Gut filling, gut content and fatty acid composition of demersal fish species sampled during POLARSTERN cruise ANT-XXIV/2

The gut contents and fatty acid composition of 49 fish belonging to five Antarctic demersal families (Nototheniidae, Macrouridae, Channichtyidae, Bathydraconidae and Artedidraconidae) sampled at two stations at the Southern Ocean shelf and deep sea (600 and 2150 m) were analysed in order to identify their main food resource by linking trophic biomarkers with the dietary items found in the fish guts. Main food items of most fish analysed were amphipod crustaceans (e.g. in 63% of Trematomus bernachii guts) and polychaetes (e.g. in 80% of Bathydraco sp. guts), but other food items including fish, other crustaceans and gastropods were also ingested. The most prominent fatty acids found were 20:5(n-3), 16:0, 22:6(n-3) and 18:1(n-9). The results of gut content and fatty acid analyses indicate that all fish except the Channichthyidae share similar food resources irrespective of their depth distribution, i.e. benthic amphipods and polychaetes. A difference of the dietary spectrum can be observed with ontogenetic phases rather than between species, as high values of typical calanoid copepod marker fatty acids as 22:1(n-11) indicate that younger (smaller) specimens include more zooplankton in their diet.

Figure 2. Downcore variations of total diatom concentration in core MD02-2529

The modern eastern equatorial Pacific (EEP) is a major natural source for atmospheric carbon dioxide and is thought to be connected to high-latitude ocean dynamics by oceanic teleconnections on glacial-interglacial timescales. A wealth of sedimentary records aiming at reconstructing last Quaternary changes in primary productivity and nutrient utilization have been devoted to understanding those linkages between the EEP and other distant oceanic areas. Most of these records are, however, clustered in the pelagic EEP cold tongue, with comparatively little attention devoted to coastal areas. Here we present downcore measurements of the composition and concentration of the diatom assemblage together with opal (biogenic silica) concentration at site MD02-2529 recovered in the coastal Panama Basin. Piston core MD02-2529, collected in an area affected by a multitude of processes, provides evidence for strong variations in diatom production at the millennial timescale during the last glacial cycle. The maxima in total diatom concentration occurred during the early marine isotopic stage (MIS) 4 as well as during the MIS 4/3 transition and MIS 3. Rapid changes in diatom concentrations during the MIS 3 mimics Bond cycles as independently recorded by the SSS estimation derived from planktonic foraminifera from the same core. Such patterns indicate a clear linkage between diatom production in the coastal EEP and rapid climate changes in the high-latitude North Atlantic. In parallel, the long-term succession of the diatom community from coastal diatoms, predominantly thriving during MIS 5 and 4, towards pelagic diatoms, dominant during MIS 3 and 2, points to a long-term change in the surface hydrology. During Heinrich Events, diatoms strongly reduced their production, probably due to enhanced stratification in the upper water column. After the last glacial maximum, diatom production and valve preservation strongly decreased in response to the advection of nutrient (H2SiO4)-depleted, warmer water masses. Our high-resolution record highlights how regional climatic processes can modulate rapid changes in siliceous primary production as triggered by wind-induced local upwelling, indicating that millennial climatic variability can overtake other prominent hydrological processes such as those related to silicic acid leakage.

(Table 2) Radiocarbon ages on Arctic box and multicores

Paleo-sea-ice history in the Arctic Ocean was reconstructed using the sea-ice dwelling ostracode Acetabulastoma arcticum from late Quaternary sediments from the Mendeleyev, Lomonosov, and Gakkel Ridges, the Morris Jesup Rise and the Yermak Plateau. Results suggest intermittently high levels of perennial sea ice in the central Arctic Ocean during Marine Isotope Stage (MIS) 3 (25-45 ka), minimal sea ice during the last deglacial (16-11 ka) and early Holocene thermal maximum (11-5 ka) and increasing sea ice during the mid-to-late Holocene (5-0 ka). Sediment core records from the Iceland and Rockall Plateaus show that perennial sea ice existed in these regions only during glacial intervals MIS 2, 4, and 6. These results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon.

