Southeastern Atlantic Research Articles

Regional algal biofuel production potential in the coterminous United States as affected by resource availability trade-offs

A warm sunny climate and unoccupied arid land as in the American Southwest are favorable for algal cultivation. However, additional resource constraints affect the overall viability of specific sites and regions. We investigated tradeoffs between growth rate, water, and CO2 availability and costs for two strains: Nannochloropsis salina and Chlorella sp. We conducted site selection exercises to produce 7.95E+10Lyr−1 (21billiongalyr−1 (BGY)) of renewable diesel (RD). Experimental trials from the National Alliance for Advanced Biofuels and Bio-Products (NAABB) team informed the growth model of our Biomass Assessment Tool. We simulated RD production by both lipid extraction (LE) and hydrothermal liquefaction (HTL). Sites were screened for the availability of freshwater and flue gas, and prioritized by the net value of biofuel minus water (the least-expensive and available source) and flue gas delivery costs. Water sources considered were ground waters ranging in salinity from fresh to brines and seawater. We found that HTL produced more RD per unit biomass than LE, resulting in an improvement in economic efficiency of 76%. Selections constrained by production and water were concentrated along the Gulf of Mexico and southeastern Atlantic coasts. Adding flue gas constraints increased the spatial distribution to include sites nationwide. The 21BGY target required ~3.8millionha of mainly forest (41.3%) and pasture (35.7%). Exclusion in favor of barren and scrub lands forced most production to the southwestern US, but with increased water consumption (5.7 times) and decreased economic efficiency (−38%).

Review: The World of the Salt Marsh: Appreciating and Protecting the Tidal Marshes of the Southeastern Atlantic Coast

Review: The World of the Salt Marsh: Appreciating and Protecting the Tidal Marshes of the Southeastern Atlantic Coast

Role of the global oceans and land–atmosphere interaction on summertime interdecadal variability over northern Argentina

This study uses experiments with an atmospheric general circulation model (AGCM) to address the role of the oceans and the effect of land–atmosphere coupling on the predictability of summertime rainfall over northern Argentina focusing on interdecadal time scales during 1901–2006. Ensembles of experiments where the AGCM is forced with historical sea surface temperature (SST) in the global, Pacific and tropical-North Atlantic domains are used. The role of land–atmosphere interaction is assessed comparing the output of simulations with active and climatological soil moisture. A maximum covariance analysis between precipitation and SST reveals the impact of the Pacific Decadal Oscillation, the Atlantic Multidecadal Oscillation and the equatorial–tropical South Atlantic on rainfall over northern Argentina. Model simulations further show that while the dominant influence comes from the Pacific basin, the Atlantic influence can explain a large transition from dry to wet decades over northern Argentina during the beginning of the 1970s. Analysis of anomalies before and after the transition reveals an upper level anticyclonic circulation off the Patagonian coast with barotropic structure. This circulation enhances the moisture transport and convergence in northern Argentina and, together with enhanced evaporation, increased the rainfall after 1970. The SST pattern is dominated by cold conditions in the equatorial Atlantic and warm eastern Pacific and South Atlantic. We also found that land–atmosphere interaction leads to a representation of the long term rainfall evolution over northern Argentina that is closer to the observed one. Moreover, it leads to a smaller dispersion among ensemble members, thus resulting in a larger signal-to-noise ratio.

Population connectivity and phylogeography of a coastal fish, Atractoscion aequidens (Sciaenidae), across the Benguela Current region: evidence of an ancient vicariant event.

