Woods Hole Oceanographic Institution

About: Woods Hole Oceanographic Institution is a nonprofit organization based out in Falmouth, Massachusetts, United States. It is known for research contribution in the topics: Population & Mantle (geology). The organization has 5685 authors who have published 18396 publications receiving 1202050 citations. The organization is also known as: WHOI.

Alkalinity changes generated by phytoplankton growth1

Abstract: Continuous cultures of three marine phytoplankton species, Phaeodactylum tricornutum, Dunaliella tertiolecta, and Monochrysis lutheri, were monitored for changes in alkalinity of the culture medium resulting From NO, and NHa+ uptake. Uptake of NO,caused an increase in alkalinity, whereas uptake of NH,+ produced a decrease. These results are consistent with the type of schematic equation proposed by Redfield, Ketchum, and Richards for photosynthetic assimilation of inorganic nitrogen, in which NO, uptake is balanced by OHproduction and NHa+ uptake leads to H+ generation. These reactions suggest active uptake of nitrogen species by microbes. We have been unable to demonstrate the exact stoichiometry of this relationship, and the role of P uptake in the alkalinity change is unclear. An offset in the data, functionally equivalent to the production of some strong acid, may be due to reactions on the walls of the vessel, active uptake of cations, or extrusion of H’ ions by the growing cells. An understanding of the oceanic CO2 system is important in many branches of marine chemistry and biolo,gy. Experimentally, this may be approached through measurement of any two of the four variablcs pH, alkalinity, pCOa, and total COz, and from any two of these properties the others can be calculated (Skirrow 1965). Many recent data have been obtained by the potentiometric titration technique ( Dyrsscn 1965; Edmond 1970) that enables the alkalinity and total COz to be measured in a single sample. The alkalinity of scawater is defined as the number of equivalents of strong acid required to titrate 1 liter of seawater to the C02-HC03end point. Analytically, this is equivalent to the sum of the concentrations of the anions of carbonic and other weaker acids. Alkalinity is thus inherently associated with charge balance ( Stumm and Morgan 1970), and the addition or removal of neutral CO2 during respiration or photosynthesis has no cffcct on this property. All this is frequently taken to mean that the photosynthetic or decomposition processes occurring in aquatic environments do not generate alkalinity changes. This is ’ Contribution No. 3595 from the Woods IIole Oceanographic Institution. This research was supported by NSF grants GA-22292 and GX-33295 (P.G.B. ) and ERDA contract AT( 11-l )2532 ( J.C.G. ) . by no means correct. Goldman c t al. (1972) have pointed out that uptake of N03during photosynthesis generates strong base, whereas NH4+ assimilation leads to acid production. Brewer et al. ( 1975) have discussed the reverse effect in which the dccomposition of marine organic matter csscntially leads to the liberation of nitric acid. This strong acid reacts with carbonate ion derived from calcium carbonate dissolution, thus leaving an excess of calcium over that predicted from observed alkalinity changes. These effects have been inferred for many years (Trelease and Trelease 1935; Cramer and Myers 1948; Rcdfield ct al. 1963; Richards 1965; Berner et al. 1970; Gaines and Pilson 1972) and indeed are implicit in the Redficld-Ketchum-Richards phytoplankton equations. Yet, as far as we are aware, these phenomena have not been adequately documented and no cxpcrimental prooE cxis ts. Here, we report our mcasurcmcnts of alkalinity changes during the growth of phytoplankton on both NOaand NI-IJ+ as nitrogen sources. We thank J. M. Edmond and F. Morel for their critical review and R. Smith, S. Kadar, A. Fleer, and R. Carbon for their technical assistance.

Central role of detachment faults in accretion of slow-spreading oceanic lithosphere

Abstract: Oceanic detachment faults are associated with one of two contrasting modes of accretion at mid-ocean ridges and can accommodate extension for millions of years. The main mode of accretion has been thought to be symmetrical, dominated by magmatic processes with subsidiary high-angle faulting and the formation of abyssal hills on both flanks. The other is asymmetrical involving active detachment faults along at least one ridge flank. Escartin et al. present an examination of approximately 2,500 km of the mid-Atlantic ridge that reveals that asymmetrical accretion surprisingly occurs along half of the studied ridge section. Much of the variability in seafloor morphology, seismicity and basalt chemistry found along slow-spreading ridges may thus be attributed to the frequent involvement of detachment faults in oceanic lithospheric accretion. The formation of oceanic detachment faults is well established from inactive, corrugated fault planes exposed on sea floor formed along ridges spreading at less than 80 km Myr–1 (refs 1–4). These faults can accommodate extension for up to 1–3 Myr (ref. 5), and are associated with one of the two contrasting modes of accretion operating along the northern Mid-Atlantic Ridge. The first mode is asymmetrical accretion involving an active detachment fault6 along one ridge flank. The second mode is the well-known symmetrical accretion, dominated by magmatic processes with subsidiary high-angle faulting and the formation of abyssal hills on both flanks. Here we present an examination of ∼2,500 km of the Mid-Atlantic Ridge between 12.5 and 35° N, which reveals asymmetrical accretion along almost half of the ridge. Hydrothermal activity identified so far in the study region is closely associated with asymmetrical accretion, which also shows high levels of near-continuous hydroacoustically and teleseismically recorded seismicity. Increased seismicity is probably generated along detachment faults that accommodate a sizeable proportion of the total plate separation. In contrast, symmetrical segments have lower levels of seismicity, which occurs primarily at segment ends. Basalts erupted along asymmetrical segments have compositions that are consistent with crystallization at higher pressures than basalts from symmetrical segments, and with lower extents of partial melting of the mantle. Both seismic evidence and geochemical evidence indicate that the axial lithosphere is thicker and colder at asymmetrical sections of the ridge, either because associated hydrothermal circulation efficiently penetrates to greater depths or because the rising mantle is cooler. We suggest that much of the variability in sea-floor morphology, seismicity and basalt chemistry found along slow-spreading ridges can be thus attributed to the frequent involvement of detachment faults in oceanic lithospheric accretion.

Nitrogenous Nutrition of Marine Phytoplankton in Nutrient-Depleted Waters

Abstract: Variability in the small-scale temporal and spatial patterns in nitrogenous nutrient supply, coupled with an enhanced uptake capability for nitrogenous nutrients induced by nitrogen limitation, make it possible for phytoplankton to maintain nearly maximum rates of growth at media nutrient concentrations that cannot be quantified with existing analytical techniques.

Biomineralization of Ferrimagnetic Greigite (Fe3S4) and Iron Pyrite (FeS2) in a Magnetotactic Bacterium

Abstract: THE ability of magnetotactic bacteria to orientate and navigate along geomagnetic field lines is due to the controlled intracellular deposition of the iron oxide mineral, magnetite (Fe3O4)1,2. The function and crystal chemical specificity of this mineral has been considered to be unique amongst the prokaryotes3. Moreover, the bacterial production of magnetite may represent a significant contribution to the natural remanent magnetism of sediments4,5. Here we report, the intracellular biomineralization of single crystals of the ferrimagnetic iron sulphide, greigite (Fe3S4), in a multicellular magnetotactic bacterium common in brackish, sulphide-rich water and sediment. We show that these crystals are often aligned in chains and associated with single crystals of the non-magnetic mineral, iron pyrite (FeS2). Our results have important implications for understanding biomineralization processes and magnetotaxis in micro-organisms inhabiting sulphidic environments. Furthermore, the biogenic production of magnetic iron sulphides should be considered as a possible source of remanent magnetization in sediments.