Atlantic Ocean Basin Research Articles

Atmospheric rivers moisture sources from a Lagrangian perspective

Abstract. An automated atmospheric river (AR) detection algorithm is used for the North Atlantic Ocean basin, allowing the identification of the major ARs affecting western European coasts between 1979 and 2012 over the winter half-year (October to March). The entire western coast of Europe was divided into five domains, namely the Iberian Peninsula (9.75° W, 36–43.75° N), France (4.5° W, 43.75–50° N), UK (4.5° W, 50–59° N), southern Scandinavia and the Netherlands (5.25° E, 50–59° N), and northern Scandinavia (5.25° E, 59–70° N). Following the identification of the main ARs that made landfall in western Europe, a Lagrangian analysis was then applied in order to identify the main areas where the moisture uptake was anomalous and contributed to the ARs reaching each domain. The Lagrangian data set used was obtained from the FLEXPART (FLEXible PARTicle dispersion) model global simulation from 1979 to 2012 and was forced by ERA-Interim reanalysis on a 1° latitude–longitude grid. The results show that, in general, for all regions considered, the major climatological areas for the anomalous moisture uptake extend along the subtropical North Atlantic, from the Florida Peninsula (northward of 20° N) to each sink region, with the nearest coast to each sink region always appearing as a local maximum. In addition, during AR events the Atlantic subtropical source is reinforced and displaced, with a slight northward movement of the sources found when the sink region is positioned at higher latitudes. In conclusion, the results confirm not only the anomalous advection of moisture linked to ARs from subtropical ocean areas but also the existence of a tropical source, together with midlatitude anomaly sources at some locations closer to AR landfalls.

Variation of ocean sediment thickness with crustal age

AbstractGlobal ocean sediment thickness and present‐day ocean sediment accumulation rates are analyzed with respect to the age of the underlying ocean crust. Trends in average sediment thickness and present‐day accumulation rate are well fit by cubic polynomials in crustal age for the global ocean and for individual ocean basins. Sediment thickness and accumulation rates are larger in the North and South Atlantic and Indian Oceans compared to the Pacific Ocean, primarily because the anomalous sediment accumulations that followed continental rifting and collision in the Atlantic and Indian Ocean basins are missing in the Pacific Ocean. Modern ocean sediment accumulation rates, extrapolated into the past assuming steady state conditions, account within uncertainties for the global average sediment thickness on 0–65 Ma (Cenozoic age) ocean crust, while the profile of anomalously thick sediments on older (Mesozoic age) ocean crust is well fit by adding localized, diffusive sediment transport from a steady state source referenced to the adjacent continental margin. Apart from a distinct 0–5 Ma (Quaternary age) sediment pulse, deviations in average sediment thickness from this simple model are generally small and are uncorrelated across ocean basins.

Regional Wave Modeling and Evaluation for the North Atlantic Coast Comprehensive Study

AbstractAccurate estimation of storm surge along the coasts subject to extreme storm conditions requires proper wind and pressure forcing and quantification of the wind waves resulting from local and far-field energy sources. This paper summarizes the steps involved in accurately representing the offshore wave climate for the North Atlantic Coast Comprehensive Study (NACCS) domain, defined from the United States–Canadian border in Maine to the Virginia–North Carolina border. The motivation of the regional wave modeling is to provide offshore boundary conditions for the simulation of extreme extratropical and synthetic tropical events to drive the nearshore wave and surge modeling efforts within the NACCS. The offshore wave conditions were estimated using the third-generation WAve Modelling (WAM) model. Value-added wind fields were defined for each of the four wave model grids (North Atlantic Ocean Basin, U.S. Coastal Regional scale, and two subregional-scale grid systems covering the NACCS coastal domain)...

