Divisao de Geologia e Georecursos Marinhos

Modern diatom and C org distribution patterns were investigated in 39 surface sediment samples of the Canary region in order to quantitatively determine the in¯uence of coastal upwelling and Saharan dust on the¯ux of these sedimentary components.

High-resolution grain size and magnetic susceptibility records from the eastern Gulf of Cadiz (site MD99-2339; 1170m water depth) reveal contourites formed by the Mediterranean Outflow (MOW) during the last 47 kyr BP. Oscillations in the MOW's intensity occurred in phase with Greenland temperature variations with a stronger outflow during northern hemisphere coolings such as Dansgaard-Oeschger stadials, Heinrich events, and the Younger Dryas. Benthic δ 13 C data implies the Western Mediterranean Deep Water as one of the main sources feeding the outflow current, while differential changes in the properties of the Mediterranean source and entrained North Atlantic Central Water largely control the MOW's strength. Detailed studies for Heinrich events 1, 4 and 5 show that the flow strength peaked only when subtropical surface waters prevailed in the eastern Gulf of Cadiz, while incursions of icebergs and subpolar surface water were not favorable for the MOW's intensification. As the MOW was strong when the Atlantic's thermohaline circulation (THC) was weakened, the heat and salt injected by the MOW into the intermediate North Atlantic waters might have preconditioned the THC to switch from the stadial to the interstadial mode.

Sea Surface Temperature (SST), river discharge and biological productivity have been reconstructed from a multi-proxy study of a high-temporal-resolution sedimentary sequence recovered from the Tagus deposition center off Lisbon (Portugal) for the last 2000 years. SST shows 2 °C variability on a century scale that allows the identification of the Medieval Warm Period (MWP) and the Little Ice Age (LIA).High Iron (Fe) and fine-sediment deposition accompanied by high nn-alkane concentrations and presence of freshwater diatoms during the LIA (1300–1900 AD) (Science 292 (2001) 662) suggest augmented river discharge, whereas higher total-alkenone concentrations point to increased river-induced productivity. During the MWP (550–1300 AD) (Science 292 (2001) 662) larger mean-grain size and low values of magnetic susceptibility, and concentrations of Fe, nn-alkanes, and nn-alcohols are interpreted to reflect decreased runoff. At the same time, increased benthic and planktonic foraminifera abundances and presence of upwelling related diatoms point to increased oceanic productivity. On the basis of the excellent match found between the negative phases of the North Atlantic Oscillation (NAO) index and the intensified Tagus River discharge observed for the last century, it is hypothesized that the increased influx of terrigenous material during the LIA reflects a negative NAO-like state or the occurrence of frequent extreme NAO minima. During the milder few centuries of the MWP, stronger coastal upwelling conditions are attributed to a persistent, positive NAO-like state or the frequent occurrence of extreme NAO maxima.The peak in magnetic susceptibility, centered at 90 cm composite core depth (ccd), is interpreted as the result of the well-known 1755 AD Lisbon earthquake. The Lisbon earthquake and accompanying tsunami are estimated to have caused the loss of 39 cm of sediment (355 years of record—most of the LIA) and the instantaneous deposition of a 19-cm sediment bed.

Several are the hypotheses proposed to explain the occurrence of Ethmodiscus oozes in tropical sediments representative of some glacial periods. In this paper, a review of those hypotheses within a paleoclimatic perspective is presented. Flux records of Ethmodiscus fragments found in site M16772 (1321 S, 11358 W) during the last 190 ka are compared to the other marine and freshwater diatom accumulation rates (AR) and diatom assemblages composition. Ethmodiscus is present all along the core, but Ethmodiscus-rich levels are found at 185}170 and 150}140 ka (stages 6.6 and 6.4), and at 70}60 ka (stage 4.2), levels where a concomitant increase in the #ux of the other marine diatoms, and in the contribution to the assemblage of diatom species related to equatorial and coastal upwelling, and river plume waters is also observed. Climatic conditions favouring simultaneous occurrence of strong equatorial upwelling, coincident with increased advection of waters from coastal upwelling areas and important river run-o! are proposed as the explanation for these Ethmodiscus-rich levels.

