bottom sediments.     

Characterization of North Atlantic right-whale (Eubalaena glacialis) sounds in the Bay of Fundy

Hydrophone recordings, made in the presence of North Atlantic right whales (Eubalaena glacialis) in the Bay of Fundy during the daytime in July 1999, are used to determine the characteristics of the recorded sounds. A spectrogram-based method was implemented to discriminate whale sounds from background noise and the time-frequency envelope of the primary harmonic in the spectrogram was used as the basis for sound characterization. Sounds were typically (82%, n=45) in the 300- to 600-Hz range with up- and downsweeping modulations. Lower (<200 Hz) and higher (>900 Hz) frequency sounds were relatively rare. Most sounds were frequency modulated, with 95% of the observed instantaneous relative frequency variation being within /spl plusmn/4.5% of the mean peak frequency. Harmonics were observed in 18% of the sounds. The average sound duration was 0.42 s/spl plusmn/0.26 SD. The sounds occurred at a rate of between 0.3 and 0.7 min/sup -1/. The time intervals between adjacent sounds (2-700 s) were not randomly distributed. The number of sounds occurring among different waiting times did not reflect a Poisson distribution and a clustering of sounds (2 to 5 cluster/sup -1/) was observed. The sound characteristics are compared to those documented elsewhere and as reported for the southern right whale.     

Assemblages of hydroids (Cnidaria) from three seamounts near Bermuda in the western North Atlantic

Three seamounts flanking the oceanic island of Bermuda were sampled for hydroids. Collecting was undertaken by submersible (SDL-1) and by dredge at depths between 48 and 107 m on the summits of Argus and Challenger banks. A shallower collection (<20 m) from the pilings of a tower on Argus Bank was made using SCUBA. Major bottom types on both banks were aggregations of rhodoliths, limestone reefs, and areas of calcareous sand. Hydroids were ubiquitous, but quite sparse, on firm substrata. None was collected on sandy bottoms. Of 45 species identified from the two oceanic banks, over half (25) were found on both. On Bowditch Seamount, samples were obtained at depths between 1285 and 1381 m by dredge and grab. Of four species found, only one (Filellum serratum) occurred in shallower collections from Argus and Challenger banks. Most species (43 of 48) from the three seamounts have been reported elsewhere in the Western Atlantic Tropical region, and many (38 of 48) are known from Bermuda. No endemics were discovered, and no relicts or exotics were recognized. Gonophores in >70% of the species are fixed sporosacs instead of free medusae. This conforms with a hypothesis that invertebrates of oceanic islands and seamounts tend to have short-lived pelagic larval stages, ensuring the greatest retention and conservation of propagules.     

北极海盆的深海热液

从海底地壳开裂处涌出一般带有大量生物的深海热泉的现象已众所周知。一开始在太平洋和大西洋中找到了它们 ,而在 2 0世纪和 2 1世纪交接期印度洋中也发现了热液 ,而后就输到高纬度的北极海区了。在极区盆地中应当有热液已有过报道。例如 ,1 993年 9月 ,俄 德联合北极考察队乘坐“极地”(Polarstern)号破冰船 ,在拉普帖夫海加克利 (Гакке х)海岭东端 (77°45′N、1 2 5° 55′E ,水深 1 990m) ,获得了对研究热液非常有意义的样品 ,证实了在这个海岭上存在着热液活动 ;但是 ,在 2 0 0 1年 ,美国和德国破冰船“健康”(Healy)号和“极…     

Manganese in the Western North Atlantic Ocean

Dissolved and total dissolvable manganese concentrations have been measured at four stations in the western North Atlantic Ocean. Total dissolvable manganese concentrations are high in surface waters, decrease to uniformly low levels throughout the bulk of the water column, and increase in the bottom nepheloid layer. Dissolved Mn (Mn_d) concentrations follow the total dissolvable concentrations throughout the surface and deep waters but do not increase in the near-bottom waters.Deep water concentrations of Mn_d decrease from 30 ng l^?1 in the Newfoundland Basin to 20 ng l^?1 in the Sargasso Sea. This change and other features of the deep water distribution of dissolved manganese could be associated with the slow oxidation of Mn²⁺ to MnO₂. There is also evidence at one station of scavenging of manganese from the dissolved phase in the near-bottom layer which may again be related to the kinetics of manganese oxidation.     

