Investigations on two sediment cores from the Arctic Ocean

During the "RV Polarstem"-Expedition ARK VIII/2 sediment samples were obtained at the continental slope of NW-Spitsbergen. Detailed sedimentological and geochemical analysis were carried out at two undisturbed box cores (PS2122-1GKG, PS2123-2GKG) as well as two gravity cores (PS2122-1SL, PS2123-2SL). The following parameters were deterrnined: Organic carbon, nitrogen and carbonate contents, hydrogen index, stable isotopes, ice rafted debris, grain-size distribution and biogenic opal. The main objective of this study was the reconstruction of paleoenvironmental changes off the northwest coast of Spitsbergen during the last glacial/interglacial-cycle, i.e., during the last about 128.000 years. The results of the investigations can be summarized as follows: - During isotope stage 1 (Holocene) and 5.5 (Eemian Interglacial), light stable isotopes (d180: 3.4-2 %o; d13C: 0.26-0.5 %o), increased bioturbation, high content of planktonic foraminifera and biogenic opal and low quantity of ice-rafted material, indicate seasonally ice-free conditions along the northwest coast due to the intfluence of the Westspitsbergen Current. - Additionally, the sediment characteristics of the middle of isotope stage 2 (Last Glacial Maximum) and at the end of stage 3 confirms an inflow of warmer Atlantic water. The highest production of planktonic and benthic foraminifera (N. pachyderma sin., Cassidulina teretis) (CaC03: 10 %) may reflect the expansion of the 'Whalers Bay'-Polynya as a result of the influence of the Westspitsbergen Current. Presumably, occasionally open-ice conditions provide sufficient precipitation to buildup the Svalbard/Barents Ice Sheet. - The time intervals for the glacier advances on Svalbard given by Mangerud et al. (1992), can be correlated with increased accumulation of ice-rafted material in the sediments at the northwest coast of Spitsbergen. Especially during isotope stage 4 and at the beginning of the Last Glacial Maximum (isotope stage 2), a drastically increased supply of coarse terrigenous material occurs. The high accumulation rate (0.18-0.21 g/cm**2/ka) of terrigenous organic carbon is indicated by high C/N ratios (until 16) and low hydrogen index (50 mg HC/gC). In constrast to deep sea sediments in the Fram-Strait (Hebbeln 1992), the glacier advance between 118.000 and 108.000 years B.P. ist documented in the continental slope sediments. - At the end of the Weichselian ice age, the deglaciation at the northwest coast starts with a typical melt-water signal in the stables isotope record (d18O: 3.5 %o; d13C: -0.16 %o) and high contents of gravel (6-13 %). The signal can be assigned to an event at the westcoast of Spitsbergen (core NP90-39), dated to 14.500 years B.P. (Andersen et al. 1993).

Mass accumulation rates of IODP Hole 320-U1333C

Understanding changes in export production through time provides insight into the response of the biological pump to global climate change, particularly during periods of rapid climate change. In this study we consider what role changes in export production may have had on carbon sequestration and how this may have contributed to the onset of the Eocene-Oligocene transition (EOT). In addition, we consider if these export production variations are dominantly controlled by orbitally driven climate variability. To accomplish these objectives, we report changes in export production in the Eastern Equatorial Pacific (EEP) from Site U1333 across the EOT reconstructed from a high-resolution record of marine barite accumulation rates (BAR). BAR fluctuations suggest synchronous declines in export production associated with the two-step increases in oxygen isotopes that define the transition. The reduction in productivity across the EOT suggests that the biological pump did not contribute to carbon sequestration and the cooling over this transition. We also report a previously undocumented peak in EEP export productivity before the EOT onset. This peak is consistent with export production proxies from the Southern Ocean, potentially implying a global driver for this precursor event. We propose that this enhanced export production and the associated carbon sequestration in the late Eocene may have contributed to the pCO2 drawdown at the onset of Antarctic glaciation.

