Central North Atlantic Research Articles

Synoptic and dynamic aspects of an extreme springtime Saharan dust outbreak

AbstractIn March 2004, a large‐scale, strong and persistent outbreak of Saharan dust on to the adjacent tropical and subtropical Atlantic Ocean was observed in satellite imagery. Surface observations show that the event was accompanied by unusual weather conditions across large parts of North Africa including low temperatures and strong winds over the Sahara, extreme precipitation in Libya and a heat wave on the Guinea coast. The dust outbreak was associated with an unseasonally southerly position of the Intertropical Convergence Zone and a delayed northward progression of the African monsoon.The dust front was initially related to a density current caused by strong evaporational cooling along a precipitating cloud‐band that penetrated into the northern Sahara ahead of an upper‐level trough. At later stages, massive upper‐level convergence, sinking, low‐level divergence and an explosive anticyclogenesis over northwest Africa caused strong northerly flow and a quick spreading of the dust front to the south and west. The strong pressure gradients over North Africa were further enhanced by the formation of a cyclone ahead of the upper‐trough. A dynamical analysis based on potential‐vorticity (PV) theory provides new insights into the generation of North African harmattan surges. Using a PV inversion, it is shown that the explosive anticyclogenesis was caused largely by unbalanced dynamics related to the density current, divergent outflow from the precipitation over Libya and inertial instability in the entrance region of the strong subtropical jet and tropical plume along the eastern side of the upper trough. These processes enhanced the effects of the balanced advection of negative vorticity and cold air by the large‐scale wave. Moreover, we show the importance of an explosive cyclogenesis event over the central North Atlantic for the amplification of the downstream wave associated with the penetration of the cold front into North Africa. Copyright © 2006 Royal Meteorological Society.

Ocean Color Reveals Phase Shift Between Marine Plants and Yellow Substance

Daily high-resolution Sea-viewing Wide Field-of-view Sensor (SeaWiFS) images of the central North Atlantic Ocean (1998-2003) show that temporal changes in the absorption coefficient of colored dissolved organic matter (CDOM) or "yellow substance" follow changes in phytoplankton pigment absorption coefficient in time. CDOM peaks (between January and March) and troughs (late summer and fall) followed pigment peaks and troughs by approximately two and four weeks, respectively. This phase shift is additional strong evidence that CDOM in the marine environment is derived from phytoplankton degradation. The common assumption of linear covariation between chlorophyll and CDOM is a simplification even in this ocean gyre. Due to the temporal changes in CDOM, chlorophyll concentration estimated based on traditional remote sensing band-ratio algorithms may be overestimated by about 10% during the spring bloom and underestimated by a similar 10% during the fall. These observations are only possible through use of synoptic, precise, accurate, and frequent measurements afforded by space-based sensors because in situ technologies cannot provide the required sensitivity or synoptic coverage to observe these natural phenomena.

Iron limits primary productivity during spring bloom development in the central North Atlantic

AbstractWe present in situ biophysical measurements and bioassay experiments that demonstrate iron limitation of primary productivity during the spring bloom in the central North Atlantic. Mass balance calculations indicate that nitrate drawdown is iron (Fe)‐limited and that aeolian Fe supply to this region cannot support maximal phytoplankton growth during the bloom. Using a simple simulation model, we show that relief of Fe limitation during the spring bloom can increase nitrate drawdown and, hence, new primary production, by 70%. We conclude that the episodic nature of iron supplied by dust deposition is an important factor controlling the dynamics of the spring bloom. From this, we hypothesize that variability in the timing and magnitude of the spring bloom in response to aeolian Fe supply will affect carbon drawdown and food web dynamics in the central North Atlantic.

