Ocean Water Column Research Articles

Antagonistic interactions among marine pelagic bacteria.

Recent studies suggest that bacterial abundance and species diversity in the ocean's water column are variable at the millimeter scale, apparently in response to the small-scale heterogeneity in the distribution of organic matter. We hypothesized that bacterium-bacterium antagonistic interactions may contribute to variations in community structure at the microscale. We examined each of the 86 isolates for their inhibition of growth of the remaining 85 isolates by the Burkholder agar diffusion assay. More than one-half of the isolates expressed antagonistic activity, and this trait was more common with particle-associated bacteria than with free-living bacteria. This was exemplified by members of the alpha subclass of the class Proteobacteria (alpha-proteobacteria), in which production of antagonistic molecules was dominated by attached bacteria. We found that gamma-proteobacteria (members of the orders Alteromonadales and Vibrionales) are the most prolific producers of inhibitory materials and also the most resilient to them, while members of the Bacteriodetes were the organisms that were least productive and most sensitive to antagonistic interactions. Widespread interspecies growth inhibition is consistent with the role of this phenomenon in structuring bacterial communities at the microscale. Furthermore, our results suggest that bacteria from pelagic marine particles may be an underutilized source of novel antibiotics.

Phylogenetic study of pelagic nemerteans (Pelagica, Polystilifera)

Pelagic polystiliferous nemerteans, often referred to as Pelagica, represent one of the most enigmatic groups of nemerteans. The group includes 98 valid species assorted into 41 genera and 3–11 families, depending on the classification. Pelagica inhabit the water column of the world oceans, occupying depths from several hundred to several thousand meters. As is the case with most meso- or bathypelagic soft-bodied animals, specimens are few and numerous difficulties are associated with obtaining and preserving them, resulting in incomplete descriptions and, therefore, an obscure classification. Most genera and families of pelagic nemerteans are based upon unique combinations of two or three characters. Here, we present results of the first cladistic analysis of pelagic nemertean phylogeny. The analysis is based on morphological character data available from the primary literature and personal observations. A large percentage of missing entries in the data (21.5%), due to incompleteness of descriptions, results in a large number of maximum parsimonious cladograms, which translates into a drastic lack of resolution on the strict consensus tree. Traditional families supported by the cladistic analysis are Armaueriidae Brinkmann, 1917 and Pelagonemertidae (sensu Korotkevitsch, 1955). We propose a new diagnosis for Armaueriidae and discuss morphological characters traditionally used in pelagic nemertean classification. A few potentially informative characters are suggested for greater attention in future studies of specimens.

Ocean thermohaline circulation and sedimentary 231Pa/230Th ratio

Holocene sediments from the Atlantic are characterized by 231Pa/230Th ratios below the production ratio of the two radionuclides in the water column (0.093), whereas Holocene sediments from the Southern Ocean have 231Pa/230Th > 0.093. This pattern of 231Pa deficit and excess was ascribed to southward 231Pa export from the Atlantic by the Atlantic thermohaline circulation (THC) as Pa is scavenged less efficiently by marine particles and more effectively transported by the THC than Th. The same pattern is observed in deposits of the Last Glacial Maximum (LGM), which led to a previous contention that the THC strength did not vary markedly through the last glacial termination. Here we embed a description of trace metal scavenging into a zonally averaged, circulation‐biogeochemistry ocean model to explore the sensitivity of 231Pa/230Th in Atlantic and Southern Ocean sediments to THC changes. Our results show that the production of biogenic opal (which, unlike other marine particles, poorly fractionates Th and Pa) in the Southern Ocean water column determines the spatial pattern of the sensitivity. Also, 231Pa/230Th increases in the North Atlantic but changes little in the South Atlantic and decreases in the Southern Ocean as THC is reduced. The mean 231Pa/230Th of the whole Atlantic is therefore less sensitive to THC changes than the mean 231Pa/230Th of the North Atlantic. The current uncertainties in Atlantic mean 231Pa/230Th are too large to rule out a twofold reduction of the THC at the LGM. However, the increase in North Atlantic mean 231Pa/230Th simulated in response to a twofold THC reduction is larger than the observed change in the North Atlantic mean 231Pa/230Th from the LGM to Holocene. Comparing this change with the modeled sensitivity of North Atlantic 231Pa/230Th to THC variations indicates that the THC at the LGM could not have been reduced by >30% of its present strength. Experiments of transient THC changes indicate that high‐resolution 231Pa/230Th records from North Atlantic sediments could also document thermohaline oscillations on century‐to‐millennial timescales.

