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.

Corg, CaCO3, bulk densities, accumulation rates and ages of ODP Leg 167 sites and three piston cores, California margin

Sediments from five Leg 167 drill sites and three piston cores were analyzed for Corg and CaCO3. Oxygen isotope stratigraphy on benthic foraminifers was used to assign age models to these sedimentary records. We find that the northern and central California margin is characterized by k.y.-scale events that can be found in both the CaCO3 and Corg time series. We show that the CaCO3 events are caused by changes in CaCO3 production by plankton, not by dissolution. We also show that these CaCO3 events occur in marine isotope Stages (MIS) 2, 3, and 4 during Dansgaard/Oeschger interstadials. They occur most strongly, however, on the MIS 5/4 glaciation and MIS 2/1 deglaciation. We believe that the link between the northeastern Pacific Ocean and North Atlantic is primarily transmitted by the atmosphere, not the ocean. Highest CaCO3 production and burial occurs when the surface ocean is somewhat cooler than the modern ocean, and the surface mixed layer is somewhat more stable.

Mean snow accumulation rate, and mean methane sulfonate, chloride and nitrate concentration in snow pits and firn cores of Dronning Maud Land

We quantified postdepositional losses of methane sulfonate (MSA-), nitrate, and chloride at the European Project for Ice Coring in Antarctica (EPICA) drilling site in Dronning Maud Land (DML) (75°S, 0°E). Analyses of four intermediate deep firn cores and 13 snow pits were considered. We found that about 26 ± 13% of the once deposited nitrate and typically 51 ± 20% of MSA- were lost, while for chloride, no significant depletion could be observed in firn older than one year. Assuming a first order exponential decay rate, the characteristic e-folding time for MSA- is 6.4 ± 3 years and 19 ± 6 years for nitrate. It turns out that for nitrate and MSA- the typical mean concentrations representative for the last 100 years were reached after 5.4 and 6.5 years, respectively, indicating that beneath a depth of around 1.2-1.4 m postdepositional losses can be neglected. In the area of investigation, only MSA- concentrations and postdepositional losses showed a distinct dependence on snow accumulation rate. Consequently, MSA- concentrations archived at this site should be significantly dependent on the variability of annual snow accumulation, and we recommend a corresponding correction. With a simple approach, we estimated the partial pressure of the free acids MSA, HNO3, and HCl on the basis of Henry's law assuming that ionic impurities of the bulk ice matrix are localized in a quasi-brine layer (QBL). In contrast to measurements, this approach predicts a nearly complete loss of MSA-, NO3 - , and Cl-.

Accumulation and climate at Peyto Glacier, Canada

The eight-year record of mass balance of Peyto Glacier is correlated to meteorological data measured near the glacier and at Lake Louise 30 km to the south. The period investigated includes the llighest and lowest accumulations for the past 40 years. The primar'y controls of net annual balance are seen to be the depth of the 'winter sno,y pack and the temperature record during the summer. Extensive summer snowfalls in the ablation area can slow down melt rates very considerably and affect the net annual balance positively. The variable nature of winter accumulation and its influence on snowline retreat and ice melt is illustrated by three years' data.

(Table 2) Actual and synthetic mass accumulation rate data and their absolute differences for ODP Site 115-707

Synthetic mass accumulation rates have been calculated for ODP Site 707 using depth-density and depth-porosity functions to estimate values for these parameters with increasing sediment thickness, at 1 Ma time intervals determined on the basis of published microfossil datums. These datums were the basis of the age model used by Peterson and Backman (1990, doi:10.2973/odp.proc.sr.115.163.1990) to calculate actual mass accumulation rate data using density and porosity measurements. A comparison is made between the synthetic and actual mass accumulation rate values for the time interval 37 Ma to the Recent for 1 Myr time intervals. There is a correlation coefficient of 0.993 between the two data sets, with an absolute difference generally less than 0.1 g/cm**2/kyr. We have used the method to extend the mass accumulation rate analysis back to the Late Paleocene (60 Ma) for Site 707. Providing age datums (e.g. fossil or magnetic anomaly data) are available the generation of synthetic mass accumulation rates can be calculated for any sediment sequence.