Contemporary patterns of genetic diversity and population connectivity within species can be influenced by both historical and contemporary barriers to gene flow. In the marine environment, present day oceanographic features such as currents, fronts and upwelling systems can influence dispersal of eggs/larvae and/juveniles/adults, shaping population substructuring. The Benguela Current system in the southeastern Atlantic is one of the oldest upwelling systems in the world, and provides a unique opportunity to investigate the relative influence of contemporary and historical mechanisms shaping the evolutionary history of warm-temperate fish species. Using the genetic variation in the mitochondrial DNA Control Region and eight nuclear microsatellite DNA loci, we identified the presence of two highly divergent populations in a vagile and warm-temperate fish species, Atractoscion aequidens, across the Benguela region. The geographical distributions of the two populations, on either side of the perennial upwelling cell, suggest a strong correlation between the oceanographic features of the system and the breakdown of gene flow within this species. Genetic divergence (mtDNA φ ST = 0.902, microsatellite F ST = 0.055: probability of genetic homogeneity for either marker = p<0.001), absence of migrants (less than 1% per generation) between populations and coalescent estimates of time since most recent common ancestor suggest that the establishment of the main oceanographic features of the system (2 million years ago), particularly the strengthening and position of the perennial upwelling cell, is the most likely mechanism behind the observed isolation. Concordance between mitochondrial and nuclear genetic markers indicates that isolation and divergence of the northern and southern Benguela populations of A. aequidens occurred deep in the past and has continued to the present day. These findings suggest that the Benguela Current system may constitute an ancient and impermeable barrier to gene flow for warm-temperate fish species.

Mineralization of biogenic materials in the water masses of the South Atlantic Ocean. II: Stoichiometric ratios and mineralization rates

The variability of nitrate (N), phosphate (P), silicate (Si) and Apparent Oxygen Utilization (AOU) due to water mass mixing was objectively separated from the variability due to mineralization of biogenic materials in the western and eastern South Atlantic Ocean on basis of the constrained Optimum MultiParameter (OMP) analysis implemented in the companion manuscript. Using a consensus linear regression model, AOU/N/P/Si mineralization ratios and the corresponding oxygen utilisation rates (OURs) were obtained for the realm of each water mass defined after the OMP analysis. Combining these results with a stoichiometric model, the organic carbon to nitrogen (C/N) ratios and the biochemical composition (carbohydrates+lipids, proteins and phosphorus compounds) of the mineralized material, were derived. The vertical variability of the AOU/N, AOU/P and AOU/C mineralization ratios pointed to a significant fractionation during the mineralization of sinking organic matter. This fractionation was confirmed by preferential consumption of organic phosphorous compounds and proteins in shallower levels, which produced an increase of the C/N ratio of the mineralised materials of 0.5±0.2molCmolN–1 every 1000dbar. OURs in the twilight zone decreased quadratically with the C/N molar ratio of the mineralised material and exponentially with pressure (p, in 103dbar) according to the following regression equation: Ln (OUR)=6.2(±1.2)−2.0(±0.7)*Ln (C/N)−0.6(±0.2)*p (r2=0.87, p<0.006, n=8). This variability in the rates and stoichiometric ratios of the biogenic material mineralization compromises our capacity to predict the ocean biogeochemistry response to global change, including the CO2 uptake and storage and the corresponding feedback mechanisms.

Does temporal and spatial segregation explain the complex population structure of humpback whales on the coast of West Africa?

Humpback whales (Megaptera novaeangliae) in the Southeastern Atlantic Ocean (International Whaling Commission ‘Breeding Stock B’—BSB) are distributed from the Gulf of Guinea to Western South Africa. Genetic data suggest that this stock may be sub-structured, but it remains unknown if this is due to reproductive segregation. This paper evaluates the spatial and temporal population structure of BSB humpback whales using a combination of maternally and bi-parentally inherited markers. The genetic differentiation that we identify in this study could be due to a combination of (1) spatial and/or temporal segregation on breeding grounds in the greater Gulf of Guinea, (2) the possibility of maternally inherited site fidelity to specific feeding grounds and (3) the use of two generalized but exclusive migratory routes (coastal and offshore) between feeding and breeding areas. Further, photo-identification and genetic sampling efforts in other areas of the Sub-Saharan Western Africa winter range and targeted deployment of satellite tags would help to clarify some of the apparent complexity in the population structure of animals biopsied in this region.