Living in suboxia: Ecology of an Arabian Sea oxygen minimum zone copepod

Oxygen minimum zones (OMZs) are permanent suboxic features of the oceanic water column that strongly influence zooplankton distributions and biogeochemical cycles. The lower interface of prominent OMZs is characterized by a subsurface zooplankton biomass peak and high biological activity. The calanoid copepod Lucicutia grandis is an indicator species for this habitat. Its ecology in the Arabian Sea was studied during the U.S. Joint Global Ocean Flux Study (JGOFS) program to understand planktonic distributional and developmental adaptations to oxygen gradients in suboxic environments and the role of the OMZ zooplankton in food webs, vertical flux processes, and carbon cycles. Zooplankton samples were obtained in vertically stratified multiple opening‐closing net and environmental sensing system (MOCNESS) tows to 1,000 m during four seasonal cruises. The vertical distribution of L. grandis was associated with the steep oxygen gradient from 0.07 to 0.15 ml L−1 at the base of the OMZ about 600–1,000 m. There was a clear progression with age of the depths and oxygen levels inhabited by different developmental stages within this zone, a phenomenon attributed to both physiological constraints and ecological interactions. The seasonal and spatial pattern of reproduction and development was keyed in part to the seasonal monsoon cycle, with final maturation of young stages into reproducing adults probably triggered by the direct and indirect effects of the seasonal or episodic input to depth of sinking particles. Gut contents included surface flux material, deep‐sea detrital material, zooplankton remains, and deep‐sea aggregate material, indicating that L. grandis occupies at least four different trophic levels. This was an active, not a diapausing, population, since both adults and immature stages fed and reproduced during all seasons. In contrast to the pelagic fauna that are severely impacted by coastal episodic hypoxia, the animals of the oceanic OMZ are uniquely adapted to the very low oxygen and strong spatial and temporal patterns of this widespread suboxic environment.

Distribution, partitioning and fluxes of dissolved and particulate organic C, N and P in the eastern North Pacific and Southern Oceans

Concurrent distributions of dissolved and suspended particulate organic carbon (DOC and POC susp), nitrogen (DON and PON susp) and phosphorus (DOP and POP susp), and of suspended particulate inorganic phosphorus (PIP susp), are presented for the open ocean water column. Samples were collected along a three-station transect from the upper continental slope to the abyssal plain in the eastern North Pacific and from a single station in the Southern Ocean. The elemental composition of surface sedimentary organic matter (SOM) was also measured at each location, and sinking particulate organic matter (POM sink) was measured with moored sediment traps over a 110-d period at the abyssal site in the eastern North Pacific only. In addition to elemental compositions, C : N, C : P and N : P ratios were also calculated. Surface and deep ocean concentrations of dissolved organic matter (DOM) and inorganic nutrients between the two sites displayed distinct differences, although suspended POM (POM susp) concentrations were similar. Concentrations of DOM and POM susp displayed unique C, N and P distributions, with POM susp concentrations generally about 1–2 orders of magnitude less than the corresponding DOM concentrations. These differences were likely influenced by different biogeochemical factors: whereas the dissolved constituents may have been influenced more by the physical regime of the study site, suspended particulate matter may have been controlled to a greater extent by biological and chemical alteration. Up to 80% of total particulate P in POM susp, POM sink and SOM consisted of PIP. For all organic matter pools measured, elemental ratios reveal that organic P is preferentially remineralized over organic C and organic N at both sites. Increases in C : P and N : P ratios with depth were also observed for DOM at both sites, suggesting that DOP is also preferentially degraded over C and N as a function of depth. A simple one-dimensional vertical eddy diffusion model was applied to estimate the contributions of dissolved and suspended particulate organic C, N and P fluxes from the upper mixed layer into the permanent thermocline. Estimated vertical DOM fluxes were 28–63% of the total organic matter fluxes; POM susp and POM sink fluxes were 8–20 and 28–52% of the total.

