Data compilation of ESOP

The work in this sub-project of ESOP focuses on the advective and convective transforma-tion of water masses in the Greenland Sea and its neighbouring areas. It includes observational work on the sub-mesoscale and analysis of hydrographic data up to the gyre-scale. Observations of active convective plumes were made with a towed chain equipped with up to 80 CTD sensors, giving a horizontal and vertical resolution of the hydrographic fields of a few metres. The observed scales of the penetrative convective plumes compare well with those given by theory. On the mesoscale the structure of homogeneous eddies formed as a result of deep convection was observed and the associated mixing and renewal of the intermediate layers quantified. The relative importance and efficiency of thermal and haline penetrative convection in relation to the surface boundary conditions (heat and salt fluxes and ice cover) and the ambient stratification are studied using the multi year time series of hydro-graphic data in the central Greenland Sea. The modification of the water column of the Greenland Sea gyre through advection from and mixing with water at its rim is assessed on longer time scales. The relative contributions are quantified using modern water mass analysis methods based on inverse techniques. Likewise the convective renewal and the spreading of the Arctic Intermediate Water from its formation area is quantified. The aim is to budget the heat and salt content of the water column, in particular of the low salinity surface layer, and to relate its seasonal and interannual variability to the lateral fluxes and the fluxes at the air-sea-ice interface. This will allow to estimate residence times for the different layers of the Greenland Sea gyre, a quantity important for the description of the Polar Ocean carbon cycle.

Radionuclides in sediment cores of the Atlantic sector of the Southern Ocean

We present time series of export productivity proxy data including 230Thex-normalized deposition rates (rain rates) of 10Be, dissolution-corrected biogenic Ba, and biogenic opal as well as authigenic U concentrations which are complemented by rain rates of total (detrital) Fe and sea ice indicating diatom abundances from five sediment cores across the Atlantic sector of the Southern Ocean covering the past 150,000 years. The results suggest that 10Be rain rates and authigenic U concentration cannot serve as quantitative paleoproductivity proxies because they have also been influenced by detrital particle fluxes in the case of 10Be and bulk sedimentation rates (sediment focussing) and deep water oxygenation in the case of U. The combined results of the remaining productivity proxies of this study (rain rates of biogenic opal and biogenic Ba in those sections without authigenic U) and other previously published proxy data from the Southern Ocean (231Pa/230Th and nitrogen isotopes) suggest that a combination of sea ice cover, shallow remineralization depth, and stratification of the glacial water column south of the present position of the Antarctic Polar Front and possibly Fe fertilization north of it have been the main controlling factors of export paleoproductivity in the Southern Ocean over the last 150,000 years. An overall glacial increase of export paleoproductivity is not supported by the data, implying that bioproductivity variations in the Southern Ocean are unlikely to have contributed to the major glacial atmospheric CO2 drawdown observed in ice cores.

The late Pliocene pollen record of ODP Site 108-658 off Cape Blanc, Atlantic Ocean

A 200 m long marine pollen record from ODP Site 658 (21°N, 19°W) reveals cyclic fluctuations in vegetation and continental climate in northwestern Africa from 3.7 to 1.7 Ma. These cycles parallel oxygen isotope stages. Prior to 3.5 Ma, the distribution of tropical forests and mangrove swamps reached Cape Blanc, 5°N of the present distribution. Between 3.5 and 2.6 Ma, forests occurred at this latitude during irregular intervals and nearly disappeared afterwards. Likewise, a Saharan paleoriver flowed continuously until isotope Stage 134 (3.35 Ma). When river discharge ceased, wind transport of pollen grains prevailed over fluvial transport. Pollen indicators of trade winds gradually increased between 3.3 and 2.5 Ma. A strong aridification of the climate of northwestern Africa occurred during isotope Stage 130 (3.26 Ma). Afterwards, humid conditions reestablised followed by another aridification around 2.7 Ma. Repetitive latitudinal shifts of vegetation zones ranging from wooded savanna to desert flora dominated for the first time between between 2.6 and 2.4 Ma as a response to the glacial stages 104, 100 and 98. Although climatic conditions, recorded in the Pliocene, were not as dry as those of the middle and Late Pleistocene, latitudinal vegetation shifts near the end of the Pliocene resembled those of the interglacial-glacial cycles of the Brunhes chron.

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.