Absorption characteristics, major elements and chl a content of samples from Pond 19 at Zackenberg, NE Greenland

1. Shallow arctic lakes and ponds have simple and short food webs, but large uncertainties remain about benthic-pelagic links in these systems. We tested whether organic matter of benthic origin supports zooplankton biomass in a pond in NE Greenland, using stable isotope analysis of carbon and nitrogen in the pond itself and in a 13C-enrichment enclosure experiment. In the latter, we manipulated the carbon isotope signature of benthic algae to enhance its isotopic discrimination from other potential food sources for zooplankton. 2. The cladoceran Daphnia middendorffiana responded to the 13C-enrichment of benthic mats with progressively increasing d13C values, suggesting benthic feeding. Stable isotope analysis also pointed towards a negligible contribution of terrestrial carbon to the diet of D. middendorffiana. This agreed with the apparent dominance of autochthonous dissolved organic matter in the pond revealed by analysis of coloured dissolved organic matter. 3. Daily net production by phytoplankton in the pond (18 mg C/m**2/day) could satisfy only up to half of the calculated minimum energy requirements of D. middendorffiana (35 mg C/m**2/day), whereas benthic primary production alone (145 mg C/m**2/day) was more than sufficient. 4. Our findings highlight benthic primary production as a major dietary source for D. middendorffiana in this system and suggest that benthic organic matter may play a key role in sustaining pelagic secondary production in such nutrient-limited high arctic ponds.

Concentrations of tektites and chemical elements in sediments from ODP Holes 121-758B and 124-769A

Recently published studies of Ocean Drilling Project (ODP) cores from near southeast Asia revealed microtektite contents much higher than those in previously studied cores, suggesting that Ir contents might be enhanced in the tektite-bearing horizons. We determined a positive Ir anomaly in ODP core 758B from the Ninetyeast Ridge, eastern Indian Ocean; the peak Ir concentration of 190 pg/ g was ~2X the continuum level. The net Ir fluence is 1.8+/-0.5 ng/cm**2 over the depth interval from 10.87 to 11.32 m; a small additional peak also associated with microtektites contributes another 0.5 ng Ir/cm**2. Concentrations of Ir in core 769A show more scatter, but a small Ir enhancement is associated with the peak microtektite abundance; our best estimate of the poorly constrained fluence is 1.3+/-0.7 ng/cm**2. Data on deep-sea cores show that the microtektite fluence falls exponentially away from southeast Asia, the fluence dropping a factor of 2 in ~400 km. In southeast Asia the trend merges with a roughly estimated mass fluence of ~1.1 g/cm**2 inferred from evidence of a melt sheet in northeast Thailand. Integration of the inferred distribution yields a total mass of Australasian tektites of 3.2x10**16 g, much higher than previous estimates. Assuming a similar fallout distribution for the impactor and a chondritic composition allows us to calculate its mass to be 1.5x10**15 g, about 3 orders of magnitude smaller than the minimum mass of the impactor responsible for the extinctions at the end of the Cretaceous.

