Oceanic Suspended Matter Research Articles

Single particle analysis of oceanic suspended matter during the SEEDS II iron fertilization experiment

Suspended particles collected from surface seawater during the SEEDS II (Subarctic Iron Experiment for Ecosystem and Dynamics Study II) experiment were analyzed individually using an electron probe X-ray micro analyzer and characterized by size and elemental composition. Their numbers, relative abundances, and relative particle volume all showed clear differences between samples collected inside vs. outside the phytoplankton bloom that developed following the addition of iron. Throughout the study, Si-rich, Ca-rich and Organic particles were dominant and their number increased inside the fertilized patch; these particles accounted for 21%, 13% and 58% of the particles examined, respectively. Si-rich or Ca-rich particles commonly consisted of fragments of diatom frustules and coccolithophorids. There was consistently greater percentage of Ca-rich particles and lower percentage of Si-rich particles inside the patch than outside of it in number, but both types of these particles apparently occupied a larger volume inside the patch than outside of it. Organic particles, that showed having peaks in smaller diameter particles, increased apparently inside the patch with time after iron fertilization. The Organic particles had a more diverse mixture of both bio-related and crustal trace elements than the other types of particles. These results suggest that the increase in suspended particles following the iron enrichment was due to a combination of detrital material and live phytoplankton.

Particulate barium stocks and oxygen consumption in the Southern Ocean mesopelagic water column during spring and early summer: relationship with export production

Particulate barium was analysed in the upper 600 m of the Southern Ocean water column during repeated transects along the 6°W meridian in October–November 1992. The transects extended between the northern edge of the Weddell Gyre (57°30′S) in the south to 47°S within the Polar Front Zone (PFZ) in the north. From earlier studies, it is known that the largest fraction of Ba in oceanic suspended matter occurs as barite micro-crystals. In the PFZ, an increase in the particulate Ba content in surface waters and at mesopelagic depths can be significant over the investigation period (1 month) and follows the increase of primary production during bloom development. Using an inverse one-dimensional advection-diffusion-consumption model, O 2 consumption between the base of the mixed layer and 1000 m was estimated. The shapes of the vertical particulate Ba profiles are very similar to those of calculated O 2 consumption rates, emphasizing the close link between organic matter oxidation and Ba-barite release at a mesopelagic depth. For the southern Antarctic Circumpolar Current (ACC), depth-integrated rates of O 2 consumption correlate significantly with primary production and mesopelagic particulate Ba concentration. For the PFZ, these relationships are subject to more speculation since this is a region of intense mixing, and the appropriate value of the turbulent diffusion coefficient is uncertain. For the ACC, the observed relationship presents the possibility of defining a transfer function between export production to the mesopelagic depth zone and mesopelagic Ba accumulation. The observed regression between rate of O 2 consumption and primary production in the southern ACC suggests that about 10% of the synthesized organic carbon can be oxidized in the upper 1000 m of the water column.

Chemical speciation of particulate 238U, 239,240Pu and Th isotopes in seawater

Chemical speciation of uranium, 239,240Pu and thorium isotopes (232Th, 230Th and 228Th) in oceanic suspended matter was studies by sequential leaching method. The leaching experiments reveal that most of the uranium in the suspended matter, released in the leaching solution from pH 4.0 to pH 1.0, is directly associated with the organic binding site. In contrast to uranium, the main species of particulate thorium isotopes cannot be released at pH 1.0, which is presumed a stable organic complex associated directly with the organic binding site in the suspended matter. A typical partitioning feature of thorium isotopes is that leaching behaviour of thorium isotopes differed from each other. The proportion of organic complex to the total is the following order: 228Th > 230Th > 232Th, which implies that 228Th produced in situ from 228Ra forms preferentially inert species via an active biological uptake process whereas particulate 232Th consists of both inert species and inorganic minerals due to aeolian flux. Particulate plutonium, whose main species is the organic complex of Pu(IV), shows intermediate partitioning properties between U and Th.

Multi-element neutron activation analysis measurements towards the geochemistry of particulate matter exchange between continent—Atmosphere—Ocean

Sampling of marine aerosol and ocean water particulate matter yields very small quantities of material. INAA is used for routine analysis since it provides measurements of as many as 25 elements and permits multiple use of the small samples. Results are given for the mean elemental composition of Atlantic marine aerosols and oceanic suspended matter. Such analyses are essential for the interpretation of global geochemical cycles.

Variable influence of the atmospheric flux on the trace metal chemistry of oceanic suspended matter

The particulate concentrations of 17 trace metals, Al, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Ag, Sb, Au, Hg, Pb and Th have been measured in the marine atmosphere (58 samples) and in the deep waters (35 samples) of the Tropical North Atlantic. For oceanic suspended matter, our results are similar to those in samples from the Atlantic and the Pacific Oceans collected during the GEOSECS Program. Based on these results, we have made a flux balance for the mixed layer between input via the atmosphere and removal through small and large particles. These data show that the primary flux of suspended aluminosilicates in the Tropical North Atlantic is attributable to the atmospheric input. Elements Sc, Th, Fe, V, Mn, Co and Cr show high correlation with Al in the marine atmosphere. Of these elements, Fe, Mn, V, Co and Cr are influenced by additional processes such as biological, in the marine environment. For elements Ni, Cu, Zn, Se, Ag, Sb, Au, Hg and Pb, we observe high enrichments (relative to average crustal material) in the marine atmosphere which may be due, at least partially, to the influence of anthropogenic sources. These metals also show similar enrichments in deep ocean suspended matter. Model calculations indicate that the atmospheric flux may not control the deep ocean particulate chemistry of Ni, Cu, Zn, Ag, Sb, Au and Hg. Hence it is likely that, for these elements, the enrichment in the ocean is due to processes within the marine regime, for example their involvement in the biological cycle of the ocean. For Se and Pb, the atmospheric source looks to be the dominant contribution to their particulate concentration in seawater. In the deep North Atlantic, particulate Pb appears to be mostly of anthropogenic origin, which is not the case for Se.