Oxygen and carbon isotopic composition of benthic and planktonic foraminifers at DSDP Site 610

A record of carbon and oxygen isotopes in benthic and planktonic foraminifers has been obtained from the interval corresponding to the last 2.4 m.y. of Site 610, Holes 610 and 610A, with a sample resolution of about 30 kyr. The record from the late Quaternary (<0.9 Ma) shows large amplitudes and high frequencies in oxygen isotopic variation. Prior to 0.9 Ma the isotopic variability record is reduced in amplitude (but not in frequency) compared with the late Quaternary, suggesting lower ice-volume and climatic fluctuations, and higher average eustatic sea level. Left-coiling (L, polar) Neogloboquadrinapachyderma were not found in samples between 1.0 and 2.2 Ma, indicating less influence of polar front migrations in the Northeast Atlantic. Both polar planktonic faunas and larger isotope fluctuations reappear in the lowermost samples (2.3 to 2.4 Ma), pointing toward a period of larger climatic variability in the late Pliocene than in the early Quaternary. The variation in benthic d13C and hence in deep-water d13C seems to have been constant through the analyzed section, reflecting a stable variability in the production of North Atlantic Deep Water (NADW) and possibly in Norwegian-Greenland Sea Overflow. Preliminary analyses of amino-acid epimerization in N. pachyderma (L) indicate a constant rate of epimerization to approximately 0.3 Ma. Beneath this level the average epimerization rate is much reduced.

Data compilation of ESOP

The work in this sub-project of ESOP focuses on the advective and convective transforma-tion of water masses in the Greenland Sea and its neighbouring areas. It includes observational work on the sub-mesoscale and analysis of hydrographic data up to the gyre-scale. Observations of active convective plumes were made with a towed chain equipped with up to 80 CTD sensors, giving a horizontal and vertical resolution of the hydrographic fields of a few metres. The observed scales of the penetrative convective plumes compare well with those given by theory. On the mesoscale the structure of homogeneous eddies formed as a result of deep convection was observed and the associated mixing and renewal of the intermediate layers quantified. The relative importance and efficiency of thermal and haline penetrative convection in relation to the surface boundary conditions (heat and salt fluxes and ice cover) and the ambient stratification are studied using the multi year time series of hydro-graphic data in the central Greenland Sea. The modification of the water column of the Greenland Sea gyre through advection from and mixing with water at its rim is assessed on longer time scales. The relative contributions are quantified using modern water mass analysis methods based on inverse techniques. Likewise the convective renewal and the spreading of the Arctic Intermediate Water from its formation area is quantified. The aim is to budget the heat and salt content of the water column, in particular of the low salinity surface layer, and to relate its seasonal and interannual variability to the lateral fluxes and the fluxes at the air-sea-ice interface. This will allow to estimate residence times for the different layers of the Greenland Sea gyre, a quantity important for the description of the Polar Ocean carbon cycle.

Solar radiation over and under sea ice during the POLARSTERN cruise ARK-XXVI/3 (TransArc) in summer 2011

Arctic sea ice has declined and become thinner and younger (more seasonal) during the last decade. One consequence of this is that the surface energy budget of the Arctic Ocean is changing. While the role of surface albedo has been studied intensively, it is still widely unknown how much light penetrates through sea ice into the upper ocean, affecting sea-ice mass balance, ecosystems, and geochemical processes. Here we present the first large-scale under-ice light measurements, operating spectral radiometers on a remotely operated vehicle (ROV) under Arctic sea ice in summer. This data set is used to produce an Arctic-wide map of light distribution under summer sea ice. Our results show that transmittance through first-year ice (FYI, 0.11) was almost three times larger than through multi-year ice (MYI, 0.04), and that this is mostly caused by the larger melt-pond coverage of FYI (42 vs. 23%). Also energy absorption was 50% larger in FYI than in MYI. Thus, a continuation of the observed sea-ice changes will increase the amount of light penetrating into the Arctic Ocean, enhancing sea-ice melt and affecting sea-ice and upper-ocean ecosystems.

(Table 1) Bulk carbonate content of ODP Hole 194-1198A sediments, east of the Great Barrier Reef

Upper Quaternary sediment sequences east of the Great Barrier Reef are characterized by alternating siliciclastic- and carbonate-rich horizons caused by changes in the input of various sedimentary components and reflected in cores by variations in bulk carbonate content. A total of 153 measurements of bulk carbonate content were determined using the carbonate-bomb technique for late Pleistocene sediments between 0 and 23.69 meters below sea floor (mbsf) in Ocean Drilling Program Hole 1198A. Average sample resolution was 15 cm and multiple analyses were performed on each sample. Bulk carbonate content ranges from a maximum of 94 wt% at 13.63 mbsf to a minimum of 73 wt% at 14.54 mbsf. Five cyclic trends are observed that may relate to five major glacial events during the last 500 k.y. of the Quaternary.

