Barium in sediments off northwest Africa: A tracer for paleoproductivity or meltwater events?

Abstract

[1] High-resolution down-core analyses of the solid phase content of total barium (Ba tot ) and total organic carbon (TOC) back to 25 kyr B.P. were performed on a gravity core from the upper continental slope off Cape Yubi (Morocco). The observed discrepancy between the two potential paleoproductivity proxies, Ba tot and TOC, initiated supplementary examinations of the pore water, the geochemistry of the clay fraction, X-ray diffraction analyses, and the application of a sequential Ba extraction method of selected samples. Additionally, we analyzed down-core samples of the planktonic foraminifera Turborotalita quinqueloba and Globorotalia inflata for their Ba/Ca ratios. These analyses, which were performed for the first time on these species, were used to reconstruct past oceanic Ba concentrations. We suggest that in the study area, which is characterized by high accumulation rates, the preserved TOC content is a valuable proxy for past primary productivity, whereas the solid phase Ba tot contents appear to be affected by other mechanisms and factors. Peaks of total barium content in the clay fraction and of Ba/Ca ratios in the planktonic foraminifera shells found during the Younger Dryas and the Heinrich 1 event are likely to result from increased meltwater influx into the northern North Atlantic. We suggest that Ba-enriched meltwater was transmitted by the eastern boundary current system from higher latitudes to the region of the Canary Islands. Total barium contents of the clay fraction (Ba tot,clay ) and Ba/Ca in planktonic foraminifera shells seem to be reliable proxies for this discharge of meltwater.

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

“…This finding is in accordance with the results of a study based on a sediment core retrieved nearshore off Cape Yubi (Plewa et al, 2006) showing that Ba is mainly associated with the clay fraction in this region. The results demonstrate that in the study area Ba -except for a few sites off Cape Ghir (c.f.…”

“…Based on these findings we suggest that the suitability of Ba, respectively Ba/Al, as a productivity proxy is limited in this region. We assume that this limitation is mainly based on two different facts: (1) barium is mainly discharged by terrigenous material in this region as discussed in detail by e.g., (Plewa et al, 2006); and/or (2) barite precipitation in the water column is strongly influenced by the variable water depths of the studied sediments (e.g., Von Breymann et al, 1992; Klump et al, 2000).…”

Paleonutrient and productivity records from the subarctic North Pacific for Pleistocene glacial terminations I to V

“…On the contrary, the maxima in Ba bio only occur during the early Holocene, likewise during preceding peak interglacials, when chlorins and biogenic opal already had decreased. Thus the maxima are coeval with pronounced minima in planktic productivity (and in relative nutrient utilization; Galbraith et al [2008]), and on the other hand with prominent preservation spikes of CaCO 3 , for reasons not properly understood, but in harmony with caveats discussed by Plewa et al [2006]. In contrast to Site 882, a Holocene maximum of biogenic Ba in the Bering Sea (Core JPC 17; Brunelle et al [2007]) slightly precedes that of biogenic opal, but clearly lags behind a deglacial CaCO 3 maximum near 15 cal.…”

“…[30] Biogenic Ba (Ba bio ) forms a further much cited, although still controversial sediment proxy of paleoproductivity [De La Rocha, 2007;Plewa et al, 2006]. Jaccard et al [2005] established an XRF-based Ba bio record for neighbor ODP Site 882.…”

Oxygen isotope geochemistry of Laurentide ice-sheet meltwater across Termination I

“…Several recent studies have demonstrated that Ba/Ca shell in foraminifera from marine environments proximal to riverine outflow can be used as an independent proxy for reconstructing paleosalinity (Hall and Chan, 2004;Plewa et al, 2006;Sprovieri et al, 2008;Weldeab et al, 2007). The relationship between riverine Ba/Ca and salinity varies geographically.…”