Barium in Deep‐Sea Sediment: A Geochemical Proxy for Paleoproductivity

Abstract

We used sediment traps to define the particulate fluxes of barium and organic carbon and investigate the use of barium as a proxy for ocean fertility. Strong correlations between Corg and Ba fluxes indicate a link between upper ocean biological processes and barium flux to the seafloor. The ratio of organic carbon to barium decreases systematically with water depth. Data from 10 sites indicate that organic debris settling from the 200-m depth has a Corg/Ba ratio of approximately 200. The systematic decrease in this ratio with increasing water depth results from the simultaneous decay of organic matter and uptake of Ba in settling particles. This behavior provides additional evidence that the formation of barite in oceanic particles is a consequence of decomposition/uptake in microenvironments rather than the secretion of barite by specific organisms. The decrease of the Corg/Ba ratio with depth is greatest in the North Pacific followed by the equatorial Pacific and is lowest in the western Atlantic. Since this spatial pattern is consistent with the variations in the deep-ocean barium contents which increase along the path of bottom water flow from the Atlantic to the North Pacific, it suggests that the particulate barium ut•take and flux is enhanced by higher barium contents in the intermediate and deep waters of the ocean. Consequently, we have combined our particle flux data with existing water column Ba data to define an algorithm relating new productivity, dissolved barium contents, water depth, and particulate barium flux. This relationship provides a basis of applying barium flux measurements in sediments to estimating new production. In order to use barium as an indicator of productivity, it will be necessary to evaluate inputs from hydrothermal and aluminosilicate sources and xenophyophors. The application of a sequential leach procedure to the trap material indicates that 50-70% of the Ba in settling particles is in the form of barite and the remaining is adsorbed or bound to carbonates. Normafive analysis demonstrates that in nearshore areas the contribution of barium from aluminosilicate sources can dominate that from biogenic inputs. It appears that normative estimates of biogenic barium contents can be made with accuracy if less than 50% of the Ba is associated with aluminosilicates; i.e., is of terrigenous origin. Since diagenefic mobilization of Ba can occur in reduced and suboxic sediments, highly productive nearshore areas also are likely to be inappropriate sites to use Ba measurements as productivity indicators. Comparisons between the rain rates of particulate Bato the seafloor and the burial rate indicate that approximately 30% of the Ba rain is preserved. Although the preservation factor does not appear to be constant, it may be possible to predict the extent of preservation from an empirical relationship with the mass accumulation rate. These observations indicate that measurement of Ba burial fluxes in sediments can provide quantitative information on the paleoproductivity of the oceans. J...

Characterization of metalliferous sediment from a low-temperature hydrothermal environment on the Eastern Flank of the East Pacific Rise

“…The barite from 12 to 70 cm in core GC50 may therefore be of hydrothermal origin (Bonatti et al, 1972;Dymond et al, 1992). Immediately below this interval, the highest Ba concentration of core GC50 occurs in the Mn-oxides rich layer at 100 cm.…”

Transport and burial rates of10Be and231Pa in the Pacific Ocean during the Holocene period

“…Cu chemistry in the ocean seems to be substantially influenced, and often dominated, by organic complexation [46,47]. The sedimentary distribution of Ba, an element known to be associated with biogenic opal [48], has been proposed as a paleoproductivity indicator [e.g., 49,50]. The association of Ba with 23°Th, 231pa, 1°Be, Cu and Mn (Fig.…”

Geochemical distribution patterns as indicators for productivity and terrigenous input off NW Africa

“…A variety of studies has established a relationship between the marine geochemistry of barium and ocean surface water productivity (e.g., Goldberg and Arrhenius, 1958;Dehairs et al, 1980;Bishop, 1988;Dymond et al, 1992;Gingele and Dahmke, 1994;Klump et al, 2001). Fluxes of barium and organic matter, based on sediment trap data of different oceanic regions have been used to develop algorithms, which link the barium flux to export production (Dymond et al, 1992;Francois et al, 1995;Nürnberg et al, 1997).…”

“…A variety of studies has established a relationship between the marine geochemistry of barium and ocean surface water productivity (e.g., Goldberg and Arrhenius, 1958;Dehairs et al, 1980;Bishop, 1988;Dymond et al, 1992;Gingele and Dahmke, 1994;Klump et al, 2001). Fluxes of barium and organic matter, based on sediment trap data of different oceanic regions have been used to develop algorithms, which link the barium flux to export production (Dymond et al, 1992;Francois et al, 1995;Nürnberg et al, 1997). Solid phase barium -or more precisely biogenic barite -may therefore be used to trace changes in recent and past primary production (e.g., Gingele and Dahmke, 1994;Francois et al, 1995;Ganeshram et al, 1995;Paytan et al, 1996;Ganeshram and Pedersen, 1998;Kasten et al, 2001;Pfeifer et al, 2001).…”