The Tagus Prodelta (W Portugal) and the Muros Ría (NW Spain) are areas of high deposition rates registering high-resolution palaeoclimatic records for western Iberia. We compare the climatic conditions of the two areas over the last two millennia based on proxies of temperature (sea surface temperatures and oxygen isotopes), continental input (grain size, iron and magnetic susceptibility) and productivity (inorganic and organic carbon, carbon isotopes, benthic foraminifera and diatoms). Biogeochemical changes in the Tagus Prodelta reflect widely recognized North Atlantic climatic periods encompassing the Roman Period (AD 0-350), the Dark Ages (AD 400-700), the ‘Mediaeval Warm Period’ (MWP; AD 800-1200) and the ‘Little Ice Age’ (LIA; AD 1300-1750). The atmospheric North Atlantic Oscillation (NAO) drives the Tagus Prodelta multidecadal, long-term variability in precipitation-river input during cold periods (negative NAO) and marine upwelling during warmer periods (positive NAO), a scheme that is reversed in the Galician region. The Muros Ría shows only local hydrodynamics until AD 1150, including a ‘suboxic’ event in the inner Ría around AD 500-700. Since AD 1150 Atlantic warm upwelled waters have ventilated the outer Ría but only reach the inner Ría at AD 1750. The twentieth-century records are also interpreted as a reflex of the inverse NAO mode in both areas, resulting in amplification of the LIA biogeochemical water conditions. Centennial-scale solar activity appears to be another important forcing mechanism (or the only one, if solar activity drives the NAO and ‘Bond-cycles’) behind changes in the hydrography of the Tagus Prodelta, and primary production, bottom ventilation and organic carbon degradation in the Muros Ría.
Abrantes, F.1988: Diatom assemblages as upwelling indicators in surface sediments off Portugal . Marine Geology85, 15-39 .
2.
Abrantes, F. and Moita, T.1999: Water column and recent sediment data on diatoms and coccolithophorids, off Portugal, confirm sediment record as a memory of upwelling events . Oceanologica Acta22, 319-336 .
3.
Abrantes, F. , Lebreiro, S. , Rodrigues, T. , Gil, I. , Bartels-Jónsdóttir, H. , Oliveira, P. , Kissel, C. and Grimalt, J. O.2005a: Shallow marine sediment cores record climate variability and earthquake activity off Lisbon (Portugal) for the last 2,000 years . Quaternary Science Reviews24, 2477-2494 .
4.
Abrantes, F. , Gil, I. , Lopes, C. and Castro, M.2005b: Quantitative diatom analyses a faster cleaning procedure . Deep-Sea Research I52, 189-198 .
5.
Adgebie, A. T. , Schneider, R. R. , Röhl, U. and Wefer, G.2003: Glacial millennial-scale fluctuations in central African precipitation recorded in terrigenous sediment supply and freshwater signals offshore Cameroon . Palaeogeography, Palaeoclimatology, Palaeoecology197, 323-333 .
6.
Á lvarez, M. C. , Flores, J. A. , Sierro, F. J. , Diz, P. , Francés, G. , Pelejero, C. and Grimalt, J.2005: Millennial surface water dynamics in the Ría de Vigo during the last 3000 years as revealed by coccoliths and molecular biomarkers . Palaeo-geography, Palaeoclimatology, Palaeoecology218, 1-13 .
7.
Á lvarez-Salgado, X. A. , Rosón, G. , Pérez, F. F. and Pazos, Y.1993: Hydrographic variability off the Rías Baixas (NW Spain) during the upwelling season . Journal of Geophysical Research98, 14 447-14 455 .
8.
Antoine, D. and Morel, A.1996: Oceanic primary production 1. Adaptation of a spectral light-photosynthesis model in view of application to satellite chrorophyll observations . Global Biogeochemical Cycles10, 43-55 .
9.
Arz, H. W. , Patzold, J. and Wefer, G.1999: Climatic changes during the last deglaciation recorded in the sediment cores from the northeastern Brazilian Continental Margin . Geo-Marine Letters19, 209-218 .
10.
Bao, R. , Varela, M. and Prego, R.1997: Mesoscale distribution patterns of diatoms in surface sediments as tracers of coastal upwelling on the Galician Shelf (NW Iberian Peninsula) . Marine Geology144, 117-130 .
11.
Barber, R. T. and Smith, R. L.1981: Coastal upwelling ecosystems. In Longhurst, A. R. , editor, Analysis of marine systems. Academic Press , 33-68.
12.
Bard, E. , Raisbeck, G. , Yiou, F. and Jouzel, J.2000: Solar irradiance during the last 1200 years based on cosmogenic nuclides . Tellus B52, 985-991 .