(Table 2) Stratigraphic marker taxa in ODP Hole 162-985A sediments

The rich and diverse dinocyst assemblages in Cores 162-985A-32X through 62X confirm the importance of these microfossils in unraveling the evolution of the Norwegian Sea. Cosmopolitan taxa, with well-documented stratigraphic ranges in northwest Europe, indicate the following ages: Sections 162-985A-62X-1 through 51X-2, Rupelian (early Oligocene); 50X-5, Oligocene, possibly Chattian; 48X-6, Aquitanian? (early Miocene); 48X-4 through 37X-5, Aquitanian (early Miocene); and 36X-5 through 32X-1, Burdigalian (early Miocene). This stratigraphic interpretation suggests that a major hiatus, which can be correlated with an apparently coeval hiatus at Site 643, occurs within the Chattian at Site 985. Several endemic dinocyst taxa with unusual morphology and restricted stratigraphic occurrences are present in Hole 985A and other Norwegian Sea sites, especially Site 643. By using Hole 985A data for control, the Oligocene-Miocene sediments can be correlated with some degree of confidence in the Norwegian Basin.

(Table 2) Age determination of sediment cores from the Panama Basin

Application of the 230Th normalization method to estimate sediment burial fluxes in six cores from the eastern equatorial Pacific (EEP) reveals that bulk sediment and organic carbon fluxes display a coherent regional pattern during the Holocene that is consistent with modern oceanographic conditions, in contrast with estimates of bulk mass accumulation rates (MARs) derived from core chronologies. Two nearby sites (less than 10 km apart), which have different MARs, show nearly identical 230Th-normalized bulk fluxes. Focusing factors derived from the 230Th data at the foot of the Carnegie Ridge in the Panama Basin are >2 in the Holocene, implying that lateral sediment addition is significant in this part of the basin. New geochemical data and existing literature provide evidence for a hydrothermal source of sediment in the southern part of the Panama Basin and for downslope transport from the top of the Carnegie Ridge. The compilation of core records suggests that sediment focusing is spatially and temporally variable in the EEP. During oxygen isotope stage 2 (OIS 2, from 13-27 ka BP), focusing appears even higher compared to the Holocene at most sites, similar to earlier findings in the eastern and central equatorial Pacific. The magnitude of the glacial increase in focusing factors, however, is strongly dependent on the accuracy of age models. We offer two possible explanations for the increase in glacial focusing compared to the Holocene. The first one is that the apparent increase in lateral sediment redistribution is partly or even largely an artifact of insufficient age control in the EEP, while the second explanation, which assumes that the observed increase is real, involves enhanced deep sea tidal current flow during periods of low sea level stand.

Dinoflagellate cysts in surface sediment samples of METEOR cruises M20/2, M23/1, M34/1, M34/2, M34/3 and M34/4

To enhance the limited information available about the palaeo-ecological significance of calcareous dinoflagellates, we have studied their lateral distribution in surface sediments of the equatorial and south Atlantic between 13°N and 36°S. Calcareous dinoflagellate cysts appear to be widely distributed throughout the studied area. In the surface sediments, concentrations (cyst per gram dry sediment) of the vegetative stage Thoracosphaera heimii are generally higher than that of the (presumably) calcareous resting cysts. Distribution patterns in surface sediments of Orthopithonella granifera (Fütterer) Keupp and Versteegh, Rhabdothorax spp. Kamptner., Sphaerodinella albatrosiana (Kamptner) Keupp and Versteegh S. albatrosiana praratabulated, Sphaerodinella tuberosa var. 1 (Kamptner) Keupp and Versteegh and S. tuberosa var. 2 and the ratios between these species have been compared with temperature, salinity, density and stratification gradients in the upper water column. Rhabdothorax spp. is characteristically present in sediments of more temperate regions characterized by high seasonality. Dinoflagellates producing these cysts are able to tolerate high nutrient concentrations, and mixing of the water column. S. albatrosiana is abundant in regions characterized by high sea surface temperatures and oligotrophic surface water conditions. In contrast, the distribution of S. tuberosa var. 2 is negatively related to temperature. The other cyst species did not show a characteristic pattern in relation to the studied environmental gradients. The ratio of Sphaerodinella tuberosa var. 2 to Orthopithonella granifera can be used for reconstructing the presence of stratification in the upper 50 m of the water column, whereas the ratios of S. tuberosa var. 2 to Sphaerodinella albatrosiana and of O. granifera to Rhabdothorax spp. might be used for palaeotemperature reconstructions. Calcareous dinoflagellate cysts are abundant in oligotrophic areas and may be useful for the reconstruction of palaeoenvironmental conditions.