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Giraudeau J.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Grelaud M.,British Petroleum | Solignac S.,University of Quebec at Montreal | Andrews J.T.,University of Colorado at Boulder | And 3 more authors.
Quaternary Science Reviews | Year: 2010

Abundance patterns of coccolith species in two Holocene marine cores retrieved off Norway and northern Iceland are indicative of millennial-scale modulations in the flow of the main (Norwegian Atlantic Current) and secondary (North Iceland Irminger Current) branches of the North Atlantic Drift to the Nordic Seas. Long-term trends in coccolith abundance changes reflect major Holocene steps in Atlantic Water transfer to the Nordic Seas at orbital scale with important constraints on the convective activity of the Nordic Seas that leads to the formation of the precursor water mass of North Atlantic Deep Water. Millennial-scale Holocene episodes of increased advection of Atlantic waters off Norway are associated with enhanced winter precipitation over Scandinavia, increased sea-salt fluxes over Greenland, and strengthened wind over Iceland, thereby suggesting a common atmospheric forcing: the location and intensity of the westerlies and the associated changes in mid- to high-latitude pressure gradients. Our biotic data indicate an opposite pattern of Atlantic water inflow at suborbital scale between the western (Denmark) and eastern (Iceland-Scotland) straits of the northern Atlantic throughout the Holocene. This, as supported by present observational and simulated data, further highlights the role of atmospheric oscillations in the recent history of the North Atlantic-Nordic Seas water mass exchanges across the Greenland-Scotland Ridge. Such atmospheric processes are thought to explain the observed coupling between periods of excess export of arctic sea-ice to the Nordic Seas and intervals of maximum inflow of Atlantic water to the Norwegian Sea throughout the last 11 000 years. © 2010 Elsevier Ltd. All rights reserved. Source


Voelker A.H.L.,Instituto Portugues Do Mar e da Atmosfera IPMA | Voelker A.H.L.,CIMAR Associated Laboratory | Colman A.,University of Chicago | Olack G.,University of Chicago | And 2 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2015

Only a few studies have examined the variation of oxygen and hydrogen isotopes of seawater in NE Atlantic water masses, and data are especially sparse for intermediate and deep-water masses. The current study greatly expands this record with 527 δ18O values from 47 stations located throughout the mid- to low-latitude NE Atlantic. In addition, δD was analyzed in the 192 samples collected along the GEOTRACES North Atlantic Transect GA03 (GA03_e=KN199-4) and the 115 Iberia-Forams cruise samples from the western and southern Iberian margin. An intercomparison study between the two stable isotope measurement techniques (cavity ring-down laser spectroscopy and magnetic-sector isotope ratio mass spectrometry) used to analyze GA03_e samples reveals relatively good agreement for both hydrogen and oxygen isotope ratios. The surface (0-100m) and central (100-500m) water isotope data show the typical, evaporation related trend of increasing values equatorward with the exception for the zonal transect off Cape Blanc, NW Africa. Off Cape Blanc, surface water isotope signatures are modified by the upwelling of fresher Antarctic Intermediate Water (AAIW) that generally has isotopic values of 0.0 to 0.5‰ for δ18O and 0 to 2‰ for δD. Along the Iberian margin the Mediterranean Outflow Water (MOW) is clearly distinguished by its high δ18O (0.5-1.1‰) and δD (3-6‰) values that can be traced into the open Atlantic. Isotopic values in the NE Atlantic Deep Water (NEADW) are relatively low (δ18O: -0.1 to 0.5‰ δD: -1 to 4‰) and show a broader range than observed previously in the northern and southern convection areas. The NEADW is best observed at GA03_e Stations 5 and 7 in the central NE Atlantic basin. Antarctic Bottom Water isotope values are relatively high indicating modification of the original Antarctic source water along the flow path. The reconstructed δ18O-salinity relationship for the complete data set has a slope of 0.51, i.e., slightly steeper than the 0.46 described previously by Pierre et al. (1994, J. Mar. Syst. 5 (2), 159-170.) for the tropical to subtropical Northeast Atlantic. This slope decreases to 0.46 for the subtropical North Atlantic Central Water (NACW) and the MOW and to 0.32 for the surface waters of the upper 50m. The δD-salinity mixing lines have estimated slopes of 3.01 for the complete data, 1.26 for the MOW, 3.47 for the NACW, and 2.63 for the surface waters. The slopes of the δ18O-δD relationship are significantly lower than the one for the Global Meteoric Water Line with 5.6 for the complete data set, 2.30 for the MOW, 4.79 for the NACW, and 3.99 for the surface waters. The lower slopes in all the relationships clearly reflect the impact of the evaporation surplus in the subtropics. © 2015 Elsevier Ltd. Source


