Sediment total reflectance measurements from the Cariaco Basin (MD03-2621) and northeastern Arabian Sea (SO130-289KL)

During the last glacial period, the North Atlantic region experienced pronounced, millennial-scale alternations between cold, stadial conditions and milder interstadial conditions-commonly referred to as Dansgaard-Oeschger oscillations-as well as periods of massive iceberg discharge known as Heinrich events. Changes in Northern Hemisphere temperature, as recorded in Greenland, are thought to have affected the location of the Atlantic intertropical convergence zone and the strength of the Indian summer monsoon. Here we use high-resolution records of sediment colour-a measure of terrigenous versus biogenic content-from the Cariaco Basin off the coast of Venezuela and the Arabian Sea to assess teleconnections with the North Atlantic climate system during the last glacial period. The Cariaco record indicates that the intertropical convergence zone migrated seasonally over the site during mild stadial conditions, but was permanently displaced south of the basin during peak stadials and Heinrich events. In the Arabian Sea, we find evidence of a weak Indian summer monsoon during the stadial events. The tropical records show a more variable response to North Atlantic cooling than the Greenland temperature records. We therefore suggest that Greenland climate is especially sensitive to variations in the North Atlantic system-in particular sea-ice extent-whereas the intertropical convergence zone and Indian monsoon system respond primarily to variations in mean Northern Hemisphere temperature.

Stable isotope record of northeastern Australian Margin

Stable isotopic data obtained from planktonic and benthic foraminifers were used to study paleoceanographic changes along the northeastern Australian margin from late Miocene (10 Ma) to Holocene time, and to evaluate the influence of these changes on reef growth. The data indicate that variations in surface-water temperatures may have had an important effect on the reef complexes on the Queensland Plateau and possibly off the northeastern Australian margin. Three sites were studied: Leg 21, Site 209 on the eastern edge of the Queensland Plateau, and Leg 133, Site 811 on the western margin, and Site 817 on the lower southern slope of the plateau. Shallow-water bioclasts recovered from Holes 811A and 817A indicate extensive reef growth on the Queensland Plateau during the middle Miocene (before 12 Ma), signifying surface-water temperatures of 20°C or greater. The amount of reefal detritus produced during the late Miocene (10.0-5.2 Ma) decreased progressively, resulting in a reduction in area of the reef complexes. The isotopic data from planktonic foraminifers in these late Miocene age sediments indicate the presence of relatively cool surface waters (16°-19°C), which may have been a major factor contributing to the demise of the reefs on the Queensland Plateau. Surface waters remained cool until the middle Pleistocene (1.2-0.5 Ma), when the surface-water temperature apparently increased to approximately 25°C, recorded both in the isotopic data and by renewed reef growth. This increase occurred simultaneously (within the error of the age model) with the initiation of the Great Barrier Reef. We propose that cooling of surface waters during the early late Miocene contributed to reef decline on the Queensland Plateau, and that subsequent warming of surface waters during the middle Pleistocene promoted the initiation of reef growth on the northeastern Australian margin. Reef development on the Queensland Plateau never recovered to the middle Miocene extent because of a combination of tectonic (accelerated subsidence of the plateau) and paleoceanographic (the cooler surface waters present from the late Miocene throughout the Pliocene) factors. Variations in seafloor d18O appear to be controlled by regional factors, as indicated by the similarity of data from Sites 811 and 817 to those from Site 590 on Lord Howe Rise.

