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Sample records for atlantic period ca

  1. Differential success in sampling of Atlantic Forest amphibians among different periods of the day.

    PubMed

    Rocha, C F D; Siqueira, C C; Ariani, C V; Vrcibradic, D; Guedes, D M; Kiefer, M C; Almeida-Gomes, M; Goyannes-Araújo, P; Borges-Júnior, V N T; Van Sluys, M

    2015-05-01

    In general, anurans tend to be nocturnal, though diurnal activity is characteristic of some groups. Studies show that frog activity may be inferred based on the number of individuals collected at different periods of the day, during large-scale field surveys. We investigated the best period of the day to conduct amphibian sampling in nine Atlantic Rainforest areas in southeastern Brazil, based on intensive field surveys. At each locality we employed similar sampling effort during diurnal, crepuscular and nocturnal searches (totaling 704.5 sampling hours). We pooled data from all localities for each period and estimated the proportion of frogs of each species active at each period based on the total number of individuals and on the number of species found during all surveys for that period. We recorded a total of 817 individual frogs from 69 species. Species richness was highest at night (median = 12 species), intermediate at dusk (median = 8), and lowest during the day (median = 4). The percentage of the total number of individual frogs found (pooled species) was highest during the night (ca. 53%) and lowest during the day (ca. 14%). Analyzing each species separately, the number of individuals recorded was consistently higher at dusk and night for most species. Our study evidences a trend for nocturnal activity for most Atlantic Rainforest frogs, with few species having primarily diurnal habits. Those results may favor future studies and conservation efforts for amphibian species. PMID:26132005

  2. Links between tropical rainfall and North Atlantic climate during the last glacial period

    NASA Astrophysics Data System (ADS)

    Deplazes, Gaudenz; Lückge, Andreas; Peterson, Larry C.; Timmermann, Axel; Hamann, Yvonne; Hughen, Konrad A.; Röhl, Ursula; Laj, Carlo; Cane, Mark A.; Sigman, Daniel M.; Haug, Gerald H.

    2013-03-01

    During the last glacial period, the North Atlantic regionexperienced pronounced, millennial-scale alternations between cold, stadial conditions and milder interstadial conditions--commonly referred to as Dansgaard-Oeschger oscillations--as well as periods of massive iceberg discharge known as Heinrich events. Changes in Northern Hemisphere temperature, as recorded in Greenland, are thought to have affected the location of the Atlantic intertropical convergence zone and the strength of the Indian summer monsoon. Here we use high-resolution records of sediment colour--a measure of terrigenous versus biogenic content--from the Cariaco Basin off the coast of Venezuela and the Arabian Sea to assess teleconnections with the North Atlantic climate system during the last glacial period. The Cariaco record indicates that the intertropical convergence zone migrated seasonally over the site during mild stadial conditions, but was permanently displaced south of the basin during peak stadials and Heinrich events. In the Arabian Sea, we find evidence of a weak Indian summer monsoon during the stadial events. The tropical records show a more variable response to North Atlantic cooling than the Greenland temperature records. We therefore suggest that Greenland climate is especially sensitive to variations in the North Atlantic system--in particular sea-ice extent--whereas the intertropical convergence zone and Indian monsoon system respond primarily to variations in mean Northern Hemisphere temperature.

  3. REPRODUCTIVE ECOLOGY AND SPAWNING PERIODICITY OF THE ATLANTIC SILVERSIDE, 'MENIDIA MENIDIA' (PISCES: ATHERINIDAE)

    EPA Science Inventory

    The reproduction ecology and spawning periodicity of the Atlantic silverside, Menidia menidia, living in the North Edisto River estuary, South Carolina, was studied at two sites, Bears Bluff and the Point of Pines, during the spring and summer of 1976, 1977, and 1978. A specific ...

  4. Evidence for cooler European summers during periods of changing meltwater flux to the North Atlantic.

    PubMed

    Heiri, Oliver; Tinner, Willy; Lotter, André F

    2004-10-26

    We analyzed fossil chironomids (nonbiting midges) and pollen in two lake-sediment records to reconstruct and quantify Holocene summer-temperature fluctuations in the European Alps. Chironomid and pollen records indicate five centennial-scale cooling episodes during the early- and mid-Holocene. The strongest temperature declines of approximately 1 degrees C are inferred at approximately 10,700-10,500 and 8,200-7,600 calibrated 14C years B.P., whereas other temperature fluctuations are of smaller amplitude. Two forcing mechanisms have been presented recently to explain centennial-scale climate variability in Europe during the early- and mid-Holocene, both involving changes in Atlantic thermohaline circulation. In the first mechanism, changes in meltwater flux from the North American continent to the North Atlantic are responsible for changes in the Atlantic thermohaline circulation, thereby affecting circum-Atlantic climate. In the second mechanism, solar variability is the cause of Holocene climatic fluctuations, possibly triggering changes in Atlantic thermohaline overturning. Within their dating uncertainty, the two major cooling periods in the European Alps are coeval with substantial changes in the routing of North American freshwater runoff to the North Atlantic, whereas quantitatively, our climatic reconstructions show a poor agreement with available records of past solar activity. Thus, our results suggest that, during the early- and mid-Holocene, freshwater-induced Atlantic circulation changes had stronger influence on Alpine summer temperatures than solar variability and that Holocene thermohaline circulation reductions have led to summer-temperature declines of up to 1 degrees C in central Europe. PMID:15492214

  5. South Atlantic intermediate water advances into the North-east Atlantic with reduced Atlantic meridional overturning circulation during the last glacial period

    NASA Astrophysics Data System (ADS)

    Dubois-Dauphin, Quentin; Bonneau, Lucile; Colin, Christophe; Montero-Serrano, Jean-Carlos; Montagna, Paolo; Blamart, Dominique; Hebbeln, Dierk; Van Rooij, David; Pons-Branchu, Edwige; Hemsing, Freya; Wefing, Anne-Marie; Frank, Norbert

    2016-06-01

    The Nd isotopic composition (ɛNd) of seawater and cold-water coral (CWC) samples from the Gulf of Cádiz and the Alboran Sea, at a depth of 280-827 m were investigated in order to constrain middepth water mass dynamics within the Gulf of Cádiz over the past 40 ka. ɛNd of glacial and Holocene CWC from the Alboran Sea and the northern Gulf of Cádiz reveals relatively constant values (-8.6 to -9.0 and -9.5 to -10.4, respectively). Such values are similar to those of the surrounding present-day middepth waters from the Mediterranean Outflow Water (MOW; ɛNd ˜ -9.4) and Mediterranean Sea Water (MSW; ɛNd ˜ -9.9). In contrast, glacial ɛNd values for CWC collected at thermocline depth (550-827 m) in the southern Gulf of Cádiz display a higher average value (-8.9 ± 0.4) compared to the present-day value (-11.7 ± 0.3). This implies a higher relative contribution of water masses of Mediterranean (MSW) or South Atlantic origin (East Antarctic Intermediate Water, EAAIW). Our study has produced the first evidence of significant radiogenic ɛNd values (˜ -8) at 19, 23-24, and 27 ka, which are coeval with increasing iceberg discharges and a weakening of Atlantic Meridional Overturning Circulation (AMOC). Since MOW ɛNd values remained stable during the last glacial period, it is suggested that these radiogenic ɛNd values most likely reflect an enhanced northward propagation of glacial EAAIW into the eastern Atlantic Basin.

  6. Orbital and suborbital variability in North Atlantic bottom water temperature obtained from deep-sea ostracod Mg/Ca ratios

    USGS Publications Warehouse

    Cronin, T. M.; Dwyer, G.S.; Baker, P.A.; Rodriguez-Lazaro, J.; DeMartino, D.M.

    2000-01-01

    Magnesium/calcium (Mg/Ca) ratios were measured in the deep-sea ostracod (Crustacea) genus Krithe from Chain core 82-24-4PC from the western mid-Atlantic Ridge (3427 m) in order to estimate ocean circulation and bottom water temperature (BWT) variability over the past 200,000 years. Mg/Ca ratios have been used as a paleothermometer because the ratios are controlled primarily by ambient water temperatures at the time the organism secretes its adult carapace. Over the past two glacial-interglacial cycles, Mg/Ca values oscillated between about 7 mmol/mol and 12 mmol/mol, equivalent to a BWT range of 0 to > 3.5??C. The lowest values were obtained on specimens from glacial marine isotope stages (MISs) 2, 4 and 6; the highest values were obtained from specimens from the early part of the Holocene interglacial (MIS 1), and also from MISs 5 and 7. These trends suggest that BWTs in the North Atlantic Ocean fluctuate over orbital time scales. Suborbital variability in Mg/Ca ratios and BWT was also observed for the past 100,000 years. Ratios rose from ~8 mmol/mol to ~10 mmol/mol (implying a BWT increase of ~1 to 3??C) during 14 Mg/Ca excursions. The highest ratios were found in Krithe dated at approximately 32, 36-38, 43, 48, 73, 85 and 93 ka. Although the age model for the Chain 82-24-4PC and temporal resolution do not allow precise correlation, some of these deep-sea bottom temperature excursions appear to correspond to Heinrich events recorded in other regions of the North Atlantic and perhaps Dansgaard-Oeschger interstadial events recorded in Greenland ice cores. If confirmed, this would support the hypothesis that millennial-scale oscillations of climate in the North Atlantic are capable of affecting global climate via thermohaline circulation changes. (C) 2000 Elsevier Science B.V.

  7. North Atlantic Surface and Deep-Water Hydrography during the Early Pliocene Warm Period

    NASA Astrophysics Data System (ADS)

    Voelker, A. H. L.; Evans, H. F.; Naafs, B. D.; Cavaleiro, C. D.; Rebotim, A.; Ventura, C.; Stein, R. H.; Channell, J. E. T.

    2014-12-01

    The early Pliocene, with atmospheric carbon dioxide concentrations at levels similar to today, is seen as a case study for Earth's future climate evolution. During this period the progressive closing of the Central American Seaway led to increased poleward heat and salt transport within the Atlantic with North Atlantic Deep Water (NADW) becoming warmer and saltier and resulting in an enhanced Atlantic Meridional Overturning Circulation (AMOC). In order to understand how stable the AMOC really was we produced millennial-scale (1-2 kyr) surface and deep-water records for IODP Site U1313 (41°N, 33°W, 3412m) for the interval from 3.4 to 4.1 Ma. This site is ideally located to monitor past AMOC changes with North Atlantic Drift waters at the surface and NADW in the deep. Although interglacial/glacial cycles are visible, the higher frequency oscillations recorded in both the planktonic G. ruber (white) and benthic Cibicidoides sp. δ18O records impede tuning to the LR04 stack (Lisiecki and Raymo, 2005). We therefore exploit a different approach: using the magnetic polarity chrons (Gilbert, Cochiti) as recorded at Site U1313 as framework, we tune our benthic δ18O record to that of ODP Site 1085 (on LR04 ages). The benthic δ13C record shows millennial-scale oscillations, and the values indicate nearly continuous NADW presence and confirm a strong AMOC, also during most of the glacial periods. Varying surface water conditions, especially during the younger interglacial periods, are reflected in the G. ruber isotope data and appear to be linked to salinity changes since they are not recorded in the alkenone sea-surface temperature data. Although glacial stages Gi 2 and Gi 4 show the expected higher benthic δ18O values, Gi 6 was the glacial period with the strongest impact on the AMOC as revealed by cooler, less ventilated surface waters and a less ventilated NADW. Overall, the AMOC was strong throughout, but experienced high frequency oscillations at a level similar to

  8. Multi-Centennial Record of North Atlantic Freshwater Variability since the Little Ice Age Archived in Coralline Algal Ba/Ca

    NASA Astrophysics Data System (ADS)

    Chan, P. T. W.; Halfar, J.; Adey, W.; Zack, T.

    2014-12-01

    Declining Arctic sea-ice cover in recent decades has driven large-scale freshwater transport into the North Atlantic, possibly influencing the strength of the Meridional Overturning Circulation and even global climate. However, due to the lack of long-term oceanographic observations, little is known about the natural freshwater variability of the Northwestern Atlantic. Crustose coralline algae Clathromorphum compactum are extremely long-lived shallow marine calcareous plants that are abundant along the subarctic eastern Canadian coastline. They are particularly well-suited as recorders of paleoclimate signals due to the formation of annual growth increments, allowing for the precise calendar dating and geochemical sampling of hard tissue. Here, we provide the first annually-resolved multi-centennial record of coralline algal Ba/Ca from Labrador, Canada, as a proxy for North Atlantic freshwater variability extending well into the Little Ice Age (LIA) (1665 AD). Barium-to-calcium ratios (Ba/Ca) from coralline algae have previously been used as an indicator of freshwater runoff. This is because barium-rich clay sediments are transported by terrestrial runoff into coastal waters, and barium is released from the clay minerals upon encountering more alkaline elements present in seawater. We observe higher algal barium concentrations during the LIA, followed by a steady decline to recent times. In addition, coralline algal Ba/Ca shows significant positive relationships to Hudson Strait runoff, as well as Canadian Arctic and North Atlantic sea-ice extent. This suggests that more riverine Ba is transported from the Hudson Strait into the Labrador Sea during periods of increased sea-ice cover. Multiyear sea-ice can block incoming solar radiation thereby diminishing the effects of nutrient scavenging by phytoplankton, resulting in a more conservative transport of Ba into northern Labrador. However as sea-ice continues to thin, more sunlight is able to penetrate through the

  9. The North Atlantic Oscillation Reconstructed at Bermuda for 220 Years Using Sr/Ca Ratios in Diploria labyrinthiformis (brain coral)

    NASA Astrophysics Data System (ADS)

    Goodkin, N. F.; Hughen, K. A.; Cohen, A. L.; Curry, W. B.; Doney, S. C.

    2006-12-01

    The North Atlantic Oscillation (NAO) is a meridional oscillation in atmospheric mass measured by pressure anomalies between Iceland (65°N, 23°W) and the Azores (38°N, 26°W) (Hurrell, 1995). Changes between the positive and negative phase of the NAO strongly influence weather patterns across the US, Europe and the Middle East. A shift in recent decades toward a sustained positive NAO has raised questions about the influence of greenhouse gas emissions on this system. Unfortunately, instrumental records are too short to identify the natural baseline variability of the NAO, and NAO reconstructions generally encompass only land-based proxies, excluding ocean processes. Winter-time sea surface temperatures (SST) in the Sargasso Sea have previously been shown to correlate to the NAO (Visbeck et al., 2001), and thus a long winter SST record based on proxy data could be used to reconstruct NAO variability back in time. Here we present an annually resolved winter-time strontium to calcium ratio (Sr/Ca) record from a 220-year old brain coral (Diploria labyrinthiformis) collected from the south shore of Bermuda. Brain coral is prevalent in Bermuda and shows distinct annual banding in its skeleton providing precise age models. Winter-time coral Sr/Ca has previously been shown to accurately record winter SST free from growth rate influences (Goodkin et al., 2005), and that relationship is confirmed here. Cross-spectral analysis between winter-time coral Sr/Ca and four instrumental and proxy records of the NAO (Hurrell, 1995, Jones et al., 1997, Luterbacher et al., 2001, Cook et al., 2002) show two frequencies of coherence with >95% confidence. At periods greater than 20 years and between 3 and 5 years, the coral Sr/Ca effectively captures the NAO variability. Filtering the coral record to these frequencies and comparing to the instrumental and proxy records, including another marine-based NAO reconstruction from the North and Norwegian Seas (Schoene et al., 2003), show

  10. Nutrient conditions in the North Atlantic during the last glacial period

    NASA Astrophysics Data System (ADS)

    Tremblay, M. M.; Straub, M.; Ellis, K. K.; Wang, X.; Rafter, P. A.; Sigman, D. M.; Haug, G. H.; Toggweiler, J. R.

    2011-12-01

    One proposed mechanism for lower atmospheric CO2 during past glacial periods is reduced overturning in the Southern Ocean, which reduces the leakage of deeply sequestered CO2 back into the atmosphere from this region. This mechanism relies on the assumption that nutrient consumption in the North Atlantic surface has remained relatively constant across glacial/interglacial cycles. Due to isotope fractionation during nitrate assimilation, nitrate in the sunlit surface waters is progressively elevated in 15N/14N as it is consumed by phytoplankton. The 15N/14N of organic matter bound within the walls of planktonic foraminiferal tests covary with the 15N/14N of nitrate consumed in surface waters across the global ocean and is thus expected to record past changes in nutrient consumption in high latitude surface waters, an assertion currently being tested with core top measurements. We have measured a down-core record of foraminifera-bound 15N/14N in the subpolar North Atlantic in an effort to reconstruct nutrient conditions in this region during the last glacial period. The foraminifera species N. pachyderma (sin.) was picked from regular depth intervals in core VM28-73 (57.2°N, 20.9°W). After chemical cleaning of the tests, the test-bound organic N was released by acid digestion of the tests, oxidized to nitrate with potassium persulfate, converted bacterially to nitrous oxide, and finally analyzed on an isotope ratio mass spectrometer. Foraminifera-bound 15N/14N is generally lower during the last glacial period than during the Holocene, suggesting less complete nutrient consumption during the former. However, at least two single-point maxima in 15N/14N are observed within the glacial section; these coincide with distinct sedimentological changes in the core and may be associated with Heinrich events. Full interpretation of the data awaits an improved age model for the core as well as a suite of ancillary measurements.

  11. Atlantic cooling associated with a marine biotic crisis during the mid-Cretaceous period

    NASA Astrophysics Data System (ADS)

    McAnena, A.; Flögel, S.; Hofmann, P.; Herrle, J. O.; Griesand, A.; Pross, J.; Talbot, H. M.; Rethemeyer, J.; Wallmann, K.; Wagner, T.

    2013-07-01

    Most of the marine biotic crises that occurred during the hot Mesozoic era have been linked to episodes of extreme warmth. Others, however, may have occurred during cooler intervals that interrupted Cretaceous greenhouse warmth. There are some indications of cooling in the late Aptian (116-114Myr ago), but it has not been definitively linked to biotic crisis. Here we assess the timing and magnitude of late Aptian cooling and its association with biotic crises using a suite of geochemical and micropalaeontological assessments from a marine sediment core from the North Atlantic Ocean as well as global biogeochemical modelling. Sea surface temperatures derived from the TEX86 proxy suggest that surface waters cooled by about 5°C during the two million years, coincident with a positive δ13C excursion of approximately 2‰ in carbonates and organic carbon. Surface productivity was enhanced during this period, but the abundance of planktonic foraminifera and nannoconid phytoplankton declined. Our simulations with a biogeochemical model indicate that the δ13C excursion associated with the cooling could be explained by the burial of about 812,000 gigatons of carbon over 2.5 million years. About 50% of the this carbon burial occurred in the Atlantic, Southern and Tethys ocean basins. We conclude that global cooling during greenhouse conditions can cause perturbations to marine ecosystems and biogeochemical cycles at scales comparable to those associated with global warming.

  12. Ocean climate prior to breeding affects the duration of the nestling period in the Atlantic puffin

    PubMed Central

    Durant, Joël M; Anker-Nilssen, Tycho; Stenseth, Nils Chr

    2006-01-01

    Time-series covering 23 years for a long-lived seabird, the Atlantic puffin (Fratercula arctica L.) at Røst, northern Norway, was used to explore any indirect effects of climatic variations on chick production. By fitting statistical models on the duration of the nestling period, we found that it may be estimated using the average sea temperature and salinity at 0–20 m depth in March (having a positive and a negative effect, respectively). We propose that when the phytoplankton bloom occurs in early spring, adverse oceanographic conditions, i.e. low temperature and high salinity in March, have a negative effect on puffin reproduction by degradation of the prey availability (mainly Clupea harengus) for chick-feeding adults three months later. PMID:17148306

  13. Ocean climate prior to breeding affects the duration of the nestling period in the Atlantic puffin.

    PubMed

    Durant, Joël M; Anker-Nilssen, Tycho; Stenseth, Nils Chr

    2006-12-22

    Time-series covering 23 years for a long-lived seabird, the Atlantic puffin (Fratercula arctica L.) at Røst, northern Norway, was used to explore any indirect effects of climatic variations on chick production. By fitting statistical models on the duration of the nestling period, we found that it may be estimated using the average sea temperature and salinity at 0-20 m depth in March (having a positive and a negative effect, respectively). We propose that when the phytoplankton bloom occurs in early spring, adverse oceanographic conditions, i.e. low temperature and high salinity in March, have a negative effect on puffin reproduction by degradation of the prey availability (mainly Clupea harengus) for chick-feeding adults three months later. PMID:17148306

  14. High precision glacial-interglacial benthic foraminiferal Sr/Ca records from the eastern equatorial Atlantic Ocean and Caribbean Sea

    NASA Astrophysics Data System (ADS)

    Shen, Chuan-Chou; Hastings, David W.; Lee, Typhoon; Chiu, Chin-Hsin; Lee, Meng-Yang; Wei, Kuo-Yen; Edwards, R. Lawrence

    2001-08-01

    Glacial-interglacial variation in the marine Sr/Ca ratio has important implications for coral Sr thermometry [J.W. Beck et al., Science 257 (1992) 644-647]. A possible variation of 1-3% was proposed based on ocean models [H.M. Stoll and D.P. Schrag, Geochim. Cosmochim. Acta 62 (1998) 1107-1118]. Subsequently, studies have used fossil foraminifera to test this prediction [P.A. Martin et al., Geochem. Geophys. Geosyst. 1 (1999); H.M. Stoll et al., Geochim. Cosmochim. Acta 63 (1999) 3535-3547; H. Elderfield et al., Geochem. Geophys. Geosyst. 1 (2000)]. But whether some component of foraminiferal Sr/Ca variation can be uniquely ascribed to seawater Sr variation is still not clear. To address this question, we developed cleaning and analysis techniques and measured Sr/Ca ratios on individual shells of the modern benthic foraminifer Cibicidoides wuellerstorfi. We showed that different size shells have different Sr/Ca ratios; however, samples with shell sizes of 355-500 μm appear to have normally distributed Sr/Ca ratios (1σ=1.8%). For multi-shell measurements (with estimated errors of 0.12-0.39%), the ratio varied by as much as 7.2±0.5% during the last glaciation for two Caribbean records at the same site and by 3.7±0.5% over the past 40,000 yr for one record from the Sierra Leone Rise in the eastern equatorial Atlantic. The two Caribbean records are very similar indicating that the behavior of shell Sr uptake was identical locally and that the shell Sr/Ca ratio faithfully reflects the local environment. The Atlantic record differs from the Caribbean records by as much as several percent. Thus, the foraminiferal Sr/Ca changes cannot be solely due to changes in seawater Sr/Ca unless the glacial deep ocean had spatial variation in Sr/Ca well in excess of the modern ocean. Certain similarities between the three records do exist. Notably, the rate of change of Sr/Ca is similar between 9 and 0 ka (-0.25%/kyr) and between 25 and 16 ka (+0.16%/kyr). This suggests that

  15. An 800-Year Record of Sediment-Derived, Instrumentally-Calibrated Foraminiferal Mg/Ca SST Estimates From the Tropical North Atlantic

    NASA Astrophysics Data System (ADS)

    Black, D. E.; Abahazi, M. A.; Thunell, R. C.; Tappa, E. J.

    2005-12-01

    Most geochemical paleoclimate proxies are calibrated to different climate variables using laboratory culture, surface sediment, or sediment trap experiments. The varved, high-deposition rate sediments of the Cariaco Basin (Venezuela) provide the nearly unique opportunity to compare and calibrate paleoceanographic proxy data directly against true oceanic historical instrumental climate records. Here we present one of the first sediment-derived foraminiferal-Mg/Ca to SST calibrations spanning A. D. 1870-1990. The record of Mg/Ca-estimated tropical North Atlantic SSTs is then extended back to approximately A. D. 1200. Box core PL07-73 BC, recovered from the northeastern slope of Cariaco Basin, was sampled at consecutive 1 mm increments and processed for foraminiferal population, stable isotope, and Mg/Ca (by ICP-AES) analyses. The age model for this core was established by correlating faunal population records from PL07-73 to a nearby very well-dated Cariaco Basin box core, PL07-71 BC. The resulting age model yields consecutive sample intervals of one to two years. Mg/Ca ratios measured on Globigerina bulloides in samples deposited between A. D. 1870 and 1990 were calibrated to monthly SSTs from the Met Office Hadley Centre's SST data set for the Cariaco Basin grid square. Annual correlations between G. bulloides Mg/Ca and instrumental SST were highest (r=0.6, p<.0001, n=120) for the months of March, April, and May, the time when sediment trap studies indicate G. bulloides is most abundant in the basin. The full-length Mg/Ca-estimated SST record is characterized by decadal- and centennial-scale variability. The tropical western North Atlantic does not appear to have experienced a pronounced Medieval Warm Period relative to the complete record. However, strong Little Ice Age cooling of as much as 3 ° C occurred between A. D. 1525 and 1625. Spring SSTs gradually rose between A. D. 1650 and 1900 followed by a 2.5 ° C warming over the 20th century.

  16. Evaluating the Utility of Multiple Proxies (Mg/Ca, Li/Ca, Cd/Ca, δ13C and Nd isotopes) in Foraminiferal Shells: New calibrations from the Demerara Rise, western tropical Atlantic

    NASA Astrophysics Data System (ADS)

    Huang, K.; Oppo, D.; Curry, W. B.; Blusztajn, J.

    2011-12-01

    Reconstructions of changes in Antarctic Intermediate Water (AAIW) circulation and its properties across abrupt climate events provides crucial information about the role of AAIW in regulating the climate system and how AAIW responds to changes in North Atlantic overturning. In order to better constrain the ocean conditions in the past, we systematically examine the utility of temperature (Mg/Ca and Mg/Li), carbonate saturation state (B/Ca and Li/Ca), nutrient (Cd/Ca, Zn/Ca and δ13C) and watermass proxies (Nd isotopes) in foraminifera shells using a set of 22 multicore tops (KNR197-3, spanning depths of 380 to 3300 m) and ambient seawaters collected from the Demerara Rise in the tropical northwestern Atlantic. In this study new core-top calibrations will be presented for calcitic foraminifera (i.e., Cibicidoides pachyderma, Cibicidoides wuellerstorfi, Uvigerina peregrina) and aragonitic Hoeglundina elegans through a direct comparison of shell chemistry to physical/chemical properties of ambient seawaters. We will also present new Nd isotope calibrations based on measurements on seawaters, mixed planktonic foraminifera and Fe-Mn oxyhydroxides from the core-top samples, to refine the utility of the Nd isotopes in authigenic marine precipitates as a watermass proxy. These new results enable us to evaluate the impact of environmental parameters (T, S, and Δ[CO32-]) on these paleo-proxies, and to further assess the robustness of down-core reconstructions and interpretations.

  17. Seasonality in the tropical Atlantic: an 800-year record of seasonally-representative Mg/Ca data from the Cariaco Basin

    NASA Astrophysics Data System (ADS)

    Black, D. E.; Rahman, S.; Wurtzel, J.; Thunell, R.; Mauer, B.; Tappa, E. J.

    2009-12-01

    The Cariaco Basin, Venezuela is well-positioned to record a detailed history of surface ocean changes along the southern margin of the Caribbean and the tropical Atlantic. Varved, high deposition rate sediments deposited under anoxic conditions and an abundance of well-preserved microfossils result in one of the few marine records capable of preserving evidence of interannual- to decadal-scale climate variability in the tropical Atlantic. Boreal winter/spring sea surface temperatures (SST) spanning the last eight centuries have previously been reconstructed using Mg/Ca measurements on the planktic foraminifer Globigerina bulloides. Here we present the complementary record using Globigerinoides ruber (pink), a summer/fall indicator. Globigerinoides ruber Mg/Ca values are generally greater than those of G. bulloides from the same sample, reflecting warmer calcification temperatures. Both species’ records display similar long-term trends, yet there are some distinctive differences. The Medieval Warm Period (MWP) and Little Ice Age (LIA) as distinctly separate climate events are more apparent in the G. ruber record than that of G. bulloides. Additionally, greater variability in the G. ruber data may indicate a stronger than expected bias from productivity during the local upwelling season. As G. bulloides and pink G. ruber are thought to be winter/spring and summer/fall SST indicators, respectively (albeit with the potential upwelling season bias), the intersample differences between the two records can potentially be interpreted as a record of seasonality. Our seasonality reconstruction shows a distinctive oscillation of 4 °C with a period of approximately 200 years. The proxy seasonality is slightly less than what has been instrumentally measured (5 to 6 °C) over the last 15 years, and does not appear related to or affected by the MWP or LIA events.

  18. A comparison of benthic foraminiferal Mn / Ca and sedimentary Mn / Al as proxies of relative bottom-water oxygenation in the low-latitude NE Atlantic upwelling system

    NASA Astrophysics Data System (ADS)

    McKay, C. L.; Groeneveld, J.; Filipsson, H. L.; Gallego-Torres, D.; Whitehouse, M. J.; Toyofuku, T.; Romero, O. E.

    2015-09-01

    Trace element incorporation into foraminiferal shells (tests) is governed by physical and chemical conditions of the surrounding marine environment, and therefore foraminiferal geochemistry provides a means of palaeo-oceanographic reconstructions. With the availability of high-spatial-resolution instrumentation with high precision, foraminiferal geochemistry has become a major research topic over recent years. However, reconstructions of past bottom-water oxygenation using foraminiferal tests remain in their infancy. In this study we explore the potential of using Mn / Ca determined by secondary ion mass spectrometry (SIMS) as well as by flow-through inductively coupled plasma optical emission spectroscopy (FT-ICP-OES) in the benthic foraminiferal species Eubuliminella exilis as a proxy for recording changes in bottom-water oxygen conditions in the low-latitude NE Atlantic upwelling system. Furthermore, we compare the SIMS and FT-ICP-OES results with published Mn sediment bulk measurements from the same sediment core. This is the first time that benthic foraminiferal Mn / Ca is directly compared with Mn bulk measurements, which largely agree on the former oxygen conditions. Samples were selected to include different productivity regimes related to Marine Isotope Stage 3 (35-28 ka), the Last Glacial Maximum (28-19 ka), Heinrich Event 1 (18-15.5 ka), Bølling Allerød (15.5-13.5 ka) and the Younger Dryas (13.5-11.5 ka). Foraminiferal Mn / Ca determined by SIMS and FT-ICP-OES is comparable. Mn / Ca was higher during periods with high primary productivity, such as during the Younger Dryas, which indicates low-oxygen conditions. This is further supported by the benthic foraminiferal faunal composition. Our results highlight the proxy potential of Mn / Ca in benthic foraminifera from upwelling systems for reconstructing past variations in oxygen conditions of the sea floor environment as well as the need to use it in combination with other proxy records such as faunal

  19. A seesaw in Mediterranean precipitation during the Roman Period linked to millennial-scale changes in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Dermody, B. J.; de Boer, H. J.; Bierkens, M. F. P.; Weber, S. L.; Wassen, M. J.; Dekker, S. C.

    2012-03-01

    We present a reconstruction of the change in climatic humidity around the Mediterranean between 3000-1000 yr BP. Using a range of proxy archives and model simulations we demonstrate that climate during this period was typified by a millennial-scale seesaw in climatic humidity between Spain and Israel on one side and the Central Mediterranean and Turkey on the other, similar to precipitation anomalies associated with the East Atlantic/West Russia pattern in current climate. We find that changes in the position and intensity of the jet stream indicated by our analysis correlate with millennial changes in North Atlantic sea surface temperature. A model simulation indicates the proxies of climatic humidity used in our analysis were unlikely to be influenced by climatic aridification caused by deforestation during the Roman Period. That finding is supported by an analysis of the distribution of archaeological sites in the Eastern Mediterranean which exhibits no evidence that human habitation distribution changed since ancient times as a result of climatic aridification. Therefore we conclude that changes in climatic humidity over the Mediterranean during the Roman Period were primarily caused by a modification of the jet stream linked to sea surface temperature change in the North Atlantic. Based on our findings, we propose that ocean-atmosphere coupling may have contributed to regulating Atlantic Meridional Overturning Circulation intensity during the period of analysis.

  20. Modeling the Canadian southern Atlantic region oxidants: A study of a Canadian EMEFS-1 hyperintensive period

    NASA Astrophysics Data System (ADS)

    Gong, Wanmin; Lin, Xiude; MéNard, Sylvain; Pellerin, Pierre; Benoit, Robert

    1999-08-01

    The roles and mechanisms of transport and chemical transformation affecting surface ozone in the Canadian southern Atlantic region (SAR) are investigated using a three-dimensional Eulerian comprehensive modeling system. The investigation is focused a regional ozone episode over the eastern North America during the first week of August 1988. The model performance is evaluated with available observations during this period. The model is shown to reproduce the general features of this regional episode, with better performance for the sites with clear local photochemical activities than for those strongly influenced by complex coastal flow. It is shown from the reconstructed time history of various processes along the backward trajectories originating from a site in Nova Scotia that the elevated ground-level ozone in the SAR during the study period was associated with transport at low levels, under a strong southwesterly flow. The high ozone brought to the site was mostly produced within the stable marine boundary layer from precursors picked up earlier over the emission area on the east coast of the United States. A second transport situation was also simulated and shown to be associated with transport aloft that was never mixed to the surface. This study also shows that differential advection, due to stable stratification and vertical shear of horizontal wind, can deform surface-based plumes to produce elevated layers of pollutants over the Gulf of Maine.

  1. Effects Of The Thermohaline Circulation Slowdown On Vegetation And Climate Around The Tropical Atlantic During The Younger Dryas Period

    NASA Astrophysics Data System (ADS)

    Hermann, B.; Lydie, D. M.

    2005-12-01

    The Younger Dryas (YD) event is thought to be caused by a slowdown of the thermohaline circulation as a result of large input of freshwater into the Arctic Ocean (Tarasov and Peltier 2005). Decreased heat transport to the Arctic region would have resulted in higher sea surface temperatures of the tropical Atlantic (Rühlemann et al. 1999). Modelling studies show that a weaker Atlantic overturning circulation thus has consequences for the amount and geographical distribution of rain fall over and around the tropical Atlantic (Lohmann 2003). According to this study, northern South America would have become drier and eastern Brazil wetter. No significant changes in rainfall were predicted for Africa. We test these predictions comparing pollen studies from Africa, South America and the tropical Atlantic. Terrestrial and marine pollen sequences record changes in the tropical vegetation which responds to changes in precipitation. In south and south-eastern Brazil, a transect of three pollen sequences document the southern limit of a positive precipitation anomaly during the latter part of the YD period (Behling et al. 2004, 2005, unpublished data). In Africa, a dry YD period is recorded in Nigeria and Ghana (Talbot and Johannessen 1992, Salzmann et al. 2002). However, in Cameroon (Maley and Brenac 1998) and offshore Angola (Dupont and Behling in press) vegetation records are unambiguous or do not show changes in precipitation regime during the YD period.

  2. Quasi-periodic Climate Teleconnections via the North Atlantic Oscillation: A New Perspective From Tree Rings

    NASA Astrophysics Data System (ADS)

    Meyers, S. R.; Pagani, M.

    2004-12-01

    Internal modes of climate variability such as the North Atlantic Oscillation (NAO) and the El Nino-Southern Oscillation (ENSO) significantly contribute to regional weather patterns on an inter-annual basis. Changes in the behavior of these modes over decadal and/or centennial timescales may represent an important driver of past climate events and future climate change. Importantly, if the internal modes express band-limited (periodic to quasi-periodic) variability, they provide a useful template for climate forecasting. Unfortunately, our ability to directly quantify the periodic/quasi-periodic nature of climate response to the internal modes is constrained by the limited temporal extent of instrumental records. In this study we present a novel approach toward recognition of band-limited climatic effects of the NAO in proxy records that span the past 400 years. The spatial climatic response of the NAO between northern and southern Europe provides a framework for detecting the influence of the NAO in proxy climate records. Specifically, if the NAO-forced climate signal is present it should be strongly correlated and anti-phased between the northern and southern regions of western Europe. To prospect for the NAO signal in paleoclimate data we employ independent networks of tree ring width series from Scandinavia and the Mediterranean. These locations were selected because modern instrumental records of the NAO and precipitation are significantly correlated in these regions, and tree ring width sensitivity to climate variability is maximized. The tree-ring width data from western Europe reveals a distinct 25-year quasi-periodic synchronization of climate change between Scandinavia and the Mediterranean during the 17th-20th centuries. Based on the dipole character of this signal, we propose that it is representative of climate forcing via the NAO. On this timescale of climate variability, dry/cold climate events in northern Europe are closely tied to wet events in

  3. A plant 35S CaMV promoter induces long-term expression of luciferase in Atlantic salmon

    PubMed Central

    Seternes, Tore; Tonheim, Tom C.; Myhr, Anne I.; Dalmo, Roy A.

    2016-01-01

    The long-term persistence and activity of a naked plasmid DNA (pGL3-35S) containing a luc gene (reporter gene) controlled by a plant 35S CaMV promoter was studied in Atlantic salmon (Salmo salar L.) after injection. Atlantic salmon (mean weight 70 grams) were injected intramuscularly with 100 μg of plasmid DNA. Blood, different tissues and organs were sampled at different time points up to day 535 after injection. Southern blot analysis suggested the presence of extra-chromosomally open circular, linear and supercoiled topoforms of pGL3-35S at day 150 after injection. At day 536 open circular and supercoiled topoforms were detected. Luciferase activity was detected at the injection site up to 536 days post-injection of pGL3-35S, where it peaked at day 150 and decreased to approximately 17% of its maximum activity by day 536. Our study demonstrated that a plasmid containing the 35S promoter was able to induce expression of a reporter gene/protein in fish in vivo and that the plasmid DNA persisted for a prolonged time after intramuscular injection. PMID:27114167

  4. A plant 35S CaMV promoter induces long-term expression of luciferase in Atlantic salmon.

    PubMed

    Seternes, Tore; Tonheim, Tom C; Myhr, Anne I; Dalmo, Roy A

    2016-01-01

    The long-term persistence and activity of a naked plasmid DNA (pGL3-35S) containing a luc gene (reporter gene) controlled by a plant 35S CaMV promoter was studied in Atlantic salmon (Salmo salar L.) after injection. Atlantic salmon (mean weight 70 grams) were injected intramuscularly with 100 μg of plasmid DNA. Blood, different tissues and organs were sampled at different time points up to day 535 after injection. Southern blot analysis suggested the presence of extra-chromosomally open circular, linear and supercoiled topoforms of pGL3-35S at day 150 after injection. At day 536 open circular and supercoiled topoforms were detected. Luciferase activity was detected at the injection site up to 536 days post-injection of pGL3-35S, where it peaked at day 150 and decreased to approximately 17% of its maximum activity by day 536. Our study demonstrated that a plasmid containing the 35S promoter was able to induce expression of a reporter gene/protein in fish in vivo and that the plasmid DNA persisted for a prolonged time after intramuscular injection. PMID:27114167

  5. Development of the Wintertime Sr/Ca-SST Record from Red Sea Corals as a Proxy for the North Atlantic Oscillation

    NASA Astrophysics Data System (ADS)

    Bernstein, W. N.; Hughen, K. A.

    2009-12-01

    The North Atlantic Oscillation (NAO) is one of the most pronounced and influential patterns in winter atmospheric circulation variability. This meridional redistribution of atmospheric mass across the Atlantic Ocean produces large changes in the intensity, number and direction of storms generated within the basin, and the regional climate of surrounding continents. The NAO exerts a significant impact on society, through influences on agriculture, fisheries, water management, energy generation and coastal development. NAO effects on climate extend from eastern North America across Europe to the eastern Mediterranean and Middle East. Changes in NAO behavior during the late 20th century have been linked to global warming; yet despite its importance, the causes and long-term patterns of NAO variability in the past remain poorly understood. In order to better predict the influence of the NAO on climate in the future, it is critical to examine multi-century NAO variability. The Red Sea is an excellent location from which to generate long NAO records for two reasons. First, patterns of wintertime sea surface temperature (SST) and salinity (SSS) in the Red Sea are highly correlated with NAO variability (Visbeck et al. 2001; Hurrell et al. 2003). Second, the tropical/subtropical Red Sea region contains fast growing long-lived massive Porites spp. corals with annually banded skeletons. These corals are ideal for generating well-dated high-resolution paleoclimatic records that extend well beyond the instrumental period. Here we present a study of winter SST and NAO variability in the Red sea region based on coral Sr/Ca data. In 2008, we collected multiple drill cores ranging in length from 1 to 4.1 meters from Porites corals at six sites spanning a large SST gradient. Sr/Ca measurements from multiple corals will be regressed against 23 years of satellite SST data, expanding the SST range over which we calibrate. A sampling resolution of 0.5mm will yield greater than bi

  6. Rhodolith beds are major CaCO3 bio-factories in the tropical South West Atlantic.

    PubMed

    Amado-Filho, Gilberto M; Moura, Rodrigo L; Bastos, Alex C; Salgado, Leonardo T; Sumida, Paulo Y; Guth, Arthur Z; Francini-Filho, Ronaldo B; Pereira-Filho, Guilherme H; Abrantes, Douglas P; Brasileiro, Poliana S; Bahia, Ricardo G; Leal, Rachel N; Kaufman, Les; Kleypas, Joanie A; Farina, Marcos; Thompson, Fabiano L

    2012-01-01

    Rhodoliths are nodules of non-geniculate coralline algae that occur in shallow waters (<150 m depth) subjected to episodic disturbance. Rhodolith beds stand with kelp beds, seagrass meadows, and coralline algal reefs as one of the world's four largest macrophyte-dominated benthic communities. Geographic distribution of rhodolith beds is discontinuous, with large concentrations off Japan, Australia and the Gulf of California, as well as in the Mediterranean, North Atlantic, eastern Caribbean and Brazil. Although there are major gaps in terms of seabed habitat mapping, the largest rhodolith beds are purported to occur off Brazil, where these communities are recorded across a wide latitudinal range (2°N-27°S). To quantify their extent, we carried out an inter-reefal seabed habitat survey on the Abrolhos Shelf (16°50'-19°45'S) off eastern Brazil, and confirmed the most expansive and contiguous rhodolith bed in the world, covering about 20,900 km(2). Distribution, extent, composition and structure of this bed were assessed with side scan sonar, remotely operated vehicles, and SCUBA. The mean rate of CaCO(3) production was estimated from in situ growth assays at 1.07 kg m(-2) yr(-1), with a total production rate of 0.025 Gt yr(-1), comparable to those of the world's largest biogenic CaCO(3) deposits. These gigantic rhodolith beds, of areal extent equivalent to the Great Barrier Reef, Australia, are a critical, yet poorly understood component of the tropical South Atlantic Ocean. Based on the relatively high vulnerability of coralline algae to ocean acidification, these beds are likely to experience a profound restructuring in the coming decades. PMID:22536356

  7. Rhodolith Beds Are Major CaCO3 Bio-Factories in the Tropical South West Atlantic

    PubMed Central

    Amado-Filho, Gilberto M.; Moura, Rodrigo L.; Bastos, Alex C.; Salgado, Leonardo T.; Sumida, Paulo Y.; Guth, Arthur Z.; Francini-Filho, Ronaldo B.; Pereira-Filho, Guilherme H.; Abrantes, Douglas P.; Brasileiro, Poliana S.; Bahia, Ricardo G.; Leal, Rachel N.; Kaufman, Les; Kleypas, Joanie A.; Farina, Marcos; Thompson, Fabiano L.

    2012-01-01

    Rhodoliths are nodules of non-geniculate coralline algae that occur in shallow waters (<150 m depth) subjected to episodic disturbance. Rhodolith beds stand with kelp beds, seagrass meadows, and coralline algal reefs as one of the world's four largest macrophyte-dominated benthic communities. Geographic distribution of rhodolith beds is discontinuous, with large concentrations off Japan, Australia and the Gulf of California, as well as in the Mediterranean, North Atlantic, eastern Caribbean and Brazil. Although there are major gaps in terms of seabed habitat mapping, the largest rhodolith beds are purported to occur off Brazil, where these communities are recorded across a wide latitudinal range (2°N - 27°S). To quantify their extent, we carried out an inter-reefal seabed habitat survey on the Abrolhos Shelf (16°50′ - 19°45′S) off eastern Brazil, and confirmed the most expansive and contiguous rhodolith bed in the world, covering about 20,900 km2. Distribution, extent, composition and structure of this bed were assessed with side scan sonar, remotely operated vehicles, and SCUBA. The mean rate of CaCO3 production was estimated from in situ growth assays at 1.07 kg m−2 yr−1, with a total production rate of 0.025 Gt yr−1, comparable to those of the world's largest biogenic CaCO3 deposits. These gigantic rhodolith beds, of areal extent equivalent to the Great Barrier Reef, Australia, are a critical, yet poorly understood component of the tropical South Atlantic Ocean. Based on the relatively high vulnerability of coralline algae to ocean acidification, these beds are likely to experience a profound restructuring in the coming decades. PMID:22536356

  8. On the role of periodic structures in the lower jaw of the atlantic bottlenose dolphin (Tursiops truncatus).

    PubMed

    Dible, S A; Flint, J A; Lepper, P A

    2009-03-01

    This paper proposes the application of band-gap theory to hearing in the atlantic bottlenose dolphin (Tursiops truncatus). Using the transmission line modelling (TLM) technique and published computed tomography (CT) data of an atlantic bottlenose dolphin (Tursiops truncatus), a series of sound propagation experiments have been carried out. It is shown that the teeth in the lower jaw can be viewed as a periodic array of scattering elements which result in the formation of an acoustic stop band (or band gap) that is angular dependent. It is shown through simple and complex geometry simulations that performance enhancements such as improved gain and isolation between the two receive paths can be achieved. This mechanism has the potential to be exploited in direction-finding sonar. PMID:19258687

  9. A Millennial-Scale Reduction in Ventilation of the Deep South Atlantic During the Last Interglacial Period

    NASA Astrophysics Data System (ADS)

    Hayes, C. T.; Martinez-Garcia, A.; Hasenfratz, A. P.; Jaccard, S.; Hodell, D. A.; Sigman, D. M.; Haug, G. H.; Anderson, R. F.

