Nicolas Dittert

Carbonate dissolution in the South Atlantic Ocean : evidence from ultrastructure breakdown in Globigerina bulloides

Abstract Ultrastructure dissolution susceptibility of the planktic foraminifer Globigerina bulloides , carbonate ion content of the water column, calcium carbonate content of the sediment surface, and carbonate/carbon weight percentage ratio derived from sediment surface samples were investigated in order to reconstruct the position of the calcite saturation horizon, the sedimentary calcite lysocline, and the calcium carbonate compensation depth (CCD) in the modern South Atlantic Ocean. Carbonate ion data from the water column refer to the GEOSECS locations 48, 103, and 109 and calcium carbonate data come from 19 GeoB sediment surface samples of 4 transects into the Brazil, the Guinea, and the Cape Basins. We present a new (paleo-) oceanographic tool, namely the Globigerina bulloides dissolution index (BDX). Further, we give evidence (a) for progressive G. bulloides ultrastructural breakdown with increasing carbonate dissolution even above the lysocline; (b) for a sharp BDX increase at the sedimentary lysocline; and (c) for the total absence of this species at the CCD. BDX puts us in the position to distinguish the upper open ocean and the upwelling influenced continental margin above from the deep ocean below the sedimentary lysocline. Carbonate ion data from water column samples, calcite weight percentage data from surface sediment samples, and carbonate/carbon weight percentage ratio appear to be good proxies to confirm BDX. As shown by BDX both the calcite saturation horizon (in the water column) and the sedimentary lysocline (at the sediment–water interface) mark the boundary between the carbonate ion undersaturated and highly corrosive Antarctic Bottom Water and the carbonate ion saturated North Atlantic Deep Water (NADW) of the modern South Atlantic.

Scientific data must be made available to all

An internationally binding regulation should be the first step towards securing vital data.

Transfer of Particles into the Deep Atlantic and the Global Ocean: Control of Nutrient Supply and Ballast Production

Particle fluxes from 20 trap sites in the Atlantic/Southern Ocean have been compiled to study the regional variations in comparison with important environmental variables. In turn, these results have been compared to other study sites from the world ocean, mainly regarding the relations-hip between bulk fluxes/various flux ratios to nutrient supply. It is shown that the supply of dissolved silicic acid to the surface waters (the ‘silicate pump’, Dugdale et al. 1995) plays a central role in opal fluxes, BSi:Corg ratios, BSi:carbonate ratios, and thus carbon rain ratios. The mean annual BSi:Corg ratio (mol/mol) normalized to 1000 m was 0.05 in the Atlantic, 0.4 in the Indian, 0.5 in the Pacific, and 0.1–3 in the Southern Ocean and follow s the general path of the conveyor belt (Ragueneau et al. 2000). A shift in the primary producer community from coccolithophorids to diatoms, reflected by an exponential increase of the annual BSi:carbonate flux ratios, occurs above a molar Si:N(250m) nutrient threshold of about 1.7. The surface sediment opal:carbonate ratios (%) versus the Si:N(250m) nutrient values produce a threshold of 2–2.5, however, this value may be biased by opal dissolution during early diagenesis. We also tested the most recent findings about particle ballast which presume that carbonate is most important for the rapid downward transport of organic particles to bathypelagic depths. Our compilation of global flux data confirms such a general relationship. However, at certain sites and in particular years /seasons, other minerals may serve as ballast for organic carbon. Off NW Africa, for instance, lithogenic components were the major particle carriers. There, relationships between carbonate/lithogenic/total ballast fluxes versus daily organic carbon fluxes may even vary from year to year. Off Cape Blanc, the carbonate-Corg-relationship is highly significant during a strong coccolithophorid bloom in 1991, probably resulting in an efficient downward transfer of organic carbon. Interannual variation of fluxes was highest in high production systems combined with high seasonality of fluxes. We obtained ca. 20% variability in oligotrophic regions and up to 100% in the Southern Ocean where seasonality is most pronounced.