Suspended particulate matter (SPM) data from two surveys carried as part of the Canary Islands Azores Gibraltar Observations (CANIGO) project, in September 1997 and January 1998, are presented for the Gulf of Cadiz and the SW coast of Portugal. Analysis of total suspended mass, particulate organic to inorganic matter ratio, d 13 C (PDB) , and a microscopic analysis of particle composition were performed. Our objective was to quantify and characterise SPM in the water masses present in the study area, North Atlantic central water (NACW), North Atlantic deep water (NADW), and especially in the Mediterranean water (MW). MW was usually characterised by values of SPM higher than NADW but similar to NACW, and was different in terms of SPM composition: higher d 13 C (PDB) values and relative abundance of mineral and biogenic particles, but lower relative abundance of particles o10 mm. The higher values of d 13 C (PDB) and biogenic material in MW suggest the presence of ''fresher'' particulate material relative to the other water masses. In terms of SPM, two different MW can be described, a well-defined high-salinity and hightemperature slope MW, and an offshore MW in areas away from the continental slope and the seafloor. Slope MW showed higher particle abundance than offshore MW. It also showed a different particle composition, with higher values of d 13 C (PDB) , mineral particles, biogenic particles, and lower values of particles o10 mm than offshore MW. No significant difference in SPM composition was observed between the upper and lower cores of MW. Three SPM sources to MW are proposed: a MW origin source (Gibraltar Straits or Mediterranean Sea), bottom sediment resuspension, and surface waters. We suggest the occurrence of a constant particle source in surface waters near Gibraltar and/or in the Mediterranean Sea during both surveys. In the eastern Gulf of Cadiz, the input of sedimentary particle into slope MW was slight or non-existent. On the western Gulf of Cadiz and off the west coast of Portugal, both surface and sediment inputs appear to be important particle sources into slope MW. r

The Canary Islands region occupies a key position with respect to biogeochemical cycles, with the zonal transition from oligotrophic to nutrient-rich waters and the contribution of Saharan dust to the particle flux. We present the distribution of geochemical proxies (TOC, carbonate, d 15 N, d 13 C org , C/N-ratio) and micropaleontological parameters (diatoms, dinoflagellates, foraminifera, pteropods), in 80 surface-sediment samples in order to characterise the influence of coastally upwelled water on the domain of the subtropical gyre.

Particle supply and sediment accumulation in the Canary Basin are strongly modified by seasonal coastal upwelling and dust input from the Sahara. Along an E-W depth profile and fertility gradient north of the Canary Islands, we demonstrate an increase in total mass accumulation rates from a low of 1-2 g cm À2 ka À1 in the outer oceanic domain to 6-12 g cm À2 ka À1 closer to the Moroccan shelf in Holocene sediments. During the Last Glacial Maximum (LGM, oxygen isotopic event 2.2), a steeper gradient was found, with two to four times higher mass accumulation rates at the near-shore sites. Total mass accumulation rates during the Last Interglacial Climax (LIC, isotopic event 5.5) and end of the Penultimate Glaciation (ePG, isotopic event 6.2) resemble Holocene values, with lowered near-shore maxima of 3 and 4 g cm À2 ka À1 , respectively.

We present results from the investigation of the primary productivity record over the last 250 kyr in the North Canary Basin (30 ‡N) off Northwest Africa. Two distinct productive systems interfere in this area: the oligotrophic open ocean and the upwelling filament off Cape Ghir, that occasionally carries offshore cool nutrient-rich waters. The following geochemical and micropaleontological paleoproductivity proxies have been used in our study: calcium carbonate, barium excess (Ba excess ), total organic carbon (TOC) and diatoms. Time series analysis of these proxies indicates that paleoproductivity in the North Canary Basin underwent important changes following precession and eccentricity cycles. While the precessional signal appears to be mainly related to trade wind strength, superimposed peaks in Ba excess , TOC and diatom records point to large productivity events at Terminations I, II and III. Lowering of the North Atlantic sea surface temperatures by melt water discharges which in turn strengthened the Azores highpressure center and increased trade wind velocities is postulated as the mechanism to explain the enhancement of the coastal upwelling and associated filaments at terminations. Additionally, the Canary Current may play a role in transmitting cold melt waters and nutrients from higher latitudes to the North Canary Basin. ß