    2014-12-01

    During the last interglacial period, global temperatures were ~2°C warmer than present and sea level was 6-8 m higher. Southern Ocean sediments from ODP Site 1094 reveal a spike in authigenic uranium 127,000 years ago, within the last interglacial, reflecting decreased oxygenation of deep water by Antarctic Bottom Water (AABW). Increased deep storage of respired carbon due to this circulation event may explain an observed decline in atmospheric CO2 at this time. Unlike ice age reductions in AABW, the interglacial stagnation event appears decoupled from open ocean conditions and may have resulted from coastal freshening due to mass loss from the Antarctic ice sheet. AABW reduction coincided with increased North Atlantic Deep Water (NADW) formation, and the subsequent reinvigoration in AABW coincided with reduced NADW formation. Alternation of deep water formation between the Antarctic and the North Atlantic, believed to characterize ice ages, apparently also occurs in warm climates.

  10. Periodic increases in elongation rate precede increases in cytosolic Ca2+ during pollen tube growth.

    PubMed

    Messerli, M A; Créton, R; Jaffe, L F; Robinson, K R

    2000-06-01

    Pollen tubes grown in vitro require an intracellular tip-high gradient of Ca2+ in order to elongate. Moreover, after about 2 h in vitro both the tip Ca2+ and the elongation rate of lily tubes begin to oscillate regularly with large amplitudes. This raises the question of the phase relation between these two oscillations. Previous studies lacked the temporal resolution to accurately establish this relationship. We have studied these oscillations with a newly developed, high temporal resolution system and the complementary use of both luminescent and fluorescent calcium reporters. We hereby show that the periodic increases in elongation rate during oscillatory growth of Lilium longiflorum pollen tubes clearly precede those in subtip calcium and do so by 4.1 +/- 0.2 s out of average periods of 38.7 +/- 1.8 s. Also, by collecting images of the light output of aequorin, we find that the magnitude of the [Ca2+] at the tip oscillates between 3 and 10 microM, which is considerably greater than that reported by fluorescent indicators. We propose an explanatory model that features cyclic growth and secretion in which growth oscillations give rise to secretion that is essential for the subsequent growth oscillation. We also critically compile data on L. longiflorum stylar growth rates, which show little variation from in vitro rates of pollen tubes grown in optimal medium. PMID:10885748

  11. Moroccan speleothem and tree ring records suggest a variable positive state of the North Atlantic Oscillation during the Medieval Warm Period

    NASA Astrophysics Data System (ADS)

    Wassenburg, J. A.; Immenhauser, A.; Richter, D. K.; Niedermayr, A.; Riechelmann, S.; Fietzke, J.; Scholz, D.; Jochum, K. P.; Fohlmeister, J.; Schröder-Ritzrau, A.; Sabaoui, A.; Riechelmann, D. F. C.; Schneider, L.; Esper, J.

    2013-08-01

    We present a magnesium (Mg) and strontium (Sr) record from an aragonitic speleothem (Grotte de Piste, Morocco, 34‬°N; 04°W) providing a reconstruction of effective rainfall from 619 to 1962 AD. The corresponding drip site was monitored over 2 yr for drip water Mg/Ca and Sr/Ca ratios. Results show evidence for prior aragonite precipitation, which can explain negative correlations between speleothem Mg and Sr concentrations. The data shown here have important climate implications concerning the evolution of the North Atlantic Oscillation (NAO). A comparison of the stalagmite data from Grotte de Piste with an updated tree ring based drought reconstruction from Morocco and other NAO related proxy records confirms that the Medieval Warm Period (MWP) was dominated by NAO+ conditions. The stalagmite record and multiple proxy records from the Iberian Peninsula, however, suggest that considerable rainfall variability occurred during the MWP. This implies that the NAO has been more variable during the MWP than formerly suggested.

  12. Modeling dust emission variations in Eastern Europe related to North-Atlantic abrupt climate changes of the last glacial period

    NASA Astrophysics Data System (ADS)

    Sima, A.; Kageyama, M.; Rousseau, D.; Ramstein, G.; Schulz, M.; Balkanski, Y.; Antoine, P.; Dulac, F.; Hatte, C.; Lagroix, F.; Gerasimenko, N.

    2010-12-01

    The European loess sequences of the last glacial period (~ 100-15 kyr BP) show periods of strong dust accumulation alternating with episodes of reduced (or no) sedimentation, allowing soil development. For the main loess sedimentation period (~ 40 - 15 kyr BP), data indicate a correlation between these variations and the North Atlantic rapid climate changes: the Dansgaard-Oeschger (DO) and Heinrich (H) events. We use numerical modeling to investigate the relationship between the North-Atlantic abrupt changes and the sedimentation variations in Europe. A first study (Sima et al, QSR, 2009) focused on western Europe, and addressed the impact on dust emission of North-Atlantic SST changes as those associated to DO and H events. It proposed that vegetation played a key role in modulating dust emission variations in western European source areas. Here we focus on eastern Europe, especially on the areas north and north-east of the Carpathian Mountains, where loess deposits have recorded DO and H events (Rousseau et al. Clim. Past D, 2010). As in the previous study, we use the LMDZ AGCM and the SECHIBA land-surface models to simulate a reference glacial state (“stadial”), a cold (“HE”) and a warm (“DO interstadial”) perturbation, all corresponding to Marine Isotope Stage 3 conditions. We follow the same protocol as for the study on the west-European sector to analyze the impact of the climate factors and surface conditions on dust emission. The simulated most active emission areas are compatible with the loess deposit distribution, and the key role of vegetation in stadial-interstadial dust emission variations is confirmed.

  13. Physiologic and metagenomic attributes of the rhodoliths forming the largest CaCO3 bed in the South Atlantic Ocean.

    PubMed

    Cavalcanti, Giselle S; Gregoracci, Gustavo B; dos Santos, Eidy O; Silveira, Cynthia B; Meirelles, Pedro M; Longo, Leila; Gotoh, Kazuyoshi; Nakamura, Shota; Iida, Tetsuya; Sawabe, Tomoo; Rezende, Carlos E; Francini-Filho, Ronaldo B; Moura, Rodrigo L; Amado-Filho, Gilberto M; Thompson, Fabiano L

    2014-01-01

    Rhodoliths are free-living coralline algae (Rhodophyta, Corallinales) that are ecologically important for the functioning of marine environments. They form extensive beds distributed worldwide, providing a habitat and nursery for benthic organisms and space for fisheries, and are an important source of calcium carbonate. The Abrolhos Bank, off eastern Brazil, harbors the world's largest continuous rhodolith bed (of ∼21,000 km(2)) and has one of the largest marine CaCO3 deposits (producing 25 megatons of CaCO3 per year). Nevertheless, there is a lack of information about the microbial diversity, photosynthetic potential and ecological interactions within the rhodolith holobiont. Herein, we performed an ecophysiologic and metagenomic analysis of the Abrolhos rhodoliths to understand their microbial composition and functional components. Rhodoliths contained a specific microbiome that displayed a significant enrichment in aerobic ammonia-oxidizing betaproteobacteria and dissimilative sulfate-reducing deltaproteobacteria. We also observed a significant contribution of bacterial guilds (that is, photolithoautotrophs, anaerobic heterotrophs, sulfide oxidizers, anoxygenic phototrophs and methanogens) in the rhodolith metagenome, suggested to have important roles in biomineralization. The increased hits in aromatic compounds, fatty acid and secondary metabolism subsystems hint at an important chemically mediated interaction in which a functional job partition among eukaryal, archaeal and bacterial groups allows the rhodolith holobiont to thrive in the global ocean. High rates of photosynthesis were measured for Abrolhos rhodoliths (52.16 μmol carbon m(-2 )s(-1)), allowing the entire Abrolhos rhodolith bed to produce 5.65 × 10(5) tons C per day. This estimate illustrates the great importance of the Abrolhos rhodolith beds for dissolved carbon production in the South Atlantic Ocean. PMID:23985749

  14. Physiologic and metagenomic attributes of the rhodoliths forming the largest CaCO3 bed in the South Atlantic Ocean

    PubMed Central

    Cavalcanti, Giselle S; Gregoracci, Gustavo B; dos Santos, Eidy O; Silveira, Cynthia B; Meirelles, Pedro M; Longo, Leila; Gotoh, Kazuyoshi; Nakamura, Shota; Iida, Tetsuya; Sawabe, Tomoo; Rezende, Carlos E; Francini-Filho, Ronaldo B; Moura, Rodrigo L; Amado-Filho, Gilberto M; Thompson, Fabiano L

    2014-01-01

    Rhodoliths are free-living coralline algae (Rhodophyta, Corallinales) that are ecologically important for the functioning of marine environments. They form extensive beds distributed worldwide, providing a habitat and nursery for benthic organisms and space for fisheries, and are an important source of calcium carbonate. The Abrolhos Bank, off eastern Brazil, harbors the world's largest continuous rhodolith bed (of ∼21 000 km2) and has one of the largest marine CaCO3 deposits (producing 25 megatons of CaCO3 per year). Nevertheless, there is a lack of information about the microbial diversity, photosynthetic potential and ecological interactions within the rhodolith holobiont. Herein, we performed an ecophysiologic and metagenomic analysis of the Abrolhos rhodoliths to understand their microbial composition and functional components. Rhodoliths contained a specific microbiome that displayed a significant enrichment in aerobic ammonia-oxidizing betaproteobacteria and dissimilative sulfate-reducing deltaproteobacteria. We also observed a significant contribution of bacterial guilds (that is, photolithoautotrophs, anaerobic heterotrophs, sulfide oxidizers, anoxygenic phototrophs and methanogens) in the rhodolith metagenome, suggested to have important roles in biomineralization. The increased hits in aromatic compounds, fatty acid and secondary metabolism subsystems hint at an important chemically mediated interaction in which a functional job partition among eukaryal, archaeal and bacterial groups allows the rhodolith holobiont to thrive in the global ocean. High rates of photosynthesis were measured for Abrolhos rhodoliths (52.16 μmol carbon m−2 s−1), allowing the entire Abrolhos rhodolith bed to produce 5.65 × 105 tons C per day. This estimate illustrates the great importance of the Abrolhos rhodolith beds for dissolved carbon production in the South Atlantic Ocean. PMID:23985749

  15. Tropical Atlantic SSTS at the Last Glacial Maximum derived from Sr/Ca ratios of fossil coral

    NASA Astrophysics Data System (ADS)

    Cohen, A. L.; Saenger, C. P.

    2006-12-01

    The sensitivity of the tropics to climate change is a particularly controversial issue in paleoclimatology. At the heart of this controversy are disagreements amongst different proxy datasets regarding the amplitude of glacial-interglacial changes in temperature, particularly at the sea surface. Data obtained from the aragonitic skeletons of massive reef corals have contributed in no small measure to the debate, yielding LGM and deglacial SSTs 5-6°C cooler than today (Guilderson et al., 1994; McCulloch et al., 1999; Correge et al., 2004), that imply a high sensitivity of Earth's climate to changes in boundary conditions (Crowley, 2000). We used SIMS ion microprobe to analyze Sr/Ca ratios of small pieces of Montastrea coral retrieved from a Barbados drillcore (Guilderson et al., 2001). U/Th dates place the samples between 22 and 24 kyr BP. Localized areas of dissolution and re-growth of secondary (diagenetic) aragonite crystals were identified at centers of septa. Sr/Ca ratios of these crystals were higher than Sr/Ca ratios of original coral crystals preserved in adjacent fasciculi and yielded relatively cooler derived SSTs. The original coral crystals, recognized by their size and orientation, were selectively targeted for analysis using a 20 micron-diameter sample spot. Our calibration study using modern corals from Bermuda, St Croix (USVI) and Barbados indicates that Montastrea Sr/Ca is strongly correlated with SST and with annual extension (growth) rate (Saenger et al., 2006). Growth rate of the fossil corals was determined from measurement of daily growth bands identified in petrographic thin-sections. Application of a growth-dependent Sr/Ca-T calibration yielded Barbados SSTs that were, on average, 2.5°C cooler than today during the LGM and ~1°C cooler than today during Heinrich Event 2. Our LGM SSTs are consistent with the original CLIMAP estimates (CLIMAP, 1976) and with more recent Mg/Ca-based SSTs derived from calcitic foraminifera in the Caribbean

  16. 77 FR 75654 - Nomination Period Extension for the Carrizo Plain National Monument Advisory Council, CA

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-21

    ... Management, Bakersfield Field Office, 3801 Pegasus Drive, Bakersfield, CA 93308. FOR FURTHER INFORMATION CONTACT: Johna Hurl, Monument Manager, Bakersfield Field Office, 3801 Pegasus Drive, Bakersfield, CA...

  17. Substantial Downregulation of Myogenic Transcripts in Skeletal Muscle of Atlantic Cod during the Spawning Period

    PubMed Central

    Edvardsen, Vigdis

    2016-01-01

    Gonadal maturation is an extremely energy consuming process for batch spawners and it is associated with a significant decrease in growth and seasonal deterioration in flesh quality. Our knowledge about the molecular mechanisms linking sexual maturation and muscle growth is still limited. In the present study, we performed RNA-Seq using 454 GS-FLX pyrosequencing in fast skeletal muscle sampled from two-year-old Atlantic cod (Gadus morhua) at representative time points throughout the reproductive cycle (August, March and May). In total, 126,937 good quality reads were obtained, with 546 nucleotide length and 52% GC content on average. RNA-Seq analysis using the CLC Genomics Workbench with the Atlantic cod reference UniGene cDNA data revealed 59,581 (46.9%) uniquely annotated reads. Pairwise comparison for expression levels identified 153 differentially expressed UniGenes between time points. Notably, we found a significant suppression of myh13 and myofibrillar gene isoforms in fast skeletal muscle during the spawning season. This study uncovered a large number of differentially expressed genes that may be influenced by gonadal maturation, thus representing a significant contribution to our limited understanding of the molecular mechanisms regulating muscle wasting and regeneration in batch spawners during their reproductive cycle. PMID:26844771

  18. Changes in the Northwest Atlantic circulation for the 1992 95 high NAO period from a numerical model

    NASA Astrophysics Data System (ADS)

    Luo, Yiyong; Prater, Mark D.; Durbin, Edward G.; Rothstein, Lewis M.

    2006-09-01

    Present research suggests that the North Atlantic Oscillation (NAO) has a significant impact on the circulation in the Northwest Atlantic. An ocean general circulation model was used to quantify the changes of circulation patterns and transport on this region during a high NAO period (between 1992 and 1995) when compared to climatological mean forcing. Upstream of the study region, the maximum barotropic transport in the Labrador Sea was decreased by 8 Sv (1 Sv=10 6 m 3s -1) during the high NAO conditions, leading to a reduction in transport of the Labrador Current by ˜1.6 Sv east of Newfoundland and by ˜0.4 Sv south of Newfoundland. In addition, a Lagrangian analysis was performed to examine the pathways of transport that advect water properties across the Grand Banks and how those pathways are modified owing to the high-NAO forcing. The potential implications of these changes for biological production processes in the adjacent downstream shelf regions such as the Scotian Shelf, Gulf of Maine, and Georges Bank are discussed.

  19. Diel variation in summer habitat use, feeding periodicity, and diet of subyearling Atlantic salmon in the Salmon River Basin, New York

    USGS Publications Warehouse

    Johnson, James H.

    2013-01-01

    The habitat use, diet composition, and feeding periodicity of subyearling Atlantic salmon (Salmo salar) was examined during both day and night periods during summer in tributaries of Lake Ontario. The amount of cover used was the major habitat variable that differed between day and night periods in both streams. At night subyearling Atlantic salmon were associated with significantly less cover than during the day. Principal Component Analysis showed that habitat selection of subyearling Atlantic salmon was more pronounced during the day in both streams and that salmon in Orwell Brook exhibited more diel variability in habitat use than salmon in Trout Brook. Subyearling salmon fed primarily from the benthic substrate on baetids, chironomids, and leptocerids. There was a substantial amount of diel variation in diet composition with peak feeding occurring from 0400 h to 0800 h on July 21–22, 2008.

  20. Mid-term quasi-periodicities in the CaII-K plage index of the Sun and their implications

    NASA Astrophysics Data System (ADS)

    Chowdhury, Partha; Gokhale, M. H.; Singh, Jagdev; Moon, Y.-J.

    2016-02-01

    We present results of the fast Fourier transform (FFT), the MEM analysis, and the wavelet analysis (WA), of the temporal variation of the monthly disk integrated "CaII-K plage-area and enhanced network (EN) area" hereafter called `plage index' derived by Tlatov et al. (2009), from spectro-heliograms taken in Ca II K line at Kodaikanal Observatory, from February 1907 to April, 1998, In the range {>}3 months and < decade, the Fourier transform power spectra reveal solar cycle periodicity {˜}122 months, its sub-harmonic ˜61 months, two short quasi-periodicities ({>}2 and <4 months), and nine `intermediate-range' quasi-periodicities (≳ 4 mo and <11 yr), in the variation of the plage index. The quasi-periodicities include Rieger, Rieger type and quasi-biennial. The presence of quasi-periodicities and the mean values of the periods are confirmed by the maximum entropy method (MEM). The temporal spans of the quasi-periodicities during different solar cycles are determined from the complex Morlet-wavelet analyses. The Rieger quasi-periodicity (150-160 days) appeared during cycle 21 and cycle 22. Each of the quasi-periodicities in the studied range lies close to one or more planetary periodicities (orbital, or spring tidal, or heliocentric conjunction frequency). We discuss possible interpretations of our results, and those of similar results obtained earlier by other authors, towards understanding the mechanisms of excitation of various quasi-periodicities detected in solar variability parameters.

  1. A simulated lagged response of the North Atlantic Oscillation to the solar cycle over the period 1960-2009

    NASA Astrophysics Data System (ADS)

    Andrews, M. B.; Knight, J. R.; Gray, L. J.

    2015-05-01

    Numerous studies have suggested an impact of the 11 year solar cycle on the winter North Atlantic Oscillation (NAO), with an increased tendency for positive (negative) NAO signals to occur at maxima (minima) of the solar cycle. Climate models have successfully reproduced this solar cycle modulation of the NAO, although the magnitude of the effect is often considerably weaker than implied by observations. A leading candidate for the mechanism of solar influence is via the impact of ultraviolet radiation variability on heating rates in the tropical upper stratosphere, and consequently on the meridional temperature gradient and zonal winds. Model simulations show a zonal mean wind anomaly that migrates polewards and downwards through wave-mean flow interaction. On reaching the troposphere this produces a response similar to the winter NAO. Recent analyses of observations have shown that solar cycle-NAO link becomes clearer approximately three years after solar maximum and minimum. Previous modelling studies have been unable to reproduce a lagged response of the observed magnitude. In this study, the impact of solar cycle on the NAO is investigated using an atmosphere-ocean coupled climate model. Simulations that include climate forcings are performed over the period 1960-2009 for two solar forcing scenarios: constant solar irradiance, and time-varying solar irradiance. We show that the model produces significant NAO responses peaking several years after extrema of the solar cycle, persisting even when the solar forcing becomes neutral. This confirms suggestions of a further component to the solar influence on the NAO beyond direct atmospheric heating and its dynamical response. Analysis of simulated upper ocean temperature anomalies confirms that the North Atlantic Ocean provides the memory of the solar forcing required to produce the lagged NAO response. These results have implications for improving skill in decadal predictions of the European and North American

  2. Calcium isotope (δ 44/40Ca) fractionation along hydrothermal pathways, Logatchev field (Mid-Atlantic Ridge, 14°45'N)

    NASA Astrophysics Data System (ADS)

    Amini, Marghaleray; Eisenhauer, Anton; Böhm, Florian; Fietzke, Jan; Bach, Wolfgang; Garbe-Schönberg, Dieter; Rosner, Martin; Bock, Barbara; Lackschewitz, Klas S.; Hauff, Folkmar

    2008-08-01

    We investigate the Logatchev Hydrothermal Field at the Mid-Atlantic Ridge, 14°45'N to constrain the calcium isotope hydrothermal flux into the ocean. During the transformation of seawater to a hydrothermal solution, the Ca concentration of pristine seawater ([Ca] SW) increases from about 10 mM to about 32 mM in the hydrothermal fluid endmember ([Ca] HydEnd) and thereby adopts a δ 44/40Ca HydEnd of -0.95 ± 0.07‰ relative to seawater (SW) and a 87Sr/ 86Sr isotope ratio of 0.7034(4). We demonstrate that δ 44/40Ca HydEnd is higher than that of the bedrock at the Logatchev field. From mass balance calculations, we deduce a δ 44/40Ca of -1.17 ± 0.04‰ (SW) for the host-rocks in the reaction zone and -1.45 ± 0.05‰ (SW) for the isotopic composition of the entire hydrothermal cell of the Logatchev field. The values are isotopically lighter than the currently assumed δ 44/40Ca for Bulk Earth of -0.92 ± 0.18‰ (SW) [Skulan J., DePaolo D. J. and Owens T. L. (1997) Biological control of calcium isotopic abundances in the global calcium cycle. Geochim. Cosmochim. Acta61,(12) 2505-2510] and challenge previous assumptions of no Ca isotope fractionation between hydrothermal fluid and the oceanic crust [Zhu P. and Macdougall J. D. (1998) Calcium isotopes in the marine environment and the oceanic calcium cycle. Geochim. Cosmochim. Acta62,(10) 1691-1698; Schmitt A. -D., Chabeaux F. and Stille P. (2003) The calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance. Earth Planet. Sci. Lett. 6731, 1-16]. Here we propose that Ca isotope fractionation along the fluid flow pathway of the Logatchev field occurs during the precipitation of anhydrite. Two anhydrite samples from the Logatchev Hydrothermal Field show an average fractionation of about Δ 44/40Ca = -0.5‰ relative to their assumed parental solutions. Ca isotope ratios in aragonites from carbonate veins from ODP drill cores indicate aragonite precipitation directly from seawater at low

  3. TRACEing Last Glacial Period (25-80 ka b2k) tephra horizons within North Atlantic marine cores and exploring links to the Greenland ice-cores

    NASA Astrophysics Data System (ADS)

    Abbott, P. M.; Davies, S. M.; Griggs, A. J.; Bourne, A. J.; Cook, E.; Pearce, N. J. G.; Austin, W. E. N.; Chapman, M.; Hall, I. R.; Purcell, C. S.; Scourse, J. D.; Rasmussen, T. L.

    2015-12-01

    Tephrochronology is a powerful technique for the correlation and synchronisation of disparate palaeoclimatic records from different depositional environments and has considerable potential for testing climatic phasing. For example, the relative timing of atmospheric and marine changes caused by the abrupt climatic events that punctuated the last glacial period within the North Atlantic region. Here we report on efforts to establish a framework of tephra horizons within North Atlantic marine sequences that can correlate these records and if traced in the Greenland ice-cores can act as isochronous tie-lines. Investigations have been conducted on a network of marine cores from a number of sites across the North Atlantic. Tephra horizons have been identified using cryptotephra extraction techniques more commonly applied to the study of terrestrial sequences. There are two main challenges with assessing cryptotephras in the glacial North Atlantic; i) determining the transportation processes and ii) assessing the influence of secondary reworking processes and the stratigraphic integrity of the isochrons. These processes and their influence are investigated for each cryptotephra using shard size variations, major element heterogeneity and co-variance of IRD input for some cores. Numerous Icelandic cryptophras have been successfully identified in the marine records and we will discuss the integration of a number of these with an isochronous nature into a marine tephra framework and how potential correlations to the Greenland ice-core tephra framework are determined. Spatial patterns in the nature of tephra records that are emerging from the core network will be highlighted to outline some of the key areas that could be explored in the future. In addition, the synchronisation of multiple North Atlantic records to the Greenland ice-cores using the North Atlantic Ash Zone II to test the synchroneity of an abrupt cooling in the North Atlantic will be discussed.

  4. Influence of the Saharan Air Layer on Atlantic tropical cyclone formation during the period 1-12 September 2003

    NASA Astrophysics Data System (ADS)

    Pan, Weiyu; Wu, Liguang; Shie, Chung-Lin

    2011-01-01

    Atmospheric Infrared Sounder (AIRS) data show that the Saharan air layer (SAL) is a dry, warm, and well-mixed layer between 950 and 500 hPa over the tropical Atlantic, extending westward from the African coast to the Caribbean Sea. The formations of both Hurricane Isabel and Tropical Depression 14 (TD14) were accompanied with outbreaks of SAL air during the period 1-12 September 2003, although TD14 failed to develop into a named tropical cyclone. The influence of the SAL on their formations is investigated by examining data from satellite observations and numerical simulations, in which AIRS data are incorporated into the MM5 model through the nudging technique. Analyses of the AIRS and simulation data suggest that the SAL may have played two roles in the formation of tropical cyclones during the period 1-12 September 2003. First, the outbreaks of SAL air on 3 and 8 September enhanced the transverse-vertical circulation with the rising motion along the southern edge of the SAL and the sinking motion inside the SAL, triggering the development of two tropical disturbances associated with Hurricane Isabel and TD14. Second, in addition to the reduced environmental humidity and enhanced static stability in the lower troposphere, the SAL dry air intruded into the inner region of these tropical disturbances as their cyclonic flows became strong. This effect may have slowed down the formation of Isabel and inhibited TD14 becoming a named tropical cyclone, while the enhanced vertical shear contributed little to tropical cyclone formation during this period. The 48-h trajectory calculations confirm that the parcels from the SAL can be transported into the inner region of an incipient tropical cyclone.

  5. Measuring rotation periods of solar-like stars using TIGRE. A study of periodic CaII H+K S-index variability

    NASA Astrophysics Data System (ADS)

    Hempelmann, A.; Mittag, M.; Gonzalez-Perez, J. N.; Schmitt, J. H. M. M.; Schröder, K. P.; Rauw, G.

    2016-02-01

    Context. The rotation period of a star is a key parameter both for the stellar dynamo that generates magnetic fields as well as for stellar differential rotation. Aims: We present the results from the first year of monitoring a sample of solar-like stars by the TIGRE facility in Guanajuato (Mexico), which will study rotation in solar analogs. Methods: TIGRE is an automatically operating 1.2 m telescope equipped with an Échelle spectrograph with a spectral resolution of 20 000, which covers a spectral range of between 3800 and 8800 Å. A main task is the monitoring the stellar activity of cool stars, mainly in the emission cores of the CaII H and K lines. We observed a number of stars with a sampling between 1-3 days over one year. Results: A total number of 95 stars were observed between August 1 2013 and July 31 2014, the total number of spectra taken for this program was appoximately 2700. For almost a third of the sample stars the number of observations was rather low (less than 20), mainly because of bad weather. Fifty-four stars show a periodic signal but often with low significance. Only 24 stars exhibit a significant period. We interpret these signals as stellar rotation. For about half of them the rotation periods were already previously known, in which case our period measurements are usually in good agreement with the literature values. Besides the periodic signals, trends are frequently observed in the time series. Conclusions: TIGRE is obviously able to detect stellar rotation periods in the CaII H+K emission cores when the time series contains a sufficient number of data points. However, this is frequently not achievable during the wet summer season in Guanajuato. Hence, future estimates of rotation periods will concentrate on stars that are observable during the winter season from October until April.

  6. Can d44Ca be a Proxy for Paleoceanography? - A Case Study of Globigerinoides Sacculifer from Western Equatorial Atlantic

    NASA Astrophysics Data System (ADS)

    Yang, S.; Wei, K.; Shen, J. J.

    2007-12-01

    The δ 44Ca, δ 18O, and Mg/Ca ratios of fossil Globigerinoides sacculifer over the past 20 ka extracted from a Caribbean core, TT9108-1GC, have been measured in order to examine the possibility of using δ 44Ca as a proxy for paleoceanography. Our results indicate that the δ 44Ca of G. sacculifer varies as a function of sea surface temperature (SST) and sea surface salinity (SSS). The Caribbean Sea SSS, reconstructed by combining the δ 18O and Mg/Ca ratios of G. sacculifer and sea level change data, shows significant fluctuations between 36.5 and 39.5 psu during the last 20 ka. After isolating the temperature effect, the δ 44Ca of G. sacculifer exhibits a positive correlation with SSS, ca 0.27±0.02 ‰ per 1 psu. On the other hand, no significant relationship is observed between δ 44Ca and seawater [CO3 -2]. Moreover, variation of G. sacculifer δ 44Ca can also be explained using a Rayleigh fractionation model. As a function of temperature and salinity, the metabolic rate may influence the utilization of vacuole Ca+2 in G. sacculifer, resulting in different δ 44Ca values. The results of this study are inconsistent with the "rate-controlled fractionation model" of Lemarchand et al. (2004), instead, the results are more in-line with the foraminiferal biomineralization model of Erez (2003), where δ 44Ca reflects the adjustments of temperature, salinity, and pH of seawater isolated in vacuoles during the growth of G. sacculifer.

  7. The optimal period of Ca-EDTA treatment for parthenogenetic activation of porcine oocytes during maturation culture

    PubMed Central

    MORITA, Yasuhiro; TANIGUCHI, Masayasu; TANIHARA, Fuminori; ITO, Aya; NAMULA, Zhao; DO, Lanh Thi Kim; TAKAGI, Mitsuhiro; TAKEMOTO, Tatsuya; OTOI, Takeshige

    2016-01-01

    The changes triggered by sperm-induced activation of oocytes, which are required for normal oocyte development, can be mediated by other agents, thereby inducing the parthenogenesis. In this study, we exposed porcine oocytes to 1 mM Ca-EDTA, a metal-ion chelator, at various intervals during 48 hr of in vitro maturation to determine the optimum period of Ca-EDTA treatment for parthenogenetic activation. When the oocytes were cultured with or without Ca-EDTA from 36 hr (post-12), 24 hr (post-24), 12 hr (post-36) and 0 hr (post-48) after the start of maturation culture, the blastocyst formation rates were significantly higher (P<0.05) in the post-24, post-36 and post-48 groups (3.3%, 4.0% and 2.6%, respectively) than those in the control group without treatment (0%). Furthermore, when the oocytes were cultured with Ca-EDTA for 0 hr (control), 12 hr (pre-12), 24 hr (pre-24), 36 hr (pre-36) and 48 hr (pre-48) from the start of maturation culture, the oocytes formed blastocysts only in the pre-36 and pre-48 groups (0.4% or 0.8%, respectively). Pronuclei (<66.7%) were observed only when the periods of Ca-EDTA treatment were more than 12 hr during maturation culture. In the control group, no pronuclei were detected. Our findings demonstrate that porcine immature oocytes can be parthenogenetically activated by Ca-EDTA treatment for at least 24 hr to 36 hr during maturation culture, leading to pronucleus formation followed by the formation of blastocysts. PMID:26947170

  8. Vigorous exchange between the Indian and Atlantic oceans at the end of the past five glacial periods.

    PubMed

    Peeters, Frank J C; Acheson, Ruth; Brummer, Geert-Jan A; De Ruijter, Wilhelmus P M; Schneider, Ralph R; Ganssen, Gerald M; Ufkes, Els; Kroon, Dick

    2004-08-01

    The magnitude of heat and salt transfer between the Indian and Atlantic oceans through 'Agulhas leakage' is considered important for balancing the global thermohaline circulation. Increases or reductions of this leakage lead to strengthening or weakening of the Atlantic meridional overturning and associated variation of North Atlantic Deep Water formation. Here we show that modern Agulhas waters, which migrate into the south Atlantic Ocean in the form of an Agulhas ring, contain a characteristic assemblage of planktic foraminifera. We use this assemblage as a modern analogue to investigate the Agulhas leakage history over the past 550,000 years from a sediment record in the Cape basin. Our reconstruction indicates that Indian-Atlantic water exchange was highly variable: enhanced during present and past interglacials and largely reduced during glacial intervals. Coherent variability of Agulhas leakage with northern summer insolation suggests a teleconnection to the monsoon system. The onset of increased Agulhas leakage during late glacial conditions took place when glacial ice volume was maximal, suggesting a crucial role for Agulhas leakage in glacial terminations, timing of interhemispheric climate change and the resulting resumption of the Atlantic meridional overturning circulation. PMID:15295596

  9. Long periods (1 -10 mHz) geomagnetic pulsations variation with solar cycle in South Atlantic Magnetic Anomaly

    NASA Astrophysics Data System (ADS)

    Rigon Silva, Willian; Schuch, Nelson Jorge; Guimarães Dutra, Severino Luiz; Babulal Trivedi, Nalin; Claudir da Silva, Andirlei; Souza Savian, Fernando; Ronan Coelho Stekel, Tardelli; de Siqueira, Josemar; Espindola Antunes, Cassio

    The occurrence and intensity of the geomagnetic pulsations Pc-5 (2-7 mHz) and its relationship with the solar cycle in the South Atlantic Magnetic Anomaly -SAMA is presented. The study of geomagnetic pulsations is important to help the understanding of the physical processes that occurs in the magnetosphere region and help to predict geomagnetic storms. The fluxgate mag-netometers H, D and Z, three axis geomagnetic field data from the Southern Space Observatory -SSO/CRS/INPE -MCT, São Martinho da Serra (29.42° S, 53.87° W, 480m a.s.l.), RS, Brasil, a were analyzed and correlated with the solar wind parameters (speed, density and temperature) from the ACE and SOHO satellites. A digital filtering to enhance the 2-7 mHz geomagnetic pulsations was used. Five quiet days and five perturbed days in the solar minimum and in the solar maximum were selected for this analysis. The days were chosen based on the IAGA definition and on the Bartels Musical Diagrams (Kp index) for 2001 (solar maximum) and 2008 (solar minimum). The biggest Pc-5 amplitude averages differences between the H-component is 78,35 nT for the perturbed days and 1,60nT for the quiet days during the solar maximum. For perturbed days the average amplitude during the solar minimum is 8,32 nT, confirming a direct solar cycle influence in the geomagnetic pulsations intensity for long periods.

  10. Tephra constraints on Rapid Climate Events (TRACE): precise correlation of marine and ice-core records during the last glacial period in the North Atlantic region

    NASA Astrophysics Data System (ADS)

    Davies, S. M.; Griggs, A. J.; Abbott, P. M.; Bourne, A. J.; Purcell, C. S.; Hall, I. R.; Scourse, J. D.

    2014-12-01

    Little has challenged our understanding of climate change more so than the abruptness with which large-scale shifts in temperature occurred during the last glacial period. Atmospheric temperature jumps occurring within decades over Greenland were closely matched by rapid changes in North Atlantic sea surface temperatures and major re-organisation of the deep ocean circulation. Although these climatic instabilities are well-documented in various proxy records, the causal mechanisms of such short-lived oscillations remain poorly understood, largely due to the dating uncertainties that prevent the integration of different archives. Synchronisation of palaeoclimate records on a common timescale is inherently problematic, and unravelling the lead/lag responses (hence cause and effect) between the Earth's climate components is currently beyond our reach. TRACE - a 5 year project funded by the European Research Council - exploits the use of microscopic traces of tephra deposits to precisely correlate the Greenland ice-cores with North Atlantic marine records. Here we draw upon examples of how these time-lines can be used to constrain the lead/lag responses between the atmospheric and oceanic systems during the last glacial period. High-resolution proxy data from North Atlantic marine cores MD04-2829CQ from the Rosemary Bank and MD04 2820CQ from the Goban Spur are integrated with the Greenland ice-cores according to the position of common tephra isochrons. These direct tie-lines allow us to focus in detail on the relative timing of rapid warming transitions between Greenland and the North Atlantic ocean during the last glacial period.

  11. Soybean cell enlargement oscillates with a temperature-compensated period length of ca. 24 min

    NASA Technical Reports Server (NTRS)

    Morre, D. J.; Pogue, R.; Morre, D. M.

    2001-01-01

    Rate of enlargement of epidermal cells from soybean, when measured at intervals of 1 min using a light microscope equipped with a video measurement system, oscillated with a period length of about 24 min. This oscillation parallels the 24-min periodicity observed for the oxidation of NADH by the external plasma membrane NADH oxidase. The increase in length was not only non-linear, but intervals of rapid increase in area alternated with intervals of rapid decrease in area. The length of the period was temperature compensated, and was approximately the same when measured at 14, 24 and 34 degrees C even though the rate of cell enlargement varied over this same range of temperatures. These observations represent the first demonstration of an oscillatory growth behavior correlated with a biochemical activity where the period length of both is independent of temperature (temperature compensated) as is the hallmark of clock-related biological phenomena.

  12. The Once and Future North Atlantic: How the Mid-Pliocene Warm Period Can Increase Stakeholder Preparedness in a Warming World

    NASA Astrophysics Data System (ADS)

    Jacobs, P.; de Mutsert, K.

    2013-12-01

    Paleoclimatic reconstructions, particularly from periods that may serve as an analog to the present and future greenhouse-driven warming, are increasingly being used to validate climate models as well as to provide constraints on broad impacts such as global temperature and sea level change. However, paleoclimatic data remains under-utilized in decision-making processes by stakeholders, who typically rely on scenarios produced by computer models or naive extrapolation of present trends. We hope to increase the information available to stakeholders by incorporating paleoclimatic data from the mid-Pliocene Warm Period (mPWP, ~3ma) into a fisheries model of the North Atlantic. North Atlantic fisheries are economically important and are expected to be sensitive to climatic change. State of the art climate models remain unable to realistically simulate the North Atlantic, both over the observational record as well as during times in the geologic past such as the mPWP. Given that the mPWP shares many of the same boundary conditions as those likely to be seen in the near future, we seek to answer the question 'What if the climate of the future looks more like the climate of the past?' relative to what state of the art computer models currently project. To that end we have created a suite of future North Atlantic Ocean scenarios using output from the CMIP3 and CMIP5 modeling experiments, as well as the PRISM group's Mid-Pliocene ocean reconstruction. We use these scenarios to drive an ecosystem-based fisheries model using the Ecopath with Ecosim (EwE) software to identify differences between the scenarios as the North Atlantic Ocean changes through time. Additionally, we examine the spatial component of these differences by using the Ecospace module of EwE. Whereas the Ecosim realizations are intended to capture the dynamic response to changing oceanographic parameters (SST, SSS, DO) over time, the Ecospace experiments are intended to explore the impact of different

  13. A core-top study of dissolution effect on B/Ca in Globigerinoides sacculifer from the tropical Atlantic: Potential bias for paleo-reconstruction of seawater carbonate chemistry

    NASA Astrophysics Data System (ADS)

    Coadic, R.; Bassinot, F.; Dissard, D.; Douville, E.; Greaves, M.; Michel, E.

    2013-04-01

    has been recently shown that B/Ca in planktonic foraminiferal calcite can be used as a proxy for seawater pH. Based on the study of surface sediments (multi-cores) retrieved along a depth transect on the Sierra Leone Rise (Eastern Equatorial Atlantic), we document the decrease of B/Ca and Mg/Ca of Globigerinoides sacculifer shells with increasing water depth and dissolution. This effect of dissolution on B/Ca may potentially represent a severe bias for paleo-pH reconstructions using this species. Samples of G. sacculifer were analyzed independently at two laboratories for B/Ca and Mg/Ca. Both sets of results show a systematic decrease of B/Ca and Mg/Ca along the depth transect, with an overall loss of ~14 µmol/mol (~15%) for B/Ca and of ~0.7 mmol/mol (~21%) for Mg/Ca between the shallowest (2640 m) and the deepest (4950 m) sites. Because of this dissolution effect, surface water pH reconstructed from B/Ca of G. sacculifer decreases by ~0.11 units between the shallowest site and the deepest site, a magnitude similar to the expected glacial/interglacial surface water pH changes.

  14. Inter-annual variability of aerosol optical depth over the tropical Atlantic Ocean based on MODIS-Aqua observations over the period 2002-2012

    NASA Astrophysics Data System (ADS)

    Gkikas, Antonis; Hatzianastassiou, Nikolaos

    2013-04-01

    The tropical Atlantic Ocean is affected by dust and biomass burning aerosol loads transported from the western parts of the Saharan desert and the sub-Sahel regions, respectively. The spatial and temporal patterns of this transport are determined by the aerosol emission rates, their deposition (wet and dry), by the latitudinal shift of the Intertropical Convergence Zone (ITCZ) and the prevailing wind fields. More specifically, in summer, Saharan dust aerosols are transported towards the Atlantic Ocean, even reaching the Gulf of Mexico, while in winter the Atlantic Ocean transport takes place in more southern latitudes, near the equator, sometimes reaching the northern parts of South America. In the later case, dust is mixed with biomass burning aerosols originating from agricultural activities in the sub-Sahel, associated with prevailing north-easterly airflow (Harmattan winds). Satellite observations are the appropriate tool for describing this African aerosol export, which is important to atmospheric, oceanic and climate processes, offering the advantage of complete spatial coverage. In the present study, we use satellite measurements of aerosol optical depth at 550nm (AOD550nm), on a daily and monthly basis, derived from MODIS-Aqua platform, at 1ox1o spatial resolution (Level 3), for the period 2002-2012. The primary objective is to determine the pixel-level and regional mean anomalies of AOD550nm over the entire study period. The regime of the anomalies of African export is interpreted in relation to the aerosol source areas, precipitation, wind patterns and temporal variability of the North Atlantic Oscillation Index (NAOI). In order to ensure availability of AOD over the Sahara desert, MODIS-Aqua Deep Blue products are also used. As for precipitation, Global Precipitation Climatology Project (GPCP) data at 2.5ox2.5o are used. The wind fields are taken from the National Center for Environmental Prediction (NCEP). Apart from the regime of African aerosol export

  15. Key role of the Atlantic Multidecadal Oscillation in 20th century drought and wet periods over the Great Plains

    NASA Astrophysics Data System (ADS)

    Nigam, Sumant; Guan, Bin; Ruiz-Barradas, Alfredo

    2011-08-01

    The Great Plains of North America are susceptible to multi-year droughts, such as the 1930s ‘Dust Bowl’. The droughts have been linked to SST variability in the Pacific and Atlantic basins. This observationally rooted analysis shows the SST influence in multi-year droughts and wet episodes over the Great Plains to be significantly more extensive than previously indicated. The remarkable statistical reconstruction of the major hydroclimate episodes attests to the extent of the SST influence in nature, and facilitated evaluation of the basin contributions. We find the Atlantic SSTs to be especially influential in forcing multi-year droughts; often, more than the Pacific ones. The Atlantic Multidecadal Oscillation (AMO), in particular, contributed the most in two of the four reconstructed episodes (Dust Bowl Spring, 1980s fall wetness), accounting for almost half the precipitation signal in each case. The AMO influence on continental precipitation was provided circulation context from analysis of NOAA's 20th Century Atmospheric Reanalysis. A hypothesis for how the AMO atmospheric circulation anomalies are generated from AMO SSTs is proposed to advance discussion of the influence pathways of the mid-to-high latitude SST anomalies. Our analysis suggests that the La Nina-US Drought paradigm, operative on interannual time scales, has been conferred excessive relevance on decadal time scales in the recent literature.

  16. Timing of vegetation changes at the end of the Holocene Humid Period in desert areas at the northern edge of the Atlantic and Indian monsoon systems

    NASA Astrophysics Data System (ADS)

    Lézine, Anne-Marie

    2009-08-01

    This article aims at discussing the ecological response of the terrestrial and fresh water dependant environments to the installation of arid conditions at the end of the Holocene Humid Period in the Atlantic and Indian monsoon domains. It is mainly focused on dry environments from Chad, Oman and Pakistan where new, high-resolution pollen sequences have been provided. Pollen data show that local hydrological conditions have played a major role in the destruction or survival of tropical tree populations at the end of the Holocene Humid Period, as well as partly explaining the asynchronous pattern of recorded environmental changes in most tropical regions. In desert areas, the response of the fresh water dependant systems to the shift from humid to arid climate conditions appears to have followed a threshold-like pattern. In contrast, terrestrial ecosystems have gradually adapted to increased drought, as shown by the progressive decrease of tropical tree species at Yoa or the gradual expansion in dry plant types in Oman and Pakistan from 6000 cal yrs BP to the present. A remarkable synchroneity in environmental change is recorded at the northern edge of the Atlantic and Indian monsoon systems, with the extreme end of the Holocene Humid Period corresponding to the last occurrence of tropical trees in the desert and the last record of prolonged SW monsoon rainfall over north-western Asia around 4700-4500 cal yrs BP.

