Changes in Ocean Heat, Carbon Content, and Ventilation: A Review of the First Decade of GO-SHIP Global Repeat Hydrography.

Global ship-based programs, with highly accurate, full water column physical and biogeochemical observations repeated decadally since the 1970s, provide a crucial resource for documenting ocean change. The ocean, a central component of Earth's climate system, is taking up most of Earth's excess anthropogenic heat, with about 19% of this excess in the abyssal ocean beneath 2,000 m, dominated by Southern Ocean warming. The ocean also has taken up about 27% of anthropogenic carbon, resulting in acidification of the upper ocean. Increased stratification has resulted in a decline in oxygen and increase in nutrients in the Northern Hemisphere thermocline and an expansion of tropical oxygen minimum zones. Southern Hemisphere thermocline oxygen increased in the 2000s owing to stronger wind forcing and ventilation. The most recent decade of global hydrography has mapped dissolved organic carbon, a large, bioactive reservoir, for the first time and quantified its contribution to export production (∼20%) and deep-ocean oxygen utilization. Ship-based measurements also show that vertical diffusivity increases from a minimum in the thermocline to a maximum within the bottom 1,500 m, shifting our physical paradigm of the ocean's overturning circulation.

Contribution of fish to the marine inorganic carbon cycle.

Oceanic production of calcium carbonate is conventionally attributed to marine plankton (coccolithophores and foraminifera). Here we report that marine fish produce precipitated carbonates within their intestines and excrete these at high rates. When combined with estimates of global fish biomass, this suggests that marine fish contribute 3 to 15% of total oceanic carbonate production. Fish carbonates have a higher magnesium content and solubility than traditional sources, yielding faster dissolution with depth. This may explain up to a quarter of the increase in titratable alkalinity within 1000 meters of the ocean surface, a controversial phenomenon that has puzzled oceanographers for decades. We also predict that fish carbonate production may rise in response to future environmental changes in carbon dioxide, and thus become an increasingly important component of the inorganic carbon cycle.

Consistent fractionation of 13C in nature and in the laboratory: growth-rate effects in some haptophyte algae.

The carbon isotopic fractionation accompanying formation of biomass by alkenone-producing algae in natural marine environments varies systematically with the concentration of dissolved phosphate. Specifically, if the fractionation is expressed by epsilon p approximately delta e - delta p, where delta e and delta p are the delta 13C values for dissolved CO2 and for algal biomass (determined by isotopic analysis of C37 alkadienones), respectively, and if Ce is the concentration of dissolved CO2, micromole kg-1, then b = 38 + 160*[PO4], where [PO4] is the concentration of dissolved phosphate, microM, and b = (25 - epsilon p)Ce. The correlation found between b and [PO4] is due to effects linking nutrient levels to growth rates and cellular carbon budgets for alkenone-containing algae, most likely by trace-metal limitations on algal growth. The relationship reported here is characteristic of 39 samples (r2 = 0.95) from the Santa Monica Basin (six different times during the annual cycle), the equatorial Pacific (boreal spring and fall cruises as well as during an iron-enrichment experiment), and the Peru upwelling zone. Points representative of samples from the Sargasso Sea ([PO4] < or = 0.1 microM) fall above the b = f[PO4] line. Analysis of correlations expected between mu (growth rate), epsilon p, and Ce shows that, for our entire data set, most variations in epsilon p result from variations in mu rather than Ce. Accordingly, before concentrations of dissolved CO2 can be estimated from isotopic fractionations, some means of accounting for variations in growth rate must be found, perhaps by drawing on relationships between [PO4] and Cd/Ca ratios in shells of planktonic foraminifera.

A massive phytoplankton bloom induced by an ecosystem-scale iron fertilization experiment in the equatorial Pacific Ocean.

The seeding of an expanse of surface waters in the equatorial Pacific Ocean with low concentrations of dissolved iron triggered a massive phytoplankton bloom which consumed large quantities of carbon dioxide and nitrate that these microscopic plants cannot fully utilize under natural conditions. These and other observations provide unequivocal support for the hypothesis that phytoplankton growth in this oceanic region is limited by iron bioavailability.

Conditions for the occurrence of large near-wall excesses of small particles during blood flow.