Quantifying changes and their uncertainties in probability distribution of climate variables using robust statistics

Robust tools are presented in this manuscript to assess changes in probability density function (pdf) of climate variables. The approach is based on order statistics and aims at computing, along with their standard errors, changes in various quantiles and related statistics. The technique, which is nonparametric and simple to compute, is developed for both independent and dependent data. For autocorrelated data, serial correlation is addressed via Monte Carlo simulations using various autoregressive models. The ratio between the average standard errors, over several quantiles, of quantile estimates for correlated and independent data, is then computed. A simple scaling-law type relationship is found to hold between this ratio and the lag-1 autocorrelation. The approach has been applied to winter monthly Central England Temperature (CET) and North Atlantic Oscillation (NAO) time series from 1659 to 1999 to assess/quantify changes in various parameters of their pdf. For the CET, significant changes in median (or scale) and also in low and high quantiles are observed between various time slices, in particular between the pre- and post-industrial revolution. Observed changes in spread and also quartile skewness of the pdf, however, are not statistically significant (at 95% confidence level). For the NAO index we find mainly large significant changes in variance (or scale), yielding significant changes in low/high quantiles. Finally, the performance of the method compared to few conventional approaches is discussed.

Early stages of Atlantic fishes: an identification guide for the western central North Atlantic

Introduction. Background. Geographic Coverage. Taxonomic Coverage. List of Taxa. Principles and Terminology. Egg Stage. Yol-sac Stage. Larval Stage. Transformation Stage. Juvenile Stage. Abbreviations. Glossary. Explanation of Format and Methods. Introduction to Orders. Introduction to Families. Species Descriptions. How to Identify Early Stages of Fishes with this Guide. Descriptions. For a complete listing of the contents of all 214 family chapters look up the book's description at www.crcpress.com.

Gas chromatography system for the automated, unattended, and cryogen-free monitoring of C2 to C6 non-methane hydrocarbons in the remote troposphere

An unattended, automated, on-line, cryogen-free, remotely controlled gas chromatography (GC) system was developed and has been deployed for more than 1 year for the continuous determination of C 2 to C 6 hydrocarbons at an observatory located at 2225 m elevation, on the summit caldera of an inactive volcano on the island of Pico, Azores. The GC instrument is tailored to the measurement challenges at this remote and high altitude site. All consumable gases are prepared in situ. Total power use remains below 700 W at all times. Sample collection and analysis is performed without use of cryogen. Hydrocarbons are concentrated on a one-stage trapping/injection system consisting of a Peltier-cooled multi-bed solid adsorbent trap. Analytes are detected after thermal desorption and separation on an alumina-PLOT (porous-layer open tubular) column by flame ionization detection (FID). Sample focusing, desorption, separation and detection parameters were thoroughly investigated to ensure quantitative collection and subsequent injection onto the GC system. GC operation is controlled remotely and data are downloaded daily. Sample volumes (600 and 3000 ml) are alternated for analysis of C 2 to C 3 and C 3 to C 6 hydrocarbons, respectively. Detection limits are in the low parts per trillion by volume (pptv) range, sufficient for quantification of the compounds of interest at their central North Atlantic lower free troposphere background concentrations.

Evidence for genetic differentiation in the European conger eel Conger conger based on mitochondrial DNA analysis

The European conger eel Conger conger is an important marine benthic fish in the North-East Atlantic and represents a valuable fishery resource. However, little is known about its reproductive biology. In an attempt to gain a better understanding of the conger eel population structure, mitochondrial DNA (mtDNA) sequences were examined. A region with 432 bp of the control region of the mtDNA was sequenced from 40 individuals from six different locations around the central and eastern North Atlantic Ocean. Thirty variable positions defined 28 distinct haplotypes. The average sequence difference within samples (1.3–4.2%) was comparable to those between samples (1.4–3.6%). MtDNA sequence-based statistical tests showed significant geographic differentiation between some local population samples, suggesting that the conger eel does not comprise a single panmictic population. However, given our sample sizes, these preliminary results should be interpreted with caution and more individuals from more sites, including the Mediterranean Sea, should be analyzed in detail. The genetic variability detected in this study is an initial step to elucidate the genetic back-ground of the conger eel population structure.