Dinoflagellates of multicorer surface sediments

Only very few studies focus on recent calcareous dinoflagellate cyst diversity, geographic distribution and ecology, so that information on the distribution patterns and environmental affinities of individual cyst species is extremely limited. This information is, however, essential if we want to use calcareous dinoflagellate cysts for palaeoenvironmental reconstruction. Surface sediment samples from the generally oligotrophic western equatorial Atlantic Ocean, offshore northeast Brazil, were therefore quantitatively analysed for their calcareous dinoflagellate cyst content, including the calcareous vegetative coccoid Thoracosphaera heimii. Seven calcareous dinoflagellate cyst species/morphotypes and T. heimii were encountered in high concentrations throughout the area. Substantial differences in the distribution patterns were observed. The highest concentrations of cysts are found in sediments of the more oligotrophic, oceanic regions, beyond the influence of Amazon River discharge waters. Dinoflagellates producing calcareous cysts thus appear to be capable of surviving low nutrient concentrations and produce large numbers of cysts in relatively stable and predictable environments affected by minimal seasonality. To test for the environmental affinities of individual species, distribution patterns in surface sediments were compared with temperature, salinity, density and stratification gradients within the upper water column (0-100 m) over different times of the year, using principal components analysis and redundancy analysis. T. heimii and four of the seven encountered cyst species (Sphaerodinella? albatrosiana, two morphotypes of Sphaerodinella? tuberosa and Scrippsiella regalis) relate to these parameters significantly and the variations in the cyst associations appear to be associated with the different surface water currents characterising the area. The results imply that calcareous dinoflagellate cyst distributions can potentially be used to distinguish between different open oceanic environments and they could, therefore, be useful in tracing water mass movements throughout the late Quaternary.

(Table 1) Age determination of Barents Sea sediment cores

he separate roles of oceanic heat advection and orbital forcing on influencing early Holocene temperature variability in the eastern Nordic Seas is investigated. The effect of changing orbital forcing on the ocean temperatures is tested using the 1DICE model, and the 1DICE results are compared with new and previously published temperature reconstructions from a transect of five cores located underneath the pathway of Atlantic water, from the Faroe-Shetland Channel in the south to the Barents Sea in the north. The stronger early Holocene summer insolation at high northern latitudes increased the summer mixed layer temperatures, however, ocean temperatures underneath the summer mixed layer did not increase significantly. The absolute maximum in summer mixed layer temperatures occurred between 9 and 6 ka BP, representing the Holocene Thermal Maximum in the eastern Nordic Seas. In contrast, maximum in northward oceanic heat transport through the Norwegian Atlantic Current occurred approximately 10 ka BP. The maximum in oceanic heat transport at 10 ka BP occurred due to a major reorganization of the Atlantic Ocean circulation, entailing strong and deep rejuvenation of the Atlantic Meridional Overturning Circulation, combined with changes in the North Atlantic gyre dynamic causing enhanced transport of heat and salt into the Nordic Seas.

Seasonal variations in surface metabolite composition of Fucus vesiculosus and Fucus serratus sampled at outer Kiel Fjord (August 2012 - July 2013)

The chemical composition of surface associated metabolites of two Fucus species (Fucus vesiculosus and Fucus serratus) was analysed by means of gas chromatography-mass spectrometry (GC-MS) to describe temporal patterns in chemical surface composition. Method: The two perennial brown macroalgae F. vesiculosus and F. serratus were sampled monthly at Bülk, outer Kiel Fjord, Germany (54°27'21 N / 10°11'57 E) over an entire year (August 2012 - July 2013). Per month and species six non-fertile Fucus individuals were collected from mixed stands at a depth of 0.5 m under mid water level. For surface extraction approx. 50 g of the upper 5-10 cm apical thalli tips were cut off per species. The surface extraction of Fucus was performed according to the protocol of de Nys and co-workers (1998) with minor modifications (see Rickert et al. 2015). GC/EI-MS measurements were performed with a Waters GCT premier (Waters, Manchester, UK) coupled to an Agilent 6890N GC equipped with a DB-5 ms 30 m column (0.25 mm internal diameter, 0.25 mM film thickness, Agilent, USA). The inlet temperature was maintained at 250°C and samples were injected in split 10 mode. He carrier gas flow was adjusted to 1 ml min-1. Alkanes were used for referencing of retention times. For further details (GC-MS sample preparation and analysis) see the related publication (Rickert et al. submitted to PLOS ONE).