  17. Ca2+ signaling and early embryonic patterning during the blastula and gastrula periods of zebrafish and Xenopus development.

    PubMed

    Webb, Sarah E; Miller, Andrew L

    2006-11-01

    It has been proposed that Ca(2+) signaling, in the form of pulses, waves and steady gradients, may play a crucial role in key pattern forming events during early vertebrate development [L.F. Jaffe, Organization of early development by calcium patterns, BioEssays 21 (1999) 657-667; M.J. Berridge, P. Lipp, M.D. Bootman, The versatility and universality of calcium signaling, Nat. Rev. Mol. Cell Biol. 1 (2000) 11-21; S.E. Webb, A.L. Miller, Calcium signalling during embryonic development, Nat. Rev. Mol. Cell Biol. 4 (2003) 539-551]. With reference to the embryos of zebrafish (Danio rerio) and the frog, Xenopus laevis, we review the Ca(2+) signals reported during the Blastula and Gastrula Periods. This developmental window encompasses the major pattern forming events of epiboly, involution, and convergent extension, which result in the establishment of the basic germ layers and body axes [C.B. Kimmel, W.W. Ballard, S.R. Kimmel, B. Ullmann, T.F. Schilling, Stages of embryonic development of the zebrafish, Dev. Dyn. 203 (1995) 253-310]. Data will be presented to support the suggestion that propagating waves (both long and short range) of Ca(2+) release, followed by sequestration, may play a crucial role in: (1) Coordinating cell movements during these pattern forming events and (2) Contributing to the establishment of the basic embryonic axes, as well as (3) Helping to define the morphological boundaries of specific tissue domains and embryonic structures, including future organ anlagen [E. Gilland, A.L. Miller, E. Karplus, R. Baker, S.E. Webb, Imaging of multicellular large-scale rhythmic calcium waves during zebrafish gastrulation, Proc. Natl. Acad. Sci. USA 96 (1999) 157-161; J.B. Wallingford, A.J. Ewald, R.M. Harland, S.E. Fraser, Calcium signaling during convergent extension in Xenopus, Curr. Biol. 11 (2001) 652-661]. The various potential targets of these Ca(2+) transients will also be discussed, as well as how they might integrate with other known pattern forming

  18. TRACEing Last Glacial Period (25-80 ka b2k) Tephra Horizons between North Atlantic marine-cores and the Greenland ice-cores

    NASA Astrophysics Data System (ADS)

    Abbott, Peter; Davies, Siwan; Griggs, Adam; Bourne, Anna; Cook, Eliza; Austin, William; Chapman, Mark; Hall, Ian; Purcell, Catriona; Rasmussen, Tine; Scourse, James

    2014-05-01

    Tephrochronological investigations are currently being undertaken on a network of marine cores from a range of locations and depositional settings within the North Atlantic. This work forms a component of the ERC-funded project Tephra constraints on Rapid Climate Events (TRACE). The main aim of this project is to utilise isochronous tephra horizons as direct tie-lines to correlate North Atlantic marine sequences and the Greenland ice-cores to determine the relative timing of oceanic and atmospheric changes associated with the rapid climate events that dominated the last glacial period. Early comparisons of six North Atlantic marine records (MD99-2251, MD04-2820CQ, MD04-2829CQ, MD04-2822, MD01-2461 and JM11-19PC) and the Greenland ice-cores highlight six tephra horizons common to the ice record and one or more marine sequences. These horizons are within GS-3 (26,740 ± 390 a b2k and 29,130 ± 456 a b2k), GS-9 (38,300 ± 703 a b2k), GS-10 (40,220 ± 792 a b2k) and GS-12 (43,680 ± 877 a b2k) and the widespread North Atlantic Ash Zone II (55,380 ± 1184 a b2k). New high-resolution proxy information from MD04-2820CQ allows us to explore the relative timing of climatic changes between the Goban Spur, North Atlantic and Greenland over GI-12 to GI-8 using two tephra correlations that link the records. Tephra horizons have been identified in the marine records through the successful use of cryptotephra extraction techniques more commonly applied to the study of terrestrial sequences. All horizons have an Icelandic source with horizons of both rhyolitic and basaltic composition isolated. The acquisition of high-resolution profiles of shard concentration and comprehensive geochemical characterisations for horizons is vital to this work. This allows us to disentangle the processes that transported material to core sites, which can include primary airfall, sea-ice rafting and iceberg rafting, and the potential impact of secondary reworking processes such as bottom current

  19. Shipwreck rates and tree rings suggest reduced North Atlantic tropical cyclone activity during the Maunder Minimum.

    NASA Astrophysics Data System (ADS)

    Harley, G. L.; Trouet, V.; Dominguez Delmas, M.

    2014-12-01

    The observational record of North Atlantic TCs is too short to inform our understanding of decadal-scale climatic controls on TC regimes. We combined two new annual-resolution proxies of Atlantic storm activity to extend the observational TC record back to the 16th Century. A tree-growth suppression chronology (1707-2010 CE) from the Florida Keys, U.S.A. captures 91% of observed North Atlantic TCs (1850-2010 CE) and shares significant peak events with a documentary time series of Spanish shipwrecks in the Caribbean (1495-1820). Decadal-scale shipwreck rates were lowest during the Maunder Minimum (ca. 1645-1715), indicating that cooler Atlantic sea surface temperatures (SSTs) during this period reduced Caribbean TC activity. Our results support global-scale climate proxy data and suggest that cooler tropical Atlantic SSTs and a generally negative mode of the North Atlantic Oscillation during the Little Ice Age reduced TC frequency.

  20. Reduced admixture of North Atlantic Deep Water to the deep central South Pacific during the last two glacial periods

    NASA Astrophysics Data System (ADS)

    Molina-Kescher, Mario; Frank, Martin; Tapia, Raúl; Ronge, Thomas A.; Nürnberg, Dirk; Tiedemann, Ralf

    2016-06-01

    The South Pacific is a sensitive location for the variability of the global oceanic thermohaline circulation given that deep waters from the Atlantic Ocean, the Southern Ocean, and the Pacific Basin are exchanged. Here we reconstruct the deep water circulation of the central South Pacific for the last two glacial cycles (from 240,000 years ago to the Holocene) based on radiogenic neodymium (Nd) and lead (Pb) isotope records complemented by benthic stable carbon data obtained from two sediment cores located on the flanks of the East Pacific Rise. The records show small but consistent glacial/interglacial changes in all three isotopic systems with interglacial average values of -5.8 and 18.757 for ɛNd and 206Pb/204Pb, respectively, whereas glacial averages are -5.3 and 18.744. Comparison of this variability of Circumpolar Deep Water (CDW) to previously published records along the pathway of the global thermohaline circulation is consistent with reduced admixture of North Atlantic Deep Water to CDW during cold stages. The absolute values and amplitudes of the benthic δ13C variations are essentially indistinguishable from other records of the Southern Hemisphere and confirm that the low central South Pacific sedimentation rates did not result in a significant reduction of the amplitude of any of the measured proxies. In addition, the combined detrital Nd and strontium (87Sr/86Sr) isotope signatures imply that Australian and New Zealand dust has remained the principal contributor of lithogenic material to the central South Pacific.

  1. An electron localization function study of the geometry of d(0) molecules of the period 4 metals Ca to Mn.

    PubMed

    Gillespie, Ronald J; Noury, Stéphane; Pilmé, Julien; Silvi, Bernard

    2004-05-17

    We have studied the geometry of the formally d(0) MX(n)() (X = F, H, CH(3) and O; n = 2-6) molecules of the period 4 metals from Ca to Mn by studying the topology of the electron localization function (ELF) in order to try to understand why many of these molecules have non-VSEPR geometries. The quantitative analysis of the core basin population shows that it is always larger than its conventional value (18) because, in the LCAO-MO scheme, the 3d basis functions centered on the metal noticeably contribute to the electron density within the core region associated with the M shell. Therefore, the density available to form the bonds is less than Z(M) - 18, the value adopted in electron counts. Under the influence of the ligands, these electrons cause the core to lose its spherical symmetry by the formation of opposite-spin pair localization basins, which in turn influence the geometry of the ligands if the interaction of the ligands with the core is sufficiently strong. All of the ligands considered in this study, except F, interact with the core sufficiently strongly to give non-VSEPR geometries, which we have rationalized on the basis of the ELF topology. PMID:15132634

  2. Rapid subtropical North Atlantic salinity oscillations across Dansgaard-Oeschger cycles.

    PubMed

    Schmidt, Matthew W; Vautravers, Maryline J; Spero, Howard J

    2006-10-01

    Geochemical and sedimentological evidence suggest that the rapid climate warming oscillations of the last ice age, the Dansgaard-Oeschger cycles, were coupled to fluctuations in North Atlantic meridional overturning circulation through its regulation of poleward heat flux. The balance between cold meltwater from the north and warm, salty subtropical gyre waters from the south influenced the strength and location of North Atlantic overturning circulation during this period of highly variable climate. Here we investigate how rapid reorganizations of the ocean-atmosphere system across these cycles are linked to salinity changes in the subtropical North Atlantic gyre. We combine Mg/Ca palaeothermometry and oxygen isotope ratio measurements on planktonic foraminifera across four Dansgaard-Oeschger cycles (spanning 45.9-59.2 kyr ago) to generate a seawater salinity proxy record from a subtropical gyre deep-sea sediment core. We show that North Atlantic gyre surface salinities oscillated rapidly between saltier stadial conditions and fresher interstadials, covarying with inferred shifts in the Tropical Atlantic hydrologic cycle and North Atlantic overturning circulation. These salinity oscillations suggest a reduction in precipitation into the North Atlantic and/or reduced export of deep salty thermohaline waters during stadials. We hypothesize that increased stadial salinities preconditioned the North Atlantic Ocean for a rapid return to deep overturning circulation and high-latitude warming by contributing to increased North Atlantic surface-water density on interstadial transitions. PMID:17024090

  3. Multiregional periodic matrix for modeling the population dynamics of sardine (Sardina pilchardus) along the moroccan atlantic coast: management elements for fisheries.

    PubMed

    Serghini, Mansour; Boutayeb, Abdesslam; Auger, Pierre; Charouki, Najib; Ramzi, Azeddine; Ettahiri, Omar; Tchuente, Maurice

    2009-12-01

    In this paper, we present a deterministic time discrete mathematical model based on multiregional periodic matrices to describe the dynamics of Sardina pilchardus in the Central Atlantic area of the Moroccan coast. This model deals with two stages (immature and mature) and three spatial zones where sardines are supposed to migrate from one zone to another. The population dynamics is described by an autonomous recurrence equation N(t + 1) = A.N(t), where A is a positive matrix whose entries are estimated using data collected during biannual acoustic surveys carried out from 2001 to 2003 onboard the Norwegian research vessel "Dr Fridtjof Nansen". The dominant eigenvalue lambda of A that gives the long-term growth rate of fish population is smaller than one. This agrees with the stock decrease observed in the data collected. We show that lambda is highly sensitive to the recruitment rate and much less sensitive to the reproduction rate. These results can clearly be used to define an efficient scenario in order to fight for instance against a stock decrease. PMID:19842047

  4. Hepatic retention and toxicological responses during feeding and depuration periods in Atlantic salmon ( Salmo salar ) fed graded levels of the synthetic antioxidant, butylated hydroxytoluene.

    PubMed

    Holaas, Eivind; Bohne, Victoria B; Hamre, Kristin; Arukwe, Augustine

    2008-12-10

    The human safety aspects of seafood production require the expansion of vital knowledge of both nutrients and possible contaminants along the entire production chain. Thus, production of safer seafood can be achieved by using feed materials that are low in contaminants, while maintaining balanced nutrition, in order to secure optimal fish and consumer health. Our understanding of primary responses of fish health and production related diseases, as well as biological processes that influence carry-over and lowering of contaminants in farmed fish, will contribute to a sustainable production of safer seafood products. Therefore, we have studied the liver deposition and toxicological effects in salmon fed graded levels of BHT during a 12-week feeding followed by a 2-week depuration period using chemical, molecular, and catalytic assays. In general, our data showed that BHT was significantly retained in the liver and selectively modulated toxicological responses in the xenobiotic biotransformation pathways during the feeding period. Specifically, BHT produced consistent dose- and time-specific gene expression patterns for AhR2alpha, AhR2beta, CYP1A1, CYP3A, UGT1, and GSTpi. The effect of BHT on the gene expression of biotransformation enzyme did not parallel enzyme activity levels, suggesting a possible inhibition by parent BHT or its metabolites. As a safety precaution, the production of farmed Atlantic salmon in Norway requires a mandatory 2-week depuration period prior to slaughtering and market delivery to ensure the elimination of veterinary medicaments, additives, and other undesirable components. Comparison of feeding and depuration periods showed that BHT was highly retained in fish liver, as only 8-13% of fed BHT was eliminated during the 2-week depuration period. This is just a part of the total concentration in the whole fish, since BHT may have been distributed and accumulated in other organs. Since BHT or its metabolites putatively inhibited

  5. A regional overview of the last glacial period in the temperate NE Atlantic: varying paleoproductivity centers over the last 50 ka BP

    NASA Astrophysics Data System (ADS)

    Penaud, Aurélie; Eynaud, Frédérique; Ganne, Axelle

    2015-04-01

    Recent palynological investigations carried out in the eastern Gulf of Cadiz (MD99-2339 core) over MIS 3 enable to consider dinoflagellate cyst assemblage patterns over the last 50 ka BP through a compilation of 6 cores from the NE subtropical Atlantic to the Northern Bay of Biscay (also including cores MD95-2042, MD95-2043, MD04-2805CQ, VK03-58bis). Dinocyst signals depict hydrological front latitudinal shifts over the last glacial and associated sea-surface consequences regarding past regimes of primary productivity. We show here new data clearly evidencing subtropical latitudes of Cadiz as being as productive areas over the last glacial as recorded today in the septentrional part of the Bay of Biscay, especially between GI 8 and GI 12. We especially focus on dinocyst-species Lingulodinium machaerophorum relative abundances and absolute concentrations that we first evidence as a powerful tool to reconstruct and discuss productivity shifts through time in the temperate North Atlantic. This spatio-temporal synthesis bring important evidences of fast migrating paleoproductiviy centers from the last glacial period to present, implying also large consequences on the biological pump through time. Regarding this specific session, 5 of the 6 cores discussed here were retrieved by the R/V Marion Dufresne through 3 different cruises: Core MD99-2339 (35.89°N, 7.53°W, 1170m water depth, 18.54m long) was retrieved in a contouritic field in the oriental part of the Gulf of Cadiz by the oceanographic R/V Marion Dufresne during the 1999 International Marine Global Change Studies V (IMAGES V) cruise (Labeyrie, Jansen and Cortijo, 2003). Cores MD95-2042 (37°48'N, 10°10'W, 3146m water depth, 39.56m long) and MD95-2043 (36°8.6'N, 2°37.3'W, 1841m water depth, 36m long) were retrieved from the SW Iberian margin and the central Alboran Sea, respectively, by the oceanographic R/V Marion Dufresne during the 1995 IMAGES I cruise (Bassinot and Labeyrie, 1996). Core MD04-2805 CQ (34

  6. Tropical Rain Forest and Climate Dynamics of the Atlantic Lowland, Southern Brazil, during the Late Quaternary

    NASA Astrophysics Data System (ADS)

    Behling, Hermann; Negrelle, Raquel R. B.

    2001-11-01

    Palynological analysis of a core from the Atlantic rain forest region in Brazil provides unprecedented insight into late Quaternary vegetational and climate dynamics within this southern tropical lowland. The 576-cm-long sediment core is from a former beach-ridge "valley," located 3 km inland from the Atlantic Ocean. Radio-carbon dates suggest that sediment deposition began prior to 35,000 14C yr B.P. Between ca. 37,500 and ca. 27,500 14C yr B.P. and during the last glacial maximum (LGM; ca. 27,500 to ca. 14,500 14C yr B.P.), the coastal rain forest was replaced by grassland and patches of cold-adapted forest. Tropical trees, such as Alchornea, Moraceae/Urticaceae, and Arecaceae, were almost completely absent during the LGM. Furthermore, their distributions were shifted at least 750 km further north, suggesting a cooling between 3°C and 7°C and a strengthening of Antarctic cold fronts during full-glacial times. A depauperate tropical rain forest developed as part of a successional sequence after ca. 12,300 14C yr B.P. There is no evidence that Araucaria trees occurred in the Atlantic lowland during glacial times. The rain forest was disturbed by marine incursions during the early Holocene period until ca. 6100 14C yr B.P., as indicated by the presence of microforaminifera. A closed Atlantic rain forest then developed at the study site.

  7. In search of "Organ III" strata-a sedimentary record of the Medieval Warm Period (ca. AD 900 to 1300)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The period AD 900 to 1300, internationally referred to as the Medieval Warm Period, is a critical time for the archaeological record of the Southwestern USA. During the Medieval Warm Period both alluvial and eolian sedimentation increased, but not to the magnitude of the middle Holocene (the Altithe...

  8. Impact of volcanism on the evolution of Lake Van (eastern Anatolia) III: Periodic (Nemrut) vs. episodic (Süphan) explosive eruptions and climate forcing reflected in a tephra gap between ca. 14 ka and ca. 30 ka

    NASA Astrophysics Data System (ADS)

    Schmincke, Hans-Ulrich; Sumita, Mari

    2014-09-01

    Fifteen Lateglacial to Holocene rhyolitic, dominantly primary tephra layers piston-cored and drilled (ICDP Paleovan drilling project) in western Lake Van (eastern Anatolia, Turkey) were precisely correlated to either of the two adjacent and active large volcanoes Nemrut and Süphan based on shard textures, mineralogy and mineral and glass compositions. The young peralkaline (comenditic to pantelleritic) primary rhyolitic Nemrut tephras are characterized by anorthoclase, hedenbergitic to augitic clinopyroxene, fayalitic olivine, minor quartz, and rare accessory chevkinite and zircon. Phenocrysts in subalkaline primary rhyolitic Süphan tephras are chiefly oligoclase-labradorite, with minor K-rich sanidine in some, biotite, amphibole, hypersthene, rare augitic clinopyroxene, relatively common allanite and rare zircon. Two contrasting explosive eruptive modes are distinguished from each other: episodic (Süphan) and periodic (Nemrut). The Lateglacial Süphan tephra swarm covers a short time interval of ca. 338 years between ca. 13,078 vy BP and 12,740 vy BP, eruptions having occurred statistically every ca. 42 years with especially short intervals between V-11 (reworked) and V-14. Causes for the strongly episodic Süphan explosive behavior might include seismic triggering of a volcano-magma system unable to erupt explosively without the benefit of external triggering, as reflected in pervasive faulting preceding the Süphan tephra swarm. Seismic triggering may have caused the rise of more mafic ("trachyandesitic") parent magma, heating near-surface pockets of highly evolved magma - that might have formed silicic domes during this stage of volcano evolution - resulting in ascent and finally explosive fragmentation of magma essentially by external factors, probably significantly enhanced by magma-water/ice interaction. Explosive eruptions of the Nemrut volcano system, interpreted to be underlain by a large fractionating magma reservoir, follow a more periodic mode of (a

  9. Linkage of annual laminae formation in the Bering Sea and the Bølling-Allerød and Preboreal warm periods in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Gottschalk, J.; Max, L.; Tiedemann, R.; Schulz, M.; Merkel, U.

    2011-12-01

    The cause of the wide-spread occurrence of laminated sediments in the North Pacific and its linkage to oceanographic and climatic changes in the North Atlantic are still elusive due to the limited number of sediment records and the poor preservation of carbonate-bearing sediments in the North Pacific. New results from both climate modelling and proxy data of the partly laminated sediment core SO201-2-114-KL from the western Bering Sea (1394 m WD) provide new insights into the origin of laminations in the Bering Sea and possible Atlantic-Pacific teleconnections during the last deglacial. Alkenone-based, reconstructed sea surface temperatures in conjunction with ultra high-resolution XRF scanning (step size of 100 μm) of the laminae reveal that their formation is linked to a warming in both, the North Atlantic and North Pacific. Spectral analyses support the interpretation that laminations represent varves which are formed by the seasonally alternating sediment input of ice-rafted detritus and biogenic material from ice margin-related blooming events. The δ13C variability of epibenthic foraminifera at the northwest Kamtchatka margin reveals reduced ventilation of the North Pacific Intermediate Water facilitating the laminae formation. This suggests an inverse pattern of overturning in the North Pacific and North Atlantic, in accordance with the suggested North Atlantic - North Pacific seesaw.

  10. New results to discuss possibility of irrigation in Bat (Wadi Sharsah, northwestern Oman) before Hafit period (ca. 3100-2700 BCE)

    NASA Astrophysics Data System (ADS)

    Fouache, Eric; Desruelles, Stéphane; Eddargach, Wassel; Cammas, Cecilia; Wattez, Julia; Martin, Chloé; Tengberg, Margareta; Beuzen-Waller, Tara; Cable, Charlotte; Thornton, Christopher

    2014-05-01

    Registered as a World Heritage Site by UNESCO in 1989, the extensive archaeological site of Bat is situated within the Wadi Sharsah and around the modern village and palm grove of Bat, 24 km from the modern city of Ibri in northwestern Oman. The archaeological remains from the Bronze Age excavated by the Bat Archaeological Project are located in two mains areas. The northern area consists of a chain of low limestone hills cut by wadi tributaries leading to the main Wadi Sharsah. It is characterised by an exceptionnally high density of graves from two successive Bronze Age periods : Hafit (ca. 3100-2700 BCE) and Umm an-Nar (ca. 2700-2000 BCE). South of the Bat cemetery, in the flat part of the valley, there are several large circular structures (known historically as « towers ») and remains from both Hafit and Umm an-Nar periods, as well as later periods. Geomorphological mapping of the floodplain, associated with archaeological survey, have identified walls suggesting that during the Umm an-Nar period there was a system of irrigation which controlled flood water. Sedimentological, malacological, C14 dating and micromorphological studies of a 10 m long and 2.5 m high section located 143 m northeast of the Tower 1146 on the left bank of a small tributary of the Wadi Sharsah provide strong argument for the presence of an irrigation system that began before the Hafit period. New C14 datings confirm this hypothesis. Botanical macro-remains collected during the excavation of early Bronze Age structures at Bat further indicate the presence of date palm gardens since the 3rd millenium BCE allowing the cultivation of several crop species, in particular cereals. Most generally the global palaeoenvironmental reconstruction from our data supports a model of a general trend of aridification from Bronze Age to iron Age. Key words : Bronze Age, Holocene, Geomoephology, Micromorphology, Irrigation, Oman.

  11. Cell enlargement of plant tissue explants oscillates with a temperature-compensated period of ca. 24 min

    NASA Technical Reports Server (NTRS)

    Morre, D. James; Ternes, Philipp; Morre, Dorothy M.

    2002-01-01

    Rate of plant cell enlargement, measured at intervals of 3 min using a sensitive linear transducer, oscillates with a minimum period of about 24 min that parallels the 24-min periodicity observed with the oxidation of NADH by the external plasma membrane NADH oxidase and of single cells measured previously by video-enhanced light microscopy. Also exhibiting 24-min oscillations is the steady-state rate of cell enlargement induced by the addition of the auxin herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) or the natural auxin indole-3-acetic acid (IAA). Immediately following 2,4-D addition, a very complex pattern of oscillations is frequently observed. However, after several hours a dominant 24-min period emerges. The length of the 24-min period is temperature compensated and remains constant at 24 min when measured at 15, 25 or 35 degrees C, despite the fact that the rate of cell enlargement approximately doubles for each 10 degree C rise over this same range of temperatures.

  12. Impact of abrupt climate change in the tropical southeast Atlantic during Marine Isotope Stage (MIS) 3

    NASA Astrophysics Data System (ADS)

    Hessler, Ines; Steinke, Stephan; Groeneveld, Jeroen; Dupont, Lydie; Wefer, Gerold

    2011-12-01

    High resolution planktonic foraminifera Mg/Ca paleotemperatures and oxygen isotopes of seawater of Ocean Drilling Program (ODP) Site 1078 (off Angola) have been reconstructed and reveal insights into the seasonal thermal evolution of the Angola Current (AC), the Angola-Benguela Front (ABF), and the Benguela Current (BC) during the last glacial (50-23.5 ka BP). Special emphasis is put on time intervals possibly associated with the North Atlantic Heinrich Stadials (HS), which are thought to lead to an accumulation of heat in the South Atlantic due to a reduction of the Atlantic Meridional Overturning Circulation (AMOC). Within dating uncertainties, Globigerinoides ruber (pink) Mg/Ca-based sea surface temperature (SST) estimates that represent southern hemisphere summer surface conditions show several warming episodes that coincide with North Atlantic HS, thus supporting the concept of the bipolar thermal seesaw. In contrast, the Mg/Ca-based temperatures of Globigerina bulloides, representing the SST of the ABF/BC system during southern hemisphere winter, show no obvious response to the North Atlantic HS in the study area. We suggest that surface water cooling during the winter season is due to enhanced upwelling or upwelling of colder water masses which has most likely mitigated a warming of the ABF/BC system during HS. We further speculate that the seasonal asymmetry in our SST record results from seasonal differences in the dominance of atmospheric and oceanic teleconnections during periods of northern high latitude cooling.

  13. An 800-Year Tropical Atlantic Sea Surface Temperature Variability Record From the Cariaco Basin, Venezuela

    NASA Astrophysics Data System (ADS)

    Black, D. E.; Thunell, R. C.; Kaplan, A.; Abahazi, M. A.; Tappa, E. J.

    2007-05-01

    Here we present an eight century tropical Atlantic SST record based on foraminiferal Mg/Ca recovered from Cariaco Basin sediments that have been calibrated to historical instrumental SSTs. Spatial correlations indicate that the proxy record is representative of SSTs over much of the Caribbean and tropical Atlantic. The Mg/Ca-SST record also correlates well with global land and sea surface temperature anomalies, and captures decadal-scale variations in Atlantic tropical storm and hurricane frequency over the late-19th and 20th centuries. The long-term record displays a surprising amount of variability for a tropical location under essentially modern boundary conditions. The tropical North Atlantic does not appear to have experienced a pronounced Medieval Warm Period relative to the complete record. However, strong Little Ice Age cooling of as much as 3 °C occurred between A. D. 1525 and 1625. Spring SSTs gradually rose between A. D. 1650 and 1900 followed by a 2.5 °C warming over the twentieth century. Viewed in the context of the complete record, twentieth century temperatures are not the warmest in the entire record on average, but they do show the largest increase in magnitude and fastest rate of SST change over the last eight hundred years. Spectral analysis of the Mg/Ca-SST data suggests that 2-5 and ~13 year SST variability that is characteristic of tropical Atlantic instrumental records may change through time.

  14. Synchrony of the Central Atlantic magmatic province and the Triassic-Jurassic boundary climatic and biotic crisis

    NASA Astrophysics Data System (ADS)

    Marzoli, Andrea; Bertrand, Hervé; Knight, Kim B.; Cirilli, Simonetta; Buratti, Nicoletta; Vérati, Chrystèle; Nomade, Sébastien; Renne, Paul R.; Youbi, Nasrrddine; Martini, Rossana; Allenbach, Karin; Neuwerth, Ralph; Rapaille, Cédric; Zaninetti, Louisette; Bellieni, Giuliano

    2004-11-01

    The evolution of life on Earth is marked by catastrophic extinction events, one of which occurred ca. 200 Ma at the transition from the Triassic Period to the Jurassic Period (Tr-J boundary), apparently contemporaneous with the eruption of the world's largest known continental igneous province, the Central Atlantic magmatic province. The temporal relationship of the Tr-J boundary and the province's volcanism is clarified by new multidisciplinary (stratigraphic, palynologic, geochronologic, paleomagnetic, geochemical) data that demonstrate that development of the Central Atlantic magmatic province straddled the Tr-J boundary and thus may have had a causal relationship with the climatic crisis and biotic turnover demarcating the boundary.

  15. Administration of nicotinic receptor antagonists during the period of memory consolidation affects passive avoidance learning and modulates synaptic efficiency in the CA1 region in vivo.

    PubMed

    Dobryakova, Y V; Gurskaya, O Ya; Markevich, V A

    2015-01-22

    We examined whether a non-selective antagonist of nAChRs mecamylamine and selective antagonists of α4β2-containing nAChRs dihydro-β-erythroidine (DHβE) and α7-containing nAChRs methyllycaconitine (MLA) affect learning performance and synaptic efficiency in the CA1 area of the hippocampus of freely moving rats during the memory consolidation period. Adult male Wistar rats received mecamylamine (0.5 mg/kg), DHβE (1 mg/kg), MLA (2 mg/kg) or saline immediately after training in a passive avoidance task. Memory retention was examined 24 h after the training. The changes in the latency of the first entry into a dark compartment of a test chamber were chosen as a criterion of learning. The ability of nAChRs antagonists to induce changes in the basal level of focal potentials (fEPSP, field excitatory postsynaptic potential) was estimated before training (baseline), 90 min after the training (consolidation period) and 24 h after the training (retention period). We found that in untrained rats mecamylamine, DHβE and MLA diminished the amplitude of fEPSP within the first 90 min after the injection; similar effect was observed in DHβE- and MLA-treated trained animals. These suppressive effects of DHβE and MLA were associated with memory loss. In contrast, mecamylamine, when applied to trained animals, tended to increase latency to enter the dark chamber and did not influence fEPSP during first 90 min after injection. Thus, the nAChRs antagonists with different selectivity induced different changes in fEPSP and behavior which suggests that nAChRs with different subunit composition are diversely involved in memory consolidation. PMID:25450966

  16. Subsurface North Atlantic warming as a trigger of rapid cooling events: evidence from the early Pleistocene (MIS 31-19)

    NASA Astrophysics Data System (ADS)

    Hernández-Almeida, I.; Sierro, F.-J.; Cacho, I.; Flores, J.-A.

    2015-04-01

    Subsurface water column dynamics in the subpolar North Atlantic were reconstructed in order to improve the understanding of the cause of abrupt ice-rafted detritus (IRD) events during cold periods of the early Pleistocene. We used paired Mg / Ca and δ18O measurements of Neogloboquadrina pachyderma (sinistral - sin.), deep-dwelling planktonic foraminifera, to estimate the subsurface temperatures and seawater δ18O from a sediment core from Gardar Drift, in the subpolar North Atlantic. Carbon isotopes of benthic and planktonic foraminifera from the same site provide information about the ventilation and water column nutrient gradient. Mg / Ca-based temperatures and seawater δ18O suggest increased subsurface temperatures and salinities during ice-rafting, likely due to northward subsurface transport of subtropical waters during periods of weaker Atlantic Meridional Overturning Circulation (AMOC). Planktonic carbon isotopes support this suggestion, showing coincident increased subsurface ventilation during deposition of IRD. Subsurface accumulation of warm waters would have resulted in basal warming and break-up of ice-shelves, leading to massive iceberg discharges in the North Atlantic. The release of heat stored at the subsurface to the atmosphere would have helped to restart the AMOC. This mechanism is in agreement with modelling and proxy studies that observe a subsurface warming in the North Atlantic in response to AMOC slowdown during Marine Isotope Stage (MIS) 3.

  17. Sea surface temperatures in the central southern Indian Ocean over the period 1790 to 2007 inferred from two monthly resolved Sr/Ca and oxygen isotope records

    NASA Astrophysics Data System (ADS)

    Zinke, J.; Wassenburg, J.; Hardman, E.

    2009-04-01

    We obtained two monthly resolved Sr/Ca records from Rodrigues island (Mauritius) located in the trade wind belt of the central southern Indian Ocean. The longest core was obtained at a nearshore fringing reef and covers the period 1790-2005. This coral records surface air temperatures from the local weather station available from 1950 to the present. The most remarkable signal is a slight cooling after the 1950's. The second core was obtained from the open ocean and records a long-term warming trend between 1947 to 2007. The warming accelerated after the late 1970's in agreement with instrumental data. The oxygen isotope record is affected by salinity variations and shows a strong freshening trend after the late 1970's. The freshening trend is probably related to advection of low salinity waters with the South Equatorial Current and/or increased cyclonicity. We will discuss our results in light of interannual and decadal variability and present long-term seawater monitoring data.

  18. Sea Surface Temperature Variability in the Atlantic Sector of the Southern Ocean (odp Site 1090) across the Middle Pleistocene Transition Inferred from Mg/Ca Ratios in Planktonic Foraminifera.

    NASA Astrophysics Data System (ADS)

    Rodriguez-Sanz, L.; Mortyn, P. G.; Martinez-Garcia, A.; Rosell-Mele, A.

    2009-04-01

    Many paleoceanographic studies have focused on the Middle Pleistocene Transition (MPT), since during this period of time the frequency of glacial-interglacial (G/I) cycles changed from 41ky to 100ky, despite no fundamental differences in insolation forcing. Concomitant changes in ocean circulation and glacier dynamics, as well as a decrease in atmospheric CO2 concentrations have been suggested to be involved in this climatic transition. However, controversy on specific cause-effect mechanisms still remains. The Southern Ocean plays a key role in the ocean circulation system and global climate not only due to the exchange among different water masses from major basins, but also because it facilitates CO2 exchange between the deep ocean and the atmosphere. The Ocean Drilling Program (ODP) Site 1090, located in the present- day Subantarctic zone (42°54.8´S - 8°54´E, 3702m), spans the entire MPT, and allows sampling at moderate temporal resolution (2ky). The sediments accumulated above the calcium carbonate compensation depth, ensuring the preservation of calcareous microfossils through G/I periods. Sea surface temperature (SST) was reconstructed with planktonic foraminiferal Mg/Ca ratios (from Neogloboquadrina pachyderma (sinistral)), spanning the MPT from 1250-588Ka. Our results show G/I temperature variability between 4.2 and 14.2 °C when we use the Nurnberg (1995) equation to calculate SST, and between 2.9 and 11.9 °C when the Elderfield and Ganssen (2000) equation is used. The variability obtained from the latter calibration is in good agreement with that derived from other paleothermometers: Modern Analog Technique (MAT) and organic biomarkers from calcareous phytoplankton (UK37). Differences between Mg/Ca calibrations are probably the result of contrasting materials and approaches (culture vs. core-top). SST showed the expected lower G/I variability around 1000ka, and an increase of G/I variability after 900ka. Proxy comparison between our new Mg/Ca

  19. Enhanced Mediterranean-Atlantic exchange during Atlantic freshening phases

    NASA Astrophysics Data System (ADS)

    Rogerson, M.; Colmenero-Hidalgo, E.; Levine, R. C.; Rohling, E. J.; Voelker, A. H. L.; Bigg, G. R.; SchöNfeld, J.; Cacho, I.; Sierro, F. J.; LöWemark, L.; Reguera, M. I.; de Abreu, L.; Garrick, K.

    2010-08-01

    The Atlantic-Mediterranean exchange of water at Gibraltar represents a significant heat and freshwater sink for the North Atlantic and is a major control on the heat, salt and freshwater budgets of the Mediterranean Sea. Consequently, an understanding of the response of the exchange system to external changes is vital to a full comprehension of the hydrographic responses in both ocean basins. Here, we use a synthesis of empirical (oxygen isotope, planktonic foraminiferal assemblage) and modeling (analytical and general circulation) approaches to investigate the response of the Gibraltar Exchange system to Atlantic freshening during Heinrich Stadials (HSs). HSs display relatively flat W-E surface hydrographic gradients more comparable to the Late Holocene than the Last Glacial Maximum. This is significant, as it implies a similar state of surface circulation during these periods and a different state during the Last Glacial Maximum. During HS1, the gradient may have collapsed altogether, implying very strong water column stratification and a single thermal and δ18Owater condition in surface water extending from southern Portugal to the eastern Alboran Sea. Together, these observations imply that inflow of Atlantic water into the Mediterranean was significantly increased during HS periods compared to background glacial conditions. Modeling efforts confirm that this is a predictable consequence of freshening North Atlantic surface water with iceberg meltwater and indicate that the enhanced exchange condition would last until the cessation of anomalous freshwater supply into to the northern North Atlantic. The close coupling of dynamics at Gibraltar Exchange with the Atlantic freshwater system provides an explanation for observations of increased Mediterranean Outflow activity during HS periods and also during the last deglaciation. This coupling is also significant to global ocean dynamics, as it causes density enhancement of the Atlantic water column via the

  20. Last interglacial temperature seasonality reconstructed from tropical Atlantic corals

    NASA Astrophysics Data System (ADS)

    Brocas, William M.; Felis, Thomas; Obert, J. Christina; Gierz, Paul; Lohmann, Gerrit; Scholz, Denis; Kölling, Martin; Scheffers, Sander R.

    2016-09-01

    Reconstructions of last interglacial (LIG, MIS 5e, ∼127-117 ka) climate offer insights into the natural response and variability of the climate system during a period partially analogous to future climate change scenarios. We present well preserved fossil corals (Diploria strigosa) recovered from the southern Caribbean island of Bonaire (Caribbean Netherlands). These have been precisely dated by the 230Th/U-method to between 130 and 120 ka ago. Annual banding of the coral skeleton enabled construction of time windows of monthly resolved strontium/calcium (Sr/Ca) temperature proxy records. In conjunction with a previously published 118 ka coral record, our eight records of up to 37 years in length, cover a total of 105 years within the LIG period. From these, sea surface temperature (SST) seasonality and variability in the tropical North Atlantic Ocean is reconstructed. We detect similar to modern SST seasonality of ∼2.9 °C during the early (130 ka) and the late LIG (120-118 ka). However, within the mid-LIG, a significantly higher than modern SST seasonality of 4.9 °C (at 126 ka) and 4.1 °C (at 124 ka) is observed. These findings are supported by climate model simulations and are consistent with the evolving amplitude of orbitally induced changes in seasonality of insolation throughout the LIG, irrespective of wider climatic instabilities that characterised this period. The climate model simulations suggest that the SST seasonality changes documented in our LIG coral Sr/Ca records are representative of larger regions within the tropical North Atlantic. These simulations also suggest that the reconstructed SST seasonality increase during the mid-LIG is caused primarily by summer warming. A 124 ka old coral documents, for the first time, evidence of decadal SST variability in the tropical North Atlantic during the LIG, akin to that observed in modern instrumental records.

  1. Mid-Pliocene deep-sea bottom-water temperatures based on ostracode Mg/Ca ratios

    USGS Publications Warehouse

    Cronin, T. M.; Dowsett, H.J.; Dwyer, G.S.; Baker, P.A.; Chandler, M.A.

    2005-01-01

    We studied magnesium:calcium (Mg/Ca) ratios in shells of the deep-sea ostracode genus Krithe from a short interval in the middle Pliocene between 3.29 and 2.97 Ma using deep-sea drilling sites in the North and South Atlantic in order to estimate bottom water temperatures (BWT) during a period of climatic warmth. Results from DSDP and ODP Sites 552A, 610A, 607, 658A, 659A, 661A and 704 for the period Ma reveal both depth and latitudinal gradients of mean Mg/Ca values. Shallower sites (552A, 610A and 607) have higher mean Mg/Ca ratios (10.3, 9.7, 10.1 mmol/mol) than deeper sites (661A, 6.3 mmol/mol), and high latitude North Atlantic sites (552A, 610A, 607) have higher Mg/Ca ratios than low latitude (658A: 9.8 mmol/mol, 659A: 7.7 mmol/mol, 661A: 6.3 mmol/mol) and Southern Ocean (704: 8.0 mmol/mol) sites. Converting Mg/Ca ratios into estimated temperatures using the calibration of Dwyer et al. (1995) [Dwyer, G.S., Cronin, T.M., Baker, P.A., Raymo, M.E., Buzas, J.S., Corre??ge, T., 1995. North Atlantic deepwater temperature change during late Pliocene and late Quaternary climatic cycles. Science 270, 1347-1351] suggests that mean middle Pliocene bottom water temperatures at the study sites in the deep Atlantic were about the same as modern temperatures. However, brief pulses of elevated BWT occurred several times between 3.29 and 2.97 Ma in both the North and South Atlantic Ocean suggesting short-term changes in deep ocean circulation.

  2. Impact of abrupt deglacial climate change on tropical Atlantic subsurface temperatures.

    PubMed

    Schmidt, Matthew W; Chang, Ping; Hertzberg, Jennifer E; Them, Theodore R; Ji, Link; J, Link; Otto-Bliesner, Bette L

    2012-09-01

    Both instrumental data analyses and coupled ocean-atmosphere models indicate that Atlantic meridional overturning circulation (AMOC) variability is tightly linked to abrupt tropical North Atlantic (TNA) climate change through both atmospheric and oceanic processes. Although a slowdown of AMOC results in an atmospheric-induced surface cooling in the entire TNA, the subsurface experiences an even larger warming because of rapid reorganizations of ocean circulation patterns at intermediate water depths. Here, we reconstruct high-resolution temperature records using oxygen isotope values and Mg/Ca ratios in both surface- and subthermocline-dwelling planktonic foraminifera from a sediment core located in the TNA over the last 22 ky. Our results show significant changes in the vertical thermal gradient of the upper water column, with the warmest subsurface temperatures of the last deglacial transition corresponding to the onset of the Younger Dryas. Furthermore, we present new analyses of a climate model simulation forced with freshwater discharge into the North Atlantic under Last Glacial Maximum forcings and boundary conditions that reveal a maximum subsurface warming in the vicinity of the core site and a vertical thermal gradient change at the onset of AMOC weakening, consistent with the reconstructed record. Together, our proxy reconstructions and modeling results provide convincing evidence for a subsurface oceanic teleconnection linking high-latitude North Atlantic climate to the tropical Atlantic during periods of reduced AMOC across the last deglacial transition. PMID:22908256

  3. Impact of abrupt deglacial climate change on tropical Atlantic subsurface temperatures

    PubMed Central

    Schmidt, Matthew W.; Chang, Ping; Hertzberg, Jennifer E.; Them, Theodore R.; Ji, Link; Otto-Bliesner, Bette L.

    2012-01-01

    Both instrumental data analyses and coupled ocean-atmosphere models indicate that Atlantic meridional overturning circulation (AMOC) variability is tightly linked to abrupt tropical North Atlantic (TNA) climate change through both atmospheric and oceanic processes. Although a slowdown of AMOC results in an atmospheric-induced surface cooling in the entire TNA, the subsurface experiences an even larger warming because of rapid reorganizations of ocean circulation patterns at intermediate water depths. Here, we reconstruct high-resolution temperature records using oxygen isotope values and Mg/Ca ratios in both surface- and subthermocline-dwelling planktonic foraminifera from a sediment core located in the TNA over the last 22 ky. Our results show significant changes in the vertical thermal gradient of the upper water column, with the warmest subsurface temperatures of the last deglacial transition corresponding to the onset of the Younger Dryas. Furthermore, we present new analyses of a climate model simulation forced with freshwater discharge into the North Atlantic under Last Glacial Maximum forcings and boundary conditions that reveal a maximum subsurface warming in the vicinity of the core site and a vertical thermal gradient change at the onset of AMOC weakening, consistent with the reconstructed record. Together, our proxy reconstructions and modeling results provide convincing evidence for a subsurface oceanic teleconnection linking high-latitude North Atlantic climate to the tropical Atlantic during periods of reduced AMOC across the last deglacial transition. PMID:22908256

  4. Reproductive biology of female Norway lobster, Nephrops norvegicus (Linnaeus, 1758) Leach, in Icelandic waters during the period 1960-2010: comparative overview of distribution areas in the Northeast Atlantic and the Mediterranean.

    PubMed

    Eiríksson, Hrafnkell

    2014-01-01

    Maturity size, reproductive cycle, sex ratio and fecundity of female Nephrops were investigated at SW, S and SE Iceland for the period 1960-2010. Time series of biological parameters and fisheries data displayed significant relationships. In addition, female biological data from 20 areas in the Atlantic and Mediterranean were compared. Fifty percentage maturity estimates had an overall range of 23.9-34.4mm CL with some anomalies in the 2000s. The reproductive cycle in Iceland has been biennial during the whole study period from mid-1960s to 2010 with minor change in phase in the 2000s. Biennial moulting retards female growth more than annual spawning, and the length of incubation and hatch time of year show significant relationships with latitude and sea temperature. Variations in sex ratio were observed and relationships found between female sex ratio and CL, CPUE and stock biomass during 1961-2010, displaying apparent fishery-induced effects on sex ratio. Potential and realized fecundity estimates in Iceland are 35-50% of those reported from more southerly waters. Biennial spawning and low fecundity limit the number of progeny in Icelandic Nephrops and necessitate lower fishing mortality. Ambient temperature in Icelandic waters has risen by 1°C since the late 1990s, generating around 30 days shorter incubation time in the 2000s, but around 3°C rise is necessary for possible annual spawning. PMID:24981733

  5. Characterization of Ca(2+) signaling in the external yolk syncytial layer during the late blastula and early gastrula periods of zebrafish development.

