Radiocarbon, isotope, biogenic, and 230Th measurements for sediment core RC10-196

The subarctic North Pacific Ocean holds a large CO2 reservoir that is currently isolated from the atmosphere by a low-salinity layer. It has recently been hypothesized that the reorganization of these high-CO2 waters may have played a crucial role in the degassing of carbon dioxide to the atmosphere during the last deglaciation. This reorganization would leave some imprint on paleo-productivity records. Here we present 230Th-normalized biogenic fluxes from an intermediate depth sediment core in the Northwest Pacific (RC10-196, 54.7°N, 177.1°E, 1007 m) and place them within the context of a synthesis of previously-published biogenic flux data from 49 deep-sea cores north of 20°N, ranging from 420 to 3968 m water depth. The 230Th-normalized opal, carbonate, and organic carbon fluxes from RC10-196 peak approximately 13,000 calendar years BP during the Bølling/Allerød (B/A) period. Our data synthesis suggests that biogenic fluxes were in general lowest during the last glacial period, increased somewhat in the Northwest Pacific during Heinrich Event 1, and reached a maximum across the entire North Pacific during the B/A period. We evaluate several mechanisms as possible drivers of deglacial change in biogenic fluxes in the North Pacific, including changes in preservation, sediment focusing, sea ice extent, iron inputs, stratification, and circulation shifts initiated in the North Atlantic and North Pacific. Our analysis suggests that while micronutrient sources likely contributed to some of the observed changes, the heterogeneity in timing of glaciogenic retreat and sea level make these mechanisms unlikely causes of region-wide contemporaneous peaks in export production. We argue that paleo-observations are most consistent with ventilation increases in both the North Pacific (during H1) and North Atlantic (during B/A) being the primary drivers of increases in biogenic flux during the deglaciation, as respectively they were likely to bring nutrients to the surface via increased vertical mixing and shoaling of the global thermocline.

Recent distribution and accumulation of organic carbon on the continental margin west off Spitsbergen

The study compiles the controlling factors for organic matter sedimentation patterns from a suite of organogeochemical parameters in surface sediments off Spitsbergen and direct seabed observations using a Remotely Operated Vehicle (ROV). In addition we assess its storage rates as well as the potential of carbon sinks on the northwestern margin of the Barents Sea with short sediment cores from a selected fjord environment (Storfjord). While sedimentation in the fjords is mainly controlled by river/meltwater discharge and coastal erosion by sea ice/glaciers resulting in high supply of terrigenous organic matter, Atlantic water inflow, and thus enhanced marine organic matter supply, characterizes the environment on the outer shelf and slope. Local deviations from this pattern, particularly on the shelf, are due to erosion and out washing of fine-grained material by bottom currents. Spots dominated by marine productivity close to the island have been found at the outer Isfjord and west off Prins Karls Forland as well as off the Kongsfjord/Krossfjord area and probably reflect local upwelling of nutrient-rich Atlantic water-derived water masses. Accumulation rates of marine organic carbon as well as reconstructed primary productivities decreased since the middle of the last century. Negative correlation of the Isfjord temperature record with reconstructed productivities in the Storfjord could be explained by a reduced annual duration of the marginal ice zone in the area due to global warming. Extremely high accumulation rates of marine organic carbon between 5.4 and 17.2 g/m**2/yr mark the Storfjord area, and probably high-latitude fjord environments in general, as a sink for carbon dioxide.

Oxygen isotopes, IRD and SST reconstruction for the interval MIS31-19 of IODP Site 306-U1314

Early and Mid-Pleistocene climate, ocean hydrography and ice sheet dynamics have been reconstructed using a high-resolution data set (planktonic and benthic d18O time series, faunal-based sea surface temperature (SST) reconstructions and ice-rafted debris (IRD)) record from a high-deposition-rate sedimentary succession recovered at the Gardar Drift formation in the subpolar North Atlantic (Integrated Ocean Drilling Program Leg 306, Site U1314). Our sedimentary record spans from late in Marine Isotope Stage (MIS) 31 to MIS 19 (1069-779 ka). Different trends of the benthic and planktonic oxygen isotopes, SST and IRD records before and after MIS 25 (~940 ka) evidence the large increase in Northern Hemisphere ice-volume, linked to the cyclicity change from the 41-kyr to the 100-kyr that occurred during the Mid-Pleistocene Transition (MPT). Beside longer glacial-interglacial (G-IG) variability, millennial-scale fluctuations were a pervasive feature across our study. Negative excursions in the benthic d18O time series observed at the times of IRD events may be related to glacio-eustatic changes due to ice sheets retreats and/or to changes in deep hydrography. Time series analysis on surface water proxies (IRD, SST and planktonic d18O) of the interval between MIS 31 to MIS 26 shows that the timing of these millennial-scale climate changes are related to half-precessional (10 kyr) components of the insolation forcing, which are interpreted as cross-equatorial heat transport toward high latitudes during both equinox insolation maxima at the equator.