Life cycles of North Atlantic teleconnections under strong and weak polar vortex conditions

AbstractThis paper investigates the role of the strength of the polar stratospheric winter vortex in the dynamics of the life cycles of North Atlantic teleconnections. A new set of teleconnection patterns was produced from low‐pass‐filtered daily 300 hPa height data of NCEP (National Centers for Environmental Prediction) reanalysis data 1958–1998. All teleconnections are meridional dipoles, which to a certain degree resemble the North Atlantic Oscillation based on surface pressure data. There are two distinct teleconnections (one over the eastern and one over the western North Atlantic) during episodes of weak polar vortex, and only one, over the central North Atlantic, during strong polar vortex episodes. The teleconnections have periods of about two weeks. Stream function tendency analysis of the life cycles shows that the relatively simple resulting teleconnections evolve from very complex structures. During the growth phase of the teleconnection indices there are strong and systematic differences between the two polar vortex regimes. While in the weak vortex regime the anomaly growth is mainly driven by transient eddy vorticity fluxes from the low‐frequency domain, in the strong vortex regime there is also low‐frequency advection of relative vorticity resulting from the interaction of low‐frequency eddies with stationary eddies. Copyright © 2006 Royal Meteorological Society

Reconstructing climate variability from Greenland ice sheet accumulation: An ERA40 study

Re‐analysis data covering the period 1958–2001 are used to investigate the relationship between regional, inter‐annual snow accumulation variability over the Greenland Ice Sheet (GrIS) and large scale circulation patterns, cyclone frequency, and strength. Four regions of the GrIS have been identified that are highly independent with respect to accumulation variability. Accumulation indices of three of these regions are associated with distinct large‐scale circulation patterns: Central‐western GrIS reveals an inverse relationship with a NAO‐like pattern, the south‐west a positive correlation with a high pressure bridge from central North Atlantic to Scandinavia, and the south‐eastern GrIS a positive correlation with a high‐pressure anomaly over the Greenland Sea. These large‐scale patterns also impact European climate in different ways. Accumulation variability in north‐eastern GrIS, however, is dominated by cyclones originating from the Greenland Sea. Thus, Greenland ice core accumulation records offer the potential to reconstruct various large‐scale circulation patterns and regional storm activity.

Mid-Cretaceous oceanic red beds in the Umbria–Marche Basin, central Italy: Constraints on paleoceanography and paleoclimate

Detailed studies of the mid-Cretaceous sedimentary strata in the Umbria–Marche Basin in Italy revealed that aside from several well-known organic-rich “black shale” horizons that record OAEs, several varicolored, mainly reddish horizons indicate oxic conditions at the ocean bottom. Eight such horizons have been identified in Aptian–Cenomanian sequences in the Umbria–Marche Basin. The dysoxic/oxic beds alternate regularly but not cyclically and seem to be the result of non-random processes. Their occurrence is not a completely random process. The duration of deposition of these oceanic red beds (ORBs) varies from ∼0.13 my (ORB4) recorded in the Ticinella primula zone, to ∼4.54 my for ORB1, which spans the Globigerinelloides ferreolensis zone to the Ticinella bejaouaensis zone in the Piobbico core. Mid-Cretaceous ORBs are not a local phenomenon because they occur in the Tethyan deposits in the Southern and Austrian Alps, the Carpathians, the Northern Caucasus, the central North Atlantic, in northeastern England and in the western Himalayas. They provide evidence for periodic changes in redox conditions at the ocean bottom. Such changes could have been caused by changes in bioproductivity, basin geometry, sedimentation rates, paleocirculation and/or production of bottom waters with higher content of dissolved oxygen in response to changes in paleoclimate. We suggest that the periodic inflow of colder, more oxygenated bottom waters was the probable cause of ORBs development, either as a result of changes in the ocean bottom topography, or as a result of brief cool climate periods. However, reliable proxies for changes in deep ocean circulation are still lacking. If ORBs were the result of the paleoclimate and, therefore, indirectly caused by changes in CO 2 in atmosphere, they document the increased sensitivity and instability of the mid-Cretaceous climate. Thus, changes in ocean dynamics were on a scale of several hundred thousand years to several million years, which has not been considered by most theories of CO 2 cycling, mid-Cretaceous greenhouse paleoclimate and paleocean dynamics.