New scenario for speciation in the benthic dinoflagellate genus Coolia (Dinophyceae)

In this study, inter- and intraspecific genetic diversity within the marine harmful dinoflagellate genus Coolia Meunier was evaluated using isolates obtained from the tropics to subtropics in both Pacific and Atlantic Ocean basins. The aim was to assess the phylogeographic history of the genus and to clarify the validity of established species including Coolia malayensis. Phylogenetic analysis of the D1-D2 LSU rDNA sequences identified six major lineages (L1–L6) corresponding to the morphospecies Coolia malayensis (L1), C. monotis (L2), C. santacroce (L3), C. palmyrensis (L4), C. tropicalis (L5), and C. canariensis (L6). A median joining network (MJN) of C. malayensis ITS2 rDNA sequences revealed a total of 16 haplotypes; however, no spatial genetic differentiation among populations was observed. These MJN results in conjunction with CBC analysis, rDNA phylogenies and geographical distribution analyses confirm C. malayensis as a distinct species which is globally distributed in the tropical to warm-temperate regions. A molecular clock analysis using ITS2 rDNA revealed the evolutionary history of Coolia dated back to the Mesozoic, and supports the hypothesis that historical vicariant events in the early Cenozoic drove the allopatric differentiation of C. malayensis and C. monotis.

Molybdenum drawdown during Cretaceous Oceanic Anoxic Event 2

During the Cretaceous greenhouse, episodes of widespread ocean deoxygenation were associated with globally occurring events of black shale deposition. Possibly the most pronounced of these oceanic anoxic events (OAE's) was the Cenomanian–Turonian OAE2 (∼94 Ma). However, although certain redox sensitive trace metals tend to be preferentially sequestered in sediments deposited under anoxic conditions, with Mo drawdown being specifically prone to euxinic settings, these elements are generally somewhat depleted in sediments deposited during OAE2. To understand the driving factors responsible for this depleted trace metal drawdown, we have studied a low latitude section from the proto-North Atlantic Ocean (Tarfaya S57), where existing biomarker and iron–sulphur data point to a dominantly euxinic water column, with periodic transitions to ferruginous (Fe-rich) water column conditions. We utilise a variety of redox proxies (Fe-speciation, redox sensitive trace metals and Mo isotopes), which, in combination, allows us to evaluate the detailed nature of ocean redox conditions and hence controls on trace metal drawdown. The results suggest that seawater δ98Mo values may have ranged between ∼0.6 and 1.1‰ during OAE2, likely connected to changes in the local Mo reservoir as a consequence of low and probably heterogeneous concentrations of Mo in the ocean. The very low Mo/TOC ratios at Tarfaya and elsewhere in the proto-North Atlantic may support a model in which deep-water circulation was partially restricted within and between the North Atlantic and other ocean basins. We propose that the combination of a low and possibly heterogeneous δ98Mo of seawater Mo, together with low Mo/TOC ratios, points to a large decrease in the global oceanic Mo reservoir during OAE2, reflecting a major global scale increase in Mo drawdown under persistent euxinic conditions.

Knowledge of marine fish trematodes of Atlantic and Eastern Pacific Oceans.

A brief summary of the early history of the study of Atlantic Ocean marine fish digeneans is followed by a discussion of the occurrence and distribution of these worms in the Atlantic Ocean and adjacent Eastern Pacific Ocean, using the Provinces of the ‘Marine Ecoregions’ delimited by Spalding et al. (Bioscience 57:573–583, 2007). The discussion is based on a database of 9,880 records of 1,274 species in 430 genera and 45 families. 8,633 of these records are from the Atlantic Ocean, including 1,125 species in 384 genera and 45 families. About 1,000 species are endemic to the Atlantic Ocean Basin. The most species-rich families in the Atlantic Ocean are the Opecoelidae Ozaki, 1925, Hemiuridae Looss, 1899 and Bucephalidae Poche, 1907, and the most wide-spread the Opecoelidae, Hemiuridae, Acanthocolpidae Lühe, 1906, Lepocreadiidae Odhner, 1905 and Lecithasteridae Odhner, 1905. A total of 109 species are shared by the Atlantic Ocean and the Eastern Pacific, made up of cosmopolitan, circum-boreal, trans-Panama Isthmus and Magellanic species. The lack of genetic evaluation of identifications is emphasised and the scope for much more work is stressed.