1] We present new annually resolved d 18 O, d 13 C, Mg/Ca, and Sr/Ca ratio records for two shells of the fast growing Mediterranean fan mussel Pinna nobilis, collected from proximal Spanish coast sea grass meadows. The relationship between the potential geochemical proxies and ontogenetic and environmental controlling factors is investigated. Specifically, the use of shell Mg/Ca and Sr/Ca ratios as potential calcification temperature proxies, the latter calculated from measured shell d 18 O values, has been assessed. The d 18 O cycles along the growth axis indicate that our P. nobilis specimens are $10.5 and $4.5 years old Shell Sr/Ca ratios do not exhibit any consistent interannual cyclicity and are not correlated to temperature. A subtle ontogenetic effect on shell Mg/Ca ratios was observed during the first 4.5 years of recorded growth but was highly evident during the organism's later growth years. In P. nobilis shells, different mechanisms influence ontogenetic variation in shell Mg/Ca and d 18 O records. Shell Mg/Ca ratios from the first 4.5 years of growth correlate significantly to temperature, in a best fit relationship described by the equation Mg/Ca = 17.16 ± 1.95 * exp(0.022 ± 0.004 * T). P. nobilis shell Mg/Ca records therefore are a valid temperature proxy only during an early growth phase. For the same range of temperatures, shell Mg/Ca ratios in P. nobilis are approximately 1/3 lower than those reported for inorganic calcite but 3 to 4 times higher than in another bivalve species, Mytilus trossulus, and 4 to 16 times higher than in foraminifera. We suggest these offsets are due to a higher degree of similarity between seawater and calcification-fluid composition in P. nobilis than in other bivalves and foraminifera. The observed shell Mg/Ca ratio change per°C of 2.2% also is lower than that observed for inorganic and other biogenic calcites. Our findings strongly support taxon-and species-specific Mg/Ca-temperature relationships for bivalves and other calcifying organisms. An appreciation of the physiology and calcification mechanisms of any biogenic carbonate archive therefore is paramount prior to the application of stable-isotope and element/Ca ratio proxies for paleotemperature reconstructions.

The relationship between potential elemental proxies (Mg/Ca, Sr/Ca and Mn/Ca ratios) and environmental factors was investigated for the bivalve Pecten maximus in a detailed field study undertaken in the Menai Strait, Wales, U.K. An age model constructed for each shell by comparison of measured and predicted oxygen-isotope ratios allowed comparison on a calendar time scale of shell elemental data with environmental variables, as well as estimation of shell growth rates. The seasonal variation of shell Mn/Ca ratios followed a similar pattern to one previously described for dissolved Mn 2+ in the Menai Strait, although further calibration work is needed to validate such a relationship. Shell Sr/Ca ratios unexpectedly were found to co-vary most significantly with calcification temperature, whilst shell Mg/Ca ratios were the next most significant control. The temporal variation in the factors that control shell Sr/Ca ratios strongly suggest the former observation most likely to be the result of a secondary influence on shell Sr/Ca ratios by kinetic effects, the latter driven by seasonal variation in shell growth rate that is in turn influenced in part by seawater temperature. P. maximus shell Mg/Ca ratio to calcification temperature relationships exhibit an inverse correlation during autumn to early spring (October to March-April) and a positive correlation from late spring through summer (May-June to September). No clear explanation is evident for the former trend, but the similarity of the records from the three shells analysed indicate that it is a real signal and not a spurious observation. These observations confirm that application of the Mg/Ca proxy in P. maximus shells remains problematic, even for seasonal or absolute temperature reconstructions. For the range of calcification temperatures of 5-19°C, our shell Mg/Ca ratios in P. maximus are approximately one-fourth those in inorganic calcite, half those in the bivalve Pinna nobilis, twice those in the bivalve Mytilus trossulus, and four to five times higher than Mg/Ca ratios in planktonic and benthonic foraminifera. Our findings further support observations that Mg/Ca ratios in bivalve shell calcite are an unreliable temperature proxy, as well as substantial taxon-and species-specific variation in Mg incorporation into bivalves and other calcifying organisms, with profound implications for the application of this geochemical proxy to the bivalve fossil record.

