Areas of shallow water in the North Atlantic

We report here estimates of the areas of water that are between 1 and 100 m and between 1 and 200 m deep in the North Atlantic, including the Caribbean Sea, the Gulf of Mexico, Hudson Bay and the North Sea, but excluding estuaries. The total areas within these depths, from the equator to 70° N, are 3.91 × 10⁶ km² and 5.66 × 10⁶ km², respectively. We also report the respective areas by selected geographic regions.     

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

We 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.     

Raiding the Landscape: Human Impact in the Scandinavian North Atlantic

Between ca. A.D. 800–1000, Scandinavian chiefly societies with a mixed maritime and agricultural economy expanded into the North Atlantic, colonizing Shetland, Orkney, Caithness, Hebrides, Faeroes, Iceland, Greenland, and Vinland. The settlers brought continental European economics and expectations to a widely varied set of island ecosystems. In many regions, rapid degradation of flora and soils took place associated with social and climate change. Recent research coordinated by the North Atlantic Bicultural Organization (NABO) highlights the extent of pre-modern impacts.     

Phylogeography and historical ecology of the North Atlantic intertidal

Abstract Recent glaciation covered the full extent of rocky intertidal habitat along the coasts of New England and the Canadian Maritimes. To test whether this glaciation in fact caused wholesale extinction of obligate rocky intertidal invertebrates, and thus required a recolonization from Europe, we compared American and European populations using allelic diversity and techniques adapted from coalescent theory. Mitochondrial DNA sequences were collected from amphi-Atlantic populations of three cold-temperate obligate rocky intertidal species (a barnacle, Semibalanus balanoides , and two gastropods, Nucella lapillus and Littorina obtusata ) and three cold-temperate habitat generalist species (a seastar, Asterias rubens ; a mussel, Mytilus edulis , and an isopod, Idotea balthica ). For many of these species we were able to estimate the lineage-specific mutation rate based on trans-Arctic divergences between Pacific and Atlantic taxa. These data indicate that some obligate rocky intertidal taxa have colonized New England from European populations. However, the patterns of persistence in North America indicate that other life-history traits, including mechanisms of dispersal, may be more important for surviving dramatic environmental and climatic change.     

Spawning-strategy-dependent diets in two North American populations of Atlantic salmon Salmo salar

The diet of repeat-spawner Atlantic salmon Salmo salar was investigated using carbon and nitrogen stable-isotope values from the outer growth band of scales, which reflect the fish's consumption and growth during their most recent marine phase. Isotope values for S. salar displaying different spawning strategies were compared between and within the Miramichi and Nashwaak Rivers, New Brunswick, Canada and a Bayesian mixing model was used to infer dietary contributions from potential prey items. Significant differences in the stable-isotope values were found among spawning strategies and between rivers, indicating differences in diet and feeding area, consistent with hypotheses. Bayesian mixing model results inferred the main prey items consumed during marine feeding by S. salar to consist of hyperiid amphipods and capelin Mallotus villosus for repeat alternate spawners from both rivers, sandlance Ammodytes sp. for repeat consecutive spawners from the Miramichi River and amphipods for repeat consecutive spawners from the Nashwaak River. These results demonstrate the diversity of feeding tactics among S. salar spawning strategies from the same river and between populations from different rivers. Accounting for differences in prey availability and the subsequent impact on S. salar diet and spawner return rates (i.e., marine survival) will facilitate the application of ecosystem-based management practices, such as ensuring that fisheries for forage species do not indirectly adversely affect S. salar return rates.     