    PubMed

    Yuen, Michael Y F; Webb, Sarah E; Chan, Ching Man; Thisse, Bernard; Thisse, Christine; Miller, Andrew L

    2013-07-01

    Preferential loading of the complementary bioluminescent (f-aequorin) and fluorescent (Calcium Green-1 dextran) Ca(2+) reporters into the yolk syncytial layer (YSL) of zebrafish embryos, revealed the generation of stochastic patterns of fast, short-range, and slow, long-range Ca(2+) waves that propagate exclusively through the external YSL (E-YSL). Starting abruptly just after doming (~4.5h post-fertilization: hpf), and ending at the shield stage (~6.0hpf) these distinct classes of waves propagated at mean velocities of ~50 and ~4μm/s, respectively. Although the number and pattern of these waves varied between embryos, their initiation site and arcs of propagation displayed a distinct dorsal bias, suggesting an association with the formation and maintenance of the nascent dorsal-ventral axis. Wave initiation coincided with a characteristic clustering of YSL nuclei (YSN), and their associated perinuclear ER, in the E-YSL. Furthermore, the inter-YSN distance (IND) appeared to be critical such that Ca(2+) wave propagation occurred only when this was <~8μm; an IND >~8μm was coincidental with wave termination at shield stage. Treatment with the IP3R antagonist, 2-APB, the Ca(2+) buffer, 5,5'-dibromo BAPTA, and the SERCA-pump inhibitor, thapsigargin, resulted in a significant disruption of the E-YSL Ca(2+) waves, whereas exposure to the RyR antagonists, ryanodine and dantrolene, had no significant effect. These findings led us to propose that the E-YSL Ca(2+) waves are generated mainly via Ca(2+) release from IP3Rs located in the perinuclear ER, and that the clustering of the YSN is an essential step in providing a CICR pathway required for wave propagation. This article is part of a Special Issue entitled: 12th European Symposium on Calcium. PMID:23142640

  6. North atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles

    USGS Publications Warehouse

    Dwyer, G.S.; Cronin, T. M.; Baker, P.A.; Raymo, M.E.; Buzas, Jeffrey S.; Correge, T.

    1995-01-01

    Variations in the ratio of magnesium to calcium (Mg/Ca) in fossil ostracodes from Deep Sea Drilling Project Site 607 in the deep North Atlantic show that the change in bottom water temperature during late Pliocene 41,000-year obliquity cycles averaged 1.5??C between 3.2 and 2.8 million years ago (Ma) and increased to 2.3??C between 2.8 and 2.3 Ma, coincidentally with the intensification of Northern Hemisphere glaciation. During the last two 100,000-year glacial-to-interglacial climatic cycles of the Quaternary, bottom water temperatures changed by 4.5??C. These results show that glacial deepwater cooling has intensified since 3.2 Ma, most likely as the result of progressively diminished deep-water production in the North Atlantic and of the greater influence of Antarctic bottom water in the North Atlantic during glacial periods. The ostracode Mg/Ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from Site 607, as well as derivation of a hypothetical sea-level curve for the late Pliocene and late Quaternary. The effects of dissolution on the Mg/Ca ratios of ostracode shells appear to have been minimal.

  7. Evolution of the southeast Atlantic thermocline during Marine Isotopic Stages 6-5: is it related to variations in the Agulhas Leakage?

    NASA Astrophysics Data System (ADS)

    Scussolini, P.; Peeters, F. J. C.

    2012-04-01

    The inter-basin exchange of Indian Ocean waters into the South Atlantic via the Agulhas Leakage (AL) is considered a modulator of Atlantic Meridional Overturning Circulation. Paleoceanographic studies show that increased inputs of saline and relatively warm Agulhas Current waters are associated with late Pleistocene deglaciations. This suggests that this transfer of water masses may effectively regulate the buoyancy of the (South) Atlantic Ocean, and consequently the strength of the Atlantic thermohaline overturning. Our aim is to detect changes in the southeast Atlantic thermocline that may be dynamically linked to variations in the intensity of the AL. To test this relationship, within the frame of EU Marie Curie GATEWAYS project, we are studying a marine sediment record from the central Walvis Ridge, a site that is presently underneath the trajectory of northwest migrating Agulhas Rings. We focus on the δ18O and Mg/Ca ratio of certain planktic foraminifera species that are known to dwell at different depths in the upper ocean, in order to reconstruct the properties of water masses during the last two glacial cycles. The results so far show changes in the δ18O difference (Δδ18O) between surface and thermocline species along Marine Isotopic Stage 6. Such difference is interpreted as a proxy for the thermal gradient of the upper ca. 400 m of the water column. We conclude that the observed changes in the southeast Atlantic thermocline do not coincide with the AL peaks as indicated by published faunal counts (Peeters et al. 2004). The Mg/Ca paleotemperature proxy will be implemented to improve the interpretation of the hydrographic mechanisms underlying the observed changes in thermocline properties. Ref.: Peeters, F.J.C. et al., 2004. Vigorous exchange between the Indian and Atlantic oceans at the end of the past five glacial periods. Nature, 430(7000): 661-665.

  8. Subsurface North Atlantic warming as a trigger of rapid cooling events: evidences from the Early Pleistocene (MIS 31-19)

    NASA Astrophysics Data System (ADS)

    Hernández-Almeida, I.; Sierro, F.-J.; Cacho, I.; Flores, J.-A.

    2014-10-01

    Subsurface water column dynamics in the subpolar North Atlantic were reconstructed in order to improve the understanding of the cause of abrupt IRD events during cold periods of the Early Pleistocene. We used Mg / Ca-based temperatures of deep-dwelling (Neogloboquadrina pachyderma sinistral) planktonic foraminifera and paired Mg / Ca-δ18O measurements to estimate the subsurface temperatures and δ18O of seawater at Site U1314. Carbon isotopes on benthic and planktonic foraminifera from the same site provide information about the ventilation and water column nutrient gradient. Mg / Ca-based temperatures and δ18O of seawater suggest increased temperatures and salinities during ice-rafting, likely due to enhanced northward subsurface transport of subtropical waters during periods of AMOC reduction. Planktonic carbon isotopes support this suggestion, showing coincident increased subsurface ventilation during deposition of ice-rafted detritus (IRD). Warm waters accumulated at subsurface would result in basal warming and break-up of ice-shelves, leading to massive iceberg discharges in the North Atlantic. Release of heat and salt stored at subsurface would help to restart the AMOC. This mechanism is in agreement with modelling and proxy studies that observe a subsurface warming in the North Atlantic in response to AMOC slowdown during the MIS3.

  9. Habitat Suitability Index Models: Juvenile Atlantic Croaker

    USGS Publications Warehouse

    Diaz, Robert J.; Onuf, Christopher P.

    1982-01-01

    INTRODUCTION The Atlantic croaker is an important commercial and recreational species. In the 1940's, the foodfish catch of Atlantic croakers was concentrated in Chesapeake Bay; in the 1950's and early 1970's, the catch was concentrated in the Gulf of Mexico; and in the late 1970's, the catch was concentrated in the South Atlantic States (Wilk 1981). Industrial and recreational catches of Atlantic croakers have been concentrated in the Gulf of Mexico, where the Atlantic croaker is the most important species of bottomfish for industrial uses (Knudsen and Herke 1978), and has ranked first, second, or third in number caught by recreational anglers, depending on survey year (Nakamura 1981). Today, Virginia or Delaware is considered to be the northern extent of the species. During climatically warmer periods, such as the 1930's and 1940's, the croaker extended its range north at least to New York, where it was commercially fished. The southern extent of its range is Argentina.

  10. Multiple 'Stable' States of Antarctic Intermediate Water: A Study from the Subantarctic South-West Atlantic.

    NASA Astrophysics Data System (ADS)

    Roberts, J.; Hodell, D. A.; Peck, V. L.; Kender, S.

    2014-12-01

    Modelling studies suggest that density changes in Antarctic Intermediate Water (AAIW) played a significant role in the reorganisation of Atlantic Meridional Overturning Circulation over the last glacial period. From its principal site of formation in the SE Pacific, a significant proportion of AAIW is entrained in the Antarctic circumpolar current and enters the Atlantic through Drake Passage. Air-sea interaction within the subAntarctic SW Atlantic modifies this AAIW further, producing a cooler and fresher Atlantic end member of AAIW. Our core site is located where this branch of AAIW subducts and travels northwards along the western margin of the Atlantic basin. We present the first high-resolution, multi-proxy study of AAIW in the sub-Antarctic SW Atlantic over the last 140 kyrs. Here, we focus on the temperature and salinity records over the last two glacial terminations and at the onset of the last glaciation. We use a combination of benthic stable isotopes and elemental ratios (Mg/Ca) on the shallow infaunal species Uvigerina peregrina to reconstruct AAIW temperature and salinity. Our records suggest that AAIW temperature both increased and decreased in a step-wise manner over the last 120 kyrs hinting at 3 'stable' states for AAIW through the last glacial cycle (see shaded areas within figure). Another common feature is a transient interval of apparently warm, saline AAIW observed at the onset of both glacial terminations - could this be evidence of the 'deep, salty blob' or of increased outflow of Pacific surface waters? We identify some fundamental differences between termination I and termination II; AAIW appears to have been markedly warmer during MIS6 than at the LGM. Furthermore, the glacial-interglacial potential density difference is much greater over termination I than termination II.

  11. Late Holocene sea surface temperature seesaw between the subpolar North Atlantic and the Norwegian Sea inferred from two marine sediment cores

    NASA Astrophysics Data System (ADS)

    Miettinen, Arto; Divine, Dmitry; Koç, Nalan; Godtliebsen, Fred; Hall, Ian R.

    2013-04-01

    A 2800-yr-long August sea surface temperature (aSST) record based on fossil diatom assemblages is generated from a marine sediment core Rapid 21-COM recovered in the Iceland Basin (northern subpolar North Atlantic). The record has a resolution of 2-10 years for interval 800-2004 AD representing the best resolved diatom SST reconstruction from the subpolar North Atlantic for this period, and 40 years for interval 800 BC-800 AD. The record is compared with the high-resolution (4-20 years) aSST record from core CR948/2011 from the Vøring Plateau, in the Norwegian Sea, to explore the variability of the aSST gradient between these areas during the late Holocene. The two aSST records show persistent opposite climate trends toward warming in the subpolar North Atlantic and cooling in the Norwegian Sea throughout the late Holocene. The wavelet analysis reveals an apparent tendency to coherent antiphased aSST variations between the sites for the shorter time scales too, implying a possible aSST seesaw between the northern subpolar North Atlantic and the Norwegian Sea to operate during the late Holocene. At the multicentennial scale of aSST variability of 600-900 years, the records are nearly in antiphase with warmer (colder) periods in the subpolar North Atlantic corresponding to the colder (warmer) periods in the Norwegian Sea. At the shorter time scale of 200-450 years the records display a nearly phase-locked behaviour with a tendency for the positive aSST anomalies in the Norwegian Sea to lead by ca. 30 years the negative aSST anomalies in the subpolar North Atlantic. This aSST seesaw might have had a strong effect, or be associated, with the two major climate anomalies in the northwest Europe during the past Millennium: Medieval Warm Period (MWP) and the Little Ice Age (LIA). During the MWP warming of the sea surface in the Norwegian Sea occurred in parallel with cooling in the northern subpolar North Atlantic, whereas the opposite pattern emerged during the LIA

  12. Two millennia of North Atlantic seasonality and implications for Norse colonies

    PubMed Central

    Patterson, William P.; Dietrich, Kristin A.; Holmden, Chris; Andrews, John T.

    2010-01-01

    δ18O values of mollusks recovered from near-shore marine cores in northwest Iceland quantify significant variation in seasonal temperature over the period from ∼360 B.C. to ∼A.D. 1660. Twenty-six aragonitic bivalve specimens were selected to represent intervals of climatic interest by using core sedimentological characteristics. Carbonate powder was sequentially micromilled from shell surfaces concordant with growth banding and analyzed for stable oxygen (δ18O) and carbon (δ13C) isotope values. Because δ18O values record subseasonal temperature variation over the lifetime of the bivalves, these data provide the first 2,000-year secular record of North Atlantic seasonality from ca. 360 cal yr B.C. to cal yr A.D. 1660. Notable cold periods (360 B.C. to 240 B.C.; A.D. 410; and A.D. 1380 to 1420) and warm periods (230 B.C. to A.D. 140 and A.D. 640 to 760) are resolved in terms of contrast between summer and winter temperatures and seasonal temperature variability. Literature from the Viking Age (ca. 790 to 1070) during the establishment of Norse colonies (and later) in Iceland and Greenland permits comparisons between the δ18O temperature record and historical records, thereby demonstrating the impact of seasonal climatic extremes on the establishment, development, and, in some cases, collapse of societies in the North Atlantic. PMID:20212157

  13. Two millennia of North Atlantic seasonality and implications for Norse colonies.

    PubMed

    Patterson, William P; Dietrich, Kristin A; Holmden, Chris; Andrews, John T

    2010-03-23

    delta(18)O values of mollusks recovered from near-shore marine cores in northwest Iceland quantify significant variation in seasonal temperature over the period from approximately 360 B.C. to approximately A.D. 1660. Twenty-six aragonitic bivalve specimens were selected to represent intervals of climatic interest by using core sedimentological characteristics. Carbonate powder was sequentially micromilled from shell surfaces concordant with growth banding and analyzed for stable oxygen (delta(18)O) and carbon (delta(13)C) isotope values. Because delta(18)O values record subseasonal temperature variation over the lifetime of the bivalves, these data provide the first 2,000-year secular record of North Atlantic seasonality from ca. 360 cal yr B.C. to cal yr A.D. 1660. Notable cold periods (360 B.C. to 240 B.C.; A.D. 410; and A.D. 1380 to 1420) and warm periods (230 B.C. to A.D. 140 and A.D. 640 to 760) are resolved in terms of contrast between summer and winter temperatures and seasonal temperature variability. Literature from the Viking Age (ca. 790 to 1070) during the establishment of Norse colonies (and later) in Iceland and Greenland permits comparisons between the delta(18)O temperature record and historical records, thereby demonstrating the impact of seasonal climatic extremes on the establishment, development, and, in some cases, collapse of societies in the North Atlantic. PMID:20212157

  14. Hydrographic changes in the subpolar North Atlantic at the MCA to LIA transition

    NASA Astrophysics Data System (ADS)

    Divine, Dmitry; Miettinen, Arto; Husum, Katrine; Koc, Nalan

    2016-04-01

    A network of four marine sediment cores from the northern North Atlantic is used to study hydrographic changes in surface water masses during the last 2000 years with a special focus on the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA) transition. Three of the cores are recovered from the sites located on main pathways of warm Atlantic water to the Arctic: M95-2011 (Vøring plateau, Norwegian Sea), Rapid-21 COM and LO-14 (Reykjanes Ridge, south of Iceland). The fourth core MD99-2322 is from the SE Greenland shelf (Denmark Strait), and it is influenced by the cold water outflow from the Arctic. The cores were analyzed continuously for planktonic diatoms with a high decadal to subdecadal temporal resolution. Past changes in the spatial distribution of surface water masses have been studied identifying factors, or typical species compositions, in downcore diatom assemblages. To derive the factors a Q-mode factor analysis has been applied to the extended modern calibration data set of 184 surface sediment samples from the North Atlantic, the Labrador Sea, the Nordic Seas, and Baffin Bay. SSTs have also been reconstructed using transfer functions. Variations of the reconstructed SSTs and loadings of major contributing factors reveal a complex regional pattern of changes in the structure of circulation during the MCA/LIA transition (1200-1400 AD). In the Norwegian Sea, the factors associated with assemblages typical for warmer and saline North Atlantic waters are partly displaced by colder and fresher water dwelling diatoms suggesting an eastward migration of mixed Arctic/Atlantic water masses into the Norwegian Sea. The two cores south of Iceland show a westward propagation of a warm water pulse as evidenced by the dominance of assemblages, which today are typical for the waters ca 5° further south than the current study sites. At the SE Greenland shelf an abrupt shift (ca. 50 years) in factors associated with different sea ice zone dwelling diatoms

  15. Photocopy of ground floor plan, ca. 12939. Plans and renovations ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Photocopy of ground floor plan, ca. 12939. Plans and renovations required for the 1940-1941 addition are overlaid on the original plan - Stamford Post Office, 421 Atlantic Street, Stamford, Fairfield County, CT

  16. A modelling study of the influence of anomalous wind forcing over the Barents Sea on the Atlantic water flow to the Arctic Ocean in the period 1979-2004

    NASA Astrophysics Data System (ADS)

    Marciniak, Jakub; Schlichtholz, Pawel; Maslowski, Wieslaw

    2016-04-01

    Arctic climate system is influenced by oceanic heat transport with the Atlantic water (AW) streaming towards the Arctic Ocean in two branches, through the deep Fram Strait and the shallow Barents Sea. In Fram Strait, the AW submerges below the Polar surface water and then flows cyclonically along the margin of the Arctic Ocean as a subsurface water mass in the Arctic Slope Current. In contrast to the Fram Strait branch, which is the major source of heat for the Arctic Ocean, most of the heat influx to the Barents Sea through the Barents Sea opening (BSO) is passed to the atmosphere. Only cold remnants of AW outflow to the Arctic Ocean through the northeastern gate of the Barents Sea. Some AW entering the Barents Sea recirculates westward, contributing to an outflow from the Barents Sea through the BSO along the shelf slope south of Bear Island, in the Bear Island Slope Current. Even though the two-branched AW flow toward the Arctic Ocean has been known for more than a century, little is known about co-variability of heat fluxes in the two branches, its mechanisms and climatic implications. Recent studies indicate that the Bear Island Slope Current may play a role in this co-variability. Here, co-variability of the flow through the BSO and Fram Strait is investigated using a pan-Arctic coupled ice-ocean hindcast model run for the period 1979-2004 and forced with daily atmospheric data from the ECMWF. Significant wintertime co-variability between the volume transport in the Bear Island and Arctic slope currents and its link to wind forcing over the Barents Sea is confirmed. It is found that the volume transports in these currents are, however, not correlated in the annual mean and that the wintertime co-variability of these currents has no immediate effect on either the net heat flux through the BSO or the net heat flux divergence in the Barents Sea. It is shown that the main climatic effect of wind forcing over the northern Barents Sea shelf is to induce temperature

  17. Sex-structure, depth distribution, intermoult period and reproductive pattern of the deep-sea red crab Chaceon affinis (Brachyura, Geryonidae) in two populations in the north-eastern Atlantic

    NASA Astrophysics Data System (ADS)

    Biscoito, Manuel; Freitas, Mafalda; Pajuelo, José G.; Triay-Portella, Raül; Santana, José I.; Costa, Ana L.; Delgado, João; González, José A.

    2015-01-01

    This work investigated the biology of Chaceon affinis in two isolated populations of the Atlantic Ocean, including depth distribution, sexual structure, reproductive patterns and intermoult period. Males were larger and heavier than females. Mean size decreased with depth for both males and females. The highest abundance was found at 600-799 m of depth for males and at 800-999 m depth stratum for females. The highest abundance of ovigerous females was found at the 800-999 m depth stratum. Of the different ovaries' colour or colour shades recorded, only six categories were histologically characterized. The presence of spermatophores in the spermatheca of females in carapace stages II and III suggests that spermatophores are viable and used during the intermoult period. The size at sexual maturity in females was estimated at 104.4-104.7 mm carapace width (CW) in Madeira, and 109.3-110.5 mm CW in the Canary Islands. Only three categories of testes were identified. Mature testes consisted in a large mass, with highly coiled vasa deferentia visible to the naked eye. The size at sexual maturity in males was estimated at 113.8 mm CW in Madeira and 118.9 mm CW in the Canaries. The relative growth of males showed significant changes along the ontogeny and size at which allometric growth changes, as an indicator of morphometric maturity, occurred between 103.2 and 103.6 mm CW in Madeira and between 111.4 and 113.1 mm CW in the Canaries. In females, size at which allometric growth changes was found for maximum width of fifth abdominal somite (AS5W) at 98.2 mm CW in Madeira and 103.0 mm CW in the Canaries. The size at maturity obtained for C. affinis indicates that the minimum landing size (MLS) should not be set smaller than 125 mm CW in Madeira and 130 mm CW in the Canaries. This conservative MLS, higher than length at functional maturity, would safeguard immature individuals until they reach the size at which they can contribute to the reproductive capacity of the

  18. International Conference on the Application and Theory of Periodic Structures, Diffraction Gratings, and Moire Phenomena, III, San Diego, CA, Aug. 19, 20, 1987, Proceedings

    NASA Astrophysics Data System (ADS)

    Lerner, Jeremy M.

    Theoretical and applications aspects of optical periodic structures (PSs) are examined in reviews and reports of recent investigations. Sections are devoted to the electromagnetic theory of PSs, the propeties and applications of PSs, and classical and holographic PS manufacturing techniques. Topics discussed include the EM theory of gratings in anisotropic materials, replacement of very fine gratings by stratified layers, laser-beam sampling gratings with low absorption and specified efficiency, micromachined Si PSs for mm-wave and submm-wave applications, and numerical analysis of multistep dielectric gratings.

  19. Meltwater routing and the Atlantic meridional overturning circulation: A Gulf of Mexico perspective

    NASA Astrophysics Data System (ADS)

    Flower, B. P.; Williams, C.; Randle, N.; Hastings, D. W.

    2008-12-01

    Routing of low-salinity meltwater from the Laurentide Ice Sheet (LIS) into the North Atlantic via eastern outlets (e.g., St. Lawrence and Hudson River systems) and northern outlets (e.g., Hudson Bay and Arctic Ocean) is thought to have reduced Atlantic meridional overturning circulation (AMOC) and thereby triggered rapid regional to global climate change during the last glacial cycle. In contrast, southward meltwater flow to the Gulf of Mexico is generally thought to allow enhanced AMOC and warmer climates in the North Atlantic region. Situated at the outlet of the Mississippi River system, Orca Basin is ideally located to record meltwater input from the LIS. Orca Basin core MD02-2550 collected by the R/V Marion Dufresne in 2002 on IMAGES cruise VIII allows sub-centennial-scale records of Mg/Ca sea-surface temperature (SST) and δ18Oseawater back to ca. 23.9 ka. Accumulation rates average about 40 cm/k.y. Our current data extend from ca. 16.5-7 ka, with age control provided by 40 AMS radiocarbon dates (nearly all in stratigraphic order; calibrated using Calib 5.0.2). We use paired Mg/Ca and oxygen isotope data on Globigerinoides ruber to isolate changes in the oxygen isotopic composition of seawater. Four major episodic δ18O decreases of more than 2 per mil indicate substantial LIS meltwater input. Intervals of major meltwater discharge to the Gulf of Mexico do not appear to match known pulses of global sea level increase. However, abrupt reductions in southward meltwater input to the Gulf of Mexico seem to correlate with abrupt coolings in the North Atlantic region (e.g., Younger Dryas, Intra-Allerod cold period, and Oldest Dryas). In particular, a 3.5 per mil δ18O increase centered at 10,970 radiocarbon years B.P. (the "cessation event") appears to coincide with the onset of the Younger Dryas in European lakes and with Δ14C evidence from Cariaco Basin for AMOC reduction. Furthermore, recent results with the NCAR Community Climate System model (CCSM3) indicate

  20. Atlantic forcing of Pacific decadal variability

    NASA Astrophysics Data System (ADS)

    Kucharski, Fred; Ikram, Farah; Molteni, Franco; Farneti, Riccardo; Kang, In-Sik; No, Hyun-Ho; King, Martin P.; Giuliani, Graziano; Mogensen, Kristian

    2016-04-01

    This paper investigates the Atlantic Ocean influence on equatorial Pacific decadal variability. Using an ensemble of simulations, where the ICTPAGCM ("SPEEDY") is coupled to the NEMO/OPA ocean model in the Indo-Pacific region and forced by observed sea surface temperatures in the Atlantic region, it is shown that the Atlantic Multidecadal Oscillation (AMO) has had a substantial influence on the equatorial Pacific decadal variability. According to AMO phases we have identified three periods with strong Atlantic forcing of equatorial Pacific changes, namely (1) 1931-1950 minus 1910-1929, (2) 1970-1989 minus 1931-1950 and (3) 1994-2013 minus 1970-1989. Both observations and the model show easterly surface wind anomalies in the central Pacific, cooling in the central-eastern Pacific and warming in the western Pacific/Indian Ocean region in events (1) and (3) and the opposite signals in event (2). The physical mechanism for these responses is related to a modification of the Walker circulation because a positive (negative) AMO leads to an overall warmer (cooler) tropical Atlantic. The warmer (cooler) tropical Atlantic modifies the Walker circulation, leading to rising (sinking) and upper-level divergence (convergence) motion in the Atlantic region and sinking (rising) motion and upper-level convergence (divergence) in the central Pacific region.

  1. Estimation of return periods for extreme sea levels: a simplified empirical correction of the joint probabilities method with examples from the French Atlantic coast and three ports in the southwest of the UK

    NASA Astrophysics Data System (ADS)

    Pirazzoli, Paolo Antonio; Tomasin, Alberto

    2007-04-01

    The joint probability method (JPM) to estimate the probability of extreme sea levels (Pugh and Vassie, Extreme sea-levels from tide and surge probability. Proc. 16th Coastal Engineering Conference, 1978, Hamburg, American Society of Civil Engineers, New York, pp 911 930, 1979) has been applied to the hourly records of 13 tide-gauge stations of the tidally dominated Atlantic coast of France (including Brest, since 1860) and to three stations in the southwest of the UK (including Newlyn, since 1916). The cumulative total length of the available records (more than 426 years) is variable from 1 to 130 years when individual stations are considered. It appears that heights estimated with the JPM are almost systematically greater than the extreme heights recorded. Statistical analysis shows that this could be due: (1) to surge tide interaction (that may tend to damp surge values that occur at the time of the highest tide levels), and (2) to the fact that major surges often occur in seasonal periods that may not correspond to those of extreme astronomical tides. We have determined at each station empirical ad hoc correction coefficients that take into account the above two factors separately, or together, and estimated return periods for extreme water levels also at stations where only short records are available. For seven long records, for which estimations with other computing methods (e.g. generalized extreme value [GEV] distribution and Gumbel) can be attempted, average estimations of extreme values appear slightly overestimated in relation to the actual maximum records by the uncorrected JPM (+16.7 ± 7.2 cm), and by the Gumbel method alone (+10.3 ± 6.3 cm), but appear closer to the reality with the GEV distribution (-2.0 ± 5.3 cm) and with the best-fitting correction to the JPM (+2.9 ± 4.4 cm). Because the GEV analysis can hardly be extended to short records, it is proposed to apply at each station, especially for short records, the JPM and the site-dependent ad

  2. PRISM3 DOT1 Atlantic Basin Reconstruction

    USGS Publications Warehouse

    Dowsett, Harry; Robinson, Marci; Dwyer, Gary; Chandler, Mark; Cronin, Thomas

    2006-01-01

    PRISM3 DOT1 (Pliocene Research, Interpretation and Synoptic Mapping 3, Deep Ocean Temperature 1) provides a three-dimensional temperature reconstruction for the mid-Pliocene Atlantic basin, the first of several regional data sets that will comprise a global mid-Pliocene reconstruction. DOT1 is an alteration of modern temperature values for the Atlantic Ocean in 4 degree x 5 degree cells in 13 depth layers for December 1 based on Mg/Ca-derived BWT estimates from seventeen DSDP and ODP Sites and SST estimates from the PRISM2 reconstruction (Dowsett et al., 1999). DOT1 reflects a vaguely modern circulation system, assuming similar processes of deep-water formation; however, North Atlantic Deep Water (NADW) production is increased, and Antarctic Bottom Water (AABW) production is decreased. Pliocene NADW was approximately 2 degreesC warmer than modern temperatures, and Pliocene AABW was approximately 0.3 degreesC warmer than modern temperatures.

  3. Blue whale (Balaenoptera musculus) sounds from the North Atlantic

    NASA Astrophysics Data System (ADS)

    Mellinger, David K.; Clark, Christopher W.

    2003-08-01

    Sounds of blue whales were recorded from U.S. Navy hydrophone arrays in the North Atlantic. The most common signals were long, patterned sequences of very-low-frequency sounds in the 15-20 Hz band. Sounds within a sequence were hierarchically organized into phrases consisting of one or two different sound types. Sequences were typically composed of two-part phrases repeated every 73 s: a constant-frequency tonal ``A'' part lasting approximately 8 s, followed 5 s later by a frequency-modulated ``B'' part lasting approximately 11 s. A common sequence variant consisted only of repetitions of part A. Sequences were separated by silent periods averaging just over four minutes. Two other sound types are described: a 2-5 s tone at 9 Hz, and a 5-7s inflected tone that swept up in frequency to ca. 70 Hz and then rapidly down to 25 Hz. The general characteristics of repeated sequences of simple combinations of long-duration, very-low-frequency sound units repeated every 1-2 min are typical of blue whale sounds recorded in other parts of the world. However, the specific frequency, duration, and repetition interval features of these North Atlantic sounds are different than those reported from other regions, lending further support to the notion that geographically separate blue whale populations have distinctive acoustic displays.

  4. Deep South Atlantic carbonate chemistry and increased interocean deep water exchange during last deglaciation

    NASA Astrophysics Data System (ADS)

    Yu, Jimin; Anderson, Robert F.; Jin, Zhangdong; Menviel, Laurie; Zhang, Fei; Ryerson, Fredrick J.; Rohling, Eelco J.

    2014-04-01

    Carbon release from the deep ocean at glacial terminations is a critical component of past climate change, but the underlying mechanisms remain poorly understood. We present a 28,000-year high-resolution record of carbonate ion concentration, a key parameter of the global carbon cycle, at 5-km water depth in the South Atlantic. We observe similar carbonate ion concentrations between the Last Glacial Maximum and the late Holocene, despite elevated concentrations in the glacial surface ocean. This strongly supports the importance of respiratory carbon accumulation in a stratified deep ocean for atmospheric CO2 reduction during the last ice age. After ˜9 μmol/kg decline during Heinrich Stadial 1, deep South Atlantic carbonate ion concentration rose by ˜24 μmol/kg from the onset of Bølling to Pre-boreal, likely caused by strengthening North Atlantic Deep Water formation (Bølling) or increased ventilation in the Southern Ocean (Younger Drays) or both (Pre-boreal). The ˜15 μmol/kg decline in deep water carbonate ion since ˜10 ka is consistent with extraction of alkalinity from seawater by deep-sea CaCO3 compensation and coral reef growth on continental shelves during the Holocene. Between 16,600 and 15,000 years ago, deep South Atlantic carbonate ion values converged with those at 3.4-km water depth in the western equatorial Pacific, as did carbon isotope and radiocarbon values. These observations suggest a period of enhanced lateral exchange of carbon between the deep South Atlantic and Pacific Oceans, probably due to an increased transfer of momentum from southern westerlies to the Southern Ocean. By spreading carbon-rich deep Pacific waters around Antarctica for upwelling, invigorated interocean deep water exchange would lead to more efficient CO2 degassing from the Southern Ocean, and thus to an atmospheric CO2 rise, during the early deglaciation.

  5. Electronic structure of HgBa{sub 2}Ca{sub n-1}Cu{sub n}O{sub 2n+2} (n= 1, 2, 3) superconductor parent compounds from periodic hybrid density functional theory

    SciTech Connect

    Moreira, Iberio de P. R.; Rivero, Pablo; Illas, Francesc

    2011-02-21

    The electronic structure of HgBa{sub 2}Ca{sub n-1}Cu{sub n}O{sub 2n+2} (n= 1, 2, and 3) high T{sub c} superconductor parent compounds has been investigated by means of periodic hybrid density functional theory. Similar to other cuprates, these materials are predicted to exhibit an antiferromagnetic ground state with well localized S= 1/2 magnetic centers at the Cu{sup 2+} sites. However, the presence of the HgO{sub 2} structural units largely defines the nature of states dominating the energy range around Fermi energy. This results in a complex charge transfer character of the insulating gap which decreases when increasing the number of CuO{sub 2} planes in the unit cell, to the point that in the HgBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8} compound it becomes so small that one can claim that the resulting material is metallic. Nevertheless, the metallic character arises from the HgO{sub 2} structural units and coexists with the antiferromagnetic order arising from the localized spins at the Cu{sup 2+} sites.

  6. Response of the subtropical North Atlantic surface hydrography on deglacial and Holocene AMOC changes

    NASA Astrophysics Data System (ADS)

    Repschläger, Janne; Weinelt, Mara; Kinkel, Hanno; Andersen, Nils; Garbe-Schönberg, Dieter; Schwab, Christian

    2015-05-01

    The North Atlantic subtropical gyre (STG) circulates warm waters between 10 and 40°N and is a potential area of heat storage during periods of reduced North Atlantic Meridional Overturning Circulation (AMOC), when warm salt-rich waters are retained in the subtropics. In this study, we investigated multicentennial to millennial scale changes in subtropical North Atlantic hydrography in response to AMOC changes during the last deglaciation and early Holocene, using sediment cores MD08-3180 and GEOFAR KF16. The coring site (38°N) is situated near the boundary between transitional eastern North Atlantic waters and STG waters that is formed by the Azores Front. Hydrographic changes are reconstructed using new stable isotope data of benthic and subsurface dwelling planktonic foraminifera, Mg/Ca measurements on planktonic foraminifera, and planktonic foraminifera abundances that are supplemented with published sea surface temperature and stable isotope data. These multiproxy data indicate a close coupling between the latitudinal position of the northern STG boundary and deglacial AMOC modes. During weak AMOC phases (Heinrich event 1, Younger Dryas (YD), 8.2 ka event), Northern Hemisphere subpolar water reached down to the northern STG boundary, displacing the boundary southward. During the Bølling-Allerød warm period, a strong warming trend of the subtropical region to 19°C is observed. A cooling of the sea surface temperature by 6°C during the YD is accompanied by ongoing northward transport of warm subsurface water that might have contributed to the restart of AMOC.

  7. Late Holocene climate change in the western Mediterranean: centennial-scale vegetation and North Atlantic Oscillation variability

    NASA Astrophysics Data System (ADS)

    Ramos Román, M. J.; Jimenez-Moreno, G.; Anderson, R. S.; García-Alix, A.; Toney, J. L.; Jiménez-Espejo, F. J. J.; Carrión, J. S.

    2015-12-01

    Sediments from alpine peat bogs and lakes from the Sierra Nevada in southeastern Spain (western Mediterranean area) have been very informative in terms of how vegetation and wetland environments were impacted by past climate change. Recently, many studies try to find out the relationship between solar activity, atmosphere and ocean dynamics and changes in the terrestrial environments. The Mediterranean is a very sensitive area with respect to atmospheric dynamics due to (1) its location, right in the boundary between subtropical and temperate climate systems and (2) the North Atlantic Oscillation (NAO) is one of the main mechanism that influence present climate in this area. Here we present a multi-proxy high-resolution study from Borreguil de la Caldera (BdlC), a peat bog that records the last ca. 4500 cal yr BP of vegetation, fire, human impact and climate history from the Sierra Nevada. The pollen, charcoal and non-pollen palynomorphs (NPPs) reconstruction in the BdlC-01 record evidence relative humidity changes in the last millennia interrupting the late Holocene aridification trend. This study shows a relative arid period between ca. 4000 and 3100 cal yr BP; the Iberian Roman humid period (ca. 2600 to 1600 cal yr BP); a relative arid period during the Dark Ages (from ca. AD 500 to AD 900) and Medieval Climate Anomaly (from ca. AD 900 to ca. AD 1300) and predominantly wetter conditions corresponding with The Little Ice Age period (from ca. AD 1300 to AD 1850). This climate variability could be explained by centennial scale changes in the NAO and solar activity.

  8. Climatic and limnological changes associated with the Younger Dryas in Atlantic Canada

    SciTech Connect

    Wilson, S.E.; Smol, J.P.; Walker, I.R.

    1993-03-01

    Pollen, diatom and chironomid fossils from the sediments of a core from Brier Island Bog Lake, Nova Scotia were studied in an attempt to relate changes in microfossil composition to a climatic cooling in Atlantic Canada correlative with the European Younger Dryas ca. 10 to 11 ka. Our paleolimnological data were then compared to similar types of data from Splan Pond, New Brunswick to determine if there were any significant differences between a coastal and a more inland site. Nonarboreal pollen was dominant throughout the Brier Island core and the interval 10.0-11.0 ka did not show the typical decline in Picea and increases in tundra-like vegetation characteristic of many sites in Atlantic Canada. However, the limnological indicators did undergo marked changes in taxon composition. The chironomid assemblage was initially dominated by shallow-water, warm-adapted chironomid taxa followed by abundant Sergentia (a cold stenotherm) during 10-11 ka. Sergentia disappeared in the {open_quotes}post Younger Dryas{close_quotes} interval and the warm-adapted genera resumed dominance. Chironomid-inferred paleotemperature reconstructions revealed that at both Brier Island Bog Lake and Splan Pond, summer surface-water temperatures dropped abruptly to between 13 and 17{degrees}C during the 10-11 ka interval, suggesting that a cooler climate was present in Atlantic Canada correlative with the European Younger Dryas. Diatom assemblage changes during the same period corroborate the occurrence of limnological fluctuations. 40 refs., 8 figs., 1 tab.

  9. Rain rate statistics and fade distributions at 20 and 30 GHz derived from a network of rain gauges in the Mid-Atlantic coast over a five year period

    NASA Technical Reports Server (NTRS)

    Goldhirsh, Julius; Krichevsky, Vladimir; Gebo, Norman E.

    1992-01-01

    A network of ten tipping bucket rain gauges located within a grid 70 km north-south and 47 km east-west in the Mid-Atlantic coast of the United States was used to analyze rain rate and modeled slant path attenuation distributions at 20 and 30 GHz. It was shown that, for realistic fade margins at 20 GHz and above, the variable integration times results are adequate to estimate slant path attenuations using models which require 1 min averages. Crane's Global Model was used to derive fade distributions at 20 and 30 GHz.

  10. Subsurface warming in the subpolar North Atlantic during rapid climate events in the Early and Mid-Pleistocene

    NASA Astrophysics Data System (ADS)

    Hernández-Almeida, Iván; Sierro, Francisco; Cacho, Isabel; Abel Flores, José

    2014-05-01

    A new high-resolution reconstruction of the temperature and salinity of the subsurface waters using paired Mg/Ca-δ18O measurements on the planktonic foraminifera Neogloboquadrina pachyderma sinistrorsa (sin.) was conducted on a deep-sea sediment core in the subpolar North Atlantic (Site U1314). This study aims to reconstruct millennial-scale subsurface hydrography variations during the Early and Mid-Pleistocene (MIS 31-19). These rapid climate events are characterized by abrupt shifts between warm/cold conditions, and ice-sheet oscillations, as evidenced by major ice rafting events recorded in the North Atlantic sediments (Hernández-Almeida et al., 2012), similar to those found during the Last Glacial period (Marcott et al, 2011). The Mg/Ca derived paleotemperature and salinity oscillations prior and during IRD discharges at Site U1314 are related to changes in intermediate circulation. The increases in Mg/Ca paleotemperatures and salinities during the IRD event are preceded by short episodes of cooling and freshening of subsurface waters. The response of the AMOC to this perturbation is an increased of warm and salty water coming from the south, transported to high latitudes in the North Atlantic beneath the thermocline. This process is accompanied by a southward shift in the convection cell from the Nordic Seas to the subpolar North Atlantic and better ventilation of the North Atlantic at mid-depths. Poleward transport of warm and salty subsurface subtropical waters causes intense basal melting and thinning of marine ice-shelves, that culminates in large-scale instability of the ice sheets, retreat of the grounding line and iceberg discharge. The mechanism proposed involves the coupling of the AMOC with ice-sheet dynamics, and would explain the presence of these fluctuations before the establishment of high-amplitude 100-kyr glacial cycles. Hernández-Almeida, I., Sierro, F.J., Cacho, I., Flores, J.A., 2012. Impact of suborbital climate changes in the North

  11. The Evolution of the South Atlantic.

    ERIC Educational Resources Information Center

    McCoy, Floyd W.; Rabinowitz, Philip D.

    1979-01-01

    The development of the South Atlantic continental margins through geological time is discussed in a series of three time slices, all of which depict various characteristics in the initial formation of this margin during the Cretaceous period (180 to 65 million years ago) of the Mesozoic era. (BT)

  12. Retracing the Quaternary history of sea-level changes in the Spanish Mediterranean-Atlantic coasts: Geomorphological and sedimentological approach

    NASA Astrophysics Data System (ADS)

    Zazo, C.; Goy, J. L.; Dabrio, C. J.; Lario, J.; González-Delgado, J. A.; Bardají, T.; Hillaire-Marcel, C.; Cabero, A.; Ghaleb, B.; Borja, F.; Silva, P. G.; Roquero, E.; Soler, V.

    2013-08-01

    This study analyses coastal geomorphic responses to the various sea-level changes that occurred throughout the Quaternary period in the Mediterranean and Atlantic coasts of Spain. Particular emphasis is paid to the geomorphic and stratigraphic record of the changes in amplitude, duration and frequency associated with the major gradual climate changes observed in marine cores and ice oxygen-isotope records during the Early and Middle Pleistocene (ca. 2.6 Myr; ca. ~ 1.4-0.8 Myr; ca. ~ 0.4-0.2 Myr) and also with the rapid and abrupt Late Pleistocene and Holocene climate changes. With this aim, the best preserved and most complete sedimentary sequences known in the Spanish Mediterranean and Atlantic coasts covering diverse geodynamic and climatic contexts were selected and analyses. This study is mainly based on field investigation of geomorphic, sedimentologic and stratigraphic features of mapped morphosedimentary units, combined with reliable chronological data. The analyses include the interpretation of sedimentary environments, the 3-D reconstruction of facies and morphosedimentary unit arrangement, paying special attention to the lateral geomorphic relationships between marine and terrestrial morphosedimentary units developed during interglacials under sea-level highstand scenarios. The interglacials occurred during four key Quaternary periods might be related with major gradual changes associated with glacial climate cycles reported from marine and ice oxygen-isotope records. Almost coeval changes in geomorphological styles are reported from all studied areas, regardless of their specific geodynamic context. Results from the Mediterranean realm suggest that this area is more sensitive to climatic and sea level variability than the Spanish Atlantic coast, particularly in the case of rapid and abrupt changes.

  13. Evidence of multidecadal climate variability and the Atlantic Multidecadal Oscillation from a Gulf of Mexico sea-surface temperature-proxy record

    USGS Publications Warehouse

    Poore, R.Z.; DeLong, K.L.; Richey, J.N.; Quinn, T.M.

    2009-01-01

    A comparison of a Mg/Ca-based sea-surface temperature (SST)-anomaly record from the northern Gulf of Mexico, a calculated index of variability in observed North Atlantic SST known as the Atlantic Multidecadal Oscillation (AMO), and a tree-ring reconstruction of the AMO contain similar patterns of variation over the last 110 years. Thus, the multidecadal variability observed in the instrumental record is present in the tree-ring and Mg/Ca proxy data. Frequency analysis of the Gulf of Mexico SST record and the tree-ring AMO reconstruction from 1550 to 1990 found similar multidecadal-scale periodicities (???30-60 years). This multidecadal periodicity is about half the observed (60-80 years) variability identified in the AMO for the 20th century. The historical records of hurricane landfalls reveal increased landfalls in the Gulf Coast region during time intervals when the AMO index is positive (warmer SST), and decreased landfalls when the AMO index is negative (cooler SST). Thus, we conclude that alternating intervals of high and low hurricane landfall occurrences may continue on multidecadal timescales along the northern Gulf Coast. However, given the short length of the instrumental record, the actual frequency and stability of the AMO are uncertain, and additional AMO proxy records are needed to establish the character of multidecadal-scale SST variability in the North Atlantic. ?? 2009 US Government.