13.
Bartels-Jónsdóttir, H. B. , Knudsen, K. L. , Abrantes, F. , Lebreiro, S. and Eiríksson, J.2006: Climate variability during the last 2000 years in the Tagus Prodelta, western Iberian Margin: benthic foraminifera and stable isotopes . Marine Micropaleontology59, 83-103 .
14.
Battarbee, R. W.1973: A new method for estimation of absolute microfossil numbers with reference especially to diatoms . Limnology Oceanography18, 647-652 .
15.
Behrenfeld, M. J. , Randerson, J. T. , McClain, C. R. , Feldman, G. C. , Los, S. O. , Tucker, C. J. , Falkowski, P. G. , Field, C. B. , Frouin, R. , Esaias, W. E. , Kolber, D. D. and Ollack, N. H.2001: Biosphere primary production during an ENSO transition . Science291, 2594-2597 .
16.
Bernárdez, P. , Francés, G. and Prego, R.2006: Benthic pelagic coupling and postdepositional processes as revealed by the distribution of opal in sediments: the case of the Ría de Vigo (NW Iberian Peninsula) . Estuarine, Coastal and Shelf Science, in press.
17.
Bond, G. , Kromer, B. , Beer, J. , Musceler, R. , Evans, M. N. , Showers, W. , Hoffmann, S. , Lotti-Bond, R. , Hajdas, I. and Bonani, G.2001: Persistent solar influence on North Atlantic climate during the Holocene . Science294, 2130-2136 .
18.
Bode, A. , Casas, B. and Varela, M.1994: Size-fractioned primary productivity and biomass in the Galizian shelf (NW Spain): net plankton versus nanoplankton dominance . Sciencia Marina58, 131-141 .
19.
Bradley, R. S. and Jones, P. D.1993: ‘Little Ice Age’ summer temperature variations: their nature and relevance to recent global warming trends . The Holocene3, 367-367 .
20.
Broecker, W. S. and Peng, T. H.1982: Tracers in the sea. Eldigio Press .
21.
Brown, P. and Field, J.1986: Factors limiting phytoplankton production in a nearshore upwelling area . Journal of Plankton Research8, 55-68 .
22.
Brown, P. , Painting, S. and Cochraine, K.1991: Estimates of phytoplankton and bacterial biomass and production in the northern and southern Benguela ecosystems . South African Journal of Marine Science11, 537-564 .
23.
Cabeçadas, G. and Brogueira, M. J.1997: Sediments in a Portuguese coastal area pool sizes of mobile and immobile forms of nitrogen and phosphorus . Marine Freshwater Research48, 559-563 .
24.
Chapman, M. R. and Shackleton, I. N.2000: Evidence of 550-year and 1000-year cyclicities in North Atlantic circulation patterns during the Holocene . The Holocene10, 287-291 .
25.
Crowley, T.2000: Causes of climate change over the past 1000 years . Science289, 270-277 .
26.
Desprat, S. , Sánchez-Goñi, M. F. and Loutre, M.-F.2003: Revealing climatic variability of the last three millennia in northwestern Iberia using pollen influx data . Earth and Planetary Science Letters213, 63-78 .
27.
Diz, P. , Francés, G. , Pelejero, C. , Grimalt, J. O. and Vilas, F.2002: The last 3000 years in the Ría de Vigo (NW Iberian Margin): climatic and hydrographic signals . The Holocene12, 459-468 .
28.
Diz, P. , Francés, G. , Costas, S. , Souto, C. and Alejo, I.2004: Distribution of benthic foraminifera in coarse sediments, Ría de Vigo, NW Iberian Margin . Journal of Foraminiferal Research34, 258-275 .
29.
Diz, P. , Francés, G. and Rosón, G.2006: Effects of contrasting upwelling downwelling on benthic foraminiferal distribution in the Ría de Vigo (NW Spain) . Journal of Marine Systems60, 1-18 .
30.
Estrada, M.1984: Phytoplankton distribution and composition off the coast of Galizia (NW Spain) . Journal of Plankton Research6, 417-434 .
31.
Fisher, G. and Wefer, G. , editors 1999: Use of proxies in paleoceanography: examples from the south Atlantic. Springer , 1-68.
32.
Fiúza, A. F. G.1983: Upwelling pattern off Portugal. In Suess, E. and Thiede, J. , editors, Coastal upwelling: its sediment record. Plenum , 85-98.
33.
Fraga, F.1981: Upwelling off the Galician coast, NW Spain. In Richards, F. A. , editor, Coastal upwelling. American Geophysical Union , 176-182.
34.
Fraga, F. and Margalef, R. 1979: Las Rías Gallegas. In Universidad de Santiago de Compostera, editor, Estudio y explotación del mar en Galicia, La Coruña. University of Santiago, 101-21.