2. Coastal Zone Management

The twelfth Conference of the Parties (COP-12) to the CBD met in Pyeongchang, Korea, on 6–17 October. Several decisions from COP-12 expressly touched marine and coastal resources, particularly Decisions XII/22 and XII/23. Decision XII/22 concerned ecologically or biologically significant marine areas (EBSAS) that are being designated via a process established in Decisions X729 and XI/17. To date, seven regional workshops (Southern Indian Ocean, Eastern Tropical and Temperate Pacific, North Pacific, South-Eastern Atlantic, Arctic, North-West Atlantic, and Mediterranean) have described EBSAS using criteria established by the Subsidiary Body on Scientific, Technical and Technological Advice (SBSTTA). Criteria include uniqueness, special importance for life history stages of species, importance for threatened or endangered species or their habitats, vulnerability or fragility, biological productivity, biological diversity, and naturalness). Decision XII/22 requests the CBD executive secretary to include the summary reports for the listed EBSAS in the EBSAS repository and to submit them before COP-13 to the UN General Assembly (UNGA) to study issues related to conservation and sustainable use of these resources in the high seas. The decision stressed that the EBSA process does not affect the sovereign rights of coastal states, rather it is strictly a scientific and technical exercise. It also called the CBD executive secretary, contracting parties, and governments to continue to designate EBSAS in accordance with the established scientific criteria. The decision also encouraged the use of marine spatial planning, network of marine protected areas, impact assessments, and other area-based management tools to promote enhanced conservation and sustainable use of the EBSAS. Decision XII/22 originated via SBSTTA Recommendation XVIII/3 adopted in the eighteenth SBSTTA meeting on 23–28 June in Montreal, Canada.

Holocene climate variability in the winter rainfall zone of South Africa

Abstract. We established a multi-proxy time series comprising analyses of major elements in bulk sediments, Sr and Nd isotopes, grain size of terrigenous fraction, and δ18O and δ13C in tests of Neogloboquadrina pachyderma (sinistral) from a marine sediment sequence recovered off the Orange River. The records reveal coherent patterns of variability that reflect changes in wind strength, precipitation over the river catchments, and upwelling of cold and nutrient-rich coastal waters off western South Africa. The wettest episode of the Holocene in the winter rainfall zone (WRZ) of South Africa occurred during the "Little Ice Age" (700–100 cal years BP) most likely in response to a northward shift of the austral westerlies. Wet phases and strengthened coastal water upwellings are companied by a decrease of Agulhas water leakage into the South Atlantic and a reduced dust incursion over Antarctica, as indicated in previous studies. A continuous aridification trend in the WRZ and a weakening of the southern Benguela Upwelling System (BUS) between 9000 and 5500 cal years BP parallel with increase of dust deposition over Antarctica and an enhanced leakage of warm Agulhas water into the eastern South Atlantic. The temporal relationship between precipitation changes in the WRZ, the thermal state of the coastal surface water, and leakage of warm water in the South Atlantic, and variation of dust incursion over Antarctica suggests a causal link that most likely was related to latitudinal shifts of the Southern Hemisphere westerlies. Our results of the mid-Holocene time interval may serve as an analogue to a possible long-term consequence of the current and future southward shift of the westerlies. Furthermore, warming of the coastal surface water as a result of warm Agulhas water incursion into the southern BUS may affect coastal fog formation.

Subregionalization of Low-Frequency Summer Drought Variability in the Southeastern United States*

Freshwater resources are particularly limited in the Southeastern United States. In recent years, severe summer droughts have placed substantial strain on municipal and industrial water resources, emphasizing the need for further research on the causes of long-term moisture deficits. Previous research has identified a Southeast drought region and specific low-frequency ocean-atmosphere influences on drought. In this article, we identify three distinct subregions of low-frequency summer drought variability in the Southeastern United States using principal components analysis. Multidecadal drought variability is most pronounced in the Southeastern Atlantic Coastal States (SEACS) subregion. The SEACS drought variability is significantly associated with ocean-atmosphere variability in the Atlantic and Pacific basins. The significance of ocean-atmosphere influences on drought in the Southeast is spatially confined within only the SEACS subregion. The Eastern Gulf States (EGS) subregion exhibits a long-term increase in summer moisture that is significantly associated with Northern Hemisphere surface temperature increases during the last century. The peninsular Florida subregion is characterized by high-frequency drought variability that is not associated with any of the climate indexes included in this study.

Phylogenetic identification of marine bacteria isolated from deep-sea sediments of the eastern South Atlantic Ocean.