  14. 3. VIEW LOOKING NORTH WEST OVER CENTRAL ATLANTIC WITH ATLANTIC ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. VIEW LOOKING NORTH WEST OVER CENTRAL ATLANTIC WITH ATLANTIC OCEAN IN THE FOREGROUND. DENNIS HOTEL, BLENHEIM HOTEL, AND MARLBOROUGH HOTEL (LEFT TO RIGHT) ARE LOCATED IN THE CENTER OF THE PHOTOGRAPH. THE CLARIDGE HOTEL IS THE HIGHRISE IMMEDIATELY TO THE RIGHT OF THE MARLBOROUGH HOTEL - Marlborough, Blenheim & Dennis Hotels (aerial views), Between Park Place, Michigan Avenue & Boardwalk, Atlantic City, Atlantic County, NJ

  15. Tropical Atlantic temperature seasonality at the end of the last interglacial.

    PubMed

    Felis, Thomas; Giry, Cyril; Scholz, Denis; Lohmann, Gerrit; Pfeiffer, Madlene; Pätzold, Jürgen; Kölling, Martin; Scheffers, Sander R

    2015-01-01

    The end of the last interglacial period, ~118 kyr ago, was characterized by substantial ocean circulation and climate perturbations resulting from instabilities of polar ice sheets. These perturbations are crucial for a better understanding of future climate change. The seasonal temperature changes of the tropical ocean, however, which play an important role in seasonal climate extremes such as hurricanes, floods and droughts at the present day, are not well known for this period that led into the last glacial. Here we present a monthly resolved snapshot of reconstructed sea surface temperature in the tropical North Atlantic Ocean for 117.7±0.8 kyr ago, using coral Sr/Ca and δ(18)O records. We find that temperature seasonality was similar to today, which is consistent with the orbital insolation forcing. Our coral and climate model results suggest that temperature seasonality of the tropical surface ocean is controlled mainly by orbital insolation changes during interglacials. PMID:25609544

  16. Tropical Atlantic temperature seasonality at the end of the last interglacial

    PubMed Central

    Felis, Thomas; Giry, Cyril; Scholz, Denis; Lohmann, Gerrit; Pfeiffer, Madlene; Pätzold, Jürgen; Kölling, Martin; Scheffers, Sander R.

    2015-01-01

    The end of the last interglacial period, ~118 kyr ago, was characterized by substantial ocean circulation and climate perturbations resulting from instabilities of polar ice sheets. These perturbations are crucial for a better understanding of future climate change. The seasonal temperature changes of the tropical ocean, however, which play an important role in seasonal climate extremes such as hurricanes, floods and droughts at the present day, are not well known for this period that led into the last glacial. Here we present a monthly resolved snapshot of reconstructed sea surface temperature in the tropical North Atlantic Ocean for 117.7±0.8 kyr ago, using coral Sr/Ca and δ18O records. We find that temperature seasonality was similar to today, which is consistent with the orbital insolation forcing. Our coral and climate model results suggest that temperature seasonality of the tropical surface ocean is controlled mainly by orbital insolation changes during interglacials. PMID:25609544

  17. Tropical Atlantic temperature seasonality at the end of the last interglacial

    NASA Astrophysics Data System (ADS)

    Felis, Thomas; Giry, Cyril; Scholz, Denis; Lohmann, Gerrit; Pfeiffer, Madlene; Pätzold, Jürgen; Kölling, Martin; Scheffers, Sander R.

    2015-04-01

    The end of the last interglacial period, ~118 kyr ago, was characterized by substantial ocean circulation and climate perturbations resulting from instabilities of polar ice sheets. It has been suggested that these perturbations at the end of the last interglacial are crucial for a better understanding of future climate change. The seasonal temperature changes of the tropical ocean, however, which play an important role in seasonal climate extremes such as hurricanes, floods and droughts at the present day, are not well known for this period that led into the last glacial. Here we present a monthly resolved snapshot of reconstructed sea surface temperature in the tropical North Atlantic Ocean for 117.7 ± 0.8 kyr ago, using coral Sr/Ca and δ18O records in a precisely 230Th/U dated shallow-water fossil coral recovered from the southern Caribbean (Bonaire). We find that temperature seasonality was similar to today, which is consistent with the orbital insolation forcing. Our coral records and simulations with a coupled atmosphere-ocean general circulation model (COSMOS) indicate an orbital control on temperature seasonality in the tropical North Atlantic at the end of the last interglacial, despite the large-scale perturbations of ocean circulation and climate during this period, and suggest that temperature seasonality of the tropical surface ocean is controlled mainly by orbital insolation changes during interglacials.

  18. Tracing the history of the South Atlantic Anomaly on an Archeomagnetic Timescale

    NASA Astrophysics Data System (ADS)

    Tarduno, J. A.; Huffman, T. N.; Watkeys, M. K.; Cottrell, R. D.; Wagner, C. L.

    2013-12-01

    The dramatic decay of the dipole geomagnetic field during the last 160 years has been driven by growth of a low intensity region in the South Atlantic that we refer to as the South Atlantic Anomaly (SAA). The rapid decay relative to ohmic resistance has motivated models of core flux expulsion. A prominent core patch of reversed polarity flux beneath South Africa has been called for on the basis of analyses of modern field data recorded by satellites. The rapid decay and similarity of the SAA to patterns seen in some numerical simulations of reversals has driven speculation that Earth is heading toward a field reversal. Putting the SAA in a longer temporal context, however, has been difficult because of the lack of archeomagnetic data from this key region of the Southern Hemisphere. To address this data deficiency, we report the first archeomagnetic curve from Early, Middle and Late Iron Age sites from South Africa, dated between ca. 700 and 1650 AD. The floors of burnt structures (huts, grain bins and kraals) resulting from ritualistic village cleansing provide opportunities to obtain directional data. Directions reveal times of modest change (ca. 0.04 degrees/yr, ca. 730 to 1225 AD), followed by a time of rapid change (ca. 0.11 to 0.15 degrees/yr, 1225 to 1580 AD). Preliminary paleointensity data from the burnt structures and coeval pottery show field strengths that are comparable to the lowest values seen in the SAA today during the period of rapid field directional change. Implications of these data for core processes will be discussed.

  19. Catastrophic meltwater discharge down the Hudson Valley: A potential trigger for the Intra-Allerød cold period

    NASA Astrophysics Data System (ADS)

    Donnelly, Jeffrey P.; Driscoll, Neal W.; Uchupi, Elazar; Keigwin, Lloyd D.; Schwab, William C.; Thieler, E. Robert; Swift, Stephen A.

    2005-02-01

    Glacial freshwater discharge to the Atlantic Ocean during deglaciation may have inhibited oceanic thermohaline circulation, and is often postulated to have driven climatic fluctuations. Yet attributing meltwater-discharge events to particular climate oscillations is problematic, because the location, timing, and amount of meltwater discharge are often poorly constrained. We present evidence from the Hudson Valley and the northeastern U.S. continental margin that establishes the timing of the catastrophic draining of Glacial Lake Iroquois, which breached the moraine dam at the Narrows in New York City, eroded glacial lake sediments in the Hudson Valley, and deposited large sediment lobes on the New York and New Jersey continental shelf ca. 13,350 yr B.P. Excess 14C in Cariaco Basin sediments indicates a slowing in thermohaline circulation and heat transport to the North Atlantic at that time, and both marine and terrestrial paleoclimate proxy records around the North Atlantic show a short-lived (<400 yr) cold event (Intra-Allerød cold period) that began ca. 13,350 yr B.P. The meltwater discharge out the Hudson Valley may have played an important role in triggering the Intra-Allerød cold period by diminishing thermohaline circulation.

  20. Catastrophic meltwater discharge down the Hudson Valley: a potential trigger for the Intra-Allerød cold period

    USGS Publications Warehouse

    Donnelly, Jeffrey P.; Driscoll, Neal W.; Uchupi, Elazar; Keigwin, Loyd D.; Schwab, William C.; Thieler, E. Robert; Swift, Stephen A.

    2005-01-01

    Glacial freshwater discharge to the Atlantic Ocean during deglaciation may have inhibited oceanic thermohaline circulation, and is often postulated to have driven climatic fluctuations. Yet attributing meltwater-discharge events to particular climate oscillations is problematic, because the location, timing, and amount of meltwater discharge are often poorly constrained. We present evidence from the Hudson Valley and the northeastern U.S. continental margin that establishes the timing of the catastrophic draining of Glacial Lake Iroquois, which breached the moraine dam at the Narrows in New York City, eroded glacial lake sediments in the Hudson Valley, and deposited large sediment lobes on the New York and New Jersey continental shelf ca. 13,350 yr B.P. Excess 14C in Cariaco Basin sediments indicates a slowing in thermohaline circulation and heat transport to the North Atlantic at that time, and both marine and terrestrial paleoclimate proxy records around the North Atlantic show a short-lived (<400 yr) cold event (Intra-Aller??d cold period) that began ca. 13,350 yr B.P. The meltwater discharge out the Hudson Valley may have played an important role in triggering the Intra-Aller??d cold period by diminishing thermohaline circulation. ?? 2005 Geological Society of America.

  1. Sensitivity of the Oceanic Turbulent Boundary Layer to Cyclic Insolation Change with Response Periods of 23 to 2.5 Ky: an Equatorial Atlantic Record for the Last 200 Ka

    NASA Technical Reports Server (NTRS)

    Mcintyre, Andrew

    1990-01-01

    Time series of sea-surface temperature in cores sited beneath the region of maximum divergence centered on 10 degrees W are characterized by two sets of periodic signals. The dominant signal is centered on a period of 23 Ky and is coherent with and lags, approx. 2.5 Ky, the precessional component of orbitally controlled insolation. The subdominant periods occur between 4.0 and 2.5 Ky. Both sets of signals record variation in the seasonal intensity of oceanic divergence modulated by variation in tropical easterly intensity. The longer periods are a response to precessional forcing. The forcing responsible for the shorter periods is unknown.

  2. Very early Archean crustal-accretion complexes preserved in the North Atlantic craton

    SciTech Connect

    Nutman, A.P. ); Collerson, K.D. )

    1991-08-01

    The North Atlantic craton contains very early Archean supracrustal rocks, orthogneisses, and massive ultramafic rocks. Most units of supracrustal rocks are dominated by mafic volcanic rocks, layered gabbros, and banded iron formations, bust some also contain abundant felsic volcanic-sedimentary rocks, quartzites, and marbles. Some quartzites contain detrital zircons derived from rocks identical in age to felsic volcanic-sedimentary rocks in these sequences (ca. 3800 Ma) and also from older (ca. 3850 Ma) sources. The presence of the ca. 3850 Ma detrital zircons suggests that the supracrustal units containing them were deposited on, or close to, ca. 3850 Ma sialic crust. The massive ultramafic rocks have chemical affinities to upper mantle rocks. The voluminous suites of tonalitic gneisses are dominated by 3700-3730 Ma bodies that intrude the supracrustal sequences, but they also locally contain components with ages between 3820 and 3920 Ma. The diverse supracrustal units, upper mantle rocks, and {ge} 3820 Ma components in the gneisses were tectonically interleaved in very early Archean convergent plate boundaries, giving rise to accretion complexes. In the period 3700-3730 Ma, voluminous tonalitic magmas produced by partial melting of predominantly mafic rocks in the base of the accretion complexes were emplaced at higher levels, forming juvenile continental crust and leaving behind a refractory lower crustal to upper mantle substrate.

  3. Sea Surface Temperature Seesaw between the Subpolar North Atlantic and the Norwegian Sea during the Late Holocene

    NASA Astrophysics Data System (ADS)

    Miettinen, A.; Divine, D.; Koc, N.; Godtliebsen, F.; Hall, I. R.

    2012-12-01

    August sea surface temperature (aSST) record based on fossil diatom assemblages is generated from a 2800-year-long marine sediment core Rapid 21-COM from the Iceland Basin, in the northern subpolar North Atlantic. The record has a resolution of 2-10 years for interval 800-2004 AD representing the highest-resolution diatom SST reconstruction from the subpolar North Atlantic for this period, and 40 years for interval 800 BC-800 AD. The record is compared with the high-resolution aSST record from core CR948/2011 from the Vøring Plateau, in the Norwegian Sea, to explore the variability of the aSST gradient between these areas during the late Holocene. The aSST records show persistent opposite climate trends toward warming in the subpolar North Atlantic and cooling in the Norwegian Sea during the late Holocene. An apparent tendency to coherent antiphased aSST variations between the sites is also revealed for the shorter time scales implying an aSST seesaw between the northern subpolar North Atlantic and the Norwegian Sea to operate during the late Holocene. At the multicentennial scale of aSST variability of 600-900 years, the records are nearly in antiphase with warmer (colder) periods in the subpolar North Atlantic corresponding to the colder (warmer) periods in the Norwegian Sea. At the shorter time scale of 200-450 years, the records display a phase-locked behaviour with a tendency for the positive aSST anomalies in the Norwegian Sea to lead by ca. 30 years the negative aSST anomalies in the subpolar North Atlantic. This aSST seesaw might have had a strong effect on two major climate anomalies in the northwest Europe during the past Millennium: Medieval Warm Period (MWP) and the Little Ice Age (LIA). During the MWP warming of the sea surface in the Norwegian Sea occurred in parallel with cooling in the northern subpolar North Atlantic, whereas the opposite pattern emerged during the LIA. Coupled changes in aSST between the northern subpolar North Atlantic and the

  4. 600 yr High-Resolution Climate Reconstruction of the Atlantic Multidecadal Oscillation deduced from a Puerto Rican Speleothem

    NASA Astrophysics Data System (ADS)

    Vieten, Rolf; Winter, Amos; Scholz, Denis; Black, David; Spoetl, Christoph; Winterhalder, Sophie; Koltai, Gabriella; Schroeder-Ritzrau, Andrea; Terzer, Stefan; Zanchettin, Davide; Mangini, Augusto

    2016-04-01

    periods of decreased rainfall. Before 1800 there were two intervals of increased Mg/Ca and δ13C values (dryer conditions) lasting several decades in our speleothem record centered around 1680 CE and 1470 CE. The elevated ratios indicate that drier conditions than present may have occurred in the region during periods of warm Atlantic surface waters.

  5. Similarities and dissimilarities between the last two deglaciations and interglaciations in the North Atlantic region

    NASA Astrophysics Data System (ADS)

    Martrat, Belen; Jimenez-Amat, Patricia; Zahn, Rainer; Grimalt, Joan O.

    2014-09-01

    Sea surface temperatures (SSTs) recorded by alkenones and oxygen isotopes in the Alboran basin are used here to describe, at an unprecedented fine temporal resolution, the present interglaciation (PIG, initiated at 11.7 ka BP), the last interglaciation (LIG, onset approximately at 129 ka) and respective deglaciations. Similarities and dissimilarities in the progression of these periods are reviewed in comparison with ice cores and stalagmites. Cold spells coeval with the Heinrich events (H) described in the North Atlantic include multi-decadal scale oscillations not previously obvious (up to 4 °C in less than eight centuries within the stadials associated with H1 and H11, ca 133 ka and 17 ka respectively). These abrupt oscillations precede the accumulation of organic rich layers deposited when perihelion moves from alignment with NH spring equinox to the summer solstice, a reference for deglaciations. Events observed during the last deglaciation at 17 ka, 14.8 ka and 11.7 ka are reminiscent of events occurred during the penultimate deglaciation at ca 136 ka, 132 ka and 129 ka, respectively. The SST trend during the PIG is no more than 2 °C (from 20 °C to 18 °C; up to -0.2 °C/ka). The trend is steeper during the LIG, i.e. up to a 5 °C change from the early interglaciation to immediately before the glacial inception (from 23 °C to 18 °C; up to -0.4 °C/ka). Events are superimposed upon a long term trend towards colder SSTs, beginning with SST maxima followed by temperate periods until perihelion aligned with the NH autumn equinox (before ca 5.3 ka for the PIG and 121 ka for the LIG). A cold spell of around eight centuries at 2.8 ka during the PIG was possibly mimicked during the LIG at ca 118 ka by a SST fall of around 1 °C in a millennium. These events led interglacial SST to stabilise at around 18 °C. The glacial inception, barely evident at the beginning ca 115 ka (North Atlantic event C25, after perihelion passage in the NH winter solstice), culminated

  6. South Atlantic interbasin exchange

    NASA Technical Reports Server (NTRS)

    Rintoul, Stephen Rich

    1991-01-01

    The exchange of mass and heat between the South Atlantic and the neighboring ocean basins was estimated using hydrographic data and inverse methods, in order to gain information on the links between the deep-water formation processes occurring within the Atlantic and the global thermohaline circulation. Results demonstrate that the global thermohaline cell associated with the formation and export of North Atlantic deep water (NADW) is closed primarily by a 'cold water path' in which deep water leaving the Atlantic ultimately returns as intermediate water entering the basin through Drake Passage. This conclusion conflicts with the suggestion by Gordon (1986) that the global thermohaline circulation associated with the formation of NADW is closed primarily by a 'warm water path', in which the export of NADW is compensated by an inflow of warm Indian Ocean thermocline water south of Africa.

  7. Early Holocene variability in the Arctic Gateway - High-resolution records reflecting Atlantic Water advection and ice coverage

    NASA Astrophysics Data System (ADS)

    Spielhagen, Robert F.; Bauch, Henning A.; Maudrich, Martin; Not, Christelle; Telesinski, Maciej M.; Werner, Kirstin

    2015-04-01

    The Arctic Gateway between Greenland and Svalbard is the main passage for the advection of Atlantic Water to the Arctic Ocean. Water temperature and intensity of this advection largely determine the degree of ice coverage which is fed by sea ice export from the north. Supported by a maximum in insolation, the Early Holocene was a period of extraordinarily strong advection and relatively high near-surface water temperatures in the eastern Nordic Seas (cf. Risebrobakken et al., 2011, Paleoceanography v. 26). Here we present a synthesis of radiocarbon-dated records from the northern and western part of this area, reaching from the SW Greenland Sea (73°N) to the Yermak Plateau (81°N) and revealing temporal and spatial differences in the development of the so-called Holocene Thermal Maximum (HTM). In the northern part of this region, the HTM started ca. 11-10.5 ka as indicated by rapidly increasing amounts of subpolar planktic foraminifers in the sediments. In the eastern Fram Strait and on the Yermak Plateau, our records of (sub)millennial scale resolution show that the maximum influx terminated already 2,000 years later (9-8 ka). Most likely, this development went along with a N-S relocation of the sea ice margin. According to the current stratigraphic model for a core with submillennial-scale resolution from Vesterisbanken seamount (73°N) in the Greenland Sea, the timing was different there. Increasing total amounts of planktic foraminifers in the sediment indicate an early (11-10 ka) reduction in sea ice coverage also in this region. However, evidence from subpolar planktic foraminifers for maximum Atlantic Water advection is younger (9-6 ka) than in the north. Apparently, the site in the SW Greenland Sea was affected by Atlantic Water in the Greenland Gyre that decoupled from the northward flowing Norwegian Atlantic Current/Westspitsbergen Current south of the Fram Strait. Thus, in a suite of events, strong Atlantic Water advection first affected the

  8. 76 FR 17789 - Fisheries of the Northeastern United States; Atlantic Bluefish Fishery; 2011 Atlantic Bluefish...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-31

    ... Register on January 14, 2011 (76 FR 2640), with a 15-day comment period which ended on January 31, 2011...), the NMFS Assistant Administrator has determined that this final rule is consistent with the Atlantic... Assistant Administrator for Regulatory Programs, National Marine Fisheries Service. For the reasons set...

  9. 76 FR 1153 - Atlantic Grid Operations A LLC, Atlantic Grid Operations B LLC, Atlantic Grid Operations C LLC...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-07

    ... Energy Regulatory Commission Atlantic Grid Operations A LLC, Atlantic Grid Operations B LLC, Atlantic Grid Operations C LLC, Atlantic Grid Operations D LLC and Atlantic Grid Operations E LLC; Notice of... (Commission) Rules of Practice and Procedure, 18 CFR 385.207, and Order No. 679,\\1\\ Atlantic Grid Operations...

  10. Medieval Warm Period, Little Ice Age and 20th century temperature variability from Chesapeake Bay

    USGS Publications Warehouse

    Cronin, T. M.; Dwyer, G.S.; Kamiya, T.; Schwede, S.; Willard, D.A.

    2003-01-01

    We present paleoclimate evidence for rapid (< 100 years) shifts of ??? 2-4??C in Chesapeake Bay (CB) temperature ???2100, 1600, 950, 650, 400 and 150 years before present (years BP) reconstructed from magnesium/calcium (Mg/Ca) paleothermometry. These include large temperature excursions during the Little Ice Age (???1400-1900 AD) and the Medieval Warm Period (???800-1300 AD) possibly related to changes in the strength of North Atlantic thermohaline circulation (THC). Evidence is presented for a long period of sustained regional and North Atlantic-wide warmth with low-amplitude temperature variability between ???450 and 1000 AD. In addition to centennial-scale temperature shifts, the existence of numerous temperature maxima between 2200 and 250 years BP (average ???70 years) suggests that multi-decadal processes typical of the North Atlantic Oscillation (NAO) are an inherent feature of late Holocene climate. However, late 19th and 20th century temperature extremes in Chesapeake Bay associated with NAO climate variability exceeded those of the prior 2000 years, including the interval 450-1000 AD, by 2-3??C, suggesting anomalous recent behavior of the climate system. ?? 2002 Elsevier Science B.V. All rights reserved.

  11. Atlantic multi-decadal oscillation covaries with Agulhas leakage

    SciTech Connect

    Biastoch, Arne; Durgadoo, Jonathan V.; Morrison, Adele K.; van Sebille, Erik; Weijer, Wilbert; Griffies, Stephen M.

    2015-12-10

    The interoceanic transfer of seawater between the Indian Ocean and the Atlantic, ‘Agulhas leakage’, forms a choke point for the overturning circulation in the global ocean. Here, by combining output from a series of high-resolution ocean and climate models with in situ and satellite observations, we construct a time series of Agulhas leakage for the period 1870–2014. The time series demonstrates the impact of Southern Hemisphere westerlies on decadal timescales. Agulhas leakage shows a correlation with the Atlantic Multi-decadal Oscillation on multi-decadal timescales; the former leading by 15 years. Lastly, this is relevant for climate in the North Atlantic.

  12. Atlantic multi-decadal oscillation covaries with Agulhas leakage

    PubMed Central

    Biastoch, Arne; Durgadoo, Jonathan V.; Morrison, Adele K.; van Sebille, Erik; Weijer, Wilbert; Griffies, Stephen M.

    2015-01-01

    The interoceanic transfer of seawater between the Indian Ocean and the Atlantic, ‘Agulhas leakage', forms a choke point for the overturning circulation in the global ocean. Here, by combining output from a series of high-resolution ocean and climate models with in situ and satellite observations, we construct a time series of Agulhas leakage for the period 1870–2014. The time series demonstrates the impact of Southern Hemisphere westerlies on decadal timescales. Agulhas leakage shows a correlation with the Atlantic Multi-decadal Oscillation on multi-decadal timescales; the former leading by 15 years. This is relevant for climate in the North Atlantic. PMID:26656850

  13. Atlantic multi-decadal oscillation covaries with Agulhas leakage

    NASA Astrophysics Data System (ADS)

    Biastoch, Arne; Durgadoo, Jonathan V.; Morrison, Adele K.; van Sebille, Erik; Weijer, Wilbert; Griffies, Stephen M.

    2015-12-01

    The interoceanic transfer of seawater between the Indian Ocean and the Atlantic, `Agulhas leakage', forms a choke point for the overturning circulation in the global ocean. Here, by combining output from a series of high-resolution ocean and climate models with in situ and satellite observations, we construct a time series of Agulhas leakage for the period 1870-2014. The time series demonstrates the impact of Southern Hemisphere westerlies on decadal timescales. Agulhas leakage shows a correlation with the Atlantic Multi-decadal Oscillation on multi-decadal timescales; the former leading by 15 years. This is relevant for climate in the North Atlantic.

  14. Atlantic multi-decadal oscillation covaries with Agulhas leakage.

    PubMed

    Biastoch, Arne; Durgadoo, Jonathan V; Morrison, Adele K; van Sebille, Erik; Weijer, Wilbert; Griffies, Stephen M

    2015-01-01

    The interoceanic transfer of seawater between the Indian Ocean and the Atlantic, 'Agulhas leakage', forms a choke point for the overturning circulation in the global ocean. Here, by combining output from a series of high-resolution ocean and climate models with in situ and satellite observations, we construct a time series of Agulhas leakage for the period 1870-2014. The time series demonstrates the impact of Southern Hemisphere westerlies on decadal timescales. Agulhas leakage shows a correlation with the Atlantic Multi-decadal Oscillation on multi-decadal timescales; the former leading by 15 years. This is relevant for climate in the North Atlantic. PMID:26656850

  15. Radiocarbon age of waters in the deep Atlantic revisited

    SciTech Connect

    Broecker, W.S.; Virgilio, A. ); Peng, T.H. )

    1991-01-01

    The authors use a simple box model to evaluate the impact of temporal changes of the atmosphere's {sup 14}C/C on ventilation fluxes for the deep Atlantic calculated from radiocarbon measurements. The conclusion is that despite the fact that over the 300 year period from 1650 to 1950 the atmosphere's radiocarbon content declined at the same rate as radiocarbon decays, this temporal change has a relatively small impact (10-15%) on radiocarbon-based estimates of the ventilation rate of the deep Atlantic. The reason is that the radiocarbon content of the source waters for deep Atlantic are reasonably well buffered against changes in atmospheric {sup 14}C/C.

  16. Deglacial Subsurface Temperature Change in the Tropical North Atlantic Linked to Atlantic Meridional Overturning Circulation Variability

    NASA Astrophysics Data System (ADS)

    Schmidt, M. W.; Chang, P.; Otto-Bliesner, B. L.

    2010-12-01

    Coupled ocean-atmosphere modeling experiments indicate that Atlantic meridional overturning circulation (AMOC) variability is tightly coupled to abrupt tropical North Atlantic (TNA) climate change through both atmospheric and oceanic processes (Zhang, 2007; Chang et al., 2008; and Chiang et al., 2008). While a slowdown of AMOC in these experiments results in an atmospheric-induced surface cooling in the entire TNA, the subsurface experiences an even larger warming due to rapid reorganizations of ocean circulation patterns (Wan et al., 2009). In addition, observational records of detrended 20th century ocean temperature and salinity variability show a strong anticorrelation between surface cooling and subsurface warming in the TNA over the past several decades, suggesting changing vertical temperature gradients in this region may be a distinct fingerprint of AMOC variability (Zhang 2007). In order to test the hypothesis that subsurface temperature change in the TNA is coupled to AMOC variability across abrupt climate events over the last deglacial, we reconstructed high-resolution Mg/Ca-temperature and δ18O records from both surface (G. ruber) and sub-thermocline dwelling (G. truncatulinoides, 350-500 m depth and G. crassaformis, 450-580 m) planktonic foraminifera in the southern Caribbean Sea sediment core VM12-107 (11.33oN, 66.63oW; 1079 m; 18 cm/kyr sedimentation rate). Sea surface temperatures indicate a gradual warming in the TNA starting at ~19 kyr BP with small cold reversals of ~1.5oC during Heinrich Event 1 (H1) and the Younger Dryas (YD). In contrast, last glacial maximum subsurface temperatures were as much as 2.5oC warmer than Late Holocene values and H1 and the YD are marked by the warmest subsurface temperatures characterized by abrupt temperature increases as large as 4-5oC. Furthermore, a comparison of our subsurface temperature record with the Bermuda Rise 231Pa/230Th proxy record of AMOC variability (McManus et al., 2004) indicates a strong

  17. Tropical North Atlantic Subsurface Temperature Change Linked to Atlantic Meridional Overturning Circulation Variability During the Last Deglacial

    NASA Astrophysics Data System (ADS)

    Schmidt, M. W.; Chang, P.

    2009-12-01

    Water hosing experiments using coupled ocean-atmosphere models indicate that Atlantic meridional overturning circulation (AMOC) variability can have a major impact on abrupt tropical North Atlantic (TNA) climate change through both atmospheric and oceanic processes (Zhang, 2007; Chang et al., 2008; Chiang et al., 2008). While a slowdown of AMOC results in an atmospheric-induced surface cooling in the entire TNA, the subsurface experiences an even larger warming due to rapid reorganizations of ocean circulation patterns (Wan et al., 2009). In addition, observed records of detrended 20th century ocean temperature and salinity variability show a strong anticorrelation between surface cooling and subsurface warming in the TNA over the past several decades, suggesting changing vertical temperature gradients in this region may be a distinct fingerprint of AMOC variability (Zhang 2007). In order to test the hypothesis that surface and subsurface temperature change in the TNA are sensitive indicators of AMOC variability over the last deglacial, we reconstructed Mg/Ca-temperature and δ18O records from surface (G. ruber) and deeper thermocline dwelling (G. truncatulinoides, 200 - 500 m depth habitat) planktonic foraminifera from southern Caribbean Sea core VM12-107 (11.33oN, 66.63oW; 1079 m; 15 cm/kyr sedimentation rate). As a result, we present the first deglacial subsurface Mg/Ca-temperature record for this region. Results show that glacial sea surface temperatures (SST) were 4oC cooler than those in the late Holocene. SSTs during the deglacial show little or no SST rise (1oC) during Heinrich Event 1 (H1), and a 2oC SST decrease during the Younger Dryas (YD). In contrast, last glacial maximum subsurface temperatures were 2oC warmer than Late Holocene values of 12 - 13oC and periods of reduced AMOC are marked by abrupt subsurface warming events. Subsurface temperatures increased by almost 3oC during H1 and the YD, warming to as much as 16.5oC. Furthermore, a comparison of

  18. Holocene sea surface temperatures in the East African Coastal Current region and their relationship with North Atlantic climate

    NASA Astrophysics Data System (ADS)

    Kuhnert, Henning; Kuhlmann, Holger; Mohtadi, Mahyar; Pätzold, Jürgen

    2013-04-01

    The East African Coastal Current (EACC) is one of the western boundary currents of the Indian Ocean and represents the only pathway for southern water masses to enter the Arabian Sea. Today, sea surface temperatures (SST) in the western boundary currents region covary with those in large parts of the central tropical Indian Ocean. The latter play an important role in global climate by influencing the mean state of the North Atlantic Oscillation (NAO) and associated Atlantic SST anomalies (Hoerling et al., 2001). In the EACC region paleoclimate data are sparse and its Holocene temperature history is unexplored. We present data from a 5 m long sediment core retrieved off northern Tanzania where the EACC flows northward year-round. Proximity to the Pangani River mouth provides a steady sediment supply. We have reconstructed SST from Mg/Ca and stable oxygen isotope ratios (^18O) of the surface-dwelling planktonic foraminifera species Globigerinoides ruber (sensu stricto). Our record spans the time period from 9700 to 1400 years BP at an average temporal resolution of 40 years. The Holocene is characterized by a sequence of intervals representing cool, warm, cool, and intermediate SST, with boundaries at 7.8, 5.6, and 4.4 ka BP. SST anomalies relative to the series mean range from -0.6 to +0.75 ° C. This pattern strikingly resembles a Northwest Atlantic foraminiferal ^18O record (Cléroux et al., 2012), with warm Indian SST corresponding to low Atlantic foraminiferal ^18O (indicating low sea surface density). This matches the modern situation on the interdecadal time-scale, where a warm Indian Ocean leads to a shift of the NAO towards a positive mean state, which is accompanied by SST warming over much of the low- and mid-latitude western Atlantic and a displacement of the Gulf Stream path. We hypothesize that this mechanism also operates on millennial time-scales to explain the obvious similarities in the SST patterns observed in the Northwest Atlantic and western

  19. Decadal predictions of the North Atlantic CO2 uptake

    NASA Astrophysics Data System (ADS)

    Li, Hongmei; Ilyina, Tatiana; Müller, Wolfgang

    2015-04-01

    Oceanic uptake of anthropogenic CO2 is critical for predicting and projecting climate and ocean acidification. The North Atlantic Ocean plays a crucial role in modulating global carbon cycle as a major CO2 sink region, and the subpolar gyre (SPG) region contributes the most to the variation of the North Atlantic CO2 uptake. Previous studies revealed abrupt warming/cooling events in the SPG region, with sea surface temperature (SST) increasing/decreasing by 1°C in only a few years. The abrupt SPG warming/cooling events can be predicted several years in advance by initialization of the earth system models. The CO2 uptake in the North Atlantic is largely driven by ocean mixing variations and SST anomalies. In this study, we investigate the response of the North Atlantic CO2 uptake to observed SST variations and explore the decadal predictability of the North Atlantic CO2 uptake during the period of 1961-2013 with the Max Planck Institute Earth System Model (MPI-ESM). Our results suggest significant inter-annual and decadal variability of the North Atlantic CO2 uptake which is closely related to the evolution of North Atlantic Oscillation (NAO) and corresponding oceanic mixing strength, and this coherence is confined to the western SPG region. We show that the potential predictability of CO2 uptake in the western SPG region is up to 4 years, which is similar to the prediction skill of SPG SST. Direct comparison of initialized simulations with observations implies prediction skill of the North Atlantic CO2 uptake. The predictability of both CO2 uptake and SST in the North Atlantic is assured by initialization of the Atlantic meridional overturning circulation (AMOC).

  20. South Atlantic meridional fluxes

    NASA Astrophysics Data System (ADS)

    Garzoli, Silvia L.; Baringer, Molly O.; Dong, Shenfu; Perez, Renellys C.; Yao, Qi

    2013-01-01

    The properties of the meridional overturning circulation (MOC) and associated meridional heat transport (MHT) and salt fluxes are analyzed in the South Atlantic. The oceanographic data used for the study consist of Expendable bathythermograph (XBT) data collected along 27 sections at nominally 35°S for the period of time 2002-2011, and Argo profile data collected in the region. Previous estimates obtained with a shorter record are improved and extended, using new oceanographic sections and wind fields. Different wind products are analyzed to determine the uncertainty in the Ekman component of the MHT derived from their use. Results of the analysis provide a 9-year time series of MHT, and volume transport in the upper layer of the MOC. Salt fluxes at 35°S are estimated using a parameter introduced by numerical studies, the Mov that represents the salt flux and helps determine the basin scale salt feedback associated with the MOC. Volume and heat transport by the western and eastern boundary currents are estimated, and their covariablity is examined. Analysis of the data shows that the South Atlantic is responsible for a northward MHT with a mean value of 0.54±0.14 PW. The MHT exhibits no significant trend from 2002 to 2011. The MOC varies from 14.4 to 22.7 Sv with a mean value of 18.1±2.3 Sv and the maximum overturning transport is found at a mean depth of 1250 m. Statistical analysis suggests that an increase of 1 Sv in the MOC leads to an increase of the MHT of 0.04±0.02 PW. Estimates of the Mov from data collected from three different kinds of observations, contrary to those obtained from models, feature a positive salt advection feedback (Mov<0) suggesting that freshwater perturbations will be amplified and that the MOC is bistable. In other words, the MOC might collapse with a large enough freshwater perturbation. Observations indicate that the mean value of the Brazil Current is -8.6±4.1 Sv at 24°S and -19.4±4.3 Sv at 35°S, increasing towards the

  1. Problem Periods

    MedlinePlus

    ... gov/ Home Body Getting your period Problem periods Problem periods It’s common to have cramps or feel ... doctor Some common period problems Signs of period problems top One way to know if you may ...

  2. The Influence of Ca2+ Buffers on Free [Ca2+] Fluctuations and the Effective Volume of Ca2+ Microdomains

    PubMed Central

    Weinberg, Seth H.; Smith, Gregory D.

    2014-01-01

    Intracellular calcium (Ca2+) plays a significant role in many cell signaling pathways, some of which are localized to spatially restricted microdomains. Ca2+ binding proteins (Ca2+ buffers) play an important role in regulating Ca2+ concentration ([Ca2+]). Buffers typically slow [Ca2+] temporal dynamics and increase the effective volume of Ca2+ domains. Because fluctuations in [Ca2+] decrease in proportion to the square-root of a domain’s physical volume, one might conjecture that buffers decrease [Ca2+] fluctuations and, consequently, mitigate the significance of small domain volume concerning Ca2+ signaling. We test this hypothesis through mathematical and computational analysis of idealized buffer-containing domains and their stochastic dynamics during free Ca2+ influx with passive exchange of both Ca2+ and buffer with bulk concentrations. We derive Langevin equations for the fluctuating dynamics of Ca2+ and buffer and use these stochastic differential equations to determine the magnitude of [Ca2+] fluctuations for different buffer parameters (e.g., dissociation constant and concentration). In marked contrast to expectations based on a naive application of the principle of effective volume as employed in deterministic models of Ca2+ signaling, we find that mobile and rapid buffers typically increase the magnitude of domain [Ca2+] fluctuations during periods of Ca2+ influx, whereas stationary (immobile) Ca2+ buffers do not. Also contrary to expectations, we find that in the absence of Ca2+ influx, buffers influence the temporal characteristics, but not the magnitude, of [Ca2+] fluctuations. We derive an analytical formula describing the influence of rapid Ca2+ buffers on [Ca2+] fluctuations and, importantly, identify the stochastic analog of (deterministic) effective domain volume. Our results demonstrate that Ca2+ buffers alter the dynamics of [Ca2+] fluctuations in a nonintuitive manner. The finding that Ca2+ buffers do not suppress intrinsic domain [Ca2

  3. Linking North Atlantic Teleconnections to Latitudinal Variability of Wave Climate Along the North American Atlantic Coast

    NASA Astrophysics Data System (ADS)

    Provancha, C.; Adams, P. N.; Hegermiller, C.; Storlazzi, C. D.

    2015-12-01

    Shoreline change via coastal erosion and accretion is largely influenced by variations in ocean wave climate. Identifying the sources of these variations is challenging because the timing of wave energy delivery varies over multiple timescales within ocean basins. We present the results of an investigation of USACE Wave Information Studies hindcast hourly wave heights, periods, and directions along the North American Atlantic coast from 1980-2012, designed to explore links between wave climate and teleconnection patterns. Trends in median and extreme significant wave heights (SWHs) demonstrate that mean monthly SWHs increased from 1 to 5 cm/yr along the roughly 3000 km reach of study area, with changes in hurricane season waves appearing to be most influential in producing the overall trends. Distributions of SWHs categorized by North Atlantic Oscillation (NAO) phase, show that positive-period NAO SWHs are greater than negative-period NAO SWHs along the entire eastern seaboard (25°N to 45°N). The most prominent wave direction off Cape Cod, MA during positive-period NAO is approximately 105°, as compared to approximately 75° during negative-period NAO. Prominent wave directions between Cape Canaveral, FL, and Savannah, GA exhibit a similar shift but during opposite phases of the NAO. The results of this analysis suggest that the atmosphere-ocean interactions associated with contrasting NAO phases can significantly change the wave climate observed offshore along the North American Atlantic coast, altering alongshore wave energy fluxes and sediment transport patterns along the coast.

  4. Atlantic City memories.

    PubMed

    Epstein, Franklin H

    2008-04-01

    Fifty years ago, the Atlantic City meetings, held the first week in May of every year, were attended by all the elite of American academic medicine and all who wanted to join that group. Part of the magic of those meetings was that professors and neophytes took each other seriously and talked to each other. PMID:18382726

  5. Surface heat storage in the subtropical North Atlantic during the LGM

    NASA Astrophysics Data System (ADS)

    Repschlaeger, Janne; Weinelt, Mara; Garbe-Schönberg, Dieter; Andersen, Nils; Schneider, Ralph

    2016-04-01

    The transport of warm saline waters from the subtropical into the subpolar North Atlantic plays a major role in the stabilization of AMOC. During the Late Pleistocene this system experienced millennial scale variability with weak AMOC phases that are associated with heat and salt storage within the subtropics. The subsequent onset of AMOC is supposed to be fueled by the release and transport of the warm saline water into the northern hemisphere deepwater convection sites. Despite this conceptual model, contradicting reconstructions for such warm water storage exist for the Deglaciation to early Holocene and full glacial periods, either asserting a southward movement of the Subtropical gyre (STG) and subsurface heat storage or northward extension of the STG with warming of the surface waters. Here we investigate the heat and salt storage patterns and extension of the warm subtropical gyre (STG) during MIS 2 well into MIS 3 (16- 30 ka BP) at centennial scale resolution using sediment core MD08-3181 (38°N; 31.13°W, 3060 m w.d.) retrieved immediately east of the Mid Atlantic Ridge south of the Azores Islands with sedimentation rates up to 100 cm/ ka. At present, this site is located at the northern rim of the Azores Current, which delineates the STG, recirculating warm waters of the North Atlantic Current. Due to its position at the boundary between temperate Northeast Atlantic waters and warm STG waters, the coring site is ideal to trace past changes in the influence of both water masses. Parallel stable-oxygen isotope and Mg/Ca temperature records of surface-water dwelling foraminifera Globigerina bulloides (habitat depth 0-200 m) and subsurface dweller Globorotalia inflata (habitat depth 100-300 m) and foraminiferal transfer functions are used to reconstruct the temperature and salinity structure of the mixed layer. Additionally, the AF position is reconstructed using the abundance of the tropical to subtropical species Globigerinoides ruber white. Preliminary

  6. Heterogeneous oxygenation states in the Atlantic and Tethys oceans during Oceanic Anoxic Event 2

    NASA Astrophysics Data System (ADS)

    Westermann, Stéphane; Vance, Derek; Cameron, Vyllinniskii; Archer, Corey; Robinson, Stuart A.

    2014-10-01

    The Cenomanian-Turonian boundary (ca. 93.5 Ma) is marked by an episode of profound environmental change, including a major perturbation of the carbon cycle and an Oceanic Anoxic Event (OAE-2). Here, we present molybdenum (Mo) isotope variations within the OAE-2 interval for four sections from the western Tethys (Furlo and La Contessa) and the North-Atlantic (ODP site 1276 and DSDP site 367). The main target of this study is to investigate the extent of reducing conditions (truly global in extent or restricted to poorly-ventilated restricted deep basins), with particular reference to the relationship between the change in the oxygenation state of the ocean and the link to global perturbations of the carbon cycle recorded in carbon isotopes. All four sections show fluctuations in the redox sensitive trace metal (RSTE) distribution, suggesting rapid variations in local redox conditions, ranging from anoxic to euxinic. The RSTE enrichment factors (EFs) also suggest different depositional conditions and paleoceanographic processes in the western Tethys versus the North Atlantic. Whereas the North Atlantic sites show evidence of weak watermass restriction associated with the action of a particulate shuttle within the water column, the EFs of the Tethyan sections are characteristic of unrestricted marine systems. Mo isotopes show surprisingly negative values through the Tethyan sections. At the onset of OAE-2, an increasing trend in δMo98 is observed, with values ranging from -0.6 to 0.6‰. During the second half of OAE-2, the δMo98 curve shows a progressive shift towards more negative values. In the North Atlantic, δMo98 signatures from ODP site 1276 show a similar behaviour as observed in the western Tethys. At DSDP site 367, Mo isotopes are generally heavier during OAE-2, fluctuating around an average value of 1.1‰. This is consistent with fully euxinic conditions and the black shales deposited may have recorded the seawater signature during OAE-2. The Mo isotope

  7. Interhemispheric Atlantic seesaw response during the last deglaciation.

    PubMed

    Barker, Stephen; Diz, Paula; Vautravers, Maryline J; Pike, Jennifer; Knorr, Gregor; Hall, Ian R; Broecker, Wallace S

    2009-02-26

    The asynchronous relationship between millennial-scale temperature changes over Greenland and Antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the Atlantic Ocean. Here we present new records from the South Atlantic that show rapid changes during the last deglaciation that were instantaneous (within dating uncertainty) and of opposite sign to those observed in the North Atlantic. Our results demonstrate a direct link between the abrupt changes associated with variations in the Atlantic meridional overturning circulation and the more gradual adjustments characteristic of the Southern Ocean. These results emphasize the importance of the Southern Ocean for the development and transmission of millennial-scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide. PMID:19242468

  8. Atlantic tropical cyclones revisited

    NASA Astrophysics Data System (ADS)

    Mann, Michael E.; Emanuel, Kerry A.; Holland, Greg J.; Webster, Peter J.

    Vigorous discussions have taken place recently in Eos [e.g., Mann and Emanuel, 2006; Landsea, 2007] and elsewhere [Emanuel, 2005; Webster et al., 2005; Hoyos et al., 2006; Trenberth and Shea, 2006; Kossin et al., 2007] regarding trends in North Atlantic tropical cyclone (TC) activity and their potential connection with anthropogenic climate change. In one study, for example [Landsea, 2007], it is argued that a substantial underestimate of Atlantic tropical cyclone counts in earlier decades arising from insufficient observing systems invalidates the conclusion that trends in TC behavior may be connected to climate change. Here we argue that such connections are in fact robust with respect to uncertainties in earlier observations.Several recent studies have investigated trends in various measures of TC activity. Emanuel [2005] showed that a measure of total power dissipation by TCs (the power dissipation index, or PDI) is highly correlated with August-October sea surface temperatures (SST) over the main development region (MDR) for Atlantic TCs over at least the past half century. Some support for this conclusion was provided by Sriver and Ruber [2006]. Webster et al. [2005] demonstrated a statistically significant increase in recent decades in both the total number of the strongest category cyclones (categories 4 and 5) and the proportion of storms reaching hurricane intensity. Hoyos et al. [2006] showed that these increases were closely tied to warming trends in tropical Atlantic SST, while, for example, the modest decrease in vertical wind shear played a more secondary role. Kossin et al. [2007] called into question some trends in other basins, based on a reanalysis of past TC data, but they found the North Atlantic trends to be robust.