A Holocene lacustrine record in the central North Atlantic: proxies for volcanic activity, short-term NAO mode variability, and long-term precipitation changes

Lake and peat corings on three Azores islands in the central North Atlantic, resulted in the discovery of a 6000 year long lacustrine sequence in a small crater lake, Lake Caveiro, on the island of Pico. This island is dominated by Pico mountain (2351 m), Portugal's highest mountain, and the lake site is situated at 903 m asl. Two sediment profiles, one central and one littoral, were sampled. Due to large facial shifts and disconformities in the littoral cores the analyses were concentrated on the central core; only the earliest 1000 years of the littoral core were studied to complement the central profile. We used sedimentology, geochemistry, diatom analyses, magnetic properties, and multivariate statistics, together with 14C and 210Pb dating techniques, to analyse the environmental history of the lake. Volcanic activity seems to have had a dominating impact on sediment changes and partly also on the diatom assemblages; a large number of tephras are found and seem to be connected with large (diatom) inferred pH variations. However, by a combination of methods, including multivariate techniques, we infer that precipitation changes can be detected through the volcanic noise. In the youngest part of the record (AD 1600–2000), with its decadal resolution, these humidity variations seem partly related to shifts in dominating NAO mode. The more long-term precipitation changes further back in time (350–5100 cal yr BP) roughly correspond to the well-known North Atlantic drift-ice variations as well as other North Atlantic records; low precipitation during drift-ice periods. We think these alterations were driven by changes in the thermohaline circulation as large-scale equivalences to the Great Salt Anomaly; low sea surface temperatures and changes in circulation patterns of the central North Atlantic decreased the regional precipitation. Cooler/drier periods occurred 400–800, 1300–1800, 2600–3000, 3300–3400 and possibly also 4400–4600 cal yr BP, while 300–400, 900–1000, 2000–2400, 3100–3200, 3800–4000 and 4700–5000 cal yr BP seem to have been more humid phases on the Azores.

Suppression of deep convection over the tropical North Atlantic by the Saharan Air Layer

The effects of the dust‐laden Saharan Air Layer (SAL) on the occurrence of deep convection over the eastern and central tropical North Atlantic Ocean off‐shore of the African continent during August–September 2002 are investigated. We show that the SAL is associated with suppressed convection in this region. To determine the possible cause of the suppressed convection, the thermodynamic structure and dust content of the SAL are investigated. We find that the SAL is associated with warmer and dryer air below 700 hPa with the largest temperature anomalies located around 850 hPa. This warm and dry air layer raises the lifting condensation level and level of free convection, and increases the energetic barrier to convection that leads to reduced occurrence of deep convection.

Larval development of five species of blenny (Teleostei: Blenniidae) from the western central North Atlantic, with a synopsis of blennioid family characters

Light trap collections on oil and gas platforms in the northern Gulf of Mexico off Louisiana from 1995 to 1997 contained young of tessellated blenny Hypsoblennius invemar, freckled blenny Hypsoblennius ionthas, featherduster blenny Hypleurochilus multifilis, molly miller Scartella cristata and seaweed blenny Parablennius marmoreus, which are described. Interspecific differences were: number of dorsal, anal, pelvic and caudal fin elements; number of mandibular pores; presence or absence of canine teeth, hypural 5 and pectoral fin pigment; width of gill openings; length of preopercular spines (in larvae). Size at settlement differed among some taxa, but all five species settled within a narrow size window of c. 1·5 mm standard length (LS). Hypsoblennius invemar, H. ionthas, H. multifilis and S. cristata settled at mean sizes between 11·3 and 12·1 mm LS, whereas P. marmoreus settled at a mean size of 19·3 mm LS. Sexually dimorphic differences were consistently evident by 17–18 mm LS in all species but P. marmoreus. The two smallest blennies with external characters normally associated with sexual maturity were a 20 mm male and 21 mm female H. multifilis. Primary caudal fin rays began to bifurcate between 17·0 and 18·3 mm LS in H. invemar, H. ionthas, H. multifilis and S. cristata. Hypleurochilus multifilis displayed the external characteristics of being sexually mature at 20–21 mm LS. Thus, bifurcation of primary caudal fin rays was an indicator of approaching sexual maturity in H. multifilis and this may also be true in the other species studied.