The deep-sea environments of the South Atlantic Ocean are less studied in comparison to the North Atlantic and Pacific Oceans. With the aim of identifying the deep-sea bacteria in this less known ocean, 70 strains were isolated from eight sediment samples (depth range between 1905 to 5560 m) collected in the eastern part of the South Atlantic, from the equatorial region to the Cape Abyssal Plain, using three different culture media. The strains were classified into three phylogenetic groups, Gammaproteobacteria, Firmicutes and Actinobacteria, by the analysis of 16s rRNA gene sequences. Gammaproteobacteria and Firmicutes were the most frequently identified groups, with Halomonas the most frequent genus among the strains. Microorganisms belonging to Firmicutes were the only ones observed in all samples. Sixteen of the 41 identified operational taxonomic units probably represent new species. The presence of potentially new species reinforces the need for new studies in the deep-sea environments of the South Atlantic.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-2-127) contains supplementary material, which is available to authorized users.

Geochronologic evidence for a possible MIS-11 emergent barrier/beach-ridge in southeastern Georgia, USA

Predominantly clastic, off-lapping, transgressive, near-shore marine sediment packages that are morphologically expressed as subparallel NE-trending barriers, beach ridges, and associated back-barrier areas, characterize the near-surface stratigraphic section between the Savannah and the Ogeechee Rivers in Effingham County, southeastern Georgia. Each barrier/back-barrier (shoreline) complex is lower than and cut into a higher/older complex. Each barrier or shoreline complex overlies Miocene strata. No direct age data are available for these deposits. Previous researchers have disagreed on their age and provenance. Using luminescence and meteoric beryllium-10 (10Be) inventory analyses, we estimated a minimum age for the largest, westernmost, morphologically identifiable, and topographically-highest, barrier/beach-ridge (the Wicomico shoreline barrier) and constrained the age of a suite of younger barrier/beach-ridges that lie adjacent and seaward of the Wicomico shoreline barrier.At the study site, the near-shore marine/estuarine deposits underlying the Wicomico shoreline barrier are overlain by eolian sand and an intervening zone-of-mixing. Optically stimulated luminescence (OSL) data indicate ages of ≤43 ka for the eolian sand and 116 ka for the zone-of-mixing. Meteoric 10Be and pedostratigraphic data indicate minimum residence times of 33.4 ka for the eolian sand, 80.6 ka for the zone-of-mixing, and 247 ka for the paleosol. The combined OSL and 10Be age data indicate that, at this locality, the barrier/beach ridge has a minimum age of about 360 ka. This age for the Wicomico shoreline-barrier deposit is the first for any Pleistocene near-shore marine/estuarine deposit in southeast Georgia that is conclusively older than 80 ka. The 360-ka minimum age is in agreement with other geochronologic data for near-coastline deposits in Georgia and South Carolina. The geomorphic position of this barrier/beach-ridge is similar to deposits in South Carolina considered to be ∼450 ka to >1 Ma. The age and geomorphic data for Georgia and South Carolina possibly suggest the presence of MIS-11 (∼420−360 ka) shoreline deposits between 15 m and 28 m above present sea level in the Southeastern Atlantic Coastal Plain.

Color and odor of artificial fruit used to signal potential dispersers in the Atlantic forest in Brazil

Fruit color and odor are the main features regulating the rate of fruit predation and dispersal. The aim of this study was to analyze the effect of odor and color on fruit predators and dispersers. The present study was conducted in a 30ha area of secondary forest in Southeastern Atlantic Brazil. This area was divided into two transects, in which four points were marked with a 30m distance from each other. Each sampling point contained a total of 30 artificial fruit which belong to six different treatment groups, with five artificial fruit per group. Each group was randomly placed on the ground and that artificial fruit was checked every seven days. For each group of five fruit, 5mL of essence (vanilla or pineapple) were placed, and no essence was used in the control group. Artificial fruit was made with green and red nontoxic modeling clay, as well as artificial essences (vanilla and pineapple). A total of 960 fruits were used. Predated fruit equaled 26.9% (258 units), from which the red/pineapple had the highest predation rate (81.9%), followed by red/vanilla (46.3%), while green/control fruits were not predated. Throughout the experiment, bitten fruit and pecked fruit equaled 58.3% and 41.7%, respectively. No significant differences were recorded (x2=7.57, df=5, p=0.182) between bitten and pecked fruit. Fruit color and odor are important in attracting predators and dispersers, which explains the high rate of predation of red/ vanilla and red/pineapple, and the absence of predated fruits in the green/control group. Regarding the potential disperser, there was no statistically significant difference between pecked fruit and bitten fruit. As a result, it should be taken into consideration that zoochory (mammalochory and ornithochory) is the most important dispersal; therefore, it should be concluded that birds are more attracted by color and mammals by odor.

