First Record of Plicaherpia (Mollusca: Solenogastres: Phyllomeniidae) from the North Atlantic with Description of Two New Species

North Atlantic circulation and variability, reviewed for the CNLS conference

Atlantic decadal climate variations are studied using marine meteorological observations. To remove artificial interhemispheric correlation, we perform empirical orthogonal function (EOF) analysis of sea surface temperature (SST) variability separately for the North and South Atlantic. The first EOF for the North (South) Atlantic in the decadal (8‐16 years) band features a meridional tripole (dipole). In the tropics, the northern and southern leading EOFs form a meridional dipole with a center of action at 15 � on either side of the equator. The leading sea level pressure (SLP) EOFs for the North and South Atlantic each feature a center of action that is displaced poleward of the tropical SST extreme, at 30 � latitude. The SLP center of action in the North Atlantic has a barotropic structure and contributes significantly to surface wind variability in the tropics. Despite being derived from statistically independent data samples, the principle components for the leading SST and SLP EOFs (four in total) are significantly correlated with one another, indicative of the existence of an interhemispheric mode spanning the entire Atlantic Ocean. The same analysis for a longer SST record suggests that this pan-Atlantic decadal variability exists throughout the 20th century. In the North Atlantic, composite analysis of wind velocity and heat fluxes based on the PCs of the leading SST modes indicates that wind-induced latent heat flux is the major forcing for decadal SST variability. In the South Atlantic, by contrast, wind anomalies are neither organized in space nor in geostrophic balance with SLP, a problem likely due to poor sampling there as indicated by a comparison with well-sampled satellite measurements. Spatially coherent anomalies of low-level cloud cover are found to be associated with the tropical Atlantic dipole, with increased (decreased) cloudiness over the cold (warm) lobe. These low-level cloud anomalies do not appear to be associated with significant surface wind convergence, unlike the deep convective clouds near the equator. By shielding solar radiation, these low-level cloud anomalies act to reinforce the underlying SST anomalies, reducing the Newtonian cooling rate for SST by as much as 30%.

The wreckfishPolyprion americanus, a large [>1 m total length (LT)] demersal teleost, is distributed globally in temperate waters, including both sides of the North and South Atlantic Oceans, the Mediterranean, the western South Pacific, and the southern Indian Ocean. Wreckfish spawn off the south‐eastern U.S. on an area of the Blake Plateau (the Charleston Bump) characterized by an extensive ridge having approximately 100 m relief, in 450–600 m depths. Juvenile wreckfish (<60 cmLT) are pelagic and, in the North Atlantic, are not reported from the Blake Plateau fishing area, but occur in by‐catch and fishery landings in the eastern Atlantic. Analysis of nine restriction fragment length profiles from a PCR‐amplified fragment (∼1.5 kb) of the ND1 mitochondrial gene indicated no stock separation between eastern North Atlantic (Azores, Majorca, Madeira), and western North Atlantic (Blake Plateau) wreckfish. Restriction site differences separate western South Atlantic wreckfish from the North Atlantic; however, South Atlantic wreckfish share restriction‐site similarities with western Pacific wreckfish that are not shared with North Atlantic wreckfish. North Atlantic circulation provides a mechanism for a long‐lived pelagic stage to be dispersed from Blake Plateau spawning grounds to the eastern North Atlantic. Global circulation patterns may explain both the dispersal of mtDNA haplotypes and the disjunct distribution of wreckfish body lengths in a temperate, deep‐water vagile species with an extended pelagic juvenile stage such as wreckfish.