Geographical Differentiation In Clelandella (Gastropoda: Trochidae) In The Northeastern Atlantic

The trochid genus Clelandella is reviewed, taking into account new material collected on northeastern Atlantic seamounts and archipelagos, and in deep water of the Mediterranean. The type species C. miliaris (Brocchi, 1814) is illustrated with topotypic material, and living representatives are reported ranging from north Norway to West Africa and into the Mediterranean. The insular populations of Clelandella are found to constitute discrete groups, which are treated as new species: Clelandella dautzenbergi n. sp. on the Lusitanian seamounts, C. perforata n. sp. in the Meteor group of the central North Atlantic, C. azorica n. sp. in the Azores and C. madeirensis n. sp. in Madeira. Within such groups, differentiation is not appreciable and variability is continuous notwithstanding distances of the order of 200 km. Between such groups, the geographical isolation of the insular populations has resulted in substantial divergence over distances in the range 300– 600 km. A further species, C. myriamae n. sp., was collected on deep-water mud volcanoes of the eastern Mediterranean, and is broadly sympatric with C. miliaris.

Effects of the Mixed Layer Time Variability on Kinematic Subduction Rate Diagnostics

Abstract An eddy-resolving primitive equation general circulation model is used to estimate water-mass subduction rates in the North Atlantic Ocean subtropical gyre. The diagnostics are based on the instantaneous kinematic approach, which allows the calculation of the annual rate of water-mass subduction at a given density range, following isopycnal outcrop positions over the annual cycle. It is shown that water-mass subduction is effected rapidly (∼1–2 months) as the mixed layer depth decreases in spring, consistent with Stommel’s hypothesis, and occurs mostly over the area of deep late-winter mixed layers (≥150 m) across the central North Atlantic in the density range 26 ≤ σ ≤ 27.2. Annual subduction rates O(100–200 m yr–1) are found south and east of the Gulf Stream extension in the density range of subtropical mode waters from roughly 26.2 to 26.6. In the northeastern part of the subtropical gyre, annual subduction rates are somewhat larger, O(250 m yr–1), from a density of about 26.9 east of the North Atlantic Current to 27.4 (upper cutoff in this study). The overall basin-integrated subduction rate for subtropical mode waters (26.2 ≤ σ ≤ 26.6) is about 12.2 Sv (Sv ≡ 106 m3 s−1), comparable to the total formation rate inferred from the surface density forcing applied in the model of roughly 11 Sv in this density range. In contrast, basin-integrated rates for denser central water (26.8 ≤ σ ≤ 27.2) provide a vanishingly small net subduction. In this range, eddy correlations (<30 days) between the surface outcrop area and the local subduction rate counteract the net subduction by the mean flow (deduced from monthly averaged model fields). Comparison with estimates of the annual subduction rate based on the annual mean velocity and late-winter mixed layer properties alone, as is usual in climatological and coarse-resolution model analyses, indicates a mismatch of at least 8 Sv in the density range where the model forms subtropical mode water. This mismatch is primarily due to time-varying mixed layer processes rather than small-scale mixing not resolved explicitly by the model. Our diagnostics based on the instantaneous kinematic approach provide a more complete picture of the water-mass formation process than diagnostics based only on air–sea flux or late-winter mixed layer model data. They reveal the crucial importance of both the seasonal mixed layer cycle and mesoscale eddies to the overall formation rate and provide thus a valuable tool for the analysis of water-mass formation rates in eddy-resolving numerical simulations at basin scale.

A simulation model for capelin migrations in the North Atlantic

Some pelagic fish species undertake extensive feeding and spawning migrations covering distances of several hundred miles. We present a model of such migrations where the dynamics are governed by an advection–diffusion type equation with the advection being determined by environmental fields for temperature, food density and oceanic currents, in addition to a force field generated by an attracting spawning region. The model is motivated by the migrations of the capelin stock in the Central North Atlantic. Simulations of the spawning migrations of this stock are presented. We also discuss how the continuous migration model can be reduced to a simpler model based on transition or migration matrices.