The relationship between potential elemental proxies (Mg/Ca, Sr/Ca and Mn/Ca ratios) and environmental factors was investigated for the bivalve Pecten maximus in a detailed field study undertaken in the Menai Strait, Wales, U.K. An age model constructed for each shell by comparison of measured and predicted oxygen-isotope ratios allowed comparison on a calendar time scale of shell elemental data with environmental variables, as well as estimation of shell growth rates. The seasonal variation of shell Mn/Ca ratios followed a similar pattern to one previously described for dissolved Mn2+ in the Menai Strait, although further calibration work is needed to validate such a relationship. Shell Sr/Ca ratios unexpectedly were found to co-vary most significantly with calcification temperature, whilst shell Mg/Ca ratios were the next most significant control. The temporal variation in the factors that control shell Sr/Ca ratios strongly suggest the former observation most likely to be the result of a secondary influence on shell Sr/Ca ratios by kinetic effects, the latter driven by seasonal variation in shell growth rate that is in turn influenced in part by seawater temperature. P. maximus shell Mg/Ca ratio to calcification temperature relationships exhibit an inverse correlation during autumn to early spring (October to March–April) and a positive correlation from late spring through summer (May–June to September). No clear explanation is evident for the former trend, but the similarity of the records from the three shells analysed indicate that it is a real signal and not a spurious observation. These observations confirm that application of the Mg/Ca proxy in P. maximus shells remains problematic, even for seasonal or absolute temperature reconstructions. For the range of calcification temperatures of 5–19 °C, our shell Mg/Ca ratios in P. maximus are approximately one-fourth those in inorganic calcite, half those in the bivalve Pinna nobilis, twice those in the bivalve Mytilus trossulus, and four to five times higher than Mg/Ca ratios in planktonic and benthonic foraminifera. Our findings further support observations that Mg/Ca ratios in bivalve shell calcite are an unreliable temperature proxy, as well as substantial taxon- and species-specific variation in Mg incorporation into bivalves and other calcifying organisms, with profound implications for the application of this geochemical proxy to the bivalve fossil record.

Abstract[1] We present new annually resolved δ18O, δ13C, Mg/Ca, and Sr/Ca ratio records for two shells of the fast growing Mediterranean fan mussel Pinna nobilis, collected from proximal Spanish coast sea grass meadows. The relationship between the potential geochemical proxies and ontogenetic and environmental controlling factors is investigated. Specifically, the use of shell Mg/Ca and Sr/Ca ratios as potential calcification temperature proxies, the latter calculated from measured shell δ18O values, has been assessed. The δ18O cycles along the growth axis indicate that our P. nobilis specimens are ∼10.5 and ∼4.5 years old. Shell Sr/Ca ratios do not exhibit any consistent interannual cyclicity and are not correlated to temperature. A subtle ontogenetic effect on shell Mg/Ca ratios was observed during the first 4.5 years of recorded growth but was highly evident during the organism's later growth years. In P. nobilis shells, different mechanisms influence ontogenetic variation in shell Mg/Ca and δ18O records. Shell Mg/Ca ratios from the first 4.5 years of growth correlate significantly to temperature, in a best fit relationship described by the equation Mg/Ca = 17.16 ± 1.95 * exp(0.022 ± 0.004 * T). P. nobilis shell Mg/Ca records therefore are a valid temperature proxy only during an early growth phase. For the same range of temperatures, shell Mg/Ca ratios in P. nobilis are approximately 1/3 lower than those reported for inorganic calcite but 3 to 4 times higher than in another bivalve species, Mytilus trossulus, and 4 to 16 times higher than in foraminifera. We suggest these offsets are due to a higher degree of similarity between seawater and calcification-fluid composition in P. nobilis than in other bivalves and foraminifera. The observed shell Mg/Ca ratio change per °C of 2.2% also is lower than that observed for inorganic and other biogenic calcites. Our findings strongly support taxon- and species-specific Mg/Ca–temperature relationships for bivalves and other calcifying organisms. An appreciation of the physiology and calcification mechanisms of any biogenic carbonate archive therefore is paramount prior to the application of stable-isotope and element/Ca ratio proxies for paleotemperature reconstructions.

A multidisciplinary study of the Mediterranean outflow in the region west of the Strait of Gibraltar and off the southern and southwestern coasts of the Iberian Peninsula was developed in the frame of the Canary Islands Azores Gibraltar Observations Project. Two high-resolution CTD surveys, which included water sampling for chemical (nutrients and dissolved oxygen) and sedimentological analyses, took place in September 1997 (summer cruise) and January 1998 (winter cruise) in the study region. The correspondence between the high-salinity Mediterranean Water (MW) layer and the low-nutrient content and relatively high abundance of particles was a general result. Further details of the thermohaline analysis and of the geostrophic computations, especially for the layer of MW, are compared with the results obtained for the chemical properties and the sedimentological characteristics.

