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).

Sea surface temperature and primary productivity reconstruction of sediment core SO130-275KL from the northeastern Arabian Sea during the late Holocene

Variability in the oceanic environment of the Arabian Sea region is strongly influenced by the seasonal monsoon cycle of alternating wind directions. Prominent and well studied is the summer monsoon, but much less is known about late Holocene changes in winter monsoon strength with winds from the northeast that drive convective mixing and high surface ocean productivity in the northeastern Arabian Sea. To establish a high-resolution record of winter monsoon variability for the late Holocene, we analyzed alkenone-derived sea surface temperature (SST) variations and proxies of primary productivity (organic carbon and d15N) in a well-laminated sediment core from the Pakistan continental margin. Weak winter monsoon intensities off Pakistan are indicated from 400 B.C. to 250 A.D. by reduced productivity and relatively high SST. At about 250 A.D., the intensity of the winter monsoon increased off Pakistan as indicated by a trend to lower SST. We infer that monsoon conditions were relatively unstable from ~500 to 1300 A.D., because primary production and SST were highly variable. Declining SST and elevated biological production from 1400 to 1900 A.D. suggest invigorated convective winter mixing by strengthening winter monsoon circulation, most likely a regional expression of colder climate conditions during the Little Ice Age on the Northern Hemisphere. The comparison of winter monsoon intensity with records of summer monsoon intensity suggests that an inverse relationship between summer and winter monsoon strength exists in the Asian monsoon system during the late Holocene, effected by shifts in the Intertropical Convergence Zone.

Winter sea surface temperature reconstruction from planktic foraminiferal transfer functions in the northeastern Arabian Sea over the last two millennia

The Indian monsoon system is an important climate feature of the northern Indian Ocean. Small variations of the wind and precipitation patterns have fundamental influence on the societal, agricultural, and economic development of India and its neighboring countries. To understand current trends, sensitivity to forcing, or natural variation, records beyond the instrumental period are needed. However, high-resolution archives of past winter monsoon variability are scarce. One potential archive of such records are marine sediments deposited on the continental slope in the NE Arabian Sea, an area where present-day conditions are dominated by the winter monsoon. In this region, winter monsoon conditions lead to distinctive changes in surface water properties, affecting marine plankton communities that are deposited in the sediment. Using planktic foraminifera as a sensitive and well-preserved plankton group, we first characterize the response of their species distribution on environmental gradients from a dataset of surface sediment samples in the tropical and sub-tropical Indian Ocean. Transfer functions for quantitative paleoenvironmental reconstructions were applied to a decadal-scale record of assemblage counts from the Pakistan Margin spanning the last 2000?years. The reconstructed temperature record reveals an intensification of winter monsoon intensity near the year 100 CE. Prior to this transition, winter temperatures were >1.5°C warmer than today. Conditions similar to the present seem to have established after 450 CE, interrupted by a singular event near 950 CE with warmer temperatures and accordingly weak winter monsoon. Frequency analysis revealed significant 75-, 40-, and 37-year cycles, which are known from decadal- to centennial-scale resolution records of Indian summer monsoon variability and interpreted as solar irradiance forcing. Our first independent record of Indian winter monsoon activity confirms that winter and summer monsoons were modulated on the same frequency bands and thus indicates that both monsoon systems are likely controlled by the same driving force.

Sea-surface temperature and salinity reconstruction for sediment core GeoB5844-2

We present high-resolution paleoceanographic records of surface and deep water conditions within the northern Red Sea covering the last glacial maximum and termination I using alkenone paleothermometry, stable oxygen isotopes, and sediment compositional data. Paleoceanographic records in the restricted desert-surrounded northern Red Sea are strongly affected by the stepwise sea level rise and appear to record and amplify well-known millennial-scale climate events from the North Atlantic realm. During the last glacial maximum (LGM), sea surface temperatures were about 4°C cooler than the late Holocene. Pronounced coolings associated with Heinrich event 1 (~2°C below the LGM level) and the Younger Dryas imply strong atmospheric teleconnections to the North Atlantic. Owing to the restricted exchange with the Indian Ocean, Red Sea salinity is particularly sensitive to changes in global sea level. Paleosalinities exceeded 50 psu during the LGM. A pronounced freshening of the surface waters is associated with the meltwater peaks MWP1a and MWP1b owing to an increased surface-near inflow of "normal" saline water from the Indian Ocean. Vertical delta18O gradients are also increased during these phases, indicating stronger surface water stratification. The combined effect of deglacial changes in sea surface temperature and salinity on water column stratification initiated the formation of two sapropel layers, which were deposited under almost anoxic condition in a stagnant water body.