Ventilation of the equatorial Atlantic by the equatorial deep jets

Equatorial deep jets (EDJs) are a prominent flow feature of the equatorial Atlantic below the Equatorial Undercurrent down to about 3000 m. Here we analyze long‐term moored velocity and oxygen observations, as well as shipboard hydrographic and current sections acquired along 23°W and covering the depth range of the oxygen minimum zones of the eastern tropical North and South Atlantic. The moored zonal velocity data show high‐baroclinic mode EDJ oscillations at a period of about 4.5 years. Equatorial oxygen observations which do not resolve or cover a full 4.5‐yr EDJ cycle nevertheless reveal large variability, with oxygen concentrations locally spanning a range of more than 60μmol kg−1. We study the effect of EDJs on the equatorial oxygen concentration by forcing an advection‐diffusion model with the velocity field of the gravest equatorial basin mode corresponding to the observed EDJ cycle. The advection‐diffusion model includes an oxygen source at the western boundary and oxygen consumption elsewhere. The model produces a 4.5‐yr cycle of the oxygen concentration and a temporal phase difference between oxygen concentration and eastward velocity that is less than quadrature, implying a net eastward oxygen flux. The comparison of available observations and basin‐mode simulations indicates that a substantial part of the observed oxygen variability at the equator can be explained by EDJ oscillations. The respective role of mean advection, EDJs, and other possible processes in shaping the mean oxygen distribution of the equatorial Atlantic at intermediate depth is discussed.

Large-scale phylogeography of the disjunct Neotropical tree species Schizolobium parahyba (Fabaceae-Caesalpinioideae)

Neotropical rainforests exhibit high levels of endemism and diversity. Although the evolutionary genetics of plant diversification has garnered increased interest, phylogeographic studies of widely distributed species remain scarce. Here we describe chloroplast and nuclear variation patterns in Schizolobium parahyba (Fabaceae), a widespread tree in Neotropical rainforests that harbor two varieties with a disjunct distribution. Chloroplast and nuclear sequence analyses yielded 21 and 4 haplotypes, respectively. Two genetic diversity centers that correlate with the two known varieties were identified: the Southeastern Atlantic forest and the Amazonian basin. In contrast, the populations from southern and northeastern Atlantic forests and Andean-Central American forests exhibited low levels of genetic diversity and divergent haplotypes, likely related to historical processes that impact the flora and fauna in these regions, such as a founder’s effect after dispersion and demographic expansion. Phylogeographic and demographic patterns suggest that episodes of genetic isolation and dispersal events have shaped the evolutionary history for this species, and different patterns have guided the evolution of S. parahyba. Moreover, the results of this study suggest that the dry corridor formed by Cerrado and Caatinga ecoregions and the Andean uplift acted as barriers to this species’ gene flow, a picture that may be generalized to most of the plant biodiversity tropical woodlands and forests. These results also reinforce the importance of evaluating multiple genetic markers for a more comprehensive understanding of population structure and history. Our results provide insight into the conservation efforts and ongoing work on the genetics of population divergence and speciation in these Neotropical rainforests.

Drought-Busting Tropical Cyclones in the Southeastern Atlantic United States: 1950–2008

