Sedimentology and paleontology on core Lz1104 from Lake Hjort, Greenland

Two sediment cores of 70 and 252 cm length were recovered from Hjort Sø, a small lake on Store Koldewey, Northeast Greenland, and studied with a multidisciplinary approach in order to reconstruct the local environmental history and to test the relevance of proxies for paleoenvironmental information. The basal sediments from the longer core are dominated by clastic matter, which was likely deposited during deglaciation of the lake basin. These clastic sediments are overlain by gyttja, which is also present throughout the shorter core. AMS radiocarbon dating was conducted on plant macrofossils of 11 samples from the gyttja in both cores. A reliable chronology was established for both cores, which dated the onset of organic accumulation at 9,500 cal. year BP. The Holocene temperature development, with an early to mid Holocene thermal maximum, is best reflected in the grain-size composition. Nutrient availability was apparently low during the early Holocene and led to low productivity in the lake and its vicinity. From ca. 7,000 cal. year BP, productivity in the lake increased significantly, probably induced by external nutrient input from goose excrements. From this time, micro- and macrofossil remains reflect relatively well the climate history of East Greenland, with a cooling during the middle Holocene, the medieval warming, and the Little Ice Age. The amount of organic matter in the sequence seems to be more affected by lake ice cover or by nutrient supply from the catchment than by temperature changes. The record from Hjort Sø thus reveals the difficulties in interpreting sedimentary records from high arctic regions.

Palynology from surface sediment samples of the Arctic Ocean

Freshwater chlorophycean algae are characteristic organic-walled microfossils in recent coastal and shelf sediments from the Beaufort, Laptev and Kara seas (Arctic Ocean). The persistent occurrence of the chlorophycean algae Pediastrum spp. and Botryococcus cf. braunii in marine palynomorph assemblages is related to the discharge of freshwater and suspended matter from the large Siberian and North American rivers into the Arctic shelf seas. The distribution patterns of these algae in the marine environments reflect the predominant deposition of riverine sediments and organic matter along the salinity gradient from the outer estuaries and prodeltas to the shelf break. Sedimentary processes overprint the primary distribution of these algae. Resuspension of sediments by waves and bottom currents may transport sediments in the bottom nepheloid layer along the submarine channels to the shelf break. Bottom sediments and microfossils may be incorporated into sea ice during freeze-up in autumn and winter leading to an export from the shelves into the deep sea. The presence of these freshwater algae in sea-ice and bottom sediments in the central Arctic Ocean confirm that transport in sea ice is an important process which leads to a redistribution of shallow water microfossils.

Organic carbon and biomarker record from the Laptev Sea continental margin

In order to understand the processes controlling organic carbon deposition (i.e., primary productivity vs. terrigenous supply) and their paleoceanographic significance, three sediment cores (PS2471, PS2474. and PS2476) from the Laptev Sea continental margin were investigated for their content and composition of organic carbon. The characterization of organic matter indudes the determination of buk parameters (hydrogen index values and C/N ratios) and the analysis of specific biomarkers (n-alaknes, fatty acids, alkenones, and pigments). Total organic carbon (TOC) values vary between 0.3 and 2%. In general, the organic matter from the Laptev Sea continental margin is dominated by terrigenous matter throughout. However. significant amounts of marine organic carbon occur. The turbidites, according to a still preliminary stratigraphy probably deposited during glacial Oxygen Isotope Stages 2 and 4, are characterized by maximum amounts of organic carbon of terrigenous origin. Marine organic carbon appears to show enhanced relative abundances in the Termination I (?) and early Holocene time intervals, as indicated by maximum amounts of short chain n-alkanes, short-chain fatty acids, and alkenones. The increased amounts of faity acids, however, may also have a freshwater origin due to increased river discharge at that time. The occurrence of alkenones is suggested to indicate an intensification of Atlantic water inflow along the Eurasian continental margin starting at that time. Oxygen Isotope Stage l accumutation rates of total organic carhon are 0.3, 0.17, and 0.02 C/cm**2/ky in cores PS2476, PS2474, and PS2471, respectively.