Silver in the far North Atlantic Ocean

Total (unfiltered) silver concentrations in higher latitudes of the North Atlantic (52–68°N) are reported for the second Intergovernmental Oceanographic Commission (IOC) Global Investigation of Pollutants in the Marine Environment (GIPME) baseline survey of 1993. These silver concentrations (0.69–7.2 pM) are oceanographically consistent with those (0.24–9.6 pM) previously reported for lower latitudes in the eastern North and South Atlantic (Flegal et al., 1995). However, surface (⩽200 m) water concentrations of silver (0.69–4.6 pM) in the northern North Atlantic waters are, on average, ten-fold larger than those (0.25 pM) considered natural background concentrations in surface waters of the central Atlantic. In contrast, variations in deep far North Atlantic silver concentrations are associated with discrete water masses. Consequently, the cycling of silver in the far North Atlantic appears to be predominantly controlled by external inputs and the advection of distinct water masses, in contrast to the nutrient-like biogeochemical cycling of silver observed in the central Atlantic and Pacific oceans.     

Transport variability in the Lanzarote passage (eastern boundary current of the North Atlantic subtropical Gyre)

Observations from a four-year current meter mooring at 28°44′N, 13°28′W in the Lanzarote passage are used to describe the transport variability of the Eastern Boundary Current of the North Atlantic Subtropical Gyre. Three different water masses are found in the passage: North Atlantic Central Water in the upper levels (roughly $\text{0}\text{–}\text{600}\text{m}$), Antarctic Intermediate Water (roughly $\text{600}\text{–}\text{1100}\text{m}$) and Mediterranean Water in the layer above the bottom at $\text{1300}\text{m}$. The mean southward transport of NACW is $\text{−0.8±1.1}\text{Sv}$ $\text{(1}\text{Sv}\text{=10}{}^9\text{kg}\text{s}{}^{\mathrm{-1}}\text{)}$ which is the transport of the easternmost branch of the Canary Current. Fluctuations of NACW transport are large, ranging from $\text{−3.4}\text{Sv}$ southward to $\text{1.7}\text{Sv}$ northward. Every autumn a consistent northward transport is observed, which may be related with the eastern boundary upwelling dynamics. The mean transports of AAIW and MW are $\text{0.1±0.4}\text{Sv}$ northward and $\text{−0.05±0.09}\text{Sv}$ southward, respectively. Fluctuations of transport of AAIW and MW are large, from 1.0 to $\text{−1.0}\text{Sv}$ and from −0.32 to $\text{0.23}\text{Sv}$, respectively. Thus, the mass transports for each water mass show a high standard deviation of comparable magnitude to the mean. This highlights the importance of the temporal variability of the currents in this passage. A remarkable feature of our observations is that the mean transports of NACW and AAIW during an El Niño event are significantly different.     

中大西洋塞拉里昂断裂的热液矿化

对热液场、受震烈度和卫星高程测量资料的分析证明 ,在扩张速度不高的洋中脊中 ,热液场一般位于断裂与具有较低受震烈度背景的裂谷区的交汇处。据此可以设想 ,气液的迁移是沿着裂谷与裂隙走向一致的方向实现的。在这种情况下 ,矿石组分的卸代地点应当位于裂谷最稳定的部位 ,在该区为热液提供了长期 (达数万年 )稳定的环流条件。在 2 0 0 0年“尼古拉·斯特拉霍夫院士”号科学研究船第 2 2航次中 ,采用ＳＩＭＲＡＤ1 2Ｓ多道回声测深仪 ,对塞拉里昂断裂区进行了全面的海底深度测量和标本采集工作 ,并揭露了具热液蚀变和硫化物矿化的岩石。斯…     

Deep-sea reef fish assemblage patterns on the Blake Plateau(Western North Atlantic Ocean)

Deep‐water coral habitats are scattered throughout slope depths (360–800 m) off the Southeastern United States (SEUS, Cape Lookout, North Carolina, to Cape Canaveral, Florida), contributing substantial structure and diversity to bottom habitats. In some areas (e.g. off North Carolina) deep corals form nearly monotypic (Lophelia pertusa) high profile mounds, and in other areas (e.g. off Florida) many species may colonize hard substrata. Deep coral and hard substrata ecosystems off the SEUS support a unique fish assemblage. Using the Johnson‐Sea‐Link submersible (in 2000–2005, 65 dives), and a remotely operated vehicle (in 2003, five dives), fishes were surveyed in nine deep reef study areas along the SEUS slope. Forty‐two benthic reef fish species occurred in deep reef habitats in these study areas. Species richness was greatest on the two coral banks off Cape Lookout, North Carolina (n = 23 and 27 species) and lowest on the two sites off Cape Canaveral, Florida (n = 7 and 8 species). Fish assemblages exhibited significantly (ANOSIM, Global R = 0.69, P = 0.001) different patterns among sites. Stations sampled off North Carolina (three study areas) formed a distinct group that differed from all dives conducted to the south. Although several species defined the fish assemblages at the North Carolina sites, Laemonema barbatulum, Laemonema melanurum, and Helicolenus dactylopterus generally had the most influence on the definition of the North Carolina group. Fish assemblages at three sites within the central survey area on the Blake Plateau were also similar to each other, and were dominated by Nezumia sclerorhynchus and L. melanurum. Synaphobranchus spp. and Neaumia sclerorhynchus differentiated the two southern sites off Cape Canaveral, Florida, from the other station groups. Combinations of depth and habitat type had the most influence on these station groups; however, explicit mechanisms contributing to the organization of these assemblages remain unclear.     