Absolute and relative abundances of zooplankton taxa in Kongsfjorden during 2002

Seasonal changes in the zooplankton composition of the glacially influenced Kongsfjorden, Svalbard (79°N, 12°E), and its adjacent shelf were studied in 2002. Samples were collected in the spring, summer and autumn in stratified hauls (according to hydrographic characteristics), by means of a 0.180-mm Multi Plankton Sampler. A strong front between the open sea and the fjord waters was observed during the spring, preventing water mass exchange, but was not observed later in the season. The considerable seasonal changes in zooplankton abundance were related to the seasonal variation in hydrographical regime. The total zooplankton abundance during the spring (40-2010 individuals/m**3) was much lower than in the summer and autumn (410-10,560 individuals/m**3). The main factors shaping the zooplankton community in the fjord include: the presence of a local front, advection, the flow pattern and the decreasing depth of the basin in the inner fjord. Presumably these factors regulate the gross pattern of zooplankton density and distribution, and override the importance of biological processes. This study increased our understanding of seasonal processes in fjords, particularly with regard to the strong seasonal variability in the Arctic.

Sedimentological and benthic foraminiferal data pertaining to ODP Holes 208-1262A and 208-1263C

Eocene Thermal Maximum 2 (ETM2) occurred ~1.8 Myr after the Paleocene Eocene Thermal Maximum (PETM) and, like the PETM, was characterized by a negative carbon isotope excursion coupled with warming. We combined benthic foraminiferal and sedimentological records for Southeast Atlantic Sites 1263 (1500 m paleodepth) and 1262 (3600 m paleodepth) to show that benthic foraminiferal diversity and accumulation rates declined more precipitously and severely at the shallower site during peak ETM2. The sites are in close proximity, so differences in surface productivity cannot have caused this differential effect. Instead, on the basis of an analysis of climate modelling experiments, we infer that changes in ocean circulation pattern across ETM2 may have resulted in more pronounced warming at intermediate depths (Site 1263). The effects of more pronounced warming include increased metabolic rates, leading to a decrease in effective food supply and increased deoxygenation, thus potentially explaining the more severe benthic impacts at Site 1263. In response to more severe benthic disturbance, bioturbation may have decreased at Site 1263 as compared to Site 1262, hence differentially affecting the bulk carbonate record. We use a sediment-enabled Earth system model to test whether a reduction in bioturbation and/or the likely reduced carbonate saturation of more poorly ventilated waters can explain the more extreme excursion in bulk d13C and sharper transition in wt% CaCO3 at Site 1263. We find that both enhanced acidification and reduced bioturbation during peak ELMO conditions are needed to account for the observed features. Our combined ecological and modelling analysis illustrates the potential role of ocean circulation changes in amplifying local environmental changes and driving temporary, but drastic, loss of benthic biodiversity and abundance.

Inorganic carbon and geochemistry measurements from landfast sea ice in Resolute Passage, Nunavut, Canada, as part of the Arctic-ICE project, May - June 2010

We conducted a six-week investigation of the sea ice inorganic carbon system during the winter-spring transition in the Canadian Arctic Archipelago. Samples for the determination of sea ice geochemistry were collected in conjunction with physical and biological parameters as part of the 2010 Arctic-ICE (Arctic - Ice-Covered Ecosystem in a Rapidly Changing Environment) program, a sea ice-based process study in Resolute Passage, Nunavut. The goal of Arctic-ICE was to determine the physical-biological processes controlling the timing of primary production in Arctic landfast sea ice and to better understand the influence of these processes on the drawdown and release of climatically active gases. The field study was conducted from 1 May to 21 June, 2010.

Chlorophyll a and carbon fluxes, and characteristics of the water column during summer 2008 in the Beaufort Sea

Following the extreme low ice year of 2007, primary production and the sinking export of particulate and gel-like organic material, using short-term particle interceptor traps deployed at 100 m, were measured in the southeastern Beaufort Sea during summer 2008. The combined influence of early ice retreat and coastal upwelling contributed to exceptionally high primary production (500 ± 312 mg C/m**2/day, n = 7), dominated by large cells (>5 µm, 73% ± 15%, n = 7). However, except for one station located north of Cape Bathurst, the sinking export of particulate organic carbon (POC) was relatively low (range: 38-104 mg C/m**2/day, n = 12) compared to other productive Arctic shelves. Estimates indicate that 80% ± 20% of the primary production was cycled through large copepods or the microbial food web. Exopolymeric substances were abundant in the sinking material but did not appear to accelerate POC sinking export. The use of isotopic signatures (d13C, d15N) and carbon/nitrogen ratios to identify sources of the sinking material was successful only at two stations with a strong marine or terrestrial signature, indicating the limitations of this approach in hydrographically and biologically complex Arctic coastal waters such as in the Beaufort Sea. At these two stations influenced by either coastal upwelling or erosion, the composition and magnitude of particulate sinking fluxes were markedly different from other stations visited during the study. These observations underscore the fundamental role of mesoscale circulation patterns and hydrodynamic singularities on the export of particulate organic material on Arctic shelves.