35.
Gil, I. M. , Abrantes, F. and Hebbeln, D.2006: The North Atlantic Oscillation forcing through the last 2000 years: spatial variability as revealed by high-resolution marine diatom records from N and SW Europe . Marine Micropaleontology60, 113-129 .
36.
Hass, H. C.1996: Northern Europe climate variations during the late Holocene: evidence from marine Skagerrak . Palaeogeography, Palaeoclimatology, Palaeoecology123, 121-145 .
37.
Hughes, M. K. and Diaz, H. F.1994: Was there a ‘Medieval Warm Period’ and if so, where and when?Climate Change26, 109-109 .
38.
Hurrell, J. W.1995: Decadal trends in the North Atlantic Oscillation: regional temperatures and precipitation . Science269, 676-679 .
39.
Jansen, J. H. F. , van der Gaast, S. J. , Koster, B. and Vaars, A. J.1998: CORTEX, a shipboard XRF-scanner for element analysis in split sediment cores . Marine Geology151, 143-153 .
40.
Jones, P. D. and Mann, M.2004: Climate over the past millennia . Reviews of Geophysics42, 1-42 .
41.
Jones, P. D. , Osborn, T. J. and Briffa, K. R.2001: The evolution of climate over the last millennium . Science292, 662-667 .
42.
Keigwin, L. D.1996: The Little Ice Age and Medieval Warm Period in the Sargasso Sea . Science274, 1504-1508 .
43.
Keigwin, L. D. and Pickart, R. S.1999: Slope water current over the Laurentian Fan on interannual to millenial time scales . Science286, 520-523 .
44.
Keller, C. F.2004: 1000 years of climate change . Advances in Space Research34, 315-322 .
45.
Kirov, B. and Georgieva, K.2002: Long-term variations of ENSO, NAO and solar activity . Physics and Chemistry of the Earth27, 441-448 .
46.
Lamb, H. H.1985: Climate history and the future. Princeton University Press , 835-835 pp.
47.
Lean, J. and Rind, D.2001: Earth’s response to a variable sun . Science292, 234-236 .
48.
Levy, A. , Mathieu, R. , Poignant, A. , Rosset-Moulinier, M. , Ubaldo, M. L. and Ambroise, D.1993: Recent foraminifera from the continental margin of Portugal . Micropaleontology39, 75-87 .
49.
Loureiro, J.M. 1979: Curvas de duração dos caudais médios diários no rio Tejo. Technical Report, Serviço Hidráulico (DGRAH), Lisbon.
50.
Mann, M. E. and Jones, P. D.2003: Global surface temperatures over the past two millennia . Geophysical Research Letters30, 5.1-5.4 .
51.
Masarik, J. and Beer, J.1999: Simulation of particle fixes and cosmogenic nuclide production in the Earth’s atmosphere . Journal of Geophysics Research104, D10-D10, 12099-12099 .
52.
Mayewski, P. A. , Rohling E. E. , Stager, J. C. , Karlén, W. , Maasch, K. A. , Meeker, L. D. , Meyerson, E. A. , Gasse, F. , van Kreveld, S. , Holmgren, K. , Lee-Thorp, J. , Rosqvist, G. , Rack, F. , Staubwasser, M. , Schneider, R. R. and Steig, E. J.2004: Holocene climate variability . Quaternary Research62, 243-255 .
53.
Mikkelsen, N. and Kuijpers, A.2001: Natural climate variations in a geological perspective. Gads Forlag .
54.
Moita, M.T. 2001: Estructura, variabilidade e dinâmica do fitoplâncton na costa de Portugal continental. Ph.D. Thesis, Universidade de Lisboa, 272 pp.
55.
Monteiro, H. and Moita, I. 1971: Morfologia e sedimentos da plataforma continental e vertente continental superior ao largo da Penísula de Setúbal. Congresso de Geologia, 301-30.
56.
Nogueira, E. , Pérez, F. and Ros, A.1997: Seasonal patterns and long-term trends in an estuarine upwelling ecosystem (Ría de Vigo, Spain) . Estuarine, Coastal and Shelf Science44, 285-300 .
57.
Nunes, T. , Mariño, J. , Iglesias, M. , González, N. , Campos, M. J. and Cabanas, J. M.1984: Condiciones ambientales, producción primaria y sucesión de especies fitoplanctónicas en la Ría de Arousa (NW de España) . Cuadernos Area Ciencias Mariñas, Sem. Estudios Galegos1, 163-172 .
58.
Oliveira, A. , Rocha, F. , Jouanneau, J. , Dias, A. , Weber, O. and Gomes, C.2002: Clay minerals from the sedimentary cover from the Northwest Iberian shelf . Progress in Oceanography52, 233-247 .