Planktic foraminifera of sediment core GeoB1710-3

In this study, we test various parameters in deep-sea sediments (bulk sediment parameters and changes in microfossil abundances and preservation character) which are generally accepted as indicators of calcium carbonate dissolution. We investigate sediment material from station GeoB 1710-3 in the northern Cape Basin (eastern South Atlantic), 280 km away from the Namibian coast, well outside today's coastal upwelling. As northern Benguela upwelling cells were displaced westward and periodically preceded the core location during the past 245 kyr (Volbers et al., submitted), GeoB 1710-3 sediments reflect these changes in upwelling productivity. Results of the most commonly used calcium carbonate dissolution proxies do not only monitor dissolution within these calcareous sediments but also reflect changes in upwelling intensity. Accordingly, these conventional proxy parameters misrepresent, to some extent, the extent of calcium carbonate dissolution. These results were verified by an independent dissolution proxy, the Globigerina bulloides dissolution index (BDX') (Volbers and Henrich, 2002, doi:10.1016/S0025-3227(02)00333-X). The BDX' is based on scanning electronic microscope ultrastructural investigation of planktonic foraminiferal tests and indicates persistent good carbonate preservation throughout the past 245 kyr, with the exception of one pronounced dissolution event at early oxygen isotopic stage (OIS) 6. The early OIS 6 is characterized by calcium carbonate contents, sand contents, and planktonic foraminiferal concentrations all at their lowest levels for the last 245 kyr. At the same time, the ratio of radiolarian to planktonic foraminiferal abundances and the ratio of benthic to planktonic foraminiferal tests are strongly increased, as are the rain ratio, the fragmentation index, and the BDX'. The sedimentary calcite lysocline rose above the core position and GeoB 1710-3 sediments were heavily altered, as attested to by the unusual accumulation of pellets, aggregates, sponge spicules, radiolaria, benthic foraminifera, and planktonic foraminiferal assemblages. Solely the early OIS 6 dissolution event altered the coarse fraction intensely, and is therefore reflected by all conventional calcium carbonate preservation proxies and the BDX'. We attribute the more than 1000 m rise of the sedimentary calcite lysocline to the combination of two processes: (a) a prominent change in the deep-water mass distribution within the South Atlantic and (b) intense degradation of organic material within the sediment (preserved as maximum total organic carbon content) creating microenvironments favorable for calcium carbonate dissolution.

Ogranic geochemistry and SST reconstruction for Pliocene and Miocene Madeira Abyssal Plain turbidites

Free and "bound" long-chain alkenones (C37?2 and C37?3) in oxidized and unoxidized sections of four organic matter-rich Pliocene and Miocene Madeira Abyssal Plain turbidites (one from Ocean Drilling Program site 951B and three from site 952A) were analyzed to determine the effect of severe post depositional oxidation on the value of Uk'37. The profiles of both alkenones across the redox boundary show a preferential degradation of the C37?3 compared to the C37?2 compound. Because of the high initial Uk'37 values and the way of calculating the Uk'37 this degradation hardly influences the Uk'37 profiles. However, for lower Uk'37 values, measured selective degradation would increase Uk'37 up to 0.17 units, equivalent to 5°C. For most of the Uk'37 band-width, much smaller degradation already increases Uk'37 beyond the analytical error (0.017 units). Consequently, for interpreting the Uk'37 record in terms of past sea surface temperatures, selective degradation needs serious consideration.

Sea-surface temperature reconstruction and calibration-function of sediment cores from the Southern Ocean

We provide a new multivariate calibration-function based on South Atlantic modern assemblages of planktonic foraminifera and atlas water column parameters from the Antarctic Circumpolar Current to the Subtropical Gyre and tropical warm waters (i.e., 60°S to 0°S). Therefore, we used a dataset with the abundance pattern of 35 taxonomic groups of planktonic foraminifera in 141 surface sediment samples. Five factors were taken into consideration for the analysis, which account for 93% of the total variance of the original data representing the regional main oceanographic fronts. The new calibration-function F141-35-5 enables the reconstruction of Late Quaternary summer and winter sea-surface temperatures with a statistical error of ~0.5°C. Our function was verified by its application to a sediment core extracted from the western South Atlantic. The downcore reconstruction shows negative anomalies in sea-surface temperatures during the early-mid Holocene and temperatures within the range of modern values during the late Holocene. This pattern is consistent with available reconstructions.