Distribution of dimethylsulfide and dimethylsulfoniopropionate and its relation with phytoneuston in the surface microlayer of the western North Atlantic during summer

One of the key steps towards predicting dimethylsulfide (DMS) emission to the atmosphere is to understand the distribution and cycling of biogenic sulfur in the microlayer. In this study, we examined the distribution of DMS and dissolved and particulate fractions of dimethylsulfoniopropionate (DMSPd and DMSPp) in the surface microlayer and bulk water of the western North Atlantic during July 2003. DMS concentrations in the bulk water varied from 0.71 to 7.65 nM. In contrast, DMS concentrations in the surface microlayer were fairly low (0.17–1.33 nM). Average concentrations of DMSPd and DMSPp in the bulk water were 2.09 (1.87–6.25) and 44.1 (8.06–119.8) nM, respectively, and those in the surface microlayer were 15.4 (4.06–54.3) and 29.9 (7.32–97.0) nM. In general, DMS was depleted in the microlayer (mean concentration: 0.60 nM) relative to the bulk water (mean concentration: 2.38 nM) with enrichment factors (the ratio of the microlayer concentration to bulk water concentration) ranging from 0.13 to 0.54. There was no consistent enrichment of DMSPp and chlorophyll a in the microlayer. On the contrary, DMSPd appeared to be highly enriched in the microlayer with an average EF of 4.89. The concentration of phaeopigments was also generally greater in the microlayer than in the bulk water, presumably due to enhanced photo-oxidation of chlorophyll a under high surface light intensities in the microlayer. In the study area, the concentration of DMSPp was significantly correlated with the abundance of dinoflagellates in the microlayer. Moreover, a significant correlation between the distributions of DMS, DMSPp, chlorophyll a and phaeopigment concentrations in the microlayer and the bulk water demonstrated that the biogenic materials in the microlayer come primarily from the bulk water below.     

Causes and projections of abrupt climate-driven ecosystem shifts in the North Atlantic

Warming of the global climate is now unequivocal and its impact on Earth' functional units has become more apparent. Here, we show that marine ecosystems are not equally sensitive to climate change and reveal a critical thermal boundary where a small increase in temperature triggers abrupt ecosystem shifts seen across multiple trophic levels. This large-scale boundary is located in regions where abrupt ecosystem shifts have been reported in the North Atlantic sector and thereby allows us to link these shifts by a global common phenomenon. We show that these changes alter the biodiversity and carrying capacity of ecosystems and may, combined with fishing, precipitate the reduction of some stocks of Atlantic cod already severely impacted by exploitation. These findings offer a way to anticipate major ecosystem changes and to propose adaptive strategies for marine exploited resources such as cod in order to minimize social and economic consequences.     

The North Atlantic Oscillation and the Arctic Oscillation favour harmful algal blooms in SW Europe

The ecological factors driving the occurrence of harmful algal blooms (HAB) have been traditionally analysed from a hydrological point of view, whereas the interplay between atmospheric oscillations and HAB has been scarcely explored. Here we address the possible link between atmospheric oscillations in SW Europe, using as proxies the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) indices and the interannual variability in HAB. The yearly series (1973–2005) of mortality of water birds and fish in Doñana National Park (SW Spain) due to toxins associated with the cyanobacterium Microcystis aeruginosa, and the monthly incidence (January 1999 to December 2007) of the paralytic shellfish poisoning (PSP) toxin produced by the dinoflagellate Gymnodinium catenatum in the Rías Baixas (NW Spain), were selected as models of HAB in SW Europe. The incidences of both toxic algal events were fitted to a binary logistic regression as a function of the atmospheric oscillation indices (with different delays in accordance with each toxic event) and a favourability function was then computed. The favourability for the wildlife mortality in Doñana National Park was as a function of the AO averaged for the summer period (June–August) whereas the favourability for the incidence of PSP in the Rías Baixas was a function of the NAO recorded 1 month before the event. Since HAB have a relevant impact on ecosystems and human health, there is great interest in deciphering the ecological conditions favouring these events. Here we show that the atmospheric oscillations could be drivers of ecological processes linked to the occurrence of HAB in SW Europe. Moreover, the favourability functions relating NAO and AO indices with algal toxic events in SW Europe could be used as a powerful tool to predict toxic events.     