In-situ spectrophotometric pH measurements: the effect of pressure on thymol blue protonation and absorbance characteristics

Abstract Previous studies of the indicator thymol blue in seawater have characterized the temperature and salinity dependence of thymol blue protonation and molar absorbance. In this work, observations of thymol blue absorbance in synthetic solutions and natural seawater between 0- and 900-bar gauge pressure have been used to calculate the influence of pressure on absorbance ratios and the p K 2 for the equilibrium HI − ⇌H + +I 2− (where I denotes thymol blue). The influence of pressure on indicator absorbance ratios is small but significant. The molar volume change and compressibility for the thymol blue dissociation reaction at 25°C in seawater are: Δ V i =−17.2 8 ±0.1 cm 3 mol −1 and Δ κ =(−38±4)×10 −4 cm 3 mol −1 bar −1 . The pressure dependence of p K 2 at 25°C is given as log K 2 P K 2 0 =+[2.99(±0.02)×10 −4 ]×P−[3.3(±0.3)×10 −8 ]×P 2 , where K 2 P and K 2 0 are the dissociation constants for HI − at a gauge pressure P (bars) and atmospheric pressure, respectively. The influence of pressure on thymol blue absorbance ratios ( e i ) in the expression pH= p K 2 +log( R − e 1 )/( e 2 − Re 3 ) are given as e 1 =0.0035, e 2 =2.386−(2.7×10 −6 )× P , and e 3 =0.139+(6.6×10 −6 )× P . This indicator calibration in conjunction with previous studies of thymol blue equilibria at atmospheric pressure allows in-situ spectrophotometric measurements of seawater pH throughout the oceanic water column.

Marine barite and celestite saturation in seawater

The stoichiometric solubility product , K sp,T *, of barite and celestite in seawater has been calculated using thermodynamic constants, K s0 , and the activity coefficients for barium, strontium , and sulfate in seawater. An equation of the form: ln K sp,T *=A+B ln T+ C T +DS n has been used. The constants A , B , C , D and n are derived from the calculated stoichiometric (or total) solubility product of barite and celestite in seawater as a function of temperature and salinity. T is the absolute temperature (K) and S is the salinity. The effect of pressure on K sp,T * is also calculated. Comparing the solubility products determined from this equation and the pressure effect equation to the distribution of Ba, Sr and SO 4 in seawater, we conclude that the upper surface water of the Southern Ocean is likely supersaturated with respect to pure barite, in agreement with Jeandel et al. [Jeandel, C., Dupre, B., Lebaron, G., Monnin, C., Minster, J.F., 1996. Longitudinal distributions of dissolved barium, silica and alkalinity in the western and southern Indian Ocean. Deep-Sea Res. 43, 1–31.] and Monnin et al. [Monnin, C., Jeandel, C., Cattaldo, T., Dehairs, F., 1999. The marine barite saturation state of the world oceans. Mar. Chem. 65, 253–261.] and that the oceanic water column is typically <30% saturated with respect to celestite. The model, which includes the thermodynamic solid–solution behavior of barite in seawater at 25°C and 1 atm, suggests that this mineral may contain up to 13 mol% SrSO 4 at equilibrium. Accordingly, we have determined the stoichiometric solubility products of strontian barite as a function of salinity and temperature: ln Ba K sp ′=247.88−38.333 ln T− 15421 T +1.27S 0.3 Using our model results for the total solubility product of the Sr-barite phase and seawater Ba and SO 4 concentration data, we conclude that the maximum saturation level of the oceans with respect to marine barite is 63% in the North Atlantic, 88% in the Indian Ocean, and 111% in the North Pacific. The depth of this maximum saturation level is shallower in the Atlantic Ocean (about 1000 m) than in the Pacific and Indian oceans (about 2000 m).

