Aprubt climate change events in the Northeastern Atlantic Ocean

The western Iberian margin has been one of the key locations to study abrupt glacial climate change and associated interhemispheric linkages. The regional variability in the response to those events is being studied by combining a multitude of published and new records. Looking at the trend from Marine Isotope Stage (MIS) 10 to 2, the planktic foraminifer data, conform with the alkenone record of Martrat et al. [2007], shows that abrupt climate change events, especially the Heinrich events, became more frequent and their impacts in general stronger during the last glacial cycle. However, there were two older periods with strong impacts on the Atlantic meridional overturning circulation (AMOC): the Heinrich-type event associated with Termination (T) IV and the one occurring during MIS 8 (269 to 265 ka). During the Heinrich stadials of the last glacial cycle, the polar front reached the northern Iberian margin (ca. 41°N), while the arctic front was located in the vicinity of 39°N. During all the glacial periods studied, there existed a boundary at the latter latitude, either the arctic front during extreme cold events or the subarctic front during less strong coolings or warmer glacials. Along with these fronts sea surface temperatures (SST) increased southward by about 1°C per one degree of latitude leading to steep temperature gradients in the eastern North Atlantic and pointing to a close vicinity between subpolar and subtropical waters. The southern Iberian margin was always bathed by subtropical water masses - surface and/ or subsurface ones -, but there were periods when these waters also penetrated northward to 40.6°N. Glacial hydrographic conditions were similar during MIS 2 and 4, but much different during MIS 6. MIS 6 was a warmer glacial with the polar front being located further to the north allowing the subtropical surface and subsurface waters to reach at minimum as far north as 40.6°N and resulting in relative stable conditions on the southern margin. In the vertical structure, the Greenland-type climate oscillations during the last glacial cycle were recorded down to 2465 m during the Heinrich stadials, i.e. slightly deeper than in the western basin. This deeper boundary is related to the admixing of Mediterranean Outflow Water, which also explains the better ventilation of the intermediate-depth water column on the Iberian margin. This compilation revealed that latitudinal, longitudinal and vertical gradients existed in the waters along the Iberian margin, i.e. in a relative restricted area, but sufficient paleo-data exists now to validate regional climate models for abrupt climate change events in the northeastern North Atlantic Ocean.

Calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea

The distribution of calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea was quantitatively analysed. The samples contain 11 cyst species and the vegetative coccoid Thoracosphaera heimii. Cyst abundance increases towards the deeper parts of the basins and is generally higher in the eastern Mediterranean Sea. Three major distribution characteristics exist: (1) different assemblages in oceanic and neritic regions, (2) little agreement with the associations of areas studied so far like the Atlantic Ocean, and (3) a unique oceanic assemblage in the eastern Mediterranean Sea. A gradual change in cyst assemblages from the western to the eastern Mediterranean Sea was observed and statistically compared with the main environmental gradients in the upper water column. Temperature, nitrate concentration and possibly salinity appear to be the most important factors controlling cyst production. Three groups containing cysts with similar environmental preferences can be distinguished: (1) an eastern Mediterranean group related to relatively high temperature and salinity but low nitrate concentration, (2) a group of more or less consistently abundant cosmopolitan species tolerating or even preferring relatively low temperature and salinity but high nitrate concentration, and (3) a group containing species that are possibly adapted to neritic environments and have probably been transported from coastal areas into the studied regions. In contrast to other calcareous plankton, calcareous dinoflagellate cysts correlate strongly with the main environmental gradients in the Mediterranean Sea, bearing a high potential for palaeoenvironmental reconstructions.

Fatty acid and stable isotope composition of calanoid copepods in the open eastern Atlantic Ocean during POLARSTERN cruise ANT-XXIX/1