Fatty acid composition, element concentration and isotope ratios of sea ice algae sampled in Rijpfjorden, Svalbard

The accelerating decrease of Arctic sea ice substantially changes the growth conditions for primary producers, particularly with respect to light. This affects the biochemical composition of sea ice algae, which are an essential high-quality food source for herbivores early in the season. Their high nutritional value is related to their content of polyunsaturated fatty acids (PUFAs), which play an important role for successful maturation, egg production, hatching and nauplii development in grazers. We followed the fatty acid composition of an assemblage of sea ice algae in a high Arctic fjord during spring from the early bloom stage to post bloom. Light conditions proved to be decisive in determining the nutritional quality of sea ice algae, and irradiance was negatively correlated with the relative amount of PUFAs. Algal PUFA content decreased on average by 40 % from April to June, while algal biomass (measured as particulate carbon, C) did not differ. This decrease was even more pronounced when algae were exposed to higher irradiances due to reduced snow cover. The ratio of chlorophyll a (chl a) to C, as well as the level of photoprotective pigments, confirmed a physiological adaptation to higher light levels in algae of poorer nutritional quality. We conclude that high irradiances are detrimental to sea ice algal food quality, and that the biochemical composition of sea ice algae is strongly dependent on growth conditions.

Vegetation in the coastal area of East Greenland

This paper deals with the syntaxonomy and ecology of debris, scree and alluvium vegetation of the Ammassalik district, Southeast Greenland, on more or less moist soil. The Oxyria digyna- and Chamaenerion latifoliumvegetation types are classified as Saxifrago-Oxyrietum digynae (Böcher 1933 ap. Nordh. 1943) Gjaerevoll 1950 respectively Chamaenerietum latifolii Böcher 1933 in the class Thlaspietea rotundifolii Br.-BI. ap. Br.-BI. et al. 1947. The chionophytic Saxifrago-Oxyrietum digynae and the Chamaenerietum latifolii occurring on river-banks are classified in the alliance Saxifrago stellaris-Oxyrion digynae Gjaerevoll 1950. This alliance belongs to the order Androsacetalia alpinae Br.-BI. ap. Br.-BI. & Jenny 1926, Thlaspietea rotundifolii Br.-BI. ap. Br.-BI. et al. 1947. The following syntaxa are described as new: Saxifrago-Oxyrietum digynae stellarietosum humifusae and typicum with two variants and one variant of the subassociation inops De Molenaar 1976, and the Chamaenerietum latifolii typicum with two variants and salicetosum herbaceae with three variants.

Isotopic composition of interstitial fluids in sediment at DSDP Sites 87-582 and 87-583

The isotopic compositions of dissolved CO2 and CH4 in sediments of the Nankai Trough indicate that CH4 is formed during early diagenesis by microbial reduction of CO2. At the shallowest sampled depths, the CO2 dissolved in the pore water is unusually enriched in 12C (d13C = -35.2 per mil), indicating contribution of CO2 from oxidation of CH4. The most intense microbiological activity appears to be confined to the uppermost 50 m of sediment, based on relative lack of change in the isotopic compositions below this depth. Gas hydrate probably is not present at these localities (Sites 582, 583) because of CH4 concentrations that are insufficient to saturate the pore water with respect to gas hydrate stability.