Water Column Biogeochemistry below the Euphotic Zone

The main focus of the International JGOFS research inititiatives was on the cycling of carbon and of associated elements within the surface layer, and their downward export from the upper ocean. Relatively few coordinated measurements and experiments were made below the photic zone so our understanding and modeling of the biogeochemistry of the ocean’s interior is still in its infancy. However from the numerous data acquired in the 1990s during JGOFS and JGOFS-like process studies it is possible to extract sufficient information to make preliminary statements about the biogeochemistry of the water column below the euphotic zone. An important preliminary result of these studies is that we now are beginning to realize that the biogeochemistry of the surface ocean, of the ocean’s interior, and of the surface sediments appears to be more coupled than was thought fifteen years ago.

Archiving and distributing earth-science data with the PANGAEA information system

PANGAEA Publishing Network for Geoscientific and Environmental Data (http://www.pangaea.de) is an information system aimed at archiving, publishing, and distributing data related to climate variability, the marine environment, and the solid earth. The system is a public “data library” distributing any kind of data to the scientific community through the Internet. Data are stored in a relational database in a consistent format with related meta-information following international standards. Data are georeferenced in space and/or time, individually configured subsets may be extracted. Any type of information, data and documents may be served (profiles, maps, photos, graphics, text and numbers). Operation by Alfred Wegener Institute for Polar and Marine Research (AWI) and Center for Marine Environmental Sciences (MARUM) is assured in the long-term. Both institutions provide the technical infrastructure, system management and support for data management of projects as well as for individual scientists. Most important collections from Antarctic research archived in PANGAEA so far are the data of the Cape Roberts Project, geological maps and age determinations of rock outcrops, a complete set of JGOFS, WOCE, DSDP and ODP data including those from the Southern Ocean, any marine sediment cores, documentation and analytical data from German expeditions and an increasing inventory of data published by the running EPICA project.

Biogeochemical Transformations of Silicon Along the Land–Ocean Continuum and Implications for the Global Carbon Cycle1

In the context of a changing Earth, one central interest is an improved understanding of the global carbon cycle and an improved prediction of its likely changes as consequence of global changes. Largescale programs investigated the oceanic cycling of carbon (C) and associated biogenic elements, mainly nitrogen (N) and phosphorus (P), as limiting nutrients of the global production by marine phytoplankton (Falkowski 1997; Tyrrell 1999). However, continental margins play an essential role in the global C cycle, accounting for 14% of global primary production, 80–90% of new production, and 80% of global organic carbon (Corg) burial (Smith and Hollibaugh 1993; Rabouille et al. 2001). Continental margins also represent a filter that removes riverine dissolved and suspended constituents along their path from land to the open ocean (Billen et al. 1991). In order to characterize the C cycle on continental margins, their contribution to carbon dioxide (CO2) sequestration and to determine horizontal C and associated biogenic element fluxes, some 200 N and P flux budgets have been constructed around the world (cf. Smith et al. 2003b, LOICZ 1998). One biogenic element, silicon (Si) has been largely ignored. Silicon is required by diatoms, (Guillard et al. 1973) which play a critical role in the marine C cycle (e.g., Smetacek 1999).

Toward a Networked Publication and Library System for Scientific Data

Almost 50 years ago, the World Data Center (WDC) system was founded through the International Council for Scientific Unions (ICSU) in order to archive and distribute data collected from the observational programs of the 1957–1958 International Geophysical Year. Originally established in the United States, Europe, Russia, and Japan, the WDC system has since expanded to 51 centers in 12 countries. Its current holdings are transdisciplinary and include a wide range of solar, geophysical, environmental, and human dimensions data covering timescales ranging from seconds to millennia. These data provide the baseline information for research in many ICSU disciplines, but especially for monitoring changes in the geosphere and biosphere.

World Data Center for Marine Environmental Sciences provides lessons in marine geosciences data management

World Data Centers (WDCs) provide scientific data and information systems that help transfer comprehensive knowledge among researchers in a straightforward manner and under a sensitive data policy. However, use and acceptance of a WDC within the scientific community depends on respective knowledge and individual scientific needs. For that reason, the staff of the World Data Center for Marine Environmental Sciences (WDC-MARE) (www.wdc-mare.org) is providing lessons in information and data management in marine geosciences at the University of Bremen in Germany Recently, WDC-MARE expanded this service to scientific programs outside of Germany.