Editorial: Wet and Dry Periods in Regions Surrounding the Atlantic Ocean Basin

AD acknowledges the Spanish Government and FEDER through the support of the SETH project (CGL2014-60849-JIN). BR received funding from the EU FP7/2007-2013 under grant agreement no. 603521.

Etheliaceae fam. nov. (Gigartinales, Rhodophyta), with a clarification of the generitype of Ethelia and the addition of six novel species from warm waters.

Based upon COI-5P, LSU rDNA, and rbcL sequence data and morphological characteristics, six new members of the noncalcified crustose genus of red algae Ethelia are described in a new family, Etheliaceae (Gigartinales), sister to the recently described Ptilocladiopsidaceae. The novel species are described from subtropical to tropical Atlantic and Indo-Pacific Ocean basins; E.mucronata sp. nov. and E.denizotii sp. nov. from southern and northern Western Australia respectively, E.wilcei sp. nov. from the Cocos (Keeling) Islands of Australia, E.suluensis sp. nov. from the Philippines, E.umbricola sp. nov. from Bermuda and E.kraftii sp. nov. from Lord Howe Island, Australia. The generitype, Ethelia biradiata, originally reported from the Seychelles, Indian Ocean, is added to the Western Australian flora.

Melting barriers to faunal exchange across ocean basins.

Accelerated loss of sea ice in the Arctic is opening routes connecting the Atlantic and Pacific Oceans for longer periods each year. These changes may increase the ease and frequency with which marine birds and mammals move between the Pacific and Atlantic Ocean basins. Indeed, recent observations of birds and mammals suggest these movements have intensified in recent decades. Reconnection of the Pacific and Atlantic Ocean basins will present both challenges to marine ecosystem conservation and an unprecedented opportunity to examine the ecological and evolutionary consequences of interoceanic faunal exchange in real time. To understand these changes and implement effective conservation of marine ecosystems, we need to further develop modeling efforts to predict the rate of dispersal and consequences of faunal exchange. These predictions can be tested by closely monitoring wildlife dispersal through the Arctic Ocean and using modern methods to explore the ecological and evolutionary consequences of these movements.

Experimental Tropical Cyclone Forecasts Using a Variable-Resolution Global Model

Abstract Tropical cyclone (TC) forecasts at 14-km horizontal resolution (0.125°) are completed using variable-resolution (V-R) grids within the Community Atmosphere Model (CAM). Forecasts are integrated twice daily from 1 August to 31 October for both 2012 and 2013, with a high-resolution nest centered over the North Atlantic and eastern Pacific Ocean basins. Using the CAM version 5 (CAM5) physical parameterization package, regional refinement is shown to significantly increase TC track forecast skill relative to unrefined grids (55 km, 0.5°). For typical TC forecast integration periods (approximately 1 week), V-R forecasts are able to nearly identically reproduce the flow field of a globally uniform high-resolution forecast. Simulated intensity is generally too strong for forecasts beyond 72 h. This intensity bias is robust regardless of whether the forecast is forced with observed or climatological sea surface temperatures and is not significantly mitigated in a suite of sensitivity simulations aimed at investigating the impact of model time step and CAM’s deep convection parameterization. Replacing components of the default physics with Cloud Layers Unified by Binormals (CLUBB) produces a statistically significant improvement in forecast intensity at longer lead times, although significant structural differences in forecasted TCs exist. CAM forecasts the recurvature of Hurricane Sandy into the northeastern United States 60 h earlier than the Global Forecast System (GFS) model using identical initial conditions, demonstrating the sensitivity of TC forecasts to model configuration. Computational costs associated with V-R simulations are dramatically decreased relative to globally uniform high-resolution simulations, demonstrating that variable-resolution techniques are a promising tool for future numerical weather prediction applications.