Cholesterol and C30 of sediment profile MD90-963

In a deep-sea sediment core recovered from a site lying well above the local lysocline, several organic geochemical proxies, and two different calcite dissolution indicators, are compared in order to evaluate the relationship between calcite dissolution and paleoproductivity over the past three glacial-interglacial cycles. The degree of foraminiferal break-up, and the CaCO3 particle size distribution, both point to significant periods of dissolution every 22 kyr during glacial stages and substages. These dissolution events are concomitant with periods of enhanced primary productivity, as indicated by the abundance of several biomarkers (alkenones, cholesterol, brassicasterol, keto-ol), used here to indicate changes in paleoproductivity. Dissolution fluctuations are highly coherent and in phase with the estimated paleoproductivity variations providing strong evidence that the observed dissolution is due to organic matter remineralization within the sediments rather, than to changes in CO32? concentration in the overlying water column.

Micropaleontology and stable isotope record of ODP Hole 178-1098C

Detailed study of four Holocene sediment intervals from Ocean Drilling Program Site 1098 (Palmer Deep, Antarctic Peninsula) reveals that in situ dissolution of calcareous foraminifers in the core repository has significantly altered and in some cases eliminated calcareous foraminifers. Despite dissolution, the foraminifer and supporting diatom data show that the most open-ocean and reduced sea-ice conditions occurred in the early Holocene. The influence of Circumpolar Deep Water was greatest during the early Holocene but continued to be important throughout the Holocene. An increase in sea-ice proximal diatoms at 3500 cal. BP documents an expansion in the amount of persistent sea ice. The inferred increase in sea ice corresponds with an overall increase in magnetic susceptibility values. Benthic foraminifers are present in all samples from the Palmer Deep, including the middle Holocene pervasively laminated sediments with low magnetic susceptibility values. The consistent presence of mobile epifaunal benthic foraminifers in the laminated sediments demonstrates that the laminations do not represent anoxic conditions. The uniform composition of the agglutinated foraminifer fauna throughout the late Holocene suggests that the Palmer Deep did not experience bottom-water-mass changes associated with the alternating deposition of bioturbated or laminated sediments.

Plant leaf wax (n-alkane) data from sediment core MD96-2048

In this study we investigate Pleistocene vegetation and climate change in southern East Africa by examining plant leaf waxes in a marine sediment core that receives terrestrial runoff from the Limpopo River. The plant leaf wax records are compared to a multi-proxy sea surface temperature (SST) record and pollen assemblage data from the same site. We find that Indian Ocean SST variability, driven by high-latitude obliquity, exerted a strong control on the vegetation of southern East Africa during the past 800,000 yr. Interglacial periods were characterized by relatively wetter and warmer conditions, increased contributions of C3 vegetation, and higher SST, whereas glacial periods were marked by cooler and arid conditions, increased contributions of C4 vegetation, and lower SST. We find that Marine Isotope Stages (MIS) 5e, 11c, 15e and 7a-7c are strongly expressed in the plant leaf wax records but MIS 7e is absent while MIS 9 is rather weak. Our plant leaf wax records also record the climate transition associated with the Mid-Brunhes Event (MBE) suggesting that the pre-MBE interval (430-800 ka) was characterized by higher inputs from grasses in comparison to relatively higher inputs from trees in the post-MBE interval (430 to 0 ka). Differences in vegetation and SST of southern East Africa between the pre- and post-MBE intervals appear to be related to shifts in the location of the Subtropical Front. Comparison with vegetation records from tropical East Africa indicates that the vegetation of southern East Africa, while exhibiting glacial-interglacial variability and notable differences between the pre- and post-MBE portions of the record, likely did not experience such dramatic extremes as occurred to the north at Lake Malawi.

