ALBERT

Description: Ten ODP sites drilled in a depth transect (2164–4775 m water depth) during Leg 172 recovered high-deposition rate (〉20 cm/kyr) sedimentary sections from sediment drifts in the western North Atlantic. For each site an age model covering the past 0.8–0.9 Ma has been developed. The time scales have a resolution of 10–20 kyr and are derived by tuning variations of estimated carbonate content to the orbital parameters precession and obliquity. Based on the similarity in the signature of proxy records and the spectral character of the time series, the sites are divided into two groups: precession cycles are better developed in carbonate records from a group of shallow sites (2164–2975 m water depth, Sites 1055–1058) while the deeper sites (2995–4775 m water depth, Sites 1060–1063) are characterized by higher spectral density in the obliquity band. The resulting time scales show excellent coherence with other dated carbonate and isotope records from low latitudes. Besides the typical Milankovitch cyclicity significant variance of the resulting carbonate time series is concentrated at millennial-scale changes with periods of about 12, 6, 4, 2.5, and 1.5 kyr. Comparisons of carbonate records from the Blake Bahama Outer Ridge and the Bermuda Rise reveal a remarkable similarity in the time and frequency domain indicating a basin-wide uniform sedimentation pattern during the last 0.9 Ma.

Description: In the present work responses of carp (Cyprinus carpio) head kidney-derived neutrophils to the blood parasite T. borreli, and the consequences of these responses for parasite survival and other host response mechanisms, were studied. In co-cultures of head kidney leucocytes (HKL) with viable and lysed T. borreli a prominent shape change of neutrophilic granulocytes towards increased size and complexity was observed. In addition, the longevity of neutrophils in vitro was prolonged in the presence of T. borreli antigens. In these cultures, neutrophils also exhibited an increased phagocytosis activity. An up regulation of the production of nitric oxide (NO) and reactive oxygen species (ROS) was observed in T. borreli- and mitogen-stimulated HKL cultures. However, addition of live, fluorescence-labelledT. borreli to previously stimulated HKL cultures, revealed neither killing nor phagocytosis of the parasite by activated neutrophils. Moreover, viable T. borreli, when added to HKL cultures of infected carp, reduced their phagocytosis activity and NO production. Supernatants of co-cultures between T. borreli and HKL also contained mediators, which suppressed a mitogen-induced proliferative response of peripheral blood leucocytes (PBL) in vitro. Thus, while T. borreli itself appeared not to be sensitive to responses of activated neutrophils, the flagellates interferes with the production of immunomodulatory signals of these cells, probably resulting in a partial immunosuppression, which may favour the parasite development in vivo.

Description: This paper is an observational study of small-scale coherent eddies in the Labrador Sea, a region of dense water formation thought to be of considerable importance to the North Atlantic overturning circulation. Numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat, yet their small size has hindered observational progress. A large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms, current meter moorings and satellite altimetry. Details of the current and water mass structure of individual eddy events, as they are swept past by an advecting flow, can then be extracted from the mooring data. A transition is seen during mid-1997, with long-lived boundary current eddies dominating the central Labrador Sea year-round after this time, and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time. The TOPEX / Poseidon altimeter covers the Labrador Sea with a loose “net” of observations, through which coherent eddies can seem to appear and disappear. By concentrating on locating and describing anomalous events in individual altimeter tracks, a portrait of the spatial and temporal variability of the underlying eddy field can be constructed. The altimeter results reveal an annual “pulsation” of energy and of coherent eddies originating during the late fall at a particular location in the boundary current, pinpointing the time and place of the boundary current-type eddy formation. The interannual variability seen at the mooring is reproduced, but the mooring site is found to be within a localized region of greatly enhanced eddy activity. Notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling. These eddy observations, as well as hydrographic evidence, suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region.

Description: The spatio-temporal pattern of peak Holocene warmth (Holocene thermal maximum, HTM) is traced over 140 sites across the Western Hemisphere of the Arctic (0–180°W; north of ∼60°N). Paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer-than-present conditions at 120 of these sites. At the 16 terrestrial sites where quantitative estimates have been obtained, local HTM temperatures (primarily summer estimates) were on average 1.6±0.8°C higher than present (approximate average of the 20th century), but the warming was time-transgressive across the western Arctic. As the precession-driven summer insolation anomaly peaked 12–10 ka (thousands of calendar years ago), warming was concentrated in northwest North America, while cool conditions lingered in the northeast. Alaska and northwest Canada experienced the HTM between ca 11 and 9 ka, about 4000 yr prior to the HTM in northeast Canada. The delayed warming in Quebec and Labrador was linked to the residual Laurentide Ice Sheet, which chilled the region through its impact on surface energy balance and ocean circulation. The lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change. The spatial asymmetry of warming during the HTM resembles the pattern of warming observed in the Arctic over the last several decades. Although the two warmings are described at different temporal scales, and the HTM was additionally affected by the residual Laurentide ice, the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing. Unlike the HTM, however, future warming will not be counterbalanced by the cooling effect of a residual North American ice sheet.