Prior work showed that the near-wall concentration of platelet-sized latex beads (2.38 microns diam) in flowing blood suspensions can be greater than three times the concentration in the central region of the flow. Similar methods were used to explore the dependence of the near-wall excess (NWE) of beads on the channel height and suspension composition. The bead diameter, suspending fluid viscosity, and red blood cell deformability were varied; the hematocrit was fixed at 15%. Results showed that NWEs greater than or equal to three times the central concentration were associated with shear stress, rather than with strain rate, required red cell deformability, and occurred with bead diameters of 2.2 microns or larger. The amplitude of NWEs observed in the 30- and 50-microns channels changed sharply from small to large as the wall shear rate (WSR) was increased, while those observed in 100-microns channels exhibited a more gradual dependence on WSR.

Adsorption mediated decrease in the biodegradation rate of organic compounds.

A negative correlation between adsorption of low molecular weight organic acids and sugars onto a hydroxyapatite surface and biodegradation rates of the compounds in the presence of the mineral was observed. Qualitatively, the effect was the same whether the organics were equilibrated with the surface prior to the addition of organisms or the organisms were preattached to the surface. Glucose, acetic acid, succinic acid, glutamic acid, and citric acid showed equilibrium adsorption values ranging from 0-94% from a 2µM solution. Changes in both respiration and assimilation of the substrates in the presence of hydroxyapatite were inversely correlated with adsorption.

Electrolyte effects on attachment of an estuarine bacterium.

The effect of electrolyte concentration on attachment of Vibrio alginolyticus to hydroxyapatite was determined. Bacterial affinity for attachment to the surface and surface capacity were derived from linearization of bacterial adsorption isotherms. At low concentrations (<0.1 M) the affinity of the bacteria for the surface increased with increasing ionic strength, in agreement with the D.L.V.O. theory of colloid interaction. At higher concentrations, bacterial affinity for the surface decreased with increasing concentration of cations and was not related to ionic strength changes in the medium. These results demonstrate a change in the mechanism by which salts affect bacterial attachment at salt concentrations above 0.1 M. The results are consistent with the relationship between the proportion of attached bacteria and salinity observed in previously published field studies. The results may also resolve differences between various attachment studies carried out in different ionic strength media, utilizing different bacteria, surfaces, and experimental methods.

Effects of inorganic particles on metabolism by a periphytic marine bacterium.

Measurements were made of adsorption of a periphytic marine bacterium, glucose, and glutamic acid to inorganic particles in seawater and defined bacterial growth medium. Measurements of the metabolism of bacteria were made in the presence and absence of particles by microcalorimetry and radiorespirometry. It was found that hydroxyapatite adsorbs glutamic acid, but not glucose, from the experimental medium. It was also found that hydroxyapatite adsorbs essentially all of the bacteria from the medium when the bacterial concentration is approximately 6 x 10 bacteria per ml. If the bacterial concentration is approximately 6 x 10, then only a small fraction of cells become attached. It was therefore possible to select bacterial concentrations and organic nutrients so that bacterial attachment, organic nutrient adsorption, or both would occur in different experiments. In this experimental system the metabolism by attached and nonattached bacteria of adsorbing and nonadsorbing organic nutrients was measured. The results show that bacterial activity in this model system was not enhanced by the particles, regardless of whether the bacteria, the organic nutrient, or both were associated with the surface. In fact, the respiratory activity of the attached bacteria was diminished in comparison with that of free bacteria.

Microcalorimetric Measurements of Glucose Metabolism by Marine Bacterium Vibrio alginolyticus.

Microcalorimetric measurements of heat production from glucose by Vibrio alginolyticus were made to assess the viability of calorimetry as a technique for studying the metabolism of marine bacteria at organic nutrient concentrations found in marine waters. The results show that the metabolism of glucose by this bacterium can be measured by calorimetry at submicromolar concentrations. A linear correlation between glucose concentration and total heat production was observed over a concentration range of 8 mM to 0.35 muM. It is suggested that these data indicate a constant efficiency of metabolism for this bacterium over the wide range of glucose concentrations studied.

Partial specific volume, expansibility, compressibility, and heat capacity of aqueous lysozyme solutions.

Density measurements have been made on aqueous lysozyme solutions at 20, 25, and 30 degrees. The apparent specific volumes, phi v, and expansibilities, phi e, have been determined from the density measurements and fitted to a function of concentration (weight per cent). Sound velocities and heat capacities have also been measured for various concentrations of lysozyme-water solutions at 25 degrees. From the density, expansibility, heat capacity, and sound velocity data at 25 degrees, the isothermal compressibility, phi k, for the lysozyme solutions have been calculated over a range of concentrations. All the physicochemical properties measured were found to be a linear function of the weight per cent of lysozyme. The number of water molecules hydrated to 1 mol of lysozyme was estimated from the volume and compressibility and found to be 162 at 25 degrees.