Documentation of sediment cores from the Great Meteor Seamount, North Atlantic

Sedimentological and biostratigraphic investigations of 15 cores (total length: 88 m) from the vicinity of Great Meteor seamount (about 30° N, 28° W) showed that the calcareous ooze are asymmetrically distributed around the seamount and vertically differentiated into two intervals. East and west of the seampunt, the upper "A"-interval is characterized by yellowish-brown sediment colors and bioturbation; ash layers and diatoms are restricted to the eastern cores. On both seamount flanks, the sediment of the lower "B"-interval are white and very rich in CaCO3 with a major fine silt (2-16 µ) mode (mainly coccoliths). Lamination, manganese micronodules, Tertiary foraminifera and discoasters, and small limestone and basalt fragments are typical of the "B"-interval of the eastern cores only. The sediments contain abundant displaced material which was reworked from the upper parts of the seamount. The sedimentation around the seamount is strongly influenced by the kind of displaced material and the intensity of its differentiated dispersal: the sedimentation rates are generally higher on the east than on the west flank /e.g. in "B": 0.9 cm/1000 y in the W; 3.1 cm/1000 y in the E), and lower for the "A" than for the "B"-interval. The lamination is explained by the combination of increased sedimentation rates with a strong input of material poor in organic carbon producing a hostile environment for benthic life. The CaCO3 content of the core is highly influenced by the proportion of displaced bigenous carbonate material (mainly coccoliths). The genuine in-situ conditions of the dissolution facies are only reflected by the minimum CaCO3 values of the cores (CCD = about 5,500 m; first bend in dissolution curve = 4,000 m; ACD = about 3,400 m). The preservation of the total foraminiferal association depends on the proportions of in-situ versus displaced specimens. In greater water depths (stronger dissolution), for example, the preservation can be improved by the admixture of relatively well preserved displaced foraminifera. Carbonate cementation and the formation of manganese micronodules are restricted to microenvironments with locally increased organic carbon contents (e.g. pellets; foraminifera). The ash layers consist of redeposited, silicic volcanic glass of trachytic composition and Mio-Pliocene age; possibly, they can be derived from the upper part of the seamount. Siliceous organisms, especially diatoms, are frequent close to the ash layers and probably also redeposited. Their preservation was favoured by the increase of the SiO2 content in the pore water caused by the silicic volcanic glass. The cores were biostraftsraphically subdivided with the aid of planktonic foraminifera and partly alsococcoliths. In most cases, the biostratigraphically determined cold- and warm sections could be correlated from core to core. Almost all cores do not penetrate the Late Pleistocene. All Tertiary fossils are reworked. In general, the warm/cold boundary W2/C2 corresponds with the lithostratigraphic A/B boundray. Benthonic foraminifera indicate the original site deposition of the displaced material (summit plateau or flanks of the seamount). The asymmetric distribution of the sediments around the seamount east and west of the NE-directed antarctic bottom current (AABW) is explained by the distortion of the streamlines by the Coriolis force; by this process the current velocity is increased west of the seamount and decreased east of it. The different proportion of displaced material within the "A" and "B" interval is explained by changes of the intensity of the oceanic circulation. At the time of "B" the flow of the AABW around the seamount was stronger than during "A"; this can be inferred from the presence of characteristic benthonic foraminifera. The increased oceanic circulation implies an enhanced differentiation of the current velocities, and by that, also of the sedimentation rates, and intensifies the winnowed sediment material was transported downslope by turbid layers into the deep-sea, incorporated into the current system of the AABW, and asymmetrically deposited around the seamount.

Mesozooplankton biomass data from the Kapisigdlit an inner fjord branch of the Godthaabsfjord system, West Greenland, 2010

Sampling was conducted from March 24 to August 5 2010, in the fjord branch Kapisigdlit located in the inner part of the Godthåbsfjord system, West Greenland. The vessel "Lille Masik" was used during all cruises except on June 17-18 where sampling was done from RV Dana (National Institute for Aquatic Resources, Denmark). A total of 15 cruises (of 1-2 days duration) 7-10 days apart was carried out along a transect composed of 6 stations (St.), spanning the length of the 26 km long fjord branch. St. 1 was located at the mouth of the fjord branch and St. 6 was located at the end of the fjord branch, in the middle of a shallower inner creek . St. 1-4 was covering deeper parts of the fjord, and St. 5 was located on the slope leading up to the shallow inner creek. Mesozooplankton was sampled by vertical net tows using a Hydrobios Multinet (type Mini) equipped with a flow meter and 50 µm mesh nets or a WP-2 net 50 µm mesh size equipped with a non-filtering cod-end. Sampling was conducted at various times of day at the different stations. The nets were hauled with a speed of 0.2-0.3 m s**-1 from 100, 75 and 50 m depth to the surface at St. 2 + 4, 5 and 6, respectively. The content was immediately preserved in buffered formalin (4% final concentration). All samples were analyzed in the Plankton sorting and identification center in Szczecin (www.nmfri.gdynia.pl). Samples containing high numbers of zooplankton were split into subsamples. All copepods and other zooplankton were identified down to lowest possible taxonomic level (approx. 400 per sample), length measured and counted. Copepods were sorted into development stages (nauplii stage 1 - copepodite stage 6) using morphological features and sizes, and up to 10 individuals of each stage was length measured.