The North Atlantic variability structure, storm tracks, and precipitation depending on the polar vortex strength

Abstract. Motivated by the strong evidence that the state of the northern hemisphere vortex in boreal winter influences tropospheric variability, teleconnection patterns over the North Atlantic are defined separately for winter episodes where the zonal wind at 50hPa and 65° N is above or below the critical velocity for vertical propagation of zonal planetary wave 1. We argue that the teleconnection structure in the middle and upper troposphere differs considerably between the two regimes of the polar vortex, while this is not the case at sea level. If the polar vortex is strong, there exists one meridional dipole structure of geopotential height in the upper and middle troposphere, which is situated in the central North Atlantic. If the polar vortex is weak, there exist two such dipoles, one over the western and one over the eastern North Atlantic. Storm tracks (and precipitation related with these) are determined by mid and upper tropospheric conditions and we find significant differences of these parameters between the stratospheric regimes. For the strong polar vortex regime, in case of a negative upper tropospheric "NAO" index we find a blocking height situation over the Northeast Atlantic and the strongest storm track of all. It is reaching far north into the Arctic Ocean and has a secondary maximum over the Denmark Strait. Such storm track is not found in composites based on a classic NAO defined by surface pressure differences between the Icelandic Low and the Azores High. Our results suggest that it is important to include the state of the polar vortex strength in any study of the variability over the North Atlantic.

Iron, manganese, and lead at Hawaii Ocean Time-series station ALOHA: Temporal variability and an intermediate water hydrothermal plume

Trace metal clean techniques were used to sample Hawaii Ocean Time-series (HOT) station ALOHA on seven occasions between November 1998 and October 2002. On three occasions, full water-column profile samples were obtained; on the other four occasions, surface and near-surface euphotic zone profiles were obtained. Together with three other published samplings, this site may have been monitored for “dissolved” (≤0.4 or ≤0.2 μm) Fe more frequently than any other open ocean site in the world. Low Fe concentrations (<0.1 nmol kg −1) are seen in the lower euphotic zone, and Fe concentrations increase to a maximum in intermediate waters. In the deepwaters (>2500 m), the concentrations we observe (0.4–0.5 nmol kg −1) are significantly lower than some other deep North Pacific stations but are similar to values that have been reported for a station 350 miles to the northeast. We attribute these low deepwater values to transport of low-Fe Antarctic Bottom Water into the basin and a balance between Fe regeneration and scavenging in the deep water. Near-surface waters have higher Fe levels than observed in the lower euphotic zone. Significant temporal variability is seen in near-surface Fe concentrations (ranging from 0.2–0.7 nmol kg −1); we attribute these surface Fe fluctuations to variable dust deposition, biological uptake, and changes in the mixed layer depth. This variability could occur only if the surface layer Fe residence time is less than a few years, and based on that constraint, it appears that a higher percentage of the total Fe must be released from North Pacific aerosols compared to North Atlantic aerosols. Surprisingly, significant temporal variability and high particulate Fe concentrations are observed for intermediate waters (1000–1500 m). These features are seen in the depth interval where high δ 3He from the nearby Loihi Seamount hydrothermal fields has been observed; the total Fe/ 3He ratio implies that the hydrothermal vents are the source of the high and variable Fe. The vertical profile of Mn at ALOHA qualitatively resembles other North Pacific Mn profiles with surface and intermediate water maxima, but there are some significant quantitative differences from other reported profiles. The ≤0.4 μm Mn concentration is highest near the surface, decreases sharply in the upper 500 m, then shows an intermediate water maximum at 800 m and then decreases in the deepest waters; these concentrations are higher than observed at a station 350 miles to the northeast that shows similar vertical variations. It appears that there is a significant Mn gradient (throughout the water column) from HOT towards the northeast. Compared to the first valid oceanic Pb data for samples collected in 1976, Pb at ALOHA in 1997–1999 shows decreases in surface waters and waters shallower than 200 m. Pb concentrations in central North Pacific surface waters have decreased by a factor of 2 during the past 25 yr (from ∼65 to ∼30 pmol kg −1); surface water Pb concentrations in the central North Atlantic and central North Pacific are now comparable. We attribute the surface water Pb decrease to the elimination of leaded gasoline in Japan and to some extent by the U.S. and Canada. We attribute most of the remaining Pb in Pacific surface waters to Asian emissions, more likely due to high-temperature industrial activities such as coal burning rather than to leaded gasoline consumption. A 3-year mixed-layer time series from the nearby HALE-ALOHA mooring site (1997–1999) shows that there is an annual cycle in Pb with concentrations ∼20% higher in winter months; this rise may be created by downward mixing of the winter mixed layer into the steep gradient of higher Pb in the upper thermocline (Pb concentrations double between the surface and 200 m). From 200 m to the bottom, Pb concentrations decrease to levels of 5–9 pmol kg −1 near the bottom; for most of the water column, thermocline and deepwater Pb concentrations do not appear to have changed significantly during the 23-yr interval.