Skin lesions on yellowfin tuna Thunnus albacares from Gulf of Mexico outer continental shelf: Morphological, molecular, and histological diagnosis of infection by a capsalid monogenoid

We characterize lesion-associated capsaline infections on yellowfin tuna, Thunnus albacares, in the Gulf of Mexico by comparing our specimens with published descriptions and museum specimens ascribed to Capsala biparasiticum and its synonyms: vouchers of C. biparasiticum from parasitic copepods; the holotype of Capsala neothunni; and vouchers of Capsala abidjani. Those from parasitic copepods differed by having a small, rounded body, large anterior attachment organs, closely spaced dorsomarginal body sclerites, small testes, and a short and wide testicular field. No morphometric feature in the holotype of C. neothunni ranged outside of that reported for the newly-collected specimens, indicating conspecificity of our specimens. The specimens of C. abidjani differed by having a large anterior attachment organ, few and dendritic testes, and a short, wide testicular field. Large subunit ribosomal DNA (28S) sequences grouped our specimens and Capsala sp. as sister taxa and indicated a phylogenetic affinity of Nasicola klawei. The haptoral attachment site comprised a crater-like depression surrounded by a blackish-colored halo of extensively rugose skin, with abundant pockmarked-like, irregularly-shaped oblong or semi-circular epidermal pits surrounding these attachment sites. Histology confirmed extensive folding of epidermis and underlying stratum laxum, likely epidermal hyperplasia, foci of weak cell-to-cell adhesions among apical malpighian cells as well as that between stratum germinativum and stratum laxum, myriad goblet cells in epidermis, rodlet cells in apical layer of epidermis, and lymphocytic infiltrates and melanin in dermis. The present study comprises (i) the first published report of this parasite from yellowfin tuna captured in the Gulf of Mexico–NW Atlantic Ocean Basin, (ii) confirmation of its infection on the skin (rather than on a parasitic copepod), (iii) the first molecular data for this capsaline, and (iv) the first observations of histopathological changes associated with a capsalid infection on a wild-caught epipelagic fish.

Variability of the coherent arrivals extracted from low-frequency deep-ocean ambient noise correlations

Correlation processing of ocean noise can be used to develop totally passive ocean monitoring methods. Using various hydrophone pair orientations, this study investigates the frequency dependence, seasonal variability, and emergence rate of coherent arrivals from cross-correlations of low frequency ambient noise (f < 40 Hz) recorded on triangular hydrophones arrays. These arrays are located at five existing hydroacoustic stations of the International Monitoring System (IMS), situated in the deep-sound channel, and distributed across the Atlantic, Pacific, and Indian Ocean basins. For the majority of studied sites, persistent and fast-emerging coherent arrivals are reliably obtained if the axis connecting the selected hydrophone pair has a direct line-of-sight with regions of the globe containing stable and diffuse noise sources (e.g., polar-ice or seismic noise). Furthermore, for this favorable orientation, the emergence rate of coherent arrivals extracted between hydrophone pairs separated by long ranges (here ∼130 km) can be approximated based on measurements made between hydrophone pairs separated by short ranges (∼2 km) in the Atlantic Ocean. Hence, results from this study, obtained using existing hydrophone configurations of the IMS hydroacoustic stations, could be used to guide the placement of other hydrophone arrays over the globe for future long-range passive ocean monitoring experiments.

Improvements in the Probabilistic Prediction of Tropical Cyclone Rapid Intensification with Passive Microwave Observations

Abstract The probabilistic prediction of tropical cyclone (TC) rapid intensification (RI) in the Atlantic and eastern Pacific Ocean basins is examined here using a series of logistic regression models trained on environmental and infrared satellite-derived features. The environmental predictors are based on averaged values over a 24-h period following the forecast time. These models are compared against equivalent models enhanced with additional TC predictors created from passive satellite microwave imagery (MI). Leave-one-year-out cross validation on the developmental dataset shows that the inclusion of MI-based predictors yields more skillful RI models for a variety of RI and intensity thresholds. Compared with the baseline forecast skill of the non-MI-based RI models, the relative skill improvements from including MI-based predictors range from 10.6% to 44.9%. Using archived real-time data during the period 2004–13, evaluation of simulated real-time models is also carried out. Unlike in the model development stage, the simulated real-time setting involves using Global Forecast System forecasts for the non-satellite-based predictors instead of “perfect” observational-based predictors in the developmental data. In this case, the MI-based RI models still generate superior skill to the baseline RI models lacking MI-based predictors. The relative improvements gained in adding MI-based predictors are most notable in the Atlantic, where the non-MI versions of the models suffer acutely from the use of imperfect real-time data. In the Atlantic, relative skill improvements provided from the inclusion of MI-based predictors range from 53.5% to 103.0%. The eastern Pacific relative improvements are less impressive but are still uniformly positive.