Modeled radar surface signature of deep ocean convection

Deep ocean convection, the process by which the deep waters of the world's oceans are created and renewed, plays a key role in the global thermohaline circulation and hence the world's heat balance. The process of deep ocean convection involves a vigorous overturning of the ocean water column down to depths of 2000-3000 m in an area probably not larger than 50 km in diameter. This paper details the results of a theoretical study to identify remotely sensible surface signatures for deep ocean convection. Due to the all-weather capability, efforts have focused on the microwave part of the spectrum, particularly the high resolution imaging capability of synthetic aperture radar (SAR). The goal of this research is to use the SAR surface signature or fingerprint to identify and characterize areas- of convection in the open ocean. This information is then used to improve model parameterizations for deep convection used in general circulation models. Electromagnetic simulations of remote sensing signatures of deep ocean convection have been performed based on existing hydrodynamic models. Simulated surface signatures of deep convection are presented for various hydrodynamic and imaging conditions along with a discussion of applicability of these simulations to real SAR data. Key findings are the existence of a definite identifiable radar surface signature in convective regions and a set of conditions under which one would expect to observe these signatures.

Extensive bloom of a N2-fixing diatom/cyanobacterial association in the tropical Atlantic Ocean

We encountered an extensive bloom of the colonial diatom Hemiaulus hauckii along a 2500 km cruise track off the NE coast of South America in autumn 1996. Each diatom cell contained the heterocystous, N 2 -fixing cyanobacterial endosymbiont Richelia intracellularis. Surface Richelia heterocyst (and filament) densities increased from 10 6 heterocyst 1 -1 in the bloom. Total abundance ranged from 10 6 heterocyst m -2 outside the bloom to over 10 10 heterocyst m -2 within the bloom. Rates of primary production averaged 1.2 g C m -2 d -1 , higher than typical for oligotrophic open ocean waters. N 2 fixation during the bloom by the Richelia/Hemiaulus association added an average of 45 mg N m -2 d -1 to the water column. The relative importance of NH 4 + uptake over the course of the bloom increased from 0 to 42% of total N uptake by the Hemiaulus/Richelia association. N 2 fixation by Richelia exceeded estimates of 'new' N flux via NO 3 diffusion from deep water and, together with additional N 2 fixation by the cyanobacterium Trichodesmium, could supply about 25 % of the total N demand through the water column during the bloom. Suspended particles and zooplankton collected within the bloom were depleted in 15 N, reflecting the dominant contribution of N 2 fixation to the planktonic N budget. The bloom was spatially extensive, as revealed by satellite imagery, and is calculated to have contributed about 0.5 Tg N to the euphotic zone. Such blooms may represent an important and previously unrecognized source of new N to support primary production in nutrient-poor tropical waters. Furthermore, this bloom demonstrates that heterocystous cyanobacteria can also make quantitatively important contributions of N in oceanic water column environments.

Folic acid and glutathione in the water column of the North East Atlantic

Reactive folic acid and glutathione were determined in the water column of the north east Atlantic between 30 and 54°N, 20°W. Cathodic stripping voltammetry (CSV) was used to determine these compounds on board ship at low nanomolar levels after minimal sample pretreatment. Folic acid was found to occur throughout the water column, whereas glutathione was found only in the upper water column as it was undetectable in deep waters. The concentration of glutathione ranged from <1 to 15 nmol/l, the folic acid concentrations generally between 0.10 and 4.0 nmol/l. Folic acid was found to follow the same trend as the Chl- a fluorescence in the upper water column but not in deeper waters. The data show that both folic acid and glutathione are very reactive in the oceanic water column, presumably as a result of in situ production and uptake by microorganisms. The high bioactivity was confirmed by rapid decreases in the concentrations of folic acid and glutathione in unfiltered seawater during storage over periods of hours.

Biotic and Abiotic Controls of the Barium Distribution in the Southern Ocean Water Column