Terrigenous input and marine productivity for the Pacific sector of the Southern Ocean based on lipid biomarkers

In this study, we present a new multiproxy data set of terrigenous input, marine productivity and sea surface temperature (SST) from 52 surface sediment samples collected along E-W transects in the Pacific sector of the Southern Ocean. Allochtonous terrigenous input was characterized by the distribution of plant wax n-alkanes and soil-derived branched glycerol dialkyl glycerol tetraethers (brGDGTs). 230Th-normalized burial rates of both compound groups were highest close to the potential sources in Australia and New Zealand and are strongly related to lithogenic contents, indicating common sources and transport. Detection of both long-chain n-alkanes and brGDGTs at the most remote sites in the open ocean strongly suggests a primarily eolian transport mechanism to at least 110°W, i.e. by prevailing westerly winds. Two independent organic SST proxies were used, the UK'37 based on long-chain alkenones, and the TEX86 based on isoprenoid GDGTs. Both, UK'37 and TEX86 indices show robust relationships with temperature over a temperature range between 0.5 and 20°C, likely implying different seasonal and regional imprints on the temperature signal. While alkenone-based temperature estimates reliably reflect modern SST even at the low temperature end, large temperature residuals are observed for the polar ocean using the TEX86 index. 230Th-normalized burial rates of alkenones are highest close to the Subtropical Front and are positively related to lithogenic fluxes throughout the study area. In contrast, highest isoGDGT burial south of the Antarctic Polar Front is not related with dust flux but may be largely controlled by diatom blooms, and thus high opal fluxes during austral summer.

Major ion chemistry and selected snow accumulation rates of snow cores along two transects in central Dronning Maud Land and Princess Elizabeth Land

This dataset includes basic information (location and depth) and major ion chemistry (Sodium, Chloride, Calcium, Nitrate) of snow cores from East Antarctic ice sheet. The snow cores were collected from two different regions - central Dronning Maud Land (cDML) and Princess Elizabeth Land (PEL) during the austral summer of 2008-09.

Accumulation of organic carbon in the Laptev Sea

Composition and accumulation rates of organic carbon in Holocene sediments provided data to calculate an organic carbon budget for the Laptev Sea continental margin. Mean Holocene accumulation rates in the inner Laptev Sea vary between 0.14 and 2.7 g C cm**2/ky; maximum values occur close to the Lena River delta. Seawards, the mean accumulation rates decrease from 0.43 to 0.02 g C cm**2/ky. The organic matter is predominantly of terrigenous origin. About 0.9*10**6 t/year of organic carbon are buried in the Laptev Sea, and 0.25*10**6 t/year on the continental slope. Between about 8.5 and 9 ka, major changes in supply of terrigenous and marine organic carbon occur, related to changes in coastal erosion, Siberian river discharge, and/or Atlantic water inflow along the Eurasian continental margin.

Sediment and physical record of ODP Site 178-1095

Sediments recovered from a drift deposit lying along the Pacific margin of the Antarctic Peninsula, (ODP Leg 178, Site 1095) provide a physical record of the Antarctic Circumpolar Current since late Miocene time. Determination of the strength of the magnetic fabric, anisotropy of magnetic susceptibility, provides a proxy for current strength. Fabric strength declines throughout the record from high values in the late Miocene; a pronounced step occurs between 5.0 and 5.5 Ma, and values decrease more gradually since about 3.0 Ma. The mass accumulation rate of terrigenous sediment derived from the Antarctic Peninsula indicates stabilization of the Antarctic Peninsula Ice Cap prior to about 8.5 Ma.

