(Table 2) Radiocarbon age determination from the polar planktonic foraminifera Neogloboquadrina pachyderma s for sediment core HU90-013-029

An additional Heinrich ice-rafting event is identified between Heinrich events 5 and 6 in eight cores from the Labrador Sea and the northwest Atlantic Ocean. It is characterized by sediment rich in detrital carbonate (40% CaCO3) with high concentration of floating dropstones, high coarse-fraction (% > 150 µm) content, and has a sharp contact with the underlying but grades into the overlying hemipelagic sediment. It also shows lighter d18ONpl values, indicating freshening due to iceberg rafting and/or meltwater discharge. This event is correlated with Dansgaard-Oeschger event 14 and interpreted as an additional Heinrich event, H5a. The thickness of H5a in the Labrador Sea reaches up to 220 cm. This additional Heinrich event has also been reported in cores PS2644 and SO82-5 from the northern North Atlantic. With the recognition of H5a the temporal spacing between Heinrich events 1 to 6 becomes more uniform (~7 ka).

Meteorological measurements from 8 dropsondes released during POLAR 4 flight on 1993-03-04 along a track orthogonal to the pack ice edge north west of Svalbard

Different parameterizations of subgrid-scale fluxes are utilized in a nonhydrostatic and anelastic mesoscale model to study their influence on simulated Arctic cold air outbreaks. A local closure, a profile closure and two nonlocal closure schemes are applied, including an improved scheme, which is based on other nonlocal closures. It accounts for continuous subgrid-scale fluxes at the top of the surface layer and a continuous Prandtl number with respect to stratification. In the limit of neutral stratification the improved scheme gives eddy diffusivities similar to other parameterizations, whereas for strong unstable stratifications they become much larger and thus turbulent transports are more efficient. It is shown by comparison of model results with observations that the application of simple nonlocal closure schemes results in a more realistic simulation of a convective boundary layer than that of a local or a profile closure scheme. Improvements are due to the nonlocal formulation of the eddy diffusivities and to the inclusion of heat transport, which is independent of local gradients (countergradient transport).

Radionuclides in the water column at stations near the Antarctic Polar Front in the South Atlantic

Vertical profiles of dissolved and particulate 230Th and 231Pa were obtained across the Antarctic Circumpolar Current (ACC) in the southern Atlantic. North of the Polar Front, dissolved and total 230Th increase with depth in conformity with published scavenging models. There is no depletion of 230Th or 231Pa in the water column south of the Polar Front, thought to be an area of enhanced biological productivity. 230Th concentrations increase three-fold to the Weddell Sea across the ACC. Dissolved and total 231Pa concentrations are relatively constant below 500 m depth at about 0.3 dpm m**-3, and change little with depth or latitude. The results from the Weddell Gyre are explained by a mixing-scavenging model that takes into account the input of lower Circumpolar Deep Water through upwelling, which is the main source of water in the Weddell Gyre and is enriched in 230Th but not in 231Pa. 230Th accumulates in the Weddell Gyre as a result of a reduction in the scavenging rate and by ingrowth from 234U. Ingrowth is more significant for 230Th than for 231Pa because the residence time of water in the gyre (about 35 years) is similar to the scavenging residence time of Th in the south Atlantic (29 years) but shorter than that of Pa (120 years). It is argued that changes in 230Th accumulation in the past may reflect changes in water residence time and in the formation rate of Weddell Sea Deep Water.

In situ pore water oxygen microprofiles from the Polar Front, Southern South Atlantic Ocean

Without doubt, global climate change is directly linked to the anthropogenic release of greenhouse gases such as carbon dioxide (CO2) and methane (UN IPCC-Report 2007). Therefore, research efforts to comprehend the global carbon cycle have increased during the last years. In the context of the observed changes, it is of particular interest to decipher the role of the hydro-, bio- and atmospheres and how the different compartments of the earth system are affected by the increase of atmospheric CO2. Due to its huge carbon inventory, the marine carbon cycle represents the most important component in this respect. Numerous findings suggest that the Southern Ocean plays a key role in terms of oceanic CO2 uptake. However, an exact quantification of such fluxes of material is hard to achieve for large areas, not least on account of the inaccessibility of this remote region. In particular, there exist so far only few accurate data for benthic carbon fluxes. The latter can be derived from high resolution pore water oxygen profiles, as one possible method. However the ex situ flux determinations carried out on sediment cores, tend to suffer from temperature and pressure artefacts. Alternatively, oxygen microprofiles can be measured in situ, i.e. at the seafloor. Until now, no such data have been published for the Southern Ocean. During the Antarctic Expedition ANT-XXI/4, within the framework of this thesis, in situ and ex situ oxygen profiles were measured and used to derive benthic organic carbon fluxes. Having both types of measurements from the same locations, it was possible to establish a depth-related correction function which was applied subsequently to revise published and additional unpublished carbon fluxes to the seafloor. This resulted in a consistent data base of benthic carbon inputs covering many important sub-regions of the Southern Ocean including the Amundsen and Bellingshausen Seas (southern Pacific), Scotia and Weddell Seas (southern South Atlantic) as well as the Crozet Basin (southern Indian Ocean). Including additional locations on the Antarctic Shelf, there are now 134 new and revised measurement locations, covering almost 180° of the Southern Ocean, for which benthic organic carbon fluxes and sedimentary oxygen penetration depth values are available. Further, benthic carbon fluxes were empirically related to dominant diatom distributions in surface sediments as well as to long-term remotely sensed chlorophyll-a estimates. The comparison of these results with benthic carbon fluxes of the entire Atlantic Ocean reveals significantly higher export efficiencies for the Southern Ocean than have previously been assumed, especially for the area of the opal belt.

Global database of surface ocean particulate organic carbon export fluxes diagnosed from the 234Th technique

Through the processes of the biological pump, carbon is exported to the deep ocean in the form of dissolved and particulate organic matter. There are several ways by which downward export fluxes can be estimated. The great attraction of the 234Th technique is that its fundamental operation allows a downward flux rate to be determined from a single water column profile of thorium coupled to an estimate of POC/234Th ratio in sinking matter. We present a database of 723 estimates of organic carbon export from the surface ocean derived from the 234Th technique. Data were collected from tables in papers published between 1985 and 2013 only. We also present sampling dates, publication dates and sampling areas. Most of the open ocean Longhurst provinces are represented by several measurements. However, the Western Pacific, the Atlantic Arctic, South Pacific and the South Indian Ocean are not well represented. There is a variety of integration depths ranging from surface to 220m. Globally the fluxes ranged from -22 to 125 mmol of C/m**2/d. We believe that this database is important for providing new global estimate of the magnitude of the biological carbon pump.