Contrasting demographic history and gene flow patterns of two mangrove species on either side of the Central American Isthmus.

Comparative phylogeography offers a unique opportunity to understand the interplay between past environmental events and life-history traits on diversification of unrelated but co-distributed species. Here, we examined the effects of the quaternary climate fluctuations and palaeomarine currents and present-day marine currents on the extant patterns of genetic diversity in the two most conspicuous mangrove species of the Neotropics. The black (Avicennia germinans, Avicenniaceae) and the red (Rhizophora mangle, Rhizophoraceae) mangroves have similar geographic ranges but are very distantly related and show striking differences on their life-history traits. We sampled 18 Atlantic and 26 Pacific locations for A. germinans (N = 292) and R. mangle (N = 422). We performed coalescence simulations using microsatellite diversity to test for evidence of population change associated with quaternary climate fluctuations. In addition, we examined whether patterns of genetic variation were consistent with the directions of major marine (historical and present day) currents in the region. Our demographic analysis was grounded within a phylogeographic framework provided by the sequence analysis of two chloroplasts and one flanking microsatellite region in a subsample of individuals. The two mangrove species shared similar biogeographic histories including: (1) strong genetic breaks between Atlantic and Pacific ocean basins associated with the final closure of the Central American Isthmus (CAI), (2) evidence for simultaneous population declines between the mid-Pleistocene and early Holocene, (3) asymmetric historical migration with higher gene flow from the Atlantic to the Pacific oceans following the direction of the palaeomarine current, and (4) contemporary gene flow between West Africa and South America following the major Atlantic Ocean currents. Despite the remarkable differences in life-history traits of mangrove species, which should have had a strong influence on seed dispersal capability and, thus, population connectivity, we found that vicariant events, climate fluctuations and marine currents have shaped the distribution of genetic diversity in strikingly similar ways.

Elevated middle and upper troposphere ozone observed downstream of Atlantic tropical cyclones

During the peak period of hurricane activity in the summer of 2010, vertical profiles of ozone using ozonesondes were taken downstream of tropical cyclones in the Western and Eastern Atlantic Ocean basin at Barbados and Cape Verde. Measurements are taken for tropical cyclones Danielle, Earl, Fiona, Gaston, Julia and Igor. The measurements show an increase in ozone mixing ratios with air originating from the tropical cyclones at 5–10 km altitude. We suggest that observed lightning activity associated tropical cyclones and the subsequent production of NOX followed by upper level outflow and subsidence ahead of the tropical cyclones and aged continental outflow from West Africa thunderstorms produced observed increases in ozone mixing ratios. Hurricane Danielle showed the largest changes in ozone mixing ratio with values increasing from 25 ppb to 70 ppb between 22 and 25 August in the middle troposphere, near 450 hPa; warming and drying in the middle and lower troposphere. Measurements of ozone mixing ratios in Cape Verde show higher ozone mixing ratios prior to the passage of tropical storm Julia but low ozone mixing ratios and high relative humidity up to 300 hPa when the storm was in close proximity. This is due most likely the vertically transported from the marine boundary layer.

Far-Field Tsunami Impact in the North Atlantic Basin from Large Scale Flank Collapses of the Cumbre Vieja Volcano, La Palma