Genesis of the lithosphere of the Iceland region (North Atlantic) according to geophysical data

The geothermal and geomagnetic data on the Iceland region are mapped. On the basis of the analysis of geological, tectonic, geothermal, and geomagnetic data and on the information on the age and character of the volcanism at the European and Greenland rifting margins, the principal evolution stages of the Iceland region are substantiated. The modeling estimation of the rates of thermal subsidence of the Reykjanes and Kolbeinsey ridges and of the Greenland-Iceland and Iceland-Faeroes sills shows their more than 20% difference. The different rates of thermal subsidence of the structures are caused by various effects of hot matter of the mantle plume, its volume, and the different genesis of the lithosphere. The formation of the lithosphere of Iceland Island, besides the plate and plume tectonics, involved the thermophysical processes of the transformation of the lithosphere of continental genesis. This is confirmed by the analysis of the spreading rates, basalt age, and the data of the geochemical and isotope studies of volcanic rocks. The numerical modeling performed points to the presence of an additional heat source related to the plume hot matter in the Iceland region (Iceland Island, 30 mW/m²; the Reykjanes and Kolbeinsey ridges, 15 mW/m²), which conforms to the data of magnetotelluric geochemical studies.     

Nutrient irrigation of the North Atlantic

The North Atlantic, as all major oceans, has a remarkable duality in primary production, manifested by the existence of well-defined high and low mean primary production regions. The largest region is the North Atlantic Subtropical Gyre (NASTG), an anticyclone characterized by bowl shaped isopycnals and low production. The NASTG is surrounded at its margins by smaller cyclonic high-production regions, where these isopycnals approach the sea surface. The most extensive cyclonic regions are those at the latitudinal extremes, i.e. the subpolar and tropical oceans, though smaller ones do occur at the zonal boundaries. In this article we review historical data and present new analyses of climatological data and a selected number of hydrographic cruises in the western/northwestern and eastern/southeastern boundaries of the NASTG, with the objective of investigating the importance of upward epipycnal advection of nutrient-rich subsurface layers (irrigation) in maintaining high primary production in the euphotic layers. In the North Atlantic Subpolar Gyre (NASPG) irrigation implies intergyre exchange caused by the outcropping extension of the Gulf Stream (GS), following the formation of the deep winter mixed-layer. In the eastern boundary of the NASTG irrigation is attained through a permanent upwelling cell, which feeds the Canary Upwelling Current (CUC). In the southeastern corner irrigation occurs in fall, when the Guinea Dome (GD) is reinforced, and in winter, when the CUC reaches its southernmost extension. Other characteristics of the north/south extension of the GS/CUC are the seasonal nutrient replenishing of subsurface layers (spring restratification of NASPG and winter relaxation of the GD) and the maintenance of high levels of diapycnal mixing during the last phase of nutrient transfer to the euphotic layers. Off the Mid-Atlantic Bight the GS transports a total of about 700 kmol s⁻¹ of nitrate, with almost 100 kmol s⁻¹ carried in the surface (σ_θ < 26.8) layers and some 350 kmol s⁻¹ in the intermediate (26.8 < σ_θ < 27.5) layers. A box model suggests that north of Cape Hatteras most surface and upper-thermocline nitrates are used to sustain the high levels of primary production in the NASPG. Off Cape Blanc there is winter along-shore convergence of order 10 kmol s⁻¹ of nitrate in the near-surface layers (possibly larger in summer), with only a small fraction used to sustain local primary production in the coastal upwelling band and the remainder carried to the interior ocean. Nutrients and biomass exported from these cyclonic regions may account for the concentration levels observed within the NASTG.     

Larval fish distribution in shallow coastal waters off North Western Iberia (NE Atlantic)

Monthly sampling for ichthyoplankton was conducted at three stations very near to the coast (near to shore shallow stations before the surf zone in direction to the shoreline) of Atlantic northwestern Portugal within contrasting localities: rocky shore, in front of a sandy beach receiving an estuary and a fishing port with heavy anthropogenic impact. Sampling was conducted from August 2002 to October 2003, always at full moon, at low tide and high tide in daylight hours, at the water column using a 48 cm diameter plankton net with 335 μm mesh. Analysis of the physico-chemical parameters pointed out the spatial (horizontal) homogeneity of the sampling area. Fish larvae from 41 taxa belonging to 17 families were identified; Blenniidae, Labridae, Ammodytidae, Clupeidae, Gobiidae, Soleidae and Gobiesocidae were the most representative during the study period. Parablennius gattorugine, Ammodytes tobianus, Symphodus melops, Sardina pilchardus, Lipophrys pholis and Coryphoblennius galerita were the most representative species (percentage contribution to total abundance). Peak abundance of fish eggs occurred during May, June and August 2003 and fish larvae occurred during May and July 2003 and August 2002 and 2003; there was a pronounced winter/early spring (March 2003) peak in larval abundance dominated by the small sandeel A. tobianus. This study identifies the occurrence of a conspicuous assemblage of larval fishes at very nearshore shallow environments of a variety of species with different adult habitats: the fish larvae assemblage was dominated by intertidal species. The present study has shown that temporal and spatial variations in the larval fish assemblage are related to environmental conditions and biological dynamics: the results suggest that abiotic conditions mediate biotic parameters, and that both abiotic and biotic characteristics regulated the larval fishes at very nearshore shallow environments.     