The majority of global ocean production and total export production is attributed to oligotrophic oceanic regions due to their vast regional expanse. However, energy transfers, food-web structures and trophic relationships in these areas remain largely unknown. Regional and vertical inter- and intra-specific differences in trophic interactions and dietary preferences of calanoid copepods were investigated in four different regions in the open eastern Atlantic Ocean (38°N to 21°S) in October/November 2012 using a combination of fatty acid (FA) and stable isotope (SI) analyses. Mean carnivory indices (CI) based on FA trophic markers generally agreed with trophic positions (TP) derived from d15N analysis. Most copepods were classified as omnivorous (CI ~0.5, TP 1.8 to ~2.5) or carnivorous (CI >=0.7, TP >=2.9). Herbivorous copepods showed typical CIs of <=0.3. Geographical differences in d15N values of epi- (200-0 m) to mesopelagic (1000-200 m) copepods reflected corresponding spatial differences in baseline d15N of particulate organic matter from the upper 100 m. In contrast, species restricted to lower meso- and bathypelagic (2000-1000 m) layers did not show this regional trend. FA compositions were species-specific without distinct intra-specific vertical or spatial variations. Differences were only observed in the southernmost region influenced by the highly productive Benguela Current. Apparently, food availability and dietary composition were widely homogeneous throughout the oligotrophic oceanic regions of the tropical and subtropical Atlantic. Four major species clusters were identified by principal component analysis based on FA compositions. Vertically migrating species clustered with epi- to mesopelagic, non-migrating species, of which only Neocalanus gracilis was moderately enriched in lipids with 16% of dry mass (DM) and stored wax esters (WE) with 37% of total lipid (TL). All other species of this cluster had low lipid contents (< 10% DM) without WE. Of these, the tropical epipelagic Undinula vulgaris showed highest portions of bacterial markers. Rhincalanus cornutus, R. nasutus and Calanoides carinatus formed three separate clusters with species-specific lipid profiles, high lipid contents (>=41% DM), mainly accumulated as WE (>=79% TL). C. carinatus and R. nasutus were primarily herbivorous with almost no bacterial input. Despite deviating feeding strategies, R. nasutus clustered with deep-dwelling, carnivorous species, which had high amounts of lipids (>=37% DM) and WE (>=54% TL). Tropical and subtropical calanoid copepods exhibited a wide variety of life strategies, characterized by specialized feeding. This allows them, together with vertical habitat partitioning, to maintain high abundance and diversity in tropical oligotrophic open oceans, where they play an essential role in the energy flux and carbon cycling.

Miocene Mediterranean Nd, Sr, C and O isotope composition

Isotopic compositions of marine sediments and fossils have been investigated from northern basins of the Mediterranean to help constrain local oceanographic and climatic changes adjacent to the uplifting Alps. Stable C and O isotope compositions of benthic and planktonic foraminifera from the Umbria-Marche region (UMC) have an offset characteristic for their habitats and the changes in composition mimic global changes, suggesting that the regional conditions of climate and the carbon cycle were controlled by global changes. The radiogenic isotope composition of these fossil assemblages allows recognition of three distinct periods. In the first period, from 25 to 19 Ma, high epsilon-Nd values and low 87Sr/86Sr of sediments and fossils support intense tectonism and volcanism, related to the opening of the western Mediterranean. In the second period, from 19 to 13 Ma the 87Sr/86Sr ratio of Mediterranean (UMC) deviate from the global ocean, which is compatible with rapid uplift of the hinterland and intense influx of Sr from Mesozoic carbonates of the western Apennines. This local control on the seawater was driven by a humid and warm climate and indicates restricted exchange of water with the global ocean. Generally, the epsilon-Nd values of the fossils are very similar to those of Indian Ocean water, with brief periods of a decrease in the epsilon-Nd values coinciding with volcanic events and maybe sea level variation at 15.2 Ma. In the third period, from 13 to 10 Ma the fossils have 87Sr/86Sr similar to those of Miocene seawater while their epsilon-Nd values change considerably with time. This indicates fluctuating influence of the Atlantic versus the Paratethys and/or locally evolved seawater in the Mediterranean driven by global sea level changes. Other investigated localities near the Alps and from the ODP 900 site are compatible with this oceanographic interpretation. However, in the late early Miocene, enhanced local control, reflecting erosion of old crustal silicate rocks near the Alps, results in higher 87Sr/86Sr.