  9. Atlantic Multidecadal Oscillation (AMO) forcing on the late Holocene Cauca paleolake dynamics, northern Andes of Colombia

    NASA Astrophysics Data System (ADS)

    Martínez, J. I.; Obrochta, S.; Yokoyama, Y.; Battarbee, R. W.

    2015-07-01

    The Atlantic Multidecadal Oscillation (AMO), is a major driving climate mechanism, in the eastern Caribbean Sea and the South Atlantic Ocean in relation to the dynamics of the South American Monsoon System (SAMS) for the late Holocene. Here we document the AMO signal in the San Nicolás-1 core of the Cauca paleolake (Santa Fé-Sopetrán Basin) in the northern Andes. Wavelet spectrum analysis of the gray scale of the San Nicolás-1 core provides evidence for a 70 yr AMO periodicity for the 3750 to 350 yr BP time interval, whose pattern is analogous to the one documented for the Cariaco Basin. This supports a possible correlation between enhanced precipitation and ENSO variability with a positive AMO phase during the 2000 to 1500 yr BP interval, and its forcing role on the Cauca ria lake deposits, which led to increased precipitation and to the transition from a igapo (black water) to a varzea (white water) environment ca. 3000 yr BP.

  10. Matching spatial scales of variation in mussel recruitment and adult densities across southwestern Atlantic rocky shores

    NASA Astrophysics Data System (ADS)

    Arribas, Lorena P.; Bagur, María; Gutiérrez, Jorge L.; Palomo, M. Gabriela

    2015-01-01

    The recruitment of aquatic invertebrate larvae often differs in space and time thus contributing to variation in the abundance of adults. In the present study, we examined spatial scales of variation in mussel (Brachidontes spp.) recruitment and adult abundance across rocky intertidal areas in the Southwestern Atlantic. Recruitment and adult densities were compared between two regions separated ca. 700 km from each other, two locations (10-20 km from each other) within each region, and two sites (100-500 m from each other) within each location. Variance components analysis indicates that most variation in mussel recruitment and adult densities occurs at the scale of locations, irrespective of if mussel recruitment is quantified on mussel bed samples or artificial substrates (plastic mesh collectors). Increased mussel recruitment and adult densities at this scale are associated with higher time-averaged chlorophyll a concentration and wave exposure, which can potentially affect the supply of larvae to rocky shores by increasing their survival and delivery rates. There was close correspondence between the spatial patterns of variation in cumulative recruitment on natural substrates during the study period and the density of adults at its end. This suggests that differences in mussel abundance along Southwestern Atlantic rocky shores could be primarily determined by larval recruitment.

  11. 600 yr High-Resolution Climate Reconstruction of the Atlantic Multidecadal Variability deduced from a Puerto Rican Speleothem

    NASA Astrophysics Data System (ADS)

    Winter, A.; Vieten, R.

    2015-12-01

    A multi-proxy speleothem study tracks the regional hydrological variability in Puerto Rico and highlights its close relation to the Atlantic Multidecadal Oscillation. Our proxy record extends instrumental observations 600 years into the past, and reveals the range of natural hydrologic variability for the region. A detailed interpretation and understanding of the speleothem climate record is achieved by the combination of multi-proxy measurements, thin section petrography, XRD analysis and cave monitoring results. The speleothem was collected in Cueva Larga, a one mile-long cave system that has been monitored since 2012. MC-ICPMS 230Th/U-dating reveals that the speleothem grew constantly over the last 600 years. Trace element ratios (Sr/Ca and Mg/Ca) as well as stable isotope ratios (δ18O and δ13C) elucidate significant changes in atmospheric precipitation at the site. Monthly cave monitoring results demonstrate that the epikarst system responds to multi-annual changes in seepage water recharge. The drip water isotope and trace element composition lack short term or seasonal variability. This hydrological system creates favorable conditions to deduce decadal climate variability from Cueva Larga's climate record. The speleothem time series mimics the most-recently published AMO reconstruction over the last 200 years with a time lag of 10-20 years. The time lag seems to results from slow atmospheric signal transmission through the epikarst but the effect of dating uncertainties cannot be ruled out. Warm SSTs in the North Atlantic are related to drier conditions in Puerto Rico. During times of decreased rainfall a relative increase in prior calcite precipitation seems to be the main process causing increased Mg/Ca trace element ratios. High trace element ratios correlate to higher δ13C values. The increase in both proxies indicates a shift towards time periods of decreased rainfall. Over the past 600 years there are two intervals of increased Mg/Ca and δ13C values

  12. Deglacial Subsurface Temperature Change in the Tropical North Atlantic Linked to Atlantic Meridional Overturning Circulation Variability

    NASA Astrophysics Data System (ADS)

    Schmidt, M. W.; Hertzberg, J. E.; Them, T. R.; Parker, A. O.; Chang, P.

    2011-12-01

    Coupled ocean-atmosphere modeling experiments conducted under both the present and Last Glacial Maximum (LGM) conditions indicate that Atlantic meridional overturning circulation (AMOC) variability is tightly coupled to abrupt tropical North Atlantic (TNA) climate change through both atmospheric and oceanic processes (Zhang, 2007; Chang et al., 2008; Chiang et al., 2008; Otto-Bliesner and Brady, 2009). While a slowdown of AMOC in these experiments results in an atmospheric-induced surface cooling in the entire TNA, the subsurface experiences an even larger warming due to rapid reorganizations of ocean circulation patterns (Wan et al., 2009). To test the hypothesis that subsurface temperature change in the TNA is coupled to AMOC variability across abrupt climate events over the last deglacial, we reconstruct Mg/Ca-temperature and δ18O records from both surface (Globigerinoides ruber, upper mixed layer) and sub-thermocline dwelling (Globorotalia truncatulinoides, 350-500 m depth) planktonic foraminifera, as well as from the benthic species Cibicidoides pachyderma in the southern Caribbean Sea sediment core VM12-107 (11.33 °N, 66.63 °W; 1079 m; 18 cm/kyr sedimentation rate). Reconstructed sea surface temperatures (SSTs) indicate a gradual warming in the TNA starting at ~19 kyr BP with small cold reversals of ~1.5 °C during Heinrich Event 1 (H1) and the Younger Dryas (YD). In contrast, LGM subsurface temperatures were as much as 2.5 °C warmer than Late Holocene values and H1 and the YD are marked by the warmest subsurface temperatures characterized by abrupt temperature increases as large as 4-5 °C. In addition, benthic Mg/Ca ratios during the YD and H1 increase by 50% relative to Holocene intervals, suggesting significant warming extending to 1079 m water depth across these events. Comparison of our subsurface temperature records with the Bermuda Rise 231Pa/230Th proxy record of AMOC variability (McManus et al., 2004) indicates a strong correlation between

  13. Evolution of South Atlantic density and chemical stratification across the last deglaciation.

    PubMed

    Roberts, Jenny; Gottschalk, Julia; Skinner, Luke C; Peck, Victoria L; Kender, Sev; Elderfield, Henry; Waelbroeck, Claire; Vázquez Riveiros, Natalia; Hodell, David A

    2016-01-19

    Explanations of the glacial-interglacial variations in atmospheric pCO2 invoke a significant role for the deep ocean in the storage of CO2. Deep-ocean density stratification has been proposed as a mechanism to promote the storage of CO2 in the deep ocean during glacial times. A wealth of proxy data supports the presence of a "chemical divide" between intermediate and deep water in the glacial Atlantic Ocean, which indirectly points to an increase in deep-ocean density stratification. However, direct observational evidence of changes in the primary controls of ocean density stratification, i.e., temperature and salinity, remain scarce. Here, we use Mg/Ca-derived seawater temperature and salinity estimates determined from temperature-corrected δ(18)O measurements on the benthic foraminifer Uvigerina spp. from deep and intermediate water-depth marine sediment cores to reconstruct the changes in density of sub-Antarctic South Atlantic water masses over the last deglaciation (i.e., 22-2 ka before present). We find that a major breakdown in the physical density stratification significantly lags the breakdown of the deep-intermediate chemical divide, as indicated by the chemical tracers of benthic foraminifer δ(13)C and foraminifer/coral (14)C. Our results indicate that chemical destratification likely resulted in the first rise in atmospheric pCO2, whereas the density destratification of the deep South Atlantic lags the second rise in atmospheric pCO2 during the late deglacial period. Our findings emphasize that the physical and chemical destratification of the ocean are not as tightly coupled as generally assumed. PMID:26729858

  14. Evolution of South Atlantic density and chemical stratification across the last deglaciation

    PubMed Central

    Skinner, Luke C.; Peck, Victoria L.; Kender, Sev; Elderfield, Henry; Waelbroeck, Claire; Hodell, David A.

    2016-01-01

    Explanations of the glacial–interglacial variations in atmospheric pCO2 invoke a significant role for the deep ocean in the storage of CO2. Deep-ocean density stratification has been proposed as a mechanism to promote the storage of CO2 in the deep ocean during glacial times. A wealth of proxy data supports the presence of a “chemical divide” between intermediate and deep water in the glacial Atlantic Ocean, which indirectly points to an increase in deep-ocean density stratification. However, direct observational evidence of changes in the primary controls of ocean density stratification, i.e., temperature and salinity, remain scarce. Here, we use Mg/Ca-derived seawater temperature and salinity estimates determined from temperature-corrected δ18O measurements on the benthic foraminifer Uvigerina spp. from deep and intermediate water-depth marine sediment cores to reconstruct the changes in density of sub-Antarctic South Atlantic water masses over the last deglaciation (i.e., 22–2 ka before present). We find that a major breakdown in the physical density stratification significantly lags the breakdown of the deep-intermediate chemical divide, as indicated by the chemical tracers of benthic foraminifer δ13C and foraminifer/coral 14C. Our results indicate that chemical destratification likely resulted in the first rise in atmospheric pCO2, whereas the density destratification of the deep South Atlantic lags the second rise in atmospheric pCO2 during the late deglacial period. Our findings emphasize that the physical and chemical destratification of the ocean are not as tightly coupled as generally assumed. PMID:26729858

  15. In Brief: Atlantic seasonal hurricane forecast

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2007-12-01

    Two hurricane forecasters are predicting that 2008 will be an above-average Atlantic basin tropical cyclone season with an above-average probability of a major hurricane making landfall in the United States. During 2008, there could be about seven hurricanes (the annual average is 5.9) and 13 named storms (the average is 9.6), according to a 7 December report by Philip Klotzbach, research scientist at Colorado State University in Fort Collins, and William Gray, university professor emeritus of atmospheric sciences. The forecasters indicate that they believe the Atlantic basin is in an active hurricane cycle that is associated with a strong thermohaline circulation and an active phase of the Atlantic Multidecadal Oscillation. The report notes that, ``real-time operational early December forecasts have not shown forecast skill over climatology during this 16-year period [1992-2007]. This has occurred despite the fact that the skill over the hindcast period...showed appreciable skill.'' For more information, visit the Web site: http://hurricane.atmos.colostate.edu/Forecasts/2007/dec2007/dec2007.pdf.

  16. Distribution and at-sea activity of a nocturnal seabird, the Bulwer's petrel Bulweria bulwerii, during the incubation period

    NASA Astrophysics Data System (ADS)

    Dias, Maria P.; Romero, Joana; Granadeiro, José Pedro; Catry, Teresa; Pollet, Ingrid L.; Catry, Paulo

    2016-07-01

    Bulwer's petrels are nocturnal seabirds that mostly prey on mesopelagic fauna. As aerial foragers and shallow divers, their feeding opportunities are limited by near-surface availability of their prey, which is highly variable both temporally (reflecting diurnal and lunar cycles) and spatially. Here we studied how Bulwer's petrels cope with these constraints by analysing their at-sea distribution and activity during the incubation period. We tracked the movements of 20 birds from Selvagem Grande (NE Atlantic) during a complete lunar cycle, and recorded 30 foraging trips that lasted 11 days on average. Birds were both distributed around the colony and in waters close to the Azorean archipelago (mid-Atlantic) located 1700 km away, and were significantly more active at night (especially just after sunset and before sunrise), when mesopelagic fauna is also closer to the sea surface due to their diel vertical migrations. Bulwer's petrels spent significantly more time flying during moonlight, although the effect of the moon was relatively weak (ca. 10-15% difference between moonlit and dark periods of the night), and not obvious when birds were foraging in mid-Atlantic waters, which were also targeted more often during full-moon. These results reveal key adaptations of the Bulwer's petrel to the highly dynamic ecology of its mesopelagic prey.

  17. Photocopy of photograph, ca. 1915, photographer Marshall. Original photograph property ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Photocopy of photograph, ca. 1915, photographer Marshall. Original photograph property of U.S. Postal Service which is also the source for views and drawings 44 to 56. Undeveloped site of Stamford Post Office looking southwest. - Stamford Post Office, 421 Atlantic Street, Stamford, Fairfield County, CT

  18. Earthquakes at North Atlantic passive margins

    SciTech Connect

    Gregersen, S. ); Basham, P.W. )

    1989-01-01

    The main focus of this volume is the earthquakes that occur at and near the continental margins on both sides of the North Atlantic. The book, which contains the proceedings of the NATO workshop on Causes and Effects of Earthquakes at Passive Margins and in Areas of Postglacial Rebound on Both Sides of the North Atlantic, draws together the fields of geophysics, geology and geodesy to address the stress and strain in the Earth's crust. The resulting earthquakes produced on ancient geological fault zones and the associated seismic hazards these pose to man are also addressed. Postglacial rebound in North America and Fennoscandia is a minor source of earthquakes today, during the interglacial period, but evidence is presented to suggest that the ice sheets suppressed earthquake strain while they were in place, and released this strain as a pulse of significant earthquakes after the ice melted about 9000 years ago.

  19. Dynamic Proxies of Ocean Circulation in the North Atlantic During the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Praetorius, S.; McManus, J.

    2007-05-01

    The North Atlantic Deep Water (NADW) is a major component of the Atlantic's meridional overturning circulation, which is strongly linked to climate through the sea-to-air heat transfer by water transported from low to high latitudes. Changes in this circulation system have been implicated in the abrupt climate reversal of the Younger Dryas. Previous studies using nutrient proxies such as δ13C and Cd/Ca show a nutrient enrichment in the North Atlantic during the Younger Dryas, reflecting a reduction in the volume of nutrient-depleted NADW. Although valuable, water mass tracers cannot constrain the rate of overturning; a crucial factor in the overall heat flux of deep water formation. Dynamic proxies such as 231Pa/230Th disequilibria and the grain size of deep sea sediments provide tools to measure changes in the vigor of ocean circulation. 231Pa/230Th ratios act as a proxy for the export rate of subsurface waters from the North Atlantic. Changes in the non-cohesive sortable silt (SS) size fraction (10-63μm) of terrigenous sediments reflect variations in the current strength as a result of the relative entrainment capacity of flow velocity. Here we compare the grain size record from site 984, along the Rekjanes Ridge, with 231Pa/230Th data from core GGC5 on the Bermuda Rise. Site 984 is well situated to monitor both the modern deep water overflows and the intermediate depth waters of the glacial period, whereas core GGC5 offers a more basin-wide measure of circulation export. These records indicate similarly robust overturning circulation during the last glacial maximum and Holocene. In contrast, the deglacial period reveals significant reductions in the circulation. The Younger Dryas exhibits the most dramatic decrease in grain size throughout the 20,000 year record, and the 231Pa/230Th data indicate a reduction in export rate that is rivaled only by the first Heinrich iceberg discharge event. The reduction in current strength during the Younger Dryas is

  20. Fine tuning of cytosolic Ca 2+ oscillations

    PubMed Central

    Dupont, Geneviève; Combettes, Laurent

    2016-01-01

    Ca 2+ oscillations, a widespread mode of cell signaling, were reported in non-excitable cells for the first time more than 25 years ago. Their fundamental mechanism, based on the periodic Ca 2+ exchange between the endoplasmic reticulum and the cytoplasm, has been well characterized. However, how the kinetics of cytosolic Ca 2+ changes are related to the extent of a physiological response remains poorly understood. Here, we review data suggesting that the downstream targets of Ca 2+ are controlled not only by the frequency of Ca 2+ oscillations but also by the detailed characteristics of the oscillations, such as their duration, shape, or baseline level. Involvement of non-endoplasmic reticulum Ca 2+ stores, mainly mitochondria and the extracellular medium, participates in this fine tuning of Ca 2+ oscillations. The main characteristics of the Ca 2+ exchange fluxes with these compartments are also reviewed.

  1. Periodic Mesoporous Organosilica Nanorice

    NASA Astrophysics Data System (ADS)

    Mohanty, Paritosh; Landskron, Kai

    2009-02-01

    A periodic mesoporous organosilica (PMO) with nanorice morphology was successfully synthesized by a template assisted sol-gel method using a chain-type precursor. The PMO is composed of D and T sites in the ratio 1:2. The obtained mesoporous nanorice has a surface area of 753 m2 g-1, one-dimensional channels, and a narrow pore size distribution centered at 4.3 nm. The nanorice particles have a length of ca. 600 nm and width of ca. 200 nm.

  2. 231Pa/230Th evidence for a weakened but persistent Atlantic meridional overturning circulation during Heinrich Stadial 1.

    PubMed

    Bradtmiller, Louisa I; McManus, Jerry F; Robinson, Laura F

    2014-01-01

    The strength of Atlantic meridional overturning circulation is believed to affect the climate over glacial-interglacial and millennial timescales. The marine sedimentary (231)Pa/(230)Th ratio is a promising paleocirculation proxy, but local particle effects may bias individual reconstructions. Here we present new Atlantic sedimentary (231)Pa/(230)Th data from the Holocene, the last glacial maximum and Heinrich Stadial 1, a period of abrupt cooling ca. 17,500 years ago. We combine our results with published data from these intervals to create a spatially distributed sedimentary (231)Pa/(230)Th database. The data reveal a net (231)Pa deficit during each period, consistent with persistent (231)Pa export. In highly resolved cores, Heinrich (231)Pa/(230)Th ratios exceed glacial ratios at nearly all depths, indicating a significant reduction, although not cessation, of overturning during Heinrich Stadial 1. These results support the inference that weakened overturning was a driver of Heinrich cooling, while suggesting that abrupt climate oscillations do not necessarily require a complete shutdown of overturning. PMID:25520057

  3. Mechanical properties of Haynes Alloy 188 after exposure to LiF-22CaF2, air, and vacuum at 1093 K for periods up to 10,000 hours

    SciTech Connect

    Whittenberger, J.D. )

    1992-08-01

    As part of a program to provide reassurance that the cobalt-base superalloy Haynes Alloy 188 can adequately contain a LiF-CaF2 eutectic thermal energy storage salt, 4900- and 10,000-hr exposures of Haynes Alloy 188 to LiF-22CaF2, its vapor, vacuum, and air at 1093 K have been undertaken. Following such exposures, the microstructure has been characterized and the 77 to 1200 K tensile properties measured. In addition, 1050 K vacuum creep-rupture testing of as-received and molten salt- and vacuum-exposed samples has been undertaken. Although slight degradation of the mechanical properties of Haynes Alloy 188 due to prior exposure was observed, basically none of the losses could be ascribed to a particular environment. Hence, observed decreases in properties are due to thermal aging effects, not corrosive attack. In view of these findings, Haynes Alloy 188 is still deemed to be suitable for containment of the eutectic LiF-CaF2 thermal energy storage media. 8 refs.

  4. Mechanical properties of Haynes Alloy 188 after exposure to LiF-22CaF2, air, and vacuum at 1093 K for periods up to 10,000 hours

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1992-01-01

    As part of a program to provide reassurance that the cobalt-base superalloy Haynes Alloy 188 can adequately contain a LiF-CaF2 eutectic thermal energy storage salt, 4900- and 10,000-hr exposures of Haynes Alloy 188 to LiF-22CaF2, its vapor, vacuum, and air at 1093 K have been undertaken. Following such exposures, the microstructure has been characterized and the 77 to 1200 K tensile properties measured. In addition, 1050 K vacuum creep-rupture testing of as-received and molten salt- and vacuum-exposed samples has been undertaken. Although slight degradation of the mechanical properties of Haynes Alloy 188 due to prior exposure was observed, basically none of the losses could be ascribed to a particular environment. Hence, observed decreases in properties are due to thermal aging effects, not corrosive attack. In view of these findings, Haynes Alloy 188 is still deemed to be suitable for containment of the eutectic LiF-CaF2 thermal energy storage media.

  5. Potential tropical Atlantic impacts on Pacific decadal climate trends

    NASA Astrophysics Data System (ADS)

    Chikamoto, Y.; Mochizuki, T.; Timmermann, A.; Kimoto, M.; Watanabe, M.

    2016-07-01

    The tropical Pacific cooling from the early 1990s to 2013 has contributed to the slowdown of globally averaged sea surface temperatures (SSTs). The origin of this regional cooling trend still remains elusive. Here we demonstrate that the remote impact of Atlantic SST anomalies, as well as local atmosphere-ocean interactions, contributed to the eastern Pacific cooling during this period. By assimilating observed three-dimensional Atlantic temperature and salinity anomalies into a coupled general circulation model, we are able to qualitatively reproduce the observed Pacific decadal trends of SST and sea level pressure (SLP), albeit with reduced amplitude. Although a major part of the Pacific SLP trend can be explained by equatorial Pacific SST forcing only, the origin of this low-frequency variability can be traced back further to the remote impacts of equatorial Atlantic and South Atlantic SST trends. Atlantic SST impacts on the atmospheric circulation can also be detected for the Northeastern Pacific, thus providing a linkage between Atlantic climate and Western North American drought conditions.

  6. Two Distinct Roles of Atlantic SSTs in ENSO Variability: North Tropical Atlantic SST and Atlantic Nino

    NASA Technical Reports Server (NTRS)

    Ham, Yoo-Geun; Kug, Jong-Seong; Park, Jong-Yeon

    2013-01-01

    Two distinct roles of the Atlantic sea surface temperatures (SSTs), namely, the North Tropical Atlantic (NTA) SST and the Atlantic Nino, on the El Nino-Southern Oscillation (ENSO) variability are investigated using the observational data from 1980 to 2010 and coupled model experiments. It appears that the NTA SST and the Atlantic Nino can be used as two independent predictors for predicting the development of ENSO events in the following season. Furthermore, they are likely to be linked to different types of El Nino events. Specifically, the NTA SST cooling during February, March, and April contributes to the central Pacific warming at the subsequent winter season, while the negative Atlantic Nino event during June, July, and August contributes to enhancing the eastern Pacific warming. The coupled model experiments support these results. With the aid of a lagged inverse relationship, the statistical forecast using two Atlantic indices can successfully predict various ENSO indices.

  7. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (South Atlantic) - Atlantic sturgeon

    SciTech Connect

    Van Den Avyle, M.J.

    1984-07-01

    The Atlantic sturgeon, Acipenser oxyrhynchus oxyrhynchus, is an anadromous species that occupies rivers, estuaries, and nearshore waters along the entire Atlantic coast of the United States. The species once supported significant commercial fisheries throughout its range, but stocks have declined because of overfishing, deterioration of water quality, and damming of rivers. Atlantic sturgeon spawn in rivers and the young remain in freshwater for several years prior to emigration to the ocean. Little is known about spawning areas and associated environmental factors. Females typically do not mature until age X and the age at first spawning ranges from 5 to 13 years for males and 7 to 19 years for females. Longevity may frequently exceed 25 years. Immature and adult sturgeons are bottom feeders and consume a variety of mollusks, crustaceans, worms, and other small bottom-dwelling invertebrates and fishes. Little is know about competitors, predators, or effects of environmental factors on recruitment. The long period required to reach maturity, possibly irregular spawning thereafter, and prolonged reliance on river systems make juvenile and adult Atlantic sturgeon highly susceptible to habitat alterations, pollution, and over exploitation. 49 references, 2 figures, 4 tables.

  8. An electrical analogy relating the Atlantic multidecadal oscillation to the Atlantic meridional overturning circulation.

    PubMed

    Kurtz, Bruce E

    2014-01-01

    The Atlantic meridional overturning circulation (AMOC) is the northward flow of surface water to subpolar latitudes where deepwater is formed, balanced by southward abyssal flow and upwelling in the vicinity of the Southern Ocean. It is generally accepted that AMOC flow oscillates with a period of 60-80 years, creating a regular variation in North Atlantic sea surface temperature known as the Atlantic multidecadal oscillation (AMO). This article attempts to answer two questions: how is the AMOC driven and why does it oscillate? Using methods commonly employed by chemical engineers for analyzing processes involving flowing liquids, apparently not previously applied to trying to understand the AMOC, an equation is developed for AMOC flow as a function of the meridional density gradient or the corresponding temperature gradient. The equation is based on the similarity between the AMOC and an industrial thermosyphon loop cooler, which circulates a heat transfer liquid without using a mechanical pump. Extending this equation with an analogy between the flow of heat and electricity explains why the AMOC flow oscillates and what determines its period. Calculated values for AMOC flow and AMO oscillation period are in good agreement with measured values. PMID:24940739

  9. An Electrical Analogy Relating the Atlantic Multidecadal Oscillation to the Atlantic Meridional Overturning Circulation

    PubMed Central

    Kurtz, Bruce E.

    2014-01-01

    The Atlantic meridional overturning circulation (AMOC) is the northward flow of surface water to subpolar latitudes where deepwater is formed, balanced by southward abyssal flow and upwelling in the vicinity of the Southern Ocean. It is generally accepted that AMOC flow oscillates with a period of 60–80 years, creating a regular variation in North Atlantic sea surface temperature known as the Atlantic multidecadal oscillation (AMO). This article attempts to answer two questions: how is the AMOC driven and why does it oscillate? Using methods commonly employed by chemical engineers for analyzing processes involving flowing liquids, apparently not previously applied to trying to understand the AMOC, an equation is developed for AMOC flow as a function of the meridional density gradient or the corresponding temperature gradient. The equation is based on the similarity between the AMOC and an industrial thermosyphon loop cooler, which circulates a heat transfer liquid without using a mechanical pump. Extending this equation with an analogy between the flow of heat and electricity explains why the AMOC flow oscillates and what determines its period. Calculated values for AMOC flow and AMO oscillation period are in good agreement with measured values. PMID:24940739

  10. Temporal offsets between surface temperature, ice-rafting and bottom flow speed proxies in the glacial (MIS 3) northern North Atlantic

    NASA Astrophysics Data System (ADS)

    Jonkers, Lukas; Prins, Maarten A.; Moros, Matthias; Weltje, Gert Jan; Troelstra, Simon R.; Brummer, Geert-Jan A.

    2012-08-01

    Rapid climatic switches during marine isotope stage 3 (29-59 ka BP) are often attributed to ocean circulation changes caused by freshwater input into the North Atlantic through the melting of large amounts of icebergs and sea ice. However, recent studies have questioned this direct coupling between factors influencing the ocean-climate system. By combining multiple proxies from two mid depth northern North Atlantic sediment cores we assess temporal offsets and links between freshwater input and response of the near bottom flow as well as between near bottom flow and sea surface temperatures changes. Grain size, mineralogical and magnetic proxies for ice rafting and near-bottom flow speed, interpreted as indicators of freshwater input and deep circulation strength, consistently indicate a delay in the recovery of the deep circulation after freshwater perturbations. Sea surface temperature variability is inferred from foraminiferal assemblages and Mg/Ca and δ18O of Neogloboquadrina pachyderma s. The records show rapid switches towards higher temperatures following the ice-rafting events. Interestingly, near sea surface temperatures increased and decreased again during periods of accelerating bottom flow speed, likely reflecting the sudden release of heat from deeper in the water column, rather than circulation changes. Our data thus confirm the impact of freshwater forcing on the Atlantic deep circulation, but suggest that temperature variability at the surface was not directly linked to these circulation changes.

  11. Tropical North Atlantic subsurface warming events as a fingerprint for AMOC variability during Marine Isotope Stage 3

    NASA Astrophysics Data System (ADS)

    Parker, Andrew O.; Schmidt, Matthew W.; Chang, Ping

    2015-11-01

    The role of Atlantic Meridional Overturning Circulation (AMOC) as the driver of Dansgaard-Oeschger (DO) variability that characterized Marine Isotope Stage 3 (MIS 3) has long been hypothesized. Although there is ample proxy evidence suggesting that DO events were robust features of glacial climate, there is little data supporting a link with AMOC. Recently, modeling studies and subsurface temperature reconstructions have suggested that subsurface warming across the tropical North Atlantic can be used to fingerprint a weakened AMOC during the deglacial because a reduction in the strength of the western boundary current allows warm salinity maximum water of the subtropical gyre to enter the deep tropics. To determine if AMOC variability played a role during the DO cycles of MIS 3, we present new, high-resolution Mg/Ca and δ18O records spanning 24-52 kyr from the near-surface dwelling planktonic foraminifera Globigerinoides ruber and the lower thermocline dwelling planktonic foraminifera Globorotalia truncatulinoides in Southern Caribbean core VM12-107 (11.33°N, 66.63°W, 1079 m depth). Our subsurface Mg/Ca record reveals abrupt increases in Mg/Ca ratios (the largest equal to a 4°C warming) during the interstadial-stadial transition of most DO events during this period. This change is consistent with reconstructions of subsurface warming events associated with cold events across the deglacial using the same core. Additionally, our data support the conclusion reached by a recently published study from the Florida Straits that AMOC did not undergo significant reductions during Heinrich events 2 and 3. This record presents some of the first high-resolution marine sediment derived evidence for variable AMOC during MIS 3.

  12. Continuous observations of North Atlantic heat transport

    NASA Astrophysics Data System (ADS)

    Balcerak, Ernie

    2012-02-01

    The Atlantic meridional overturning circulation (AMOC), which transports warm water northward and cold water back southward, is important in transferring heat to the North Atlantic Ocean. Some models predict that AMOC will slow down as Earth's temperatures rise due to anthropogenic warming, which could have serious climate consequences for the Northern Hemisphere. However, the response of AMOC to global warming is uncertain—different models predict different rates of slowdown—and there have been few continuous observations of AMOC heat transport. Hobbs and Willis used temperature, salinity, and displacement data measured from foats in the Argo array, combined with sea surface heights measured by satellites, to estimate a continuous time series of Atlantic meridional heat transport from 2002 to 2010 at 41°N latitude. They found that the mean heat transport was about 0.5 petawatt. The authors note that this estimate is consistent with previous studies in similar latitudes based on atmospheric flux data but is lower than most hydrographic estimates. Heat transport varied on an annual cycle as well as on shorter time scales, with atmospheric variability explaining most of the short-term variance. The researchers note that the period of study was too short to infer any long-term trends, and they emphasize the need for continued monitoring of AMOC. (Journal of Geophysical Research-Oceans, doi:10.1029/2011JC007039, 2012)

  13. Recent Changes in Arctic Ocean Sea Ice Motion Associated with the North Atlantic Oscillation

    NASA Technical Reports Server (NTRS)

    Kwok, R.

    1999-01-01

    Examination of a new ice motion dataset of the Arctic Ocean over a recent eighteen year period (1978-1996) reveals patterns of variability that can be linked directly to the North Atlantic Oscillation.

  14. MAINE ATLANTIC SALMON HABITAT - GENERAL

    EPA Science Inventory

    ASDENN00 describes, at 1:24,000 scale, important Atlantic salmon habitat of the Dennys River in Maine. The coverage was developed from field surveys conducted on the Dennys River in Maine by staff of the Atlantic Salmon Authority and U.S. Fish and Wildlife Service. This survey wa...

  15. LATITUDINAL GRADIENTS IN BENTHIC COMMUNITY COMPOSITION IN WESTERN ATLANTIC ESTUARIES

    EPA Science Inventory

    The community structure of benthic macroinvertebrates from estuaries along the Atlantic coast of North America from Cape Cod, MA, to Biscayne Bay, FL, were compared. Benthic data were collected over a 5 year period (1990 to 1995) by the U.S. Environmental Protection Agency's Envi...

  16. Atlantic circulation keeps turning.

    PubMed

    Gross, Michael

    2012-10-23

    Two major research projects that are running out in November have investigated the Atlantic circulation system that includes the Gulf Stream and come to the conclusion that there is no immediate risk of it shutting down, allaying fears that were raised seven years ago. Yet a better understanding of the interaction between ocean circulation and climate change is still needed, so two new research projects are going to continue this work and extend it to the implications for fisheries and urban environments. Michael Gross reports. PMID:23256201

  17. Mid-Atlantic Regional Wind Energy Institute

    SciTech Connect

    Courtney Lane

    2011-12-20

    As the Department of Energy stated in its 20% Wind Energy by 2030 report, there will need to be enhanced outreach efforts on a national, state, regional, and local level to communicate wind development opportunities, benefits and challenges to a diverse set of stakeholders. To help address this need, PennFuture was awarded funding to create the Mid-Atlantic Regional Wind Energy Institute to provide general education and outreach on wind energy development across Maryland, Virginia, Delaware, Pennsylvania and West Virginia. Over the course of the two-year grant period, PennFuture used its expertise on wind energy policy and development in Pennsylvania and expanded it to other states in the Mid-Atlantic region. PennFuture accomplished this through reaching out and establishing connections with policy makers, local environmental groups, health and economic development organizations, and educational institutions and wind energy developers throughout the Mid-Atlantic region. PennFuture conducted two regional wind educational forums that brought together wind industry representatives and public interest organizations from across the region to discuss and address wind development in the Mid-Atlantic region. PennFuture developed the agenda and speakers in collaboration with experts on the ground in each state to help determine the critical issue to wind energy in each location. The sessions focused on topics ranging from the basics of wind development; model ordinance and tax issues; anti-wind arguments and counter points; wildlife issues and coalition building. In addition to in-person events, PennFuture held three webinars on (1) Generating Jobs with Wind Energy; (2) Reviving American Manufacturing with Wind Power; and (3) Wind and Transmission. PennFuture also created a web page for the institute (http://www.midatlanticwind.org) that contains an online database of fact sheets, research reports, sample advocacy letters, top anti-wind claims and information on how to

  18. Water level changes for Lake Turkana and climate variability during the African Humid Period

    NASA Astrophysics Data System (ADS)

    Bloszies, C.; Forman, S. L.; Wright, D. K.

    2013-12-01

    The chronology of East African paleoclimate suggests the transition through the African Humid Period (AHP) at ca. 15 to 5 ka was a binary shift from wet conditions in the Late Pleistocene to current aridity. Previous studies indicate that water levels for Lake Turkana for the AHP were stable at ~88 to 98 m above current level with outflow into the White Nile Basin. This study of relict beaches around Lake Turkana indicates surprisingly >50 m variability in water level between 14 and 4 ka. The elevation of past water level is constrained by barometric and GPS-based altimetry of relict beaches and age control by 14C dating of associated mollusks and OSL dating of quartz grains from surrounding littoral and sublittoral deposits. We also include well provenanced lake level data from prior studies to constrain more fully the timing and height of water level fluctuations in the Late Quaternary. Additionally, previous studies indicate that peak water levels may be regionally amplified by increased precipitation causing overflow into the Lake Turkana Basin from the adjacent Suguta and Chew Bahir basins, particularly during high stands at ca. >8.5 ka and at 6.3 ka. Our analysis of the Lake Turkana strandplain reveals that water level may have varied by × 60 m, potentially reaching the outlet elevation at ca.11.3, 10.3, 9.0, 6.3 and 5.1 ka. There are other possible high stands at ca. 13.0, 8.4, 7.8 and 7.0 ka with limited elevational and age constraints; it is unknown if these lake stands reached the outlet elevation. Evidence from relict strand plains indicate that lake level was probably below 20 m since ca. 4.5 ka, though there were two noticeable high stands up to >12 to 18 m at ca. 830 years ago and <100 years, the latter consistent with the historic record of lake levels. Inferences on the source of moisture to sustain these many high stands are based on the isotopic data on leaf wax (δDwax) from lakes Tanganika and Victoria and associated sea surface temperature

  19. Variability of the North Atlantic Current over the Common Era

    NASA Astrophysics Data System (ADS)

    Moffa Sanchez, P.; Hall, I. R.; Born, A.; Thornalley, D. J.; Barker, S.; Richter, T.

    2014-12-01

    Over the last 2000 years, the climate of the North Atlantic region was punctuated by centennial oscillations, which despite their small magnitude had important societal impacts, particularly in NW Europe. The most favoured explanations for this climate variability invoke changes in external forcings (such as solar activity and explosive volcanism) amplified by ocean and atmosphere feedbacks, mainly involving the Atlantic Meridional Overturning Circulation (AMOC) and the North Atlantic Oscillation. However, the scarcity of highly resolved archives has hampered our understanding of the involvement of the ocean-atmosphere interactions in these climatic oscillations. We present a subdecadally resolved temperature and salinity record derived from paired Mg/Ca-δ18O measurements on planktonic foraminifera from a marine sediment core located in the pathway of the North Atlantic Current. Our findings show a strong centennial co-variability of the temperature and salinity of the surface limb of the AMOC with solar irradiance (Moffa-Sánchez et al. 2014- NGS). Climate model results from this study show a similar correlation over the last millennium and we infer that the hydrographic changes were linked to the strength of the subpolar gyre associated with changes in atmospheric circulation. Specifically, in the simulation, low solar irradiance promotes the development of frequent and persistent atmospheric blocking events, in which a quasi-stationary high-pressure system in the eastern North Atlantic, also known as blocking event, modifies the flow of the westerly winds. To further explore the response of the upper limb of the AMOC to solar forcing found in Moffa-Sánchez et al. 14, we synthesize new and available proxy-data from the North Atlantic Current in combination with analysis from CMIP5 simulations of the last millennium.

  20. 76 FR 18504 - Atlantic Highly Migratory Species; Atlantic Bluefin Tuna Quotas and Atlantic Tuna Fisheries...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-04-04

    .... See SUPPLEMENTARY INFORMATION for further details. ADDRESSES: As published on March 14, 2011 (76 FR... Species; Atlantic Bluefin Tuna Quotas and Atlantic Tuna Fisheries Management Measures AGENCY: National... bluefin tuna (BFT) base quotas for all domestic fishing categories; establish BFT quota specifications...

  1. Irregular Periods

    MedlinePlus

    ... number of days after the last one. The Menstrual Cycle Most girls get their first period between the ... to skip periods or to have an irregular menstrual cycle. Illness, rapid weight change, or stress can also ...

  2. Reduced North Atlantic Deep Water flux to the glacial Southern Ocean inferred from neodymium isotope ratios

    PubMed

    Rutberg; Hemming; Goldstein

    2000-06-22

    The global circulation of the oceans and the atmosphere transports heat around the Earth. Broecker and Denton suggested that changes in the global ocean circulation might have triggered or enhanced the glacial-interglacial cycles. But proxy data for past circulation taken from sediment cores in the South Atlantic Ocean have yielded conflicting interpretations of ocean circulation in glacial times--delta13C variations in benthic foraminifera support the idea of a glacial weakening or shutdown of North Atlantic Deep Water production, whereas other proxies, such as Cd/Ca, Ba/Ca and 231Pa/230Th ratios, show little change from the Last Glacial Maximum to the Holocene epoch. Here we report neodymium isotope ratios from the dispersed Fe-Mn oxide component of two southeast Atlantic sediment cores. Both cores show variations that tend towards North Atlantic signatures during the warm marine isotope stages 1 and 3, whereas for the full glacial stages 2 and 4 they are closer to Pacific Ocean signatures. We conclude that the export of North Atlantic Deep Water to the Southern Ocean has resembled present-day conditions during the warm climate intervals, but was reduced during the cold stages. An increase in biological productivity may explain the various proxy data during the times of reduced North Atlantic Deep Water export. PMID:10879531

  3. North Atlantic Bloom

    NASA Technical Reports Server (NTRS)

    2007-01-01

    Reminiscent of the distinctive swirls in a Van Gogh painting, millions of microscopic plants color the waters of the North Atlantic with strokes of blue, turquoise, green, and brown. Fed by nutrients that have built up during the winter and the long, sunlit days of late spring and early summer, the cool waters of the North Atlantic come alive every year with a vivid display of color. The microscopic plants, called phytoplankton, that give the water this color are the base of the marine food chain. Some species of phytoplankton are coated with scales of calcium (chalk), which turn the water electric blue. Chlorophyll and other light-capturing pigments in others give the water a deep green hue. The proliferation of many different species in various stages of growth and decay provides many nuances of color in this concentrated bloom. The bloom stretches across hundreds of kilometers, well beyond the edges of this photo-like image, captured on June 23, 2007, by the Moderate Resolution Imaging Spectroradiometer (MODIS) flying aboard NASA's Aqua satellite. The upper left edge of the image is bounded by Greenland. Iceland is in the upper right. Plumes of dust are blowing off the island, probably adding nutrients to the surface waters to its south. NASA image courtesy Norman Kuring, Ocean Color Group at NASA Goddard Space Flight Center

  4. A survey for mallard pairs in the Atlantic flyway

    USGS Publications Warehouse

    Heusmann, H.W.; Sauer, J.R.

    1997-01-01

    During 1989-1992, spring surveys of randomly selected, 1-km2 plots, stratified by physiographic strata, were conducted in the Atlantic flyway from New Hampshire to Virginia, to estimate mallard (Anas platyrhynchos) pairs. All potential waterfowl habitat in each plot was checked by ground crews. The adjusted mean mallard pair estimate over the 4-year period was 300,849 (range 271,193-320,642, mean SE 22,455) for the region surveyed. Ground plot checks are a practical way to survey mallard pairs in the upper Atlantic flyway.

  5. North Atlantic subpolar and subtropical gyres variability during the last 2000 years: a contribution to the THOR project.

    NASA Astrophysics Data System (ADS)

    Bouinot, Thomas; Cortijo, Elsa; Govin, Aline; Mulder, Thierry; Gonthier, Eliane

    2010-05-01

    Recent oceanographic measurements showed that the Atlantic Meridional Overturning Circulation (AMOC) underwent fluctuations in decadal period of time over the past. The causes of these fluctuations are still poorly understood, and available observations are too limited in time (few decades only) to investigate the detailed mechanisms. The Gulf Stream (GS), which actively transports heat from low to high latitudes, mainly in the first few hundred meters of the water column, could play an important role in the natural variability of the AMOC. This study aims at better constraining the variability of North Atlantic surface and subsurface waters over the last 2000 years, in order to improve our understanding of the links between AMOC oscillations and variations in the upper Atlantic heat content. This work is part of the European THOR (Thermohaline Overturning - at Risk?) project. Three cores are considered in key areas of the North Atlantic: (1) IMAGES core MD08-3182 (52°41.99'N, 35°56.15'W, 3757m) is located in the main pathway of the Gulf Stream in the Charlie Gibbs Fracture Zone, a key location for monitoring the subpolar gyre dynamics. (2) IMAGES core MD99-2203 (34°58.38N, 75°12.06'W-620m) off Cape Hatteras is well located to record the past variability of the GS. (3) Core CADI2KS12 (36°42.79'N, 08°31.39'W-1120m), from the Gulf of Cádiz, monitors the return current of the subtropical gyre. All cores are radiocarbon dated by AMS. In each core, the upper water column characteristics are reconstructed by complementary geochemical analysis: paired measurements of oxygen isotopic composition and trace elements ratio (Mg/Ca) in planktonic foraminifera are combined to reconstruct the seawater temperature and oxygen isotopic composition. Both surface and deep-dwelling species are considered to obtain temperature and oxygen isotopic composition records of the first few hundred meters of the water column. We will present our first results of the variability of the

  6. Constraining the History of the North Atlantic Igneous Province: a Palaeomagnetic and Geochronologic Ballad in the British Tertiary Volcanics.

    NASA Astrophysics Data System (ADS)

    Ganerød, M.; Rousse, S.; Smethurst, M.; Prestvik, T.