Besides mixing, the dissolved barium distribution in the oceanic water column is controlled to a significant extent also by particle-solute interaction. In vi tro uptake experiments involving diatom cultures suggest that passive uptake prevails over active uptake. The overall effect of these processes is that barium behaves as a non-limiting nutrient element with ratios of dissolved over particulate concentrations varying between 100 and 1000. Uptake of barium by plankton particles eventually results in the formation of barium sulphate (baryte). There is increasing evidence that this baryte formation is closely linked with the formation of micro-environments composed of detrital organic matter, in which BaSO4 saturation is eventually reached during the process of bacterial decay (Bishop, 1988; Dehairs et al., 1980). This mechanism sets the link between oceanic baryte and oceanic productivity and as a result oceanic baryte is now increasingly recognised to represent a good proxy for palaeoproductivity (Francois e ta / . , 1995). Using an extensive data set obtained mainly from the Southern Ocean we investigated the different main processes affecting the oceanic barium cycle. For particulate barium in surface waters regional variability can be important and this is clearly associated with variation of planktonic production and biomass such as occurring, for instance, across the Polar Front Zone (PFZ). We observed that on a time scale of approximately three weeks water column stocks of micro-crystalline baryte co-vary with seasonal change in surface water productivity (Dehairs et al. 1997). This phase lag of about three weeks is consistent with the time lapse required for baryte to be formed during in vitro experiments using decaying detritus from a diatom culture. This process Department of Analytical Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, B-1050, Brussels, Belgium

Evidence for Strong Copper(I) Complexation by Organic Ligands in Seawater

Thiols like glutathione and cysteine form such stable complexes with copper(I) that they preclude the presence of copper(II). Conventionally seawater is titrated with copper(II) whilst monitoring the labile or reactive copper concentration by voltammetry or with other techniques, to determine the concentration of copper(II) binding complexing ligands in seawater. Titrations of seawater to which copper(I) binding ligands have been added reveal that the copper(I) binding ligands are detected when seawater is titrated with copper(II). The copper(II) in seawater is reduced to copper(I) within 2 to 40 minutes depending on the nature of the copper(I) binding ligand. The titrations of seawater with copper(II) thus give a response to the presence of copper(I) binding ligands indiscernible from that for copper(II) binding ligands. The stoichiometry of the detected apparent ligand concentrations for given concentrations of glutathione and cysteine suggest that 2 : 1 (thiol : Cu) complexes are formed. This was confirmed using voltammetry of free glutathione. Values of 21.2 and 22.2 were found for log β″CuL for glutathione and cysteine respectively (for the reaction of Cu′ + 2L′ ↔ CuL2). The complex stability is similar to that of natural organic species in the oceanic water column. The high stability of the copper(I) complexes was apparent from values of 32.1 and 32.6 for log β″Cu(I)L2 (for the reaction Cu+ + 2L″ ↔ CuL2) for the copper(I) complexes with glutathione and cysteine in seawater. Glutathione and other thiols are common in the marine system including the water column. It is therefore possible that at least some of the ligands detected in seawater, and previously assumed to be copper(II) binding ligands, are in fact strongly complexed as copper(I). The copper(I) oxidation state may thus be stabilised in seawater.

Cd/Ca in Planktonic Foraminifera of the Glacial Southern Ocean

Since the industrial revolution, 200 years ago, atmospheric carbon dioxide levels have risen by 90 ppmV, an amount equalling the natural variation between the last glacial maximum and pre-industrial values. To predict the fate and influence of anthropogenic carbon dioxide, it is vital to understand the natural controls on the glacial-interglacial variations in atmospheric composition. The biological pump is known to be an important draw-down of carbon dioxide today due to the complete removal of nutrients from the euphotic zone of most surface waters and regeneration at depth. An exception exists in the Southern Ocean today, where the surface waters have high phosphate concentrations indicating incomplete removal of the nutrients either due to very rapid upwelling rates or iron limitation. There is huge potential for glacial carbon dioxide draw-down if the efficiency of the biological pump had been enhanced in the glacial Southern Ocean. Particle proxies suggest that export productivity increased in the glacial subantarctic Southern Ocean (1) but there has been no clear evidence of a lowering of the glacial surface-water nutrients (2). fil3c in planktonic foraminifera has been found to be unreliable as a nutrient tracer in surface waters due to a number of factors such as susceptibility to isotopic fractionation during air-sea exchange (3). Cd/Ca in foraminifera, a reliable deep-water nutrient tracer, has been uncalibrated for surface waters and is often present at levels too low for determination by existing methods. We have developed a new isotope dilution, mass-spectrometric method for low-level determination of Cd/Ca in foraminifera which has allowed reliable and accurate planktonic analyses to be made. We have investigated the application of Cd/ Ca in planktonic foraminifera for the reconstruction of past surface water phosphate levels. Down-core records of Cd/Ca in G.Bulloides covering the last complete glacial cycle have been obtained from a latitudinal transect of cores spanning the present day Subtropical Convergence Zone (SCZ), at approximately 40~ and the Antarctic Polar Front (APF), at approximately 50~ in the Indian Ocean sector of the Southern Ocean. In each core there is a striking correlation between the Cd/Ca and the 5180 of G.Bulloides over the last glacial cycle indicating low surface water nutrient levels during the glacials and high nutrient levels during the interglacials. The greatest reduction in nutrient levels occurs in the subantarctic zone of the Southern Ocean, with little change south of the APF, consistent with the export productivity conclusions. There are two possible explanations for this glacial lowering of surface water nutrients. Firstly the rate of upwelling remains constant but the efficiency of nutrient removal is increased, possibly by iron fertilization due to an increased atmospheric dust fallout in glacial times. Secondly, the glacial Southern Ocean water column became stratified with a stable thermocline altowing the surface water productivity to deplete the nutrients without constant replenishment from upwelling. It is important to distinguish between these two mechanisms as each has a differing potential for glacial draw-down of atmospheric carbon dioxide. A simple box-model following some of the concepts in (4) has been run to resolve which of these two mechanisms is more consistent with the new surface water nutrient data and the existing export productivity conclusions.