Droughts and tropical cyclones (TCs) are climatologically common events in the southeastern United States, yet little research has examined the potential for TCs to ameliorate drought impacts. Here, we identify the frequency of TCs that abruptly end drought conditions (i.e., drought busters, or DB) and determine possible influences of coupled ocean–atmosphere teleconnections on the likelihood of a TC-induced DB (TCDB). Using the HURDAT database and Palmer Drought Severity Indexes from 1950 through 2008, we identified every TCDB for thirty-one climate divisions in the southeastern Atlantic United States. We present the spatial patterns of the total number of TCDBs and the percentage of all droughts ended by TCs using choropleth maps. To determine what teleconnections influenced TCDBs, we used logistic regression analysis and included multiple synoptic-scale circulation indexes as predictor variables. In addition, we used a Fisher's exact test to examine the association between the North Atlantic Oscillation (NAO) and TCDBs. We found that up to 41 percent of all droughts and at least 20 percent of droughts in three fourths of the climate divisions were ended by TCDBs. NAO was a significant predictor (p = 0.005) in the logistic regression model (χ2 = 10.91, p = 0.001), and the Fisher's exact test showed a significant association between NAO and TCDBs (p = 0.003). An odds-ratio calculation showed that TCDBs are 5.8 times more likely to occur during a negative NAO phase than a positive NAO phase.

Spatial and temporal trends of the toxic diatom Pseudo-nitzschia in the Southeastern Atlantic United States

Data collected by NOAA Phytoplankton Monitoring Network volunteers, from the beginning of the program (2001) through 2010, was used to assess the spatial and temporal trends of Pseudo-nitzschia spp. from North Carolina through northern Florida along the southeastern US coastline. Pseudo-nitzschia spp. was present from North Carolina to Florida, and was most common in North and South Carolina. Across the majority of the Atlantic southeast US, the highest rates of occurrence were observed in late summer, early fall, with most areas experiencing the lowest rate of occurrence in the spring. The Outer Banks of North Carolina, however, experienced a peak of occurrence in late winter to early spring in addition to a late summer, early fall peak. Pseudo-nitzschia was found in temperatures ranging from less than 5°C to 35°C and salinities from 5 to 37. Six unique bloom events were documented during this period of nine years, three of which contained detectable levels of domoic acid. The majority of these bloom events and all of the toxic events occurred in the Outer Banks of North Carolina. Given the extent and intensity of coverage afforded by the NOAA PMN, this program provides the optimal approach to not only assess past trends but to monitor environmental changes and emerging trends in the dynamics of this toxigenic species. Understanding the dynamics of this species allows resource managers to better predict the threats associated with domoic acid.

Mosquito (Diptera: Culicidae) assemblages associated with Nidularium and Vriesea bromeliads in Serra do Mar, Atlantic Forest, Brazil.

BackgroundThe most substantial and best preserved area of Atlantic Forest is within the biogeographical sub-region of Serra do Mar. The topographic complexity of the region creates a diverse array of microclimates, which can affect species distribution and diversity inside the forest. Given that Atlantic Forest includes highly heterogeneous environments, a diverse and medically important Culicidae assemblage, and possible species co-occurrence, we evaluated mosquito assemblages from bromeliad phytotelmata in Serra do Mar (southeastern Brazil).MethodsLarvae and pupae were collected monthly from Nidularium and Vriesea bromeliads between July 2008 and June 2009. Collection sites were divided into landscape categories (lowland, hillslope and hilltop) based on elevation and slope. Correlations between bromeliad mosquito assemblage and environmental variables were assessed using multivariate redundancy analysis. Differences in species diversity between bromeliads within each category of elevation were explored using the Renyi diversity index. Univariate binary logistic regression analyses were used to assess species co-occurrence. ResultsA total of 2,024 mosquitoes belonging to 22 species were collected. Landscape categories (pseudo-F value = 1.89, p = 0.04), bromeliad water volume (pseudo-F = 2.99, p = 0.03) and bromeliad fullness (Pseudo-F = 4.47, p < 0.01) influenced mosquito assemblage structure. Renyi diversity index show that lowland possesses the highest diversity indices. The presence of An. homunculus was associated with Cx. ocellatus and the presence of An. cruzii was associated with Cx. neglectus, Cx. inimitabilis fuscatus and Cx. worontzowi. Anopheles cruzii and An. homunculus were taken from the same bromeliad, however, the co-occurrence between those two species was not statistically significant.ConclusionsOne of the main findings of our study was that differences in species among mosquito assemblages were influenced by landscape characteristics. The bromeliad factor that influenced mosquito abundance and assemblage structure was fullness. The findings of the current study raise important questions about the role of An. homunculus in the transmission of Plasmodium in Serra do Mar, southeastern Atlantic Forest.