Nitrogen isotopic and opal record of sediments in the Gulf of California

High-resolution records of the nitrogen isotopic composition of organic matter (d15Norg), opal content, and opal accumulation rates from the central Gulf of California reveal large and abrupt variations during deglaciation and gradual Holocene changes coincident with climatic changes recorded in the North Atlantic. Homogenous sediments with relatively low d15Norg values and low opal content were deposited at the end of the last glacial period, during the Younger-Dryas event, and during the middle to late Holocene. In contrast, laminated sediments deposited in the two deglacial stages are characterized by very high d15Norg values (>14 per mil) and opal accumulation rates (29-41 mg/cm**2/yr). Abrupt shifts in d15Norg were driven by widespread changes in the extent of suboxic subsurface waters supporting denitrification and were amplified in the central gulf record due to variations in upwelling, vertical mixing, and/or the latitudinal position of the Intertropical Convergence Zone.

Temperature reconstruction of sediment core SO9-93KL

The Toba volcanic event, one of the largest eruptions during the Quaternary, is documented in marine sediment cores from the northeastern Arabian Sea. On the crest of the Murray Ridge and along the western Indian continental margin, we detected distinct concentration spikes and ash layers of rhyolithic volcanic shards near the marine isotope stage 5-4 boundary with the chemical composition of the "Youngest Toba Tuff". Time series of the Uk'37-alkenone index, planktic foraminiferal species, magnetic susceptibility, and sediment accumulation rates from this interval show that the Toba event occurred between two warm periods lasting a few millennia. Using Toba as an instantaneous stratigraphic marker for correlation between the marine- and ice-core chronostratigraphies, these two Arabian Sea climatic events correspond to Greenland interstadials 20 and 19, respectively. Our data sets thus depict substantial interstadial/stadial fluctuations in sea-surface temperature and surface-water productivity. We show that variable terrigenous (eolian) sediment supply played a crucial role in transferring and preserving the productivity signal in the sediment record. Within the provided stratigraphic resolution of several decades to centennials, none of these proxies shows a particular impact of the Toba eruption. However, our results are additional support that Toba, despite its exceptional magnitude, had only a minor impact on the evolution of low-latitude monsoonal climate on centennial to millennial time scales.

Glaciological characteristics and carbon dioxide record of ice cores from Antarctica

We report a decadally resolved record of atmospheric CO2 concentration for the last 1000 years, obtained from the West Antarctic Ice Sheet (WAIS) Divide shallow ice core. The most prominent feature of the pre-industrial period is a rapid ~7 ppm decrease of CO2 in a span of ~20-50 years at ~1600 A.D. This observation confirms the timing of an abrupt atmospheric CO2 decrease of ~10 ppm observed for that time period in the Law Dome ice core CO2 records, but the true magnitude of the decrease remains unclear. Atmospheric CO2 variations over the time period 1000-1800 A.D. are statistically correlated with northern hemispheric climate and tropical Indo-Pacific sea surface temperature. However, the exact relationship between CO2 and climate remains elusive due to regional climate variations and/or uneven geographical data density of paleoclimate records. We observe small differences of 0 ~2% (0 ~ 6 ppm) among the high-precision CO2 records from the Law Dome, EPICA Dronning Maud Land and WAIS Divide Antarctic ice cores. However, those records share common trends of CO2 change on centennial to multicentennial time scales, and clearly show that atmospheric CO2 has been increasing above preindustrial levels since ~1850 A.D.

Accumulation rates of bulk sediment and total organic carbon for Ontong Java Plateau sediments

Organic geochemical investigations were performed on sediments of Leg 130 to reconstruct the depositional environment of the Ontong Java Plateau. The Miocene to Quaternary sediments collected during the drilling campaign are characterized by extremely low organic carbon contents. As indicated by C/N ratios and Rock-Eval data, most of the organic matter is probably of marine origin. Based on mass-accumulation rates of organic carbon, the paleoproductivity for the Miocene-Pliocene and the late Pliocene-Pleistocene time intervals as well as the modern surface-water production were estimated. The productivity values of the surface sediments (25-59 gC/m2/yr) reflect the various influences of the equatorial upwelling cell on the different sites. The accumulation rates of organic carbon are generally low; however, they show a distinct increase at 8 Ma and a decrease at 2 Ma.