Various papers have been published during the past decade concerning Last Glacial Maximum (LGM) North Atlantic Deep Water (NADW) flow. Using somewhat different methods, they have produced somewhat contradictory results. This review considers both apparent and real conflicts concerning the data and their interpretation, and attempts to resolve them. Despite the earlier (contradictory) interpretations, currently there is a widespread belief that nutrient concentrations in deep cores from the North Atlantic increased during glacial times and that concentrations in the upper-deep and intermediate waters decreased at least slightly. It is also clear that further north in the basin (particularly at upper-deep and intermediate depths), nutrient concentrations were as low or perhaps even lower than those seen today. Data from the Caribbean Sea, ventilated by intermediate waters through an approximately 1800 m sill, indicate that lower nutrient levels were also found at intermediate depths in the North and Tropical Atlantic; this data is supported by continental margin data. The recontoured 8 13 C data of Duplessy et al. ( Paleoceanography 3, 343—360 (1988)) remain a valid expression of the broadscale LGM Atlantic nutrient distribution. Data from the South Atlantic has been the most contradictory to date, but recent 8 13 c evidence from a low-productivity South Atlantic site supports Cd data indicating a relative stability in the nutrient chemistry of waters that are presently influenced by low-nutrient NADW. Sedimentary 231 Pa/ 230 Th data appear to require the continued export of Atlantic-generated 231 Pa from the Atlantic into the Southern Ocean. Finally, radiocarbon evidence from paired planktonic/benthic foraminifera indicates that the ventilation time of the North Atlantic remained low and that the ventilation time of the entire ocean did not change much beyond the uncertainty of the 14 C data. Taken together, this evidence suggests that the NADW became ‘Glacial North Atlantic Deep/Intermediate Water’ (GNAIDW) during glacial times, with perhaps a greater flux through intermediate waters than currently combined with a lesser flux through deeper waters. Although one cannot say much with confidence about the total GNAIDW flux, the data are consistent with a persistent but perhaps somewhat diminished role for NADW in the global thermohaline circulation during glacial times. A review of recent evidence concerning the response of the deep North Atlantic during the Younger Dryas concludes that there is no inconsistency between the new evidence and the occurence of a Younger Dryas NADW event in the deep western North Atlantic.

When a permanent ice cap developed on Antarctica during the Eocene–Oligocene transition (EOT; ~34.44 to 33.65 million years ago (Ma)), Earth witnessed a transition from a greenhouse towards a glacially driven climate. Evidence of high-latitude cooling and increased latitudinal temperature gradients across the EOT has been found in both marine and terrestrial environments. However, the timing and magnitude of temperature change in the North Atlantic remains poorly constrained.Here, we used two independent organic geochemical palaeothermometers derived from (i) alkenones and (ii) Glycerol Dialkyl Glycerol Tetraether (GDGT) lipids, to reconstruct sea surface temperature (SST) evolution across the EOT from the southern Labrador Sea (Sites: ODP 647 and DSDP 112). In the Labrador Sea alkenones do not appear until the earliest Oligocene (both sites) while GDGT lipids (analysed in Site 647 only) provides a well-constrained temperature record across the EOT.  Our SST records provide the most detailed record for the northern North Atlantic through the 1 Myr leading up to the EOT onset, and reveals a distinctive cooling step of ~3 ºC (from 27 to 24 ºC), between 34.9 and 34.3 Ma, ~500 kyr prior to Antarctic glaciation. This cooling step, when compared visually to other SST records, is asynchronous across North and South Atlantic sites. This illustrates a considerable spatiotemporal variability in SST evolution in the northern sector of the North Atlantic and the Norwegian-Greenland Sea. Overall, the cooling step fits within a phase of general SST cooling recorded across sites in the North Atlantic in the 5 Myr interval bracketing the EOT.We used a modelling study (GFDL CM2.1) to try and reconcile the observation of pre-EOT cooling with the hypothesis that Atlantic Meridional Overturning Circulation (AMOC) switched on or intensified on the lead up to the EOT, which would be expected to have warmed the North Atlantic region. Results suggest that a reduction in atmospheric CO2 from 800 to 400 ppm may be sufficient to counter warming from an AMOC start-up. In the model, the AMOC start-up is initiated during closure of the Arctic–Atlantic gateway.While the model simulations applied here are not yet in full equilibrium, and the experiments are idealized, the results, together with the proxy data, highlight the heterogeneity of basin-scale surface ocean responses to the EOT thermohaline changes, with sharp temperature contrasts expected across the northern North Atlantic as positions of the subtropical and subpolar gyre systems shift in response to climatic and oceanic adjustments.