Modelling the distribution of radionuclides in deep ocean water columns. Application to 3H, 137Cs and 239,240Pu

A one-dimensional model to simulate the dispersion of radionuclides down deep water columns has been developed. The model includes the transfers of radionuclides between water, suspended matter and bottom sediments. Such transfers are formulated in terms of kinetic transfer coefficients. A suspended matter sub-model has also been developed to obtain the suspended matter concentration profile. The dependence of the settling velocity of suspended particles on the salinity profile and the dependence of the vertical turbulent diffusion coefficient on the horizontal water current profile are included in the model. The model has been validated by comparing measured and computed profiles of 3H, 137Cs and 239,240Pu in the Atlantic, the Mediterranean and the Pacific. Some predictive studies and sensitivity test have also been carried out.

Translating Milankovitch climate forcing into eustatic fluctuations via thermal deep water expansion: a conceptual link

ABSTRACTSedimentological evidence indicates metre‐scale, cyclic changes in global sea‐level during Mesozoic greenhouse climates; the cyclicity is thought to be due to Milankovitch forcing. The absence of continental ice‐caps requires other mechanisms than glacier build‐up to explain these variations. We propose that thermal expansion of the entire oceanic water column may partly explain the observed sea‐level variations on Milankovitch timescales. Using existing climate model results, we show that an increase in deep water temperature of ∼ 2°C and a corresponding sea‐level rise of 1.7 m by thermal expansion can be induced by Milankovitch forcing via increased formation of warm deep waters in low latitudes.

Distribution and cycling of terrigenous dissolved organic matter in the ocean

Terrigenous dissolved organic matter (DOM) is continuously discharged by rivers into the ocean, yet its distribution and reactivity within ocean basins remain poorly defined aspects of the global carbon cycle1. Direct evidence for the presence of terrigenous DOM in the open ocean has been found only in dissolved humic substances isolated from surface waters of the eastern equatorial Pacific Ocean2. Here we report the detection of low concentrations of lignin—a biopolymer found only in terrestrial vegetation—in DOM collected from the Pacific and Atlantic oceans, indicating that terrigenous DOM is distributed throughout the ocean water column. Higher lignin concentrations in Atlantic waters, relative to Pacific waters, reflect terrigenous DOM concentrations that are 2.6 times higher in the Atlantic. This finding is consistent with the 3.6-times greater riverine water-discharge to the Atlantic Ocean3,4, and with known patterns of ocean circulation5. It appears that terrigenous DOM comprises only a small fraction (0.7–2.4%) of the total DOM in the ocean, and that its oceanic residence time (21–132yr) is much shorter than that of marine DOM6,7. The regeneration of nutrients during rapid cycling of terrigenous DOM could contribute to high rates of primary production in the coastal ocean.