(Appendix A) Relative abundance of Emiliania huxleyi in sediment cores of the North Atlantic

The coccolithophore species Emiliania huxleyi is characterized by a wide range of sizes, which can be easily distinguished in the light microscope. In this study we have quantified the abundance of large (coccoliths > 4 µm in maximum length) E. huxleyi specimens during the last 25 kyr in sedimentary records from eleven cores and drill sites in the NE Atlantic and W Mediterranean Sea, to prove its usefulness in the reconstruction of water mass dynamics and biostratigraphic potential. During the Last Glacial Maximum this large form, a cold-water indicator, was common in the NE Atlantic and Mediterranean, and its regional variation in abundance indicates a displacement of the climatic zones southwards in agreement with the development of ice sheets and sea ice in the Northern Hemisphere during this period. On the other hand, the gradient between northern and southern surface water masses in the Subtropical Gyre appears to have been more pronounced than at present, while the Portugal and Canary Currents were more intense. In the western Mediterranean basin temperatures were cooler than in the adjacent Atlantic, provoking a quasi-endemism of these specimens until the end of Heinrich Event 1. This may have been due to a restriction in the communication between the Atlantic and Mediterranean through the Strait of Gibraltar, the arrival of cold surface water and the amplification of cooling after the development of ice sheets in the Northern Hemisphere. During the deglaciation, large E. huxleyi specimens decreased in abundance at medium and low latitudes, but were still numerous close to the Subarctic region during the Holocene. In transitional waters this decrease to present day abundances occurred after Termination Ib. The abrupt change in abundance of this large E. huxleyi form is proposed as a new biostratigraphic event to characterize the Holocene in mid- to low-latitude water masses in the North Atlantic, although this horizon seems to be diachronous by 5 kyr from tropical to subarctic regions, in agreement with the gradual onset of warm conditions.

Geochemistry of sediment cores GeoB13820-1 and GeoB13863-1 from the western South Atlantic

Here, we present results from sediments collected in the Argentine Basin, a non-steady state depositional marine system characterized by abundant oxidized iron within methane-rich layers due to sediment reworking followed by rapid deposition. Our comprehensive inorganic data set shows that iron reduction in these sulfate and sulfide-depleted sediments is best explained by a microbially mediated process-implicating anaerobic oxidation of methane coupled to iron reduction (Fe-AOM) as the most likely major mechanism. Although important in many modern marine environments, iron-driven AOM may not consume similar amounts of methane compared with sulfate-dependent AOM. Nevertheless, it may have broad impact on the deep biosphere and dominate both iron and methane cycling in sulfate-lean marine settings. Fe-AOM might have been particularly relevant in the Archean ocean, >2.5 billion years ago, known for its production and accumulation of iron oxides (in iron formations) in a biosphere likely replete with methane but low in sulfate. Methane at that time was a critical greenhouse gas capable of sustaining a habitable climate under relatively low solar luminosity, and relationships to iron cycling may have impacted if not dominated methane loss from the biosphere.

Hydrocarbons in surface waters of the Atlantic and Indian Oceans

Results of investigation of various forms of oil pollution, i.e. oil films, tar, and hydrocarbons in the Northeast Atlantic Ocean and North Indian Ocean during October-December 1980 and February-May 1981 are presented. Oil pollution was found only in regions of the heaviest ship traffic and was somewhat less than in 1976-1977. Background concentration of non-polar hydrocarbons was 8-10 ?g/l in surface waters and 14 ?g/l in the shelf zone. Infrared spectroscopy and gas-liquid chromatography indicate that hydrocarbons occurring at concentrations exceeding 50 ?g/l have composition differing from background hydrocarbons. There is considerable accumulation of hydrocarbons in the thin surface layer, and they exist in different forms close to pollution sources.

Regional ocean model for the Mediterranean, links to model files

A regional ocean general circulation model of the Mediterranean is used to study the climate of the Last Glacial Maximum. The atmospheric forcing for these simulations has been derived from simulations with an atmospheric general circulation model, which in turn was forced with surface conditions from a coarse resolution earth system model. The model is successful in reproducing the general patterns of reconstructed sea surface temperature anomalies with the strongest cooling in summer in the northwestern Mediterranean and weak cooling in the Levantine, although the model underestimates the extent of the summer cooling in the western Mediterranean. However, there is a strong vertical gradient associated with this pattern of summer cooling, which makes the comparison with reconstructions complicated. The exchange with the Atlantic is decreased to roughly one half of its present value, which can be explained by the shallower Strait of Gibraltar as a consequence of lower global sea level. This reduced exchange causes a strong increase of salinity in the Mediterranean in spite of reduced net evaporation.