    2006-12-01

    Large Igneous Provinces (LIP), overwhelmingly of basaltic affinity constitute the surface expressions of catastrophically rapid dissipation of large quantities of internal heat. Subsequent to their extrusion, most LIPs have changed position in the Earth's surface due to plate motions. With an estimated volume of ca 107 km3 the North Atlantic Igneous Province (NAIP) represents the third largest magmatic event on Earth during the last 150 Myr. The NAIP formed during two major magmatic phases: a pre- break-up phase (62-58 Ma) and a syn- break-up phase (56-54 Ma) contemporaneous with the onset of North Atlantic sea-floor spreading. The formation of the NAIP has been linked to the proto-Icelandic plume through paleogeographic reconstructions and geochemical observations. Since the late 1980's much of the research focus on the NAIP has been guided by the understanding of the genetic relationship between North Atlantic magmatism that began in the earliest Palaeocene, the genesis/position of the Iceland Hotspots and/or related mantle plume(s) through the Cenozoic, and the change at c. 54 Ma from a long period of continental rifting and thinning of sea- floor spreading. However, despite the number of data available, the temporal and physio-chemical ties between NAIP rocks, hotspot motion and continental break-up have not been demonstrated to fit a single regionally applicable and consistent geodynamic model. For example, discrepancies between recent palaeomagnetic poles from western Greenland and the Faeroe Islands (Riisager et al. 2002a,b) and older data from the British Tertiary Igneous Province (BTIP) have questioned the reliability of the latest. Therefore, to ultimately understand the Tertiary evolution of the North Atlantic, extensive palaeomagnetic and 40Ar/39Ar sampling on the lava fields of the British Igneous Provinces (Isle of Skye, Isle of Mull, Antrim Plateau) has been initiated. Our findings are in agreement with older published poles from the BTIP and support

  7. Basal Ca2+ and the oscillation of Ca2+ in caffeine-treated bullfrog sympathetic neurones.

    PubMed Central

    Nohmi, M; Hua, S Y; Kuba, K

    1992-01-01

    1. Effects of caffeine on the intracellular free Ca2+ concentration ([Ca2+]i) in single bullfrog sympathetic neurones in excised tissue were studied by recording Fura-2 fluorescence excited at 340, 361 or 380 nm and taking their ratios (R340/380 or R361/380). 2. Caffeine (3-10 mM) produced oscillation of [Ca2+]i and an 'apparent' decrease in the basal level of [Ca2+]i during a period between phasic rises. The mechanism of the latter effect was analysed in relation to the mechanism of the former. 3. Caffeine (3-10 mM) increased Fura-2 fluorescence in a range of excitation wavelength from 330 to 390 nm. The ratios of fluorescences, R340/380 and R361/380, however, were not significantly affected by caffeine. These results suggest that the 'apparent' reduction in the basal [Ca2+]i seen as a decrease in R340/380 or R361/380 results from a true decrease in [Ca2+]i. 4. Caffeine-induced decrease in [Ca2+]i persisted for every period between phasic rises of [Ca2+]i during [Ca2+]i oscillation, and after the blockade of [Ca2+]i oscillation by ryanodine. The decrease in the latter condition lasted for more than 20 min. 5. The decrease in the basal [Ca2+]i depended on the external Ca2+ concentration and was not mimicked by the action of cyclic nucleotides. 6. Possible mechanisms underlying the decrease in the basal [Ca2+]i produced by caffeine (effects on Ca2+ transport at the cell or Ca(2+)-storing organelle membrane) and their significance in relation to the [Ca2+]i oscillation were discussed. PMID:1432716

  8. Calcium distribution in the subtropical Atlantic Ocean: Implications for calcium excess and saturation horizons

    NASA Astrophysics Data System (ADS)

    Rosón, Gabriel; Guallart, Elisa F.; Pérez, Fiz F.; Ríos, Aida F.

    2016-06-01

    This study constituted the first attempt to measure dissolved calcium ([Ca2 +]meas) in the subtropical North Atlantic, during a zonal transoceanic cruise along 24.5°N (WOCE A05 section), in summer 1992. [Ca2 +]meas was obtained in 20 full-depth equidistant stations along the section, showing that their gradients are rather sensitive to horizontal and vertical water mass distribution. Deep waters along 24.5°N systematically show a positive calcium excess of 20 ± 14 μmol·kg- 1, i.e., more [Ca2 +] than expected by CaCO3 dissolution and organic matter oxidation (estimated by total alkalinity and nitrate). CaCO3 settling and benthic dissolution accounts for 70% and the North Atlantic plus Arctic riverine inputs of HCO3- for the remaining 30%. Combining [Ca2 +]meas and CO2 data sets, carbonate mineral saturation states distributions for aragonite and calcite can be obtained. The two solubility ratios resulted, on average, 0.5% smaller than if conservative behavior for Ca2 + was assumed (an approach widely followed when [Ca2 +]meas is unknown). As a result, shallower saturation horizon depths for both carbonate states (19 dbar for aragonite and 10 dbar for calcite) are yielded if [Ca2 +]meas is taken into account instead than estimated from salinity.

  9. Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age.

    PubMed

    Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

    2014-01-01

    The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400-1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO. PMID:24567051

  10. Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age

    PubMed Central

    Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

    2014-01-01

    The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400–1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO. PMID:24567051

  11. Coupling of millennial-scale changes in sea surface temperature and precipitation off northeastern Brazil with high-latitude climate shifts during the last glacial period

    NASA Astrophysics Data System (ADS)

    Jaeschke, Andrea; Rühlemann, Carsten; Arz, Helge; Heil, Gerrit; Lohmann, Gerrit

    2007-12-01

    High-resolution records of alkenone-derived sea surface temperatures and elemental Ti/Ca ratios from a sediment core retrieved off northeastern Brazil (4°S) reveal short-term climate variability throughout the past 63,000 a. Large pulses of terrigenous sediment discharge, caused by increased precipitation in the Brazilian hinterland, coincide with Heinrich events and the Younger Dryas period. Terrigenous input maxima related to Heinrich events H6-H2 are characterized by rapid cooling of surface water ranging between 0.5° and 2°C. This signature is consistent with a climate model experiment where a reduction of the Atlantic meridional overturning circulation (AMOC) and related North Atlantic cooling causes intensification of NE trade winds and a southward movement of the Intertropical Convergence Zone, resulting in enhanced precipitation off northeastern Brazil. During deglaciation the surface temperature evolution at the core site predominantly followed the Antarctic warming trend, including a cooling, prior to the Younger Dryas period. An abrupt temperature rise preceding the onset of the Bølling/Allerød transition agrees with model experiments suggesting a Southern Hemisphere origin for the abrupt resumption of the AMOC during deglaciation caused by Southern Ocean warming and associated with northward flow anomalies of the South Atlantic western boundary current.

  12. Sequestration of carbon in the deep Atlantic during the last glaciation

    NASA Astrophysics Data System (ADS)

    Yu, J.; Menviel, L.; Jin, Z. D.; Thornalley, D. J. R.; Barker, S.; Marino, G.; Rohling, E. J.; Cai, Y.; Zhang, F.; Wang, X.; Dai, Y.; Chen, P.; Broecker, W. S.

    2016-04-01

    Atmospheric CO2 concentrations declined markedly about 70,000 years ago, when the Earth’s climate descended into the last glaciation. Much of the carbon removed from the atmosphere has been suspected to have entered the deep oceans, but evidence for increased carbon storage remains elusive. Here we use the B/Ca ratios of benthic foraminifera from several sites across the Atlantic Ocean to reconstruct changes in the carbonate ion concentration and hence the carbon inventory of the deep Atlantic across this transition. We find that deep Atlantic carbonate ion concentration declined by around 25 μmol kg-1 between ~80,000 and 65,000 years ago. This drop implies that the deep Atlantic carbon inventory increased by at least 50 Gt around the same time as the amount of atmospheric carbon dropped by about 60 Gt. From a comparison with proxy records of deep circulation and climate model simulations, we infer that the carbon sequestration coincided with a shoaling of the Atlantic meridional overturning circulation. We thus conclude that changes in the Atlantic Ocean circulation may have played an important role in reductions of atmospheric CO2 concentrations during the last glaciation, by increasing the carbon storage in the deep Atlantic.

  13. Fluctuating sea surface temperatures in the subtropical North Atlantic during Oceanic Anoxic Event 1a at DSDP Site 398 and ODP Site 641

    NASA Astrophysics Data System (ADS)

    Hofmann, P.; Wiegand, R.; Handley, L.; Wagner, T.; Talbot, H. M.; Mcanena, A.

    2012-04-01

    The early Aptian is characterized by a perturbation of the global carbon cycle which occurred during Oceanic Anoxic Event 1a (OAE 1a, Selli-Event, ca. 120 Ma). OAE 1a is well documented by organic carbon-rich sediments from marine and terrestrial localities worldwide. The trigger mechanism and the environmental consequences of OAE 1a are still under dispute. Here we present sea surface temperature estimates based on TEX 86 measurements (tetraether index of tetraethers containing 86 carbons) from the Galicia Margin (subtropical North Atlantic) at DSDP Site 398 and ODP Site 641C. The investigated sites are approximately 350 km apart and located on the slope of the Vigo seamount (Site 398) and the Galicia Bank (Site 641). Sea surface temperature (SST) records at both Sites suggest a significant and sustained warming of the Galica Margin surface waters during OAE 1a. The observed warming during OAE 1a is disrupted by several SST decreases which vary in magnitude from site to site. Similar surface water cooling episodes but with different magnitudes have been reported from the central Pacific region. The exact nature and timing of these intermittent cooling periods remains to be discovered but the occurrence in both the North Atlantic and Pacific may point towards a global trigger mechanism. We speculate that the thermal development of the surface waters of the subtropical North Atlantic during OAE 1a may reflect global fluctuations in pCO2 in response to variations in the intensity of Pacific volcanic activity in the Pacific Ontong Java area with superimposed local adjustments in the oceanic circulation pattern of the North Atlantic.

  14. Relation between the wind stress curl in the North Atlantic and the Atlantic inflow to the Nordic Seas

    NASA Astrophysics Data System (ADS)

    Sandø, A. B.; Furevik, T.

    2008-06-01

    In this study an isopycnic coordinate ocean model has been used to investigate the relationships between the North Atlantic wind stress curl (WSC) and the inflow of Atlantic water to the Nordic Seas. For the period 1995-2001, there is a maximum in the correlation between the zonally averaged WSC at 55°N and the inflow with a 15-month time lag, capturing a relation already found in observational data. In the model this relation is linked to the mixing along the western flank of the Rockall Bank (56°N, 15°W). For the period 1995-2001 the atmospheric forcing in the northeastern North Atlantic is relatively weak, and the depth of the mixed layer is shallower than the sill depths of the Greenland-Scotland Ridge (GSR). Slowly moving, baroclinic disturbances caused by anomalies in the wind forcing will then be transmitted into the Nordic Seas where they are recorded as anomalous volume transports in the Norwegian Atlantic Current. In contrast, for the pentad prior to this period the atmospheric forcing is much more intense, and generates mixing well below sill depths of the GSR for all winters. Baroclinic disturbances forced by variations in the atmospheric forcing will then tend to follow f/H contours that do not enter the Nordic Seas, and the 15-month lagged relations between the wind and the volume transports will vanish. Recent observational data support this view.

  15. The Relationship between Atlantic Overturning and Climate in the Pleistocene

    NASA Astrophysics Data System (ADS)

    Howe, J. N. W.; Piotrowski, A. M.

    2015-12-01

    Changes in Atlantic Meridional Overturning Circulation play an important role in modulating global climate by controlling northward heat transport in the surface ocean and carbon storage in the deep ocean. We present a new high resolution 1.2 Myr record of neodymium isotopes (ɛNd) - a proxy for water mass mixing - measured on foraminifera and fish debris from site ODP 929 [6.0°N, 43.7°W, 4356 m] on the Ceara Rise in the western equatorial Atlantic Ocean. This record reveals a fundamental step-change in the nature of glacial Atlantic overturning across the Mid-Pleistocene Transition as well as providing new insight into the relationship between ocean circulation and greenhouse gas forcing during the period known as the "lukewarm" interglacials.Comparison with benthic foraminiferal carbon isotopes from the same core reveals periods of significant decoupling between ɛNd and δ13C, demonstrating that deep Atlantic water mass mixing proportions and nutrient chemistry can vary independently of one another. In contrast, comparison of the ɛNd record with benthic foraminiferal oxygen isotopes reveals a tight coupling, exhibiting the control of Northern Hemisphere climate on both ice volume and Atlantic overturning. The high resolution of the records allows cross spectral analysis of the phasing between authigenic ɛNd and both benthic foraminiferal δ13C and δ18O. This reveals that the different proxy records are coherent at time periods of 100-, 40- and 23-kyr which correlate with orbital forcing. However, the changes in each variable at these periods are not always in phase, indicating that the proxies exhibit different temporal responses to climatic forcings.

  16. Sea surface temperatures in the North Atlantic Ocean from 30ka to 10ka

    NASA Astrophysics Data System (ADS)

    Barrack, Kerr; Greenop, Rosanna; Burke, Andrea; Barker, Stephen; Chalk, Thomas; Crocker, Anya

    2016-04-01

    Some of the most striking features of the Late Pleistocene interval are the rapid changes in climate between warmer interstadial and cold stadial periods which, when coupled, are termed Dansgaard-Oeschger (D-O) events. This shift between warm and cold climates has been interpreted to result from changes in the thermohaline circulation (Broecker et al., 1985) triggered by, for instance, freshwater input from the collapse of the Laurentide ice sheet (Zahn et al., 1997). However, a recent study suggests that major ice rafting events cannot be the 'trigger' for the centennial to millennial scale cooling events identified over the past 500kyr (Barker at al., 2015). Polar planktic foraminiferal and lithogenic/terrigenous grain counts reveal that the southward migration of the polar front occurs before the deposition of ice rafted debris and therefore the rafting of ice during stadial periods. Based upon this evidence, Barker et al. suggest that the transition to a stadial state is a non-linear response to gradual cooling in the region. In order to test this hypothesis, our study reconstructs sea surface temperature across D-O events and the deglaciation in the North Atlantic between 30ka and 10ka using Mg/ Ca paleothermometry in Globigerina bulloides at ODP Sites 980 and 983 (the same sites as used in Barker et al., 2015) with an average sampling resolution of 300 years. With our new record we evaluate the timing of surface ocean temperature change, frontal shift movement, and ice rafting to investigate variations in the temperature gradient across the polar front over D-O events. References: Barker, S., Chen, J., Gong, X., Jonkers, L., Knorr, G., Thornalley, D., 2015. Icebergs not the trigger for North Atlantic cold events. Nature, 520(7547), pp.333-336. Broecker, W.S., Peteer, D.M., Rind, D., 1985. Does the ocean-atmosphere system have more than one stable mode of operation? Nature, 315 (6014), pp.21-26. Zahn, R., Schönfeld, J., Kudrass, H.-R., Park, M

  17. Species profiles: Life histories and environmental requirements of coastal fishes and invertebrates (Mid-Atlantic Bight): Atlantic and shortnosed sturgeons

    SciTech Connect

    Gilbert, C.R. )

    1989-12-01

    Species profiles are literature summaries of the taxonomy, morphology, range, life history, and environmental requirements of coastal species. The Atlantic and shortnose sturgeons (especially the former) were commercially important fishes between 1880 and 1900, but stocks have since decreased markedly and the shortnose sturgeon is now classified as federally endangered. Although the two species are anadromous, the shortnose sturgeon tends to spawn farther upstream, and spawning in both species usually occurs over a clean, hard substrate washed by a moderate to strong current. The shortnose sturgeon usually spawn earlier at the same latitude, with spawning of this species in the St. John River, New Brunswick, being completed by mid-May, as opposed to late June or even July for the Atlantic sturgeon. During non-spawning periods, the shortnose is largely confined to estuaries and apparently does not undergo the extensive coastal migrations that are characteristic of the Atlantic sturgeon. Atlantic sturgeon mature more slowly than shortnose sturgeon at comparable latitudes, with male and female Atlantic sturgeon from the Hudson River, New York, requiring at least 11 and 18 years, respectively, to reach maturity, compared with less than half that time for the shortnose sturgeon. Spawning in both sexes may occur thereafter only once every several years. Both species are usually indiscriminate feeders and feed by sucking materials off the bottom with their protrusible mouths. Feeding apparently occurs mostly at night in the shortnose sturgeon. 71 refs., 14 figs., 1 tab.

  18. The Atlantic Climate Change Program

    SciTech Connect

    Molinari, R.L. ); Battisti, D. ); Bryan, K. ); Walsh, J. )

    1994-07-01

    The Atlantic Climate Change Program (ACCP) is a component of NOAA's Climate and Global Change Program. ACCP is directed at determining the role of the thermohaline circulation of the Atlantic Ocean on global atmospheric climate. Efforts and progress in four ACCP elements are described. Advances include (1) descriptions of decadal and longer-term variability in the coupled ocean-atmosphere-ice system of the North Atlantic; (2) development of tools needed to perform long-term model runs of coupled simulations of North Atlantic air-sea interaction; (3) definition of mean and time-dependent characteristics of the thermohaline circulation; and (4) development of monitoring strategies for various elements of the thermohaline circulation. 20 refs., 4 figs., 1 tab.

  19. Dual Hurricanes in the Atlantic

    NASA Video Gallery

    Cameras on the International Space Station show views of Hurricane Julia and Hurricane Igor, both moving west-northwest across the Atlantic on Sept. 14, 2010. At the time the video was captured, Ju...

  20. North Atlantic Coastal Tidal Wetlands

    EPA Science Inventory

    The book chapter provides college instructors, researchers, graduate and advanced undergraduate students, and environmental consultants interested in wetlands with foundation information on the ecology and conservation concerns of North Atlantic coastal wetlands. The book c...

  1. North Atlantic Deep Water Formation

    NASA Technical Reports Server (NTRS)

    Bennett, T. (Editor); Broecker, W. S. (Editor); Hansen, J. (Editor)

    1984-01-01

    Various studies concerning differing aspects of the North Atlantic are presented. The three major topics under which the works are classified include: (1) oceanography; (2) paleoclimate; and (3) ocean, ice and climate modeling.

  2. On the North Atlantic circulation

    SciTech Connect

    Schmitz, W.J. Jr.; McCartney, M.S. )

    1993-02-01

    A summary for North Atlantic circulation is proposed to replace the circulation scheme hypothesized by Worthington in 1976. Divergences from the previous model are in thermohaline circulation, cross-equatorical transport and Florida Current sources, flow in the eastern Atlantic, circulation in the Newfoundland Basin, slope water currents, and flow pattern near the Bahamas. The circulation patterns presented here are consistent with the majority of of published accounts of flow components. 77 refs., 14 figs., 3 tabs.

  3. The Medieval Climate Anomaly and Little Ice Age in Chesapeake Bay and the North Atlantic Ocean

    USGS Publications Warehouse

    Cronin, T. M.; Hayo, K.; Thunell, R.C.; Dwyer, G.S.; Saenger, C.; Willard, D.A.

    2010-01-01

    A new 2400-year paleoclimate reconstruction from Chesapeake Bay (CB) (eastern US) was compared to other paleoclimate records in the North Atlantic region to evaluate climate variability during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). Using Mg/Ca ratios from ostracodes and oxygen isotopes from benthic foraminifera as proxies for temperature and precipitation-driven estuarine hydrography, results show that warmest temperatures in CB reached 16-17. ??C between 600 and 950. CE (Common Era), centuries before the classic European Medieval Warm Period (950-1100. CE) and peak warming in the Nordic Seas (1000-1400. CE). A series of centennial warm/cool cycles began about 1000. CE with temperature minima of ~. 8 to 9. ??C about 1150, 1350, and 1650-1800. CE, and intervening warm periods (14-15. ??C) centered at 1200, 1400, 1500 and 1600. CE. Precipitation variability in the eastern US included multiple dry intervals from 600 to 1200. CE, which contrasts with wet medieval conditions in the Caribbean. The eastern US experienced a wet LIA between 1650 and 1800. CE when the Caribbean was relatively dry. Comparison of the CB record with other records shows that the MCA and LIA were characterized by regionally asynchronous warming and complex spatial patterns of precipitation, possibly related to ocean-atmosphere processes. ?? 2010.

  4. The North Atlantic Cold Bias

    NASA Astrophysics Data System (ADS)

    Greatbatch, Richard; Drews, Annika; Ding, Hui; Latif, Mojib; Park, Wonsun

    2016-04-01

    The North Atlantic cold bias, associated with a too zonal path of the North Atlantic Current and a missing "northwest corner", is a common problem in coupled climate and forecast models. The bias affects the North Atlantic and European climate mean state, variability and predictability. We investigate the use of a flow field correction to adjust the path of the North Atlantic Current as well as additional corrections to the surface heat and freshwater fluxes. Results using the Kiel Climate Model show that the flow field correction allows a northward flow into the northwest corner, largely eliminating the bias below the surface layer. A surface cold bias remains but can be eliminated by additionally correcting the surface freshwater flux, without adjusting the surface heat flux seen by the ocean model. A model version in which only the surface fluxes of heat and freshwater are corrected continues to exhibit the incorrect path of the North Atlantic Current and a strong subsurface bias. Removing the bias impacts the multi-decadal time scale variability in the model and leads to a better representation of the SST pattern associated with the Atlantic Multidecadal Variability than the uncorrected model.

  5. The North Atlantic Oscillation as a driver of rapid climate change in the Northern Hemisphere

    NASA Astrophysics Data System (ADS)

    Delworth, Thomas L.; Zeng, Fanrong; Vecchi, Gabriel A.; Yang, Xiaosong; Zhang, Liping; Zhang, Rong

    2016-07-01

    Pronounced climate changes have occurred since the 1970s, including rapid loss of Arctic sea ice, large-scale warming and increased tropical storm activity in the Atlantic. Anthropogenic radiative forcing is likely to have played a major role in these changes, but the relative influence of anthropogenic forcing and natural variability is not well established. The above changes have also occurred during a period in which the North Atlantic Oscillation has shown marked multidecadal variations. Here we investigate the role of the North Atlantic Oscillation in these rapid changes through its influence on the Atlantic meridional overturning circulation and ocean heat transport. We use climate models to show that observed multidecadal variations of the North Atlantic Oscillation can induce multidecadal variations in the Atlantic meridional overturning circulation and poleward ocean heat transport in the Atlantic, extending to the Arctic. Our results suggest that these variations have contributed to the rapid loss of Arctic sea ice, Northern Hemisphere warming, and changing Atlantic tropical storm activity, especially in the late 1990s and early 2000s. These multidecadal variations are superimposed on long-term anthropogenic forcing trends that are the dominant factor in long-term Arctic sea ice loss and hemispheric warming.

  6. The Atlantic Meridional Overturning Circulation's Response to Variable Buoyancy Forcing

    NASA Astrophysics Data System (ADS)

    Butler, Edward; Oliver, Kevin; Hirschi, Joël

    2014-05-01

    The Meridional Overturning Circulation (MOC) is a large-scale global circulation of water (and heat) throughout the world's ocean. It is an integral part of the climate system, responsible for significant anomalous warming of the North Atlantic region. Much of our current understanding of the MOC is based on equilibrium theories. However, the MOC is not a steady circulation and exhibits variability across a broad range of timescales. We examine the transient response of global ocean overturning, with particular emphasis on the Atlantic MOC (AMOC), to periodic variations in the North Atlantic meridional density gradient on decadal, centennial, and millennial timescales within the Nucleus for European Modelling of the Ocean (NEMO) model framework. We use the ORCA2 global ocean configuration of NEMO (with realistic topography and a horizontal resolution of 2°) and impose periodic variations in air temperature over the North Atlantic. In response, we see large oscillations in the strength of the AMOC which peak in magnitude at 128-year timescales. A scaling relationship of the form Ψ ~ ΔρH2 (in which Δρ is a measure of meridional density gradient and H is the depth scale of maximal overturning) is found to hold for the AMOC in these transient simulations with strongest correlations observed at centennial timescales. We explore the validity of this scaling relationship across a broad range of spatial and temporal scales and discuss its validity in a global context.

  7. Mg/Ca, Sr/Ca and Ca isotope ratios in benthonic foraminifers related to test structure, mineralogy and environmental controls

    NASA Astrophysics Data System (ADS)

    Gussone, Nikolaus; Filipsson, Helena L.; Kuhnert, Henning

    2016-01-01

    We analysed Mg/Ca, Sr/Ca and Ca isotope ratios of benthonic foraminifers from sediment core tops retrieved during several research cruises in the Atlantic Ocean, in order to improve the understanding of isotope fractionation and element partitioning resulting from biomineralisation processes and changes in ambient conditions. Species include foraminifers secreting tests composed of hyaline low magnesium calcite, porcelaneous high magnesium calcite as well as aragonite. Our results demonstrate systematic isotope fractionation and element partitioning patterns specific for these foraminiferal groups. Calcium isotope fractionation is similar in porcelaneous and hyaline calcite tests and both groups demonstrate the previously described anomaly with enrichment of heavy isotopes around 3-4 °C (Gussone and Filipsson, 2010). Calcium isotope ratios of the aragonitic species Hoeglundina elegans, on the other hand, are about 0.4‰ lighter compared to the calcitic species, which is in general agreement with stronger fractionation in inorganic aragonite compared to calcite. However, the low and strongly variable Sr content suggests additional processes during test formation, and we propose that transmembrane ion transport or a precursor phase to aragonite may be involved. Porcelaneous tests, composed of high Mg calcite, incorporate higher amounts of Sr compared to hyaline low Mg calcite, in agreement with inorganic calcite systematics, but also porcelaneous tests with reduced Mg/Ca show high Sr/Ca. While calcium isotopes, Sr/Ca and Mg/Ca in benthonic foraminifers primarily appear to fractionate and partition with a dominant inorganic control, δ44/40Ca temperature and growth rate dependencies of benthonic foraminifer tests favour a dominant contribution of light Ca by transmembrane transport relative to unfractionated seawater Ca to the calcifying fluid, thus controlling the formation of foraminiferal δ44/40Ca and Sr/Ca proxy signals.

  8. The Response of the North Atlantic Bloom to NAO Forcing

    NASA Technical Reports Server (NTRS)

    Mizoguchi, Ken-Ichi; Worthen, Denise L.; Hakkinen, Sirpa; Gregg, Watson W.

    2004-01-01

    Results from the climatologically forced coupled ice/ocean/biogeochemical model that covers the Arctic and North Atlantic Oceans are presented and compared to the chlorophyll fields of satellite-derived ocean color measurements. Biogeochemical processes in the model are determined from the interactions among four phytoplankton functional groups (diatoms, chlorophytes, cyanobacteria and coccolithophores) and four nutrients (nitrate, ammonium, silicate and dissolved iron). The model simulates the general large-scale pattern in April, May and June, when compared to both satellite-derived and in situ observations. The subpolar North Atlantic was cool in the 1980s and warm in the latter 1990s, corresponding to the CZCS and SeaWiFS satellite observing periods, respectively. The oceanographic conditions during these periods resemble the typical subpolar upper ocean response to the NAO+ and NAO-phases, respectively. Thus, we use the atmospheric forcing composites from the two NAO phases to simulate the variability of the mid-ocean bloom during the satellite observing periods. The model results show that when the subpolar North Atlantic is cool, the NAO+ case, more nutrients are available in early spring than when the North Atlantic is warm, the NAO-case. However, the NAO+ simulation produces a later bloom than the NAO-simulation. This difference in the bloom times is also identified in SeaWiFS and CZCS satellite measurements. In the model results, we can trace the difference to the early diatom bloom due to a warmer upper ocean. The higher nutrient abundance in the NAO+ case did not provide larger total production than in the NAO- case, instead the two cases had a comparable area averaged amplitude. This leads us to conclude that in the subpolar North Atlantic, the timing of the spring phytoplankton bloom depends on surface temperature and the magnitude of the bloom is not significantly impacted by the nutrient abundance.

  9. Burst Feeding of Pelagia noctiluca ephyrae on Atlantic Bluefin Tuna (Thunnus thynnus) Eggs

    PubMed Central

    Gordoa, Ana; Acuña, José Luis; Farrés, Roser; Bacher, Kathrin

    2013-01-01

    This study investigates the predation of P. noctiluca ephyrae on Atlantic Bluefin tuna (ABFT) eggs under different experimental conditions. The specific factors considered in the experimental design were: a) water mix conditions to explore predation under two-dimensional (2D) and three-dimensional (3D) prey distributions, b) prey density to investigate the ingestion rate capacity, and c) incubation time to inspect gut saturation. The eggs and jellyfish ephyrae were collected during the 2012 ABFT spawning survey off Ibiza (Balearic Isl., Western Mediterranean). The results showed that the proportion of feeding ephyrae increased with size. The mean clearance rate of feeding ephyrae, 4.14 L h-1, was the highest ever recorded for ephyrae. Under calm conditions the eggs floated at the surface (2D spatial arrangement) and the clearance rates, at low prey densities, were at least twice those under mixed conditions (3D spatial arrangement). At high prey density, clearance rate did not differ between mix conditions, probably due to the fast gut saturation, which was reached in c.a. 15 min, as revealed by time series observations of gut contents. The fast saturation of ephyrae and their slow digestion time of approximately 18 h suggest the existence of a diel feeding periodicity. We conclude that in the Western Mediterranean, P. noctiluca ephyrae are capable of predating on ABFT eggs, a highly pulsed and spatially restricted resource that potentially switches from a 3D to a 2D configuration in the absence of wind-generated turbulence. The P. noctiluca and Atlantic Bluefin tuna egg system might represent an example of a general mechanism linking pelagic and neustonic food webs. PMID:24069335

  10. Periodized wavelets

    SciTech Connect

    Schlossnagle, G.; Restrepo, J.M.; Leaf, G.K.

    1993-12-01

    The properties of periodized Daubechies wavelets on [0,1] are detailed and contrasted against their counterparts which form a basis for L{sup 2}(R). Numerical examples illustrate the analytical estimates for convergence and demonstrate by comparison with Fourier spectral methods the superiority of wavelet projection methods for approximations. The analytical solution to inner products of periodized wavelets and their derivatives, which are known as connection coefficients, is presented, and several tabulated values are included.

  11. Mid to late Holocene strengthening of the East Greenland Current linked to warm subsurface Atlantic water

    NASA Astrophysics Data System (ADS)

    Perner, Kerstin; Moros, Matthias; Lloyd, Jeremy M.; Jansen, Eystein; Stein, Rüdiger

    2015-12-01

    The relatively fresh and cold East Greenland Current (EGC) connects the Arctic with the subpolar North Atlantic Ocean. Its strength and influence on the freshwater balance in the North Atlantic affects both the Subpolar Gyre dynamics and deep convection in the Labrador Sea. Enhanced freshwater and sea-ice expansion in the subpolar North Atlantic is suggested to modify the northward heat transport within the North Atlantic Current. High-resolution palaeoceanographic reconstructions, based on planktic and benthic foraminifera assemblage data, from the central East Greenland shelf (Foster Bugt) reveal distinct centennial to millennial-scale oceanographic variability that relates to climatic changes during the mid to late Holocene (the last c. 6.3 ka BP). Our data highlight intervals of cooling and freshening of the polar surface EGC waters that accompany warming in the subsurface Atlantic waters, which are a combination of chilled Atlantic Intermediate Water (AIW) from the Arctic Ocean and of the Return Atlantic Current (RAC) from the West Spitsbergen Current (WSC). Mid Holocene thermal optimum conditions prevailed until c. 4.5 ka BP. A thin/absent surface Polar Water layer, low drift/sea-ice occurrence and strong contribution of recirculating warm Atlantic waters at the subsurface, suggest a relatively weak EGC during this period. Subsequently, between 1.4 and 4.5 ka BP, the water column became well stratified as the surface Polar Water layer thickened and cooled, indicating a strong EGC. This EGC strengthening parallelled enhanced subsurface chilled AIW contribution from the Arctic Ocean after c. 4.5 ka BP, which culminated from 1.4 to 2.3 ka BP. This coincides with warming identified in earlier work of the North Atlantic Current, the Irminger Current, and the West Greenland Current. We link the enhanced contribution of chilled Atlantic Water during this period to the time of the 'Roman Warm Period'. The observed warming offshore East Greenland, centred at c. 1.8 ka

  12. Vacuolar Ca(2+) uptake.

    PubMed

    Pittman, Jon K

    2011-08-01

    Calcium transporters that mediate the removal of Ca(2+) from the cytosol and into internal stores provide a critical role in regulating Ca(2+) signals following stimulus induction and in preventing calcium toxicity. The vacuole is a major calcium store in many organisms, particularly plants and fungi. Two main pathways facilitate the accumulation of Ca(2+) into vacuoles, Ca(2+)-ATPases and Ca(2+)/H(+) exchangers. Here I review the biochemical and regulatory features of these transporters that have been characterised in yeast and plants. These Ca(2+) transport mechanisms are compared with those being identified from other vacuolated organisms including algae and protozoa. Studies suggest that Ca(2+) uptake into vacuoles and other related acidic Ca(2+) stores occurs by conserved mechanisms which developed early in evolution. PMID:21310481

  13. The timing of deglacial circulation changes in the Atlantic

    NASA Astrophysics Data System (ADS)

    Waelbroeck, C.; Skinner, L.; Gersonde, R.; Mackensen, A.; Michel, E.; Labeyrie, L. D.; Duplessy, J.

    2009-12-01

    We present new benthic isotopic data from core MD07-3076 retrieved in the Atlantic sector of the Southern Ocean (44°09’S, 14°13’W, 3770 m water depth), and place them in the context of well-dated published Atlantic benthic foraminifera isotopic records covering the last 30 ky. Dating of core MD07-3076 was achieved by a combination of 14C AMS measurements on planktonic foraminifera and correlation of sea surface temperature signals derived from both planktonic foraminifera Mg/Ca and census counts, with Antarctic ice isotopic records (Skinner et al., submitted). Comparison of benthic isotopic records from various depths in the North and South Atlantic reveals that circulation changes over the last deglaciation did not take place simultaneously in the 1000-2000 m and in the 3000-4500 m depth ranges. Circulation changes first occurred at lower depth, causing large and relatively rapid changes in benthic δ18O and δ13C at the beginning of Heinrich Stadial 1 (HS1) and the Younger Dryas. Below 3000 m depth, North Atlantic deep water hydrology changed only gradually until a large increase in deep water ventilation took place, resulting from the resumption of North Atlantic Deep Water formation at the end of HS1. In contrast, our deep South Atlantic record indicates that Circumpolar Deep Water around 3800 m depth remained quasi-isolated from northern water masses until the end of HS1. Furthermore, our record shows that core MD07-3076 site was then flushed with better ventilated waters for a few hundred years from ~14.5 to 14 calendar ky BP, before benthic δ18O and δ13C values resumed their progression towards Holocene levels. In conclusion, this set of well-dated Atlantic records demonstrates that benthic δ18O records followed different time evolutions across the last deglaciation, depending on the site latitude and water depth, so that benthic δ18O can not be used as a global correlation tool with a precision better than 3 ky.

  14. Granger causality and Atlantic hurricanes

    NASA Astrophysics Data System (ADS)

    Elsner, James B.

    2007-08-01

    Atlantic tropical cyclones have been getting stronger recently with a trend that is related to an increase in the late summer/early fall sea-surface temperature over the North Atlantic. Some studies attribute the increasing ocean warmth and hurricane intensity to a natural climate fluctuation, known as the Atlantic Multidecadal Oscillation; others suggest that climate change related to anthropogenic greenhouse gases emissions is the cause. Noting that the only difference between these two hypotheses is the causal connection between global mean near-surface air temperature (GT) and Atlantic sea-surface temperature (SST), the author previously showed how to use statistical tests to examine this hypothesis. Here the author expands on this research. In particular, a more comprehensive explanation of the techniques and additional tests and checks against misspecification are provided. The earlier results are confirmed in showing that preceding GT anomalies have a significant statistical relationship to current SST anomalies but not conversely so that if causality exists between Atlantic SST and global temperature, the causal direction likely goes from GT to SST. The result is robust against a small amount of noise added to the data. Identical tests applied to surrogate time series fail to identify causality as expected. The work underscores the importance of using data models to understand relationships between hurricanes and climate.

  15. Meridional Distribution of Aerosol Optical Thickness over the Tropical Atlantic Ocean

    NASA Technical Reports Server (NTRS)

    Kishcha, P.; Silva, Arlindo M.; Starobinets, B.; Long, C. N.; Kalashnikova, O.; Alpert, P.

    2015-01-01

    Previous studies showed that, over the global ocean, there is hemispheric asymmetry in aerosols and no noticeable asymmetry in cloud fraction (CF). In the current study, we focus on the tropical Atlantic (30 Deg N 30 Deg S) which is characterized by significant amounts of Saharan dust dominating other aerosol species over the North Atlantic. We found that, by contrast to the global ocean, over a limited area such as the tropical Atlantic, strong meridional asymmetry in dust aerosols was accompanied by meridional CF asymmetry. During the 10-year study period (July 2002 June 2012), NASA Aerosol Reanalysis (aka MERRAero) showed that, when the meridional asymmetry in dust aerosol optical thickness (AOT) was the most pronounced (particularly in July), dust AOT averaged separately over the tropical North Atlantic was one order of magnitude higher than dust AOT averaged over the tropical South Atlantic. In the presence of such strong meridional asymmetry in dust AOT in July, CF averaged separately over the tropical North Atlantic exceeded CF averaged over the tropical South Atlantic by 20%. Our study showed significant cloud cover, up to 0.8 - 0.9, in July along the Saharan Air Layer which contributed to above-mentioned meridional CF asymmetry. Both Multi-Angle Imaging SpectroRadiometer (MISR) measurements and MERRAero data were in agreement on seasonal variations in meridional aerosol asymmetry. Meridional asymmetry in total AOT over the Atlantic was the most pronounced between March and July, when dust presence over the North Atlantic was maximal. In September and October, there was no noticeable meridional asymmetry in total AOT and meridional CF distribution over the tropical Atlantic was almost symmetrical.

  16. A new calibration for the Sr/Ca-temperature relationship in sclerosponges reveals synchronous changes in Caribbean specimens indicative of warming and multi-decadal climate variability

    NASA Astrophysics Data System (ADS)

    Waite, A. J.; Swart, P. K.; Rosenheim, B. E.

    2009-12-01

    Previous work defined the calibration between the skeletal Sr/Ca ratio of the sclerosponge Ceratoporella nicholsoni and the ambient seawater temperature. However, application of this calibration to records throughout the Caribbean reveals a nearly 4°C warming over the last 150 years, in excess of what one might expect from global climate averages. As the original C. nicholsoni Sr/Ca-temperature relationship was calibrated between 26 and 30°C, it is possible that the relationship differed outside of the examined temperature window. This suspicion is confirmed by the measurement of Sr/Ca ratios from additional specimens of the same species. These show a significantly different slope between Sr/Ca and temperature at lower temperatures (21 to 26°C). Using this information, the calibration equation has been refined and the subsequent reconstructions of temperature are much more realistic, indicating a warming of approximately 1°C over the last 150 years. Applying this new calibration to additional published sclerosponge records of Sr/Ca reveals remarkable agreements between records from the Bahamas and Jamaica, both in amplitude of warming and smaller scale variability. In addition, the depth versus temperature relationship associated with these specimens is preserved. The refined temperature reconstruction of a 600 year record from Exuma Sound, Bahamas, demonstrates the cyclic nature of its variability (~15 and 28 year periodicities). Further use of these data and stable oxygen isotopes to calculate salinity reveals variability on multi-decadal timescales. This includes an approximately 20 year periodicity between 1400 and 1790. From 1790 to 2000, the dominant mode appears to switch to a roughly 60 year periodicity, consistent with that of the Atlantic Multi-decadal Oscillation (AMO).

  17. Periodic cages.

    PubMed

    Diudea, Mircea V; Nagy, Csaba L; Silaghi-Dumitrescu, Ioan; Graovac, Ante; Janezic, Dusanka; Vikić-Topić, Drazen

    2005-01-01

    Various cages are constructed by using three types of caps: f-cap (derived from spherical fullerenes by deleting zones of various size), kf-cap (obtainable by cutting off the polar ring, of size k), and t-cap ("tubercule"-cap). Building ways are presented, some of them being possible isomerization routes in the real chemistry of fullerenes. Periodic cages with ((5,7)3) covering are modeled, and their constitutive typing enumeration is given. Spectral data revealed some electronic periodicity in fullerene clusters. Semiempirical and strain energy calculations complete their characterization. PMID:15807490

  18. Controls on the organic chemical composition of settling particles in the Northeast Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Kiriakoulakis, Konstadinos; Stutt, Edward; Rowland, Steven J.; Annick Vangriesheim; Lampitt, Richard S.; Wolff, George A.

    The organic matter of sinking particulate material collected in the Northeast Atlantic Ocean (ca. 49°N, 16°W) was investigated in order to determine temporal and depth-related variability in its composition. Three sediment traps were deployed at nominal depths of 1000 m (below the permanent thermocline), 3000 m (representing the deep-water fluxes) and at 4700 m, about 100 m above the seafloor (just above the benthic boundary layer). The samples span a 28-month sampling period from October 1995 until February 1998, each sample representing a period of between 7 and 28 days. Total organic carbon and total nitrogen contents decrease with depth, as did the absolute concentrations of most biochemicals measured in this study, such as intact proteins and individual lipids. However, concentrations of proteins relative to total organic carbon and total nitrogen did not show any significant change with depth, implying that they are not being rapidly degraded and so may provide an important supply of nitrogen to the benthos. Fluxes of protein, TN and TOC are significantly correlated at all depths. Lipid compositions vary temporally. During periods of high flux, particularly in the summer, the lipids are richer in ‘labile components’, namely unsaturated fatty acids and low molecular weight alcohols. During periods of low flux other compounds, such as sterols, steroidal ketones and a trisnorhopan-21-one are more abundant. One sample, taken close to the seafloor, was highly enriched in lipids, sterols and fatty acids in particular; this may represent detritus derived from bottom-dwelling invertebrates.

  19. Links between salinity variation in the Caribbean and North Atlantic thermohaline circulation.

    PubMed

    Schmidt, Matthew W; Spero, Howard J; Lea, David W

    2004-03-11

    Variations in the strength of the North Atlantic Ocean thermohaline circulation have been linked to rapid climate changes during the last glacial cycle through oscillations in North Atlantic Deep Water formation and northward oceanic heat flux. The strength of the thermohaline circulation depends on the supply of warm, salty water to the North Atlantic, which, after losing heat to the atmosphere, produces the dense water masses that sink to great depths and circulate back south. Here we analyse two Caribbean Sea sediment cores, combining Mg/Ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical Atlantic surface salinity during the last glacial cycle. We find that Caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2, 4 and 6, and lower salinities during the warm stages 3 and 5, covarying with the strength of North Atlantic Deep Water formation. At the initiation of the Bølling/Allerød warm interval, Caribbean surface salinity decreased abruptly, suggesting that the advection of salty tropical waters into the North Atlantic amplified thermohaline circulation and contributed to high-latitude warming. PMID:15014495

  20. Atlantic Seaduck Project

    USGS Publications Warehouse

    Perry, M.C.

    2006-01-01

    Atlantic Seaduck Project is being conducted to learn more about the breeding and moulting areas of seaducks in northern Canada and more about their feeding ecology on wintering areas, especially Chesapeake Bay. Satellite telemetry is being used to track surf scoters wintering in Chesapeake Bay, Maryland and black scoters on migrational staging areas in New Brunswick, Canada to breeding and moulting areas in northern Canada. Various techniques used to capture the scoters included mist netting, night-lighting, and net capture guns. All captured ducks were transported to a veterinary hospital where surgery was conducted following general anaesthesia procedures. A PTT100 transmitter (39 g) manufactured by Microwave, Inc., Columbia, Maryland was implanted into the duck?s abdominal cavity with an external (percutaneous) antenna. Eight of the surf scoters from Chesapeake Bay successfully migrated to possible breeding areas in Canada and all 13 of the black scoters migrated to suspected breeding areas. Ten of the 11 black scoter males migrated to James Bay presumably for moulting. Updated information from the ARGOS Systems aboard the NOAA satellites on scoter movements was made accessible on the Patuxent Website. Habitat cover types of locations using GIS (Geographical Information Systems) and aerial photographs (in conjunction with remote sensing software) are currently being analyzed to build thematic maps with varying cosmetic layer applications. Many factors related to human population increases have been implicated in causing changes in the distribution and abundance of wintering seaducks. Analyses of the gullet (oesophagus and proventriculus) and the gizzard of seaducks are currently being conducted to determine if changes from historical data have occurred. Scoters in the Bay feed predominantly on the hooked mussel and several species of clams. The long-tailed duck appears to select the gem clam in greater amounts than other seaducks, but exhibits a diverse diet of

  1. Reddish Egret extends its breeding range along the North American Atlantic coast into South Carolina

    USGS Publications Warehouse

    Ferguson, L.M.; Jodice, P.G.R.; Post, W.; Sanders, F.I.

    2005-01-01

    We report the northernmost breeding record of the Reddish Egret (Egretta rufescens) along the North American Atlantic Coast. Nesting activity was first seen in late May 2004, and on 6 July 2004 a nest was discovered with two young chicks on Marsh Island, a barrier island located within Cape Romain National Wildlife Refuge, South Carolina, USA. Reddish Egret nestlings were last observed within 1 m of the nest on 30 July 2004. This represents a northward extension of ca. 450 km in the breeding range of this species and, for the U.S. Atlantic Coast, the only recorded instance of nesting north of Florida.