In their pioneering work, Ward and Day suggested that a large scale flank collapse of the Cumbre Vieja Volcano (CVV) on La Palma (Canary Islands) could trigger a mega-tsunami throughout the North Atlantic Ocean basin, causing major coastal impact in the far-field. While more recent studies indicate that near-field waves from such a collapse would be more moderate than originally predicted by Ward and Day [Løvholt et al. (J Geophy Res 113:C09026, 2008); Abadie et al. (J Geophy Res 117:C05030, 2012)], these would still be formidable and devastate the Canary Island, while causing major impact in the far-field at many locations along the western European, African, and the US east coasts. Abadie et al. (J Geophy Res 117:C05030, 2012) simulated tsunami generation and near-field tsunami impact from a few CVV subaerial slide scenarios, with volumes ranging from 20 to 450 km $$^3$$ ; the latter representing the most extreme scenario proposed by Ward and Day. They modeled tsunami generation, i.e., the tsunami source, using THETIS, a 3D Navier-Stokes (NS) multi-fluid VOF model, in which slide material was considered as a nearly inviscid heavy fluid. Near-field tsunami impact was then simulated for each source using FUNWAVE-TVD, a dispersive and fully nonlinear long wave Boussinesq model [Shi et al. (Ocean Modell 43–44:36–51, 2012); Kirby et al. (Ocean Modeling, 62:39–55, 2013)]. Here, using FUNWAVE-TVD for a series of nested grids of increasingly fine resolution, we model and analyze far-field tsunami impact from two of Abadie et al.’s extreme CVV flank collapse scenarios: (i) that deemed the most “credible worst case scenario” based on a slope stability analysis, with a 80 km $$^3$$ volume; and (ii) the most extreme scenario, similar to Ward and Day’s, with a 450 km $$^3$$ volume. Simulations are performed using a one-way coupling scheme in between two given levels of nested grids. Based on the simulation results, the overall tsunami impact is first assessed in terms of maximum surface elevation computed along the western European and African, and US east coasts (USEC). Strong wave elevation decay is predicted over the wide USEC shelf, which is shown to be essentially due to bottom friction effects. We then show more detailed results for the USEC, which is the object of high-resolution tsunami inundation mapping under the auspices of the US National Tsunami Hazard Mitigation Program. In this context, we compare the maximum surface elevation predicted along the coastline for each CVV scenario and show that, besides the initial directionality of the sources, coastal impact is mostly controlled by focusing/defocusing effects resulting from the shelf bathymetric features. A simplified ray-tracing analysis confirms this controlling effect of the wide USEC shelf for incident long waves. Finally, we perform high-resolution (10 m) inundation mapping for the most extreme CVV scenario and show results at one of the most vulnerable and exposed communities in the mid-Atlantic US states, in and around Ocean City, Maryland. Such maps are being generated for all exposed areas of the USEC, to be used in tsunami hazard assessment and mitigation work.

Deep crustal structure of the North-West African margin from combined wide-angle and reflection seismic data (MIRROR seismic survey)

The structure of the Moroccan and Nova Scotia conjugate rifted margins is of key importance for understanding the Mesozoic break-up and evolution of the northern central Atlantic Ocean basin. Seven combined multichannel reflection (MCS) and wide-angle seismic (OBS) data profiles were acquired along the Atlantic Moroccan margin between the latitudes of 31.5° and 33° N during the MIRROR seismic survey in 2011, in order to image the transition from continental to oceanic crust, to study the variation in crustal structure, and to characterize the crust under the West African Coast Magnetic Anomaly (WACMA).The data were modeled using a forward modeling approach. The final models image crustal thinning from 36km thickness below the continent to approximately 8km in the oceanic domain. A 100km wide zone characterized by rough basement topography and high seismic velocities up to 7.4km/s in the lower crust is observed westward of the West African Coast Magnetic Anomaly. No basin underlain by continental crust has been imaged in this region, as has been identified north of our study area. Comparison to the conjugate Nova Scotian margin shows a similar continental crustal thickness and layer geometry, and the existence of exhumed and serpentinized upper mantle material on the Canadian side only. The oceanic crustal thickness is lower on the Canadian margin.