Foraminiferal assemblage changes, size and mineralogy of lithic grains, oxygen isotopes, CaCO 3 , and dolomite content were studied along a 9-m-long core from the Meriadzek Terrace to gain insight into climate, productivity, and sediment source changes at this part of the Northeast Atlantic margin during the late Quaternary. An age model has been generated on the basis of radiocarbon dating, downcore foraminiferal assemblages, and Ž 18 O values. High sedimentation rates at this site allow very detailed records for the last glacial period down to late isotopic stage 3. Sea surface temperature (SST) inferred from the foraminiferal assemblages, Ž 18 O curve, and the temperature estimation by the SIMMAX analog technique reveal three distinctive periods during isotopic stage 2, with late stage 2 (15.3-13.4 ka) being the coldest period of the last 26 ka. A northward retreat of the polar front at 13.4 ka based on the SST record coincides with the strongest peak of primary productivity as indicated by the foraminiferal fluxes. Levels rich in large lithic grains (LLG) interpreted as ice-rafted debris (IRD) correspond to periods of low SST and are coeval with Heinrich layers 1, 2 and 3. However, the hematite-stained quartz found in the detrital fraction and the scarce dolomite and detrital carbonate content in our core point to an Iceland and=or Fenno-Scandian rather than a Laurentian or Greenland origin of this material.

Time series of diatom accumulation rates (DAR) and assemblage composition for the last 200 000 yr from the Atlantic major coastal upwelling loci of the eastern boundary currents and eastern Equator are compared together with independent proxies of export production, to upper ocean productivity and to nutrient concentration and utilization. Fluctuations in DAR are concomitant at all sites and in good correspondence to the other independent productivity proxies indicating glacial periods as the most productive times of the past 200 000 yr in both hemispheres of the eastern Atlantic. Maximum productivity, about one order of magnitude higher than at present, occurred at the last glacial maximum (LGM). Despite the ‘Atlantic’ similarities in both coastal and equatorial upwelling types, important regional and site specific variations emerge. In the southern Hemisphere site, a contradiction of proxies, diatoms and Corg, is noted at the base of stage 6 (185 000 yr). The good correlation found between the Corg and the benthic foraminifera fluxes is interpreted as a reflection of a shift in the phytoplankton community structure related to either a change in the N:P:Si ratio, or similar nutrient conditions associated with increased water column stratification.

The existence of a wide bed of the crinoid Leptometra celtica (M'Andrew and Barrett 1857), at approximately 500 m depth, off the Portuguese south coast is inferred from remotely operated vehicle (ROV) transects carried out as part of a research project (IMPACT) aimed at evaluating the impact of bottom trawling on the burrowing crustacean Norway lobster (Nephrops norvegicus) fishing grounds. The crinoid bed is located in an enclave of gravelly sand surrounded by muddy sediments, the latter constituting the typical habitat of Norway lobster. An overall description of the geological and oceanographic features off the Portuguese southern coast is presented, highlighting the complexity of factors influencing the research zone. A delimitation of the crinoid bed and a comparison of taxa richness for the epibenthic megafauna of the adjacent towed zone are carried out. This finding highlights the urgent need for a comprehensive mapping programme to allow for the identification and preservation of sensitive habitats within the scope of the European Union Habitats and Marine Strategy Framework Directives.

Foraminiferal assemblage changes, size and mineralogy of lithic grains, oxygen isotopes, CaCO 3 , and dolomite content were studied along a 9-m-long core from the Meriadzek Terrace to gain insight into climate, productivity, and sediment source changes at this part of the Northeast Atlantic margin during the late Quaternary. An age model has been generated on the basis of radiocarbon dating, downcore foraminiferal assemblages, and Ž 18 O values. High sedimentation rates at this site allow very detailed records for the last glacial period down to late isotopic stage 3. Sea surface temperature (SST) inferred from the foraminiferal assemblages, Ž 18 O curve, and the temperature estimation by the SIMMAX analog technique reveal three distinctive periods during isotopic stage 2, with late stage 2 (15.3-13.4 ka) being the coldest period of the last 26 ka. A northward retreat of the polar front at 13.4 ka based on the SST record coincides with the strongest peak of primary productivity as indicated by the foraminiferal fluxes. Levels rich in large lithic grains (LLG) interpreted as ice-rafted debris (IRD) correspond to periods of low SST and are coeval with Heinrich layers 1, 2 and 3. However, the hematite-stained quartz found in the detrital fraction and the scarce dolomite and detrital carbonate content in our core point to an Iceland and=or Fenno-Scandian rather than a Laurentian or Greenland origin of this material.