Compositions and transport of lipid biomarkers through the water column and surficial sediments of the equatorial Pacific Ocean

A systematic investigation of fluxes and compositions of lipids through the water column and into sediments was conducted along the U.S. JGOFS EgPac transect from l2°N to l5°S at 140°W. Fluxes of lipids out of the euphotic zone varied spatially and temporally, ranging from ≈0.20 – 0.6 mmol lipid-C m −2 day −1. Lipid fluxes were greatly attenuated with increasing water column depth, dropping to 0.002-0.06 mmol lipid-C m −2 day −1 in deep-water sediment traps. Sediment accumulation rates for lipids were ≈ 0.0002 – 0.00003 mmol lipid-C m −2 day −1. Lipids comprised ≈ 11–23% of C org in net-plankton, 10–30% in particles exiting the euphotic zone, 2–4% particles in the deep EgPac, and 0.1-1 % in sediments. Lipids were, in general, selectively lost due to their greater reactivity relative to bulk organic matter toward biogeochemical degradation in the water column and sediment. Qualitative changes in lipid compositions through the water column and into sediments are consistent with the reactive nature of lipids. Fatty acids were the most labile compounds, with polyunsaturated fatty acids (PUFAs) being quickly lost from particles. Branchedchain C 15 and C 17 fatty acids increased in relative abundance as particulate matter sank and was incorporated into the sediment, indicating inputs of organic matter from bacteria. Long-chain C 39 alkenones of marine origin and long-chain C 20-C 30 fatty acids, alcohols and hydrocarbons derived from land plants were selectively preserved in sediments. Compositional changes over time and space demonstrate the dynamic range of reactivities among individual biomarker compounds, and hence of organic matter as a whole. A thorough understanding of biogeochemical reprocessing of organic matter in the oceanic water column and sediments is, thus, essential for using the sediment record for reconstructing past oceanic environments.

Changes in Surface Morphology of Calcite Exposed to the Oceanic Water Column

Reactions occurring on the surfaces of biogenic carbonate minerals can have important consequences for the biogeochemical cycle of carbon. In this study, carbonate mineral surface reactions with ambient seawater were investigated by atomic force microscopy (AFM). A sampling method was developed in which calcite surfaces were hung at discrete depths on a sediment trap array line for a three-day deployment period in subtropical North Pacific waters. Changes in surface morphologies were examined at nanometer resolution and evaluated using as a constraint the depth profile of calcite saturation in these waters. Evidence suggests that: (1) organic films which develop on carbonate surfaces exposed to shallow seawater may be responsible for the oversaturated state of the upper oceanic water column, (2) dissolution of carbonate minerals within the shallow warm layer of the ocean could be responsible for part of the alkalinity anomaly observed in the North Pacific.

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.

Planktic foraminiferal turnover across the Paleocene-Eocene transition at DSDP Site 401, Bay of Biscay, North Atlantic

Planktic foraminifera across the Paleocene-Eocene transition at DSDP Site 401 indicate that the benthic foraminiferal mass extinction occurred within Subzone P 6a of Berggren and Miller (1988), or P5 of Berggren et al. (1995) and coincident with a sudden 2.0%. excursion in δ 13 C values. The benthic foraminiferal extinction event (BFEE) and δ 13 C excursion was accompanied by a planktic foraminiferal turnover marked by an influx of warm water species ( Morozovella and Acarinina), a decrease in cooler water species ( Subbotina), a sudden short-term increase in low oxygen tolerant taxa ( Chiloguembelina), and no significant species extinctions. These faunal changes suggest climatic warming, expansion of the oxygen minimum zone, and a well stratified ocean water column. Oxygen isotope data of the surface dweller M. subbotina suggest climate warming beginning with a gradual 0.5%. decrease in δ 18 O in the 175 cm preceding the benthic foraminiferal extinction event followed by a sudden decrease of 1%. (4 °C) at the BFEE. The δ 13 C excursion occurred over 27 cm of sediment and, assuming constant sediment accumulation rates, represents a maximum of 23 ka. Recovery to pre-excursion gd 13 C values occurs within 172 cm, or about 144 ka. Climate cooling begins in Subzone P 6c as indicated by an increase in cooler water subbotinids and acarininids with rounded chambers and a decrease in warm water morozovellids.