Relationships between Atlantic extra‐tropical features and Intertropical Convergence Zone (ITCZ) position close to Northeast Brazil are discussed, on the basis of atmosphere and ocean patterns in DJF and April. Composites for three situations were analysed. In the first composite, years with extreme positive North Atlantic Oscillation Index (NAOI) in DJF and the ITCZ displaced southward in April were selected. The other two composites were related only to anomalous ITCZ positions—either south or north of the equator—in April. The physical mechanism for the relation between the NAOI and the ITCZ is the influence of the southern North Atlantic Oscillation (NAO) centre on the North Atlantic subtropical high, the sea surface temperature (SST) and the intensity of the trade winds; however, this situation occurred in only a few years. Analysis of the other situations indicated the influence of a dominant mode of variability over the North and South Atlantic Oceans that affects the ITCZ position. Over the North Atlantic, this mode was related to a shifting of the NAO pattern, which modified the position of the North Atlantic subtropical high. Over the South Atlantic, this mode indicated an extra‐tropical centre of action associated with displacement of the South Atlantic subtropical high. A proposed index for monitoring ITCZ position, named the North Atlantic Index (NAI), was calculated from sea level pressure (SLP) anomalies in the two centres of action of the North Atlantic in DJF, which are related to the shifting of the NAO. Although the NAO index is related to atmospheric/oceanic features associated with ITCZ displacement, the new index presented higher and more organized correlations with atmospheric and oceanic conditions linked to ITCZ behaviour and can be useful even when the NAO is not extreme. Copyright © 2009 Royal Meteorological Society

This study analyzes decadal modulation of trans-basin variability (TBV) on extended boreal summer (May-October) tropical cyclone frequency (TCF) over the western North Pacific (WNP), central-eastern North Pacific (CENP) and North Atlantic (NATL) basins. There are distinct decadal regimes (P1:1979-1997, P2:1998-2008, and P3:2009-2019) with changes in the interannual relationship between TBV and TCF over these three basins. During P1 and P3, there is a significant inter-annual TBV-TCF relationship over the CENP and NATL, but these relationships become insignificant during P2. Changes in the interannual TBV-TCF relationship over the WNP are opposite to those over the CENP and NATL basins, with significant relationship during P2 but insignificant relationship during P1 and P3. Changes in all three basins coincide with decadal changes in large-scale parameters associated with TBV. Consistent basin-wide changes in lower-tropospheric vorticity (vertical wind shear) associated with TBV appear to be largely responsible for changes in total TCF over the NATL (CENP) during P1 and P3. In contrast, a dipole pattern in lower-tropospheric vorticity and vertical wind shear anomalies associated with TBV over the NATL and CENP basins occurs during P2, leading to an insignificant interannual TBV-TCF relationship over the NATL and CENP basins. Over the WNP, a basin-wide consistent distribution of lower-tropospheric vorticity associated with TBV is consistent with changes in total TCF during P2, while a dipole correlation pattern between TBV-associated factors and TCF during P1 and P3 leads to a weak correlation between TBV and WNP TCF. These three distinct observed decadal regimes may be associated with interactions between ENSO and the Pacific Decadal Oscillation on decadal timescales.

Silver in the far North Atlantic Ocean

The surface active group (SAG) is the most obvious social interaction of the North Atlantic right whale (Eubalaena glacialis). SAGs are typically composed of an adult female with two or more males engaged in social behavior near the surface. Distinct calls, believed to be produced by the female, are associated with these groups. Calls recorded from three North Atlantic right whale SAGs and three South Atlantic right whale (Eubalaena australis) SAGs were played back to North Atlantic right whales to determine if these sounds are sufficient to attract males to the groups. Playbacks of gunshot sounds produced by North Atlantic right whales were used as a control stimulus. Thirty‐six trials were carried out from 1999 to 2001 in the Bay of Fundy, Canada. Whales approached 27 of 31 SAG playbacks and 0 of 5 gunshot playbacks. Where sex was determined (n= 28), all approaches to North Atlantic SAG recordings were by males. Individuals (n= 22) of all age and sex classes approached South Atlantic SAG playbacks. These trials indicate that SAG calls from both populations are sufficient to attract right whales to SAGs and that males and females respond differently to stimuli from the North Atlantic. The difference in response to North and South Atlantic SAG stimuli was unexpected. Novelty, species differences in calls, and different seasonal or behavioral context for the recorded stimuli may be responsible for the differences in response.