Nausch G.,Leibniz Institute For Ostseeforschung Warnemunde
Chemie in Unserer Zeit | Year: 2011

Eutrophication, i.e. the increased supply of nutrients (nitrogen and phosphorus) due to human activities in the catchment area and the adverse follow-ups are still a major concern for the Baltic Sea. The article describes nutrient inputs to the Baltic Sea over time, the development of nutrient concentrations and gives a recent evaluation of the eutrophication status of the Baltic Sea. Finally, protection measures in the past and at present are documented. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Schiebel R.,University of Angers | Brupbacher U.,ETH Zurich | Schmidtko S.,Leibniz Institute of Marine Science | Nausch G.,Leibniz Institute For Ostseeforschung Warnemunde | And 2 more authors.
Journal of Geophysical Research: Oceans | Year: 2011

Production and dispersion of coccolithophores are assessed within their ecologic and hydrographic context across enhanced spring chlorophyll production in the surface eastern North Atlantic. Within a 4 day period from 12 to 16 March 2004, a N-S transect from 47N to 33N was sampled along 20W. Water samples from defined depths down to 200 m were analyzed for coccolithophores from 0.45 m polycarbonate filters by scanning electron microscopy. At 47N coccolithophores flourished when euphotic conditions allowed new production at deep mixing, low temperatures, and high nutrient concentrations. Emiliania huxleyi flourished at high turbulence during an early stage of the phytoplankton succession and contributed half of the total coccolithophore assemblage, with up to 150 × 103 cells L-1 and up to 12 × 109 cells m-2 when integrated over the upper 200 m of the water column. Maximum chlorophyll concentrations occurred just north of the Azores Front, at 37N-39N, at comparatively low numbers of coccolithophores. To the south, at 35N-33N, coccolithophores were abundant within calm and stratified Subtropical Mode Waters, and E. huxleyi was the dominant species again. Although the cell densities of coccolithophores observed here remained below those typical of plankton blooms visible from satellite images, the depth-integrated total mass makes them significant producers of calcite and contributors to the total carbon sedimentation at a much wider range of ecological conditions during late winter and early spring than hitherto assumed. Copyright © 2011 by the American Geophysical Union. Source


Frundt B.,Leibniz Institute For Ostseeforschung Warnemunde | Muller T.J.,Leibniz Institute of Marine Science | Schulz-Bull D.E.,Leibniz Institute For Ostseeforschung Warnemunde | Waniek J.J.,Leibniz Institute For Ostseeforschung Warnemunde
Progress in Oceanography | Year: 2013

Data from almost thirty years of time series observations from a deep-sea mooring Kiel276 (33°N, 22°W), which was operated in the northeast Atlantic Ocean between 1980 and 2009, are studied to reveal information on the long term changes in the upper thermocline. This includes daily records of temperature and currents at two depths (240. m and 500. m). Until 1988, our analysis shows decreasing temperature in the entire thermocline followed by a slight increase at both depths; from 2000 on, extensive warming began at the shallower depth (240. m) and eight years later at the deeper (500. m) level. A northward displacement of the North Atlantic Subtropical Gyre is indicated by both current measurements and calculated kinetic energy between 1991 and 1998 resulting in an altered current regime in terms of absolute velocity and current directions in the last ten years compared to the first twenty years. Coherences of the currents with large scale climatic patterns such as North Atlantic Oscillation and El Niño/ Southern Oscillation evidence the atmospheric impact even at 500. m water depth. © 2013 Elsevier Ltd. Source

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