(Table) Carbon, nitrogen and n-alkane content and isotopic composition of bottom sediments obtained in the East Siberian Sea

The chemical composition of organic matter (Corg, Norg, d13C, d1SN, and n-alkanes) was studied in the top layer of bottom sediments of the East Siberian Sea. Possible ways were proposed to estimate the amount of the terrigenous component in their organic matter (OM). The fraction of terrigenous OM estimated by the combined use of genetic indicators varied from 15% in the eastern part of the sea, near the Long Strait, to 95% in the estuaries of the Indigirka and Kolyma rivers, averaging 62% over the sea area.

Microphytobenthos composition in Heron Reef, Australia, by High Performance Liquid Chromatography (HPLC) (July 2012)

We quantified pigment biomarkers by high performance liquid chromatography (HPLC) to obtain a broad taxonomic classification of microphytobenthos (MPB) (i.e. identification of dominant taxa). Three replicate sediment cores were collected at 0, 50 and 100 m along transects 5-9 in Heron Reef lagoon (n=15) (Fig. 1). Transects 1-4 could not be processed because the means to have the samples analysed by HPLC were not available at the time of field data collection. Cores were stored frozen and scrapes taken from the top of each one and placed in cryovials immersed in dry ice. Samples were sent to the laboratory (CSIRO Marine and Atmospheric Research, Hobart, Australia) where pigments were extracted with 100% acetone during fifteen hours at 4°C after vortex mixing (30 seconds) and sonication (15 minutes). Samples were then centrifuged and filtered prior to the analysis of pigment composition with a Waters - Alliance HPLC system equipped with a photo-diode array detector. Pigments were separated using a Zorbax Eclipse XDB-C8 stainless steel 150 mm x 4.6 mm ID column with 3.5 µm particle size (Agilent Technologies) and a binary gradient system with an elevated column temperature following a modified version of the Van Heukelem and Thomas (2001) method. The separated pigments were detected at 436 nm and identified against standard spectra using Waters Empower software. Standards for HPLC system calibration were obtained from Sigma (USA) and DHI (Denmark).

Benthic foraminiferal abundances from eight sites of the Northwest Australian shelf

Foraminiferal analysis of Miocene to recent strata of the Northwest Shelf of Australia is used to chart West Pacific Warm Pool (WPWP) influence. The assemblage is typified by "larger" foraminifera with ingressions of the Indo-Pacific "smaller" taxa Asterorotalia and Pseudorotalia at around 4 Ma and from 1.6 to 0.8 Ma. A review of recent and fossil biogeography of these taxa suggests their stratigraphic distribution can be used to document WPWP evolution. From 10 to 4.4 Ma a lack of biogeographic connectivity between the Pacific and Indian Ocean suggests Indonesian Throughflow (ITF) restriction. During this period, the collision of Australia and Asia trapped warmer waters in the Pacific, creating a central WPWP biogeographic province from the equator to 26°N. By 3 Ma Indo-Pacific species migrated to Japan with the initiation of the "modern" Kuroshio Current coinciding with the intensification of the North Pacific Gyre and Northern Hemisphere ice sheet expansion. Indo-Pacific taxa migrated to the northwest Australia from 4.4 to 4 Ma possibly because of limited ITF. The absence of Indo-Pacific taxa in northwest Australia indicates possible ITF restriction from 4 to 1.6 Ma. Full northwest Australian biogeographic connectivity with the WPWP from 1.6 to 0.8 Ma suggests an unrestricted stronger ITF (compared to today) and the initiation of the modern Leeuwin Current. The extinction of some Indo-Pacific species in northwest Australia after 0.8 Ma may be related to the effects of large glacial/interglacial oscillations and uplift of the Indonesian Archipelago causing Indonesian seaway restriction.