Lithic grain and mineral composition of sand and sandstones from the North Pacific Ocean and the Bering Sea (Table 3)

Sand and sandstone compositions from different types of basins reflect provenance terranes governed by plate tectonics. One hundred and one thin sections of Upper Miocene to Holocene sand-sized material were examined from DSDP/IPOD Sites in the North Pacific Ocean and the Bering Sea. The Gazzi-Dickinson point-counting method was used to establish compositional characteristics of sands from different tectonic settings. Continental margin forearc sands from the western North America continental margin arc system are clearly different from backarc/marginal-sea sands from the Aleutian intraoceanic arc system. The forearc sands have average QFL percentages of 29-42-29, LmLvLst percentages of 32-34-34, 3 Fmwk%M and 0.82 P/F. Aleutian backarc sands have average QFL percentages of 8-22-69. LmLvLst percentages of 9-85-6, 0.5 Fmwk%M and 0.96 P/F. A trend of increasing QFL%Q and decreasing LmLvLst%Lv westward in the backarc region of the Aleutian Ridge reflects the influence of the Asiatic continental margin. Aleutian backarc sands without continental influence have average QFL percentages of 1-20-79, LmLvLst percentages of 1-98-1, 0 Fmwk%M and 0.99 P/F. Of the continental margin forearc samples, sands on the Astoria Fan (west of the Oregon-Washington trench) contain the highest LmLvLst%Lv and lowest P/F; sands from mixed transform-fault and trench settings (Delgada Fan and Gulf of Alaska samples) have slightly higher Qp/Q (0.03); and sands from the Pacific-Juan de Fuca-North America triple junction have the highest Fmwk%M. Delgada Fan and Gulf of Alaska sands have average QFL percentages of 27-38-35, LmLvLst percentages of 37-26-37, 2 Fmwk%M and 0.86 P/F. Astoria Fan sands have average QFL percentages of 35-41-24, LmLvLst percentages of 30-47-23, 3 Fmwk%M and 0.74 P/F. The triple-junction sands have average QFL percentages of 28-59-13, LmLvLst percentages of 25-26-49, 9 Fmwk%M and 0.87 P/F. The petrologic data from the modern ocean basins examined in this study can provide useful analogs for interpretation of ancient oceanic sequences. Our data suggest some refinements of, but generally substantiate, existing petrologic models relating sandstone composition to tectonic setting.

(Table 2) Seasonal flux data and percentages of major bulk components of total flux at the mesotrophic sediment trap site CB from 1988 - 2012

A more than two-decadal sediment trap record from the Eastern Boundary Upwelling Ecosystem (EBUE) off Cape Blanc, Mauritania, is analysed with respect to deep ocean mass fluxes, flux components and their variability on seasonal to decadal timescales. The total mass flux revealed interannual fluctuations which were superimposed by fluctuations on decadal timescales. High winter fluxes of biogenic silica (BSi), used as a measure of marine production (mostly by diatoms) largely correspond to a positive North Atlantic Oscillation (NAO) index (December-March). However, this relationship is weak. The highest positive BSi anomaly was in winter 2004-2005 when the NAO was in a neutral state. More episodic BSi sedimentation events occurred in several summer seasons between 2001 and 2005, when the previous winter NAO was neutral or even negative. We suggest that distinct dust outbreaks and deposition in the surface ocean in winter and occasionally in summer/autumn enhanced particle sedimentation and carbon export on short timescales via the ballasting effect. Episodic perturbations of the marine carbon cycle by dust outbreaks (e.g. in 2005) might have weakened the relationships between fluxes and large-scale climatic oscillations. As phytoplankton biomass is high throughout the year, any dry (in winter) or wet (in summer) deposition of fine-grained dust particles is assumed to enhance the efficiency of the biological pump by incorporating dust into dense and fast settling organic-rich aggregates. A good correspondence between BSi and dust fluxes was observed for the dusty year 2005, following a period of rather dry conditions in the Sahara/Sahel region. Large changes of all bulk fluxes occurred during the strongest El Niño-Southern Oscillation (ENSO) in 1997-1999 where low fluxes were obtained for almost 1 year during the warm El Niño and high fluxes in the following cold La Niña phase. For decadal timescales, Bakun (1990) suggested an intensification of coastal upwelling due to increased winds (''Bakun upwelling intensification hypothesis''; Cropper et al., 2014) and global climate change. We did not observe an increase of any flux component off Cape Blanc during the past 2 and a half decades which might support this. Furthermore, fluxes of mineral dust did not show any positive or negative trends over time which might suggest enhanced desertification or ''Saharan greening'' during the last few decades.