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.     

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.     

大西洋温盐循环的演变:早渐新世北大西洋深水开始形成

气候和大洋盆地形状的急剧变化标志了新生代的开始。不断增加的证据表明了在早新生代(约55 Ma)的极端温暖时期,主要存在于南大洋的深水层形成了与现代模式根本不同的循环模式,并在北大西洋北部及南大洋形成了深水层。早新生代模式向两极模式的转变出现于何时?该转变的主要作用力如何?巴拿马地峡(4·2 Ma)的形成被认为是代表了深水循环向两极模式转变的最后作用,它使湾流将盐度较高的暖水带到北半球高纬形成北大西洋深层水(NADW),现代NADW由来自Nordic海和拉布拉多海的深水组成。然而,通常认为北大西洋的深水形成的最初阶段只有Nordic海…     

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.     

Thermohaline Structure of Waters in the North Atlantic in Different Phases of the Atlantic Multidecadal Oscillation

Izvestiya, Atmospheric and Oceanic Physics - The meridional structure of climatic trends and anomalies of potential temperature and salinity in the North Atlantic waters in different periods of the...     

Chemical Composition of North Atlantic Aerosols

The paper presents new information on the chemical composition of the insoluble aerosol fraction in the atmospheric surface boundary layer of different climatic zones of the North Atlantic (temperate humid, arid and semiarid, equatorial humid). The material for this study was collected during 12 expeditions. Nylon meshes were used to catch aerosols along the course of vessels. Aerosols above the North Atlantic consist of lithogenic, biogenic, and anthropogenic particles transported from different regions, which governs the differences in their concentrations and mineral and chemical compositions. Significant (by more than an order of magnitude) enrichment of aerosols in Cu, Cd, Zn, Pb, Sb, and Se is related to anthropogenic atmospheric pollution.     

The North Atlantic nutrient stream

Western boundary currents are the locus of intense nutrient transport, or nutrient streams. The largest fraction of this transport takes place in the upper-thermocline layers, between the surface layers (where speed reaches a maximum) and the nutrient bearing strata of the subtropical gyres (where nutrient concentration is maximum). The core of the nutrient stream of the North Atlantic subtropical gyre is located slightly offshore the Gulf Stream, its density coordinate centered on the 26.5–27.3_–band, approximately constant along the axis of the stream. During late spring and summer the nutrient stream reaches the surface seasonal mixed layer at the outcropping of this isopycnal band. We argue that this must be a principal factor sustaining the seasonal high productivity of the subpolar North Atlantic Ocean. Additionally, we investigate the possibility of intermittent shear-induced diapycnal mixing in the upper-thermocline layers of the Gulf Stream, induced by frontogenesis taking place during some phase of the meanders. Here we illustrate that diapycnal mixing has a maximum at the location of the nutrient stream, being associated to observed nutrient anomalies. We suggest that diapycnal mixing associated to the passage of steep meanders brings nutrients from the nutrient stream to the shallow photic layers, and sustains intermittent (day-to-week) patchy (10–100 km) productivity over the stream itself.     

Atlantic meridional overturning circulation and phosphate-classified bottom-up control of Atlantic pelagic ecosystems through the 20th century

Both the Atlantic Meridional Overturning Circulation (AMOC) and the North Atlantic Ocean (NA) biosphere have recognized associations with the North Atlantic Oscillation (NAO). These multidecadal physical–biological affinities inspired a closer look at AMOC influences on bottom-up control of NA and South Atlantic Ocean (SA) pelagic ecosystem variability. Various ocean models associate changes in the AMOC with sea surface temperature (SST) differences in the western subpolar NA and SA represented as the Atlantic Dipole SST Anomaly (ADSA) index. The Extended Reconstructed SST version 2 (ERSSTv2) dataset for 2° quadrangles from 1890 to 2007 was used here to represent Atlantic Ocean SST patterns and to gauge 20th century AMOC variability using an Atlantic Dipole SST (ADS) index, an un-normalized version of ADSA index. Temperature–phosphate (T–PO₄) linear regressions were used to convert temperature to phosphate concentration ([PO₄]). The interannual stability of T–PO₄ linear regressions first was examined using 26 Bermuda area T–PO₄ datasets between 1958 and 2001. Within the constraints provided by the Bermuda analysis, climatological T–PO₄ linear regressions based on GEOSECS-derived slopes and NODC-derived X-intercepts supported the conversion of monthly Atlantic Ocean ERSSTv2 temperatures for each 2° quadrangle to monthly surface [PO₄]. A representative annual surface phosphate utilization (SPU) was calculated for each 2° quadrangle by subtracting monthly minimum surface [PO₄] from monthly maximum surface [PO₄] to determine the annual surface [PO₄] ranges from 1890 to 2007. Annual average SST tended to increase and overall annual average SPU tended to decrease through the 20th century in both the NA and SA, but the NA exhibited more temporal variability. An Atlantic Dipole Phosphate Utilization (ADPU) index related to the ADS index was calculated for each year from 1890 to 2007. The ADS and ADPU indices were inversely correlated with about 57% of the variability in the ADPU index explained by the ADS index. The ADPU index exhibited three distinct cycles through the 20th century. Cross-correlation analysis showed that the NAO led the ADS and ADPU indices by about 14 years. Differences in annual average SPU for each Atlantic Ocean 2° quadrangle between the three high and four low years of the ADPU cycles yielded six maps that, when averaged, clearly exhibited reversed east–west patterns distributed in alternating latitudinal bands in both the NA and SA. The east–west patterns spatially corresponded to the NA and SA surface circulation and temporally resembled NA patterns previously associated with the NAO. AMOC variability, mediated by Kelvin and Rossby waves associated with changes in both deep and surface arm circulation, likely contributed to meridional continuity of phosphate-classified, NA, and SA pelagic ecosystem variability, including fisheries, through the 20th century. Based on the results, future global warming influences on the AMOC, well short of shutdown, likely will have complex pelagic ecosystem impacts throughout the Atlantic Ocean.     

大西洋表层水中的的悬浮物

俄罗斯科学院海洋研究所实验室对大西洋表层水中悬浮物的物质成分及其在水中的定量分布进行了测定,以确定不同来源悬浮物的份额.研究材料来自2001-2005年间7个春季和秋季的科研船航次勘探.此外,还采集了大气中的悬浮体,作为开放性海洋中物质来源之一.     

Acoustic characteristics of the north-eastern Atlantic Ocean

The vertical structure of the climatic and seasonal fields of the estimated speed of sound in the north-east Atlantic Ocean is considered. Zonation according to typicalc(z) profiles allowing for seasonal variations was carried out. It is shown that the water areas with a dual-channel vertical hydroacoustic structure vary essentially throughout the year. The features of the structure of the sound speed field in the lenses of the Mediterranean Sea waters are investigated. The effect produced by a lens on the characteristics of the sound propagation is studied.Translated by Mikhail M. Trufanov.     

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.