High resolution benthic oxygen isotope records combined with radiocarbon datings, from cores retrieved in the North, Equatorial, and South Atlantic are used to establish a reliable cronostratigraphy for the last 60 ky. This common temporal framework enables us to study the timing of the sub-Milankovitch climate variability in the entire surface Atlantic during this period, as reflected in planktonic oxygen isotope records. Variations in sea surface temperatures in the Equatorial and South Atlantic reveal two warm periods during the mid-stage 3 which are correlated to the warming observed in the North Atlantic after Heinrich events (HL) 5 and 4. However, the records show that the warming started about 1500 y earlier in the South Atlantic. A zonally averaged ocean circulation model simulates a similar north-south thermal antiphasing between the latitudes of our coring sites, when pertubated by a freshwater flux anomaly. We infer that the observed phase relationship between the northern and the southern Atlantic is related to periods of reduced NADW production in the North Atlantic, such as during HL5 and HL4.

Previous studies showed that, over the global ocean, there is no noticeable hemispheric asymmetry in cloud fraction (CF). This contributes to the balance in solar radiation reaching the sea surface in the northern and southern hemispheres. In the current study, we focus on the tropical Atlantic (30° N–30° S), which is characterized by significant amounts of Saharan dust dominating other aerosol species over the North Atlantic. Our main point is that, over the tropical Atlantic, Saharan dust not only is responsible for the pronounced hemispheric aerosol asymmetry, but also contributes to significant cloud cover along the Saharan Air Layer (SAL). Over the tropical Atlantic in July, along the SAL, Moderate Resolution Imaging Spectroradiometer CF data showed significant cloud cover (up to 0.8–0.9). This significant CF along SAL together with clouds over the Atlantic Intertropical Convergence Zone contributes to the 20% hemispheric CF asymmetry. This leads to the imbalance in strong solar radiation, which reaches the sea surface between the tropical North and South Atlantic, and, consequently, affects climate formation in the tropical Atlantic. During the 10-year study period (July 2002–June 2012), NASA Aerosol Reanalysis (aka MERRAero) showed that, when the hemispheric asymmetry in dust aerosol optical thickness (AOT) was most pronounced (particularly in July), dust AOT averaged separately over the tropical North Atlantic was one order of magnitude higher than that averaged over the tropical South Atlantic. In the presence of such strong hemispheric asymmetry in dust AOT in July, CF averaged separately over the tropical North Atlantic exceeded that over the tropical South Atlantic by 20%. Both Multiangle Imaging Spectroradiometer measurements and MERRAero data were in agreement on seasonal variations in hemispheric aerosol asymmetry. Hemispheric asymmetry in total AOT over the Atlantic was most pronounced between March and July, when dust presence over the North Atlantic was maximal. In September and October, there was no noticeable hemispheric aerosol asymmetry between the tropical North and South Atlantic. During the season with no noticeable hemispheric aerosol asymmetry, we found no noticeable asymmetry in cloud cover.

abstractGroup velocity dispersion characteristics of fundamental mode Rayleigh waves (T = 20 to 100 sec) in the North and South Atlantic oceans have been determined from moving window analyses of seismograms. The “mixed path” velocity data combined with oceanic age information for the North and South Atlantic were inverted to yield “pure path” dispersion characteristics for four sea-floor age divisions in the North Atlantic (0 to 23 m.y., 23 to 63 m.y., 63 to 100 m.y., and older than 100 m.y.), for three sea-floor age divisions in the South Atlantic (0 to 23 m.y., 23 to 63 m.y., and older than 63 m.y.), and for one nonoceanic division. Rayleigh wave group velocities were found to increase with increasing oceanic age as has been previously described for the Pacific. The velocities in the Atlantic Ocean basins were found to be 5 to 8 per cent faster than those for waves of corresponding periods in the Pacific Ocean basins. The distinct differences in velocities between the Atlantic and Pacific oceans provide additional evidence that the upper mantles of these two oceans are not identical.