Upper Cretaceous oceanic red beds (CORBs) in the Tethys: occurrences, lithofacies, age, and environments

A major change in oceanic sedimentation from mid-Cretaceous organic carbon-enriched deep-sea deposits to predominantly Upper Cretaceous oceanic red beds (CORBs), represented mainly by deep-sea red shales and marls, occurred during the Late Cretaceous and early Tertiary in the Tethys. A variety of earth processes such as organic carbon draw-down, tectonic, palaeoceanographic, eustatic and palaeoclimatic changes, or a combination of these could cause such a change, the main significance of which is that it demonstrates that the deep ocean basins ceased to be the preferential burial site for organic carbon. A compilation of available data on CORB occurrences, composition, and age indicate that: (1) CORBs are found in a broad geographic belt extending from the Caribbean across the central North Atlantic, southern and eastern Europe to Asia; with limited occurrences in the Indian ocean; (2) both the first and the last occurrences of CORBs are diachronous; (3) CORBs are of pelagic and hemipelagic origin and were deposited in a variety of environments from continental slope to deep oceanic basin, above and below the carbonate compensation depth (CCD); (4) total organic carbon (TOC) is mostly <0.1%; haematite is relatively abundant, up to 10% in red shales; (5) the termination of CORB deposition in the Alps, Carpathians, and Himalayas was mostly a result of major tectonic events associated with intensification of continental plate migration and initial stages of collision of the Indian and Asian plates and the African and European continental plates. We suggest that changes in dissolved oxygen in the deep ocean were mainly the result of changes in the location and formation of deep water and changes in ocean circulation. It is more than probable that a score of different earth processes, including changes in climate, all acting in concert, were involved in such a major change in the deep-sea environment and location of the carbon reservoir.

Geographic variation of golden redfish (Sebastes marinus) and deep-sea redfish (S. mentella) in the North Atlantic based on otolith shape analysis

Abstract The unresolved interrelationships of North Atlantic redfish stocks have prevented adaptive fisheries assessment and management in the past. Otolith shapes of golden redfish (S. marinus) and deep-sea redfish (S. mentella) were analysed for geographic variation within the entire distribution range in the North Atlantic, in order to evaluate this technique for stock separation. Multivariate analysis of elliptical Fourier shape descriptors revealed high similarity of S. marinus within the central North Atlantic areas (West and East Greenland, Iceland) that were relatively well separated from the Flemish Cap and Barents Sea samples. A similar separation of the Barents Sea area was also observed for S. mentella, whereas the western (Flemish Cap, Davis Strait) and central areas were overlapping to a greater extent. The overall classification rate given by discriminant analysis was poor for both species (&lt;50%) but increased to 72–74% by combining sampling areas to regions (west, central, east). Geographic variation in otolith shapes of both redfish species suggests a separation of the Northeast Arctic stocks (Barents Sea) of both species from the other redfish stocks assessed within ICES and NAFO, whereas similarities observed for the highly migratory S. mentella give reason for integrated management of demersal and pelagic occurrences of this important fisheries resource that straddles the ICES/NAFO boundaries.