A link between the North Atlantic Oscillation and measles dynamics during the vaccination period in England and Wales

Ecologists have become aware of the role played by interannual climatic variability on the temporal dynamics of infectious diseases. In this report, I present evidence from data on measles cases in England and Wales showing that during the post-vaccination period, the interannual variability of winter weather (represented by the North Atlantic Oscillation, NAO) influences the annual dynamics of the disease. Using annual measles data from seven cities and simple logistic models, this study reveals how, after vaccination, NAO increases its effects on measles fluctuations. In addition, this study shows that vaccination may be represented as a simple vertical and lateral perturbation effect (Royama's classification), by reducing the maximum per capita growth rate and the equilibrium number of infected individuals . The results suggest that vaccination will not lead to outbreaks of measles from regular cyclic to irregular chaotic dynamics. In contrast, because of the reduction in per capita growth rates, the disease dynamics appear to be more stable than during the pre-vaccination period. The analysis of annual data on infectious diseases may be useful for detecting long-term effects of climate and complements the classical analyses and modeling based on monthly or seasonal time-step data.     

Review of the distribution of Mesoplodon species (order Cetacea, family Ziphiidae) in the North Atlantic

Four species of beaked whales of the genus Mesoplodon regularly occur in the North Atlantic. These are Sowerby's Beaked Whale Mesoplodon bidens, Blainville's Beaked Whale Mesoplodon densirostris, Gervais Beaked Whale Mesoplodon europaeus and True's Beaked Whale Mesoplodon mirus. These four species differ in their distribution within this area. M. bidens is the most northerly recorded species followed by M. mirus. M. densirostris and M. europaeus both generally occur further south and their distributions cross the equator. The distribution of Mesoplodon species may relate to variations in water temperature.     

Reassessing the impact of North Atlantic Oscillation on the sub-Saharan vegetation productivity

The Northern Atlantic Oscillation (NAO) has been shown to have a significant impact on the terrestrial ecosystem in the Sahelian region of Africa during the 1980s, and it has been strongly suggested that NAO may be a reliable predictor for the response of the Sahelian ecosystem to global climate variability. Using data from an extended period, we provide a reassessment for the impact of NAO on the Sahelian climate and ecosystem, and show that there is no consistent relationship between NAO and the ecosystem over Sahel. Statistical analysis on the NAO, vegetation, and precipitation data indicates that NAO influences the Sahelian vegetation productivity exclusively through its impact on precipitation. However, the relationship between the NAO index and Sahelian precipitation varies substantially with time. The correlation coefficient fluctuates between positive and negative values, and does not pass the 5% significance test during most of the twentieth century. The NAO system, although documented to govern the ecosystem dynamics over many other regions, does not have a consistent impact on the ecosystem over the Sahel. Therefore, the NAO index cannot produce a useful prediction on the ecosystem variability and changes in this region. This study provides an example that correlations based on short climate and ecological records (less than 20 years in this case) can be spurious and potentially misleading.     

Abyssal Megafaunal Necrophages: Latitudinal Differences in the Eastern North Atlantic Ocean

A pop-up time-lapse camera system (BATHYSNACK) was used to study megafaunal organisms attracted to bait at three abyssal localities in the eastern North Atlantic Ocean, a northern site on the Porcupine Abyssal Plain and two sub-tropical sites on the Madeira Abyssal Plain. Fish and decapod crustaceans appeared on 47% of photographs taken during deployments of up to seven days duration. The fishes Coryphaenoides (Nematonurus) armatus and Pachycara bulbiceps and the decapod Munidopsis spp. dominated appearances at the northern locality whereas over 95% of records at the two subtropical localities were of the decapod Plesiopenaeus armatus. Cyclical variations in necrophage abundance did not correlate with tidal cycles of near-bottom currents, although high P. armatus numbers were inversely related to current speed. Most of the frequently recorded entities showed contagious intraspecific distributions. In contrast, many of the interspecies relationships were non-random, with co-occurrences lower than expected, probably as a result of physical disturbance or potential predation. Population densities based on times of first arrival were calculated. Assemblages dominated by fish at higher latitudes and crustaceans at lower latitudes are discussed in terms of organic carbon supply to the deep sea and pelagic community structures.     

Photoperiodic regulation of gametogenesis in a North Atlantic sea star,Asterias vulgaris

Summary

Individuals of the sea star Asterias vulgaris from New Hampshire were maintained under two contrasting regimes of seasonally changing photoperiod. In one regime the lights turned on and off in phase with local sunrise and sunset; in the other, the daily photoperiod was kept 6 months out of phase with ambient photo- period. When dissected after being maintained for 18 months, the gametogenic condition of the out-of-phase animals was found to be 6 months out of phase with that of the in-phase animals. This experiment demonstrates that photoperiodic regulation of reproduction is important even in marine animals that normally experience marked seasonal changes in sea temperature.     