Biomarker in Heinrich event layers

There are controversies regarding the origin of Heinrich layer 3 (H3), the massive ice-rafting and meltwater event in the North Atlantic during the last glacial cycle spanning a time window between 29 and 30 kyr B.P. Some argue in favor of a Laurentide Ice Sheet source similar to other Heinrich layers, while a contending view argues for the European ice sheet source. Existing geochemical proxies such as 40Ar/39Ar, 206Pb/204Pb, or epsilon-Nd, etc., could not be used to distinguish among various sources of ice-rafted debris in H3 because of their low abundances, suggesting a background glacial sediment signal. In order to circumvent this problem a biomarker-based approach is used to characterize the provenance of H layers 2, 3, and 4 and other non-Heinrich layers. The presence of hopanes and steranes and their aromatic counterparts in the H layers is incompatible with Recent sediments and is attributed to the transportation of organic matter because of the glacial erosion of source rocks. The most diagnostic and useful signatures of this ancient organic matter in the H layers are the dominance of C34 hopanoids over C33 and the occurrence of isorenieratane along with palaerenieratane. Biomarkers signatures in H layers 2 and 3 of the Labrador Sea suggest no difference in their source. Hydrocarbon distributions suggest that these sediments were derived from the Middle to Late Ordovician and Silurian source rocks of the Hudson Bay of eastern Canada. Biomarker data of the H layer 4 from the northwest Atlantic reveal that the sediments of this layer have a similar source to the H layers in the Labrador Sea.

Seawater carbonate chemistry, pigments and biological processes during experiments with coralline alga Corallina sessilis

Previous studies have shown that increasing atmospheric CO2 concentrations affect calcification in some planktonic and macroalgal calcifiers due to the changed carbonate chemistry of seawater. However, little is known regarding how calcifying algae respond to solar UV radiation (UVR, UVA+UVB, 280-400 nm). UVR may act synergistically, antagonistically or independently with ocean acidification (high CO2/low pH of seawater) to affect their calcification processes. We cultured the articulated coralline alga Corallina sessilis Yendo at 380 ppmv (low) and 1000 ppmv (high) CO2 levels while exposing the alga to solar radiation treatments with or without UVR. The presence of UVR inhibited the growth, photosynthetic O2evolution and calcification rates by13%, 6% and 3% in the low and by 47%, 20% and 8% in the high CO2 concentrations, respectively, reflecting a synergistic effect of CO2 enrichment with UVR. UVR induced significant decline of pH in the CO2-enriched cultures. The contents of key photosynthetic pigments, chlorophyll a and phycobiliproteins decreased, while UV-absorptivity increased under the highpCO2/low pH condition. Nevertheless, UV-induced inhibition of photosynthesis increased when the ratio of particulate inorganic carbon/particulate organic carbon decreased under the influence of CO2-acidified seawater, suggesting that the calcified layer played a UV-protective role. Both UVA and UVB negatively impacted photosynthesis and calcification, but the inhibition caused by UVB was about 2.5-2.6 times that caused by UVA. The results imply that coralline algae suffer from more damage caused by UVB as they calcify less and less with progressing ocean acidification.

Biogeochemical parameters and processes in waters and bottom sediments of the Chukchi Sea

Study of biogeochemical processes in waters and sediments of the Chukchi Sea in August 2004 revealed atypical maxima of biogenic element (N, P, and Si) concentrations and rate of microbial sulfate reduction in the surface layer (0-3 cm) of marine sediments. The C/N/P ratio in organic matter (OM) of this layer does not fit the Redfield-Richards stoichiometric model. Specific features of biogeochemical processes in the sea are likely related to the complex dynamics of water, high primary produc¬tivity (110-1400 mg C/m**2/day), low depth of the basin (<50 m for 60% of the water area), reduced food chain due to low population of zooplankton, high density of zoobenthos (up to 4230 g/m**2), and high activity of microbial processes. Drastic decrease in concentrations of biogenic elements, iodine, total alkalinity, and population of microorganisms beneath the 0-3 cm layer testify to large-scale OM decay at the water-seafloor barrier. Our original experimental data support high annual rate of OM mineralization at the bottom of the Chukchi Sea.