Description: In an attempt to characterise the role of nitric oxide (NO) in immune responses of carp, carp leucocytes obtained during an acute T. borreli infection were examined, for their capacity to generate NO. In a second set of experiments the impact NO on viability of the parasite and on the modulation of functional carp leucocyte responses were testedin vitro . Both in carp head-kidneys and in the peripheral blood, the fractions of lymphoblasts among separated leucocytes were increased. However, the relative proportions of granulocytes among head-kidney leucocytes (HKL) significantly decreased during infection, whereas granulocytes appeared among peripheral blood leucocytes (PBL). The cellular dynamics of HKL and PBL of infected carp were paralleled by an enhanced spontaneous NO release in vitro. NO production was further increased after addition of viable parasites to these cultures. The hypothesis that NO had a possible role in granulocyte activation and lymphocyte proliferation in carp was supported by the reduction of mitogen-induced proliferative responses of PBL from healthy carp in the presence of NO donor substances. The negative effects of NO on lymphocyte proliferation were contrasted by enhancing effects on granulocyte functions: the inhibition of NO generation in T. borreli -stimulated HKL cultures by the l-arginine analogue L-NMMA reduced the viability of granulocytes and their phagocytic activity. Even massive amounts of nitric oxide produced by donor substances (up to 600 μmol l−1 NO−2) caused no reduction in the numbers of viable T. borreli flagellates in vitro. Thus, in carp, T. borreli seems to induce high amounts of NO in vivo which are apparently not harmful for the parasite but which may interfere with co-ordinated interactions of activated cells aiming at the defence of the parasite.

Description: Two cores recovered from the Discovery Basin and one reference core from a location outside the Basin were investigated in detail in order to decipher the influence of hypersaline brines on sediment geochemistry. The cores contain a tephra layer (presumable Y-5) and carbonate microfossils which permit a tentative chrono- and lithostratigraphic correlation. A layer containing up to 60 wt% biogenic opal and 6.6 wt% organic carbon was identified in one basin core, which probably represents the best preserved example of eastern Mediterranean sapropel S-1. The basin is filled with a concentrated solution of MgCl2 which is enriched in dissolved sulfate and has the highest salinity ever encountered in the marine environment. Pore water profiles demonstrate that this brine dissolves sedimentary calcite to form secondary carbonate- and sulfate-bearing minerals. Of these, dolomite, magnesite and gypsum were identified by X-ray diffractometry; thermodynamic calculations show that these phases form in equilibrium with the anomalous brine composition.

Description: Experiments have been carried out to examine the aggregation of natural estuarine suspended sediment under controlled conditions in an annular flume programmed to simulate oscillating tidal currents in an estuary. The size distribution of the suspended particles was measured in-situ using a Lasentec P-100 laser-reflectance particle sizer with the sensing probe inserted directly through the wall of the flume. Parallel measurements of the solids concentration were made using a calibrated OBS sensor. The flume was filled with river water collected from above the influence of salt water. Various quantities of natural estuary sediment were added to the flume to provide solids concentrations of nominally 100, 800 and 4000 mg 1−1. A series of experiments was performed in which the flume was run through consecutive, four hour cycles where the mean current velocity in the flume changed sinusoidally from 5 to 45 cm sec−1. For each sediment concentration the experiment was repeated with some of the fresh water replaced by particle-free seawater to give salinities of 0, 0.2, 2.0 and 10. Over a typical velocity cycle, suspended sediment concentrations decreased with decreasing current velocity, initially slowly, and then more rapidly. The concentration and size of material in suspension minimised over the low velocity period as particles settled. After a certain lag, sediment erosion occurred with increasing velocity and suspended solids concentration increased to a point where all the sediment was in suspension. The particle size data showed that during declining velocity conditions the median size of the particles initially increased as velocity decreased and then decreased as settling of the larger particles from suspension outweighed the aggregation process. During the erosion phase the median diameters increased initially but then decreased and levelled off as current velocity increased further. This was interpreted as mobilisation of aggregated particles followed by breakage as velocity increased. In general the degree of aggregation, and thus deposition, increased with salinity and with solids concentration. Solids concentration had by far the greatest effect on aggregation and deposition rate.

Description: In November 2000, a second iron enrichment experiment (EisenEx) was carried out in the Southern Ocean. Iron was added on the 8th of November in the centre of an eddy at 21°E, 48°S. During the cruise, the carbonate parameters dissolved inorganic carbon (DIC), fugacity of CO2 (fCO2) and pH on the hydrogen ion scale (pHT) were determined from water samples from both inside and outside the iron fertilized patch. Before the start of the experiment, the surface properties of the eddy were quite uniform with respect to the carbonate system and representative of the High Nutrient Low Chlorophyll (HNLC) regions in the Southern Ocean. The response of the carbon dioxide system to the initial ≈4 nM iron (Fe) infusion and to two subsequent reinfusions at 15 m depth was measured every day during the study. The changes in the carbon dioxide system and major nutrients were strongly influenced by the meteorological conditions with a rapid succession of calm, often sunny spells and storm force winds during the 21 days of experiment. Twenty days after the first Fe-infusion, the maximum changes of the carbonate parameters in surface waters of the patch relative to outside patch were −15 μmol kg−1 in DIC, −23 μatm in fCO2, +0.033 units in pHT, −1.61 μM in nitrate and −0.16 μM in phosphate in a mixed layer of 80 m depth. In addition to the daily measurements, several transects were made across the patch that showed a response of the carbonate system to the influence of iron, concomitant with a response in nutrients and chlorophyll. The relative changes in dissolved inorganic carbon to nutrient concentrations inside the patch during the experiment give N/P=12, C/P=82, C/N=5.9, C/Si=2.9 and N/Si=0.5. The effect of the influx of atmospheric CO2 on the DIC inventory was small with values between 0.05 and 0.10 μmol kg−1 day−1, and did not significantly affect these ratios. Although the observed change in DIC in the Fe-enriched surface waters was lower than in the previous Fe-enrichment experiments, the equivalent biological C-uptake of 1.08×109 mol C across the patch after 20 days was significant due to the large horizontal dispersion of the patch. The ratio of biological carbon uptake to Fe added (Cbiological uptake/Feadded) was 2.5×104 mol mol−1.