The biogeographical division of the Arctic and North Atlantic by the mysid (Crustacea: Mysidacea) fauna

The biogeographical analysis of Arctic and North Atlantic waters north of 30°N is based upon the distribution of 150 Mysidacea (Crustacea) species. The reasons for biogeographical divisions conducted independently by faunae of pelagic and benthopelagic mysids are adduced. The original schemes of the Arctic and North Atlantic division are proposed. Using the fauna of pelagic mysids, one biogeographical realm, one province and one transitional zone are designated in cold and temperate waters. Using the fauna of benthopelagic mysids, one biogeographical realm and four provinces are designated in those waters.     

Paleoecological significance of laminated diatomaceous oozes during the middle-to-late Pleistocene,North Atlantic Ocean (IODP Site U1304)

We examined diatom assemblages in a series of remarkable laminated diatomaceous ooze (LDO) horizons in the marine sediments from Integrated Ocean Drilling Program (IODP) Site U1304 to reconstruct the middle-to-late Pleistocene paleoceanographic evolution of the northern North Atlantic Ocean. Four confirmed diatom biohorizons combined with calcareous nannofossil and paleomagnetic stratigraphies established the chronological framework for the material. The planktonic, araphid, needle-like species Thalassiothrix longissima was the greatest contributor to the LDO facies. From the results of a principal component analysis using the percent abundances of 65 significant (p = 5%) diatom taxa, except for Tx. longissima, which was extremely dominant in almost all horizons observed, we identified two principal component (PC) axes. Taxa probably associated with the stratigraphic distribution of the major zonal marker Neodenticula seminae (ranging from 1.26 to 0.84 Ma in this ocean) loaded on PC1 with a high value. PC2 was related to the ocean surface temperature. The stratigraphic variability of the PC2 score indicated that switching between warm- and cold-water assemblages occurred concurrently with LDO deposition (or extreme Tx. longissima dominance) episodes in several horizons (particularly after 0.84 Ma), suggesting that the Subarctic Convergence (SAC) oceanic front passed over Site U1304 during Pleistocene glacial/interglacial cycles. Our floral evidence supports the model of nearly monospecific LDO formation caused by the enhanced physical accumulation of particular diatoms such as Tx. longissima. On the other hand, Nd. seminae, which probably contributes to spring phytoplankton blooms in the modern ocean, was present only between 1.26 and 0.84 Ma in this area. Thus, we infer that the main contributor of export flux in the regional annual primary production cycle would have shifted drastically from one of a spring phytoplankton bloom leader (Nd. seminae) to minor but mass dump assemblages (Tx. longissima etc.) in the mid-Pleistocene.     

'SSW to NNE'– North Atlantic Oscillation affects the progress of seasons across Europe

Three European plant phenological network datasets were analysed for latitudinal and longitudinal gradients of nine phenological ‘seasons’ spanning the entire year. The networks were: (1) the historical first European Phenological Network (1882–1941) by Hoffmann & Ihne, (2) the network of the International Phenological Gardens in Europe (1959–1998), founded by Schnelle & Volkert in 1957 and based on cloned plants, and (3) a dataset (1951–1998) that was recently collated during the EU Fifth Framework project POSITIVE, which included network data of seven Central and Eastern European countries. Our study is most likely the first, for over a century, to analyse average onset and year‐to‐year variability of the progress of seasons across a continent. For early, mid, and late spring seasons we found a marked progress of the seasonal onset from SW to NE throughout Europe, more precisely from WSW to ENE in early spring, then from SW to NE and finally from SSW to NNE in late spring, as exhibited by the relationship between latitudinal and longitudinal gradients. The movement of summer was more south to north directed, as the longitudinal gradient (west–east component) strongly declined or was even of opposite sign. Autumn, as shown by leaf colouring dates, arrived from NE to SW. Possible reasons for the differences among the three datasets are discussed. The annual variability of latitudinal and longitudinal gradients of the seasons across Europe was closely related to the North Atlantic Oscillation (NAO) index; in years with high NAO in both winter and spring, the west–east component of progress was more pronounced; in summer and autumn, the pattern of the seasons may be more uniform.     