Daily Precipitation Extreme Events in the Iberian Peninsula and Its Association with Atmospheric Rivers*

Abstract An automated atmospheric rivers (ARs) detection algorithm is used for the North Atlantic Ocean basin that allows the identification and a comprehensive characterization of the major AR events that affected the Iberian Peninsula over the 1948–2012 period. The extreme precipitation days in the Iberian Peninsula and their association (or not) with the occurrence of ARs is analyzed in detail. The extreme precipitation days are ranked by their magnitude and are obtained after considering 1) the area affected and 2) the precipitation intensity. Different rankings are presented for the entire Iberian Peninsula, for Portugal, and for the six largest Iberian river basins (Minho, Duero, Tagus, Guadiana, Guadalquivir, and Ebro) covering the 1950–2008 period. Results show that the association between ARs and extreme precipitation days in the western domains (Portugal, Minho, Tagus, and Duero) is noteworthy, while for the eastern and southern basins (Ebro, Guadiana, and Guadalquivir) the impact of ARs is reduced. In addition, the contribution from ARs toward the extreme precipitation ranking list is not homogenous, playing an overwhelming role for the most extreme precipitation days but decreasing significantly with the less extreme precipitation days. Moreover, and given the narrow nature of the ARs, the location of the ARs over each subdomain is closely related to the occurrence (or not) of extreme precipitation days.

Impact of SST on Tropical Cyclones in North Indian Ocean

The impact of the cyclonic activity can be measured based on annual frequency, maximum sustained intensity, landfall, duration, surge height, accumulated cyclone energy and power dissipative index of cyclones. ‘Power dissipative index’ (PDI) is function of duration, frequency and maximum sustained intensity of cyclone (Emanuel 2005). PDI can represent the cyclonic threat better than storm frequency or intensity alone as PDI measures the cyclonic energy dissipation over the basin during a cyclonic event (Emanuel, 2005). PDI of the tropical cyclone over the North Atlantic Ocean basin was related to the climate change by correlating the PDI to sea surface temperature (SST) (Emanuel, 2005). In the present study, an attempt has been made to establish a correlation between the climate change and the cyclonic activities in the North Indian Ocean (NIO) basin. The PDI over the North Indian Ocean basin and individually over Arabian Sea and Bay of Bengal basins were calculated. The PDIs over these basins were correlated to SST obtained from the HadISST1 dataset for these basins. An increasing trend in the SST and tropical cyclone PDI was observed for the past 30 year time period in the North Atlantic Ocean basin by Emanuel (2005). A similar analysis of the cyclonic activity over the North Indian Ocean basin is carried out with the help of available best-tracks of the cyclones from Indian Meteorological Department (IMD) for a period of 23 years (1990-2013). The SST was calculated on temporal period as annual, pre-monsoon and post-monsoon period for study basins. Correlation coefficients for the SSTs over these temporal periods and the PDI of basins were obtained. It was concluded from the study that the SST was not sufficient to establish the changing climate for the cyclonic activities in NIO region for the future.

Multilocus evidence for globally distributed cryptic species and distinct populations across ocean gyres in a mesopelagic copepod.

Zooplanktonic taxa have a greater number of distinct populations and species than might be predicted based on their large population sizes and open-ocean habitat, which lacks obvious physical barriers to dispersal and gene flow. To gain insight into the evolutionary mechanisms driving genetic diversification in zooplankton, we developed eight microsatellite markers to examine the population structure of an abundant, globally distributed mesopelagic copepod, Haloptilus longicornis, at 18 sample sites across the Atlantic and Pacific Oceans (n = 761). When comparing our microsatellite results with those of a prior study that used a mtDNA marker (mtCOII, n = 1059, 43 sample sites), we unexpectedly found evidence for the presence of a cryptic species pair. These species were globally distributed and apparently sympatric, and were separated by relatively weak genetic divergence (reciprocally monophyletic mtCOII lineages 1.6% divergent; microsatellite FST ranging from 0.28 to 0.88 across loci, P < 0.00001). Using both mtDNA and microsatellite data for the most common of the two species (n = 669 for microsatellites, n = 572 for mtDNA), we also found evidence for allopatric barriers to gene flow within species, with distinct populations separated by continental landmasses and equatorial waters in both the Atlantic and Pacific Ocean basins. Our study shows that oceanic barriers to gene flow can act as a mechanism promoting allopatric diversification in holoplanktonic taxa, despite the high potential dispersal abilities and pelagic habitat for these species.