Variations in Cloud Cover and Cloud Types over the Ocean from Surface Observations, 1954–2008

Abstract Synoptic weather observations from ships throughout the World Ocean have been analyzed to produce a climatology of total cloud cover and the amounts of nine cloud types. About 54 million observations contributed to the climatology, which now covers 55 years from 1954 to 2008. In this work, interannual variations of seasonal cloud amounts are analyzed in 10° grid boxes. Long-term variations O(5–10 yr), coherent across multiple latitude bands, remain present in the updated cloud data. A comparison to coincident data on islands indicates that the coherent variations are probably spurious. An exact cause for this behavior remains elusive. The globally coherent variations are removed from the gridbox time series using a Butterworth filter before further analysis. Before removing the spurious variation, the global average time series of total cloud cover over the ocean shows low-amplitude, long-term variations O(2%) over the 55-yr span. High-frequency, year-to-year variation is seen O(1%–2%). Among the cloud types, the most widespread and consistent relationship is found for the extensive marine stratus and stratocumulus clouds (MSC) over the eastern parts of the subtropical oceans. Substantiating and expanding upon previous work, strong negative correlation is found between MSC and sea surface temperature (SST) in the eastern North Pacific, eastern South Pacific, eastern South Atlantic, eastern North Atlantic, and the Indian Ocean west of Australia. By contrast, a positive correlation between cloud cover and SST is seen in the central Pacific. High clouds show a consistent low-magnitude positive correlation with SST over the equatorial ocean. In regions of persistent MSC, time series show decreasing MSC amount. This decrease could be due to further spurious variation within the data. However, the decrease combined with observed increases in SST and the negative correlation between marine stratus and sea surface temperature suggests a positive cloud feedback to the warming sea surface. The observed decrease of MSC has been partly but not completely offset by increasing cumuliform clouds in these regions; a similar decrease in stratiform and increase in cumuliform clouds had previously been seen over land. Interannual variations of cloud cover in the tropics show strong correlation with an ENSO index.

Glacial-interglacial vegetation dynamics in South Eastern Africa coupled to sea surface temperature variations in the Western Indian Ocean

Abstract. Glacial-interglacial fluctuations in the vegetation of South Africa might elucidate the climate system at the edge of the tropics between the Indian and Atlantic Oceans. However, vegetation records covering a full glacial cycle have only been published from the eastern South Atlantic. We present a pollen record of the marine core MD96-2048 retrieved by the Marion Dufresne from the Indian Ocean ∼120 km south of the Limpopo River mouth. The sedimentation at the site is slow and continuous. The upper 6 m (spanning the past 342 Ka) have been analysed for pollen and spores at millennial resolution. The terrestrial pollen assemblages indicate that during interglacials, the vegetation of eastern South Africa and southern Mozambique largely consisted of evergreen and deciduous forests. During glacials open mountainous scrubland dominated. Montane forest with Podocarpus extended during humid periods was favoured by strong local insolation. Correlation with the sea surface temperature record of the same core indicates that the extension of mountainous scrubland primarily depends on sea surface temperatures of the Agulhas Current. Our record corroborates terrestrial evidence of the extension of open mountainous scrubland (including fynbos-like species of the high-altitude Grassland biome) for the last glacial as well as for other glacial periods of the past 300 Ka.

Growth pattern of the young of the year Argentine hake Merluccius hubbsi Marini, 1933 (Gadiformes Merluccidae) along the Brazilian and Uruguayan coasts

Morphology and morphometry of the sagittae otolith were studied in young of the year Argentine hake, Merluccius hubbsi in the Southeastern Atlantic. Geographical variation in the growth pattern of the young of the year Merluccius hubbsi was correlated with the differences found in otolith morphometry, relative growth, ring positions, as well as the formation of a new ring. The otolith development of M. hubbsi throughout its area of distribution accompanies an increasing northward temperature gradient, resulting in bigger otoliths and greater variability of ring position from northern to southern area. The canonical discriminate analysis showed that the otolith length and height explained most of the variation of the first discriminant function. We found significant differences in the discriminant scores between those samples from northern and southern area. As regards the Uruguayan coast and Southern Brazil, age groups zero shared some similarity as well as differences in growth; environmental features explain these differences but their effect on the adult fishes growth is still unknown.