Late quaternary migrations of the subarctic front in the North Atlantic (Based on lithology and nannofossils)

A complex of lithological and micropaleontological methods were used for the study of sediments from the central North Atlantic (50–60°N). The data on the lithology, carbonate content, and occurrence of ash interbeds and ice-rafted material, combined with the nannofossil zonal biostratigraphy, allowed detailed subdivision of five core sections obtained during Cruise 48 of R/V Akademik Mstislav Keldysh. MIS 1–MIS 9 are established in the sections. In some of them, climatic changes related to migrations of the Subarctic Front are established based on the lithology and the characteristic coccolithophorid species: for example, a higher latitudinal position of the front is revealed for the Eemian interglacial (Substage 5e) as compared with that in the Holocene.     

Organic matter of the North Atlantic

The areas that we studied in the North Atlantic (53 and 60°N) and in the Labrador Sea in the summer were characterized by a wide variability of the concentrations of dissolved and particulate organic matter and its elemental composition both in the surface and in the deep waters. The concentrations of dissolved and particulate C_org varied within 69–360 μM and 0.7–25.6 μM, respectively; the N_org and P_org contents varied within 1.4–22.2 μM and 0.02–0.86 μM, respectively. The maximal concentrations were registered in the photic layer and in the zones of mixing between the waters of different genesis. The particulate matter contribution to the total organic matter (OM) content varied from 0.5 to 15.4%. The waters of the photic layer contained more particulate C_org than those of the near-bottom layer. The values of the C/N molar ratios from the surface to the bottom over the entire aquatic area surveyed varied 5-to 6-fold; at that, the values of the C/P molar ratios varied more than tenfold. In the most productive waters, the values of the C/N ratios were close to the Redfield ratios (6–10). The values of the C/P molar ratios varied from 160 in the photic layer to 4831 in the deep waters. The pronounced non-uniformity in the spatial distribution of the OM and its elemental composition is caused not only by the penetration of the waters of different origins but also by the changes in the microplankton metabolism under mixing of these waters.     

Crustal transect across the North Atlantic

Two dimensional crustal models derived from four different ocean bottom seismographic (OBS) surveys have been compiled into a 1,580 km long transect across the North Atlantic, from the Norwegian Møre coast, across the extinct Aegir Ridge, the continental Jan Mayen Ridge, the presently active Kolbeinsey Ridge north of Iceland, into Scoresby Sund in East Greenland. Backstripping of the transect suggests that the continental break-up at ca. 55 Ma occurred along a west-dipping detachment localized near the western end of a ca. 300 km wide basin thinned to less than 20 km crustal thickness. It is likely that an east-dipping detachment near the present day Liverpool Land Escarpment was active during the late stages of continental rifting. A lower crustal high-velocity layer (7.2–7.4 km/s) interpreted as mafic intrusions/underplating, was present beneath the entire basin. The observations are consistent with the plume hypothesis, involving the Early Tertiary arrival of a mantle plume beneath central Greenland and focused decompression melting beneath the thinnest portions of the lithosphere. The mid-Eocene to Oligocene continental extension in East Greenland is interpreted as fairly symmetric and strongly concentrated in the lower crustal layer. Continental break-up which rifted off the Jan Mayen Ridge, occurred at ca. 25 Ma, when the Aegir Ridge became extinct. The first ca. 2 m.y. of oceanic accretion along the Kolbeinsey Ridge was characterized by thin magmatic crust (ca. 5.5 km), whereas the oceanic crustal formation since ca. 23 Ma documents ca. 8 km thick crust and high magma budget.     

Reactive mercury in the central North Atlantic Ocean

The level of reactive mercury in pelagic waters near the Mid Atlantic Ridge, south of the Azores, and in the Sargasso Sea, north of Bermuda, was studied. The reactive Hg concentration in both locations was shown to be fairly uniform with depth at a level of 2.5 ± 0.5 pmol l⁻¹. The profiles show no indication of a simple Hg-nutrient relationship. The deep water from the Famous area was also sampled and showed no elevated Hg levels.