59.
Pauling, A. , Luterbacher, J. , Casty, C. and Wanner, H.2006: Five hundred years of gridded high-resolution precipitation reconstructions over Europe and the connection to large-scale circulation . Climate Dynamics26, 387-405 .
60.
Pilskaln, C. , Paduan, J. , Chavez, F. , Anderson, R. and Berelson, W.1996: Carbon export and regeneration in the coastal upwelling system of Monterey Bay, central California . Journal of Marine Research54, 1149-1178 .
61.
Prego, R.1990: Las sales nutrientes en las rías gallegas . Informe Técnico Scientia Mariña157, 31-31 .
62.
Prego, R.1993: General aspects of carbon biogeochemistry in the Ría of Vigo, northwestern Spain . Geochimica Cosmochimica Acta57, 2041-2052 .
63.
Ríos, A. F. , Pérez, F. F. and Fraga, F.1992: Water masses in the upper and middle North Atlantic Ocean east of the Azores . Deep-Sea Research39, 645-658 .
64.
Rodrigues, T. 2004: Climatic variation and terrigenous input in the Tagus Prodelta during the last 13.5 kyr. Masters Thesis, University of Aveiro, 117 pp.
65.
Schrader, H-J. and Gersonde, S.1978: Diatoms and silicoflagellates . Utrecht Micropaleontological Bulletin17, 12-17 .
66.
Shackleton, N. J.1974: Attainment of isotopic equilibrium between ocean water and the benthonic foraminifera genus Uvigerina: isotopic changes in the ocean during the last Glacial . Colloques Internationaux du C.N.R.S.219, 203-209 .
67.
Stuiver, M. , Braziunas, T. F. , Grootes, P. M. and Zielinski, G. A.1997: Is there evidence for solar forcing of climate in the GISP2 oxygen isotope record?Quaternary Research48, 259-266 .
68.
Stuiver, M. , Reimer, P. J. and Braziunas, T. F.1998a: High precision radiocarbon age calibration for terrestrial and marine samples . Radiocarbon40, 1127-1151 .
69.
Stuiver, M. , Reimer, P. J. , Bard, E. , Beck, J. W. , Burr, G. S. , Hughen, K. A. , Kromer, B. , McCormac, F. G. , van der Plicht, J. and Spurk, M.1998b: INTCAL 98 radiocarbon age calibration, 24,000 0 cal BP . Radiocarbon40, 1041-1083 .
70.
Trigo, R. M. , Osborn, T. J. and Corte-Real, J.2002a: The North Atlantic Oscillation influence on Europe: climate impacts and associated physical mechanisms . Climate Research20, 9-17 .
71.
Trigo, R. M. , Osborn, T. J. and Corte-Real, J.2002b: Influência da Oscilação do Atlântico Norte no clima do continente Europeu e o caudal dos rios ibéricos Atlânticos . Finisterra37, 5-31 .
72.
Vale, C. and Sundby, B.1987: Suspended sediment fluctuations in the Tagus estuary on semi-diurnal and fortnightly time scales . Estuarine, Coastal and Shelf Science25, 495-508 .
73.
Van der Zwaan, G. J. , Duijnstee, L. A. P. , den Dulk, M. , Ernest, S. R. , Jannink, N. T. and Kouwenhoven, T. J.1999: Benthic foraminifers, proxies or problems? A review of paleoecological concepts . Earth Science Reviews46, 213-236 .
74.
Varela, M. , Campos, M. J. , Penas, E. , Sánchez, J. , Larrañaga, A. , de Castillejo, F. F. , del Río, G. D. and Cabanas, J. M.1987: Composición y distribución del fitoplacton en la plataforma de Galicia durante la campañaBreogán-684 (junio 1984) . Boletín del Instituto Español de Oceanografía4, 75-94 .
75.
Varela, M. , Prego, R. , Belzunce, M. J. and Salas, F. M.2001: Inshore offshore differences in seasonal variations of phytoplankton assemblages: the case of a Galician Ría Alta (Ría Instituto Espande A Coruña) and its adjacent shelf (NW Spain) . Continental Shelf Research21, 1815-1838 .
76.
Varela, R. A. , Rosón, G. , Herrera, J. , Torres-López, S. and Fernández-Romero, A.2005: A general view of the hydrographic and dynamical patterns of the Rias Baixas adjacent shelf area . Journal of Marine Systems54, 97-114 .
77.
Zahn, R. and Sarnthein, M.1987: Benthic isotope evidence for changes of the Mediterranean Outflow during the late Quaternary . Paleoceanography2, 543-559 .