CaCO3, density, sedimentation and accumulation rates at DSDP Hole 68-503B

Pelagic sediments from DSDP Hole 5O3B contain, in their carbonate abundance data, a clear record of glacial-interglacial cycles. The eolian component of those sediments was analyzed over the past four carbonate cycles, and the mass accumulation rate (MAR) and grain size of the eolian component was determined. Eolian MARs range from 24 to 169 mg/cm**2/10**3y. and commonly are higher by a factor of three to five during times of glacial retreat. Reduced contribution during periods of glaciation most likely reflects glacial-age humidity in the American source. Grain-size values (phi50) range from 8.25 to a minimum of 8.79phi-a variation in grain mass by a factor of 3.1. Larger grains reflect more vigorous atmospheric circulation, but sizes do not covary with the carbonate or eolian accumulation curves. These data suggest that the intensity of atmospheric circulation in the tropics may reflect the 42,000 y.-tilt cycle rather than the 100,000 y.-cycle of glacial advance.

Organic matter preservation in sediments of the Peru and Oman continental margin

Detailed petrographical and bulk geochemical investigations of organic matter (OM) have been performed on sediments deposited below or close to upwelling areas offshore Peru (ODP-Leg 112; Sites 679, 681, 688) and Oman (ODP-Leg 117; Sites 720, 723, 724) in order to obtain a quantitative understanding of its accumulation and degradation. Microscopical as well as nanoscopical investigations reveal that the OM in sediments affected by upwelling mechanisms mainly (up to 98%) consists of unstructured (amorphous) organic aggregates without any apparent biological structures. In sediments which are not or to a lesser extent affected by upwelling (Site 720) terrestrial OM predominates. Organic carbon (TOC) contents are highly variable and range between 9.8% in sediments deposited below upwelling cells and 0.2% in sediments outside the upwelling zone. The TOC/sulphur ratios of the sediments scatter widely. The samples from the deep-water locations (Sites 688 and 720), show C/S-ratios of "normal" marine sediments, whereas at the other locations no correlation or even a negative correlation between sulphur and TOC concentration exists. In most of the upwelling-influenced sediments OM contains a significant amount of sulphur. The incorporation of sulphur into the OM followed microbial sulphate reduction and occurred in the upper meters of the sedimentary column. Below, OM is still present in vast amounts and relatively hydrogen-rich, but is nevertheless non-metabolizable and becomes the limiting factor for bacterial sulphate reduction. According to mass balance calculations 90-99% of the OM produced in the photic zone was remineralized and 1-3% was consumed by microbial sulphate reduction. The aerobic and anaerobic processes have greatly affected degradation and conservation of OM.

Distribution of organic carbon in surface sediments covered during SONNE cruise SO184

Sediments were sampled and oxygen profiles of the water column were determined in the Indian Ocean off west and south Indonesia in order to obtain information on the production, transformation, and accumulation of organic matter (OM). The stable carbon isotope composition (d13Corg) in combination with C/N ratios depicts the almost exclusively marine origin of sedimentary organic matter in the entire study area. Maximum concentrations of organic carbon (Corg) and nitrogen (N) of 3.0% and 0.31%, respectively, were observed in the northern Mentawai Basin and in the Savu and Lombok basins. Minimum d15N values of 3.7 per mil were measured in the northern Mentawai Basin, whereas they varied around 5.4 per mil at stations outside this region. Minimum bottom water oxygen concentrations of 1.1 mL L**1, corresponding to an oxygen saturation of 16.1%, indicate reduced ventilation of bottom water in the northern Mentawai Basin. This low bottom water oxygen reduces organic matter decomposition, which is demonstrated by the almost unaltered isotopic composition of nitrogen during early diagenesis. Maximum Corg accumulation rates (CARs) were measured in the Lombok (10.4 g C m**-2 yr**-1) and northern Mentawai basins (5.2 g C m**-2 yr**-1). Upwelling-induced high productivity is responsible for the high CAR off East Java, Lombok, and Savu Basins, while a better OM preservation caused by reduced ventilation contributes to the high CAR observed in the northern Mentawai Basin. The interplay between primary production, remineralisation, and organic carbon burial determines the regional heterogeneity. CAR in the Indian Ocean upwelling region off Indonesia is lower than in the Peru and Chile upwellings, but in the same order of magnitude as in the Arabian Sea, the Benguela, and Gulf of California upwellings, and corresponds to 0.1-7.1% of the global ocean carbon burial. This demonstrates the relevance of the Indian Ocean margin off Indonesia for the global OM burial.