Stable carbon isotope ratios and accumulation rates of organic carbon and nutrients of DSDP Hole 79-545 (Appendix A)

Future warming is predicted to shift the Earth system into a mode with progressive increase and vigour of extreme climate events possibly stimulating other mechanisms that invigorate global warming. This study provides new data and modelling investigating climatic consequences and biogeochemical feedbacks that happened in a warmer world ~112 Myr ago. Our study focuses on the Cretaceous Oceanic Anoxic Event (OAE) 1b and explores how the Earth system responded to a moderate ~25,000 yr lasting climate perturbation that is modelled to be less than 1 °C in global average temperature. Using a new chronological model for OAE 1b we present high-resolution elemental and bulk carbon isotope records from DSDP Site 545 from Mazagan Plateau off NW Africa and combine this information with a coupled atmosphere-land-ocean model. The simulations suggest that a perturbation at the onset of OAE 1b caused almost instantaneous warming of the atmosphere on the order of 0.3 °C followed by a longer (~45,000 yr) period of ~0.8 °C cooling. The marine records from DSDP Site 545 support that these moderate swings in global climate had immediate consequences for African continental supply of mineral matter and nutrients (phosphorous), subsequent oxygen availability, and organic carbon burial in the eastern subtropical Atlantic, however, without turning the ocean anoxic. The match between modelling results and stratigraphic isotopic data support previous studies [summarized in Jenkyns 2003, doi:10.1098/rsta.2003.1240] in that methane emission from marine hydrates, albeit moderate in dimension, may have been the trigger for OAE 1b, though we can not finally rule out alternative mechanisms. Following the hydrate mechanism a total of 1.15 * 10**18 g methane carbon (delta13C=-60 ?), equivalent to about 10% to the total modern gas hydrate inventory, generated the delta13Ccarb profile recorded in the section. Modelling suggests a combination of moderate-scale methane pulses supplemented by continuous methane emission at elevated levels over ~25,000 yr. The proposed mechanism, though difficult to finally confirm in the geological past, is arguably more likely to occur in a warmer world and apparently perturbs global climate and ocean chemistry almost instantaneously. This study shows that, once set-off, this mechanism can maintain Earth's climate in a perturbed mode over geological time leading to pronounced changes in regional climate.

(Appendix A) Sedimentation rate, geochemical and environmental magnetic proxies of the samples of the Metochia section, on the island of Gavdos, south of Crete

The upper Tortonian Metochia marls on the island of Gavdos provide an ideal geological archive to trace variations in Aegean sediment supply as well as changes in the North African monsoon system. A fuzzy-cluster analysis on the multiproxy geochemical and rock magnetic dataset of the astronomically tuned sedimentary succession shows a dramatic shift in the dominance of 'Aegean tectonic' clusters to 'North African climate' clusters. The tectonic signature, traced by the starvation of the Cretan sediment, now enables to date the late Tortonian basin foundering on Crete, related to the tectonic break-up of the Aegean landmass, at c. 8.2 Ma. The synchronous decrease in the North African climate proxies is interpreted to indicate a change in the depositional conditions of the sink rather than a climatic change in the African source. This illustrates that interpretations of climate proxies require a multiproxy approach which also assesses possible contributions of regional tectonism.

Simulating pasture growth rates in Australian and New Zealand grazing systems

DairyMod, EcoMod, and the SGS Pasture Model are mechanistic biophysical models developed to explore scenarios in grazing systems. The aim of this manuscript was to test the ability of the models to simulate net herbage accumulation rates of ryegrass-based pastures across a range of environments and pasture management systems in Australia and New Zealand. Measured monthly net herbage accumulation rate and accumulated yield data were collated from ten grazing system experiments at eight sites ranging from cool temperate to subtropical environments. The local climate, soil, pasture species, and management (N fertiliser, irrigation, and grazing or cutting pattern) were described in the model for each site, and net herbage accumulation rates modelled. The model adequately simulated the monthly net herbage accumulation rates across the range of environments, based on the summary statistics and observed patterns of seasonal growth, particularly when the variability in measured herbage accumulation rates was taken into account. Agreement between modelled and observed growth rates was more accurate and precise in temperate than in subtropical environments, and in winter and summer than in autumn and spring. Similarly, agreement between predicted and observed accumulated yields was more accurate than monthly net herbage accumulation. Different temperature parameters were used to describe the growth of perennial ryegrass cultivars and annual ryegrass; these differences were in line with observed growth patterns and breeding objectives. Results are discussed in the context of the difficulties in measuring pasture growth rates and model limitations.