To avoid an explicit simulation of the overflows across the Greenland-Scotland ridge, many models of the large-scale ocean circulation seek to include the net effect of the inflowing dense water masses by restoring temperature and salinity near the ridge to observed conditions. In this paper the authors examine the effect of different datasets for the northern restoring condition in two versions, eddy resolving and non-eddy resolving, of the model of the North and equatorial Atlantic that has been developed in recent years as a Community Modeling Effort for WOCE. It is shown that the use of smoothed climatological fields of temperature and salinity south of the Denmark Strait leads to strong deficiencies in the simulation of the deep flow field in the basin. A switch to actual hydrographic data from the Denmark Strait ignites a rapid dynamic response throughout the North Atlantic, affecting the transport and vertical structure of the deep western boundary current and, by virtue of the JEBAR efffect, the transport of the horizontal gyres. Meridional overturning and northward heat transport too weak in the cases with climatological boundary conditions, increase to more realistic levels in the subtropical North Atlantic. The initial response to switches in the high-latitude thermohaline forcing is mediated by fast waves along the westurn boundary, leading to changes in the deep western boundary current in low latitudes after about two years in the non-eddy-resolving cast. The initial timescale depends on the horizontal grid spacing of the model; in the high-resolution case, the first signal reaches the equator in a few months. The adjustment to a new, dynamic quasi equilibrium involves Kelvin waves along the equator and Rossby wave in the interior and is attained in less than two decades throughout the North Atlantic. It is suggested that these fast dynamic adjustment processes could play an important role in possible fluctuations of the thermohaline circulation, or transitions between different equilibrium states of the coupled ocean–atmosphere system, and may have determined the timescale of the observed climatic transitions before and during the last deglaciation.

Dr. Critchley's paper is available in three parts; Part 1, the "Fourth Boundary Problem," Part 2, "The Energy Shortage," and Part 3, "Military Considerations." III. Military Considerations Canadian security policy is strongly related to our participation in the NATOand NORAD alliances. NATO is seen as the defence against the Warsaw Pact threatto Western Europe. NORAD, The Canada-U.S. agreement originally formed toprovide for continental defence against the Soviet Union'sstrategic bomber threat to the United States, is now regarded as a subsidiarypart of the NATO arrangement. Several recent developments in militarytechnology, and reactions to these developments on the part of the Soviet Unionand NATO members, may cause parts of the arctic region to become a new focus ofmilitary activity and of NATO and NORAD concern. NATO-related developments willbe analyzed first. Currently, the use of the Arctic Ocean and adjacent seas by military vessels isconfined to nuclear-powered submarines. Evidence in the public domain indicatesthat such usage appears to be in the form of occasional experimental-trainingexercises(1)· The attention of strategic analysts and naval planners is concentrated not onthe Arctic, but on the North Atlantic. The reason for concentration on the North Atlantic is the build-up of the Soviet Northern Fleet, which is based in Murmansk and other ports on the Kola Peniusula. As of mid -1981, that fleetincluded approximately 82 major surface combat ships, 135 attackand cruise-missile submarines and 45 ballistic-missile-carryingsubmarines(2). Three types of nuclear-powered submarines are assigned to this and other fleetsof the Soviet navy: attack submarines and cruise-missile submarines(designated as SSNs and SSGNs respectively) have the mission ofattacking an adversary's surface shipping and submarines at sea;ballistic-missile submarines (SSBNs), armed with long-range missiles withnuclear warheads, have major military installations, industrial complexes andurban centres as probable targets in the event of a nuclear war. The veryexistence of SSBNs, along with other strategic nuclear weapons, is thought toprevent such a war from occurring. Of particular concern to NATO is the Soviet Union's assignment of a large Proportion of SSNs, SSGNs and most of their Yankee-class and Delta-class SSBNsto the Northern Fleet. More specifically, the Northern Fleet has 65% of the Soviet navy's SSBNs and 52% of all other types of Sovietsubmarines(3). The build-up of the Northern Fleet in relation to the Baltic, Black and Pacific fleets appears to relate to the existence ofchoke-points (narrow water channels or straits) which govern the exits of thelatter three fleets from their home ports and the absence of such a choke-pointfor the Northern Fleet. Submarines and surface vessels can make way from their Barents Sea ports to the Atlantic without having to pass through any narrowstraits. Although only a small portion of that fleet deploys into the North Atlantic at any given time(4), this and other evidence has led mostanalysts to conclude that the fleet's primary tasks are strategic and tactical(anti-shipping) offensive missions in the North and Central Atlantic. The NATO response to these developments and analysis has been acontinuing effort to construct a "choke-point" at the GIUK gap.

The atmospheric distribution of lead over a number of marine regions