Stable-isotope records from Dronning Maud Land, Antarctica

The European Project for Ice Coring in Antarctica (EPICA) includes a comprehensive pre-site survey on the inland ice plateau of Dronning Maud Land. This paper focuses on the investigation of the 18O content of shallow firn and ice cores. These cores were dated by profiles derived from dielectric-profiling and continuous flow analysis measurements. The individual records were stacked in order to obtain composite chronologies of 18O contents and accumulation rates with enhanced signal-to-noise variance ratios.These chronologies document variations in the last 200 and 1000 years.The 18O contents and accumulation rates decreased in the 19th century and increased during the 20th century.Using the empirical relationships between stable isotopes, accumulation rates and the 10m firn temperature, the variation of both parameters can be explained by the same temperature history.But other causes for these variations, such as the build-up of the snow cover, cannot be excluded. A marked feature of the 1000 year chronology occurs during the period AD 1180-1530 when the 18O contents remains below the long-term mean. Cross-correlation analyses between five cores from the Weddell Sea region and Dronning Maud Land show that 18O records can in some periods be positively correlated and in others negatively correlated, indicating a complex climatic history in time and space.

Chemical element contents and accumulation rates in metalliferous sediments from DSDP Hole 34-319, Bauer Deep, Southeast Pacific

Marked variations in the chemical and mineralogical composition of sediments at Site 319 have occurred during the 15 My history of sedimentation at this site. The change in composition through time parallels the variability observed in surface sediments from various parts of the Nazca Plate and can be related to variations in the proportion of hydrothermal, hydrogenous, detrital and biogenous phases reaching this site at different times. Metal accumulation rates at Site 319 reach a maximum near the basement for most elements, suggesting a strong hydrothermal contribution during the early history of this site. The hydrothermal contribution decreased rapidly as Site 319 moved away from the spreading center, although a subtle increase in this source is detectable about the time spreading began on the East Pacific Rise. The most recent sedimentation exhibits a strong detritalhydrogenous influence. Post-depositional diagenesis of amorphous phases has converted them to ironrich smectite and well-crystallized goethite without significantly altering the bulk composition of the sediment.

Vertical flux reconstruction for sediment cores off Chile

Biogenic opal and organic carbon vertical rain rates in sediment cores reveal a strong cyclicity in the productivity of the upwelling system off presently arid northern Chile during the last 100,000 years. Changes in productivity are found to be in phase with the precessional cycle (~20,000 years) and with inputs of iron from the continent. During austral summer insolation maxima, increased precipitation and river runoff in the region appear to have brought high inputs of iron, mainly from the Andes, to the coastal ocean enhancing primary productivity there. We interpret our results as providing evidence for iron control of past productivity in this upwelling system and for a tight link between productivity and orbital forcing at midlatitudes.

Accumulation rates of ODP Site 177-1090

Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean (Martin et al., 1990, doi:10.1038/345156a0; Martin, 1990, doi:10.1029/PA005i001p00001). Indeed, dust supply to the Southern Ocean increases during ice ages, and 'iron fertilization' of the subantarctic zone may have contributed up to 40 parts per million by volume (p.p.m.v.) of the decrease (80-100 p.p.m.v.) in atmospheric carbon dioxide observed during late Pleistocene glacial cycles (Watson et al., 2000, doi:10.1038/35037561; Kohfeld et al., 2005, doi:10.1126/science.1105375; Martínez-Garcia et al., 2009, doi:10.1029/2008PA001657; Sigman et al., 2010, doi:10.1038/nature09149; Hain et al., 2010, doi:10.1029/2010gb003790). So far, however, the magnitude of Southern Ocean dust deposition in earlier times and its role in the development and evolution of Pleistocene glacial cycles have remained unclear. Here we report a high-resolution record of dust and iron supply to the Southern Ocean over the past four million years, derived from the analysis of marine sediments from ODP Site 1090, located in the Atlantic sector of the subantarctic zone. The close correspondence of our dust and iron deposition records with Antarctic ice core reconstructions of dust flux covering the past 800,000 years (Lambert et al., 2008, doi:10.1038/nature06763; Wolf et al., 2006, doi:10.1038/nature04614) indicates that both of these archives record large-scale deposition changes that should apply to most of the Southern Ocean, validating previous interpretations of the ice core data. The extension of the record beyond the interval covered by the Antarctic ice cores reveals that, in contrast to the relatively gradual intensification of glacial cycles over the past three million years, Southern Ocean dust and iron flux rose sharply at the Mid-Pleistocene climatic transition around 1.25 million years ago. This finding complements previous observations over late Pleistocene glacial cycles (Martínez-Garcia et al., 2009; Lambert et al., 2008; Wolff et al., 2006), providing new evidence of a tight connection between high dust input to the Southern Ocean and the emergence of the deep glaciations that characterize the past one million years of Earth history.

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.