Regional differences in bacterial flora in harbour porpoises from the North Atlantic: environmental effects?

Aims:  Microbiological findings in harbour porpoises from different regions of the North Atlantic were compared. Results in animals from the North and Baltic Seas were evaluated over a period of 18 years for changes in the microbiological flora.
Methods and Results:  Microbiological investigations were performed on 1429 organ samples from the lung, liver, kidney, spleen, intestine, and mesenteric lymph nodes from harbour porpoises of the German North and Baltic Seas, Greenlandic, Icelandic and Norwegian waters. A large variety of bacteria, including potentially pathogenic bacteria like Brucella sp., Clostridium perfringens, Escherichia coli, Erysipelothrix rhusiopathiae , β-haemolytic streptococci and Staphylococcus aureus were isolated . Those bacteria were associated with bronchopneumonia, gastroenteritis, hepatitis, pyelonephritis, myocarditis and septicemia.
Conclusions:  Organs from animals originating from Greenlandic and Icelandic waters showed clearly less bacterial growth and fewer associated pathological lesions compared to animals from the German North and Baltic Seas and Norwegian waters.
Significance and Impact of the Study:  Differences in bacterial findings and associated lesions between harbour porpoises from the German North and Baltic Seas and animals from Greenlandic, Norwegian and Icelandic waters may result from higher stress due to anthropogenic activities such as chemical pollutants in the North and Baltic Seas.     

The role of the North Atlantic Drift in the millennial timescale glacial climate fluctuations

The Greenland ice core records show that the overall cold climate of the last glacial period was repeatedly interrupted by short, rapid warmings. The events, known as Dansgaard-Oeschger (D-O) events, are strongly imprinted in the North Atlantic marine records suggesting that they were linked to North Atlantic circulation changes. However, the causes of the D-O events are poorly understood and they represent one of the most intriguing puzzles of the last glacial period. In order to investigate a possible mechanism we have studied variations in the distribution of benthic and planktonic foraminifera, oxygen isotopes and ice rafted debris during the last glacial period in eight cores from the North Atlantic and the Nordic Seas taken at mid depth from 853 to 1760 m. The parameters indicate, in agreement with previous studies, that the circulation system during the interstadials resembled the present system. Atlantic surface water flowed north into the Nordic Seas, where most of it sank through convection and, as cold deep water, flowed back into the North Atlantic. During the stadials, a halocline was established in the Nordic Seas and in the northernmost part of the North Atlantic and the outflow from the Nordic Seas stopped. However, below the cold, light surface layer, the relatively warm water of the North Atlantic Drift continued to flow across the North Atlantic and into the Nordic Seas, here warming up the deep-water masses. We suggest that the warm water gradually made the water column unstable. The pivotal abrupt climate warmings were caused by sudden upwelling of the deep, warm water masses causing overturning of the entire water column and onset of convection.     

Nearshore fish (Pholis gunnellus) persists across the North Atlantic through multiple glacial episodes

The intertidal biota of the North Atlantic is characterized by two disjunct communities (North American and European) exposed to different climatic regimes during the Pleistocene and in the Holocene. We collect multilocus DNA sequence data from the nearshore fish Pholis gunnellus to help uncover processes determining biogeographical persistence during periodic coastal glaciations. Coalescent-based estimates from the multilocus DNA sequence data suggest that P. gunnellus persisted on both sides of the North Atlantic throughout the last two glacial maxima (> 202,000 years) with little trans-Atlantic gene flow since divergence, very little structure among populations within Europe (Phi(ST) < 0.05) and some structure within the North American coastline (Phi(ST) = 0.0-0.21). Although the ecological flexibility and high local migration of P. gunnellus could have enhanced this species' survival across the Atlantic, logistic regression did not find a significant determinant of trans-Atlantic persistence when considering 12 other North Atlantic phylogeographical studies from the literature.