  2. Correlation of lacustrine paleoclimate records from Mono Lake with the North Atlantic using paleomagnetic intensity

    NASA Astrophysics Data System (ADS)

    Zimmerman, S. R. H.; Hemming, S. R.; Kent, D. V.

    2003-04-01

    The Wilson Creek Formation of Mono Lake, CA is a Late Pleistocene lacustrine sequence that records major shifts in the paleoenvironment of the lake. It has also been shown to be an excellent recorder of the past variations of the Earth’s magnetic field, and is important as the type section of the Mono Lake Excursion (MLE). As with many terrestrial records, however, it has proven to be very challenging to date the Wilson Creek Fm. at high resolution. Radiocarbon dating has been shown to be vulnerable to contamination with modern carbon, while 40Ar/39Ar dating of the rhyolitic ashes is complicated by inclusion of older xenocrysts. Benson et al. (1998; QR, v. 49, 1-10 ) suggested a correlation to North Atlantic records using paleomagnetic inclination and intensity combined with radiocarbon ages. They argued that δ18O of the Wilson Creek sediments represents variations in lake level, with prominent dry periods (high δ18O) correlating to the North Atlantic Heinrich events. We generated a relative paleointensity record for the Wilson Creek section and propose an alternative correlation to the North Atlantic Paleomagnetic Intensity Stack (NAPIS-75; Laj et al. 2000, Phil. Trans. R. Soc., v. 358, 1009-1025) and the GISP2 age model. It was recently demonstrated by Stoner et al. (2002, QSR v. 21, 1141-1151) that variations in the Earth’s paleomagnetic field intensity are correlative both at high-resolution (10^3 yr) and over long distances (10^4 km). Assuming that the MLE is equivalent to the Laschamp Excursion and that the lake expanded early in Marine Isotope Stage 4, a simple correlation of the major features of the NAPIS-75 and Mono records places the Wilson Creek Fm. on the GISP2 age model, and allows correlation of that paleoclimate record to other records also on that time scale. We also interpret the major δ18O excursions as Heinrich correlatives; however, our correlation equates the three older excursions to H4, H5, and H6 (rather than H3, no correl., and H4

  3. Cryptotephrochronology in the North Atlantic Region : Linking Greenland Ice and North Atlantic Marine Sediments

    NASA Astrophysics Data System (ADS)

    Abbott, P. M.; Davies, S. M.; Bourne, A.; Meara, R.; Cook, E.; Griggs, A.

    2012-12-01

    Tephrochronology is a powerful technique that can be utilised for the correlation and synchronisation of disparate palaeoclimatic records. Thus, this technique has considerable potential for addressing key questions relating to rapid climatic events that characterised the last glacial period. In particular, our search for microscopic tephra layers or cryptotephras within the Greenland ice-cores and marine cores from the North Atlantic Ocean has the potential to test the phase relationships between the atmospheric and oceanic responses to these high-magnitude and abrupt climatic events. Here we report on results of investigations of the MIS 5 to 2 time period drawing on examples from several North Atlantic marine cores from various sites within the North Atlantic including the Rockall Trough, Faroe Islands region, Goban Spur, Gardar Drift and Irminger Basin. These investigations fall within the context of the SMART and TRACE projects. Several cryptotephra horizons have been identified by applying techniques first developed for terrestrial sedimentary material. The two main challenges associated with cryptotephra work in the glacial North Atlantic are i) determining the dominant transportation processes and ii) assessing the influence of secondary reworking processes and the integrity of the isochrons. The potential influence of these processes is investigated by assessing shard size, geochemical (major and trace element) heterogeneity and co-variance of IRD input and sortable silt for some cores. High-resolution investigations of the Greenland ice-cores of NGRIP, GRIP and NEEM over the same time period have identified cryptotephras from numerous previously unrecognised eruptions. The principal source of horizons is Iceland, with some correlated to specific volcanic systems such as Katla, Grimsvötn, Hekla and Veidivötn-Bardabunga. An overarching aspect of this work is the robust geochemical fingerprinting of the small glass shards within these cryptotephras using

  4. Climatic Variability over the North Atlantic

    NASA Astrophysics Data System (ADS)

    Hurrell, J.; Hoerling, M. P.; Folland, C. K.

    INTRODUCTION WHAT IS THE NORTH ATLANTIC OSCILLATION AND HOW DOES IT IMPACT REGIONAL - CLIMATE? WHAT ARE THE MECHANISMS THAT GOVERN NORTH ATLANTIC OSCILLATION VARIABILITY? Atmospheric Processes Ocean Forcing of the Atmosphere CONCLUDING COMMENTS ON THE OTHER ASPECTS OF NORTH ATLANTIC CLIMATE - VARIABILITY REFERENCES

  5. Atlantic opportunities for ENSO prediction

    NASA Astrophysics Data System (ADS)

    del Rey, Marta Martin; Rodríguez-Fonseca, Belén; Polo, Irene

    2015-04-01

    El Niño-Southern Oscillation (ENSO) is the dominant mode of tropical climate variability with worldwide impacts. Major advances in ENSO research have been done in the last decades, focusing on the mechanisms involved in its onset and development, as well as, its global climate teleconnections. Although modelling efforts have been made in ENSO forecast, the prediction of these episodes still remains a challenge for the scientific community. Recent studies put forward the role of extra-tropical and tropical regions as precursors of ENSO, but these teleconnections have changed along the 20th century. In particular, an Atlantic Niño precedes the development of a Pacific La Niña (and vice versa) 6 months in advance, taking part of an air-sea coupled mode of variability which only shows up during negative phases of the Atlantic Multidecadal Oscillation (AMO). The non-stationarity of this mode opens window opportunities for ENSO forecast, using the Tropical Atlantic Sea Surface Temperature (SST) as the predictor field. Here, we present for the first time a statistical crossvalidated hindcast of ENSO events based on an Extended Multiple Maximum Covariance Analysis (EMMCA). This method considers a unique predictor field, the summer Atlantic SSTs, and a set of predictant fields in different regions and seasons, according to the Atlantic-Pacific mechanism. The predicted tropical Pacific variables involved in ENSO development, show a good agreement with the observed ones during negative AMO phases, with a remarkable increase of the predictability skill based on correlations. During those negative AMO decades, the hindcast reproduces quite well the observed Atlantic-modulated ENSO episodes, but with stronger signal than observations. This AMO-dependency of the ENSO predictability could help to resolve some open questions about the seasonal to decadal ENSO forecast and its impacts.

  6. Metabolic priorities during starvation: enzyme sparing in liver and white muscle of Atlantic cod, Gadus morhua L.

    PubMed

    Guderley, Helga; Lapointe, Dominique; Bédard, Martin; Dutil, Jean-Denis

    2003-06-01

    Atlantic cod, Gadus morhua, respond to starvation first by mobilising hepatic lipids, then muscle and hepatic glycogen and finally muscle proteins. The dual role of proteins as functional elements and energetic reserves should lead to a temporal hierarchy of mobilisation where the nature of a function dictates its conservation during starvation. We examined (1) whether lysosomal and anti-oxidant enzymes in liver and white muscle are spared during prolonged starvation, (2) whether the responses of these enzymes in muscle vary longitudinally. Hepatic contents of lysosomal proteases decreased with starvation, whereas those of catalase (CAT) increased and lysosomal enzymes of carbohydrate metabolism and glutathione S-transferase (GST) did not change. In white muscle, starvation decreased the specific activity of lysosomal enzymes of carbohydrate degradation and doubled that of cathepsin D (CaD). The activity of anti-oxidant enzymes and acid phosphatase in muscle was unchanged with starvation. In white muscle neither lysosomal enzymes nor anti-oxidant enzymes varied significantly with sampling position. In cod muscle, antioxidant enzymes, CaD and acid phosphatase are spared during a period of starvation that decreases lysosomal enzymes of carbohydrate metabolism and decreases glycolytic enzyme activities. In cod liver, the anti-oxidant enzymes, CAT and GST, were also spared during starvation. PMID:12781835

  7. Arctic warming will promote Atlantic-Pacific fish interchange

    NASA Astrophysics Data System (ADS)

    Wisz, M. S.; Broennimann, O.; Grønkjær, P.; Møller, P. R.; Olsen, S. M.; Swingedouw, D.; Hedeholm, R. B.; Nielsen, E. E.; Guisan, A.; Pellissier, L.

    2015-03-01

    Throughout much of the Quaternary Period, inhospitable environmental conditions above the Arctic Circle have been a formidable barrier separating most marine organisms in the North Atlantic from those in the North Pacific. Rapid warming has begun to lift this barrier, potentially facilitating the interchange of marine biota between the two seas. Here, we forecast the potential northward progression of 515 fish species following climate change, and report the rate of potential species interchange between the Atlantic and the Pacific via the Northwest Passage and the Northeast Passage. For this, we projected niche-based models under climate change scenarios and simulated the spread of species through the passages when climatic conditions became suitable. Results reveal a complex range of responses during this century, and accelerated interchange after 2050. By 2100 up to 41 species could enter the Pacific and 44 species could enter the Atlantic, via one or both passages. Consistent with historical and recent biodiversity interchanges, this exchange of fish species may trigger changes for biodiversity and food webs in the North Atlantic and North Pacific, with ecological and economic consequences to ecosystems that at present contribute 39% to global marine fish landings.

  8. Interior pathways of the North Atlantic meridional overturning circulation.

    PubMed

    Bower, Amy S; Lozier, M Susan; Gary, Stefan F; Böning, Claus W

    2009-05-14

    To understand how our global climate will change in response to natural and anthropogenic forcing, it is essential to determine how quickly and by what pathways climate change signals are transported throughout the global ocean, a vast reservoir for heat and carbon dioxide. Labrador Sea Water (LSW), formed by open ocean convection in the subpolar North Atlantic, is a particularly sensitive indicator of climate change on interannual to decadal timescales. Hydrographic observations made anywhere along the western boundary of the North Atlantic reveal a core of LSW at intermediate depths advected southward within the Deep Western Boundary Current (DWBC). These observations have led to the widely held view that the DWBC is the dominant pathway for the export of LSW from its formation site in the northern North Atlantic towards the Equator. Here we show that most of the recently ventilated LSW entering the subtropics follows interior, not DWBC, pathways. The interior pathways are revealed by trajectories of subsurface RAFOS floats released during the period 2003-2005 that recorded once-daily temperature, pressure and acoustically determined position for two years, and by model-simulated 'e-floats' released in the subpolar DWBC. The evidence points to a few specific locations around the Grand Banks where LSW is most often injected into the interior. These results have implications for deep ocean ventilation and suggest that the interior subtropical gyre should not be ignored when considering the Atlantic meridional overturning circulation. PMID:19444214

  9. Periodic Polymers

    NASA Astrophysics Data System (ADS)

    Thomas, Edwin

    2013-03-01

    Periodic polymers can be made by self assembly, directed self assembly and by photolithography. Such materials provide a versatile platform for 1, 2 and 3D periodic nano-micro scale composites with either dielectric or impedance contrast or both, and these can serve for example, as photonic and or phononic crystals for electromagnetic and elastic waves as well as mechanical frames/trusses. Compared to electromagnetic waves, elastic waves are both less complex (longitudinal modes in fluids) and more complex (longitudinal, transverse in-plane and transverse out-of-plane modes in solids). Engineering of the dispersion relation between wave frequency w and wave vector, k enables the opening of band gaps in the density of modes and detailed shaping of w(k). Band gaps can be opened by Bragg scattering, anti-crossing of bands and discrete shape resonances. Current interest is in our group focuses using design - modeling, fabrication and measurement of polymer-based periodic materials for applications as tunable optics and control of phonon flow. Several examples will be described including the design of structures for multispectral band gaps for elastic waves to alter the phonon density of states, the creation of block polymer and bicontinuous metal-carbon nanoframes for structures that are robust against ballistic projectiles and quasi-crystalline solid/fluid structures that can steer shock waves.

  10. Solar wind: A possible factor driving the interannual sea surface temperature tripolar mode over North Atlantic

    NASA Astrophysics Data System (ADS)

    Xiao, Ziniu; Li, Delin

    2016-06-01

    The effect of solar wind (SW) on the North Atlantic sea surface temperature (SST) in boreal winter is examined through an analysis of observational data during 1964-2013. The North Atlantic SSTs show a pronounced meridional tripolar pattern in response to solar wind speed (SWS) variations. This pattern is broadly similar to the leading empirical orthogonal function (EOF) mode of interannual variations in the wintertime SSTs over North Atlantic. The time series of this leading EOF mode of SST shows a significant interannual period, which is the same as that of wintertime SWS. This response also appears as a compact north-south seesaw of sea level pressure and a vertical tripolar structure of zonal wind, which simultaneously resembles the North Atlantic Oscillation (NAO) in the overlying atmosphere. As compared with the typical low SWS winters, during the typical high SWS winters, the stratospheric polar night jet (PNJ) is evidently enhanced and extends from the stratosphere to the troposphere, even down to the North Atlantic Ocean surface. Notably, the North Atlantic Ocean is an exclusive region in which the SW signal spreads downward from the stratosphere to the troposphere. Thus, it seems that the SW is a possible factor for this North Atlantic SST tripolar mode. The dynamical process of stratosphere-troposphere coupling, together with the global atmospheric electric circuit-cloud microphysical process, probably accounts for the particular downward propagation of the SW signal.

  11. Parallelisms between sea surface temperature changes in the western tropical Atlantic (Guiana Basin) and high latitude climate signals over the last 140 000 years

    NASA Astrophysics Data System (ADS)

    Rama-Corredor, O.; Martrat, B.; Grimalt, J. O.; López-Otalvaro, G. E.; Flores, J. A.; Sierro, F.

    2015-10-01

    Sea surface temperatures (SST) in the Guiana Basin over the last 140 ka were obtained by measuring the C37 alkenone unsaturation index Uk'37 in the sediment core MD03-2616 (7° N, 53° W). The resulting data set is unique in the western tropical Atlantic region for this period. The SSTs range from 25.1 to 28.9 °C, i.e. glacial-interglacial amplitude of 3.8 °C, which is in the range of change of other tropical areas. During the last two interglacial stages (marine isotope stages; MIS1 and MIS5e) and warm long interstadials (MIS5d-a), a rapid transmission of climate variability from Arctic-tropical latitudes is recorded. During these periods, the MD03-2616 SSTs show a conspicuous parallelism with temperature changes observed in Greenland and SST records of North Atlantic mid-latitude cores (Iberian Margin 38° N, Martrat et al., 2007). The last deglaciation in the Guiana Basin is particularly revealing. MIS2 stands out as the coldest period of the interval analysed. The events recorded in Guiana parallel northern latitude events such as the Bølling-Allerød warming and the Younger Dryas cooling which ensued. These oscillations were previously documented in the δ18O of the Sajama tropical ice core (Bolivia) and are present in Guiana, with rates of ca. 6 °C ka-1 and changes of over 2 °C. During the glacial interval, significant abrupt variability is observed, e.g. oscillations of 0.5-1.2 °C during MIS3, which is about 30 % of the maximum glacial-interglacial SST change. In the MD03-2616 record, it is possible to unambiguously identify either the Dansgaard-Oeschger oscillations described in northern latitudes or the SST drops associated with the Heinrich events characteristic of North Atlantic records. Although these events form the background of the climate variability observed, what truly shapes SSTs in the Guiana Basin is a long-term tropical response to precessional changes, which is modulated in the opposite way to Northern Hemisphere variability. This lack

  12. Estimation of Atlantic-Mediterranean netflow variability

    NASA Astrophysics Data System (ADS)

    Guerreiro, Catarina; Peliz, Alvaro; Miranda, Pedro

    2016-04-01

    The exchanges at the Strait of Gibraltar are extremely difficult to measure due to the strong temporal and across-strait variabilities; yet the Atlantic inflow into the Mediterranean is extremely important both for climate and to ecosystems. Most of the published numerical modeling studies do not resolve the Strait of Gibraltar realistically. Models that represent the strait at high resolution focus primarily in high frequency dynamics, whereas long-term dynamics are studied in low resolution model studies, and for that reason the Strait dynamics are poorly resolved. Estimating the variability of the exchanges requires long term and high-resolutions studies, thus an improved simulation with explicit and realistic representation of the Strait is necessary. On seasonal to inter-annual timescales the flow is essentially driven by the net evaporation contribution and consequently realistic fields of precipitation and evaporation are necessary for model setup. A comparison between observations, reanalysis and combined products shows ERA-Interim Reanalysis has the most suitable product for Mediterranean Sea. Its time and space variability are in close agreement with NOC 1.1 for the common period (1980 - 1993) and also with evaporation from OAFLUX (1989 - 2014). Subinertial fluctuations, periods from days to a few months, are the second most energetic, after tides, and are the response to atmospheric pressure fluctuations and local winds. Atmospheric pressure fluctuations in the Mediterranean cause sea level oscillations that induce a barotropic flow through the Strait. Candela's analytical model has been used to quantify this response in later studies, though comparison with observations points to an underestimation of the flow at strait. An improved representation of this term contribution to the Atlantic - Mediterranean exchange must be achieved on longer time-scales. We propose a new simulation for the last 36 years (1979 - 2014) for the Mediterranean - Atlantic

  13. The effect of the Mediterranean Overflow Water on the North Atlantic

    NASA Astrophysics Data System (ADS)

    Aldama Campino, Aitor; Döös, Kristofer

    2015-04-01

    The Mediterranean Overflow Water is created due to an excess of evaporation over precipitation and river runoffs in the Mediterranean Sea. As a result, the incoming surface waters from the Atlantic become denser and saltier. These waters return to the Atlantic through Gibraltar Strait and start mixing with the surrounding waters in the vicinity of the Gulf of Cadiz forming a warm and saline tongue of water, which spreads westward. In this exchange of waters between the Atlantic and the Mediterranean, other magnitudes such as heat and salt are transported. In the last case, the salt transport between the two basins shows a variability with a period of few decades. These oscillations produce two different states, one where the Mediterranean exports salt to the Atlantic and another where the Mediterranean imports salt from it. The Mediterranean-Atlantic system alternates these two states. The aim of this study is to analyse the effects of these multidecadal oscillations on the North Atlantic. This study is performed using data from the climate model EC-EARTH run under pre-industrial conditions, where the greenhouse gas forcing is constant. Different magnitudes such as the total salt and volume transport through Gibraltar Strait, salinity profiles in the vicinity of the Gulf of Cadiz, the net freshwater fluxes in the Mediterranean basin are studied. The analysis of the total salt transport through Gibraltar show periods where salt is imported from the Atlantic and vice versa. Our guess is that the Mediterranean Sea acts as a reservoir which alternates between exporting and importing salt from the North Atlantic through the strait. The impact of this salt transport in Gibraltar on the total salt transport of the Atlantic is studied. The results show a larger impact of the outgoing salt transport on the total Atlantic salt transport north of Gibraltar strait (in a region between 40°N-50°N). These results oppose the ones obtained when the impact of the outgoing salt

  14. Regulation of endoplasmic reticulum Ca2+ oscillations in mammalian eggs

    PubMed Central

    Wakai, Takuya; Zhang, Nan; Vangheluwe, Peter; Fissore, Rafael A.

    2013-01-01

    Summary Changes in the intracellular concentration of free calcium ([Ca2+]i) regulate diverse cellular processes including fertilization. In mammalian eggs, the [Ca2+]i changes induced by the sperm unfold in a pattern of periodical rises, also known as [Ca2+]i oscillations. The source of Ca2+ during oscillations is the endoplasmic reticulum ([Ca2+]ER), but it is presently unknown how [Ca2+]ER is regulated. Here, we show using mouse eggs that [Ca2+]i oscillations induced by a variety of agonists, including PLCζ, SrCl2 and thimerosal, provoke simultaneous but opposite changes in [Ca2+]ER and cause differential effects on the refilling and overall load of [Ca2+]ER. We also found that Ca2+ influx is required to refill [Ca2+]ER, because the loss of [Ca2+]ER was accelerated in medium devoid of Ca2+. Pharmacological inactivation of the function of the mitochondria and of the Ca2+-ATPase pumps PMCA and SERCA altered the pattern of oscillations and abruptly reduced [Ca2+]ER, especially after inactivation of mitochondria and SERCA functions. We also examined the expression of SERCA2b protein and found that it was expressed throughout oocyte maturation and attained a conspicuous cortical cluster organization in mature eggs. We show that its overexpression reduces the duration of inositol-1,4,5-trisphosphate-induced [Ca2+]i rises, promotes initiation of oscillations and enhances refilling of [Ca2+]ER. Collectively, our results provide novel insights on the regulation of [Ca2+]ER oscillations, which underlie the unique Ca2+-signalling system that activates the developmental program in mammalian eggs. PMID:24101727

  15. Atlantic opportunities for ENSO prediction

    NASA Astrophysics Data System (ADS)

    Martín-Rey, Marta; Rodríguez-Fonseca, Belén.; Polo, Irene

    2015-08-01

    El Niño-Southern Oscillation (ENSO) is the dominant mode of interannual climate variability with worldwide impacts. The knowledge of ENSO drivers and the underlying mechanisms is crucial to improve ENSO prediction, which still remains a challenge. The recently discovered connection between an Atlantic Niño (Niña) and a Pacific Niña (Niño), through an air-sea coupled mechanism during the first and last decades of the twentieth century, highlights an opportunity for ENSO prediction. Here a statistical cross-validated hindcast of ENSO along the twentieth century is presented, considering the Atlantic sea surface temperatures as the unique predictor field, and a set of atmospheric and oceanic variables related to the Atlantic-Pacific connection as the predictand field. The observed ENSO phase is well reproduced, and the skill is enhanced at the beginning and the end of the twentieth century. Understanding this multidecadal modulation of the Atlantic-Pacific connection could help to improve seasonal-to-decadal forecasts of ENSO and its associated impacts.

  16. FLORIDA ATLANTIC COASTAL ENVIRONMENTAL INITIATIVE

    EPA Science Inventory

    The Florida Atlantic Coastal Environmental Initiative (FACEI) will consist of a multiyear, multidisciplinary research and monitoring program designed to detect and trace a variety of nutrient sources (point and non-point sources) and other major environmental stressors to the coa...

  17. The State of the Ca Isotope Proxy

    NASA Astrophysics Data System (ADS)

    Fantle, M. S.; Tipper, E.

    2012-12-01

    At the Earth's surface, Ca is a critical element at a variety of scales. It is both a biological nutrient and water-soluble, and is a major constituent of the dominant mineral sink for carbon in the ocean. Additionally, the 5‰ range in the stable isotope ratios of Ca (44Ca/40Ca) suggests that Ca isotopes may be a promising tracer of the Ca cycle, specifically the oceanic budget over time. Despite ~15 years of concentrated effort on high-precision Ca isotope measurements, the utility of Ca isotopes as a proxy remains far from clear. A variety of basic questions have yet to be resolved, both in the marine and terrestrial realms. To provide perspective, the current work presents a data compilation of over 60 published Ca isotope studies. The compilation includes δ44/40CaSRM-915a measurements of the modern Ca cycle, including rivers and groundwater, dust, soils and soil pore fluids, vegetation, rainwater, silicate minerals/rocks, and marine carbonates. The focus of this work is to quantify the leverage of inputs to change the isotopic composition of the ocean. One of the tenets of the weathering proxy is that there is little isotopic leverage to change seawater. If this assumption is valid, then significant variations in the isotopic composition of seawater can be explained to some extent by mass flux imbalances between Ca inputs and outputs, requiring the Ca cycle to be out of steady state for significant periods of time. Despite evidence that Ca fractionates in the modern system during continental cycling, the δ44Ca range of riverine inputs to the ocean is very narrow (especially when compared to the spread in marine carbonates). Thus, there appears to be minimal isotopic leverage amongst inputs to shift the ocean δ44Ca. In order to develop our understanding of the Ca isotope proxy, we identify two probable mechanisms for shifting ocean δ44Ca and evaluate them using a series of simple box models. In the terrestrial realm, plants exhibit a wide range of

  18. Modelling non-analogue elements of Pliocene North Atlantic warming

    NASA Astrophysics Data System (ADS)

    Hill, D. J.

    2013-12-01

    The strong warming seen in records of mid-Pliocene sea surface temperature (SST) in the North Atlantic has proved difficult to reproduce in climate model simulations. The results of the Pliocene Model Intercomparison Project (PlioMIP) Experiment 2 fail to produce a single simulation with North Atlantic sea surface temperatures (SSTs) as high as those indicated by the PRISM3 (Pliocene Research, Interpretation and Synoptic Mapping) data set. Direct comparisons between the data and models are hampered by differing techniques used in palaeoenvironmental reconstruction and physical climate simulations. However, even if current simulations are not directly comparable to the reconstructions of the North Atlantic, something must have forced these particularly high temperatures for at least parts of the mid-Pliocene warm period. The boundary condition changes defined in the PlioMIP Experiment 2 protocol are limited to CO2, ice sheets, vegetation, land area change due to sea level rise and orography. Apart from small orographic changes imposed outside of the ice sheet regions, the rest of these factors would be expected to change under future anthropogenic climate change. As such the IPCC (Intergovernmental Panel on Climate Change) has referred to the mid-Pliocene as 'an accessible example of a world that is similar in many respects to ... the late 21st century'. However, there are a number of different palaeogeographic changes documented in published literature that are not incorporated into the PRISM3 palaeoenvironmental reconstruction used as model boundary conditions, particularly in the North Atlantic region. Although some of these would be expected under future climate change, e.g. a reduction in North Atlantic icebergs, many would not. Changes in the intensity of Icelandic mantle plume upwelling have resulted in changes in the sill depth of the Greenland-Scotland ridge over at least the last 40 million years. Pleistocene glacial erosion has created new ocean areas in

  19. The Cretaceous opening of the South Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Granot, Roi; Dyment, Jérôme

    2015-03-01

    The separation of South America from Africa during the Cretaceous is poorly understood due to the long period of stable polarity of the geomagnetic field, the Cretaceous Normal Superchron (CNS, lasted between ∼121 and 83.6 Myr ago). We present a new identification of magnetic anomalies located within the southern South Atlantic magnetic quiet zones that have arisen due to past variations in the strength of the dipolar geomagnetic field. Using these anomalies, together with fracture zone locations, we calculate the first set of magnetic anomalies-based finite rotation parameters for South America and Africa during that period. The kinematic solutions are generally consistent with fracture zone traces and magnetic anomalies outside the area used to construct them. The rotations indicate that seafloor spreading rates increased steadily throughout most of the Cretaceous and decreased sharply at around 80 Myr ago. A change in plate motion took place in the middle of the superchron, roughly 100 Myr ago, around the time of the final breakup (i.e., separation of continental-oceanic boundary in the Equatorial Atlantic). Prominent misfit between the calculated synthetic flowlines (older than Anomaly Q1) and the fracture zones straddling the African Plate in the central South Atlantic could only be explained by a combination of seafloor asymmetry and internal dextral motion (<100 km) within South America, west of the Rio Grande fracture zone. This process has lasted until ∼92 Myr ago after which both Africa and South America (south of the equator) behaved rigidly. The clearing of the continental-oceanic boundaries within the Equatorial Atlantic Gateway was probably completed by ∼95 Myr ago. The clearing was followed by a progressive widening and deepening of the passageway, leading to the emergence of north-south flow of intermediate and deep-water which might have triggered the global cooling of bottom water and the end for the Cretaceous greenhouse period.

  20. Warming of surface waters in the mid-latitude North Atlantic during Heinrich events

    NASA Astrophysics Data System (ADS)

    Naafs, B. D. A.; Hefter, J.; Grützner, J.; Stein, R.

    2013-01-01

    During the six Heinrich events of the last 70 kyr, episodic calving from the circum-Atlantic ice sheets released large numbers of icebergs into the North Atlantic. These icebergs and associated meltwater flux are hypothesized to have led to a shutdown of Atlantic Meridional Overturning Circulation and severe cooling in large parts of the Northern Hemisphere. However, due to the limited availability of high-resolution records, the magnitude of sea surface temperature (SST) changes related to the impact of Heinrich events on the midlatitude North Atlantic is poorly constrained. Here we present a record of U37K'-based SSTs derived from sediments of Integrated Ocean Drilling Project Site U1313, located at the southern end of the ice-rafted debris (IRD) belt in the midlatitude North Atlantic (41°N). We demonstrate that all six Heinrich events are associated with a rapid warming of surface waters by 2-4°C in a few thousand years. The presence of IRD leaves no doubt about the simultaneous timing and correlation between rapid surface water warming and Heinrich events. We argue that this warming in the midlatitude North Atlantic is related to a northward expansion of the subtropical gyre during Heinrich events. As a wide range of studies demonstrated that in the central IRD belt Heinrich events are associated with low SSTs, these results thus identify an antiphased (seesaw) pattern in SSTs during Heinrich events between the midlatitude (warm) and northern North Atlantic (cold). This highlights the complex response of surface water characteristics in the North Atlantic to Heinrich events that is poorly reproduced by freshwater hosing experiments and challenges the widely accepted view that, within the IRD belt of the North Atlantic, Heinrich events coincide with periods of low SSTs.

  1. Variability of the northeast Atlantic sea surface Δ 14C and marine reservoir age and the North Atlantic Oscillation (NAO)

    NASA Astrophysics Data System (ADS)

    Tisnérat-Laborde, Nadine; Paterne, Martine; Métivier, Bernard; Arnold, Maurice; Yiou, Pascal; Blamart, Dominique; Raynaud, Stéphane

    2010-09-01

    We compiled new 14C analyses of mollusc shells (bivalves and gastropods) of known age from the collection of the Muséum National d'Histoire Naturelle de Paris and previously published data to investigate changes in the sea surface Δ 14C and reservoir age in the northeast Atlantic sector (NEA) between 1823 and 1952 AD. The mollusc shells are mainly located off the Atlantic margin between 45°N and 60°N downstream of the North Atlantic Current (NAC). We show that the temporal variability of the NEA Δ 14C is independent of the mollusc species, depth habitat, diet and latitudinal distribution. The quasi-null difference between mollusc Δ 14C and the marine model indicate that the mollusc Δ 14C reflects the Δ 14C values of open marine conditions. Between 1823 and 1850 AD, the pre-anthropogenic mean of Δ 14C is -45 ± 5‰, corresponding to a reservoir age of 380 ± 60 years and a Δ R value of -7 ± 50 years, in agreement with previous estimates. The Δ 14C values show a significant long-term decrease of ˜12‰ from 1823 to 1952 AD attributed to changes in 14C production between 1823 and 1900 AD and the Suess effect between 1900 and 1952 AD. Between 1885 and 1950 AD, Δ 14C fluctuations of ˜10‰ up to 18‰ occurred in the northeast Atlantic, corresponding to reservoir age variations of ˜90 years up to 170 years. These fluctuations are very similar to changes of Δ 14C in the southern Norwegian Sea. Spectral analyses of the NEA Δ 14C exhibit quasi-periodic cycles of about 7.4 years, almost equivalent to the quasi-periodic cycles of the winter index of the North Atlantic Oscillation (NAO) with a period around 6.5 years. We find that changes of NEA Δ 14C cannot be attributed to changes in river runoff or the precipitation/evaporation budget. The Δ 14C lows (or high reservoir ages) correspond to the more intense phase of the winter NAO, with a time lag of ˜1-3 years. Such a time lag may reflect the eastward transit time of upstream changes originating in the

  2. Benthic foraminiferal δ18O-Mg/Ca from the SE Nordic seas during the last 65 kyr

    NASA Astrophysics Data System (ADS)

    Ezat, M.; Rasmussen, T. L.; Groeneveld, J.

    2013-12-01

    Benthic foraminiferal δ18O-Mg/Ca from the SE Nordic seas during the last 65 kyr Mohamed M. Ezat1,2*, Tine L. Rasmussen1, Jeroen Groeneveld3 1 CAGE - Centre for Arctic Gas Hydrate, Environment and Climate, and Department of Geology, University of Tromsø, NO-9037 Tromsø, Norway. 2 Department of Geology, Faculty of Science, Beni-Suef University, Beni-Suef, Egypt. 3 Department of Geosciences, University of Bremen, Klagenfurter Strasse, 28359, Bremen, Germany. * e-mail: mohamed.ezat@uit.no The climate during the last glacial period underwent rapid millennial-scale variability known as Dansgaard-Oeschger (DO) events of warm interstadials and cold stadials. DO events are manifested in marine and continental records in the circum-North Atlantic region and throughout the globe. Several studies suggest a crucial role of the Nordic seas in regulating the climate during the last glacial period. Previous studies from the Nordic seas revealed low benthic δ18O values during stadials and high values during interstadials. The causes of the depletions in benthic 18O during stadials are highly debated. Sinking of isotope depleted-brines formed due to sea ice production has previously been proposed. Another explanation has indicated warming of the intermediate water in the Nordic seas based on the finding of warm water benthic foraminiferal species during stadials. Here we present the first benthic foraminiferal Mg/Ca-based bottom water temperature (BWT) record from the Nordic seas that, along with other proxies, aims to resolve the hydrographic changes at intermediate water depth on DO timescale during the last 65 kyr. The results show pronounced and gradual BWT increases during all cold stadials followed by an abrupt drop to modern-like BWT at interstadials onsets. The increase in BWT, caused by the subsurface inflow of warm Atlantic intermediate water, substantially contributed to the halocline collapse and onset of interstadial conditions throughout complex ocean-sea ice

  3. The Effects of Temperature and Salinity on Mg Incorporation in Planktonic Foraminifera Globigerinoides ruber (white): Results from a Global Sediment Trap Mg/Ca Database

    NASA Astrophysics Data System (ADS)

    Gray, W. R.; Weldeab, S.; Lea, D. W.

    2015-12-01

    Mg/Ca in Globigerinoides ruber is arguably the most important proxy for sea surface temperature (SST) in tropical and sub tropical regions, and as such guides our understanding of past climatic change in these regions. However, the sensitivity of Mg/Ca to salinity is debated; while analysis of foraminifera grown in cultures generally indicates a sensitivity of 3 - 6% per salinity unit, core-top studies have suggested a much higher sensitivity of between 15 - 27% per salinity unit, bringing the utility of Mg/Ca as a SST proxy into dispute. Sediment traps circumvent the issues of dissolution and post-depositional calcite precipitation that hamper core-top calibration studies, whilst allowing the analysis of foraminifera that have calcified under natural conditions within a well constrained period of time. We collated previously published sediment trap/plankton tow G. ruber (white) Mg/Ca data, and generated new Mg/Ca data from a sediment trap located in the highly-saline tropical North Atlantic, close to West Africa. Calcification temperature and salinity were calculated for the time interval represented by each trap/tow sample using World Ocean Atlas 2013 data. The resulting dataset comprises >240 Mg/Ca measurements (in the size fraction 150 - 350 µm), that span a temperature range of 18 - 28 °C and 33.6 - 36.7 PSU. Multiple regression of the dataset reveals a temperature sensitivity of 7 ± 0.4% per °C (p < 2.2*10-16) and a salinity sensitivity of 4 ± 1% per salinity unit (p = 2*10-5). Application of this calibration has significant implications for both the magnitude and timing of glacial-interglacial temperature changes when variations in salinity are accounted for.

  4. Equatorial deep jets in the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Brandt, P.; Greatbatch, R. J.; Didwischus, S.-H.; Claus, M.; Hormann, V.; Funk, A.; Dengler, M.

    2012-04-01

    Vertically alternating deep zonal jets of short vertical wavelength were discovered in the equatorial oceans more than 35 years ago. These jets that are observed to be coherent across the equatorial basins are characterized by vertically alternating eastward and westward currents lying within 1° of the equator, with amplitudes of 0.1-0.2 ms-1 and vertical wavelengths between 300 and 700 m. In the Atlantic, equatorial deep jets oscillate with a period of about 4.5 years, while their energy propagates upward. The 4.5 year signal can be seen in sea surface temperature as well as atmospheric data (e.g. surface wind and rainfall) indicating the significance of the deep jets for climate. Here we analyse velocity data from more than 7 years of moored observations at the equator, 23°W as well as shipboard hydrographic and current observations along the 23°W repeat section. Our focus is on intermediate depth levels (300-700 m), where the deep jets are superimposed on a mean flow composed of the westward flowing Equatorial Intermediate Current centred on the equator and the eastward Southern and Northern Intermediate Countercurrents located at 2°S and 2°N, respectively. The large zonal oxygen gradient from the well ventilated western boundary toward low-oxygen values near the eastern boundary makes the meridional oxygen distribution in the central equatorial Atlantic sensitive to zonal flow variations in time and latitude. We compare the observed meridional structures of the mean and anomalous oxygen and zonal velocity distributions as well as their temporal evolution with results of an advection-diffusion model driven by a prescribed velocity field, restoring to high oxygen values at the western boundary, and otherwise constant oxygen consumption. The prescribed velocity field is composed of a high order baroclinic vertical normal mode aimed at representing the 4.5-year cycle and a mean velocity field resembling the observed mean zonal current structure. Similarities

  5. An updated anthropogenic CO2 inventory in the Atlantic Ocean

    SciTech Connect

    Lee, K.; Choi, S.-D.; Park, G.-H.; Peng, T.-H.; Key, Robert; Sabine, Chris; Feely, R. A.; Bullister, J.L.; Millero, F. J.; Kozyr, Alexander

    2003-01-01

    This paper presents a comprehensive analysis of the basin-wide inventory of anthropogenic CO2 in the Atlantic Ocean based on high-quality inorganic carbon, alkalinity, chlorofluorocarbon, and nutrient data collected during the World Ocean Circulation Experiment (WOCE) Hydrographic Program, the Joint Global Ocean Flux Study (JGOFS), and the Ocean-Atmosphere Carbon Exchange Study (OACES) surveys of the Atlantic Ocean between 1990 and 1998. Anthropogenic CO2 was separated from the large pool of dissolved inorganic carbon using an extended version of the DC* method originally developed by Gruber et al. [1996]. The extension of the method includes the use of an optimum multiparameter analysis to determine the relative contributions from various source water types to the sample on an isopycnal surface. Total inventories of anthropogenic CO2 in the Atlantic Ocean are highest in the subtropical regions at 20 40, whereas anthropogenic CO2 penetrates the deepest in high-latitude regions (>40N). The deeper penetration at high northern latitudes is largely due to the formation of deep water that feeds the Deep Western Boundary Current, which transports anthropogenic CO2 into the interior. In contrast, waters south of 50S in the Southern Ocean contain little anthropogenic CO2. Analysis of the data collected during the 1990 1998 period yielded a total anthropogenic CO2 inventory of 28.4 4.7 Pg C in the North Atlantic (equator-70N) and of 18.5 3.9 Pg C in the South Atlantic (equator-70S). These estimated basin-wide inventories of anthropogenic CO2 are in good agreement with previous estimates obtained by Gruber [1998], after accounting for the difference in observational periods. Our calculation of the anthropogenic CO2 inventory in the Atlantic Ocean, in conjunction with the inventories calculated previously for the Indian Ocean [Sabine et al., 1999] and for the Pacific Ocean [Sabine et al., 2002], yields a global anthropogenic CO2 inventory of 112 17 Pg C that has accumulated

  6. Summer North Atlantic Oscillation and flood variability in Switzerland

    NASA Astrophysics Data System (ADS)

    Peña, Juan Carlos; Schulte, Lothar; Badoux, Alexandre

    2016-04-01

    The study analyses the possible links between flood frequency in Switzerland and the North Atlantic dynamics over the last two centuries. Given the intricate topography of Switzerland, it will generate a territorial division to retain main physiographic and environmental dissimilarities between different regions. The flood variability in Switzerland over the period 1800-2010 has been determined from a flood damage index for July and August months. The index considers very severe and catastrophic floods from existing flood inventories, summarizing both the severity of these events, their spatial extent and the regional differences. Special attention will be focused on the disparities between flood dynamics at northern and southern slopes of the Alps. The analysis of the possible links between floods and North Atlantic dynamics is focused on the low-frequency atmospheric circulation patterns. Summer climate in the North Atlantic-European sector shows a principal pattern of year-to-year variability, although this pattern is weaker than the North Atlantic Oscillation (NAO) in winter and is confined to northern latitudes. By analogy the climatology community refers to this pattern as the Summer North Atlantic Oscillation (SNAO), which is defined as the main empirical orthogonal function of the standardized anomalies of the European mean sea level pressure during July and August. The flood damage index provides evidences of floods clusters in: 1830-1851, 1881-1927, 1977-1990 and 2005 to present. These clusters coincide with those reported from Switzerland and from some areas of the European continent such as the Czech Republic, Italy and the eastern half of the Iberian Peninsula. This link is not so close when compared with the flood occurrences in Germany. The analysis of the principal mode of low-frequency atmospheric variability shows that the Swiss river catchments situated on the center and southern flank of the Alps are affected by atmospherically unstable areas

  7. Synchronous climate changes in Antarctica and the North Atlantic

    USGS Publications Warehouse

    Steig, E.J.; Brook, E.J.; White, J.W.C.; Sucher, C.M.; Bender, M.L.; Lehman, S.J.; Morse, D.L.; Waddington, E.D.; Clow, G.D.

    1998-01-01

    Central Greenland ice cores provide evidence of abrupt changes in climate over the past 100,000 years. Many of these changes have also been identified in sedimentary and geochemical signatures in deep-sea sediment cores from the North Atlantic, confirming the link between millennial-scale climate variability and ocean thermohaline circulation. It is shown here that two of the most prominent North Atlantic events - the rapid warming that makes the end of the last glacial period and the Bolling/Allerod-Younger Dryas oscillation - are also recorded in an ice core from Taylor Dome, in the western Ross Sea sector of Antarctica. This result contrasts with evidence from ice cores in other regions of Antarctica, which show an asynchronous response between the Northern and Southern Hemispheres.

  8. Synchronous climate changes in antarctica and the north atlantic

    PubMed

    Steig; Brook; White; Sucher; Bender; Lehman; Morse; Waddington; Clow

    1998-10-01

    Central Greenland ice cores provide evidence of abrupt changes in climate over the past 100,000 years. Many of these changes have also been identified in sedimentary and geochemical signatures in deep-sea sediment cores from the North Atlantic, confirming the link between millennial-scale climate variability and ocean thermohaline circulation. It is shown here that two of the most prominent North Atlantic events-the rapid warming that marks the end of the last glacial period and the Bolling/Allerod-Younger Dryas oscillation-are also recorded in an ice core from Taylor Dome, in the western Ross Sea sector of Antarctica. This result contrasts with evidence from ice cores in other regions of Antarctica, which show an asynchronous response between the Northern and Southern Hemispheres. PMID:9756484

  9. Hemispheric asymmetry in aerosol optical thickness and cloud fraction over the tropical Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Kishcha, Pavel; Starobinets, Boris; da Silva, Arlindo; Long, Charles; Kalashnikova, Olga; Alpert, Pinhas

    2015-04-01

    Hemispheric asymmetry in cloud fraction and aerosols could lead to hemispheric imbalance in solar radiation reaching the surface and, consequently, could affect the Earth radiation budget. Previous studies showed that, over the global ocean, there is no noticeable hemispheric asymmetry in cloud fraction (CF). This contributes to the balance in solar radiation reaching the sea surface in the Northern and Southern hemispheres. In the current study, we focus on the tropical Atlantic (30oN - 30oS) which is characterized by significant amounts of Saharan dust dominating other aerosol species over the North Atlantic. Our main point is that, over the tropical Atlantic, not only is Saharan dust responsible for the pronounced hemispheric aerosol asymmetry, but it also contributes to significant cloud cover along the Saharan Air Layer. This could lead to the hemispheric imbalance in strong solar radiation reaching the sea surface in the tropical Atlantic. During the 10-year study period (July 2002 - June 2012), NASA Aerosol Reanalysis (aka MERRAero) showed that, when the hemispheric asymmetry in dust aerosol optical thickness (AOT) was the most pronounced (particularly in July), dust AOT averaged separately over the tropical North Atlantic was one order of magnitude higher than that averaged over the tropical South Atlantic. In the presence of such strong hemispheric asymmetry in dust AOT in July, CF averaged separately over the tropical North Atlantic exceeded that over the tropical South Atlantic by 20%. In July, along the Saharan Air Layer, Moderate Resolution Imaging Spectroradiometer (MODIS) CF data showed significant cloud cover (up to 0.8 - 0.9). This significant cloud fraction along SAL together with clouds over the Atlantic Inter-tropical Convergence Zone contributes to the above-mentioned hemispheric CF asymmetry. Both Multi-Angle Imaging SpectroRadiometer (MISR) measurements and MERRAero data were in agreement on seasonal variations in hemispheric aerosol

  10. 75 FR 54597 - Fisheries of the South Atlantic; Southeast Data, Assessment, and Review (SEDAR); South Atlantic...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-09-08

    ... Data, Assessment, and Review (SEDAR); South Atlantic Red Snapper AGENCY: National Marine Fisheries... 24 Assessment Stage 2, Webinar 3. SUMMARY: The SEDAR assessment of the South Atlantic stock of...